DISTURBANCE

OF T H E T E R R E S T R I A L E C O S Y S T E M S

S T A B I L I T Y D U E TO G L O B A L - S C A L E ANTHROPOGENIC

IMPACTS

YU. A. I Z R A E L , L. M. F I L I P P O V A , G. E. I N S A R O V , F. N. S E M E V S K Y and S. M. S E M E N O V Natural Environment and Climate Monitoring Laboratory, USSR State Committee f o r Hydrometeorology and Control o f Natural Environment / USSR Academy o f Sciences

(Received February 15, 1988) Abstract. Intact natural ecosystems are fairly stable objects. In the course of natural selection proceeding

against the background of synecological interactions (trophic, competitive, symbiotic, etc.), a respective complex of coadapted species forms, each being maximally accommodated to its habitat. Such a complex is of specific composition and possesses stable structural characteristics. Fairly regular processes of changes in these characteristics, specific to the given type of environmental conditions, are observed in non-stationary cases. We analyze probable causes of the loss of stability in natural systems exposed to man made impacts of a global scale, in particular structural instability, landscape (distributive) instability, and conductive instability. The study of the mechanisms ensuring biosphere sustainability and stability of its elements is a vital ecological problem. There are applied aspects in the problem solution since identification of man-induced instability is feasible only on the basis of precise knowledge of the natural mechanisms of weak points of the relevant natural process. This circumstance makes the problem of stability one of the focal questions of applied ecology.

1. Introduction When dealing with the problem of assessing and predicting ecological consequences of man-made impacts on biota, attention was previously focussed mainly on continuous gradual transformations in the dynamics and structure, of biocenoses in response to minor changes in the state of the environment [5, 16]. That was a first and necessary stage of research which produced certain methods oriented toward vital problems of applied ecology, in particular thoses related to global environmental pollution. The study of instability of natural ecological systems which relates to discontinuous changes in ecosystems, but not to gradual smooth ones, has recently become of primary scientific concern. Applied ecology nowadays tends to use the phenomena of instability in ecological standardizing. Stability of a system, in particular of a natural system, usually implies its capability to endure 'minor' changes in its state in response to 'minor' external impacts (chronical, impulse, or combined). Instability of a system indicates 'inappropriately' great response to minor impacts. Terms 'system', 'state', 'impact', 'response', 'small', 'great', and the cited definiEnvironmental Monitoring and Assessment 11: 239-246, 1988. 9 1988 Kluwer Academic Publishers. Printed in the Netherlands.

240

V U . A. I Z R A E L ET AL.

tion might be appropriate only after formalization within a particular mathematical model of each natural phenomenon. The study of the phenomena of biosystem stability and instability by modelling is a concern of many scientists both in and outside the USSR: J. M. Svirezhev and D. O. Logofet [17], J. A. Pyh [14], N. S. Abrosov, B. G. Kovrov and O. A. Cherepanov [1], A. N. Gorban [4], Williamson [12], R. May [10], and many others. While noting considerable progress in this field we would like to stress the extreme significance of the biological foundation for model studies and the need of a developed ecological theory on stability and instability. These problems are of particular interest to modern applied ecology, and their solution requires fundamental research concerning the mechanisms of biosystem stability, and systematic analysis of possible factors affecting their stability. Such a research would demand considerable amounts of actual ecological information and new non-trivial approaches to its analysis. Though a unified ecological theory of biosystem stability has not been created so far, some investigations in this field have been carried out: A. S. Isaev and R. G. Khlebopros, et al. [11], N. S. Pechurkin [12], F. N. Semevsky and S. M. Semenov [16], and others. This paper discusses three types of man-induced instability of natural ecosystems, related global phenomena and the hypothesis concerning their ecological mechanisms.

