Across landscapes, riparian plant communities assemble under varying levels of disturbance, environmental stress, and resource availability, leading to the development of distinct riparian life-history guilds. Identifying the environmental filters that exert selective pressures and favor specific vegetation guilds within riverscapes is a critical step in setting baseline expectations for how riparia may respond to the environmental conditions anticipated under future global change scenarios. In this study, we ask (1) what functional riparian plant guilds exist across two major North American river basins? (2) What environmental filters shape riparian guild distributions? (3) Does resource partitioning between guilds influence guild distributions and co-occurrence? We identified riparian plant guilds, examining relationships between regional climate and watershed hydrogeomorphic characteristics, stream channel form, and co-occurring riparian guilds. Woody species composition was measured at 703 streams and each species’ traits were extracted from a database in five functional areas: life form, persistence and growth, reproduction, and resource use. We clustered species into guilds by morphological characteristics and attributes related to environmental tolerances, modeling guild distributions as a product of environmental filters (stressors and resources) and guild co-existence. We identified five guilds, i) a tall, deeply rooted, long-lived, evergreen tree guild, ii) a xeric disturbance tolerant shrub guild, iii) a hydrophytic, thicket-forming shrub guild, iv) a low-statured, shade-tolerant, understory shrub guild and v) a flood tolerant, mesoriparian shrub guild. Guilds were most strongly discriminated by one another species’ rooting depth, canopy height and potential to resprout and grow following biomass-removing disturbance. Hydro-climatic variables including precipitation, watershed area, water table depth, and channel form attributes reflective of hydrologic regime were predictors of guilds whose life history strategies had affinity or aversion to flooding, drought, and fluvial disturbance. Biotic interactions excluded guilds with divergent life history strategies and/or allowed for the co-occurrence of guilds that partition resources differently in the same environment. We conclude that riparian guilding provides a useful framework for assessing how disturbance and bioclimatic gradients shape riparian functional plant diversity. Multiple processes should be considered when the riparian response guilds framework is to be used as a land-use decision-support tool framework
Tree Foliar Chemistry in an African Savanna and Its Relation to Life History Strategies and Environmental Filters
