Optimizing line intercept sampling and estimation for feral swine damage levels in ecologically sensitive wetland plant communities

Abstract

Ecological sampling can be labor intensive, and logistically impractical in certain environments. We optimize line intercept sampling and compare estimation methods for assessing feral swine damage within fragile wetland ecosystems in Florida. Sensitive wetland sites, and the swine damage within them, were mapped using GPS technology. Evenly spaced parallel transect lines were simulated across a digital map of each site. The length of each transect and total swine damage under each transect were measured and percent swine damage within each site was estimated by two methods. The total length method (TLM) combined all transects as a single long transect, dividing the sum of all damage lengths across all transects by the combined length of all transect lines. The equal weight method (EWM) calculated the damage proportion for each transect line and averaged these proportions across all transects. Estimation was evaluated using transect spacings of 1, 3, 5, 10, 15, and 20 m. Based on relative root mean squared error and relative bias measures, the TLM produced higher quality estimates than EWM at all transect spacings. Estimation quality decreased as transect spacing increased, especially for TLM. Estimation quality also increased as the true proportion of swine damage increased. Diminishing improvements in estimation quality as transect spacings decreased suggested 5 m as an optimal tradeoff between estimation quality and labor. An inter-transect spacing of 5 m with TLM estimation appeared an optimal starting point when designing a plan for estimating swine damage, with practical, logistical, economic considerations determining final design details.

Fine-scale, spatial and temporal assessment methods for feral swine disturbances to sensitive plant communities in south-central Florida

“…Engeman et al (2003Engeman et al ( , 2004aEngeman et al ( , 2007c found that sampling the amount of swine rooting over time through line-intercept or plots was a cost-and labor-efficient method for estimating the extent of rooting damage and relating it to changes in swine population size in various Florida natural areas. Thomas et al (2013) optimized the application of lineintercept sampling design and estimation procedures for assessing swine damage in light of the practical considerations typical of ecological sampling. In a more spatially explicit manner, Chavarria et al (2007) used hand-held GPS units to map and estimate damage areas of "simple polygons," which were also sampled from the greater survey area using line-transects.…”

Invasive feral swine damage to globally imperiled steephead ravine habitats and influences from changes in population control effort, climate, and land use

“…As identified in recent sampling research (Thomas et al 2013), estimation of the proportion of each steephead's valley floor with damage was accomplished by first summing the total area of all strip transects within the steephead. The total area across all transects that 1 3 was under water in the steephead stream was subtracted from this total to define the total area of terrestrial steephead valley floor habitat sampled.…”

Feral swine damage to globally imperiled wetland plant communities in a significant biodiversity hotspot in Florida

“…There are also methods now available that are not as ''fieldintensive'' that can provide high-quality estimates of damage within a site (Thomas et al 2013). However, to monitor a substantial number of sites over time as we have done requires human resources that are unlikely to be available in many damage assessment circumstances.…”