Evaluating inter and intra-specific variation in leaf mass and area

Tree leaf area and mass are small but important components of forest ecosystems. There have been many efforts to model leaf mass, but face challenges in doing so because leaf mass varies within and between tree species, location, and time. Often leaf mass models are limited to species-specific, empirical models, which predict intra-specific variation from diameter at breast height (DBH). Such models have limited potential; there are many other factors than tree girth that can lead to varying tree leaf mass, and models cannot be applied to species which lack foliage mass data. We conducted destructive sampling of trees of 17 different species, covering multiple life history traits, across Michigan, in order to generate a 'trans-species' model for foliage biomass which can be used across species. In addition, four species destructively sampled were subjected to canopy stratified sampling of specific leaf area (SLA) to capture an additional species-related life history trait contrasted by shade tolerance. Our results identified the most important variables for predicting foliage mass, which were non-species-specific variables: diameter at breast height, five year basal area increment, crown class, and competition index, and species-related traits: leaf longevity and shade tolerance. Collectively, these variables describing tree size, life-history traits, and competitive environment allowed for a generalized leaf mass model with potential application to many tree species. The study of tree SLA identified a mechanism explaining why shade tolerant species might hold a greater leaf mass in the trans-species leaf biomass model. Shade tolerant trees maintained greater leaf area and leaf number and also expressed greater SLA and SLA plasticity.