The Effects of Low‐Level Consumption by Canopy Arthropods on the Growth and Nutrient Dynamics of Black Locust and Red Maple Trees in the Southern Appalachians

Abstract

The effects of low—level consumption by canopy arthropods on foliage nutrient content, canopy leachates (throughfall), and biomass of 4—yr—old black locust (Robinia pseudoacacia) and red maple (Acer rubrum) were studied in the southern Appalachians of North Carolina. A carbaryl insecticide was used to reduce foliage consumption from °10 to °2% in black locust and from °4 to °1% in red maple. Phosphorus concentrations in untreated black locust foliage were significantly lower than those of insecticide—treated foliage early in summer, but equalled concentrations of treated foliage by late summer. Potassium concentrations in untreated red maple foliage were significantly reduced during late summer; calcium concentrations in untreated red maple foliage were significantly higher later in the summer. Potassium in throughfall from black locus trees (amount of K collected below the canopy minus bulk precipitation inputs) increases from 5.7 kg/ha for insecticide—protected trees to 9.8 kg/ha for unprotected trees (P < .05). Potassium lossesw from unprotected red maple also increased. Black locust lost 0.3 kg/ha of sulfate—S from untreated trees, but adsorbed 0.4 kg/ha of sulfate—S in insecticide—treated trees (P < .05). Total biomass production (net primary production per kilogram of preseason biomass) was unaffected by the low levels of herbivory observed here. Such nominal herbivory did not stimulate biomass and nutrient accretion by these tree species but did increase the cycling of K and perhaps other elements within these systems.