2. Structural Instability and Hypothetic Definition of the Ecological Reserve for Terrestrial Ecosystems Structural instability is associated with an abrupt ecologically significant change in the biocenosis species composition resulting from growing man-made stress. A characteristic example of this is the disorder in the pattern of dominance in phytocenoses due to man-induced changes in natural processes of competition. An example of a large-scale process is the decline in major tree-species restocking illustrated by a survey of forest resources taken in the USSR after the war, which indicates certain anomalies in the process of natural reforestation (Table I). Climax dominant species in the forests in the Great Russian Plain - oak, pine, and TABLE I Natural Reforestationin Pine Woods [6] Natural zone

Taiga (boreal coniferous) Mixed forests Broad-leaved forests Forest-steppe

Percent of reforestation, ~ major species

species mixture

failure

46 33 10 4

20 16 16 9

34 51 74 87

DISTURBANCE OF T H E TERRESTRI AL ECOSYSTEMS STABILITY

241

spruce are characterized by relatively long life-spans (as compared to other tree species or competitors) and high average increases under natural conditions. As for managed forests, systematic tree felling of these species reduces the above-said advantage. At a 100-year rate of felling their average increase exceeds that of their competitive species - aspen, birch, and others by at most 10%. Hence, the ecological reserve of managed forests is rather limited, and the more or less satisfactory state of the forest resources here is ensured by forestry activities. The current situation is close to permissible limits (i.e. to a change in the dominance pattern (Table I). The felling area survey performed in the postwar years (i.e. after the period of zero forestry) revealed significant transformation of the character of plant cover in all the forest zones [6]. There are various quantification methods for the ecological reserve assessment. This paper discusses two alternatives of the method based on plant increment indices. Na(t) and N~(t) are the respective heights of the dominant and the nearest competitor at the age of t years in an assumed managed forest (the felling period being T years) with no chemical weeding. Phytocenosis transformation (dominant replacement) starts when Ha(7) < He(T). This index can be used for quantitative assessment of the ecological reserve Res 1 = _ T

He(T)

This value is positive when the initially dominating species remains dominant; it tends to zero (and then becomes negative) when the species dominance is lost. The scale of Resl is (time)-1. Index 1

1

Res 2 = ~rHa(T) - ~Hc(T) implies the difference between average increments of the dominant and their species competitors. This index possesses the same properties as the one given above, but its scale is heights/time. Let us estimate, by way of an example, the value of the ecological reserve of pine-birch forests in the Arkhangelsk and Moscow regions. To do this we use tables of growth rate from [7] containing data on pine and birch growth from 20 to 100 years. Table II shows the estimates of mean logarithmic growth rate for pine (r) for the given time period, estimated Resl and its percentage by r, as well as average increment V for the period of 0-100 years, estimated Res2 and its percentage by V. The initial estimates verify strong competition between the major coniferous species and the nearest deciduous species (birch, aspen). An increase in air pollution (sulphur and nitrogen oxides and ozone) reducing the growth of coniferous to a greater extent than that of leaved trees, might affect the result of competition. The

YU. A. 1ZRAELET AL.

242

TABLE II Assessment of pine increment and ecological reserve of pine-birch forests Region

Mean logarithmic increment of pine r, l/year

Reserve Res t assessment percentage Rest, l/year (by r)

Average increment of pine V, m/year

Res2 Res2 % assessment, (by F) m/year

Moscow Arhhangelsk

0.015 0.013

0.001 0.001

0.29 0.287

0.023 0.028

6.7 7.7

7.9 9.8

type of forest ecosystems might be completely changed over vast territories (despite artificial creation of coniferous communities).

3. Landscape (Distributive) Instability; Likely Causes of Oak Wood Degradation It fairly often occurs that ecological interaction of two or several populations does not ensure their steady co-existence in a homogeneous space. Stabilization of their state is achieved in such cases by distribution in the heterogenous space, i.e. it depends on landscape heterogeneity. Alteration of environmental features; of its specific spatial heterogeneity may bring about destruction of the stable spatially distributed biosystem 'assembled' by nature from locally unstable elements. The mentioned alteration of environmental features is a very typical consequence of man-induced stress on terrestrial ecosystems; hence, it would be right to term it landscape or distributive instability. This instability we assume significantly contributes to oak wood degradation, which has now embraced vast territories. K. B. Lossitsky [9] presents data on the area of oak-dominating forests in the USSR as a whole, and in individual constituent Republics. Some of these data are reproduced in Table III. Consideration of the expansion of oak plantations (e.g. 50 thousand ha of oak plantations in Byelorussia in 1956-1979) reveals that oak diminishes in forest areas and that forestry is the only means to slow down this process. This process has spread over 30 areas in the Russian Federation and 10 thousand ha of oak woods died out completely, and 250 thousand ha, partially during 4 years (1968-1972) [15]. The dynamics of oak forest decline in Byelorussia for 1956-1978 is given in Table IV [15]. TABLE III Oak-dominating forest area (thousands ha) Years

