Insect community response to switchgrass intercropping and stand age of loblolly pine (Pinus taeda) plantations

Abstract

Abstract Intercropping switchgrass (Panicum virgatum) between rows in managed pine stands is a potential, emerging method for biofuel feedstock production in forestry systems. Switchgrass intercropping likely alters vegetation characteristics within a stand by increasing herbaceous vegetation cover and thus influences insect communities positively. However, its effect may vary with stand age, which often determines canopy closure and vegetation structure within a stand: effects of switchgrass intercropping may be stronger in old pine stands with a closed canopy than in young pine stands with an open canopy. We examined how switchgrass intercropping and stand age, namely 3–4‐year‐old pine (YPine) and 8–9‐year‐old pine (OPine), influenced insect abundance and diversity in loblolly pine (Pinus taeda) stands in Mississippi, U.S.A., during May to August 2013–2014. We captured insects at 36 locations throughout 12 stands (three stands per each of four treatments; intercropping and non‐intercropping treatment in YPine and OPine stands), using pan traps. Abundance and family level richness were greater in YPine stands and Shannon–Wiener diversity and evenness at family level was higher in OPine stands both years. However, insect abundance and diversity did not differ between intercropping and non‐intercropping treatments. Community composition was also influenced by stand age, which explained > 90% of constrained inertia, rather than switchgrass intercropping. Our findings suggest that switchgrass intercropping is unlikely to significantly affect insect communities in managed pine stands, whereas stand age, as well as associated successional changes, can be a main factor affecting insects, as often observed in other animal taxa in managed pine landscapes.