The recent warming in the mountain regions affect forest productivity in terms of tree growth, especially in the Himalayan region. However, the effects of climate change on the response of radial growth of different age-class trees in the Himalayan region remains unclear. The sensitivity of different age-class trees can differ from younger to old age-class tree growth which create uncertainty in tree-ring calibration against the climatic parameters. In the present study, we assessed the effect of climate change on the radial growth of Cedrus deodara (cedar) from two different age classes; young (age <100 years) and old (age >100 years) in lower temperate zone of Indian Western Himalaya for the period 1950-2015 CE. We modelled basal area increment (BAI) using the Generalized additive model (GAM) which predicted the observed pattern of BAI as a function of year and random effect of tree. The trend of old age stand BAI increased significantly by 0.13 cm2/year whereas it significantly declined by -0.27 cm2/year for young deodar stand. However, from 1990 CE both age classes showed significant decline (p<0.05) in BAI indicating reduction in tree productivity of cedar species which may be due to recent accelerated rise in temperature and decline in precipitation. Correlation analysis between BAI growth and climate revealed that the BAI from both age-class trees were mainly limited by spring season (March-May) climate, moreover, the signal was statistically strong for old age deodar stand. The tree age vs DBH relationship of old age stand forest showed significant positive relationship but no relationship was found for young age stand which indicated more environmental stress condition for young age deodar forest stand. Future efforts are required to identify the factors responsible for decline productivity of young deodar stand by using wide networks of tree-ring data.
Accelerated glacier mass loss is primarily attributed to greenhouse-induced global warming. Land–climate interactions have increasingly been recognized as an important forcing at the regional-local scale, but the related effects on the Himalayan glaciers are less explored and thought to be an important factor regulating spatial heterogeneity. The aim of the present study is a multi-decadal approximation of glacier—hydroclimate interaction over the western region of the central Himalaya (WCH). Multi-species, highly coherent, tree-ring cellulose δ 18 O chronologies from three sites across the WCH were used to derive atmospheric humidity (Atmospheric Moisture Content: AMC) record of the last four centuries. Annual-scale AMC reconstruction implies a decreasing regional atmospheric moisture since the mid-19th century and a sharp decline in recent decades (1960s). Coherency analyses between regional AMC and glacier mass balance (GMB) indicate an abrupt phase-shift in the relationship after the 1960s within a common record of the last 273 years. To ascertain the cause of this phase-shift, annual AMC was disintegrated into seasonal-scale, utilizing ∼200 years of δ 18 O record of a deciduous tree species. Seasonal (winter: October–March; summer: April–September) AMC reconstructions and disaggregation results indicate higher sensitivity of regional ice-mass variability to winter moisture dynamics than summer.Winter season AMC reconstruction confirms a revival of winter westerlies-driven moisture influx in the region since the 1970 s. Meanwhile, the record for the summer season AMC indicates a gradual decline in moisture influx from the beginning of the 20th century. Interestingly, despite a prominent decline in Indian summer monsoon (ISM) precipitation after the mid-20th century, the summer season AMC—GMB relation remained stable. We hypothesize that decadal-scale greening, and consequently increased evapotranspiration and pre-monsoon precipitation might have been recycled through the summer season, to compensate for the ISM part of precipitation. However, isotope-enabled ecophysiological models and measurements would strengthen this hypothesis. In addition, high-resolution radiative forcing and long-term vegetation greening trends point towards a probable influence of valley greening on GMB. Our results indicate that attribution of ice mass to large-scale dynamics is likely to be modulated by local vegetation changes. This study contributes to the understanding of long-term hydroclimate—ice mass variability in the central Himalaya, where predictions are crucial for managing water resources and ecosystems.
This article enumerates the findings of a team research on the Indian Himalayan timberline ecotone, with focus on three sites (located in Kashmir, Uttarakhand and Sikkim).Timberline elevation increased from west to east, was higher in the warmer south aspect than the cooler north aspect, and was generally depressed.Betula, Abies, Rhododendron and Juniperus were important treeline genera.The Himalaya has not only the highest treelines (Juniperus tibetica, at 4900 m), but also the widest elevational range (>1700 m).Remotely sensed data revealed that the timberline is a long, twisting and turning ecotone, traversing a length of 8-10 km per km horizontal distance.Surface temperature lapse rate in the monsoonal regions was lower (-0.53°C/100m elevation) than generally perceived and varied considerably with season, being the lowest in December.The Himalayan treeline species are not water-stressed at least in monsoonal regions, predawn tree water potential seldom getting below -1 MPa.The upward advance of Rhododendron campanulatum (a krummholz species) may deplete alpine meadows with climatic warming.Tree-ring chronology indicated that winter warming may be favouring Abies spectabilis.Early snowmelt increased growth period and species richness.Treelines generally are stable in spite of decades of warming.Dependence of people on timberline was still high; so economic interventions are required to reduce the same.
The surface and near-surface air temperature observations are primary data for glacio-hydro-climatological studies. The in situ air temperature (Ta) observations require intense logistic and financial investments, making it sparse and fragmented particularly in remote and extreme environments. The temperatures in Himalaya are controlled by a complex system driven by topography, seasons, and cryosphere which further makes it difficult to record or predict its spatial heterogeneity. In this regard, finding a way to fill the observational spatiotemporal gaps in data becomes more crucial. Here, we show the comparison of Ta recorded at 11 high altitude stations in Western Himalaya with their respective land surface temperatures (Ts) recorded by Moderate Resolution Imagining Spectroradiometer (MODIS) Aqua and Terra satellites in cloud-free conditions. We found remarkable seasonal and spatial trends in the Ta vs. Ts relationship: (i) Ts are strongly correlated with Ta (R2 = 0.77, root mean square difference (RMSD) = 5.9 °C, n = 11,101 at daily scale and R2 = 0.80, RMSD = 5.7 °C, n = 3552 at 8-day scale); (ii) in general, the RMSD is lower for the winter months in comparison to summer months for all the stations, (iii) the RMSD is directly proportional to the elevations; (iv) the RMSD is inversely proportional to the annual precipitation. Our results demonstrate the statistically strong and previously unreported Ta vs. Ts relationship and spatial and seasonal variations in its intensity at daily resolution for the Western Himalaya. We anticipate that our results will provide the scientists in Himalaya or similar data-deficient extreme environments with an option to use freely available remotely observed Ts products in their models to fill-up the spatiotemporal data gaps related to in situ monitoring at daily resolution. Substituting Ta by Ts as input in various geophysical models can even improve the model accuracy as using spatially continuous satellite derived Ts in place of discrete in situ Ta extrapolated to different elevations using a constant lapse rate can provide more realistic estimates.
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