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.

Forest Structure, Stand Composition, and Climate-Growth Response in Montane Forests of Jiuzhaigou National Nature Reserve, China

“…7) may be the most limiting aspect of climate on growth for conifer species in JNNR. In a study on A. fargesii (AKA A. faxoniana ) from the nearby Wanglang Nature Reserve, Zhao et al [46] similarly concluded that growth was negatively correlated with temperature during the previous growing season (they also found a positive correlation with precipitation in January, as we did). Previous studies have emphasized the importance of temperature during winter, fall and spring in limiting radial growth, but also observed non-significant negative correlations or response functions between growth and summer temperatures [42], [43].…”

“…Despite our low correlation between growth and precipitation, drought stress likely has an impact on growth of trees in the region. Several studies from central and SE China have shown high correlations between Palmer Drought Severity Index (PDSI) and growth [5], [8], [43], [46]. Also, growth of P. tabuliformis has been shown to be sensitive to drought in northern China [6], [44], [45].…”

Effects of gap microsites and bamboo onAbies faxonianaregeneration in a subalpine forest, China

“…The average temperature is 11~17.5°C in July and −6~1°C in January. The mean annual precipitation is around 1100 mm (Zhao et al 2012 (Taylor et al 2006).…”

“…Besides, the number, height, and recruitment microsites (bare soil bed, moss-cover ground, decaying logs, or stumps) of A. faxoniana seedlings and saplings, as well as the number, coverage, and height of F. denudata, were counted in each plot. A. faxoniana seedlings or saplings were classified as follows: seedlings, ≥10 and <50 cm in height; saplings, ≥50 cm in height and <5 cm in DBH (Zhao et al 2012). A total of 103 gaps were recorded in the studied area, ranging from 20 to 1860 m 2 in size and 2-60 years in age, and a total of 515 plots were recorded.…”

“…The subalpine coniferous forest dominated by this tree species plays an important role in water conservation by preventing soil erosion and in keeping the Giant Panda habitats stable (Wu et al 2011). For example, in southwestern Sichuan in China, A. faxoniana is present over the entire altitudinal range in Wanglang Giant Panda Reserve (Zhao et al 2012). A. faxoniana seedling and sapling banks determine the population size of this species and strongly influence the succession and restoration of the forests.…”