Abstract
The sensitivity and response of climatic treelines in the Himalayas to climate change is still being debated. Regeneration of tree species in the treeline ecotone is considered a sensitivity indicator and thus of great scientific interest. The aim of this study is to detect predictor variables for regeneration densities of the major tree species in central Himalayan treeline ecotones (Abies spectabilis, Betula utilis, Rhododendron campanulatum), analysing five development stages from seedling to mature tree. We applied negative binomial generalized linear models with predictors selected from a wide range of soil, topography, climate and stand characteristic variables. We found considerably varying predictors across the tree species and their stages of development. Soil conditions, topography and climate, as well as competing and facilitating tree species, had high predictive power for population densities. These predictors were clearly species- and development stage-specific. Predictors’ spatial- and development-specific heterogeneity induce a high degree of complexity and diversify any potentially linear response of tree population densities and treeline position to changing climatic conditions.
Highlights
IntroductionClimatic treelines in high mountains represent elevational limits caused by heat deficiency [1–3]
Empirical studies in mountain ranges across the globe found advancing treelines, but in many cases a distinct persistence of treeline elevations [8,9], suggesting that process dynamics in many treeline ecotones are, to some extent, decoupled from climate warming
We aim at detecting predictor variables for population densities of environmental conditions during the life history from youngest seedling to mature tree
Summary
Climatic treelines in high mountains represent elevational limits caused by heat deficiency [1–3]. They are often considered to be sensitive bioindicators of global warming cf [4], supported by the response of treelines to climatic oscillations throughout the Holocene [5–7]. Treelines will shift to higher elevations as a response to climate warming, at least in the long term. Non-thermal site factors, including biotic interactions such as competition, might prevent a short- or mid-term change in treeline elevation. Many-faceted interactions between climate warming as an input variable at a global/regional scale, and the complexes of abiotic and biotic site factors, as well as anthropogenic influences and their interrelationships at the landscape/local level, might cause inconsistent response patterns [4]
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