Background/Question/Methods The survival of forest tree populations and species will increasingly depend upon their ability to either migrate to more suitable climates or evolve to withstand the stresses imposed by a new climate. Trees have long generation times, but evolution over short timescales could still be important, as ecological processes altered by climate change may speed up selection. To better understand the extent of evolutionary potential in climate responses of tree species, we quantify heritable variation in environmental response traits using data from greenhouse trials of Pinus ponderosa seedlings from 48 open-pollinated maternal families. Five seedlings from each family were exposed to either wet or dry treatments for four months. Root length, root weight, and shoot weight were measured following harvest, while stomatal density was measured approximately midway through the experiment. Height was recorded before and after treatment and the difference recorded as growth. Net dry growth for individual seedlings was calculated by subtracting individual dry growth from mean family wet growth. For all traits, heritability was estimated using a half-sib analysis. Results/Conclusions Narrow-sense heritability estimates for net dry growth, root length, root weight, shoot weight, adaxial stomatal density, and abaxial stomatal density ranged from 0.153 to 0.655, with the highest values for height growth responses. This suggests that significant heritable variation exists for drought response traits in P. ponderosa, and that variation is particularly high for shoot growth under drought conditions. These results indicate that for some traits in P. ponderosa, increasingly arid conditions could rapidly select for greater drought responsiveness.
