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CHAPTER 4 UNITED STATES TIMBER POTENTIAL TIMBER PRODUCTION UNDER INTENSIVE MANAGEMENT A wide variety of opportunities exists for increasing timber production through intensive management (Ostrom and Gibbs 1973). The principal approaches include: (1) improving the site through cultivation, fertilization, drainage, and irrigation; (2) conversion of forest areas to faster-growing species; (3) improving stocking through reforestation; (4) introduction of genetically faster- growing genotypes within a given species; (5) stimulating the growth of faster-growing trees through weeding; (6) recovering a larger share of the gross growth through thinnings; (7) reducing losses from fire, insects, and diseases through better forest protection; and (8) increas- ing the allowable cut as a result of management decisions. We will consider each of these approaches in turn. But before we do so, it may be instructive to review some earlier efforts to estimate the increased production of timber that could be achieved under intensive management. Staebler (1972) presented both the potential gains from intensive forest management and its effect upon the distribution of management effort within the forest, using the generalized example of a tree farm in the Douglas-fir region of the Pacific Northwest. Based upon existing research, he suggested an increase in production of about 140 percent over average management on median quality (Site III) Douglas-fir lands if high-order management is applied, including fertilization, thinning, and genetic improvement of tree species. He concluded that one acre of the highest quality (Site I) land so intensively managed would produce as much wood annually as eight or nine acres of the lowest quality (Site V) given average management, so that the intensive management of low-elevation, high-site land could compensate if necessary for the withdrawal of high- elevation, low-site land from timber production. In his consultant's report to the Presidents Advisory Panel on Timber and the Environment (PAPTE 1973), Marty assayed some generalized estimates of the net mean annual growth that might be anticipated for various softwood timber types, and multiplied these values by the area in each site class for each softwood forest type. By this simple method, he estimated that the United States could grow 17 billion cubic feet of softwoods per year, 77 percent more than the 1970 supply of 10.7 billion cubic feet, but less than the - 27 -
20.5 billion cubic feet indicated by the use of normal yield tables. In the southern United States, Boyce (1971) initiated a Aeries of attempts to estimate the biological potential of pine ecosystems through a refinement of the yield table approach. For loblolly pine in the southeastern states he estimated a mean annual growth of 98 cubic feet per acre per year in total stem volume. Boyce1s analysis confirmed the estimates made in The South's Third Forest (Southern Forest Resources Analysis Committee 1969) that the potential growth of softwood in that region could be doubled with intensive management. In the Outlook Study, preliminary analyses are included of the increased timber production possible through inten- sive management of: (1) National Forests, and (2) miscellan- eous private holdings, which are the two ownership classes where the greatest gains were thought to be possible. The management practices considered were reforestation, stand release, thinning, and salvage. Other measures, such as fertilization, genetic improvement, and increased use, were not taken into account. The National Forest lands occur primarily in the western United States. Possible increases in harvests would arise from a continuing series of programs of intensified management on Ian estimated to represent the most promising opportunities for intensification (i.e., lands that would return 5 percent or more on investment, assuming future prices for softwood lumber and plywood at 30 percent above 1970 levels). If 275 thousand acres were treated annually, the increased harvest would be 1.6 billion board feet by 1980 and as much as 13 billion board feet by 2020. The estimated increases in harvests from such a program would be 3 percent by 1980 and 25 percent by 2020. Most of the increase would come from increasing the capture of gross growth through thinnings and improvement cuttings. In addition, the allowable cut on these National Forest lands would be raised under present sustained yield computational practices because of the "allowable cut effect," the increase in computed permissible harvest of existing old- growth resulting from taking into account the anticipated higher yields from the managed stands. The miscellaneous private lands considered in the Out- look Study of intensive management potentials occur primarily in the southern states. For these areas, future harvest increases would arise primarily from reforestation and thus would not occur for 25 to 30 years. Assuming that 12.7 million acres were placed under accelerated management, increased harvests would be negligible until 2000 when they would reach 1.0 billion board feet annually. Harvests from - 28 -
intensified management would, however, reach 2.5 billion board feet by 2020. Site Improvement The capacity of land to grow trees is termed "site quality". Many indices are used to estimate site, among them being the height of main canopy trees at a standard age, and the identification of the particular piece of land in terms of soil type, moisture relations, topographic location, and the kinds of vegetation currently occupying it (Spurr 1952). In the Outlook Study, site is categorized directly in terms of its productive capacity. More precisely, it is classified by the mean annual growth in cubic feet at culmination of mean annual increment in fully stocked natural stands. The site classes recognized are: I. land capable of growing 165 cubic feet per acre per year or more; II. 120-165 cubic feet per acre per year; III. 85-120; IV. 50-85; and V. 20-50 cubic feet per acre per year potential growth. In much of the Outlook Study, data for Sites I and II are combined, necessitating similar grouping in this report. Also in this report, the mean annual increment within each site class is assumed to be 160 for Sites I and II combined, 110 for Site III, 70 for Site IV, and 40 for Site V. As with agricultural land, the productive capacity of forest land may be improved. Because of the length of the forest rotation and the consequent generally low return on investments, relatively little site improvement in forests has actually been undertaken in the United States to date. Forest sites may be improved physically through such measures as drainage, irrigation, and cultivation; or chemi- cally through fertilization and weed control. Many forest sites are too wet for optimal growth. Drainage has been employed successfully to improve the growth of spruce and other lowland forest types in northern Europe for many years. Some three million acres have been drained in Finland and nearly one million acres have been similarly treated in Sweden. In the latter country, growth responses of from 15 to 60 cubic feet per acre per year are not uncommon (Stoeckler 1963). Drainage in similar situations in the Lake States of the United States, however, has been inconsequential. Drainage of forest sites has far greater application in wetlands of the coastal plain of the southern United States. On many pocosin and flatwood sites, growth of loblolly and - 29 -
slash pine may be increased from negligible levels to the middle range by drainage. In North Carolina, 21-year-old loblolly and slash pines planted within 200 feet of drainage canals produced over one cord per acre per year contrasted to 0.15 cord per acre annually on a similar but undrained site (Miller and Maki 1957). Growth of 19-year-old slash pine on a wet sandy flat in northwest Florida was 50 percent greater in the 10 years after drainage (15. U feet) than that (10 feet) predicted for the undrained condition (Young and Brendemuehl 1973). Drainage of such sites will result in a release of nutrients in the soil. Several million acres fall in this category, a high percentage of which have phosphate-deficient soils. On these, a combination of drainage plus fertilization with phosphate would improve the growth of pine forests substantially. Bedding (mounding soil in long rows) also stimulates the growth of planted pines on wet sites by improving drainage and increasing soil aeration. For much of the United States, lack of soil moisture is an important factor limiting tree growth on upland sites in the late summer and early fall. It follows that irrigation increases tree growth substantially. Irrigation is only practicable, though, when a plentiful supply of cheap water is available to irrigate a level site. Irrigation may be locally feasible in growing poplars on alluvial river valleys, but its application otherwise will be strictly limited. Cultivation is also important in preparing receptive mineral seedbeds for direct seeding. Nhere an impermeable lower soil horizon or hardpan impedes the passage of water both upward and downward, deep soil plowing may be effective in breaking up the hardpan to create both a better relation between soil and moisture and more growing space for tree roots. In recent years, much research has been carried out to improve nutrient relationships in forest soils, and substantial areas of forest have been fertilized commercially. In the last decade, some 900,000 acres (mainly Douglas-fir) have been fertilized in the Pacific Northwest, and over 400,000 acres have been treated in the Southeast (slash and loblolly pine). The great bulk of this has been done by private industry. In the Douglas-fir region, a high of 220,000 acres was fertilized with nitrogen in 1972, chiefly by one company. Strand and Miller (1969) believe that the optimal rate of nitrogen fertilization would lie between 150 and 300 pounds per acre during a five-to seven-year period. More recently. - 30 -
