Impact of Imperata cylindrica on Populations of Root-feeding Bark Beetle Populations and Factors Associated with Loblolly Pine Decline in a Pinus taeda Stand

Abstract

The non-native, invasive plant, cogongrass (Imperata cylindrica (L.) Beauv) is a threat to the diversity of native plant species of the southeastern United States. Another issue facing landowners of southeastern forests is Loblolly Pine Decline (LPD). The factors associated with LPD include a complex of abiotic and biotic stressors that cause economically significant premature mortality in pine forests. A suite of root-feeding bark beetles associated with LPD could potentially have higher populations in areas containing cogongrass due to additional stresses attracting them. This is focused on determining if cogongrass is causing an increase in populations of root-feeding bark beetle populations, altering soil properties that could potentially be contributing to LPD, and the affects cogongrass is having on the tree vigor of loblolly pine (Pinus taeda L.). Twenty plots were established in loblolly pine stands in southeastern Mississippi with ten plots located in areas with cogongrass infestation (CO plots) and ten located in areas without cogongrass infestation (NCO plots). Comparisons of insect populations, soil properties, and tree vigor measurements between CO and NCO plots were made. Results suggest soil conditions were more conducive to fine root growth for loblolly pine but significantly less pine fine roots were observed in CO plots suggesting that cogongrass is outcompeting the pine roots through its extensive rhizome system. Cogongrass could be causing stress to establish pine stands through competition with the pine root system and increased stress could possibly lead to an increase in LPD associated bark beetle species populations. Continued research should be performed to see if cogongrass’ impact is compounding as stand age increases.