Variation in piñon pine growth responses to climate across gradients of environmental stress using an individual-based approach

Abstract:

1. Forest and woodland ecosystems play a crucial role in the global carbon cycle and may be strongly affected by changing climate. Here we use an individual-based approach to model piñon pine (Pinus edulis) radial growth responses to climate across gradients of environmental stress.
2. We sampled piñon pine trees at 24 sites across southwestern Colorado that varied in soil available water capacity, elevation, and latitude, obtaining a total of 552 pinon pine tree ring series. We used linear mixed effect models to assess piñon pine growth responses to climate and site-level environmental stress (mean annual climatic water deficit and soil available water capacity). Using a similar modeling approach, we also determined long-term growth trends across our gradients of environmental stress.
3. Piñon pine growth was strongly positively associated with winter precipitation and strongly negatively associated with summer vapor pressure deficit. However, the strength of the relationship between winter precipitation and piñon pine growth was affected by site-level environmental stress. Trees at sites with greater climatic water deficit (i.e. hotter, drier sites) were more sensitive to winter precipitation. Interestingly, trees at sites with greater soil available water capacity were also more sensitive to winter precipitation, as these trees had much higher growth rates during years of high precipitation.
4. We found weak evidence of long-term declines in piñon growth rates over the past century within our study area. Growth trends overtime did vary across our soil available water capacity gradient: trees growing at sites with higher soil available water capacity responded more positively to the cool, wet climate conditions of the 1910s and 1980s, whereas tree growth rates at sites with lower soil available water capacity declined more linearly over the last century.
5. Our findings suggest that the sensitivity of woodland ecosystems to changing climate will vary across the landscape due to differences in edaphic and physiographic factors. These results support recent dendroecology studies that emphasize the need to use a more individual-based approach to enhance our understanding of tree growth responses to climate.