Decoupled heatwave-tree growth in large forest patches of Larix sibirica in northern Mongolian Plateau

Abstract

Semiarid forests are experiencing unprecedented hotter drought, which could have a profound impact on tree growth. In addition to increasing temperature, the warming climate may cause more frequent and intense heatwaves further increasing the stress on tree growth. In this study, we measured tree ring width of 1139 cores collected from 12 Siberian larch (Larix sibirica) forest patches in the northern Mongolian Plateau to investigate how heatwaves affect tree growth. Our results showed a coupled relationship between tree growth and heatwaves that indicated by the extreme-hot days before 1996. After 1996, there was an increased frequency of heatwaves, which has strongly reduced tree growth, with an 8.4% growth decline in large forest patches (> 10 ha), 48.1% decline in medium patches (3–10 ha), and 39.2% decline in small patches (< 3 ha), respectively. The tree growth-heatwave relationship remained in medium and small forest patches after 1996, however, it became decoupled in large forest patches (p > 0.05), potentially through the effects of decoupled soil water-heatwave relationship in large forest patches that mostly located on thick soils. Our observations indicated that current climate warming and frequent heatwaves may have exceeded the favorable growth conditions of Siberian larch, but landscape heterogeneity (patch size and slope position) can alleviate the pressure of temperature warming and reduce tree growth rapid decline under high-frequency heatwaves climate in Mongolia Plateau.