Southern California Salt Marsh Dominance Relates to Plant Traits and Plasticity

The three most abundant tidal marsh species at Tijuana Estuary rank Salicornia virginica > Jaumea carnosa > Frankenia salina in occurrences and cover, despite being equally productive in a greenhouse study. The same abundance ranking (Sv>Jc>Fs) developed within 10 years in a restoration site that was planted with near-equal numbers per species. In this paper, we show that resistance to invasion and invasiveness also ranked Sv>Jc>Fs, helping to explain how the restored community lost diversity over time. To explain differential dominance, we assessed 20 traits (including trait ratios), expecting several traits to rank Sv>Jc>Fs, but that was not so. Nor were field abundance ranks explained by the number of superior traits, since Salicornia ranked first in only four traits; Jaumea ranked first in seven, Frankenia in three, and six traits involved ties. Instead, we found explanatory power in two traits (height and runner length) and plasticity (ability to shift trait ratios with changing conditions). We propose that Salicornia becomes dominant by growing tall (height ranked Sv>Jc = Fs) and capturing light first, and that Jaumea co-dominates by extending its runners throughout the understory. Both dominants are more plastic than the subordinate Frankenia, which allocates the greatest proportion of dry weight to roots. Our multi-trait approach explained abundance ranks where focusing on a single trait (potential productivity) could not.