Dynamics of Tree and Shrub Vegetation in the Eastern Sayan Mountain Tundra

Russian Journal of Ecology - Climate change entails shifts in the ranges of woody plants along both latitudinal and altitudinal gradients in the boreal forest biome. In this study,...     

Larch forests of Middle Siberia: long-term trends in fire return intervals

Fire history within the northern larch forests of Central Siberia was studied (65 + °N). Fires within this area are predominantly caused by lightning strikes rather than human activity. Mean fire return intervals (FRIs) were found to be 112 ± 49 years (based on firescars) and 106 ± 36 years (based on firescars and tree natality dates). FRIs were increased with latitude increase and observed to be about 80 years at 64°N, about 200 years near the Arctic Circle and about 300 years nearby the northern range limit of larch stands (~71° + N). Northward FRIs increase correlated with incoming solar radiation (r = ?0.95). Post-Little Ice Age (LIA) warming (after 1850) caused approximately a doubling of fire events (in comparison with a similar period during LIA). The data obtained support a hypothesis of climate-induced fire frequency increase.     

Fir decline and mortality in the southern Siberian Mountains

Regional Environmental Change - Increased dieback and mortality of “dark needle conifer” (DNC) stands (composed of fir (Abies sibirica), Siberian pine (Pinus sibirica) and spruce (Picea...     

The Spatiotemporal Pattern of Fires in Northern Taiga Larch Forests of Central Siberia

The periodicity of fires in larch forests of Evenkia and their relationship with landscape elements have been studied. Cross-sections with “burns” in them caused by past fires have been analyzed in 72 test plots; the fire chronology encompassed the period from the 15th to the 20th century. The between-fire intervals (BFIs) have been calculated by two methods: (I) on the basis of burns alone and (II) on the basis of burns and the start of growth of the new generation of larch after the earliest fire. The BFI depends on local orographic features; it is 86 ± 11 (105 ± 12), 61 ± 8 (73 ± 8), 139 ± 17 (138 ± 18), and 68 ± 14 (70 ± 13) years for northeastern slopes, southwestern slopes, bogs, and flatlands, respectively. The mean BFIs calculated by methods I and II are 82 ± 7 and 95 ± 7 years, respectively. The permafrost horizon rises at a mean rate of 0.3 cm per year after a forest fire. It has been shown that the number of fires regularly peaks at periods of 36 and 82 years. There is also a temporal trend in fire frequency: the mean BFI was approximately 100 years in the 19th century and 65 years in the 20th century.     

Forest-tundra larch forests and climatic trends

Climate-related changes that occurred in the Ary-Mas larch forests (the world’s northernmost forest range) in the last three decades of the 20th century have been analyzed. An analysis of remote-sensing images made by Landsat satellites in 1973 and 2000 has provided evidence for an increase in the closeness of larch forest canopy (by 65%) and the expansion of larch to the tundra (for 3–10 m per year) and to areas relatively poorly protected from wind due to topographic features (elevation, azimuth, and slope). It has also been shown that the radial tree increment correlates with summer temperatures (r = 0.65, τ = 0.39) and the amounts of precipitation in summer (r = ?0.51, τ = 0–41) and winter (r = ?0.70, τ = ?0.48), decreases with an increase in the closeness of forest canopy (r = ?0.52, p > 0.8; τ = ?0.48, p > 0.95), and increases with an increase in the depth of soil thawing (r = 0.63, p > 0.9; τ = 0.46, p > 0.9). The density of undergrowth depends on temperatures in winter (τ = 0.53, p > 0.8) and summer (r = 0.98, p > 0.99, τ = 0.9, p > 0.99) and the date of the onset of the growing period (r = ?0.60, p > 0.99; τ = ?0.4, p > 0.99) and negatively correlates with the amount of precipitation in summer (r = ?0.56, p > 0.99, τ = ?0.38, p > 0.99).     

