Viacheslav I. Kharuk

Response of Pinus sibirica and Larix sibirica to climate change in southern Siberian alpine forest–tundra ecotone

Abstract A warming climate provides competitive advantages to Siberian pine (Pinus sibirica Du Tour) in areas with sufficient precipitation. The warmer temperatures observed in central Siberia over the past three decades appear to have had a noticeable effect on growth of Siberian pine and larch (Larix sibirica Ledeb.) in the south Siberian Mountain forest–tundra ecotone. Larch is more tolerant of harsh climates and exhibits an arboreal growth form, whereas Siberian pine is in krummholz form. Larch also has an advantage at the upper tree limit and in areas with low precipitation. Since the mid-1980s there have been measurable increases in growth increments, stand densification, regeneration propagation into the alpine tundra and transformation of krummholz into arboreal forms. Warming winter temperatures have been sufficient for increased survival of regeneration. Regeneration responded to temperature increase of 1°C by migration to areas 10–40 m higher in elevation. Regeneration has propagated into the alpine tundra at the rate of ~1.0–2.0 m year−1. Siberian pine and larch regeneration surpassed their upper historical limit by 10–80 m in elevation. While increased tree growth and migration into alpine tundra areas affect the regional carbon balance, it will also decrease albedo, which may increase warming at the regional level.

NOAA/AVHRR satellite detection of Siberian silkmoth outbreaks in eastern Siberia

During 1993-1996, in central Siberia, a silkmoth (Dendrolimus superans sibiricus Tschetw.) infestation damaged approximately 700 000 ha of fir, Siberian pine and spruce stands. Temporal (1995-1997) Advanced Very High Resolution Radiometer (AVHRR) images were used for pest outbreak monitoring of this event. Damaged stands were detected, with heavy (50-75% dead and dying trees) plus very heavy (>75%) levels of damage classified. Summer and winter images were used for delineation of the northern border of the region of pest outbreaks. The Siberian taiga insects were classified with respect to their harmfulness to forests, based on the frequency of outbreaks, the size of the damaged territory, and the available food sources based on forest type.

Spatial pattern of Siberian silkmoth outbreak and taiga mortality

Abstract The latest catastrophic Siberian silkmoth (Dendrolimus superans sibiricus Tschetw.) outbreak occurred in central Siberia during 1994–1996. The relationship between forest stand mortality from insects and topographic features (azimuth, elevation, slope steepness) was analyzed based on a high-resolution digital elevation model, a pest damage map and Terra/MODIS data. It was found that pest-induced forest mortality patterns depend on topographic features. Before the outbreak the major part of host forest species was found within the elevation zone of 150–500 m. After the outbreak, surviving dark-needle stands were found mainly at elevations higher than 400 m. The greatest damage was observed at elevations between 210 and 320 m, whereas maximum mortality was observed at elevations of about 200 m and minimal mortality at elevations of 300 m. With respect to slope steepness, maximum damage for all categories was observed for slopes of 5–20°. Slightly damaged stands were most common at low slope angle (about 5° or less), whereas the highest proportion of stands with high tree mortality was found on steeper slopes. With respect to azimuth, insect damage is mostly uniform, with a small increase in damage on the south-west-facing slopes. The spatial pattern of the silkmoth outbreak can provide a basis for prioritizing Siberian silkmoth outbreak monitoring.

Tree-Line Structure and Dynamics at the Northern Limit of the Larch Forest: Anabar Plateau, Siberia, Russia