Stanley P. Gessel (personal communication, 1975, University of Washington) has concluded that stands treated with nitrogen fertilizer produce an average of 50 cubic feet per acre per year increased growth in the four years after fertilization. Low quality sites not only produce more response than high quality sites, but do so more consistently. A safe generalization based upon current knowledge would be that urea or ammonium nitrate applied at five-year intervals will result in an increase of 15 to 20 percent in the volume increment of Douglas-fir stands on average sites. In the Southeast, a high of 87,000 acres was treated in 1972, chiefly through the adding of phosphate fertilizer to poorly drained flatwoods sites in the southern Coastal Plain. Bengtson (1968) has surveyed systematically the potential increases in wood production through fertilization of forest land in the South, citing the literature on the subject to that date. Projecting his judgment for a 30-year period, he concludes that for the East Central Uplands, the outlook for profitable use of fertilizers is not promising. For the Lower Valley of the Mississippi and similar bottom- lands, forest fertilization will not contribute greatly to production until better silvicultural practices are devel- oped and applied extensively. In the Southeastern Uplands, however, judicious selection of acres to be treated can lead to increased total production in this area of perhaps 5 percent. The greatest potential gain, though, is in the Coastal Plain where a substantial increase in production, conservatively 10 percent for the region as a whole, can come through fertilization and drainage of poorly-drained and phosphate-deficient sites. Bengtson bases the largest gain on the conclusion that volume increase of 30 percent could be obtained from treating perhaps 25 percent of the flatwoods pine stands. Three to five million acres of coastal flatwoods need phosphate to be productive. The net effect of an extensive program of fertilization and drainage would be to raise the site quality of a portion of the forest land in the United States. Assuming for the sake of simplification that such efforts are confined to nitrogen fertilization of 4.7 million acres in the Douglas- fir and related mesophytic conifer types of the Pacific Coast, and to phosphate fertilization and drainage of 5.8 million acres in moist loblolly and slash pine types in the South, and assuming that the total acreages of these types remain essentially unchanged, we may tentatively modify the acreages of the different site classes as indicated in Table 5. Assuming that the growth in each site class remains the same, site amelioration would result in an increase of 5.5 percent in the productivity of Pacific Coast Douglas-fir and related types and of 3.2 percent in that of southern pine - 31 -
types. The exercise is highly speculative but at the same time indicative of possible gains. Conversion of Forest Type In the Outlook Study, forest site guality is estimated on the basis of the vegetation currently occupying the area at the time of the forest survey. Since some of our commercial forest land is currently unstocked, and since an even greater amount of it is stocked with tree species that are growing more slowly than others that are equally well adapted to grow on the same sites, the net effect is that the Outlook Study substantially underestimates the growth potential of United States commercial forests in these respects. The gains from conversion of an existing forest to a suitable faster-growing type can be estimated readily from yield tables provided that either (1) yield tables for dif- fering species or types are based upon site as defined by soil type, topographic, and other non-tree characteristics, or (2) site index of one type can be related to that for an- other type through correlation analysis. An example of the first is provided by Assman (1970) for northern Europe. He found, for example, that the yield of spruce was at least twice that of beech on the same site, and that American red oak outproduced native European oaks on the same site by more than two times. Site index correlations have been published by Doolittle (1958) for different species growing on the same site in the Southern Appalachians, by Carmean and Vasilevsky (1971) for northern Minnesota, and by Dietchman and Green (1965) for the northern Rocky Mountain region. Although no systematic study has been made of comparable American site index and yield table data, spot checks would indicate that in many cases yield of forests can be raised from 50 to 150 percent by species conversion. By far the largest opportunity for changing forest type is in the southern pine region but opportunities also exist in the Lake States, Central States and New England. In the South, a very large area that could grow pines well is currently growing hardwoods poorly (Murphy and Knight 1974). Much of this land once supported pine, but it has reverted to hardwoods through the exclusion of fire or the harvesting of the pines leaving the cut-over site to be taken over by hardwoods. The region has over 30 million acres of mixed oak-pine forest and over 88 million acres of hardwood. If we assume that one-half of the mixed-wood type and one-tenth of the upland hardwoods on sites III-V could profitably be converted to pine, the pine acreage in the South could be - 32 -
in S C 0 id N -H O O O V Tl- 00000 O 00 CN CN CN vo ro in vo O -H 4J ^i QQ ^1 f**. Cn in *3* rH rH 4J 4J at C rl 0) CN ro CN CN VO 0) 0) «4-( M kl -H O CO -Q C 4J 3 H <4-l O rH C n> o 3 >1-rt C -O rH 'c CN m -1» co (T> co en o CN on rH *"* en rH r- ^ CN CN o x r n o 5 'n H i** in in en TT CN ro en O O r7 ro CN CN in C ** 4J o 3 -H 0 4J id N 4J -H C rH 0) 1 0 4J S -s M r4 - >i ID U IH -p r*i C > --H H X o o o o vo i-t r> ^i o o o o ⢠HO v0 rH r** ^1 S O e jo « rH H rH rH P W C ⢠r^ 01 5 «4H * '* 3 in 01 C C ft 0) 'H ^i X 4J C 0) C o 6 *H -H 53 o^ 4J 2 g s -H II rH ^ -H 0 O O 0 O 0 o o o o o o o o o o o o o o o o o o o o H 4-> O O O O VO VO 0) O 0) ^ m co vo en vo ro in Tt oo rH I/) fa fl <N CN fO VO -H 'O 0) C o i id s o 0) M-l -H id MH 0) 1 01 O 'o id < rj ^H CO O O 0 O O o o o o o ^ o o o o o 00000 5 A^ O r^ in CN (N vo oo en o ro o * n \âi -j *â * o S CO VO 00 rH CTt m H CN oo oo 1 rH CN CN m vo 0) 4J id o ji p * ^- > 5 g -H M -H -O -r) (0 -H W 4> Oi (0 ^H (M C "1 |4 .H SH Id r-j Id U 0) H H 0) H H a rH O O » H > rH ITH 3HHH> Id 3 S M -P £ " H f> H 4J H H H > Id o p W H - 33 -
increased by 20 million acres. If we further assume that the site will be raised by at least one class by such conversion, the area of southern pine by site classes would be augmented as shown in Table 6. In this estimate, the base is that provided by Table 5 after site improvement from fertilization and drainage. Such a conversion could increase the potential yield of southern pine by as much as 39 percent over the projected growth after site amelioration, or 40 percent over projected growth based on acreages and site classes as delineated in the Outlook Study, without taking into consideration the effects of site improvement. Improving Stocking Through Reforestation Probably the single most important factor in maintaining the productivity of the forests of the United States is the development and maintenance of full stocking through a nationwide program of seeding and planting where and when necessary. The Outlook Study reports a total of 20.7 million acres of non-stocked commercial forest land, or 4.2 percent of our commercial forest land: 4.8 million are in the South, 3.7 million are in the Pacific Coast region, 9.6 million are in the North, and 2.7 million are in the Rocky Mountains. Many harvested areas lie idle for one, two, or even more years before regeneration is attained. If planting can be done immediately after harvesting rather than one year later, yields can be increased by 4 percent over a southern pine rotation of 25 years. Before this can be accomplished, we must improve initial survival and stocking of new stands by fully using presently available knowledge on growing, handling, and outplanting seedlings. Twenty-five year records from throughout the South showed that first year survival on 250,000 acres of planted slash and loblolly pine ranged from 53 to 83 percent; average survival for this 250,000 acres was 71 percent (Schultz 1975). Average survival for 9 conifer species planted throughout the Lake States was 50 percent at age 11 (Rudolph 1950). From 5 to 25 percent of each year's plantings is a failure due to poor survival (that is, less than 300 trees survive to age 5). During the 11-year period from 1960 to 1970, a total of 1.477 million acres was planted or direct seeded annually in the United States. Assuming a 15 percent failure rate, regeneration probably averaged 1.3 million acres. More than 60 percent of the regeneration was in the South, and 76 percent was carried out by forest industry and other private owners. - 34 -
