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OCR for page 116
MeaSUring FUnC[iOn and DiSfUnCIiOn in ECOSYS[emS
ALICIA I. BREYMEYER
Institute of Geography and Spatial Organization
Polish Academy of Sciences
Debates over the forms of environmental damage caused by increasing
and hasty human activity often revolve around a central question: How
should these deviations be measured? This is an especially difficult issue in
moving from simple situations where injury can be easily observed to more
complicated ecological systems, i.e., ecosystems composed of hundreds or
even thousands of species which, within their trophic groups, are disposed
to take over the niches and functions of eliminated competitors. These
deviations should be recognized early, when adverse effects begin to occur
in an ecosystem and when remediation is still possible; belated recognition
of dying ecosystems signals both ecological disaster and the defeat of
ecologists who have not foreseen them.
The behavior and condition of particular species do not necessarily
reflect the condition of the whole ecosystem, unless the system is dominated
by only one producer species. Except for agriculture, monocultures are
rather rare today; however, in Europe, until quite recently, pine cultures
had been maintained for several generations, i.e., for several hundred years.
Over such a long period, a specific ecosystem based on only one producer
species is formed. Such a system will be fundamentally altered if the main
producer of organic matter (e.g., pine) is devastated, and only in such a
case can the state of an ecosystem be evaluated through the condition of a
single species. Usually, however, there are many producers in an ecosystem,
and the state of the ecosystem cannot be recognized from the condition of
only one species of plant or animal.
Some very specific types of ecosystems function with one or few con-
sumers, such as the case of a tundra ecosystem described by Klekowski and
Opalinski (1984~. The tundra in the Fugleberget catchment on Spitsber-
gen, north of Norway, is supplied with allochthonous organic matter and
116
OCR for page 117
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT
117
nutrients from breeding colonies of marine birds feeding in the near-shore
waters and nesting on land. The excrement of birds is distributed by surface
waters and fertilizes a thin layer of soil. However, there are usually many
consumers in an ecosystem, and their condition is not in itself a sufficient
indicator of the state of the ecosystem. Similarly, particular plant species
commonly used as bioindicators are not adequate to diagnose the condition
of an ecosystem They may indicate the contamination of air, soil, or water,
and therefore, work as live instruments to measure concentrations of differ-
ent chemical compounds (Chapter 14, this volume). However, they do not
answer questions about the response of an ecosystem to these substances,
nor do they characterize its condition.
ECOSYSTEMS: DEFINITION AND FUNCTION
In order to make further discussions more explicit, we should define
what is meant by an ecosystem (Breymeyer, 1981b). An ecosystem is an
ecological system in which organic matter produced within this system (or
partially from outside) is transformed at successive trophic levels according
to known and described patterns of matter cycling and energy flow. This
definition is consistent with the hierarchical approach presented by O'Neill
et al. (1986~.
The ecosystem is treated as a "medium number system," consisting of
a number of smaller functional components. Such an explicitly functional
definition of an ecosystem makes its delimitation difficult; generally speak-
ing, so-called "small cycles" of basic elements are included in this system
as they are conditioned by biotic components of the ecosystem. "Large
cycles" of energy, water, and elements are dependent on atmosphere, ge-
ology, and other physical and chemical factors. These are external and can
be considered only as an environment in which the ecosystem functions.
The main inputs from this environment to the ecosystem are solar
energy, 02, C02, and water solutions of essential elements. Main outputs
are gases, the energy dispersed in metabolic processes, and the remains of
organic matter falling into the soil or sediments. Interpreted in this way,
the boundaries of an ecosystem are designated in the diagram of carbon
cycling (Figure 1~. The ecological system operates within these limits; its
environment is outside.
The creation and transformations of organic matter through a network
of functioning trophic levels are the basic ecosystem processes. These are
the production of organic matter, its consumption and incorporation into
the bodies of successive consumers, and its breakdown by decomposers.
