Changes in Community-Level Riparian Plant Traits over Inundation Gradients, Colorado River, Grand Canyon

Abstract

Comparisons of community-level functional traits across environmental gradients have potential for identifying links among plant characteristics, adaptations to stress and disturbance, and community assembly. We investigated community-level variation in specific leaf area (SLA), plant mature height, seed mass, stem specific gravity (SSG), relative cover of C4 species, and total plant cover over hydrologic zones and gradients in years 2013 and 2014 in the riparian plant community along the Colorado River in the Grand Canyon. Vegetation cover was lowest in the frequently inundated active channel zone, indicating constraints on plant establishment and production by flood disturbance and anaerobic stress. Changes in trait values over hydrologic zones and inundation gradients indicate that frequently inundated plots exhibit a community-level ruderal strategy with adaptation to submergence (high SLA and low SSG, height, seed mass, C4 relative cover), whereas less frequently inundated plots exhibit adaptation to drought and infrequent flood disturbance (low SLA and high SSG, height, seed mass, C4 relative cover). Variation in traits not associated with inundation suggests niche differentiation and multiple modes of community assembly. The results enhance understanding of future responses of riparian communities of the Grand Canyon to anticipated drying and changes in hydrologic regime.

Extending the conceptual model of river island development to incorporate different tree species and environmental conditions

“…Figure 9b provides a significant advance of the island model because, for the first time, it allows more than one tree species drawn from different families and possessing different life history traits to be incorporated, emphasizing that different species may engineer river landforms in different and complementary ways. Previous research has explored and modelled how riparian plant species with different life history traits respond to environmental conditions and their changes (e.g., Bornette et al, 2008; McCoy‐Sulentic et al, 2017; Merritt, Scott, LeRoy Poff, Auble, & Lytle, 2010; Stromberg & Merritt, 2016) and has started to consider how plant traits may be relevant to fluvial geomorphology (e.g., Hortobágyi et al, 2018; O'Hare, Mountford, Maroto, & Gunn, 2016; Tabacchi et al, 2019). The extended conceptual model of island development builds on such ideas by considering their species‐specific and complementary consequences for river landform development.…”

Hydrological regime and climate interactively shape riparian vegetation composition along the Colorado River, Grand Canyon

“…For example, an increase in temperature should not only select for species with higher temperature preferences, but also lower inundation preferences, based on the negative relationship between these two factors demonstrated among communities. For woody vegetation, a decrease in precipitation should also select for species that prefer higher elevations above the channel (McCoy‐Sulentic et al., ). In much the same way, effects of hydrological changes on species composition would be expected to be strongly influenced by climate, although major changes to the flow regime are not anticipated in the near term (US Department of the Interior ).…”

Fine‐grained sediment deposition alters the response of plant CSR strategies on the gravel bars of a highly regulated river

“…Due to the variations in disturbance (i.e., flood regime) and stress (i.e., soil moisture and nutriments) intensities from the lower to the upper parts of banks, these dynamic ecosystems encompass a wide variety of habitat geomorphology, which induces niche differentiation and a shift in trait values (Blom 1999;Lytle & Poff 2004;Steiger et al 2005). As a result, predictable successional pathways are usually reported along elevation gradients from ruderal to competitor life strategies (Kyle & Leishman 2009;McCoy-Sulentic et al 2017).…”