by Andrei IVANOV, Cand. Sc. (Geogr.), Lomonosov Moscow State University
Now who bears the palm in landscape modification-of all the beings populating the globe Man is considered to be in the lead, sure. But do we know that animals, too, are contributing to environmental modification by changing their habitats and creating specific geosystems of different hierarchical levels? Now and then they evolve into a principal formative factor of the environment.
THESE BUSY DIGGERS
Zoogenic complexes created by burrowers are fairly common here and there. In tundra plains of the north these are colonies of lemmings and Arctic (polar) foxes; these are badgers in the forest belt zone; and gophers and marmots in steppes (vast grassy plains of southeastern Europe and central Siberia) and semideserts.
Lemmings dig an intricate system of far-flung burrows with rather long passages (15 to 35 cm, or 6-14 in.), nest and feed homes, and 5 to 20 inlet holes. Their colonies give rise to specific plant communities and lumpy microrelief features that may be many inches tall. The vital activity of these rodents is responsible for the higher presence of humus (organic matter) in
soil, good humidity and aeration of surface soil and more vigorous processes within it. The depth of the active soil layer increases, too. The biogenic elements obtained from their excretions are mineralized fast to join in the circulation of substances, while the holes and "tunnels" dug by the rodents improve soil drainage and aeration, and cause to increase thaw depths from 35 cm (14 in.) to as much as 60-70 cm (24-28 in., respectively). A colony of such tireless diggers is able to move as much as 250 kg of earth per hectare (or 100 kg per acre). Depending on how long a colony of lemmings has been inhabiting a particular patch of ground, it gives birth to a specific plant community (phytocenosis), with many plants exhibiting profuse growth compared with their neighbors. Thus, if we take the Vrangel Island located between the East Siberian and Chuckchee Seas, the colonies of these animals account for 35 to 40 percent of the biomass of grasses, some remarkable for large bright blooms that jazz up the dreary tundra landscape. Here and there we come across hillocks of spent soil next to the burrows. Such spots make up only 1 to 3 percent of the total tundra area, though much larger during lemmings' population explosions. In peak years nearly all of the tundra, with the exception of water-logged patches, turns into a bumpy-lumpy terrain crisscrossed by so many furrows-the holes, subsoil passages and soil dug up by busy rodents. Although their homes are not large, the surrounding relief features are modified greatly; here we come to deal with a specific morphology of the ground surface.
Badgers: they are woodland denizens, perhaps the most active soil diggers among predatory mammalians. Their colonies may be fairly large and endure for a long time. Each home is an underground bunker supplied with the many in- and outlets, and nesting cubbyholes. It can last for decades (perhaps centuries) to give shelter to many generations who renovate, refurbish and expand it by adding new homes; in years an intricate multitier labyrinth, capa-
ble of housing several families, comes into being. Now look: young settlements are not larger than 100 m2, while older ones, inhabited by several generations, can be as 400-850 m2 large. From 90 to 95 percent of the habitation ground of badgers is studded with hillocks of soil. The burrows may be 3 meters deep, with furrows and hillocks in between up to 0.8 m high. A badger colony moves from 43 to 97 m of soil, causing trees to wither away because the rodents damage their roots all along. The forestland gets sparser, "light windows" appear here and there, and the make-up of the arboreal community changes, with endemic trees supplanted by ruderal (growing near highways, on waste ground and suchlike sites) and zoochoric (disseminated by animals) species.
Badger colonies touch off changes in the environment—in its lithogenous (stone bed) characteristics, water and heat budget, soil formative processes, vegetation... In fact, actually all natural components are modified this way or that. These rodents build feed statices* for their families—concentric fields close to their homes. Even though they may hunt for food as far as 1 to 2 km away, these animals are most active within a few hundred meters. Although the badger does not go deeper than 25 to 30 cm (10-12 in.), the area of such diggings may come up to 80-170 thousand hectares (200-425 a.), and the amount of ground thus moved—as much as 25-100 m3/ha, or 10 to 40 m3 per acre. This gives rise to restructured elements known as parcels (parcelles), or tracts characterized by specific soils and vegetation. Badger colonies constitute singular facies** within this or that locality.
* Statice (from Lat. static, or steady state)—here, a home base of an animal population used for a definite purpose.—Ed.
** Facies—a structural part of locality having one common element or form of relief (microrelief) and characterized by homogeneous mother rock, microclimate, and soil and water regime; such terrain is populated by one particular biocenosis (community).—Ed.
