The Olekminsky Natural Reserve is composed of four types of lake land, six types of river land and two types of wetlands. The wetlands can be classified into four types of spatial complexes. The main types of forest habitats may be incorporated into six types of land. Forest complex functional forms in the reserve are characterized by four types. In accordance with the predominance of land types and typological complexes, the territory can be divided into four areas.
Reserve ; Habitat ; Complexes ; Birds ; Wetlands ; Grouse
The territory of the Olekminsky State Natural Reserve represents a typical middle taiga area in conjunction with the mountain taiga complex. The outlook of the primary part of the reserve fully corresponds to the current zonal factors. Zonal factors activity clearly affects the outlook of the azonal entities that can be found in the Amginsky Mountain Ridge. This determines the limitations of wetlands, the low prevalence of lacustrine habitats and absolute dominance of forest lands.
Studies of the territory and annual field work in the reserve and adjacent areas began in 1985. Estimates of population numbers were carried out mainly in relation to wetland birds and grouse, as these groups of birds are the most extensively studied and are regularly observed. Surveys were carried out using various methods: spring/summer, autumn and winter surveys of grouse; spring/autumn and summer surveys of wetland birds; and their habitats were studied as well (Kuzyakin, 1965 ; Kumari, 1979 ; Ravkin and Chelintsev, 1990 ). The collection and processing of the field observations were recorded in the “Chronicles of Nature” (conducted continuously since 1985). Additionally, analysis of population samples from outside of the protected area is conducted regularly.
Water sites are habitats for birds adapted to living in watered landscapes. As such, the existing water bodies form a complex with the surrounding unwatered landscape elements. Wetland habitats in the observed area are characterized into four types of lacustrine lands, six types of river lands, and two types of wetlands.
Lacustrine habitat: “bayou in the valley of a small or medium river” (typological features: full-flowing, deep, narrow, stretched out, often U-shaped parts of river arms in the river valleys, 10–15% covered with quagmire). In most lakes of this type in the reserve, fish are absent, and only a few lakes are inhabited by lake minnow. This type of lake is common for the river valleys of the Amga and the Tuolba.
“Bayou in the major river valley”: (typological features: typical oxbow transformed into lakes, 5–10% covered with quagmires with a border of surface sedge and horsetail thicket). These areas have favorable feeding and protection conditions, and 70–80% of these lakes are populated with fish (river perch, northern pike and lake minnow). All of the lakes of this type are in the Olekma River Valley, and during spring migration, they become stopping places for waterbirds.
These areas are always riverside (less often intralacustrine) with quagmires that cover 50% of the water area. The basin has a deep lake and marshy meadows. This typological group includes erosion and karst lakes of the middle and late developmental stages. This lake type is common for the Amga, Olekma and Tuolba valleys.
The hollow is occupied with deep lake, and at its sides, there are outcroppings of rocks or flooded forest. In these areas, riverine aquatic vegetation is absent and shallow water areas with a depth of 1 m are less than 1% of the lake area. These include karst and thermokarst lakes in the initial stages of development. Due to scarce food resources, cave-in lakes are typically of little use for waterbirds (Degtyarev, 2007 ). Within the reserve, this type of lake is extremely rare (only in the basins of the Tuolba and Chuga Rivers). They are combined with systems of streams and apparently attract environmentally plastic duck species for nesting (mallard, teal, and tufted duck) (Vorobyov, 1963 ).
These lands are represented by “large semi-mountain river”, “medium or small semi-mountain river”, “medium or small mountain river” and “semi-mountain or mountain brook”. Typological differences are the flow velocity, the shape of the longitudinal profile of the channel and valleys, and the composition of the rock lining.
The river valley of a “large semi-mountain river” reaches 1 km wide on the bottom and the valley walls are 50–70 m. The riverbed is moderately sinuous, chisley, rocky, unramified, and typically 300–500 m wide. Riverbanks are steep, bosky and dumouse. The valley is one-sided, high and 150–200 m wide. The Olekma River, the main seasonal flight route of the waterbirds (reaching 135 km long on the reserve territory), can be referred to as this type.
