Dendroclimatology and dendroecology have entered mainstream dendrochronology research in subtropical and tropical areas. Our study focused on the use of the chronology series of Masson pine (Pinus massoniana Lamb.), the most widely distributed tree species in the subtropical wet monsoon climate regions in China, to understand the tree growth response to ecological and hydroclimatic variability. The boosted regression trees (BRT) model, a nonlinear machine learning method, was used to explore the complex relationship between tree-ring growth and climate factors on a larger spatial scale. The common pattern of an asymptotic growth response to the climate indicated that the climate-growth relationship may be linear until a certain threshold. Once beyond this threshold, tree growth will be insensitive to some climate factors, after which a nonlinear relationship may occur. Spring and autumn climate factors are important controls of tree growth in most study areas. General circulation model (GCM) projections of future climates suggest that warming climates, especially temperatures in excess of those of the optimum growth threshold (as estimated by BRT), will be particularly threatening to the adaptation of Masson pine.

Many studies reported the effect on plant functional groups and plant diversity under discontinuous slope gradient. However, studies on the effect of continuous slope gradient on plant functional groups and plant diversity in alpine meadows have rarely been conducted. We studied the effect of a continuous slope gradient on the dominance characteristics of plant functional groups and plant diversity of alpine meadows on the Tibetan plateau—in Hezuo area of Gannan Tibetan Autonomous Prefecture. Altogether, 84 samples of alpine meadows grass and 84 soil samples from seven slope gradients at sunlit slopes were collected. By using analysis of variance (ANOVA) and Pearson correlation coefficient, this study revealed: (1) Continuous slope gradient is an important factor affecting plant communities in alpine meadows, due to the physical and chemical characteristics of the soil and water content. The number of families, genera, and species increased first then decreased at the different slope gradient levels, respectively; (2) there is a close relationship between the soil and plant functional groups, and plant diversity. In other words, the slope determines the functional groups of plants and the soil nutrients; and (3) soil characteristics (pH value, Soil Total Nitrogen, Soil Water Content) are the determining factors of the plant community characteristics at each slope gradient level. To conclude, a continuous slope gradient is an important factor that affects plant communities in alpine meadows.

This study addressed the effects of climate drivers on the tree-ring width (TRW) parameters (total ring width (TR), earlywood width (EW) and latewood width (LW)) and the total ringδ¹³C series of different wood components (whole wood, α-cellulose and holocelluose) from Masson pine in subtropical China. Pairwise correlation coefficients between three ring width parameters were statistically significant. EW and LW did not reveal much stronger climate sensitivity rather than TR. This indicated that the use of intra-annual ring width has little benefit in extracting more climate information. The meanδ¹³C series of the three components of the total ring had the strongest climate response to the July–September relative humidity (r= −0.792 (whole wood), −0.758 (holocellulose) and −0.769 (α-cellulose)). There are no significant differences in the dendroclimatic relationships of theδ¹³C series of different wood components. Through both stationary temporal and spatial-statistical perspectives, the moisture drivers (summer/autumn) had a significant impact on three ring width parameters and three components of Masson pine. Overall, the radial growth and theδ¹³C series showed different responses to the same climate drivers during the same period. Moreover, the R-squared values of the strongest climate-proxy correlation coefficients were smaller than 50% for TRW. Consequently, theδ¹³C series of Masson pine may be a more representative climate proxy than TRW parameters for dendroclimatology in subtropical China.