EFFECT OF HOOFED (UNGULATE) ANIMALS
Now let's take another case of animal-caused environmental modification—the salterns, or salt gardens, that occur in many woodlands of Siberia and the Russian Far East. Such gardens combine into a peculiar zoogenic landscape. The point is that hoofed animals endemic to these parts consume certain minerals (like chlorides, carbonates, sodium and calcium sulfates, and microelements) needed to their organism and found there in sufficient amounts. Thus they rework the crust of weathering in forest glades from several meters to 100-200 m across. These populous woodlanders include the elk (moose), Manchurian and Siberian deer, wild goat and other ungulates digging in. The hoofed animals are most active in the late spring, and during summer and autumn, i.e. seasons when the ground is bare of snow. As many as 30 to 50 animals may trek to the same spot each day. A salt garden takes many years and even centuries to form. Ungulates transform the natural environment and create a specific microclimate by eating away the surface cover and exposing the stony undersoil; they destroy underwood in search of salt-spiced dishes, and thus change soil humidity and insolation, and turn the area of their ravages into rough ground, plowed to 1.5 m up and down, leaving behind pits, potholes and pools. Hoofed animals trample down the grass cover and kill the grassy turf and sod, and trigger vigorous erosion processes.
Such woodlands are the haunts of big predators (like bears and wolves), with carrion-eaters, dipterous (two-winged) bloodsuckers, ticks and the like following in their trail. Feodor Milkov (1918-1996), a Russian geographer, is absolutely right by describing such natural salt gardens as a "landscape complex in its own right". The hierarchical level of such zoogenic geosystems varies from solitary facies to isolated ter-
rain enclaves, their life period depending, first and foremost, on the mass of salt-bearing ground. Salteaters abandon their gardens upon consuming it, and these patches of ground return back to normal over time.
Beavers (Gen. Castor) are most vigorous in changing the natural environment in valleys of Eurasia and North America. Water and irrigation networks are the No. 1 factor of their activities. These hard-working creatures put up dams of every kind—small ones, not longer than three feet and tens of inches tall, and monumental dams over 5 m high and 1,000 m long in North America. In Belarus these shaggy builders have raised a cascade of four large dams, the largest one as long as 400 meters. Such structures saddling streams and rivulets work dramatic changes in the hydrology of woodland geosystems: streams and rivers turn into a cascade of pools and ponds flooding considerable tracts of land, from hundreds of square meters to dozens of acres in area, and water-logging lowlands.
Beavers fell trees along river banks (80 percent of such undercuttings are within a 10 to 20 m wide band) and cause changes in the correlation of trees and shrubs. Bottomland glades and meadows, overgrown with meadow grasses, come into being. River banks, dug under by burrows and passages, sink and collapse, giving rise to floating mats; river beds break into branches. Changes in the water regime and vegetation are followed by a different pattern of soil formation processes, and impact the behavior of other animals, too, who start using the passages and waterways made by the beavers as their routes. Glades with felled and girdled trees give more food to ungulates, rabbits and murine rodents; other mammalian species flock to such wood-cutting areas as well. Shallow waters and pools attract alien bird species, such as teals, fish and wild ducks, mallards, and other kinds of water-fowl. This way the river valley natural environment is altered. Consequently, the term "beaver landscape" is quite relevant.
A beaver family can colonize a river course, 1-2 to 10 km long and even longer. The hierarchical level of a beaver-modified natural complex varies from sepa-
rate facies and isolated terrain features to valley localities as part of the landscape. Earlier, before their mass extermination, such geosystems must have been occupying rather large areas in the woodlands of Eurasia and North America: the Castor beaver genus is estimated to be 15 mln years old, and all this time beavers have been active in landscape modification within their habitation areas.
This impact is of cyclic nature. Beaver colonies are dynamic in modified forestlands of Europe: every 5 to 10 years they pull out and move elsewhere. But they stay put in vestal sylvan landscapes of Canada for decades. The time of their residence depends on how long it will take to destroy and consume their feed base, the trees. Landscape rehabilitation sets in after beavers move out—such progressive succession takes in marsh-, meadow- and woodlands. Yet the dynamics of this process is not investigated well enough.
ORNITHOLOGICAL ECOSYSTEMS OF MINOR ISLANDS
ENVIRONMENTAL IMPACT OF LARGE GREGARIOUS UNGULATES
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