The river valley of a “medium semi-mountain river” is trapezoid, asymmetric, and up to 4 km wide. The valley is 2–3 km wide, occasionally covered with lakes. The riverbed is moderately sinuous, or meandering, chisley and rocky. The banks of the river are overgrown with sedge and rare bulrush. River bars alternate with stretches, averaging 1 km. Spring drift ice is accompanied by blocked ice. In such river valleys, whooper swan and bean goose can be found.
The valley of a “small semi-mountain river” is wide (from 2 to 3 km) and swamped. The riverbed is pebble and very curved. There are many short bars and long stretches. The overall length is between 15 and 70 km. This type of river is represented by the stream tributaries of the Olekma and Tuolba Rivers and the left tributaries of the Amga River.
Terrain adjacent to “medium mountain rivers” is mountainous with elevations of 200–250 m. Valleys are trapezoidal, asymmetric, and up to 0.8 km wide. The riverbed is sinuous with boulder–pebble bars. In the wintertime, ice blisters are formed in the river bed, and in the spring, there are blocks on the bars. This type of river is the main habitat for harlequin duck.
This type of river is common for the Amga and Olekma basins (right tributaries). The length of such a river is 25 to 60 km. Necked in the upper reaches of the river, the valley gradually expands to 1–2 km in the embouchure. Below the holdfasts, the valley expands slightly and then narrows again, forming turbulent flows, often in a large boulder riverbed. In wintertime, the rifts freeze up and the water flows over the ice, and in the spring, blocks are formed in these parts of the river.
Brooks are characterized by high dipping and hanging valleys. The bottoms of some brooks are covered with chisley and rubbly deposits. Some brooks in the upper reaches of the valley have extended areas. A common feature of the small tributaries is the lack of ground flow in the dry season or the appearance of its bed only in some areas. Brooks often disappear into underflow karst cavities. The length of these streams ranges from 3 to 8 km.
A group of wetlands is represented by two types, a “bog” and a “grass moor.” The bog type refers to dwarfs, bogs and tundras (typological features — suffruticose, shrubs or heavily depauperated sparse woody vegetation). The grass moor type includes lowland, intermediate and raised moors, tussock and small valley grounds (typological features: herbaceous plants and moss form the vegetation cover). During the spring migration and river impoundments, waterlogged marshes become the major migratory stopping places of waterbirds for feeding and resting.
In general, water bodies appropriate for waterbird habitat in the studied area are represented by four types of lake land (“bayou in the valley of small and medium rivers”, “bayou in the valley of a large river”, “quagmire lake” and “cave-in lake”), six types of the river lands and two types of wetlands. The main habitats for all groups of waterfowl (except harlequin duck) are medium or small oxbow rivers, quagmire lakes, and medium semi-mountain rivers; other wetland habitats are of secondary importance. For the harlequin duck, and to a lesser extent for the goosander and common goldeneye, the main habitats are small and medium mountain rivers.
As illustrated previously, the main types of land allocated for this region are not separate elements of water bodies (water area, riverine area of aquatic vegetation, etc.), but rather the entire body of water (lakes, rivers, swamps). Most of the land types are composed of forage, nesting and nidifugous biotopes. However, the degree of their attractiveness to birds is strongly influenced by the factor of spatial combinations of different lands. Apparently some land types without combination with others are of little importance or are inadequate for the waterbirds' habitat, as they are unpopulated. Therefore, the wetland complexes are typically full-fledged habitats for waterfowl and define the ecological capacity (Degtyarev, 2007 ).
Wetlands, in most parts of the region as a habitat of waterbirds, are realized in the form of spatial complexes. Such wetland complexes where waterfowl complete the whole life cycle in places of nesting, in the studied area, are represented by four types within three groups (large valley, small valley and watershed).
River lands outside the complex are represented by mountain river habitats. As such, the river grounds, without combination with other habitats, are marginally attractive for most waterbird species and are inhabited by specialized species, primarily by the harlequin duck (medium mountain river, small mountain river, mountain brook, and semi-mountain brook).
Mountainous terrain and climatic features of the territory cause a vertical zonation in the distribution of vegetation; therefore, the forest composition is quite diverse. The main tree species are Dahurian larch (which dominate the area), common pine, alpine stone pine, Siberian spruce, Siberian fir, cedar elfin, white and flat-leaved birch, aspen, alder shrub, shrub birch and willow (Golyakov, 1994 ). In accordance with the distribution of vegetation in the study area (Fig. 1 ), the main bird habitats can be differentiated into six types of land.
