Relating plant spatial patterning, biodiversity, ecosystem function, and management practices in experimental restored wetlands
Understanding the effects of management practices on shifting relationships between structure and function over the course of ecosystem development should be a central goal of ecosystem restoration. Yet many of these relationships, such as those between plant biodiversity, spatial pattern of vegetation and community metabolism, remain poorly understood. In a decade-long experiment, we investigated the impact of different initial planting treatments and of nutrient enrichment on relationships among plant biodiversity, plant spatial pattern, and ecosystem function in restored wetland ecosystems. In 2003, six identical and hydrologically-isolated 0.18 ha experimental wetland “cells” were constructed in marginal farmland in northeast Ohio. Cells were subjected to one of three initial planting and management treatments, which were later simplified into two treatment groups. In 2010 and 2011, nitrogen and phosphorus fertilizers were applied to one cell from each of the three treatments to simulate agricultural run-off. Changes and differences in ecosystem function were assessed by measuring aquatic community metabolism, aboveground biomass, soil organic matter, and nutrient concentrations. Structure was characterized through annual plant biodiversity inventories and aerial photographs of plant cover that were analyzed to quantify vegetation spatial patterns.
We found significant relationships among plant biodiversity, plant spatial pattern, and planting treatments. We observed significant and sustained differences in plant biodiversity, resulting from both planting treatment and habitat attributes of cells. Relationships between ecosystem function and both biodiversity and spatial pattern were more ambiguous. We found no direct relationships between biodiversity or spatial metrics and any measures of ecosystem function. These findings support the importance of initial wetland structure in achieving plant biodiversity in restored wetlands, but provide little additional evidence that species diversity has a major effect on nutrient retention, primary productivity, or soil organic matter in restored wetland systems. Over multiple years, biodiversity metrics correlated positively with spatial metrics, including mean patch shape complexity and contagion. This suggests that restored wetland landscapes comprised of patches with complex shapes (high edge-to-area ratios) that are highly clumped are home to a more diverse array of plant species. Links between biodiversity and spatial pattern suggest that aerial imagery may provide wetland managers with a robust tool for assessing plant biodiversity.