(0 O O O O 0 O O O O O 1 o in in o o r-1 M B oo Vo n ^1 CM 4-> $ 0) ro xJ1 Cft O --l-l &4 H rt EH >O en 0) C A! o O -H O O O Q 01 1 0 0 1 0 4-) V4 i in m i o co o> i » » i » i > rH CN xC c c 0 0 z u CO 0) cn G C C O -H -H -O -H ft 4-1 O CO o o o fa O M 1 O 0 1 O S 0) 1 0 O 1 O i-J rH â¢0 > (U QJ CN ro in 5 -o o id o o CO o c ~-* w o o o o M-I o c o o o i o 0 -H 01 O 0 O O 1 O 01 0) Q) -H » » » i » V0 0) M H C 01 CN o n in Oi 0) U -H H r-t l-t 0) Id P rt ft 0) 3 0) C Cl M C 1 > M O EH rt* o o 01 Id â¢O 0) 0) 0) -H <s| -U O O O O O 01 U id (u CD C 4J 3 o o o o o o o o o o 0) ft M CO co § u vo n m I1 oo c e 9 cN ro vO H 2 M O 0) M -M a <u e rt H O O O O 0 1 ^3 o o o o o 4J 3 03 CJt O CO O 9 i- > 6 CO in i-t CM oo oo O 0 CN CO VO M O fa rH 01 CO id 0 o H id 4J H H 4J -H CO » H p> O H H H > EH - 35 -
A rouqh estimate of the maximum annual planting program that might develop over the years may te derived for the Douglas-fir and related conifers on the Pacific Coast and for southern pines. For Douglas-fir and other mesophytic conifers, we esti- mate a total of 29 million acres in Sites I, II, III, and IV (capable of growing 85 cubic-feet per acre per year) after fertilization of some five million acres to improve site guality (Table 5). If we assume that conversion periods will be 50 to 60 years and that all stands will be eventually clearcut and the sites replanted, the area planted annually would be either 580 or U83 thousand acres. If the conversion were carried out over a shorter period of time, the area to be planted annually would be greater. Considering that not all stands will be regenerated by clearcutting and planting, and that more than 300 thousand acres are currently being planted in all timber types in the region, there seems to be no major biological barrier to the achievement of full stocking on all the better sites for the Douglas-fir type over the period of approximately half a century. For southern pines, we estimate a potential acreage of 68 million acres of Site IV or tetter (more than 50 cubic feet per acre per year). This includes site amelioration treatment to 5.8 million acres, planting of four million acres of non-stocked lands, and conversion by planting of 20 million acres (Table 5). Assuming that this effort is carried through over the next 30 to HO years, and assuming that the 6U million acres of southern pine on Sites I - III would be regenerated by clearcutting and planting, we see that an annual planting program of 2.2 million acres would be needed. Quicker conversion would reguire more planting each year. Again, since present planting levels already exceed a million acres per year, this goal does not seem unattainable. We may conclude, therefore, that for the two principal timber-growing regions in the country, it would be feasible to achieve full stocking as well as species conversion over 50 to 60 years for Douglas-fir and 30 to HO years for south- ern pine. Genetic Improvement It is at the time of planting the new forest that the possibility of genetic improvement becomes real. The potential increased productivity from wide-spread application of forest tree improvement practices has been summarized by Barber (1968) with particular reference to the southern pine forests. He concludes that through an - 36 -
intensive program of plus-tree selection, seed orchard establishment, and progeny testing in southern pine, the projected increase in growth from a first-generation seed orchard would be on the order of 10 to 25 percent. Each generation of seed orchards would require 10 to 12 years. In the Pacific Northwest, Forest Service geneticists simi- larly estimate an increment of 10 to 20 percent from the first generation of seed orchards, but an interval of 15 to 20 years between generations. Conservatively, we may estimate a gain for major conifer species in the United States of 10 to 15 percent per generation of seed orchards and an interval of 15 to 20 years between generations, or roughly 1 percent per year over the next century. Major gains from improved genetic selection apply only to species which are managed by a clearcutting and artificial regeneration. This restricts the choice of species to conifers (mainly southern pine and Douglas-fir), short rotation fiber crops (e.g., aspen, cottonwood, sycamore), and fine hardwoods such as walnut and ash. Within these forest types, genetic improvement would apply only to areas that are clearcut and planted, seeded or vegetatively propagated. Even for these, it would take many years to develop a sufficient supply of improved seed for regionwide application. The introduction of genetically faster-growing trees into the forest stand does not guarantee that they will in- deed grow faster. For this to occur, additional growing space is needed, and this must be achieved through regular thinnings as the stand matures. It may well be that a plantation of genetically superior trees that is regularly thinned will produce more usable timber volume than would be predicted by adding the growth improvement expected from thinning alone to that expected from genetic improvement alone. For areas actually planted, the potential increases in yield may be greater than indicated above because of gains from disease resistance. In the South, both slash and loblolly pines are attacked by fusiform rust. Although it is difficult to estimate the improvement possible through the selection of seed from parents which are fusiform-rust resistant, a doubling of resistance in plantations established from such seed is quite possible over the next 10 years. - 37 -
Weeding The cutting back or killing back of unwanted vegetation to free wanted trees in the seedling stage to grow is often an essential silvicultural practice. If sites are to be kept fully stocked with specified tree species, other plants or trees with less desirable growth or value characteristics must be prevented from taking over. For example, weeding is frequently necessary to bring planted conifer seedlings through to form the overstory of the new stand. Similarly, the cutting of mature pine stands will frequently result in turning the site over to the hardwood and brush understory which had developed under the old pine stand. The control of such unwanted vegetation through cutting it back, use of herbicides, or controlled burning must be planned for and executed if the affected sites are to be counted on to produce the desired forest stand. The costs of such treatment become a necessary part of the costs of management. Mechanical or chemical weed control can play an important role in both water and nutrient management by reducing competition from unwanted trees and plants at the time of forestation and during early stand development. For example, mechanical control of ground vegetation more than doubled the volume of 4-year-old loblolly pine in the North Carolina Coastal Plain (Hansen and Johnson 1974). Thinnings Forest stands that are frequently thinned do not produce any greater biomass than comparable healthy stands that remain unthinned. The effect of thinning is rather to concentrate the biomass production on the better quality and potentially more valuable trees (Spurr 1952). In short, a thinned stand does not produce more total volume, but it does produce bigger trees in a shorter period of time. For short rotations, therefore, the board-foot production of forest may be increased by thinning, even though the total cubic-foot volume may be unchanged or reduced. As fully-stocked forest stands develop, competition greatly reduces the number of living trees. The reduction in the gross growth or increment of the stand resulting from this natural mortality results in a substantially lessened net growth or increment. In an extreme example, Spurr (1963) reconstructed the annual mortality and gross growth of a fast-growing Monterey pine plantation in New Zealand. At age 35, the gross annual increment was 516 cubic feet per acre per year or 55 percent greater than the net annual in- crement of 332 cubic feet per acre per year. The difference will normally be less under less ideal growing conditions. - 38 -
Normal yield tables assume normal mortality. The difference between estimated stand volumes at different ages is, therefore, the net growth. In some yield studies, however, separate estimates of mortality have been provided, which, when added to net growth, produce estimates of gross growth. In addition, gross growth yield tables have been developed for a number of species in recent years. By comparing these with older normal yield tables that predict net growth, we can estimate the amount of mortality that might be salvaged through thinnings. Ostrom and Gibbs (1973) have summarized several of these comparisons for western conifers (Table 7). They concluded that, under very intensive management, harvests close to the gross yields should be attainable in most timber types unless natural disasters intervene. This could mean an increase of about 20 to 60 percent above normal yield in various species. It has been estimated that yield of Pacific Northwest conifers can be increased from 30 to 35 percent if stand density is controlled by frequent thinnings throughout a normal rotation (Robert E. Buckman 1975, personal communication, U.S. Forest Service). Recent efforts to estimate timber yields under intensive management predict similar gains. Working with Douglas-fir permanent sample plot data in New Zealand, Spurr (1963) predicted that following three thinnings at ages 30, 40, and 50, a 60-year-old managed stand would produce 427 cubic feet per acre per year, or 21 percent more than the 352 cubic feet produced by the comparable unthinned stand. Results of long-term experiments in Europe (Assman 1970) indicate that with freguent light thinning, spruce stands yielded more than 90 percent of the potential gross yield, or approximately 130 percent of normal yield. Gingrich (1971) developed yield predictions for managed upland hardwoods in the Central States. Assuming thinnings at ten-year intervals beginning at age 30, the cumulative total yield under management at age 60 for stands on medium sites (Site Index 65) would be 62 cubic feet per acre per year or 14 percent greater than the 55 cubic feet predicted by the normal yield table for unthinned stands. Summarizing a long-term study initiated in a 17-year-old loblolly pine stand in 1930, Andrulot et al. (1972) found that at age 50, gross mean annual increment was 121 to 122 cubic feet per acre per year on the thinned and unthinned plots respectively; but that the net increment on the unthinned plots was only 98 cubic feet per acre per year, while on the thinned plots, it was 119, or 20 percent greater. The Weyerhaeuser Company has carried out extensive research in conceptualizing a target forest that can be achieved through intensive management. On the assumption that growth can be recovered through an intensive thinning regime, they predict an increase in cubic-foot yield of 25 percent for Oouglas- - 39 -
