Climate-induced reversal of tree growth patterns at a tropical treeline

Globally, cold-limited trees and forests are expected to experience growth acceleration as a direct response to warming temperatures. However, thresholds of temperature limitation may vary substantially with local environmental conditions, leading to heterogeneous responses in tree ecophysiology. We used dendroecological and isotopic methods to quantify shifting tree growth and resource use over the past 143 years across topographic aspects in a high-elevation forest of central Mexico. Trees on south-facing slopes (SFS) grew faster than those on north-facing slopes (NFS) until the mid-20th century, when this pattern reversed notably with marked growth rate declines on SFS and increases on NFS. Stable isotopes of carbon, oxygen, and carbon-to-nitrogen ratios suggest that this reversal is linked to interactions between CO2 stimulation of photosynthesis and water or nitrogen limitation. Our findings highlight the importance of incorporating landscape processes and habitat heterogeneity in predictions of tree growth responses to global environmental change.

Automated summary

This study investigated the changes in tree growth and resource use on south and north-facing slopes in a high-elevation forest in central Mexico over the past 143 years using dendroecological and isotopic methods. It was found that trees on south-facing slopes grew faster until the mid-20th century, when this pattern reversed with notable growth rate declines on south-facing slopes and increases on north-facing slopes. The reversal was linked to interactions between CO2 stimulation of photosynthesis and water or nitrogen limitation, highlighting the importance of incorporating landscape processes and habitat heterogeneity in predictions of tree growth responses to global environmental change.