With growing demand for biofuel feedstocks that can reduce economic and environmental conflicts, industrial pine (Pinus spp.) landscapes have increasingly received attention as potential resources to produce biofuel feedstocks. Intercropping switchgrass (Panicum virgatum) between rows of pine tree in plantations is an emerging method for biofuel feedstock production in forestry systems. As switchgrass intercropping is expected to change vegetation characteristics within a stand, it can influence animal communities in pine plantations, but its effect likely varies with stand age which often determines canopy closure. We examined how switchgrass intercropping and stand age (3-to 4-year old, young pine [YPI], and ~10-year old, old pine [OPI]) influenced insect abundance and diversity in loblolly (P. taeda) pine plantations in Mississippi, USA during May-August, 2013-2014. We captured insects at 36 locations throughout 12 plots (3 replicates per each of 4 treatments; intercropping and non-intercropping treatment at YPI and OPI stand), using pan traps. We used a general linear mixed model to test significance of treatment effects and conducted analysis of similarity (ANOSIM) and redundancy analysis (RDA) to investigate relationships between treatment and structure of insect community.
Results/Conclusions
Abundance and family-level richness was significantly greater at YPI stand (p<0.05), whereas Shannon-Wiener diversity and evenness at family-level tended to be higher at OPI stand. Conversely, no significant differences were found in insect responses, particularly abundance, between intercropping and non-intercropping treatments. Foraging guild structure and community composition was also strongly influenced by stand age rather than switchgrass intercropping. The value of ANOSIM statistic was 0.45 (p = 0.001) and 0.45 (p = 0.001) in 2013 and 2014, respectively. The first canonical axis from RDA that represented a gradient between YPI stand and OPI stand explained 48.2% (2013) and 55.4% (2014) of variation. Our findings suggest that switchgrass intercropping is unlikely to have significant effects on arthropod communities in pine plantations whereas stand age can be a main factor affecting arthropods, as often observed in other animal taxa in pine plantations.