Table 7 Relation of Normal Yield to Gross Yield for Different Species and Sites at age 100 Site index Normal Yield Gross yield Volume increase Relative increase Species and source (cu.ft.)-1- (cu.ft.) (cu.ft.) (percent) Doualas-fir (Gurus 1967, McArdle 1961) 100 140 170 7,620 13,270 16,610 13,300 18,400 23,500 5,680 5,130 6,890 75 39 41 Lodgepole pine (Dahms 1964) 30 50 70 2,194 4,563 6,932 3,768 6,975 10,182 1,574 2,412 3,250 72 53 47 Western white pine (Watt 1960) Ponderosa pine (Meyer 1961) all 80 120 160 8,770 11,310 5,650 11,350 19,350 Volume to tip Source: Ostrom and Gibbs (1973) 7,373 14,045 23,710 2,540 1,723 2,695 4,360 29 30 24 23 - 40 -
-fir stands grown in Site II at optimum density levels on a 60-year rotation. The above citations only sample the recent work that has been done on the potential yield from intensive silvi- cultural management. The evidence presented is episodic rather than comprehensive, but the data are in broad agreement. In general, it seems safe to conclude that for most species on average to better sites managed for medium- length rotations, gross increment will range from 15 percent to 35 percent greater than the net yield indicated by normal yield tables. Furthermore, most of this gross increment (perhaps 90 percent) can be used through thinnings commenced early in the life of the stand and carried out at a maximum of 10-year intervals. In the absence of badly-needed growth data in the form of managed-stand yield tables on a gross growth basis for all major forest types in the United States, we may assume that normal yield table values can be increased by 25 percent if silvicultural management in the form of regular thinnings can be applied. However, southern pines and other fast-growing species on short rotations should be considered exceptions to this generalization. The evidence now available suggests that biomass gains from thinnings will be small or perhaps negative under such conditions. Once the rotations are extended, however, the capture of mortality becomes important. Protection Improved protection of the forest from fire, insects, and diseases is an obvious way to increase the productivity of the forest and the percentage that is actually harvested and used by man. Annual mortality losses from all natural causes are estimated in the Outlook Study to te about 4.5 billion cubic feet of growing stock. These losses nullify about one-fifth of the total annual forest growth in the United States. Reduction in these losses through improved timber, fire, and pest management may provide the single greatest means of improving timber production. According to the Outlook Study, federal and state agen- cies spent $201 million for forest fire protection in 1970. It is estimated that counties, private operators, and others spent an additional $120 million that year for hazard reduc- tion, such as slash burning and prescribed burning, and for other unreported fire protection activities. The total protected area burned was 2.1 million acres in 1970. An additional million acres of unprotected land also burned that year. Increased expenditures for fire control might well result in less forest loss from fire, although it - 41 -
should be noted that the annual area burned has changed very little in recent years. On the other hand, reducing the acreage burned by wildfires even by 10 percent could mean a savings in excess of 100 million cubic feet of wood each year. Management practices which maintain trees in healthy growing conditions (e.g., breeding for disease resistance, properly matching species to site, adequate tree spacing, prompt salvage of dead or dying timber, biological or chemical control measures for suppressing insect and disease outbreaks) must be diligently practiced if managers are to reduce this tremendous waste. On the positive side, prescribed burning has long been an important component of forest management, especially in the southern pine forests. Burning every 3 to 5 years reduces the buildup of natural fuels, forestalls damage from possible wildfires, kills invading hardwood trees, maintains subclimax conifer stands in a healthy growing condition, and may enhance tree growth. Fire is often a valuable and inexpensive adjunct to mechanical site preparation prior to planting. On many areas throughout the country fire alone is a sufficient site treatment for establishing healthy new stands. Expenditures for control of diseases, insects, and other forest pests have averaged about $12 million per year, mostly from federal funds. Again the possibility exists that greater expenditures would result in less loss and more forest products available for harvest. The Forest Service estimates that total loss from fire, insects, disease, storms, and other destructive agents has risen from 3.9 billion cubic feet in 1952 to 4.3 billion in 1962 and 4.5 billion in 1970. Under a continuation of 1970 levels of management, it is estimated that mortality will rise slightly to 4.9 billion cubic feet in 1985 and to 5.2 billion in 2000. With better forest protection, it is certainly silviculturally feasible to reduce mortality to between 3 and 4 billion cubic feet annually. To what extent it is economical to increase the costs of forest protection to achieve a greater actual harvest of one to two billion cubic feet per year from the forest is a separate and complex matter. Increasing Allowable Cut A frequent objection to increased investment in forest management is that it takes so many years to raise a tree to maturity that the small return on the investment renders it uneconomic. A contrary line of reasoning conceptualizes the - 42 -
whole forest as the management unit and concludes that what is done on one acre has immediate effects on what should be done on other acres within the same unit, and consequently upon the value of the larger operation as a whole. Another aspect of this complex subject is the "allowable cut effect.1' In a forest managed on sustained yield principles with the annual harvest related in some fashion to the annual growth, any silvicultural action that increases the annual growth will immediately permit an increase in the annual harvest. Thus, an investment in silvicultural management will immediately affect the value of the property as a whole. It is conceivable that the cost of planting will be recovered in the same year through an increased harvest. Without going into the many ramifications, we point out. that increased investments in protection should raise the annual allowable cut to the extent that future losses can be predictably reduced and, therefore, the amount of harvestable material increased. As another example, immediate planting of a cut-over site with one to two-year old nursery stock will shorten the rotation by a number of yearsâat least one and often as much as five to ten if the alternative is to wait for a periodic seed crop needed to naturally reseed the area.. The increased yield predictable from both shortening the rotation and guaranteeing full stocking (weeding must be undertaken if needed) again has an allowable cut effect in increasing the productivity of the whole management unit and permitting an immediate increased harvest. In still another situation, many acres in the Rocky Mountains and Pacific Coast are occupied by overmature timber stands with little or no net growth. Similarly, many acres in the East and South are occupied by culled and understocked forest stands, often of the wrong species with much less growth than the potential for the site if fully stocked with suitable tree species. In both cases, the conversion of the forests to fast-growing trees forming fully-stocked stands will greatly increase the productivity of the management unit and permit increased harvest. The computation of the actual amount of gain in allowable cut is complex and involves many factors including the size and age distribution of the forests in the management unit. It must be remembered, however, that the allowable cut effect occurs only when a forest working circle is managed on a sustained yield basis and when the allowable cut is computed on a volume-growth regulation basis. Furthermore, some forest economists challenge the validity of these basic assumptions. The question of the allowable cut effect is a highly controversial one, and the panel does not take any position on it, but simply draws attention to its existence. It is essentially a managerial and economic issue rather than a biological one.
