Natural history collections have been identified as being a potential source for analyzing functional traits through space and time. While herbaria have been used to study shifts in plant communities, living collections (e.g. botanic gardens and arboreta) provide a unique opportunity to research traits in long lived species, such as trees. By using living collections across environmental gradients, we can further our understanding of what abiotic factors contribute to species distribution and also better understand how species will respond to climate change. We collaborated with the Hoyt Arboretum (Oregon), the Holden Arboretum (Ohio), the National Arboretum (Washington DC), the Denver Botanic Garden (Colorado), the San Francisco Botanic Garden (CA), and the Huntington Botanic Gardens (Pasadena, CA). These sites exist across broad environmental gradients, and we explored trait plasticity in two conifer families, Pinaceae and Cupressaceae, using over 30 species common to all gardens. We chose these families because, 1) within both families are species that have either large or small geographic distributions, and 2) in response to anthropogenic pressures many Pinaceae species are undergoing range reductions and high mortality rates while many Cupressaceae are expanding their ranges. We collected functional traits at all six of the collaborating arboreta.
Results/Conclusions
Our data show that some plants exhibit greater plasticity across collections. We found that location of the arboreta had a significant effect (ANOVA F1,645 p< 0.001) on specific leaf area (SLA; m2/kg; a proxy for leaf investment) and in leaf lifespan across the sites (F2,221 p=0.03; Pinaceae only, Cupressaceae lifespans not measured). There was also evidence for the expected tradeoff between SLA and leaf lifespan, with individuals that had higher leaf investment having longer leaf lifespans (r2=0.24, F5,218=13.85, p< 0.001). We also calculated the huber value (HV:ratio of stem diameter to leaf area) as plants under greater evaporative demand are expected to maintain higher HV. We found significant differences in HV between the sites (F5,645=7.881, p< 0.001) and the two families (F5,645=10.099, p=0.002), and an interaction between site and family (F5,645=2.478, p=0.03). A posthoc analysis revealed that this was mostly driven by our most arid sites. Research on trait plasticity and climate responses in trees has been prohibitive due to the cost and time in establishing common gardens for long lived species. Established living collections provide a unique opportunity to answer these questions and will help to provide insight into the mechanisms underlying species distributions and responses to anthropogenic pressures.
