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Wood Density in California Trees and Shrubs

California Mixed Evergreen Forests

Wood density (the mass per unit volume of wood) is associated with mechanical support, carbon and nutrient storage, drought tolerance, pathogen defense, and water transport in trees and shrubs. When I was an undergraduate researcher working with Dr. Lee Anderegg in Dr. Joe Berry's lab in the Carnegie Institution for Science at Stanford University, my colleagues and I explored whether climate variables, floristic ancestry, habitat preference, and plant diameter to height ratio influenced patterns of wood density in twenty species of California trees and shrubs. Riparian trees and shrubs species that were wider in diameter for a given height had lower wood densities. For non-riparian trees and shrubs, however, we found no relationship between basal diameter to height ratio and wood density.

To learn more about this research, check out our paper in Forests and this short blog post.

The Role of Climate Niche, Geofloristic History, Habitat Preference, and Allometry on Wood Density within a California Plant CommunityResearch Highlights: To better understand within-community variation in wood density, our study demonstrated that a more nuanced approach is required beyond the climate–wood density correlations used in global analyses. Background and Objectives: Global meta-analyses have shown higher wood density is associated with higher temperatures and lower rainfall, while site-specific studies have explained variation in wood density with structural constraints and allometry. On a regional scale, uncertainty exists as to what extent climate and structural demands explain patterns in wood density. We explored the role of species climate niche, geofloristic history, habitat specialization, and allometry on wood density variation within a California forest/chaparral community. Materials and Methods: We collected data on species wood density, climate niche, geofloristic history, and riparian habitat specialization for 20 species of trees and shrubs in a California forest. Results: We found a negative relationship between wood density and basal diameter to height ratio for riparian species and no relationship for non-riparian species. In contrast to previous studies, we found that climate signals had weak relationships with wood density, except for a positive relationship between wood density and the dryness of a species’ wet range edge (species with drier wet range margins have higher wood density). Wood density, however, did not correlate with the aridity of species’ dry range margins. Geofloristic history had no direct effect on wood density or climate niche for modern California plant communities. Conclusions: Within a California plant community, allometry influences wood density for riparian specialists, but non-riparian plants are ‘overbuilt’ such that wood density is not related to canopy structure. Meanwhile, the relationship of wood density to species’ aridity niches challenges our classic assumptions about the adaptive significance of high wood density as a drought tolerance trait.

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