INCREASED USE OF THE FOREST BIOMASS The term "biomass" means the total weight of animal and plant material in an ecological community or system. The biomass of a forest ecosystem thus consists of all the trees, understory plants, animals including insects and other arthropods, total soil biota, and similar elements. Although considerable data have been accumulated over the last century on the volume, weight, and energy dynamics of the various components of the forest, it fell to Ovington (1965) in the 1950s to integrate such data into a systems context. More recently, scientists in several countries working with forest ecosystems as part of the International Biological Program have added greatly to the statistical base and to our understanding of the biological productivity of the forest in terms of biomass and energy relationships. Biomass studies are tedious, time-consuming, and expen- sive. Despite the large amount of effort invested, therefore, only a relatively few forests of small area have been studied in detail and these have not been chosen to represent statistically any larger population. We have little or no basis, therefore, for expanding data obtained from biomass sample plots to the forests of the United States as a whole. Because of the paucity of representativeness of biomass sample studies, our current effort to evaluate the biological productivity of the forests of the United States has had to rely upon conventional forest sample plots in which the measurement is concentrated upon estimating the current volume and the growth in volume of the bole of the trees in the forest, excluding the stump and the top of the tree. At the same time, we recognize the present importance and the potential applicability of forest biomass studies. It may be of value to assess rather briefly the possibilities of increasing the use of the forest biomass, ranging from the simple closer use of the bole through complete tree use, to an evaluation of total biomass potential. Closer Use of the Bole In conventional logging, many trees and portions of trees unmerchantable because of defect are left in the woods. Even for those trees taken, a large share of the bole (main stem) is left unused after completion of the manufacturing process. The amount lost is relatively small in the case of managed even-aged stands of commercial species harvested at rotation age for pulp as well as for lumber, and relatively great in the case of unmanaged old- growth stands that are highly defective and harvested primarily for lumber. The former situation is frequently encountered on industrial forest lands in the southern pine
region, while the latter is the rule where old-growth stands are harvested in the Pacific Northwest. In a recent study of the status of timber use on the Pacific Northwest, Grantham (1974) estimated that of the annual harvest of 69.2 million tons, 14 million tons or 20 percent is left in the woods as logging residues, and 5.7 million tons or 8 percent is left unused in the sawmill. If we add to this 1.1 million tons of residues from veneer logs, the total unused residue is 21.2 million tons or 31 percent of the total annual harvest. For the United States as a whole, Lassen and Hair (1970) estimated an annual (1968) volume of two billion cubic feet of logging residues, plus an additional 1.7 billion cubic feet from primary manufacturing residues. At 35 pounds per cubic foot, this represents a total of 65 million tons of unused residues. At the immediate and practical level, measurable gains can be achieved through improved efficiency in the con- version of saw logs to lumber (PAPTE 1973). At present, only 40 percent of the wood in the log is recovered in the form of lumber. Saeman (PAPTE 1973) believes that with no new equipment, but with investment in management and maintenance, the average mill can profitably increase its recovery. Furthermore, the addition of automated systems based on predetermined arithmetic solutions to optimum sawing problems could raise the recovery factor by perhaps an additional 10 percent through the elimination of human error, although the volume gain may not necessarily be in sizes and grades demanded in the market. The increase in lumber production of more than 20 percent from 40 percent of the wood in the bole to nearly 50 percent would be partly at the expense of pulp chips and other products and would not be solely at the expense of waste residues. Nevertheless, the gains would be real and well worth the effort required to achieve them. In several field tests, yields have indeed been in- creased substantially. For aspen in Michigan, Napier (1972) demonstrated that a harvesting system designed to produce chips in the forest could produce 84 tons per acre compared to 41 tons from conventional pulpwood harvest. Working with lodgepole pine in Wyoming, Gardner and Hann (1972) were able to increase yield 35 percent by near complete harvesting which used tops, all trees with a stem diameter greater than three inches and all sound residue more than six feet long and six inches in diameter at the large end. These increased yields, however, do involve the inclusion in the harvest of large amounts of bark. As a result, at the present time, the use of this small dimension material is not economic under most conditions. The stump and tap roots of southern pines contain substantial wood in a concentrated form suitable for - 45 -
chipping. Koch (1974) described a prototype tubular shear with which the tree can be sheared below the ground and removed whole, opening up the possibility of an increase in the usable harvest of as much as 20 percent from young plantations of slash pine on rock-free sites. Complete Tree Use In addition to closer use of the tree bole above the stump to a minimum diameter near the top, the possiblity exists for using part or all of stump, bole tip, branches, foliage, fruits, and root systems. As one phase of the biomass approach, considerable work has been done in recent years by forest scientists in measuring the potential of these other elements. Much of this work has been done at the Complete Tree Institute of the Dniversity of Maine (Young 1964). The literature on complete tree use has been summarized by Keays (1971). The contribution of various parts of the tree to its total weight obviously varies. In gross terms, however, rough averages may be assigned. Taking the merchantable bole as 100, an additional 5 to 10 percent will be found in the unmerchantable top, 5 or more percent in the stump root system, 5 percent in the large branches, 20 percent in the foliage and small branches, 15 percent in the small root system, and 10 percent in bark throughout the tree. Granted large variation in these values, it is apparent that not much more than 60 percent of the wood and bark in the average tree is in the part removed in the conventional logging operation. At the same time, it must be remembered that the mer- chantable bole is relatively low in mineral nutrient content, a large portion of the nutrients being concentrated in the growing tip, foliage, fruits, small branches and small roots. William Fritchett (personal communication, 1975, University of Florida) estimates that whole tree harvesting might increase pulping yields 25 percent, but that it would result in doubling the amount of nutrients taken from the site. It must be remembered, though, that such a complete withdrawal takes place only once each rotation and that the total effect is much less than it is for agricultural crops. Whereas, under normal bole logging, a balanced nutrient cycle develops in which a low level of nutrient availability can be maintained indefinitely, more complete harvest of the tree would require substantial amounts of nutrient input. From a biological point of view, the nutrient-rich parts of trees should be left in the forest. Also, nitrogen-fixing and other nutrient- accumulating plants such as red alder should be encouraged as part of the silvicultural management of the forest. - 46 -
