An Evaluation of Methods for Estimating Ground Cover and Soil Compaction as Visitor Impact Indicators

Abstract

The purpose of this study was to perform an empirical comparison of several methods of data collection for two visitor impact indicators. This study is the result of a bigger carrying capacity research endeavor in which one of the goals was to come up with indicators to monitor visitor impacts at the Boston Harbor Islands National Park Area. Specifically, the two visitor impact indicators evaluated in this study were soil compaction and ground cover estimation. These indicators were measured on two high use and two low use plots on selected islands in the Boston Harbor Islands National Park Area in Boston, Massachusetts. Georges and Grape Islands had the accessibility to the public and the soil types found on the islands that are of interest. There were three data collection periods during the visitor use season: June (beginning of season), August (middle of season), and October (end of season). A sampling plot consisting of six radial transects and two quadrats was placed randomly on each transect. The first transect was placed randomly and then there was 60° between each transect. A penetrometer and a soil compaction tester were the two methods used to measure soil compaction. Four measurements from both methods were taken in each of the twelve quadrats. Eight control measurements were taken in nearby undisturbed areas. The pocket penetrometer measurements are more variable than those of the soil compaction tester, but the pocket penetrometer is easier to carry and easier for one person to take and record readings. To estimate ground cover, specifically vegetation and bare soil, the following three methods were used: overall, quadrat, and transect. For the overall and quadrat methods the ground cover types were ranked based on a Daubenmire cover scale. The quadrat method was used as the reference method to be compared to the other methods because the quadrat method was used regularly in low herbaceous (grassy) areas. For the transect method, changes in principal cover type along the transect were recorded. The high use areas were found to have a higher percentage of bare soil cover than the low use areas. The transect method produced higher mean than did the quadrat method. The overall and quadrat methods indicated vegetation recovery from the middle to the end of the visitor use season on both islands. The transect method indicated a decrease in vegetation ground cover from the middle to the end of the visitor use season for Grape Island but not Georges Island. Researchers and managers may use the findings of this study to aid them in their data collection choices. This study contributes to the future management of BOHA by evaluating monitoring techniques of two potential visitor impact indicators. It is hopeful that through efficient monitoring of use and resource indicators and effective management BOHA will achieve a balance recreation provision and resource protection.