Invertebrate Abundances and Diversity in Surface Litters of a Six Year Old Organic Apple Orchard in Northwest Arkansas.

A more taxonomically diverse invertebrate community may contribute to a more functionally diverse and stable ecosystem. Enterprise/M26 apple trees had been planted in 2006 in a newly established, experimental, organically managed 0.4-ha orchard in Fayetteville, Arkansas. Surface mulch and nutrient applications are applied annually every April. Treatments are fully replicated,  arranged in a randomized complete block, and include combinations of four ground covers:  plant clippings left on the ground surface (mowed control, M), urban compost (C), wood chips (W), and shredded paper (P), and three fertilizers:  no fertilizer control (ground cover only), composted poultry litter, and a formulated, certified organic pelletized fertilizer. To determine if ground cover and organic fertilizer applications alter invertebrate communities in the ground surface litter, invertebrates from each treatment were extracted using Berlese funnels and hand-sorting techniques in February, 2012. Ground covers (W, C, and P) increased abundances per unit area, taxa richness, and diversity compared to M. The largest abundances on an area basis occurred in W. Ground cover applications of P did not result in a significantly greater accumulation of litter by mass compared to M, but invertebrate abundances increased on a mass litter basis compared to M and were not significantly different than W. Managing the orchard with different ground covers altered the community composition of the litter fauna such that there were greater proportions of isopods in P and W, millipedes in C and W, and earthworms in C compared to M. Repeated applications of ground covers have enhanced different macrofauna within the detrital food web. Isopods, millipedes, and earthworms may serve as useful bioindicator organisms of detrital activity in organic orchards that rely on decomposition of added ground covers to help build healthy soils.