This sequence of basic ecosystem processes included in the functional defi-
nition of an ecosystem is necessary for the self-restoration of an ecosystem
and for its theoretically unlimited duration. Under conditions of increasing
OCR for page 118
118
CO2 recRperai
~ \ _ _ ~ 1 1 ~ ~
Water—atm~ ~ ,~ /
equilibrium ~~= ~~.~ ~ AM
Fossil energetic
sources
1_~:
., plants and~nima~ ~ ~ Icanism
~ ~ (mu) S a?:
~J~/
~/Dr ~:
ECOLOGICAL RISKS
|lU[~
bit
; r MU;
'art
et totem,
A
Decompositiop7~7' as
rock'
FIGURE 1 Carbon cycle and ecosystem boundanes. The "small" carbon cycle is framed
by the ecosystem boundary (IIIIII); the "large" carbon pycle connects the ecosystem with
the outside environment (Duvigneaud and linghe, 1962, adapted).
human impact, fewer ecosystems function solely on the basis of internal
production of organic matter. Similarly, the process of decomposition,
which releases nutrients necessary for biomass production and subsequent
recycling, is often supplemented by intended or unintended fertilization
from human activities. However, in spite of the fact that basic ecosys-
tem processes are intensified or limited from outside, the fundamental
ecosystem function is still the same: energy flow and cycling of matter.
The functional definition of an ecosystem provides a convenient ba-
sis to determine the limits of ecosystem capacity for pollutants and other
stresses, i.e., the limits of ecosystem resilience can be estimated by the
resilience of ecosystem processes. These processes can obviously be inten-
sified or reduced; and the proportions among production, decomposition,
OCR for page 119
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT
119
and consumption can vary in each ecosystem. However, these processes
must continue. If any of them disappear, the ecosystem by definition no
longer exists. The disappearance of ecosystem processes is measurable, so
the capacity (vulnerability) of an ecosystem can be measured as well.
How can we determine the level at which the rates and the character of
ecosystem processes are altered from their ~`natural'' state, resulting in dis-
turbances in the functioning of the whole ecosystem? Comparative analyses
provide a useful starting point. The natural range of rates of ecosystem
processes should be determined in presently existing, ecologically stable
ecosystems operating at different levels of production and decomposition.
Comparative ecology of ecosystems provides the opportunity to utilize both
older data from literature and recent information collected intensively at
several ecological centers. Examples are the current studies of Berg et al.
in Sweden, Meentemeyer and Box in the United States, Singh in India, and
Parkinson et al. in Canada. In Poland, investigations of pine forests are
carried out on a rather wide scale; data from these studies have yet to be
published, but they are partly used in this chapter.
NATURAL INFLUENCES ON ECOSYSTEMS
Climate is the basic factor of the exterior environment that conditions
the production and decomposition of organic matter in ecosystems. Mate-
rials from the International Biosphere Program (IBP) and the older studies
compiled by O'Neill and DeAngelis (1981) show the dependence of forest
productivity upon two basic components of climate: temperature and pre-
cipitation (Figure 2~. These comparisons are based on a wide range of both
elements of climate comprising the whole earth, so that the extreme values
of forest productivity are represented. A similar, distinct pattern exists for
the productivity of grassland ecosystems over a wide range of precipita-
tion (Figure 3~. The allocation of aboveground (green) and underground
biomass in grassland ecosystems shows distinct dependence on the quan-
tity of water available to the site (Figure 4~: the fraction of underground
biomass increases with decreasing precipitation.
Litter decomposition measured along the transect from northern Swe-
den to central Poland seems to react to lower average temperatures by
decline in the decay rate (Figure 5~. Stands examined along the transect
were chosen with great care; pine forests of similar age growing on similar
sandy soil were selected. The range of precipitation is not wide, although
the two Spanish sites are situated in much drier conditions. The differen-
tiation of temperature can be assumed to be the primary limiting factor,
although the dependence is not simple, as can be seen in the variability of
measurements.
OCR for page 120
120
ECOLOGICAL RISKS
30
25
>, 20
_ .
1,~
15
10
5
(_) O 1 i- o
~ -13 -10
C 30
At:
25
llJ 20
Hi:
~ 10
C)
15
5
o
~0
oo
o
Off
Otp ~
00 10 20
TEMPERATURE (C°)
oo
o
~:e
l 1~
o
.
30
0 1000 2000 3000 4000
PRECIPITATION ~ MM ~
FIGURE 2 Forest productivity in relation to temperature and precipitation. Open and
closed circles show two sources of information (IBP data after Reichle measurements, cited
by Lieth, 1975).
Meentemeyer (1984) calculated the index of evapotranspiration and
showed its correlation with decomposition. The question of the dependence
of litter decomposition on its lignin content has provoked heated debate.
