Patterns of Plant Diversity in Georgia and Texas Salt Marshes

Abstract

A fundamental question in ecology is how biological interactions and biogeographic processes interact to determine the biodiversity of local sites. We quantified patterns of plant species diversity on transects across elevation at 59 salt marsh sites in Georgia and 49 sites in Texas. Although these regions have similar climates and floras, we anticipated that diversity might differ because of differences in tidal regime. Diversity was measured at global, regional, site, and plot scales to consider processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and plot scales, suggesting that processes occurring at the site scale differed. The greater diversity of Texas sites and plots was associated with wider distributions of individual species across the marsh landscape and proportionally more middle marsh (a high diversity zone) and less low marsh (a low diversity zone) than in Georgia marshes. Preliminary data suggested that these differences were not due to differences in salinity regime or standing biomass between regions, leaving differences in tidal regime as the most plausible hypothesis accounting for differences in plant diversity. We speculate that the less-predictable tidal regime in Texas leads to temporal variation in abiotic conditions that limit the ability of any one species to competitively exclude others from particular marsh zones.

Ecosystem Functions of Tidal Fresh, Brackish, and Salt Marshes on the Georgia Coast

“…Instead, studies at the Rio Grande Delta found a lack of variation in species richness along the salinity gradient (Judd and Lonard 2004). The relatively high richness (compared with Atlantic Coast salt marshes) found by Judd and Lonard (2004) in Gulf Coast salt marshes is consistent with other studies of Gulf Coast salt marshes (Judd and Lonard 2002;Kunza and Pennings 2008), but more studies are needed to determine why diversity patterns along the estuarine gradient might differ between the Atlantic and Gulf Coasts.…”

Biogeography of salt marsh plant zonation on the Pacific coast of South America

“…An emerging hypothesis from these studies is that geographic variation in the mechanisms underlying salt marsh plant zonation is driven by variation in climate (Bertness & Pennings, 2000;Cui et al, 2011), tidal regime (Kunza & Pennings, 2008), and species adaptation (Sanford & Bertness, 2009). For example, low-latitude salt marshes may have steeper soil salinity and moisture gradients, with hotter climates leading to increased soil salinity at high-marsh elevations due to evaporative salt accumulation (Pennings, Selig, Houser, & Bertness, 2003).…”

Constraints on host use by a parasitic plant

“…27 0 W; all work done at site 1 unless specified otherwise). Plant species composition at these sites is typical for Gulf Coast salt marshes (Kunza and Pennings 2008). Common plants (and their height during peak abundance of Cuscuta indecora in April 2005, mean (cm) ± 1 SD, n = 20 per species) included Iva frutescens (101 ± 29), Borrichia frutescens (59 ± 12), Batis maritima (28 ± 10), Salicornia virginica (43 ± 9), Suaeda linearis (21 ± 6), Distichlis spicata (41 ± 11), Lycium carolinianum (36 ± 12), Spartina spp.…”