Increased aridity is associated with stronger tradeoffs in ponderosa pine vital functions

Trees must allocate resources to core functions like growth, defense, and reproduction. These allocation patterns have profound effects on forest health, yet little is known about how core functions trade off over time, and even less is known about how a changing climate will impact tradeoffs. We conducted a 21-year survey of growth, defense, and reproduction in 80 ponderosa pine individuals spanning eight populations across environmental gradients along the Colorado Front Range, USA. We used linear mixed models to describe tradeoffs among these functions and to characterize variability among and within individuals over time. Growth and defense were lower in years of high cone production, and local drought conditions amplified year-to-year tradeoffs between reproduction and growth, where trees located at sites with hotter and drier climates showed stronger tradeoffs between reproduction and growth. Our results support the environmental stress hypothesis of masting, which predicts that greater interannual variation in tree functions will be associated with more marginal environments, such as those that are prone to drought. With warming temperatures and increased exposure to drought stress, trees will be faced with stronger interannual tradeoffs, which could lead to further decreases in growth and defensive efforts, ultimately increasing risks of mortality.

Automated summary

Trees allocate resources to core functions like growth, defense, and reproduction. However, little is known about the tradeoffs among these functions over time and how climate change will impact them. This study conducted a 21-year survey of ponderosa pine trees in Colorado, USA, and found that growth and defense were lower in high cone production years. Drought conditions amplified the tradeoffs between reproduction and growth, especially in hotter and drier climates. With climate change, stronger interannual tradeoffs could lead to decreased growth and defensive efforts, increasing the risks of tree mortality.