DE-AI09-00SR22188 JOURNAL ARTICLE 2005 05-07-P 1999; Moorman and Guynn, 2001), more than closed canopy forest. It is likely that populations of reptiles and amphibians are affected by groupselection harvests as well. Amphibians are an important part of most southeastern communities (Bennett et at., 1980) and are widely considered to be good indicators of environmental health and function (Phelps and Lancia, 1995). Because of their importance within ecosystems, seveml studies ' have sought to determine how forest management affects their populations. Gearcutting is a major Pactor altering herpetofaunal communities (Enge ar~dMarion, 1986; Pough et aL, 1987; Petranka et ul., 1993; Phelps and Lancia, 19951, bu~Greenberg (2001) found that gaps created by wind disturbance in the southern Appalachians had litde effect on terrestrial amphibian abundance relative to the surrounding intact forest. Few studies have examined how forest management affecb species such as the green tree frog (Hyla cinmea) that spend little time on the ground. In onc study, Phelps and Lancia (1995) captured green tree frogs more frequently in clearcuts using the pipe collecuon method, but thcy were uncertain if their results were due to their method of trapping or to habitat preference. Likewise, Cromer et a!. (2002) documented that tree frog abundance was positively associated with the creation of artificial canopy gaps. Terrestrial arthropods serve as food for many amphibian and repule species, but little information exists on the potential interactions among forest management, arthropods and hylid tree frogs. The objectives of this smdy were to compare the abundance of green tree frogs in artificially created canopy gaps to that at similar heigha in the surrounding dosed canopy forest and to compare frog abundance wilh ar~hropodabundance in thc same habiiats.

METHODS This study was conducted in 2003 at the U. S. Department of Energy @OE), Savannah River Site (SKS) near Aiken, South Carolina. The SRS is an 80,269 ha nuclear production facility loca~edin the upper Atlantic Coastal Plain Physiographic Province (Knox and Sharitz, 1990). The majority of the laad on the site is forcsted and managed as a DOE National Environmental Research Park. The stands used in this study consisted of 75 year- old bottomland hardwoods approximately 120 ha in total size (KiIgo, 1997'). Common overstory trees within the intact forest included bald cypress (Taxodium distichurn), laurcl oak ( Qumcus burifolia), winsect$ to enter from any direction. Arthropods entering the traps wcre coIlected in plastic bottles containing a NaCl and 1 % formaldehyde solution in which a drop ' of qetergent was added to reduce surface tension. Samples were returned to the laboratory and stored in 70% alcohol until they could be identified. Traps were operated for one 7 d period in the months of April, May, July and November 2001. Although we colIected insect data 2 y beforc the frog surveys, it is likcly that relativc insect abundance between gap and forest habitat was similar in 2001 and 2003. The reason for this assumption is because the gaps wcrc similar in their plant composition in 2001 and 2003, with the main difference being plant height, while the forest plots were unchanged between years. rkthropods were identified to order, ovendried for 48 h at 40 C, and weighed to estimate biomass. A paired k-test was used to determine if he numbers of insects or tree frogs differed between gap and forest plots.