1961

1966

1973

1978

USSR Russian Federation Byelorussian SSR

9080.6 6899.7 215.5

9387.5 7084.2 217.0

9779.7 7316.3 221.9

9743.6 7184.6 223.0

DISTURBANCE OF THE TERRESTRIAL ECOSYSTEMS STABILITY

243

T A B L E IV Percentage o f oak in the forests in Byelorussia (Ministry of Forestry) 1956

1961

1966

1973

1978

4.8

4.7

4.5

4.1

3.9

Various hypotheses have been used to explain the causes of oak wood dying: improper felling, droughts, changes in the ground water level, seedling origin, frosts, vascular mycosis and bacterial diseases, soil condensing and turfing, honey agaric, grazing, high density of wild animal populations, hay mowing, stress in recreation zones, defoliation by leaf miners (leaf-eating insects), solar activity, heliomagnetic disturbances, atmosphere pollution with gaseous pollutants and insecticides. The review of the causes of oak dying was made in our paper published in 1982 [2]. Evidently, the primary cause of all these phenomena is the exhausted resources of defence against the onslought of mortality factors. As seen from our review, oak wood die mainly after massive infestation of leaf miners - the influx of the spring concentration of harmful Lepidoptera: oak green moth, gypsy moth, winter moth, etc. Hence, one may assume that the mechanisms of oak wood defense against these first-order attackers in all these cases are significantly affected. Of course, all these processes require precise quantitative analysis, development of specific research in the sphere of fundamental and applied ecology, since the occurring effects are beyond the scope of conventional ecology methods and hence need new approaches and analysis technique. Let us consider an example of this approach to analysing the causes of oak-wood damage from the outbursts of oak green moth increase. Oak woods now consist mainly of an early oak form with a small portion of the late form; the latter unfurls leaves two weeks after the former. The late form is not affected by Lepidoptera. Mass lepidopterous species, including oak green moth, do not distinguish these two forms when laying and thus experience mortality resulting from asynchronous development with the forage plant proportional to the late form share in the oak wood [13]. The situation might be quite the opposite where the late form is dominating, since the oak moth population is capable of adapting to it in a number of generations. Oak woods, formed in the course of evolution and natural selection, consisted of a combination of these oak forms. That was a steady state relationship, since low pressure from the spring population of Lepidoptera resulted in the dominance of the early form; lepidoptera populations were to reproduce successfully under sufficient dominance of the early form which would promote favourable conditions for the late form to lead the way. Oak woods did not die under dynamic equilibrium; only the share of each form in the common canopy and acorn yield varied. Man-made impact has affected the specific inhomogeneity of the green moth habitat; the early oak form happens to occur under more favourable conditions. So far, we are not in a position to indicate all the man-induced causes. Among them

244

YU. A. IZRAEL ET AL.