Total Ecosystem Biomass Although there is no basis for assuming the use of other parts of the forest ecosystem than the mature tree, total ecosystem biomass studies currently being carried out by ecolegists are exceedingly important in adding to our understanding of the forest as a biological complex. The state of the art is well summarized in Productivity of Forest Ecosystems; Proceedings of the Brussels Symposium (UNESCO 1971), particularly in articles by Duvigneaud, Whittaker and Woodwell, and Olson. The depth of information obtained in total forest bio- mass studies is illustrated in Table 8, taken from Whittaker and Woodwell»s paper in the UNESCO Symposium (1971). For the a3-year-old oak-pine forest at the Brookhaven National Laboratory, shrubs and herbs annually produce 13 percent additional dry matter to that produced by the trees alone. Only 14 percent of the annual increment in dry matter in this one example is lodged in the stem wood. The mean annual increment of stem wood is about 45 cubic feet per acre per year. The old growth cove and spruce-fir forests have a mean annual increment of stem wood of about 115 and 120 cubic feet per acre per year. A principal result of the work of Whittaker (1966) in the Great Smoky Mountains is his conclusion that the net production of many late successional forests lie in the range of 1200 to 1500 grams dry weight per square meter per year. Assuming that 20 percent of this accrues to the merchantable bole and that the dry wood weighs 30 pounds per cubic feet, this is equivalent to 70 to 90 cubic feet per acre per year bole increment. Whittaker's estimate is, therefore, comparable with the 74 cubic feet per acre per year estimated by the Outlook Study as the potential growth of the commercial forests in the United States. Intensive Biomass Management Over and above a more complete use of the merchantable boles in the forest ecosystem lies the intriguing possibility of increasing total biomass production of the forest ecosystem through the selection of highly efficient photosynthesizers and growing them under intense cultivation over short rotations. Essentially, a return is recommended to a form of the coppice system, that was employed extensively in Europe and the eastern United States during the nineteenth century, to produce fuelwood from hardwood stands regenerated by sprouting on short rotations. In its present-day
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manifestation (Schreiner 1970), the proposal is to use such fast-growing species as cottonwood, sycamore, red alder, or aspen reproduced by sprouting (or from root suckers in the case of aspen), to cultivate them intensively and to harvest them mechanically on rotations of two to four years (Ribe 1974). Yields of several tons of oven-dry plant material per acre per year are predicted on the basis of small plot studies, a multifold increase on that actually obtained from conventional forest management (Gordon 1975). Were such yields actually attainable over extensive areas without necessitating heavy energy investments in the form of fertilization, irrigation, cultivation, and mechani- cal harvesting, short-rotation silviculture would indeed have considerable promise. Unfortunately, so far, we have not been overly successful in growing hardwoods in plantations at all, let alone growing them at the rates attained from localized trials of genetically superior stock under intensive care in the nursery or other carefully monitored conditions. This is not to say that the experimental work is less than soundly based, but rather that we have notably failed to transfer the results of such small-scale research to large-scale commercial operations. The increasing need for alternative energy sources to fossil fuels has resulted in a renewed interest in growing wood and agricultural products for fuel. Speculative inquiries into this possibility may be extremely stimulating (Alich and Inman 1974; Szego and Kemp 1973), but are all too often based upon biological and silvicultural assumptions which have not been confirmed either by basic research or by applied field trials. Nevertheless, the potential is great. For instance. Young (1975) estimates the forests of Maine contain as much biologically-produced weight (biomass) outside the merchantable boles as is contained inside them. In addition, the below-ground portions of the forest are thought to contain one-third as much biomass as the above- ground portions. But, at the same time, wood has high costs of collection in both energy and dollars required for extraction. Under present conditions. Grantham and Ellis (1974) conclude that logging residue is and will continue to be too expensive for use as fuel only, but it is a potentially attractive source of material for products. While research should be continued on the possibility of greatly increasing the total biomass potential of the forest through intensive management of genetically superior species on rotations of two to four years, it would be unrealistic at present to assume that such techniques will have any widespread application in the near future. - 49 -
AREA OF COMMERCIAL FOREST LAND IN THE UNITED STATES There are almost 500 million acres of commercial forest land in the United States. Its distribution by types of ownership and region are summarized in Table 9. The Forest Service defines commercial forest land as forested land not withdrawn from timber production (as is the case for National Park lands and Wilderness Areas) and capable of producing in excess of 20 cubic feet per acre per year of industrial wood in natural stands. Currently inaccessible areas are included. Since the Forest Service defines "commercial forest11 solely in terms of productivity, the resulting estimate will exceed the area that can be logged at any given time. As of the date of the current estimate (1970) , the acreage is high because the Forest Service's estimate of commercial timber lands includes (Greentree Associates 1973): (1) private lands where commercial harvest is not allowed; (2) areas too steep or unstable to log without unacceptable environmental damage; (3) sites on which adequately stocked stands cannot be produced; (4) areas economically inaccessible; and (5) a portion of the inventory on lands where harvest is restricted (but not excluded) by law or regulation to protect other values. These considerations are recognized by the Forest Serv- ice itself. In the Outlook Study, some five million acres of forest in the Rocky Mountain area are excluded for one or more of the reasons cited, wikstrom and Hutchison (1971) found that 22 percent of the classified commercial forest land in six western national forests was not currently available for timber management and harvest. However, the impact on allowable cut proved to be less than the reduction in area. From economic considerations, Vaux (1973) estimated that 39 percent of the commercial forest land in California could not produce timber at costs equal to or below the forecast market price. Several have argued for a concentration of timber pro- duction upon the most productive sites (PAPTE 1973, Spurr 1974, Clawson 1974), pointing out that timber growing can be deemphasized (but not discontinued) on as much as a quarter to a third of our National Forests with only a minimal impact on total timber production. It should be remembered, though, that in actual forests, highly productive sites are frequently intermixed with less productive sites on an areal basis. Blocks of land dedicated to intensive timber growing, therefore, will often contain an admixture of poor sites; while other blocks of land on which multiple-use management is emphasized and where timber management is extensive will contain areas of high site quality. - 50 -
Table 9 Area of Commercial Timberland in the United States, by Type of Ownership and Section, January 1, 1970 Type of ownership Total United States North South Rocky Pacific Mountains Coast Area Proportion Thousand Thousand Thousand Thousand Thousand Federal: acres Percent acres acres acres acres National Forest 91,924 18 10,458 10,764 39,787 30,915 Bureau of Land Management 4,762 1 75 11 2,024 2,652 Bureau of Indian Affairs 5,388 1 815 220 2,809 2,044 Other Federal 4,534 1 963 3,282 78 211 Total Federal 107,109 21 12,311 14,277 44,699 35,822 State 21,423 4 13,076 2,321 2,198 3,828 County and municipal 7,589 2 6,525 681 71 312 Forest industry 67,341 14 17,563 35,325 2,234 12,219 Farm 131,135 26 51,017 65,137 8,379 6,602 Miscellaneous private 165,101 33 77,409 74,801 4,051 8,840 All ownerships 499,697 100 177,901 192,542 61,632 67,622 Source: The Outlook for Timber in the United States, U.S. Department of Agriculture Forest Service (1974) North: Including and east of North and South Dakota, Nebraska and Kansas. Including and north of Missouri, Kentucky, West Virginia and Maryland. South: Including and south of Oklahoma, Arkansas, Tennessee and Virginia. Rocky Mountains: Montana, Idaho, Wyoming, Nevada, Utah, Colorado, Arizona, and New Mexico. Pacific Coast: Alaska, Washington, Oregon, and California. - 51 -
