Search

Background and Aims Tree growth in plateau forests is critically limited by harsh climatic conditions. Many mathematical statistical methods have been used to identify the relationships between tree growth and climatic factors, but there is still uncertainty regarding the relative importance of these factors across different regions. We tested major climatic limits at 30 sites to provide insights into the main climatic limits for juniper trees (Juniperus tibetica Kom.) across the southern Tibetan Plateau. Methods We analysed the linear and non-linear relationships between tree growth and climatic factors using Pearson correlation statistics and a process-based forward Vaganov–Shashkin-Lite (VS-Lite) model, respectively. These relationships were used to identify the strength of the influence of different climatic factors throughout the species' growing season and to identify the main climatic factors limiting tree growth. Key Results Growth of juniper trees began in April and ended in October in the study area. The radial growth of juniper trees was limited by soil moisture throughout the summer (June–August) of the current year at 24 sampling sites and was limited by temperature at the other six sites on the southern Tibetan Plateau. Conclusions Soil moisture limited juniper growth at the majority of sites. Temperature in the current summer limited the growth of juniper trees at a few sampling sites in the western part of the study area. Local climate conditions may contribute to different limiting factors in the growth response of trees on the southern Tibetan Plateau. These findings may contribute to our understanding of divergent forest dynamics and to sustainable forest management under future climate scenarios. [ABSTRACT FROM AUTHOR]

Forests in the Tibetan Plateau are thought to be vulnerable to climate extremes, yet they also tend to exhibit resilience contributing to the maintenance of ecosystem services in and beyond the plateau. So far the spatiotemporal pattern in tree resilience in the Tibetan Plateau remains largely unquantified and the influence of specific factors on the resilience is poorly understood. Here, we study ring‐width data from 849 trees at 28 sites in the Tibetan Plateau with the aim to quantify tree resilience and determine their diving forces. Three extreme drought events in years 1969, 1979, and 1995 are detected from metrological records. Regional tree resistance to the three extreme droughts shows a decreasing trend with the proportion of trees having high resistance ranging from 71.9%, 55.2%, to 39.7%. Regional tree recovery is increasing with the proportion of trees having high recovery ranging from 28.3%, 52.2%, to 64.2%. The area with high resistance is contracting and that of high recovery is expanding. The spatiotemporal resistance and recovery are associated with moisture availability and diurnal temperature range, respectively. In addition, they are both associated with forest internal factor represented by growth consistence among trees. We conclude that juniper trees in the Tibetan Plateau have increased resilience to extreme droughts in the study period. We highlight pervasive resilience in juniper trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes. Tree resilience is important for maintaining the healthy growth of forests, yet remains largely unquantified. Examination of tree resilience to drought extremes from 28 sites of juniper forests in the Tibetan Plateau reveals a temporal decreasing trend in tree resistance and an increasing trend in recovery, and a spatial contraction in the area of high resistance and expansion in high recovery. The variation of tree resilience is associated with moisture availability, diurnal temperature range, and growth consistence among trees. The results have implications for predicting tree resilience and identifying areas vulnerable to future climate extremes. [ABSTRACT FROM AUTHOR]

Elevated CO2 level in the atmosphere is expected to improve the tree growth rates and intrinsic water-use efficiency (iWUE). Although current results inferring from tree rings found the tree growth decline in water-limited area, it is still unclear whether spruce trees in humid southwestern China benefit from the increasing CO2. In this study, tree-ring width data were used to investigate the tree radial growth rate of Chuanxi spruce (Picea likiangensis var. balfouriana). Moreover, combining with the tree-ring carbon isotope date, we analyzed the physiological responses of Chuanxi spruce to rising CO2 concentrations in the atmosphere (Ca) associated with climatic change in southwestern China. From 1851 to 2009, iWUE of Chuanxi spruce rose by approximately 30.4%, and the ratio of atmospheric CO2 to leaf intercellular CO2 concentration (Ci/Ca) showed no significant trend in the study area. The result suggested that Chuanxi spruce used an active response strategy when Ca was significantly increased. iWUE showed a significant increasing trend in parallel with tree radial growth, indicating that the increasing iWUE resulted in an increase in radial growth. These results suggest that spruce forests in southwestern China have not shown declining trends under increasing Ca and climate change scenarios, in contrast to trees growing in water-limited areas. Therefore, spruce forests benefit from the increasing CO2 in the atmosphere in the humid areas of southwestern China. [ABSTRACT FROM AUTHOR]

Plants experiencing stress could develop the ability to reshape their response toward present stress based on past stress experience, called 'ecological stress memory' (ESM), which is important for plant acclimation to repeated stresses. Although ESM has been largely reported, it remains unclear whether ESM could improve tree resistance to recurrent stress in subsequent decades. Here, we explore it from a tree-ring network of 1491 trees from 50 long-living juniper forests on the Tibetan Plateau. Through comparing performances of tree radial growth in past sequential growth stresses, we found that trees could obtain ESM under antecedent stresses and elevate resistance to subsequent stress after several years or even decades. Such positive effects of ESM are associated with post-stress recovery. Trees with slow recovery trajectories after antecedent stress show significantly improved resistance to subsequent stress, while trees with extremely fast post-stress recovery showed decreased resistance to subsequent stress. These results imply that temporary depressive tree radial growth after antecedent stress might be a trigger of long storage of ESM. Incorporating positive effects of ESM and relationship between ESM activation and post-stress recovery into future Earth system models could advance our capacity to predict forest dynamics and forest ecosystem stabilization under future stress conditions.