Abstract The goal of the study was to provide an analysis of climate impact before, during, and after the Little Ice Age (LIA) on the larch (Larix gmelinii) tree line at the northern extreme of Siberian forests. Recent decadal climate change impacts on the tree line, regeneration abundance, and age structure were analyzed. The location of the study area was within the forest-tundra ecotone (elevation range 170–450 m) in the Anabar Plateau, northern Siberia. Field studies were conducted along elevational transects. Tree natality/mortality and radial increment were determined based on dendrochronology analyses. Tree morphology, number of living and subfossil trees, regeneration abundance, and age structure were studied. Locations of pre-LIA, LIA, and post-LIA tree lines and refugia boundaries were established. Long-term climate variables and drought index were included in the analysis. It was found that tree mortality from the 16th century through the beginning of the 19th century caused a downward tree line recession. Sparse larch stands experienced deforestation, transforming into tundra with isolated relict trees. The maximum tree mortality and radial growth decrease were observed to have occurred at the beginning of 18th century. Now larch, at its northern boundary in Siberia, is migrating into tundra areas. Upward tree migration was induced by warming in the middle of the 19th century. Refugia played an important role in repopulation of the forest-tundra ecotone by providing a seed source and shelter for recruitment of larch regeneration. Currently this ecotone is being repopulated mainly by tree cohorts that were established after the 1930s. The last two decades of warming did not result in an acceleration of regeneration recruitment because of increased drought conditions. The regeneration line reached (but did not exceed) the pre-LIA tree line location, although contemporary tree heights and stand densities are comparatively lower than in the pre-LIA period. The mean rate of tree line upward migration has been about 0.35 m yr-1 (with a range of 0.21–0.58), which translates to a tree line response to temperature of about 55 m °C-1.

Spectral characteristics of vegetation cover: factors of variability

The dependence of spectral diffuse reflectance coefficients on the phenology of tree stands, observation and illumination conditions, ratio of scattered and total radiation was studied on a special testing ground by an automated system. The experimental dependences obtained for high density stands are satisfactorily described on the basis of the turbid layer theory (Ross-Nilson-Kuusk model)

Climate-Induced Larch Growth Response Within the Central Siberian Permafrost Zone

Aim: estimation of larch (Larix gmelinii) growth response to current climate changes. Location: permafrost area within the northern part of Central Siberia (approximately 65.8 deg N, 98.5 deg E). Method: analysis of dendrochronological data, climate variables, drought index SPEI, GPP (gross primary production) and EVI vegetation index (both Aqua/MODIS satellite derived), and soil water content anomalies (GRACE satellite measurements of equivalent water thickness anomalies, EWTA). Results: larch tree ring width (TRW) correlated with previous year August precipitation (r = 0.63), snow accumulation (r = 0.61), soil water anomalies (r = 0.79), early summer temperatures and water vapor pressure (r = 0.73 and r = 0.69, respectively), May and June drought index (r = 0.68-0.82). There are significant positive trends of TRW since late 1980s and GPP since the year 2000. Mean TRW increased by about 50%, which is similar to post-Little Ice Age warming. TRW correlated with GPP and EVI of larch stands (r = 0.68-0.69). Main conclusions: within the permafrost zone of central Siberia larch TRW growth is limited by early summer temperatures, available water from snowmelt, water accumulated within soil in the previous year, and permafrost thaw water. Water stress is one of the limiting factors of larch growth. Larch TRW growth and GPP increased during recent decades.

Polarimetric indication of plant stress

Abstract Application of polarization characteristics of reflected radiation to indicate the water stress of plants and extent of their pollution by industrial dust is studied. Experiments were carried out under field conditions. The objects measured were the leaves and shoots of woody and agricultural plants. The measurements were carried out at the wavelengths of 1.75 μm and 2.2 μm, at the Brewster angle. The fact that the degree of polarization of reflected light can serve to diagnose 5–10% water loss by the foliage is established; the effect is due to altered spatial orientation of the foliage in the crown owing to water stress. Pollution of foliage by industrial dust is accompanied by a decrease in the degree of polarization of the reflected radiation: the model experiments demonstrated the possibility of recording pollution not more than 0.03 ton / h. The effect is based on the difference between the values of degree of polarization of pollutants and the foliage.