Despite these suggestive reports, however, we have no overall basis for discounting the acreage estimates provided for us by the Outlook Study. In using these data, we must constantly bear in mind that the acreage estimates are undoubtedly too high. In the Pacific Northwest and southern pine regions, the economic value of timber growing should, to some extent, counter pressures to withdraw commercial forest land for recreational use or to convert high quality forest land into lower quality agricultural land. The commercial forest area of the United States will continue to decline in the future. Suburban sprawl, highways, and pipelines will reduce the area available to grow trees. In addition, it is possible that some forested lands will be cleared for agriculture. Drainage and flood control in the Mississippi Delta has permitted conversion of forests to agriculture in that area. The United States Department of Agriculture Economic Research Service (USDA 1974) estimates that there are 66.5 million acres of forest and "other" lands that could be used for agriculture, of which 27.3 million acres are in the Coastal Plains and Piedmont, 12.8 million acres are in the Northeast and Northern Great Lakes, and 10.4 million acres are in the Appalachian and Ozark Mountains. All of this forested land, however, is classified by the Economic Research Service as being of low potential for conversion to cropland. Among lands remaining forested, substantial acreages are expected to be withdrawn from timber production in order to be used as parks, wilderness areas, streamside and roadside reserve strips, and protection forests on lands too steep or fragile to be logged. In the Outlook Study, the area of commercial timber land in the United States, currently 499.7 million acres, is projected to drop to 494 million acres in 1980, 489 million in 1990, and 484 million in the year 2000. These reductions seem low. In his consultant's report to PAPTE, Marty assumes a reduction in the 1970 softwood acreage base of 20 percent on public and other private lands, and of 5 percent on forest industry ownerships, resulting in a reduction overall of 17 percent in the softwood forest land acreage. Again, we have not the data to predict the decline ac- curately, but the indications are that it will be fairly substantial. Furthermore, while past withdrawals for wilderness and recreational use have been to a considerable extent from non-commercial or low site forest land, future withdrawals will inevitably be to a greater extent from more productive commercial forest lands. - 52 -
The areas of commercial forest land in the Pacific Coast region and in the South are stratified by forest type, size class and site in Tables 10 and 11. For the Pacific Coast (Table 11), the Douglas-fir, hemlock-sitka spruce, and redwood types are combined in one column as are the ponderosa pine, larch, and lodgepole pine types in another. For the South (Table 10), the longleaf-slash and loblolly- shortleaf pine types are combined with limited acreages of other softwoods in the first column. Hardwoods are divided into upland hardwoods consisting primarily of oak-hickory but also including small acreages of maple-beech-birch, and lowland hardwoods consisting primarily of oak-gum-cypress but also including smaller acreages of elm-ash-cottonwood. These acreage data provide the base for projecting the increased yield potential from intensified forest management in these two regions, a topic that is dealt with elsewhere in the report. OVERALL POTENTIAL OF UNITED STATES FORESTS In concluding the section on the potential productivity of the United States with regard to wood, we may estimate in broad terms what could be achieved at different levels of management, leaving unanswered at present the probability of each different level being economically justifiable or politically or socially feasible. We assume that the forests of the United States as a whole will be managed in all instances on a sustained yield basis, and that annual harvesting will be closely related to annual growth, at least on the average over a period of years. Continuation of 1970 Levels of Management Forest management over the past twenty years has been growing steadily more intensive. It seems appropriate, therefore, to discount the possibility of a downgrading in forest practices and to join with the Forest Service in its Outlook Study by taking the continuation of 1970 levels of management as our base line. Summarizing the projections of the Outlook Study to 1985 and 2000, we find that the United States, with an annual harvest of 14 billion cubic feet of wood (225 million tons of wood and bark) in 1970 could produce 17.5 billion cubic feet (283 million tons) in 1985 and 20.3 billion cubic feet (330 million tons) in 2000 (Table 12). Much of the increase would derive from increased use of current hardwood growth. Taking into account changes in the acreage of forest land as predicted in the Outlook Study, production per acre would rise from 30 cubic feet per acre per year in 1970 to 37 in 1985 and 43 in 2000. Much of this improvement again - 53 -
Table 10 Area of Commercial Timberland by Forest Type and Site, 1970-South* (Thousand acres) Forest Type Site Classes I,II III IV V Total Softwoods Oak-pine Upland-Hardwoods Lowland-Hardwoods Non-stocked Total 13,478 53,452 89,626 35,984 192,542 Source: The Outlook for Timber in the United States, U.S. Department of Agriculture Forest Service (1974) *Data may not add to totals because of truncating. 5,825 21,850 31,998 8,318 67,993 2,630 8,163 15,430 4,718 30,942 1,923 9,343 28,794 16,744 58,806 3,061 13,839 11,740 3,381 32,024 36 254 1,660 2,820 4,771 - 54 -
Table 11 Area of Commercial Timberland by Forest Type and Site, 1970-Pacific Coast* (Thousand acres) Forest type Site Classes I,II III IV Total Fir- spruce 2,348 2,004 2,948 727 8,029 Western Hardwoods 4,184 1,946 1,980 434 8,545 Non- stocked 1,470 680 1,113 442 3,707 Total 23,628 15,572 22,904 5,518 67,622 Douglas-fir 13,728 Hemlock-Sitka spruce Redwood Ponderosa pine 1,895 Lodgepole pine Larch-pine 6,458 8,245 4,482 8,616 1,194 29,627 2,719 17,712 Source: The Outlook for Timber in the United States. o.S Department of Agriculture Forest Service (1974) *Data may not add to totals because of truncating. - 55 -
Table 12 Prediction Production of Roundwood Timber Assuming the Continuation of 1970 Levels of Management 1970 1985 2000 billion cubic feet Production Softwoods 9.6 11.0 12.1 Hardwoods 4.4 6.5 8.2 Total 14.0 17.5 20.3 Area million acres Softwoods 207 209 213 Hardwoods 267 263 261 Non-stocked 21 15 10 Total 495 487 484 Production per acre cubic feet per acre Softwoods 46 53 57 Hardwoods 16 25 31 Total 30 37 43 Volume can be converted to weight basis by multiplying by 27.4 pounds per cubic foot for softwoods and 32.8 pounds per cubic foot for hardwoods. Source: The Outlook for Timber in the United States, U.S. Department of Agriculture Forest Service (1974) - 56 -