Initial calculations made on measurements from the temperate zone suggest
that the rate of litter decomposition could be precisely predicted by lignin
content. Very high correlations of both these values were recorded in
subsequent studies. This index was not applicable to a desert environment
in which the rate of litter decay was found not to depend on lignin content
(Schaefer et al., 1985~.
Berg (1986) surveyed the research on the dependence of litter de-
composition rate on its chemical composition, suggesting that different
stages of decomposition are controlled by different factors and that there
are "lignin-controlled" as well as "nitrogen- and phosphorus-controlled"
OCR for page 121
HUDSON EFFECTS ON THE TERRESTRIAL ENVIRONMENT
~ 1600
—1200 ·
`, 800
Om: I;: -
400 1
.
.
D
400 800 1200 1600 2000 2400 2800 3200
DRY WEIGHT 9 m~2 y-1
121
FIGURE 3 Annual precipitation and aboveground production of grasslands (Breymeyer,
1981).
~ 2000
-
Z 1600
~ 1200
tL
(3 800
or
400
f
.
.
.
.
·e
~ · ·.
~ ·S
-
4 8 12 16 20 24 28 32 36 40
UNDERGROUND TO GREEN BIOMASS RATIO
FIGURE 4 Ratio of underground/green biomass in relation to precipitation for
types of grasslands (Breymeyer, 1981).
OCR for page 122
122
60
To
of
Oh
CO
o
~ 40
CD
LL
20
ECOLOGICAL RISKS
f
2
3
·
.
·
.
.
~ D
45 50 55
LATITUDE
FIGURE 5 Litter decomposition as percent weight loss (litter-bag method) in first year
of exposure in coniferous forests of different latitudes. 1=Spain, 2=Sweden, 3=Poland
(according to data from Berg et al., 1983; Alvera, 1981; Breymeyer, in preparation).
stages. Meentemeyer and Berg (1986) attempted to link chemical and cli-
matic factors in their map of the rate of decomposition of pine needles for
all of Scandinavia (Figure 6~. The map predicts the rates of decomposition
of the material with known, constant chemical composition, using the index
of actual evapotranspiration as the driving variable.
On a geographic scale, one of the best known indices of production is
the fall of litter. This is a good comparative measure of forest productivity,
though it is known that the correlation between litter fall and production
becomes less direct in more productive forests (Figure 7~. Nevertheless,
measurement of litter fall is commonly used as a measure of forest pro-
duction, particularly in monitoring programs (Breymeyer 1981, 1984) or
OCR for page 123
HUM 4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
A / -
30 ~
~00
i
JO
JU ~
r~30
ry o
Con
f
ALL
a'
~ 1
rid
—20
123
FIGURE 6 Isolines of decomposition rates for Scandinavia. The first-year needle-litter
mass loss cloy was predicted on the basis of similar initial chemical composition of needles
(N=0.41~o, P=0.022~o, lignin=25.7~o) with changing actual evapotranspiration (AEI) value
(Meentmeyer and Berg, 1986, amended).
in modeling (Ajtay et al., 1979), since the complete estimation of forest
productivity is quite laborious.
Theoretically, it can be assumed that all biomass produced in an ecosys-
tem must at some time die and fall into the soil or sediments; error in this
estimation results from ignoring the loss of biomass eaten by consumers, as
some portion of organic matter produced is always consumed before it falls
down. In forest ecosystems, this error can be neglected. According to the
estimates of different authors, the consumption of crown herbivores does
not exceed a few percent of a canopy biomass, except in conditions of pest
outbreaks. Hence, litter fall the measure of "annual green production" of
a forest~an be assumed to be a good index of total aboveground produc-
tion of a forest ecosystem. As an example, the production and production
OCR for page 124
124
2000
1500
cat
18
_ 1000
as
-
-
-
500
to
ECOLOGICAL RISKS
-
_
/
/
/
i- S · .
/ X~-
~ ·.—
/
of- ~ I
/
··~-
/
. - · — ~
.
500 1000 1500 2000
Above ground net primary production {gm I'
FIGURE 7 Annual litterfall as a function of aboveground net primary production. The
solid line shows the situation when the loopy of production falls down (O'Neill and
DeAngelis, 1981; Debazac, 1983; Grodzinski et al., 1984~.
efficiency in four mixed-pine forests in Poland and the United States can
be analyzed (Table 13. According to these measurements, it can be assumed
that half of aboveground forest production falls to the soil annually; in the
years when cones are produced, this percentage is considerably higher.
