Climate-Driven Differences in Growth Performance of Cohabitant Fir and Birch in a Subalpine Forest in Dhorpatan Nepal

Abstract

Himalayan Silver Fir (Abies spectabilis) and Himalayan Birch (Betula utilis) are tree species often found coexisting in sub-alpine forests of the Nepal Himalayas. To assess species-specific growth performances of these species, tree-ring samples were collected from the subalpine forest in the Dhorpatan Hunting Reserve, Nepal. Standard ring width chronologies of both species were correlated with climatic variables in both static and running windows. Differential and contrasting temporal responses of radial growth of these species to climate were found. Warmer and drier springs appeared to limit birch radial growth. Whereas radial growth of fir showed weakened climate sensitivity. Moving correlation analyses revealed divergent influences of spring climate on both fir and birch. Significant warming that occurred in the 1970s coincided with growth declines in birch and an increase in fir, as indicated by basal area increment. In summary, recent warming has been unfavorable for birch, and favorable to fir radial growth.

Elevation‐dependent tree growth response to climate in a natural Scots pine/downy birch forest in northern Sweden

“…We calculated the basal area increment, that is, the ring area, for each tree and year since it is a better measure for growth than the raw tree‐ring width (Biondi & Qeadan, 2008) and also reduces age‐related growth trends (Bista et al., 2021). We used the bai.out() function in dplR which calculates the BAI series following this formula:$$$$ {\mathrm{BAI}}_t=\pi \left({w_t}^2+2{w}_t{R}_{t-1}\right), $$$$where w t is the ring width of the current year and R t − 1 is the radius of the stem (excluding the bark) prior to the current year's growing season.…”

“…We calculated the basal area increment, that is, the ring area, for each tree and year since it is a better measure for growth than the raw tree-ring width (Biondi & Qeadan, 2008) and also reduces agerelated growth trends (Bista et al, 2021). We used the bai.out() function in dplR which calculates the BAI series following this formula:…”