PS 13-146 - Species distribution model for management: influencing factors and implications for mitigation of an invasive grass in forestlands of Tennessee

Monday, August 7, 2017
Exhibit Hall, Oregon Convention Center
Lela Culpepper1, Hsiao-Hsuan Wang2, William E. Grant2 and William E. Rogers3, (1)Department of Ecosystem Science and Management, Texas A&M University, College Station, TX, (2)Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, (3)Ecosystem Science & Management, Texas A&M University, College Station, TX

Invasions by non-natives contribute to the loss of ecosystem biodiversity and productivity,

modification of biogeochemical cycles, and inhibit natural regeneration of native species. Japanese

stiltgrass (Microstegium vimineum) is one of the most prevalent invasive grasses in the forestlands of

Tennessee. Hence, we aim to identify potential determinants of invasion and quantify the relative

importance of each factor. We analyzed extensive field data collected Forest Inventory and Analysis

Program of the U.S. Forest Service to quantify the range expansion of Japanese stiltgrass from 2000 to

2011. We then conducted the analysis with a process of machine learning that uses boosted regression

trees and fitted the model in R containing at least 1000 trees. We calculated the response variance

explained, the area under the receiver operator characteristic curve (AUC), and the overall accuracy based

on the aggregated cross-validation results. We evaluated the reliability and validity of the optimal model.

We then used the gbm library to derive the relative influence of each potential explanatory variable in the

optimal model and constructed partial dependence plots and fitted values plots for the most influential



As indicated by the FIA records from 2011, Japanese stiltgrass spread extensively throughout

the forestlands of Tennessee during an eleven-year period. The range expansion has been

particularly dramatic in northern latitudes. The presence of Japanese stiltgrass almost doubled

from 269 plots (7.5%) in 2000 to 404 plots (11.3%) in 2011. Of the four most influential

variables, one was a landscape feature, two were forest features, and one was a disturbance

factor. Elevation was the most influential variable, contributing 24.12%. Basal area, road

distance, and stand age were the second, third, and fourth most important variables, contributing

20.69%, 16.17%, and 15.09%, respectively. Distance to the nearest road was the only variable

selected from the disturbance factors while no forest management activities were chosen.

Landscape features, forest features, and disturbance factors had total contributions of 38.59%,

45.24%, and 16.17%, respectively. In conclusion, our analyses suggest that the range of Japanese

stilgrass will continue to expand in forested lands of Tennessee. While predicting vulnerable

habits to invasion remains difficult, our model may provide information that guides effective

control strategies and facilitate detection of newly established invasions of Japanese stiltgrass.