Denis V. Sandanov

Rapid warming accelerates tree growth decline in semi-arid forests of Inner Asia

Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the worlds most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests.

Growth Decline Linked to Warming-Induced Water Limitation in Hemi-Boreal Forests

Hemi-boreal forests, which make up the transition from temperate deciduous forests to boreal forests in southern Siberia, have experienced significant warming without any accompanying increase in precipitation during the last 80 years. This climatic change could have a profound impact on tree growth and on the stability of forest ecosystems in this region, but at present evidence for these impacts is lacking. In this study, we report a recent dramatic decline in the growth of hemi-boreal forests, based on ring width measurements from three dominant tree-species (Pinus sylvestris, Larix sibirica and Larix gmelinii), sampled from eight sites in the region. We found that regional tree growth has become increasingly limited by low soil water content in the pre- and early-growing season (from October of the previous year to July of the current year) over the past 80 years. A warming-induced reduction in soil water content has also increased the climate sensitivity of these three tree species. Beginning in the mid-1980s, a clear decline in growth is evident for both the pine forests and the larch forests, although there are increasing trends in the proxy of soil water use efficiencies. Our findings are consistent with those from other parts of the world and provide valuable insights into the regional carbon cycle and vegetation dynamics, and should be useful for devising adaptive forest management strategies.

Topography-Controlled Soil Water Content and the Coexistence of Forest and Steppe in Northern China

The semi-arid forest-steppe ecotone in China is characterized by a patchy pattern of forest and steppe, with forest patches restricted to shady slopes. To address the effect of topography on forest distribution through regulation of available water, we calculated evaporation as a function of slope aspect and inclination. Field vegetation records from randomly selected sites with minimum slope inclination were used to test the simulated forest distribution. Seasonal and diurnal changes of surface soil temperature and moisture of shady and sunny slopes were recorded. Soil water content was measured during two growing seasons on both sunny and shady slopes with the same forest type at three sites located along the mean annual precipitation (MAP) gradient. Evaporation decreases with slope inclination on shady slopes, but increases with inclination on sunny slopes. The shady slope received 35% of the annual direct solar radiation received by the sunny slope when the slope inclination was 25°, and the contrast in annual direct solar radiation between the shady and sunny slopes further widens as slope inclination increases. Steeper shady slopes can support forests in dryer climates, with log-linear regression revealing a minimum slope inclination for forest distribution along the MAP gradient. The simulated minimum slope inclination for forest growth was larger than the observed minimum inclination, and the difference was greater in wetter conditions. A larger forest area fraction was considered to lead to a reduction in soil temperature and evaporation, as verified by soil temperature and moisture records and soil water content measurements. The slope-specific forest distribution in the semi-arid region of China can be explained by a topography-controlled soil water supply. Lower evaporation, resulting from lower direct solar radiation on shady slopes, allows shady slopes to retain a water supply sufficient for sustaining forests, and the existence of forests on shady slopes further reduces evaporation. Different tree species coexist at the xeric timberline due to regulation by slope inclination and aspect.

Long-term forest resilience to climate change indicated by mortality, regeneration, and growth in semiarid southern Siberia

Several studies have documented that regional climate warming and the resulting increase in drought stress have triggered increased tree mortality in semiarid forests with unavoidable impacts on regional and global carbon sequestration. Although climate warming is projected to continue into the future, studies examining long-term resilience of semiarid forests against climate change are limited. In this study, long-term forest resilience was defined as the capacity of forest recruitment to compensate for losses from mortality. We observed an obvious change in long-term forest resilience along a local aridity gradient by reconstructing tree growth trend and disturbance history and investigating postdisturbance regeneration in semiarid forests in southern Siberia. In our study, with increased severity of local aridity, forests became vulnerable to drought stress, and regeneration first accelerated and then ceased. Radial growth of trees during 1900-2012 was also relatively stable on the moderately arid site. Furthermore, we found that smaller forest patches always have relatively weaker resilience under the same climatic conditions. Our results imply a relatively higher resilience in arid timberline forest patches than in continuous forests; however, further climate warming and increased drought could possibly cause the disappearance of small forest patches around the arid tree line. This study sheds light on climate change adaptation and provides insight into managing vulnerable semiarid forests.

Phylogenetic relationships of the species of Oxytropis DC. subg. Oxytropis and Phacoxytropis (Fabaceae) from Asian Russia inferred from the nucleotide sequence analysis of the intergenic spacers of the chloroplast genome

The nucleotide sequence analysis of trnH–psbA, trnL–trnF, and trnS–trnG intergenic spacer regions of chloroplast DNA performed in the representatives of the genus Oxytropis from Asian Russia provided clarification of the phylogenetic relationships of some species and sections in the subgenera Oxytropis and Phacoxytropis and in the genus Oxytropis as a whole. Only the section Mesogaea corresponds to the subgenus Phacoxytropis, while the section Janthina of the same subgenus groups together with the sections of the subgenus Oxytropis. The sections Chrysantha and Ortholoma of the subgenus Oxytropis are not only closely related to each other, but together with the section Mesogaea, they are grouped into the subgenus Phacoxytropis. It seems likely that the sections Chrysantha and Ortholoma should be assigned to the subgenus Phacoxytropis, and the section Janthina should be assigned to the subgenus Oxytropis. The molecular differences were identified between O. coerulea and O. mandshurica from the section Janthina that were indicative of considerable divergence of their chloroplast genomes and the species independence of the taxa. The species independence of O. czukotica belonging to the section Arctobia was also confirmed.

