Analysis of aboveground arthropod communities and their influence on nutrient dynamics in a mature and a successional forest

Aboveground arthropod communities were analyzed and primary consumption in the canopy was measured on a control watershed (WS18) and a successional watershed (WS6) at the Coweeta Hydrologic Laboratory, North Carolina. Leaves of Carya spp. (hickories), Quercus prinus (chestnut oak), Cornus florida (dogwood), Liribdendron tulipifera (tulip poplar), Acer rubrum (red maple), and their associated arthropods were chemically analyzed for K, Ca, Mn, Fe, Cu, Zn, Br, Rb, and Sr after primary consumption measurements were made. Guild and trophic level assortments of arthropods were used for diversity calculations and nutrient analyses respectively.

Primary consumption values were similar to those reported in the literature except for high values in hickories and chestnut oak foliage—some samples over 50% consumed. Primary consumption, in sampled trees, was not significantly different between watersheds. From seasonal changes in average leaf size, average leaf density, and mid-season decrease in measured primary consumption it is proposed that insect herbivory caused premature leaf abscission in those trees which exhibited the greatest leaf damage from herbivores. Elemental concentrations in leaves, statistically higher on WS18 except for Ca, suggest a residual effect from previous applications of lime and potash on WS6. Unconsumed and consumed leaves did not have different patterns of elemental concentrations.

Arthropod weight intensities were dominated by caterpillars and sucking herbivores on the successional watershed compared with dominance by herbivorous beetles on the control watershed. Canopy arthropod diversities were similar on both watersheds. Canopy arthropods had higher concentrations of K and lower concentrations of Ca while the remaining elements did not exhibit trends in relation to concentrations of foliar elements. Differences in elemental concentrations among trophic levels were small although Zn may accumulate in predators.

The herb and low shrub layer was examined primarily for qualitative comparisons of the two watersheds. Arthropods in low vegetation were more abundant and were represented by fewer guilds on the successional watershed when compared with arthropods on the control watershed. Herbs and woody shrubs formed a thick ground cover on the successional watershed in contrast with relatively sparse low vegetation on the control watershed.