Let us analyze the dependence of litter fall on climatic conditions
(Figure 8~. (It is worth mentioning that only a small number of research
centers have undertaken studies of complete forest productivity.) A large
number of measurements show that the amount of organic matter delivered
to the soil in forests decreases with nothward movement from the equator.
This dependence is unquestionable within the gradient from 0° to 70°N
latitude. However, at a smaller scale, such as the size of the territory of
Poland (6° in latitude, 49° to 50°N), variance is relatively large and the
data do not show any correlation with latitude.
OCR for page 125
HUMAN EFFECTS ON THE TERRESTRL4L ENY7RONMENT
TABLE 1 Production and production effiacocy in four stands of mid pine forest.
MEASUREMENTS
FOREST STANDS
1 2 3 4
Tree production
Tdw ha-1 ye
% of total:
2.5 4.7 7.9 14.3
Leaves, fruits, twigs. 40.4 53.7 24.7 57.4
Production efficiency (PIB)
Trees
Leaves
1 - - - 5%
50 - - - 53%
SOURCE: Reiger et al., lS84; Whittaker and Marks, 1975.
125
On the basis of this information, one could conclude that the minimum
north-south span for observing litter fall must be 20°. Does this also
mean that the total production of these ecosystems reacts to changes in
macroclimate only when the area comprises 20°? Some data suggest that
such areas may be even more extensive. The measurements of wood
production collected during the IBP are noted in Figure 8. Although the
values maintain the general increasing trend from the north toward the
equator, they show no such clear tendency between 30° and 60°N; in these
latitudes, wood production may actually increase as one moves northwards.
These measurements are not numerous, so it is not yet known whether this
tendency is definitive or not. Nevertheless, it is an indication that climate
regulates the wood production only over large areas.
Some idea of the variability of organic matter on a global scale is
offered bv the man bv Olson et al. fl9831 entitled "Major World Ecosvstem
~ ~ , ~ , ~ _ ,
Complexes Ranked by Carbon in live Vegetation." The Eurasian continent
is reproduced from this map in Figure 9. The biome of temperate needle-
leaf forests is marked according to the UNESCO-Udvardy (1975) blame
map. This biome covers four classes of the complexes defined by Olson et
al. (1983~: tundra; northern and maritime taiga; main and southern taiga;
and cool conifer. According to the measurements collected by Olson et al.,
tundra is characterized by the smallest biomass (i.e., carbon accumulation)
at 0-1 kg cm~2. Northern and maritime taiga accumulates at 3-6 kg cm-2;
and the main and southern taiga and cool conifer complexes are both
characterized by a wide range of carbon accumulation at 4-25 kg cm-2.
Zonal distribution of these ecosystem complexes is distinct, especially in
the case of two -taiga complexes. Further analysis of the map shows that
this natural variability of needle-leaf forest takes place in the span of 20°
North-South. Does this mean that living carbon in ecosystems is more
OCR for page 126
126
~1
a:
ECOLOGICAL RISKS
18
16
14
12
10
8
6
4
2
1 o
o
X
o XX
xx
o X
o XX
X X
_~ ~ _
X
2 -
3 x
4 0
5 +
6=
7.
o
~0
AX X
.
x X ~ Ibex
~~ 4,1 X
Act; Xl it
X 0° o++ ~ O ~
0 ~ ~ ~
o + ~
· °
60 70. N
0 10 20 30 40 50
LATITUDE
FIGURE 8 Annual litterfall in relation to latitude. 1=Bray and Gorham, 1984; 2=IBP
Woodland Data Bank (Reichle, 1981~; 3=Vogt et al., 1986 (broadleaved forest); 4—Vogt et
al., 1986 (needle forest); 5=Breymeyer et al.(unpublished data); 6=Alvera, 1980; 7=means
and standard errors of measurements of wood production according to Woodland Data
Bank. Vogt et al. data are collected for northern and southern latitudes, the others for
northern latitudes only.
OCR for page 130
130 ECOLOGICAL RISINGS
T , S A
I II III IV SEASONS I
.