Mapping of Siberian forest landscapes along the Yenisey transect with AVHRR

In this paper NOAA AVHRR data acquired at the Sukachev Institute of Forest in Siberia, Russia is evaluated for forest management mapping applications. First a classification of the entire 1000km 2 3000km transect was performed, but was found to be too general to be of value. More useful interpretation procedures require a landscape-ecological approach. This means that computer classification should be made separately for segments of territory based ecologically distinct regions. This segmentation of the transect into ecological regions was found to improve the level of detail available in the classification. Using this approach AVHRR data were found to be adequate for small scale mapping at the level of vegetation types or plant formations. A limited study using AVHRR data for classification of mountainous regions showed that AVHRR-derived maps were more detailed than existing landscape maps. AVHRR derived classifications also compared favourably to larger scale forest management maps of softwood and hardwood forests. Current forest management in Siberia relies on very small-scale inventory maps. Thus, there is a potential role for AVHRR (or Terra) data for northern Siberian forest monitoring. The southern forests of the Yenisey meridian (below the 57th parallel ) are less uniform due to considerable human activity, and NOAA/AVHRR data will play a subordinate role in its monitoring.

Climate-Induced Northerly Expansion of Siberian Silkmoth Range

Siberian silkmoth (Dendrolimus sibiricus Tschetv.) is a dangerous pest that has affected nearly 2.5 × 106 ha of “dark taiga” stands (composed of Abies sibirica, Pinus sibirica and Picea obovata) within the latitude range of 52°–59° N. Here we describe a current silkmoth outbreak that is occurring about half degree northward of its formerly documented outbreak range. This outbreak has covered an area of about 800 thousand ha with mortality of conifer stands within an area of about 300 thousand ha. The primary outbreak originated in the year 2014 within stands located on gentle relatively dry southwest slopes at elevations up to 200 m above sea level (a.s.l.) Then the outbreak spread to the mesic areas including northern slopes and the low-elevation forest belts along the Yenisei ridge. Within the outbreak area, the northern Siberian silkmoth population has reduced generation length from two to one year. Our study showed that the outbreak was promoted by droughts in prior years, an increase of the sum of daily temperatures (t > +10 °C), and a decrease in ground cover moisture. Within the outbreak area, secondary pests were also active, including the aggressive Polygraphus proximus bark borer beetle. The outbreak considered here is part of the wide-spread (panzonal) Siberian silkmoth outbreak that originated during 2014–2015 with a range of up to 1000 km in southern Siberia. Our work concludes that observed climate warming opens opportunities for Siberian silkmoth migration into historically outbreak free northern “dark taiga” stands.

Climate-Induced Mortality of Spruce Stands in Belarus

The aim of this work is an analysis of the causes of spruce (Picea abies L.) decline and mortality in Belarus. The analysis was based on forest inventory and Landsat satellite (land cover classification, climate variables (air temperature, precipitation, evaporation, vapor pressure deficit, SPEI drought index)), and GRACE-derived soil moisture estimation (equivalent of water thickness anomalies, EWTA). We found a difference in spatial patterns between dead stands and all stands (i.e., before mortality). Dead stands were located preferentially on relief features with higher water stress risk (i.e., higher elevations, steeper slopes, south and southwestern exposure). Spruce mortality followed a series of repeated droughts between 1990 and 2010. Mortality was negatively correlated with air humidity (r = –0.52), and precipitation (r = –0.57), and positively correlated with the prior year vapor pressure deficit (r = 0.47), and drought increase (r = 0.57). Mortality increased with the increase in occurrence of spring frosts (r = 0.5), and decreased with an increase in winter cloud cover (r = –0.37). Spruce mortality was negatively correlated with snow water accumulation (r = –0.81) and previous year anomalies in water soil content (r = –0.8). Weakened by water stress, spruce stands were attacked by pests and phytopathogens. Overall, spruce mortality in Belarussian forests was caused by drought episodes and drought increase in synergy with pest and phytopathogen attacks. Vast Picea abies mortality in Belarus and adjacent areas of Russia and Eastern Europe is a result of low adaptation of that species to increased drought. This indicates the necessity of spruce replacement by drought-tolerant indigenous (e.g., Pinus sylvestris, Querqus robur) or introduced (e.g., Larix sp. or Pseudotsuga menzieslii) species to obtain sustainable forest growth management.