Structure of vegetation cover in the territory of the Olekminsky State Natural Reserve.
The larch forest has a total area of 2950 km2 (35.4% of the territory). Dahurian larch stands are present in both pure and mixed plantations. Ledum–moss, blueberry–alder, blueberry–moss, alder, blueberry, and cranberry larches prevail. The main inhabitants of larch forests throughout the year are black-billed capercaillie and hazel grouse.
Pine forest occupies an area of 1260 km2 (15.1%.) Pine forests are located on the southern and gentler slopes and are also found on the bottom of the river valleys. Dry forests with a lichen layer and bearberry forests extend as narrow, discontinuous strips stretching along the river on sandy terraces. The interstream area is dominated by cowberry pine, moss, Labrador tea, and cranberry–moss. In berry-yielding years, in the autumn and early winter periods, black-billed capercaillie and hazel grouse are common in pine forests and occur more often than black grouse (Degtyarev, 2004 ; Tirsky, 1999 ). Pine forests are a fairly typical accommodation spot for capercaillie and black grouse lekking.
The mixed forest has an area of 2070 km2 (24.8% of the territory). Major tree species are Dahurian larch mixed with Scots pine, Siberian spruce, Siberian fir, alpine stone pine, white birch and flat-leaved aspen. Throughout the year, black-billed capercaillie and hazel grouse regularly inhabit this type of forest.
The lowland forest covers an area of 670 km2 (8.1% of the territory) and is located on the bottoms of the valleys of the rivers and streams. Major tree species in these areas include Dahurian larch, Siberian spruce, willow, and white and flat-leaved birch. Pure spruce forests are confined to wellhead areas of the small river valleys.
The lowland forest habitat is the main winter habitat for ptarmigan and is also an important habitat for other Galliformes species and woodcock.
The small-leaved forest covers an area of 1105 km2 (13.2% of the territory) and is formed by white and flat-leaved birch, aspen, and alder shrub. Several shrub species form dwarf birch thickets. Birch and alder shrubs form continuous arrays in areas affected by forest fires. Aboriginal birch forests are rare and grow in the valleys of the rivers and brooks on well-drained soils. Here, the grouse population density is higher than in other biotopes; grouse are common in the winter, black-billed capercaillie are sporadic, and ptarmigan are rarely found.
This type covers an area of 285 km2 (3.4% of the territory). Rocky groupings are mainly concentrated in the Olekma River Valley and along the medium mountain rivers. The main tracts of pine and fir plantations are concentrated in this area type. The forest belt, at the upper limit of the forest (altitudes of 900 m or more), is very sparse and represented by bare mountain light forest, which is replaced by elfin cedar thickets moving upward. The mountain tops are covered with mountain moss–lichen rocky tundra with some bushes of procumbent Dahurian rosemary, cranberries and ericetal Cassiopeia. The bald mountain plateau is limited by steep slopes of 36–60%, covered with stone fields and corroms. During the breeding season, white and rock ptarmigan are closely related to this complex of mountain forests and rocky groupings.
With the combination of different types of forest, where the birds can nest and have access to diverse feeding habitats, conditions for Galliformes birds can be quite favorable. In the case of wetlands, the collection of forest habitats of the Galliformes forms a functional forest complex. At the reserve, there are four types of forest and wetland complexes that are full-fledged habitats for ptarmigan, grouse, black grouse and capercaillie.
Most of the bald mountain plateau area is occupied with cedar elfin thickets, alternating with outcrops of rocks covered with crustose lichens. The elfin cedar reaches 2–3 m high (sometimes up to 4–5 m high), and grows with the closeness of 60–70%. The grass–shrub story is dominated by Cladonia, Labrador tea, red bilberry and bilberry.
The materials described in the previous section demonstrate that the territory of the “Olekminsky” SNR wetlands and forests, as habitat for birds, operates mainly in the form of various typological complexes that determine the composition and nature of waterfowl and Galliformes population distributions. In accordance with the predominance of land types and typological complexes, the territory is divided into four areas: 1) “Olekma Valley”, 2) “Taiga” (from the Bederdyah River to the head of the Krestyakh River), 3) “Bog taiga” (Tuolba and Mayya Rivers), and 4)“mountain taiga” (Amginsky Ridge) (Fig. 2 ).