II III IV
FIGURE 10 Biomass of various groups of soil fauna (g fw m~2) in three grassland
ecosystems: T=non-polluted meadow of medium fertility in Poland (data from literature),
S=Szc~yglowice meadow in Silesia (moderately polluted); A=industrial Aniolki meadow
(heavily polluted). Circle size is proportional to the total biomass of soil fauna (for a
non-polluted meadow the biomass 135 g fw m-2 was assumed). In each circle three groups
of fauna are shown as percentages of total biomass: 1=microfauna, 2=oligochaeta, 3=other
invertebrates. Samples were collected in four seasons and three years (spring, summer, fall,
and winter 1978-1980) (Cianciara and Pilarska, 1984, amended).
TABLE 2 Increase in content of selected elements in the bodies of three main
groups of consumers in a NPK fertilized meadow. Calculated on the basis of
consumer biomass evaluated on fertilized and Fertilized plots (ma m~3.
Invertebrate bodies Elements Fertilized
from trophic groups analyzed Non-fertilized
Phytophagans C 1.55
N 1.70
K+Na 1.72
Saprophagans C 1.71
N 1.69
K+Na 2.00
Predators C 2.73
N 2.88
K+Na 3.00
SOURCE: Machnacka-Lawacz and Olechowicz, 1978.
there was a kind of nitric fertilization which caused substantial elongation
of needles and sprouts (shoots), but also induced their flabbiness and early
dropping from the trees (Jakubczak and Pieta, 1968~. Several years later,
the first portions of the forest began to die, and the border of living
forest moved away from the factory. Investigations on the production and
decomposition of organic matter in the area were carried out in the period
1980-1982. In successive zones moving away from the factory, a whole
range of changes could be observed a zone of bare soil; a zone of thick
litter composed of very long needles and twigs; a zone of dwarf pines;
OCR for page 131
HUAf4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT 131
~ _~.% ~] ~ Hi , ~- d., ~~%~.~% -,: ~
FIGURE 11 Distribution of coniferous and mined forests and air pollution in Poland.
The map was elaborated at the Institute of Geodesy and Cartography in Wa maw under the
supervision of Andrzej Ciolkosz on the basis of L~dsat MSS and Salut-6 images acquired
in 1978. The isolines delimit the area with SO2 mean annual concentration equal/higher
than 50 micrograms per m3; dark areas show regions above 150 micrograms. Data on
pollution Mom the map predicting air pollution in Poland in 1990 lay J. Juda et al., 1982
(manuscnpt).
and the forest wall. Living but strongly damaged forest was characterized
by already small organic fall from balding trees and a high rate of litter
decomposition. Grabinska (dissertation, 1985) suggested that this was
probably abiotic decomposition, as the litter was dissolved in the solution
of nitric and sulfur compounds in rainwater.
Let us move on to the territory of Poland as a whole and the condition
of coniferous forests as demonstrated by scientists and foresters. Satellite
pictures of pine and mixed-pine forests in Poland are shown in Figure 11.
The simulated isolines of contamination by sulfur oxides delimit the area
of real danger for conifers as projected to 1990. Present evaluations by
forestry services of the state of these forests are shown in Figures 12 and
OCR for page 132
132
,
,
to ~ ~ ,
''art:
ECOLOGICAL RISKS
NOx
FIGURE 12a Pollution of Polish coniferous forests by NOT in 1986 measured 1,800 points
as dry sediments on specifically prepared filter paper exposed for 30 days in the canopy.
Contamination expressed as mg m 2 d 1 in four classes: 1=0.000-0.200 ma; 2=0.201 -
0.5000 ma; 3=0.501-1.000 ma; 4=higher than 1.001 ma. A=winter pollution, B=summer
pollution.
13. Comparison of winter (i.e., heating season) and summer contamination
of forests provides a basis for some optimism: in many regions, forests are
not as stressed during the warm season when heating is not used.
STATUS OF FOREST ECOSYSTEMS IN POLAND
According to maps of potential vegetation and the knowledge of geo-
botanists, Poland should be covered with a mixture of forest types. Due
to various factors, however, Poland is covered primarily with coniferous
forests, which constitute more than 75% of total aboveground biomass of
forests in the country (pine alone covers 62%~. Of the total production of
OCR for page 133
HIJAL4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT 133
E
zczecln
.
NOx
FIGURE 12b
L . ~ ~ ,.,
_; ~ I,'
,,
.,
.,
Polish forests, conifers make up 74%, and pine alone is 54.4% (Figure 14~.