R~surrrsAND DISCUSSION Of 331 green tree frogs observed, more were found in the gaps (mean % SE = 58.4 2 18.5) comparcd to closed canopy forest (mean 4 SE = '9.8 -t 2.5) (P = 0.027). Greater than 88% of the total number of frogs observed were in gaps where they occurred on dwarf palmetto, switchc~ne,plume grass and sedges while frogs in the forest interior were almost exclusively on dwarf palmetto. This may be attributed to dwarf palmetto being the dominant understory plant present in closed canopy forests. Only 2.4% of the frogs observed were adults. We collected 7628 insects from the 10 plots, with significantly higher numbers (P = 0.009) collected from canopy gaps than from the forest interior {Table I).Greater than 86% of the insecb capturcd and 82% of the biomass wcrc from artificiallycreated canopy gaps. Diptera, Lepidoptera, Coleoptera and Hymenoptera, made up >75% and 80% of the total number of insects and biomass, respectively. hi general, the mean number of each insect order captured was higher in canopy gaps (Table 1) than in forests, but Diptera (P = 0.014), Hymenoptera (P = 0.0151, and Coleoptera (P = 0.080) were significantly more abundant in gaps and Lepidotera biomass {mainIy mochs) was higher in gaps (P = 0.025). The plant community response to disturbance influences many aspects of he ecosystem {Runkle, l998), and is particularly important in determining the insect community's diversity and distribution (Waltz and Whitman, 1997). The gaps created in this study had an abundance of early-successional vegetation and were dr~matically different than the undisturbed forest. The herbaceous vegetation in the gaps was more structurally complex compared to the closed canopy forest (personal observation) and this may explain why we . saw increases in insect abundance. Hylid tree frogs are generally considered to be indiscriminate predators (Oplinger, 1976; Clark, 1.9'74;.Johnsonand Christjansen, 19'76; Labanick, 1976; Tyler and Hoestenbach, 1979). ' Holbrook (1842) stated that green tree frogs fed on flies and Haber (1926) found them to commonly prey upon flies, beetles, anb and moths. Freed (1982) used stomach pumping to show that larva1 moths and beetles were the two most common prey selected in the field, while laboratory studies proved that flies in the genus Mwca were preferred over other available prey. Taken together, these studies suggest that the availability and abundance of various prey types determine the diet of green tree frogs, not preference for a particular type or species (Oplinger, 1967;Johnson and Christiansen, 1976; Labanick, 1976). TABLEI.-Mean number and biomass (g) of the four most abundan~orders of insects collected and the mean number of insects captured per plot in canopy gaps (n = 5) and interior borlomland hardwood forest (n = 5)

Gap Forest Order Mean No. T SF. Mean WL.+ sr Mcan No. Z 3: Mean Wt. Z SE Diptera 768.2 2 226.5*" 0.24 2 0.094 54.4 2 12.3 0.15 % 0.07 Lepidopiera 106.8 2 21.7 0.21 2 0.066"" 63.0 2 16.3 0.02 % 0.Ol Coleoptera 85.6 ? 23.7* 0.39 2 0.19' 97.0 r 6.2 0.07 r 0.02 Hymenoptera 45.6 ? 9.2*-* 0.13 2 0.0543 15.0 L 3.9 0.03 2 0.02 Mean (a11 orders) 1121 + 266.5** 1.26 2 0.51" 204.6 5 31.6 0.26 ? 0.09 'denotes a significant difieference {P < 0.10) "*dcnotcs a significant difference (I' < 0.05) behveen gap and forest based on a paired t-test

The distribution and abundance of food is one of the most important factors influencing the evolution of adaplauons among species (Krebs and Davies, 1987).Studies have suggested that increased food resources are correlated with higher densities of birds (Blake and Hoppes, 1986). However, little or no information exists on how amphibians, particularly hylid trce frogs, respond to increased food availability. It seems that locally abundant food : would influence the distribution and abundance of green tree frogs. Our study shows hat green tree frogs were more abundant in gaps where they had five to six times more food available compared to forested plots located only 50 m away. Presently, clearcutting is the most common method for regenerating bottomland hardwoods and provides habitat for opportunistic species that respond well to ephemeral habitats (Costello cL aL, 2000). However, some species only remain if certain attributes are relained in the surrounding forest, as in groupselection harvests. Cromer et aE. (2002) found that gap creation likely benefits some groups like tree frogs, while reducing the suitability of habitat for others like salamanders. Phelps and Eancia (1995) and Enge and Marion (1986) concluded that smaller forest clearings would benefit the diversity of local herpetofauna. Small-scale disturbances such as canopy gaps provide low-growing vegetative structure for insects and green tree frogs, while leaving the surrounding forest uncompromised. Bury and Corn (1988) found reptiles to be more common in clearcuts due to an increase in ambicnt temperature, a finding similar to that of Phelps and Lancia (1995) in South Carolina. Likewise, Greenberg (2001) suggested that increased light lcvels in wind-created canopy gaps positively influenced reptilc abundance. However, increased prey mailability is also likely to havc a strong influence on the distribution and abundance of reptiles and amphibians. Most likely, a combination of factors such as increased prey availability, moisture, light and temperature contribute to their habitat choice.

Acknowkdgments.-This research was supported by [he National Research Inilialive Compctitivc Grrlntq Program of the USDA Cooperauvc Statc Rcsearch Education and Extension Service (CSIREES Grant No. 00-35101-9307). Wc thank the U.S. Forest Service-Savannah River and U.S. Department of Energy for access and logistical support throughout the duration of this project. Mention of product names does not constitute endorsement by the U.S. Government.

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