The “Olekma“ Reserve division into districts by the structure of habitats of birds. Areas: 1) Valley of Olekma, 2) taiga, 3) Haze-taiga, and 4) mountain and taiga.
The “Valley Olekma” area is located in the Olekma River Valley. This area combines wetland habitats (“large lowland bog–lake–river complex”) and forest habitats (“lowland forest complex”).
The slopes of the valley are dominated by Dahurian larch and Scots pine. Spruce forests are found in the mouths of the rivers and streams tributing into the Olekma. The mixture of pine, cedar and Siberian fir in the forests is insignificant. Birch forests with mixed herbs are common on the banks of the Olekma River, and the herb layer is sparse and dominated by rosemary marsh horsetail, red bilberry, and meadow-rue, etc. (Golyakov, 1994 ).
Some parts of the Olekma Valley slopes form large block scree and outcrops. In crevices of rocks of the Olekma River slopes, there are Siberian juniper, creeping cedar, Siberian rowan, and prickly wild rose. Rosemary, black crowberry, and red bilberry occupy the foot of the rock outcroppings. From August to September, capercaillie and hazel grouse broods can be seen in this habitat. Additionally, colonies of northern pikas are located in such places (Fig. 2 ).
Nesting places of waterfowl are confined to oxbow-type lakes and quagmires. Within the area, 14 waterbird species have been identified: black-throated loon, mallard, green winged teal, wigeon, garganey, shoveler, tufted duck, common goldeneye, magpie diver, merganser, snipe, pintail snipe, and woodcock (Larionov et al ., 1991 ; Revin and Tirsky, 2010 ; Tirsky, 1997 ).
This is the largest area commencing from the Bederdyah River and stretching to the head of the Krestyakh River. The eastern boundary runs along the watershed between the Olekma and Tuolba Rivers, and on the west, it borders with the “Olekma Valley”. Wetlands are represented by medium mountain rivers, small mountain and semi-mountain rivers, mountain and semi-mountain brooks. Forest lands are mainly larch and pine forests.
Watersheds are occupied by larch and alder forests. Larch, blueberry, and green moss vegetation are prevalent on the smooth and steep northern slopes. The steep southern slopes are occupied with pine and mixed herb forests. Ledum-lichen pine and larch forests occupy approximately 80% of the area. Alder coniferous forests are concentrated in the middle portions of the slope. Larch and pine dwarf forests hold the foot and lower slopes of all exposures. In the upper streams of the Big and Small Dzhikimdy Rivers, on flat bottoms of the river valleys with open forests of Siberian spruce and Dahurian larch, there are bogs overgrown with skinny birch. In the autumn–winter, the population density of capercaillie reaches 4.5–5.5 un/km2 in these places.
The grass–bush cover is dominated by blueberries and black crowberry and also rarely by red bilberry, rosemary, and raspberry, etc. Flat bottoms in the middle reaches of rivers and streams are occupied by dwarf birch thickets and horsetail-sedge spruce. Spruce and larch forests run in a narrow strip along the river valleys, where the shrub layer is multi-species: alder shrub, prickly wild rose, shrub birch, willow, prairie weed, Siberian juniper, red and black currants, etc. The number of grouse in these forests is 6.2–7.5 ind./km2 .
Wetlands are represented by medium mountain rivers, small mountain and semi-mountain rivers, and mountain and semi-mountain brooks. There are no lakes. Vast upper sphagnum bogs are found on the watershed of the Krestyaha and Olekma Rivers, offering a nesting place for gray crane. The nesting waterfowl fauna are represented by harlequin duck and merganser. Additionally, Red-breasted Merganser, Common Goldeneye, teal, and mallard can be found.
There are two major rivers, the Amga and the Tuolba, in this area and numerous tributaries that can be referred to as medium semi-mountain rivers combined with river oxbows, bogs, and grassy moors.
Wetlands of this area are represented by “Shallow lowland bog–lake–river complex” and “Shallow lowland bog–river complex”. Nesting within the borders of the area, 16 species of waterbirds were identified.