Of the three species of conifers grown in Poland, pine shows the lowest
productivity and yet provides the greatest wood production in the country,
since pine forests occupy the largest area. Coniferous forests are considered
to be the terrestrial ecosystems most imperiled by air pollution; they are
affected particularly by sulfur and nitric oxides, whose concentrations in
the air have recently increased considerably (Figure 12~.
There is.still no single answer as to which mechanisms are responsible
for the dying of coniferous forests, but some are particularly worthy of
analysis. Coniferous forests, and pine forests in particular, are in general
ecosystems of cool climates and poor soils. Matter cycling is rather slow in
these ecosystems, and the rate of organic matter decomposition is distinctly
slower than. in deciduous forests (%ble 34. Interesting mechanisms for
saving essential elements in these ecosystems are described in Figure 15.
OCR for page 134
134
A
ECOLOGICAL RISKS
FIGURE 13a Pollution of Polish forests by SO2. Description as for Figure 12. Masses of
contamination: 1=0.000-10.000 mg m-2 dot; 2=10.001-30.000; 3=30.001-50.000; 4=above
50.000 ma. A = winter pollution, B = summer pollution.
Pine trees translocate some essential elements from the needles before leaf
fall. In this way, the forest accumulates a larger portion of elements in
plant tissue instead of losing them from litter and sandy soil. Moreover,
conifers shed their needles two or three times slower than do other plants
in similar climates. Consequently, pine forests can be considered to be the
ecosystems that retain in their biomass a relatively large proportion of the
elements taken from the abiotic environment.
This tendency to accumulate the elements which are difficult to acquire
can be seen as an evolutionary strategy. However, this strategy may turn
against coniferous ecosystems. When the chemical composition of the
atmosphere and water changes rapidly in the surrounding environment,
OCR for page 135
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT 135
R
~~ ART;-—
! _
so2
FIGURE 13b
/
"sparing" (nutrient-conserving) ecosystems are more susceptible to gradual
poisoning than are others that dispose of toxic substances more rapidly.
With respect to control mechanisms, the tendencies recorded in forest
ecosystems are similar to those observed in grasslands in heavy stress sit-
uations, the number of species often decreases, the percentage of predators
increases, and the dominance structure becomes more uneven (i.e., fewer
species are dominant). These tendencies were recorded by Lesniak (in
press) in his investigations of soil and epigeic (soil surface) invertebrates
carried out in 52 forest districts distributed over the entire territory of
Poland. In plots situated in pine forests of southwest Poland (which are
heavily polluted), 71% of all predators were registered in epigeic fauna,
while in northeast Poland (which is least polluted), the percentage of
predators was only 28%
The regulatory mechanisms induced by an increasing share of predators
OCR for page 136
136
ECOLOGICAL RISKS
:~: ]~ 1~' me -'5~-~(
-~U=:
4_~ --I am-_ ~=
FIGURE 14 Composition of forests in geographical units in Poland. The portion of
tree species expressed as percent of surface covered by this species. 1=pine; 2=spruce;
3=fir, 4=beach; 5=oak; 6=birch and hornbeam; 7=alder and aspen (1tampler et al., 1982,
prepared from Forestry Service Data).
and their increased metabolism rate are strengthened in stress conditions;
perhaps this is the first distinct, repeatable reaction of an ecosystem noted
in the case of changing conditions. Is the ecosystem trying to defend and
adapt itself in this way? And how does it influence the pattern of matter
circulation and the budget of production/decompostion? These are still
open questions, but the answers must come soon as the demands of society
and the interest of scientists grow simultaneously.
EVOLUTION OF ECOSYSTEMS
Considering the functioning and the character of ecosystems as de-
fined above, we often pause on the question of their evolution: How
do ecosystems make evolutionary progress since they do not inherit their
OCR for page 137
HUMAN EFFECTS ON THE TERRESTRIAL ENVIRONMENT
TABLE 3 Weight loss of litter in central Poland. Litter bags exposed on 28
stands (10-30 bags per stand) during warm season. Decomposition rate expressed
as percent of initial weight.
Site
Forest type Number of
stands
Daily decomposition
rate (%)
Bolimow
Malogoszcz
Pulawy
Bialoleka Dw.
Pine and mined 6 0.08-0.30
Pine 7 0.10-0.24
Pine ~ 0.20-0.24
Pine and mined 2 0.22
Coniferous 20 0.08-0.30
20
Bialoleka Dw.
