Dendroclimatic response of Abies spectabilis at treeline ecotone of Barun Valley, eastern Nepal Himalaya

A dendroclimatic study was conducted in the treeline ecotone of Barun Valley, eastern Nepal, to determine the tree-ring climate response and ring width trend of Abies spectabilis. A 160-year-old chronology, from 1850 to 2010, was developed from 38 tree-ring samples. No higher growth in recent decades was observed in tree-ring width in this area. The mean temperature of the current year in February and in the combined winter months of December, January, and February showed significant positive correlation with tree-ring width, although no significant correlation was found between tree-ring width and the precipitation pattern of the region. This tree-ring climate response result is different from that in other studies in Nepal, which could be attributed to location and elevation.

Response of tree-ring growth to climate at treeline ecotones in the Qilian Mountains,northwestern China

Climate constitutes the main limiting factor for tree-ring growth in high-elevation forests, and the relationship between tree-ring growth and climate is complex. Based on tree-ring chronology and meteorological data, the influence of precipitation, mean temperature and mean minimum temperature at yearly, seasonal and monthly scales on the tree-ring growth of Picea crossifolia was studied at treeline ecotones in the Qilian Mountains, northwestern China. The results show that growing season temperatures of previous and current years are important limiting factors on tree-ring growth, particularly June mean temperature and mean minimum temperature of current year. The precipitations in the previous winter and current spring have a positive correlation, and in the current fall has a negative correlation with tree-ring growth, but these correlations are not significant. Our results suggest that temperature controls tree-ring growth more strongly than precipitation at treeline ecotones in the Qilian Mountains.

Soil microbial community assemblage and its seasonal variability in alpine treeline ecotone on the eastern Qinghai-Tibet Plateau

The alpine treeline ecotone is characterized as the upper limit of the forest in the high-mountain ecosystem.Due to the freeze-thaw cycles,the soil organism community,such as microbial communities are expected to change between seasons.However,there are limited microbialcommunity studies focused on the high altitude alpine ecosystem.We conducted a study in the alpine treeline ecotone on the eastern Qinghai-Tibet Plateau,China,and investigated the seasonal variability of the soil microbial community.We collected all soil samples within the alpine treeline ecotone,between the treeline and timberline in the high-mountain region.The 16S rRNA genes of the microbial communities(bacterial and archaeal)were analyzed by highthroughput sequencing to the genus level.The results showed that soil microbial community in the alpine treeline ecotone was consistently dominated by eight phyla which consisted of 95% of the total microbial community,including Proteobacteria,Actinobacteria,Acidobacteria,Firmicutes,Planctomycetes,Chloroflexi,Bacteroidetes,and Verrucomicrobia.The overall diversity and evenness of the community were relatively stable,with an average of 0.5% difference between seasons.The highest seasonal variability occurred at the upper boundary of the alpine treeline ecotone,and few or almost no seasonal change was observed at lower elevations,indicating dense forest cover and litter deposition might have created a local microclimate that reduced seasonal variation among the surrounding environmental conditions.Our study was one of the first group that documented the microbial community assemblage in the treeline ecotone on the Qinghai-Tibet Plateau.

Alpine ecotone in the Siberian Mountains:vegetation response to warming

Birch(Betula tortuosa)is one of the treeline forming species within the Siberian Mountains.We analysed the area dynamics of birch stands and the upslope climb of birch treeline based on the Landsat time series scenes and on-ground data.We found that since the warming onset(1970th)birch area increased by 10%,birch stands and treeline boundary were moving upslope with a rate of 1.4 m/yr and 4.0 m/yr.Birch upslope shift correlated with air temperatures at the beginning(May-June)and the end(August-October)of the growth period.Meanwhile,no correlation was found between birch upslope migration and precipitation.Winds negatively influenced both birch area growth and birch upslope climb during spring,fall,and wintertime.In the windy habitats,birch,together with larch and Siberian pine,formed clusters(hedges)which mitigated the influence of adverse winds.These clusters are the adaptive pattern for trees’upslope climb within windward slopes.The other adaptation to the harsh alpine ecotone habitat is non-leaf(bark)photosynthesis which supports tree survival.Thereby,Betula tortuosa upslope climb depends on the wind impact and warming in spring and fall that extended growth period.With ongoing warming and observed wind speed decrease on the background of sufficient precipitation,it is expected to further birch advance into alpine tundra in the Siberian Mountains.

Recent treeline dynamics are similar between dry and mesic areas of Nepal, central Himalaya

Aims We investigated the treeline dynamics of two environmentally con-trasting areas in the Nepalese Himalaya to address the following questions:(i)Does the timing of establishment of the current tree-line differ between the two study areas,and can area-specific tree-line developments be identified?(ii)Do recruitment patterns and height growth indicate recent climate-driven treeline advance,fol-lowing the general prediction for the central Himalayan region,in the two study areas?Methods a dry-climate treeline dominated by Pinus wallichiana and a mesic-climate treeline with Abies spectabilis were selected for study.In each area,we sampled the size and age structure of the study spe-cies along three elevational transects(20-m wide)from the forest line to the tree species line crossing the treeline.We also sampled treeline trees from within and outside transects to reconstruct past treeline establishment dynamics.Important Findings Despite differences in moisture regimes,tree species and recent climate trends,our two study areas showed very similar treeline dynamics over the past six decades.In both areas,the recruitment of treeline trees indicates stationary treelines over the past six decades with the current treelines being dominated by trees that were established around 1990.the mesic area has experienced an overall climatic warming trend,and the stationary Abies treeline is hypothesized to be regulated by non-climatic factors,notably grazing.the dry area has not experienced warming but increased climatic variability and some very cool summers in the recent dec-ades may explain the stationary to weakly receding Pinus treeline,which appears more climatically controlled with decreased recruit-ment over the past decades and decreased growth towards higher elevations.In both areas,there is a potential for treeline advance,depending on future land use and climate change.our results highlight the importance of conducting treeline ecotone analyses for several sites or areas,and considering both climatic and non-climatic drivers of the treeline dynamics within each of these areas,for understanding regional treeline dynamics.

Environmental variables vis-a-vis distribution of herbaceous tracheophytes on northern sub-slopes in Western Himalayan ecotone

Background:In the northern hemisphere,the north face of the mountains has a high diversity of species which is attributed to the moist and shady conditions at the north face.Other environmental variables may also influence the species diversity on the northern faces of the mountain and therefore needs to be studied in detail.The northern slopes represent three different sub-slopes—north,north east,and north west.During the current investigation of Pir-Panjal and Dauladhar ranges in Bhadarwah valley,fine-scale studies on the relationship between vegetation and four variables(soil pH,moisture content,electrical conductivity,and steepness)were conducted.The study determined the role of these variables on the vegetation of three different sub-slopes.The sampling was done at the confluence of two communities(forest and grassland)at three sites on the northern sub-slopes of the lesser stratum in western Himalayan.Results:The result revealed that rich herbaceous diversity prevails on the lesser Himalayan stratum(Bhadarwah valley).As many as 65.8%species differ from site to site,whereas species commonality among the sites is minimum.The role of environmental variables on the species composition at different sub-slopes of the north mountain face is deduced through canonical correspondence analysis(CCA).Conclusions:The availability of solar light increases air and soil temperature on the north east–facing slope.All the environmental variables(soil pH,moisture,electrical conductivity,and mountain steepness)are insignificant at pure north face for the species composition.Therefore,it can be concluded that some other environmental variables may influence the species composition which are needed to be further investigated.