Structure of plant communities and cenopopulations of Astragalus serioceocanus Gontsch. on the shore of Lake Baikal

Plant communities with Astragalus sericeocanus have been studied. Data on the ontogenetic structure and quantity of cenopopulations, as well as the seed productivity of their individuals, are given. It has been revealed that the habitats on the northern shore of Lake Baikal are characterized by high phytocoenotic diversity with the dominance and codominance of A. sericeocanus. The state of cenopopulations and parameters of seed productivity indicate that the northern habitats of Lake Baikal have more favorable conditions due to the optimal climatic characteristics for the growth and development of the species.

Modern State of Populations of Endemic Oxytropis Species from Baikal Siberia and Their Phylogenetic Relationships Based on Chloroplast DNA Markers

The genetic diversity and population structure of the endemic species of Baikal Siberia Oxytropis triphylla, O. bargusinensis, and O. interposita were studied for the first time on the basis of the nucleotide polymorphism of intergenic spacers psbA–trnH, trnL–trnF, and trnS–trnG of chloroplast DNA. All populations of these species were characterized by a high haplotype (0.762–0.924) and relatively low nucleotide (0.0011–0.0022) diversity. Analysis of the distribution of variability in O. triphylla and O. bargusinensis showed that there was no significant genetic differentiation between populations of each species; the gene flow was 4.43 and 8.91, respectively. The high level of genetic diversity in the studied populations indicates a relatively stable state of these populations. A study of the phylogenetic relationships of closely related species confirms the concept of the origin of O. bargusinensis and O. tompudae as a result of intersectional hybridization of the species of the sections Orobia and Verticillares.

Effects of contemporary environment and Quaternary climate change on drylands plant diversity differ between growth forms

Previous studies on large-scale patterns in plant richness and underlying mechanisms have mostly focused on forests and mountains, while drylands covering most of the world’s grasslands and deserts are more poorly investigated for lack of data. Here, we aim to 1) evaluate the plant richness patterns in Inner Asian drylands; 2) compare the relative importance of contemporary environment, historical climate, vegetation changes, and mid-domain effect (MDE); and 3) explore whether the dominant drivers of species richness differ across growth forms (woody vs herbaceous) and range sizes (common vs rare). Distribution data and growth forms of 13 248 seed plants were compiled from literature and species range sizes were estimated. Generalized linear models and hierarchical partitioning were used to evaluate the relative contribution of different factors. We found that habitat heterogeneity strongly affected both woody and herbaceous species. Precipitation, climate change since the mid-Holocene and climate seasonality dominated herbaceous richness patterns, while climate change since the Last Glacial Maximum dominated woody richness patterns. Rare species richness was strongly correlated with precipitation, habitat heterogeneity and historical climatic changes, while common species richness was strongly correlated with MDE (woody) or climate seasonality (herbaceous). Temperature had little effects on the species richness patterns of all groups. This study represents the first evaluation of the large-scale patterns of plant species richness in the Inner Asian drylands. Our results suggest that increasing water deficit due to anthropogenic activities combined with future global warming may increase the extinction risk of many grassland species. Rare species (both herbaceous and woody) may face severe challenges in the future due to increased habitat destruction caused by urbanization and resource exploitation. Overall, our findings indicate that the hypotheses on species richness patterns based on woody plants alone can be insufficient to explain the richness patterns of herbaceous species.

Comparative assessment of population strategy of Hedysarum alpinum L. (Fabaceae family) in the Lake Baikal region

Sixteen cenopopulations of Hedysarum alpinum in the Lake Baikal region have been evaluated by a combination of the organismic and population parameters. It has been revealed that the habitat conditions of floodplain meadows with the highest total scores of the organismic and population parameters are the most favorable for this species. The cenopopulations in the permafrost zone and areas under anthropogenic impact are characterized by the lowest parameters of the species status. The main integral property of H. alpinum—tolerance—is related to its adaptive mechanism, which is determined by the ability of this species to survive for a long time under unfavorable conditions due to the great decrease in the organismic and population parameters of the plants.

Karyotype studies endemic plant species Astragalus sericeocanus Gontsch. (Fabaceae) around Lake Baikal, Siberia

A study of the karyotype and chromosome of six Astragalus sericeocanus populations from different parts of Lake Baikal’s shoreline was undertaken. Each population had the same chromosome number, 2n = 16. The population was divided into three groups depending on the karyotype formulae 2n = 16=8m+8sm, 2n = 16=6m+10sm and 2n = 16=4m+12sm. The analysis of the karyotype asymmetry indexes showed that population on Millionnyi Island had the most asymmetrical and evolutionary karyotype and the population along the River Turka had the most symmetrical karyotype in all of the populations. The plants from all studied populations have similar chromosome morphology.