Competition limits first-year growth and flowering of wiregrass (Aristida beyrichiana) at a sandhills restoration site

Abstract

Uncertainty in ecosystem restoration can be mitigated by information on drivers of variability in restoration outcomes, especially through experimental study. In southeastern USA pine savannas, efforts to restore the perennial bunchgrass wiregrass (Aristida beyrichiana) often achieve variable outcomes in the first year. Although ecotypic differentiation and competition with other native vegetation are known to influence wiregrass seedling establishment and growth, to our knowledge, no studies have examined interactions between these drivers. We experimentally quantified individual and interactive effects of competition, seed source, and soil type on wiregrass density, size, and flowering culm production in the field. We sowed seeds from dry and wet sites reciprocally into dry and wet soils and weeded half of the plots. We found that competition removal resulted in significantly larger plants and a greater proportion of flowering plants with more culms on average, regardless of seed source or soil type. Seeds sourced from a wet site resulted in more plants per plot than seeds from a dry site, which might have been influenced by the greater number of filled seeds from the wet site. After seedlings become established, competition contributes to variation in growth and reproduction. Although competition removal could help start wiregrass populations, the necessity of mitigation depends on fire management needs.

Fig 1. Study site and treatments within Lochloosa Wildlife Management Area (inset) in north-central, Alachua County, Florida.

The geographic map was obtained from http://www.naturalearthdata.com/.

Fig 2. A weeded wiregrass plot, with vegetation removed.

In the background is an unweeded plot. Weeded wiregrass plots did not have surface litter removed, and plots varied greatly in the amounts of natural litter present. Yellow flags and rebar caps mark the corners and midpoints of 1×2-m plots. Photo was taken on October 15, 2022.

Fig 3

The number of plants in 1×2 m plots for wet seeds in wet soil (A), wet seeds in dry soil (B), dry seeds in wet soil (C), and dry seeds in dry soil. Black points represent outliers, and colored points represent the raw data for each plot.

Fig 4

The average basal area of plants in 1×2 m plots for wet seeds in wet soil (A), wet seeds in dry soil (B), dry seeds in wet soil (C), and dry seeds in dry soil. Black points represent outliers, and colored points represent each plot.

Fig 5

The proportion of plants with flowering culms in 1×2 m plots for wet seeds in wet soil (A), wet seeds in dry soil (B), dry seeds in wet soil (C), and dry seeds in dry soil. Black points represent outliers, and colored points represent each plot.

Fig 6

The number of flowering culms for reproducing plants in 1×2 m plots for wet seeds in wet soil (A), wet seeds in dry soil (B), dry seeds in wet soil (C), and dry seeds in dry soil. Black points represent outliers, and colored points represent each plot.