Bialoleka Dw.
Bialoleka Dw.
2
Alder
Birch l
Oak hornbeam 5
Broadleaved 8
0.34
0.44
0.51
0.34-0.51
SOURCE: Unpublished data, Breymeyer and Grabinska.
PINE FOREST
NUTRIENTS C N K P
IN GREEN
LEAVES
(kg/ha)
17780 s7.4 3Q3 As
RET RAN SLOCATI ON
INTENSITY
LEAF FALL I
1 12072
1 ~
1 11 -
p6~/.l ~ ~ 435
57DE
1 1
1 1
~ V
N al P
13.9 2s 1.2
- o.s1
3~0
67
Lit
137
BROADLEAVED FOREST
(P 1[ N C I
I 55 138 92.3 1721.0
~~-
~ 1
. ~
2291.
~1 1
L-l 1 7°,.
l
~ l I I
t I I
P K N
L4.6 10.8 85fi
oil
V
C
.0 1
l
FIGURE l5 Pattern of nutrient transfer to soil in pine and alder forests (Stachu~ki and
Zimka, 1981; modified).
characteristics as do species? They have no mechanisms of heredity, since
they are not organisms provided with sets of features coded in their genes.
However, it appears that ecosystems adjust so as to permit the recurrence
of the composition of species (or the communities of ecologically redundant
species) worked out during long-term evolution. And perhaps ecosystems
evolve by even simpler means than the do cogeneric populations.
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138
ECOLOGICAL RISKS
If, for example, a sand dune is colonized, the first group of colonizers
is selected; there are only a small number of pioneer species that are fit
for living on dune sand. They prepare the environment for succeeding
species, which in turn do the same for the next generation. A layer of soil
appears and it grows thicker, pine seedlings attach in it, and the succession
proceeds In the same way, only to reach the climax stage as one of the
forest associations common to the climatic zone. Just as in the case of
populations where conditions select the fittest of overabundant progeny, it
can be assumed in the case of an ecosystem that only certain groups of the
overabundant seeds, spores, or juvenile forms of plants and animals which
expand in different ways and are ready to colonize a given area will be
accepted there. These sets of species or communities:
· accept the physical conditions of an area;
· can produce organic matter or feed on organic matter produced
there; and
· can defy competition or other ecological dependences which grow
in number and intensify as the colonization of niches increases.
In the conditions of a cool temperate climate, forest succession must
take more than 200-300 years to reach a climax forest stage (assuming that
the forest attains maturity at an age of about 100-150 years, and all of
the intermediary stages can develop and last for shorter penods). It is not
proven how much time is needed to develop the complex trophic structure
registered in contemporary forest stands. Probably many generations of
trees produce the pool of organic matter in the forest soil as detritivores
gradually enter the soil and put in motion the circulation of elements.
Can this be recognized as a beginning of ecosystem function? And
how many years are needed to develop sets of species ready to replace or
complete each other In all points of the trophic net? Kornas (1972) dis-
cussed the historical background of European and North American conifers
(genus Pinus, Picea, Abies, Lards) from the boreal zone of coniferous taiga.
The author believes that Eurasiatic and North American lowlands were
colonized by taiga-type forest not earlier than in the Holocene. The taiga
trees have had their long, early history in primary centers in the moun-
tains of Eastern Asia and Pacific North America, and they dispersed in
lowlands after Pleistocene glaciation (before the Tertiary Holarctic realm
divided). Moreover, there is some proof that pairs of close, vicariant taxa of
American and European flora still show distinct ecological correspondence:
Nearly all series of closely related taxa in the forests of temperate Eurasia
and North America consist of ecologically corresponding components which
have similar ranges of tolerance, occupy similar habitats, and grow in strictly
analogous plant communities. The ecological constitution of such groups must
be very ancient and very rigid. Even those nemoral taxa which are separated
OCR for page 139
HUAL4N EFFECTS ON THE TERRESTRIAL ENVIRONMENT
139
into morphologically distinct species have undergone no noticeable ecological
changes since their isolation some 1~15 million Yeats ago (Kornas, 19723.
Thus, contemporary boreal coniferous forest ecosystems began their
evolution in the Holocene 10,000 years ago, but they consist of some very
conservative taxa which did not change ecological habits for millions of
years.
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Representative terms from entire chapter:
forest ecosystems
