Climate constraints on growth and recruitment patterns of Abies faxoniana over altitudinal gradients in the Wanglang Natural Reserve, eastern Tibetan Plateau

Abstract

The radial growth and recruitment patterns of trees in subalpine areas are subject to the influence of changing environmental conditions associated with changes in elevation. To investigate responses of fir radial growth and recruitment to climate factors at different elevations, tree-ring width chronologies and age structures of Abies faxoniana were developed from five sampling sites at ~2800–3300 m elevation on the north-western and south-eastern aspects in the Wanglang Natural Reserve on the eastern edge of Tibetan Plateau. Statistical characteristics of the chronologies indicated that expressed population signal and signal-to-noise ratio increased with increasing elevation in the north-western aspect; the reverse was observed on the south-eastern aspect. Correlation analysis between chronologies and climate variables showed that fir radial growth was negatively correlated with previous growing season mean temperatures and was positively correlated with January precipitation in all plots. The amount of precipitation in the growing season (June and July) greatly influenced radial growth in the two lower sites of both the aspects. The three plots on the north-western aspect were characterised by significant rates of tree recruitment in the past five decades. There were multi-decadal periods of heightened recruitment over the past three centuries in the two south-eastern plots. Widespread disturbances after 1920s were not observed in any plots and the infrequent small-scale disturbances that occurred were not the main factors influencing recent recruitment in any plots. Correlation analysis between recruitment residuals and climate variables showed that fir seedling recruitment in the north-western aspect plots was mainly controlled by spring–summer temperatures. But recruitment was greatly restricted by competition with dense bamboos and other tree species in the south-eastern aspect. Overall, previous August mean temperature and January precipitation were the dominant factors determining fir radial growth in all plots, and recruitment was sensitive to spring–summer temperatures in the plots with sparse bamboo cover.