Growth–climate relationships of Himalayan conifers along elevational and latitudinal gradients

Abstract

High mountains are some of the most vulnerable regions to climate change and therefore a matter of global concern. Here, the climatic growth factors of conifers and their course in time and space along an elevational gradient in the northwestern Himalayan part of India were studied. Increment cores of Juniperus semiglobosa and Cedrus deodara (xeric species), and Abies pindrow and Picea smithiana (mesic species) were collected from thirteen sites. Tree‐ring width and maximum latewood density were measured and cross‐dated. The time‐series were standardized and site‐ and species‐level chronologies were built. Static and moving bootstrap correlation and response functions between the tree‐ring chronologies and monthly climatic variables were computed. The largest climate changes in the region were increasing winter and early‐spring temperatures and decreasing monsoon precipitation. The growth of all species was negatively correlated with pre‐monsoon temperature, as the higher temperatures probably increased evapotranspiration and caused water deficit. The phenomenon was most pronounced in May, but also in June for the Juniperus at the northernmost, highest, and driest sites. The pre‐monsoon temperature signal of the drought‐prone Juniperus and Cedrus endured, while the signal of the climate‐susceptible Abies and Picea at the mesic sites was unstable. Namely, the May temperature signal of Picea became significant since the second half of the last century whereas the signal of Abies shifted from May to April. This apparently related to the earlier onset of spring due to the accelerated warming in the region. Besides, maximum latewood density of Picea and Abies negatively correlated with May and June temperature, respectively. Additionally, the Cedrus benefitted from winter precipitation and the Abies and Picea from pre‐monsoon rainfall. Counterintuitively, we detected no direct effect of monsoon precipitation decrease on the conifers because their growth was driven by pre‐monsoon conditions, which changed only slightly.

Moisture-Limited Tree Growth for a Subtropical Himalayan Conifer Forest in Western Nepal

“…Even though we cannot compare the frequency of locally missing rings or narrow rings with local climate over an extended time period due to a lack of long-term instrumental records, some of the narrow tree rings from this study were synchronized with drought events across Asian monsoon-influenced areas [9]. The growth of Picea smithiana in the western Himalayas is also significantly correlated with pre-monsoon precipitation [11]. Both Chir pine and Picea smithiana had locally missing rings in 1970 and 1937, suggesting that moisture deficiency limits tree growth and even causes the formation of locally missing rings.…”

“…Previous studies in the central Himalayas have shown that pre-monsoon precipitation is the major growth-limiting factor for Himalayan birch (Betula utilis) [5,6], Himalayan fir (Abies spectabilis) [8], alpine dwarf shrubs (Cassiope fastigiata) [31], Himalayan spruce (Picea smithiana), Himalayan blue pine (Pinus wallichiana) [9,10], and Chir pine (Pinus roxburghii) [22]. Similar growth responses in different conifer trees species were also reported from surrounding areas such as in the western Himalayas [11,12,32,33], subtropical broadleaf tree Toon (Toona ciliata) in the eastern Himalayas [17], and in the southeastern Tibetan Plateau [34,35]. However, our study shows that precipitation from November of the previous year to April of the growth year limits the radial growth of Chir pine, suggesting a stronger drought stress for tree growth in the subtropical forest belt in the central Himalayas.…”

“…In recent decades, several studies have investigated forest radial-growth responses to changing climate in the central Himalayas and surrounding regions using tree-ring data [4][5][6][7][8][9][10][11][12][13][14]. However, most studies focused on subalpine forests, showing variable growth responses to climate across different species, sites, and topographical conditions.…”

Growth response of Abies spectabilis to climate along an elevation gradient of the Manang valley in the central Himalayas

“…Thus, ongoing warming is expected to further alter drought-sensitive forest ecosystems along elevations. To date, few studies have been conducted along the elevation gradients in the Himalayas (Kharal et al 2017;Sohar et al 2017).…”

“…Some studies have indicated that growth was primarily controlled by variations in temperature (Cook et al 2003;Gaire et al 2014;Thapa et al 2014;Kharal et al 2017), while other studies have shown that tree growth was significantly controlled by precipitation at higher elevations (Dawadi et al 2013;Liang et al 2014Liang et al , 2019Panthi et al 2017). Meanwhile, both temperature and precipitation can have a significant influence on tree growth (Sano et al 2005;Sohar et al 2017). To better understand different growth responses to climate change in the central Himalayas, it is necessary to investigate growth responses along elevation gradients.…”