in would be attributable to increased use of hardwoods. For softwoods, production would increase from <*6 cubic feet per acre per year in 1970 to 53 in 1985 to 57 in 2000. A Revised Estimate of Production Potential Any effort to estimate the total productivity of United States forests must be highly tentative and based upon assumptions which greatly simplify the actual situation. In our approach, we predict production in terms of the total bole volume of trees 5 inches and over in diameter, breast high above stump, and excluding the top above a top diameter of 4 inches, with the understanding that incomplete use of this portion of the bole will result in lower production and that the potential exists for substantially greater production through complete tree use. The use of forest land to grow trees for materials use and the intensity of management of such lands to grow such products are highly dependent upon economic considerations, upon political and management decisions in the case of public land, and upon ownership motivation and management decisions in the case of private forest lands. Inevitably, public lands will be withdrawn from timber production and assigned to other uses. Similarly, the owners of small tracts of forest will often neither be interested nor find it economically profitable to manage their holdings intensively for timber production. It is not our present responsibility to evaluate and predict the course of the social, political, and economic factors that will play a large part in determining the actual future course of timber production in the United States. Our assignment is rather to assess the biological productive potential. We have broadened our inguiry only by assuming that the better the forest site, the more intensive will be the management, and that management will, on the average, continue to be more intensive for softwoods in general, and for Douglas-fir and southern pine in particular, than for hardwoods and for other softwood species. The exact nature of the simplifying assumptions are detailed in the following pages. Projected Forest Areas The projected acreage of commercial forest land in the United States for each broad site productivity class and for softwood and hardwood types separately is summarized in Table 13. In developing this projection, the following assumptions were made. First, the acreage of commercial land is predicted to decline from 495 million to U75 million acres, - 57 -
Table 13 Projected Changes in Area of Commercial Forest Land under Intensive Management by Site Class and Species Group Softwoods 1970 Projected, 2020 Hardwoods 1970 Projected, 2020 Non-stocked 1970 Projected, 2020 Total 1970 Projected, 2020 I,II Site Productivity Class III IV V Total (million acres) 34 38 60 94 101 54 47 242 261 75 16 15 54 50 95 78 67 58 232 201 2 0 2 0 6 11 10 21 13 3 52 53 116 125 195 182 132 495 475 115 - 58 -
the level predicted in the Outlook Study for the year 2020. Second, all Site I, II and III non-stocked lands, three million acres of Site IV lands and one million of Site V would be reforested with softwoods. Third, 4.9 million acres of Douglas-fir types would be raised one site class through nitrogen fertilization, and 5.8 million acres of southern pine types would also be raised one site class through drainage and phosphate fertilization (Table 5). Fourth, 15 million acres of pine-hardwood and five million acres of upland hardwood in the South would be converted through clearcutting and planting to southern pines with an average increase in site quality of one class, owing to the faster growth rate of pines on these sites (Table 6). Fifth and finally, commercial forest lands would be maintained well stocked with desirable species by planting and weeding as needed to produce 90 percent of normal yield table growth on Sites I and II, 80 percent on Sites III, 70 percent on Site IV and 60 percent on Site V. Under these assumptions, and rounding off each category to the nearest million acres, it will be seen that the acre- age of softwoods would be increased from 242 million to 261 million acres despite the overall loss of 20 million acres of commercial forest land, and that most of this increase would be on the better sites. The assumptions are optimistic but technically feasible and economically well within reality. Projected Volumes To obtain the projected volume of timber produced, the number of acres in each category is multiplied by the assumed production per acre per year. If the total area was fully-stocked so that yield table predictions could actually be produced, it was assumed that the production per acre would be the mid-point in each site productivity class. (For the top site category, the mid-point was weighted down- ward to account for the fact that this class contains more acreage near the lower end of its range than at the upper end.) As previously discussed, however, yield table values cannot actually be achieved over large acreages. We assumed, therefore, that management would be sufficiently intensive to produce 90 percent of normal yield table values on the highest sites, based on European experience, and slightly less intensive on each descending site class producing 80 percent of yield on Site III lands, 70 percent on Site IV, and 60 percent on Site V. Applying these assumptions, we obtain a mean annual pro- duction of 145 cubic feet per acre per year on Sites I and II to 21 on Site V. Multiplying these values by the appropriate acreage projections, we estimate a potential - 59 -
productivity of softwoods of over 17 billion cubic feet per year and hardwoods of over 11 billion for a total of 28.5 billion cubic feet (Table 14). This estimated productive potential is twice that of 1970 consumption of 14 billion cubic feet. In this projection, anticipated production is 67 cubic feet per acre for softwoods, and 56 cubic feet per acre for hardwoods. For all species, it is 62 cubic feet per acre, compared to the present actual rate of 30 cubic feet per acre per year. These estimates are based on revised acreage projections detailed above and the simple assumption that the level of manaqement will decline with site class. In addition, there exists possible gains through realizing a greater percent of the gross production through an intensive thinning regime, and of obtaining faster growth rates through a broadly- applied tree improvement program. Thinning and Genetic Improvement The possible gains through thinning and use of improved genetic materials has been discussed earlier. We concluded that, in general, normal yield table values can be increased by 25 percent by regular thinnings, and that on those areas clearcut and planted with softwoods, growth would be increased by about one percent per year if tree improvement programs were vigorously applied on a broad scale. Just as it is highly improbable that all forest lands can be kept fully stocked so as to produce the full yields predicted by normal yield tables, it is equally improbable that intensive thinning and tree-improvement regimes can be applied to all forest lands. In the latter case, it is likely that the main applications will be on the better forest sites in the commercially important and already well- managed Douglas-fir and southern pine regions. On this assumption, and admitting the great degree of simplification inherent in it, we can make a rough estimate of the potential effect on biological productivity if thinning and genetic improvement are carried out on the better sites in these two regions. For both thinning and genetic improvement, we postulate an average improvement of yield of 15 percent on Sites I and II, of 10 percent on Site III, and of 5 percent on Site IV. No gain is predicted for Site V. These predictions are substantially less than the theoretical gain, but take into account the probability that as the site quality decreases, so does the likelihood that thinning operations will be carried out at regular intervals, that thinnings will have - 60 -
Table 14 Projected Productivity of U.S. Commercial Forests under Intensive Management by Site Classes and Species Groups I, II Site Productivity Class III IV V Total Projected Growth cubic feet per acre per year Normal yield 161.5 102.5 67.5 35.0 Management intensity 90% 80% 70% 60% Projected yield 145 82 47 21 Projected Production Softwoods U. S. Added Douglas fir Added Southern pine Total Hardwoods Total U. S. With added DP & SP million cubic feet per year 5,510 602 344 6,150 128 360 4,747 30 987 0 0 17,394 760 1,119 215 6,456 6,838 4,992 987 19,273 2,175 4,100 3,666 1,218 11,159 7,685 8,631 10,250 10,938 8,413 8,658 2,205 2,205 28,553 30,432 - 61 -
tree improvement program. As with other assumptions, this one is made to fall within the realm of being entirely feasible from a silvicultural viewpoint, and reasonably possible within the range of future economic, political and social conditions. Applying the potential gain in growth from thinning and genetic improvement, we predict an increase in productive potential of 760 million cubic feet annually in the Douglas- fir region and 1,119 million cubic feet from southern pine. Adding these two gains to the earlier estimate, we predict a total biological productive potential of 19 billion cubic feet (290 million tens of wood and bark) for all softwoods, 11 billion cubic feet for hardwoods (200 million tons), and over 30 billion cubic feet (490 million tons) for all species. - 62 -