might be: high sensitivity of the late form to air pollution, felling pattern (mostly inhibiting the late form), seed collection technique ensuring early form acorn selection. It is known, for instance, that the early form recovers with shoots better after felling. Thus, if special ecological studies confirm the above stated hypothesis, it will be quite clear that no conventional measures in oak wood maintenance will prevent oak wood losses. Quite different forest restocking strategy, based on quite different criteria inaccessible to forestry until special comprehensive studies are carried out, will be needed. The arsenal of traditional means has already been exhausted. 4. On the Adverse Global Effects of Pesticide Application in Forestry and Agriculture. Conductive Instability Under conductive instability we imply ecosystem instability occurring as a result of environmental management following a certain scheme for achieving a certain aim (most often, economic). These phenomena occur because of insufficient knowledge of consistent ecological patterns and, as a result, due to implementation of inadequate schemes of this management. Pest control with the application of pesticides might be considered as an example. The world pesticide production has reached 5 million t/yr and is still growing [3]. It is known that circulating in the environment these substances spread over great territories, poorly decompose, and bring about significant damage to biota elements in natural ecosystems, and in some cases, to human health. At the same time pesticide application in forestry and agriculture is expanding. The annual pesticide production in the USA, for example, increased in the period 1946-1976 from 90000 to 900000 t/yr. Despite this, crop losses caused by pests and mites did not decrease but even significantly increased [3]: Years Crop losses 0/0/year

1904

1920-1935

1942-1951

1951 - 1960

1970

9.8

10.5

7.1

12.9

13.0

This paradox requires detailed quantitative analysis involving synecological considerations and advanced mathematical methods of modelling of ecological processes. It cannot be explained on the basis of conventional ecological notions only. We have tried to make tentative analysis of this phenomenon. Pesticides carbaryl, methyl-parathion, malathion, toxaphene, etc., are nowadays applied mostly by small capacity and ultra-small capacity spraying (most often aerial spraying) where a part of the pesticides evaporates, another part in aerosol form is blown away (droplet diameter at sm-capacity spraying is 20 -250 ram, at ultrasmall-capacity spraying, 5-1.20 mm), still another part does not reach the target but is deposited onto various parts of plants and the soil, The'total loss might be up to 97.5% [18]. It depends on meteorological conditions, the size of the territory under treatment, flight height, characteristics of spray equipment, and so on. It should be noted that

DISTURBANCE OF THE TERRESTRIAL ECOSYSTEMS STABILITY

245

it is only particles smaller than 50 mm that reach the targets (these particles were found on 93~ of the dead insects after field treatment [18]. It is therefore only a negligible quantity of pesticides which hit the target. Although turbulent diffusion and deposition gradually decrease insecticide concentration in the moving air mass, the area of high mortality of fast flying insects exceeds the area under chemical treatment. But natural killers of harmful insects (phytophagans) - entomophagans fly much faster than the former and our tentative estimates show that the damage caused to entomophagans by small parameter spraying is by at least one order higher than that caused to phytophagans. This induces far reaching considerations. Tentative model estimations show that with the use of insecticides about 1 kg/ha over the area under direct control, the rate of insecticide entering into targets is much higher for entomophagans than for phytophagans: TABLE V The rate of insecticide entering into targets (acetylcholine esterase molecules) for two insect groups (~tgg i m i n - l ) Insects

Spraying (~tg g-J rain 1) small capacity

Phytophagans Entomophagans

ultrasmall capacity

carbaril

dimcthoatc

carbaril

dimethoate

8.5 10 -6 1.2 10 -4

7.2 10 -6 9.9 10 -5

5.5 10 -5 5.4 10 -3

4.7 10 -5 4.6 10 -3

From these estimations, it is clear that insecticide fluxes under average meteorological conditions far exceed the 50o70-death rate fluxes for entomophagans: 3.2 l0 -6 ~tg/g min for carbaryl and 3.7 10 -6 for dimethoate (dimensions - ~tg g-1 m i n - l). Thus, phytophagan control over territory under treatment causes death to their natural enemies which regulate their numbers over a much greater territory (over the distance exceeding 20 miles). It is apparent that in the future still greater territories will come under chemical treatment, and this will be causing expanding and progressive ecosystem instability on these territories. Thus, by applying pesticides (insecticides) man has 'to pay' to bring death upon the pests which used to be killed 'free of charge' by their natural enemies. In addition, pesticide application causes indirect damage to other biological objects and to human health. Modern ecology must develop a new strategy of pest control, which will not destabilize the object under management (agrocenosis, wood stand). The existing approaches, as has become evident, are no longer sufficient to provide for this. 5. Conclusion

The study of mechanisms maintaining stability in the biosphere and its components

246

YU. A. IZRAEL ET AL.