Tree vegetation of the forest-tundra ecotone in the Western Sayan mountains and climatic trends

Parameters of reproduction of the Siberian stone pine (Pinus sibirica), including radial and apical tree increments, the age structure of stands, the amount of young growth, and its distribution along an altitudinal gradient, have been studied in the forest-tundra ecotone of the Western Sayan. The results show that, over the past 30 years, P. sibirica undergrowth has expanded to the mountain tundra belt, the apical and radial tree increments and stand density have increased, and the life form of many P. sibirica plants has changed from prostrate to erect (single-or multistemmed). These changes correlate with the dynamics of summer temperatures and monthly (in May and June) and annual precipitation. The rise of summer temperatures by 1°C promotes the expansion of P. sibirica undergrowth for approximately 150 m up the altitudinal gradient.     

Spatiotemporal characteristics of wildfire frequency and relative area burned in larch-dominated forests of Central Siberia

Wildfire frequency, relative area burned, and fire return intervals (FRI) have been studied in larchdominated forests along the transect from the southern (45° N) to the northern (73° N) distribution limits of larch stands based on analysis of satellite imagery (NOAA/AVHRR, Terra/MODIS; 1996–2015) and collection of tree cross cuts with fire scars. A significant increasing trend in fire extent (R² = 0.50, p < 0.05) has been revealed. Histograms of fire extent and frequency are bimodal in the southern and middle taiga (with peaks in spring–summer and late summer–autumn periods) but become unimodal toward the north (>55° N). The length of FRI increases from 80 years at 62° N to ~200 years at the Arctic Circle and reaches ~300 years near the northern limit of larch stands, showing a significant inverse correlation with the length of fire season (r =–0.69). In turn, the length of fire season, area burned and FRI are closely correlated with latitudinal variation in solar irradiance (r = 0.97, 0.81, and –0.95, respectively).     

The Intensity of Wildfires in Fire Emissions Estimates

Russian Journal of Ecology - A method for estimating direct wildfire emissions that considers fire intensity based on infrared radiation data from the Terra/MODIS satellite is proposed. In Siberia,...     

Expansion of Evergreen Conifers to the Larch-Dominated Zone and Climatic Trends

The expansion of so-called evergreen conifers (EGCs), including Siberian stone pine, spruce, and fir, along the transect oriented from the boundary of the larch-dominated zone (LDZ; mixed forests of the Yenisei Ridge) to its center has been studied. The normalized dispersal coefficient calculated as K _i = (n _i – N _i )/(n _i + N _i ), where n _i and N _i are the relative numbers of the ith species in the undergrowth and the upper layer, respectively, serves as an indicator of the expansion. It has been found that the K _i values for EGCs (and birch) are higher than the K _i of larch even in the zone absolutely dominated by larch, where the relative numbers of EGCs in the upper layer is less than 1%. The EGC undergrowth has mainly been formed during the past 20–30 years, which is correlated with the trend of summer temperatures The spread of EGCs in the LDZ depends on the frequency of forest fires. The decrease in the time intervals between fires in the 20th century to 65 years (versus 100 years in the 19th century) may have prevented the expansion of competing species in the LDZ. The results obtained indicate that EGCs and birch penetrate into the zone traditionally dominated by larch, which is related to climatic changes during the past three decades. At the same time, tree stand density is increasing in the forest-tundra ecotone, and larch is spreading further into the tundra zone.__________Translated from Ekologiya, No. 3, 2005, pp. 186–193.Original Russian Text Copyright © 2005 by Kharuk, Dvinskaya, Ranson, Im.     

Zoning of Landscapes Exposed to Technogenic Emissions from the Norilsk Mining and Smelting Works

In this study, we have analyzed the degradation of pretundra forests and distinguished the levels of pollution using ground-based and remote-sensing data. The study region is located in the area exposed to emissions from the Norilsk Mining and Smelting Works. The main components of emissions are sulfur dioxide, nitrogen oxide, and heavy metals. Currently, the zone of damaged forests extends for more than 200 km. The comparison of the zones of degradation of pretundra vegetation distinguished in satellite images with the results of ground-based observations yielded high similarity coefficients (0.73–0.83) of the Kappa statistics. The zones of vegetation state were classified by NDVI values. The images from the NOAA/AVHRR satellite may be used for delimiting the zones of vegetation degradation by the proposed method.