Factors Limiting Radial Growth of Conifers on Their Semiarid Borders across Kazakhstan

SIMPLE SUMMARY: In the dry and hot climates of Central Asia, forested areas are small and vulnerable to climate change. Therefore, it is important to understand the reactions of tree growth to climatic factors there. We studied several habitats of Scots pine, Schrenk spruce, and Zeravschan juniper near the semiarid limits of the respective forest types across Kazakhstan, the largest country in Central Asia. Standardized chronologies of tree-ring width were obtained for each site from wood samples, and then compared among themselves with a series for temperature and precipitation. Large distances and differences between species and habitats limited similarity in the dynamics of conifer growth. However, a common pattern was found in their reactions to climate. Maximal temperatures of the current and previous growing seasons were found to be crucial factors limiting the growth of all considered forest stands. Reactions to the precipitation and drought index are positive, but their strength depends on the species and aridity of a particular habitat. Temporal intervals of climatic impact on tree growth also vary across the country. ABSTRACT: The forests of Central Asia are biodiversity hotspots at risk from rapid climate change, but they are understudied in terms of the climate–growth relationships of trees. This classical dendroclimatic case study was performed for six conifer forest stands near their semiarid boundaries across Kazakhstan: (1–3) Pinus sylvestris L., temperate forest steppes; (4–5) Picea schrenkiana Fisch. & C.A. Mey, foothills, the Western Tien Shan, southeast; (6) Juniperus seravschanica Kom., montane zone, the Western Tien Shan, southern subtropics. Due to large distances, correlations between local tree-ring width (TRW) chronologies are significant only within species (pine, 0.19–0.50; spruce, 0.55). The most stable climatic response is negative correlations of TRW with maximum temperatures of the previous (from −0.37 to −0.50) and current (from −0.17 to −0.44) growing season. The strength of the positive response to annual precipitation (0.10–0.48) and Standardized Precipitation Evapotranspiration Index (0.15–0.49) depends on local aridity. The timeframe of climatic responses shifts to earlier months north-to-south. For years with maximum and minimum TRW, differences in seasonal maximal temperatures (by ~1–3 °C) and precipitation (by ~12–83%) were also found. Heat stress being the primary factor limiting conifer growth across Kazakhstan, we suggest experiments there on heat protection measures in plantations and for urban trees, alongside broadening the coverage of the dendroclimatic net with accents on the impact of habitat conditions and climate-induced long-term growth dynamics.