Integrating functional trait frameworks into restoration : the role of seed and seedling traits in recruitment success

Graduation date: 2014Seeding is a vital tool to facilitate recovery of degraded ecosystems, but low seedling recruitment rates limit the utility of this practice in a range of ecosystems across the globe. Plant functional traits impact individual fitness through effects on growth, reproduction and survival. Consequently, seed and seedling trait variation among species provide a critical mechanism to understand and explain variation in recruitment probabilities across restoration species. I measured seed traits, seedling traits, and field probabilities of germination, emergence, seedling establishment, and established seedling survival for 47 varieties of native and introduced grasses in U.S. western drylands. Multivariate analyses were used to identify major dimensions of trait variation across early life stages and to assess whether this trait variation was related to cumulative survival probabilities through the first growing season. Ordination and cluster analysis of seed and seedling traits highlighted two central, independent aspects of functional trait variation among grasses describing seedling growth rate and germination rate, but functional trait-based clusters failed to capture variation in recruitment patterns in the\ud field. Path analysis revealed that variation in germination and emergence probabilities\ud explained over 90% of the variation in cumulative survival in the first growing season. However, functional traits including seed mass, hydrothermal time, and coleoptile tissue density, explained just 16% and 18% of the variation in germination and emergence, respectively, under ambient conditions. The majority of functional trait work has centered on linking leaf and root traits to resource acquisition, utilization, and growth. Our study suggests that germination, emergence and functional traits associated with these processes are leading drivers of recruitment variation across species in restoration scenarios. Functional traits reflecting the physiology and morphology of germinated seedlings, such as coleoptile tissue density, may play a major role in differentiating recruitment success following seeding, but remain largely unexplored. Before functional traits can facilitate practical advances in seeding and restoration efforts, we must improve our understanding of the dimensions and consequences of trait variation during germination and emergence