Forests in low-latitude (0° N–30° N) regions are important for greenhouse gas sequestration. They harbor around 25% of vegetation carbon stocks. The productivity of these forests is expected to change as the global climate changes. They may absorb less greenhouse gasses, with negative effects on the global climate. However, little is known about how exactly these forests will respond to climate change. Here, we focus on the largest pine forests in low-latitude forests areas in southwest China. These forests have experienced rapid climate warming over the past 60 years. We collected tree-ring cores from two naturally occurring key afforestation pine tree species: Pinus yunnanensis Franch. and Pinus armandii Franch. in Baoshan and Lijiang of Yunnan. We used basal area increment (BAI) to examine the productivity trends of these two species over long-time scales, and Partial Least Squares regression analysis together with Pearson correlation analysis to identify the critical climate periods for the growth of these two species. We found that: (1) regional pine tree productivity began to decline at the beginning of this century. (2) The radial growth of both species had the strongest positive correlation with the spring Palmer Drought Severity Index (PDSI) and precipitation and the strongest negative correlation with spring temperatures. (3) Climate responses differ by species with higher positive correlations between tree-ring width, PDSI, and precipitation in P. armandii than in P. yunnanensis at similar locations. (4) Climate responses differ by location with higher positive correlations between tree-ring width and PDSI in Lijiang than in Baoshan for P. yunnanensis. Our results suggest that spring moisture availability is the main limiting factor for pine tree growth, especially for P. yunnanensis in Lijiang and P. armandii in Baoshan. Future regional warming and warm-induced drought conditions may have negative effects on the growth of pine trees. These results provide reference data for the sustainable management of pine forests in low-latitude regions of southwest China and may be useful in assessing the sustainable carbon sink ability of pine forests in this region under climate change.

Mountain forests are critical for carbon sequestration, yet the effects of rapid warming on tree growth and climate sensitivity across elevational gradients remain poorly understood. Here, we focus on the largest mountain coniferous forests in southwest China and collected tree-ring cores from three key afforestation tree species, Picea likiangensis, Abies georgei, and Pinus yunnanensis, from 2600 m a.s.l. to 4100 m a.s.l. in Lijiang. Basal area increment (BAI) and Pearson correlation analyses were employed to evaluate long-term productivity trends and constrain the factors limiting tree growth, respectively. Across all elevational belts, tree growth is primarily limited by low dry-season moisture availability, with the strength of this limitation varying across the three species. Abies georgei shows the strongest positive correlation between tree-ring width and Standardized Precipitation Evapotranspiration Index, followed by Picea likiangensis, while Pinus yunnanensis exhibits the weakest correlation. We further found that tree productivity began to decline at the beginning of the twenty-first century, with larger declines in higher-elevation fir and spruce species, albeit not statistically significant. Future warming and warm-induced drought may exert more pronounced adverse effects on these three species. These results provide reference data for the potential sustainable management of mountain forests in southwest China.