GCE IV - Key Finding in 2022

Responses of salt marshes to disturbance

Disturbance responses are fundamentally important in most ecosystems, as they can affect population densities, nutrient pools, and ecological processes. However, there is a gap between simple conceptual models of disturbance recovery and the complex processes observed in empirical studies. GCE researchers are addressing that gap with ongoing and recently completed studies of disturbance in tidal marshes. Wu et al. (2021) evaluated disturbance caused by headward-eroding creeks as they move into the marsh platform over time. They found multiple patterns of disturbance magnitude and recovery trajectory over an array of 19 variables that included soil characteristics, primary producers, and benthic invertebrates, with some declining sharply, some not affected, and others increasing (and in some cases overshooting controls) (Fig. 1). These results, along with the results of following field plots as they recover from wrack disturbance (Grissett et al., in prep), belie any simple univariate understanding of "disturbance and recovery" and suggest that reducing the dimensionality of a data set can obscure disturbance response. Guo et al. (subm.) demonstrated that underlying abiotic gradients can also affect recovery rates. They found that 1) recovery from experimental disturbance of 12 coastal marsh sites located along a salinity gradient decreased with increasing soil porewater salinity, 2) variance during recovery was consistently elevated compared to both controls and recovered plots (Fig. 2 left), and 3) variance during recovery was correlated with both salinity and recovery rate (Fig. 2 right). These results have implications for the theory of critical slowing down, as this research represents an experimental demonstration that recovery times increase in response to an underlying environmental gradient. These findings also suggest that increased variance can be used to infer recent past disturbance. We are planning to follow up on these ideas with experimental manipulations that evaluate standardized disturbances across salinity and elevation gradients.