42. Age-old changes in ecosystems of Tit–Ary, the polar island in the lower reaches of the Lena river (north-east Asia)

Abstract

At the beginning of the 20th century, the expedition headed by Cajander (1903, 1904) discovered the northern outpost of a larch forest in the lower reaches of the Lena River, on a polar island Tit-Ary. At that time, the canopy density of the forest values reached 0.4; tree height was 3–5 m, and tree trunk stems were crooked. Two years later, the Australian ornithologists Hall and Trebilcock (Robin, Sirina, 2003) also explored the island, they discovered a number of migrant bird species including sandpipers that spent winters in remote Australia. In 1942–1943, the forest was cut. In the 1950s, the course of restoration of the Tit–Ary forest was studied by Tikhomirov and Shtepa (1956). Later on, the island was regularly surveyed by specialists from the Institute of Biology: in 1972, 1977, 1982, 1984, 1989, 1994. During the last three years, a special investigation of the island ecosystems has been conducted which revealed the following parameters of the forest: 2750 trees/ha, canopy density – 0.3, height – 1.5–3.2 (6.5) m, DBH – 1.7–6.2 (12) cm. After World War II, three basic waves of restoration were recorded in the 1960s, 1970s and 1980s. The study of larch height increment proves that the climatic conditions in the beginning of the 21st century favoured the growth and development of larch at the northern limits of its distribution area. And, this is reflected in growth enhancement – the average increment of axial shoot length during the last 10 years has increased from 3.1 to 7.7 cm. Recent studies yielded an increase in the number of Tit–Ary vascular plant species from 150 in the early 20th century to 206, moss species from 18 to 32, lichens from 5 to 47 species. For the first time 23 species of liverworts and 22 species of aphyllophoroid fungi were revealed (Hämet-Ahti, 1970; Labutin et al., 1985; Ivanova, 2003; Isaev et al., 2011; Poryadina, 2011). The basis of the constant composition of theriofauna of the island is represented by small mammals. Most stable are the populations of narrow skulled vole and tundra shrew, while the populations of lemmings and tundra vole feature sharp drops in number. The arthropods are represented by 59 species. The number of arthropods varies depending on annual climatic conditions. The maximal number was recorded in 2011 and characterized by moderate temperature conditions. Studies of soil microbiological composition revealed a high number of all groups of microorganisms (10 4 −10 8 ufc/g). that does not decrease within the depth of the seasonally thawed layer. This can be explained by accumulation of humus in horizons underplayed by perennially frozen grounds. Shallow thawing and considerable cold resources favour gradual saturation of soils with movable organic substance at a thawing depth and accumulation over the frozen grounds. This, in turn, yields an increased microbe population number in the seasonally thawing layer. Thus, composition and structure of ecosystems of the Tit–Ary island undergo fluctuations due to weather conditions and climatic changes that has recently taken place in higher latitudes.