The Amga River originates from the upper bogs and has a pronounced mountain character for 35 km running to the estuary of the Bestyakh River. There, the valley expands forming reaches. The channel developed into a multiple-arm type riverbed, and a continuous chain of islands was formed. The channel is 30–40 m wide and 0.8–1.5 m deep. In this area, the nesting birds harlequin duck, merganser, common goldeneye and tufted were registered. Goosander forms swarms of 40–70 molted birds. Commencing from the Olorboh River embouchement, the valley broadens and there are fewer islands. The river forms a wide bend where stretches alternate with deep rifts. Oxbow lakes are situated along the river. Occasionally, whooper swan, taiga bean goose, falcated duck, garganey, smew, and Red-breasted Merganser can be found nesting. Other common species are mallard, teal, tufted duck, common goldeneye, and common merganser (Degtyarev, 2004 ; Revin and Tirsky, 2010 ). Along the Amga River, there is a narrow band width of 10–50 m composed of sand and pebble. It is overgrown with tall-riverine meadows of 2–3 m high above the river level. The meadows are interlaced with thickets of willows and, less often, poplars.
The upper reaches of the Tuolba River pass through extensive bogs and grass marshes that flood during the spring and attract migratory waterbirds. Throughout the remainder of the reserve territory, it flows in bold, grassy banks. The composition of nestling populations of waterfowl on the Tuolba River, compared with the Amga River, is slightly depauperated. There are no falcated duck, northern pintail, or smew; the nature of the stay of the whooper swan is not fully clear.
Larch, pine, larch and bilberry–forb ledum forests prevail on the watersheds. Smooth slopes are dominated by blueberry–green moss and blueberry–Ledum–sphagnum larch forests. Flat bottoms of the trough valley are swamped and occupied with bogs and transitional upper bogs. The major forest complex is a “bog taiga forest complex.” In the autumn and winter, these places are the main habitat for capercaillie at a density of 6–8 ind./km2 . Mixed spruce and larch forests grow along the rivers and brooks. The shrub layer is dominated by alder shrub, prickly wild rose, willow leaf spiraea, and willow. The grass–shrub layer is represented by cranberries, and horsetails. Hazel grouse is always common there (4.2–5.5 ind./km2 ), and flocks of ptarmigan (from 2 to 15 birds) are often observed in the wintertime.
The watershed ridge is the eastern boundary of the reserve and is also a border of the mountain taiga area. The western boundary passes by the middle reaches of the rivers heading from the Amginsky Ridge. The southern border, capturing the Amga head, passes through the watershed of the Tas-Heiko and Krestyakh Rivers and reaches the Olekma River. Wetlands are represented by medium and small mountain rivers, mountain streams, and herbal and transitional bogs, though lakes are missing.
Valleys of the rivers flowing down from the Amginsky Ridge are occupied mainly by spruce blueberry–moss–lichen and blueberry–sphagnum. Along the channels, there are intermittent strips of humid horsetail herb–spruce forests. Throughout the year, grouse is common; grouse maximum population density is observed in August to October (5.5–7.0 ind./km2 ).
The mountain forest belt consists of dark coniferous stands with primarily stone pine and Siberian fir. Dahurian larch grows in significant numbers only on well-lit slopes. Bilberry is common for the grass and underwood layer. The medium altitude of the bald mountain plateau is 1210 m. Most of the bald mountain plateau area is occupied by dwarf Siberian pine thickets. In some years, during fall and winter periods, capercaillie presence has been noted in these stands. In the summer, it is the main nesting habitat for ptarmigan (1.2–1.5 ind./km2 ) and, rarely, the rock ptarmigan nestle as well (0.2–0.4 a./km2 ). Grouse are absent from this site.
This area, in terms of diversity of species, composition and abundance of waterbirds, occupies the last position compared to the other areas. Medium and small mountain-type rivers are the main places for harlequin duck nestling and, to a lesser extent, for Goosander. For each 10 km of riverbank, on average, there are 2.3–2.6 harlequin duck couples and 1.5–1.6 couples of Goosander. Such rivers are secondary habitats for Goldeneye and Red-breasted Merganser, and occasionally, tufted duck, mallard and teal nest there. Along the valleys of small rivers, woodcock is regularly observed.