is an ecological problem of vital importance. This problem is also of practical significance, since it is only precise knowledge of the nature mechnisms and weak points of respective natural processes that will enable us to reveal man-induced instability. This makes the problem of biosphere stability the focal issue of applied ecology-synthesizing science on the environment and man-induced changes in it. The phenomena of instability, considered in this paper, require a detailed analysis with the use of specific methods which have not so far been completely developed. The problems arising here are as follows: (-) The development of methods for assessment and prediction of the effect of environmental pollution on the processes of natural succession; (-) Assessment of the effect of the environment inhomogeneity on the degree of natural ecosystem stability; (-) Comparative analysis of the effect of pollutants (and of other man-induced factors) on various groups of inter-acting organisms, and analysis of synecological consequences of the mentioned man-made impacts.

References [1] Abrosov, N. S., Kovrov, B. G., and Cherepanov, O. A.: 1982, Ecological Mechanisms of Coexistence and Species Regulation (in Russian) Novosibirsk, Nauka. [2] Izrael, Yu. A., Filippova, L. M., Insarov, G. E., Semevsky, F. N., and Semenov, S. M.: 1982, 'Background Monitoring and Analysis of the Causes of Global changes in the State of Biota', in Pr•b•ems •f Ec•••gica• M•nit•ring and Ec•system M•de•ling (in Russian) L.• Gidr•mete•izdat• V••. 5. [3] Pimentel, D., Krymnel, J., Gallahan, D., Habgeh, J., and Merril, A.: 'Benefit-Cost of Pesticides Use in United States food production', Biol. Science, Vol. 28, No. 12, 1978. [4] Gorban, A.N.: Roundabout Equilibrium (in Russian) Novosibirsk, Nauka, 1984. [5] Izrael, Ye. A.: Ecology and Environmental State Control (in Russian) L., Gidrometeoizdat, 1984. [6] Kaldanov,V.J.: 1966,ForestSpeciesSuccessionandRestocking(inRussian)M.,LesnayaPromyshlennost. [7] Kozlovsky, V. B. and Pavlov, V. M.: 1967, Growth Rate of Major Forest-Forming Species in the USSR (in Russian) M., Lesnaya Promyshlennost. [8l Laslone, G.: 1976, 'Pesticides', in Overviews. Current Probtems of Chemistry and Chemical lndustry (in Russian) M., CMEA. [9] Lossitsky, K. B.: 1981, 'Productivity, Reproduction and Life Persistence of Oak Forests in the USSR', in Oak Woods: Increase in Productivity (in Russian) M., Kolos. [10] May, R. M.: Stability and Complexity in ModelEcosystems Princeton, Princeton University Press, 1973. [11] Isaev, A. S., Khlebopros, R. G., Nedorezov, L. V., Kondakov, J. P., and Kiselev, V. V.: 1984, Numbers Dynamics of Forest Insects (in Russian) Novosibirsk, Nauka. [12] Williamson, M.: 1972, The Analysis of Biological Populations, London, Edward Arnold. [13] Pokoziy, I. T.: 1972, 'Feasibility of Enhancing Forest Bioresistance to Leaf Miners in Oak Plantations', in Forest Protection from Pests and Diseases (in Russian) M., Kolos. [14] Pyh, J. A.: 1983, Equilibrium and Stability in Population Dynamics Models (in Russian) M., Nauka. [15] Rublevskaya, K. M.: 1980, 'Oak woods propagation and dynamics', in The State and Prospects of Improving Oak Woods Productivity and Reproduction in Byelorussia (in Russian) Minsk, Nauka. [16] Semevsky, F. N. and Semenov, S. M.: 1982, Mathematical Modelling of Ecological Processes (in Russian) L., Oidrometeoizdat. [17] Svirezhev, J. M. and Logofet, D. O.: 1978, Stability of Biocommunities (in Russian) M., Nauka. [18] Zakardinets, V. A.: 1976, 'On the Distribution and Migration of Organophosphorous Pesticides in Forest Biocenosis', in: Vital Problems of Pesticides Use (in Russian) Yerevan, Nauka.