Communtiy Structure and Nutrient Content of Canopy Arthropods in Clearcut and Uncut Forest Ecosystems

Abstract

This paper describes differences in canopy arthropod community structure, major cation content, and calculated nutrient consumption between clearcut and undisturbed hardwood forest watersheds at Coweeta Hydrologic Laboratory, North Carolina, USA, during the first two growing seasons following cutting. Although canopy arthropod biomass was about 0.08% of foliage biomass on both watersheds, aphid mass increased 23—fold and ant mass increased 6—fold per unit foliage mass following cutting. These groups in general had lower nutrient concentrations than did chewing herbivores and predators. Arthropod K concentrations were 33% lower on the clearcut; Na, K, and Mg concentrations were 20%—50% higher in 1978 than in 1977. Arthropod Mg and Ca concentrations, but not Na, and K, were reduced significantly more by the greater effect of drought on the clearcut watershed. Consumption estimates based in part on consumption rates reported by others indicated increased nutrient translocation from foliage via arthropods following cutting. These data indicated that canopy arthropod responses in nutrient availability following disturbance could have increased nutrient cycling rates and contributed to nutrient retention by the recovering ecosystem.

Short-term sodium inputs attract microbi-detritivores and their predators

“…Plants require and concentrate very little Na in general, but heterotrophs need to concentrate Na well above plant levels to maintain neural function, osmotic balance, reproduction and development (Ganguli 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 et al., 1969;Bursey and Watson, 1983;Blumwald et al, 2000;Geerling and Loewy, 2008). Schowalter et al (1981) measured plant, herbivore, and predator Na concentrations at 0.02, 0.31, 0.66% Na respectively, which demonstrates the large stoichiometric disparity between plants and herbivores. Herbivores and detritivores, as plant consumers, are thus potentially the most vulnerable to Na-limitation.…”

“…Herbivores and detritivores, as plant consumers, are thus potentially the most vulnerable to Na-limitation. Predators, in contrast, likely do not suffer from Na-deficits as their diet (other heterotrophs) is already rich in Na (Schowalter et al, 1981;Simpson et al, 2006;Kaspari et al, 2008). In fact, predators are generally insensitive to Na in choice tests (Bradshaw et al, 1996), but herbivores can taste and respond to Na even at concentrations as low as 0.005 M (Bell and Kitchell, 1966).…”

Insect Herbivory in Tropical Forests

“…Herbivory in canopies ranges from 1 to 5 percent of total leaf area production in tcmpcratc forests (Schowalter et al 1981) to more than 300 perccnt in Australian eucalypt forests where trees re-foliated several successive times aftcr lcaf loss (Lowman 1992;Lowman and Heatwolc 1992). Several studies (e.g., Seastedt and Crossley 1984;Lowman et al 1998) and literature revicws (e.g., Schowalter et al 1986;Lowman 1995b;Schowaltcr 2000) give details on herbivory rates at specific sites in tropical areas.…”

Biotic and abiotic consequences of differences in leaf structure

“…Plants have other methods of defence or avoidance or leaf herbivory to use in various combinations, as we shall see later. The defences are effective, in that leaf herbivory is estimated at only 5-20% in some representative ecosystems (Golley, 1977 ;Schowalter et al, 1981). The costs overall can be substantial, particularly for perennials.…”