Climate Change-Induced Shift of Tree Growth Sensitivity at a Central Himalayan Treeline Ecotone

Abstract

Himalayan treelines are exposed to above average climate change impact, resulting in complex tree growth-climate relationships for Himalayan Silver Fir (Abies spectabilis (D. Don) Spach) at central Himalayan treelines. The majority of recent studies detected current tree growth sensitivity to dry conditions during pre-monsoon seasons. The aim of this study was to analyze growth-climate relationships for more than a century for a treeline ecotone in east-central Nepal and to test for Blue Intensity (BI; used as a surrogate of maximum late wood density) as climate proxy. We determined the relationships of Abies spectabilis radial tree growth and BI to climate by correlating both to temperature, precipitation and drought index data. The results showed a significantly unstable dendroclimatic signal over time. Climate warming-induced moisture deficits during pre-monsoon seasons became a major factor limiting radial tree growth during recent decades. Earlier in time, the dendroclimatic signal was weaker, predominantly reflecting a positive relationship of tree growth and summer temperature. Compared to radial tree growth, BI showed a different but strong climate signal. Temporally unstable correlations may be attributed to increasing effects of above-average rates of climate warming. An extended network of Himalayan tree-ring sites is needed to further analyze cause-effect relationships and to solve this attribution problem.

Effects of climate change on treeline trees in Sagarmatha (Mt. Everest, Central Himalaya)

“…Although the used CRU database has a wide spatial resolution incapable of capturing the wide climate variability between valleys and elevation in the Himalayan region (Schwab et al. , 2018), we found that tree rings encoded a few significant signals of climate variability. Betula utilis was more sensitive than Abies spectabilis to precipitation during the driest months of the year (from October to April), i.e.…”

Increased Drought Sensitivity Results in a Declining Tree Growth of Pinus latteri in Northeastern Thailand

“…In the Baltic Sea region, summer moisture availability became increasingly important for the growth of oak (Quercus robur) and European beech (Fagus sylvatica) in the latter 20th century [26]. Increasing growth sensitivity to spring season moisture availability or drought conditions is becoming predominant during recent years for the Abies spectabilis and other conifer species in the central and western Himalaya, along with weakening responses to growing season temperatures [59][60][61]. Radial growth of Fokienia hodginsii in southwest China shows increasing responses to summer temperature (negative) and precipitation (positive) under a warming and drying climate [62].…”

Short gradient, but distinct plant strategies: The CSR scheme applied to subtropical forests

“…This may predispose these regions for conservation purposes (Fahr & Kalko, 2011), as high habitat heterogeneity provides different niches and resources for a broad range of species (Tews et al., 2004), resulting in different ecological strategies. At the same time, these regions can be very sensitive to global and local changes, especially due to climate, which affects distribution patterns of species, habitats or ecosystem types (Oliveras & Malhi, 2016; Schwab et al., 2018). For example, cold temperatures are an important environmental filter in savanna–forest boundaries in Brazil, limiting the distribution of tree species (Hoffmann et al., 2019).…”