Effects of Prescribed Fire on Canopy Foliar Chemistry and Suitability for An
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Forest Ecology and Management 160 52002) 177±187 Effects of prescribed ®re on canopy foliar chemistry and suitability for an insect herbivore L.K. Rieskea,*, H.H. Housmanb, M.A. Arthurb aDepartment of Entomology, University of Kentucky, S-225 Ag. Science North, Lexington, KY 40546-0091, USA bDepartment of Forestry, University of Kentucky, T.P. Cooper Building, Lexington, KY 40546-0073, USA Received 8October 2000; accepted 20 January 2001 Abstract We assessed the effects of a prescribed ®re on the phytochemical characteristics and vigor of overstory chestnut oak, scarlet oak, and red maple, and measured the impact of potential changes on herbivore ®tness. We compared foliar carbohydrates, tannins, nutrients, and ®ber concentrations in foliage from burned and non-burned forest canopies. There were signi®cant differences in most foliar characteristics between tree species. Total non-structural carbohydrate concentrations in scarlet oak and red maple foliage, and calcium levels in red maple foliage, were signi®cantly lower in burned plots, but other phytochemical characteristics were largely unaffected by burning. Tree growth also varied with species. Burning increased chestnut oak relative growth, decreased scarlet oak growth, and had no affect on red maple growth. Scarlet oak and red maple foliage from burned and non-burned forest canopies were assayed for gypsy moth performance. Caterpillars fed foliage from scarlet oak, the preferred host, grew larger and developed more rapidly than did those fed red maple foliage. There were no signi®cant burn treatment differences in caterpillar development within either tree species, suggesting that managers using prescribed ®re to promote oak regeneration need not worry about enhancing forest stand susceptibility to gypsy moth. However, the ®re in this study was of low to moderate intensity; more intense ®res may alter foliar palatability. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Oak; Quercus; Red maple; Phytochemistry; Gypsy moth; Defoliation 1. Introduction poor light regimes and vegetative competition from more aggressive, invasive species such as red maple Since the implementation of effective ®re suppres- 5Acer rubrum L.) 5Abrams, 1992). Lack of oak regen- sion in the early to mid-1900s, forest stand composi- eration also has signi®cant ecological consequences, tion in eastern North America has shifted to include including impacts on subsequent forest successional greater dominance by shade tolerant species, and age stages, and shifts in wildlife composition and distribu- and species mosaics have declined 5Delcourt and tion. The shift in species composition away from oak Delcourt, 1998). As a result, seedlings in oak 5Quercus dominance in eastern deciduous forests has resulted spp.) dominated forests have become suppressed by in the decline of an extremely valuable hardwood group. Repeated attempts to reduce the decline of oaks and improve regeneration suggest that ®re sup- * Corresponding author. Tel.: 1-859-257-7457/1167; fax: 1-859-323-1120. pression is an important causal factor 5Gammon et al., E-mail address: [email protected] 5L.K. Rieske). 1960; Beck and Hooper, 1986; Lorimer, 1989). Fire 0378-1127/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0378-1127501)00444-3 178 L.K. Rieske et al. / Forest Ecology and Management 160 72002) 177±187 can reduce competition and increase sunlight, allow- defoliation by the gypsy moth 5Gottschalk, 1993). ing oaks to thrive 5Carvell and Tyron, 1961; Selective harvesting, high-grading, and prescribed Gottschalk, 1985; Muick and Bartolome, 1987). Com- burning are potential methods to enhance stand vigor petitors may effectively resprout after a single ®re, but and manipulate forest species composition, thereby many oak competitors, including red maple, are suc- decreasing stand susceptibility to this and other cessfully suppressed by repeated burning 5Lorimer, invasive arthropod and plant species. Fire may impact 1985; Arthur et al., 1998). As a result of these potential herbivore populations directly by altering habitat, bene®ts of prescribed burning on oak regeneration, abundance, and species composition 5Siemann et al., prescribed ®re is being used by managers, with poten- 1997), or indirectly via cascading effects caused by tial consequences for the overstory oak. alterations in food quality and availability. Indirect Effects of ®re on overstory oaks may include effects of ®re on herbivory may manifest themselves impacts on plant vigor, alterations in susceptibility to through changes in foliar characteristics that impact mortality agents, and ®re damage to residual stems. herbivore success. For example, ®re may elicit Fire may in¯uence plant growth and foliar chemistry accumulation of foliar nutrients, resulting in enhanced by increasing nutrient concentrations in the soil nutritional substrate that could ameliorate induced 5Prieto-Fernandez et al., 1993; Blankenship and plant defenses 5Haukioja et al., 1990). Fire may also Arthur, 1999). A transitory increase in foliar nitrogen, cause plants to direct additional resources to growth potassium, and phosphorus in tree seedlings has been processes, maintaining productivity but reducing observed directly following prescribed ®re in some defensive abilities 5Price, 1991; Hunter and Schultz, systems 5Reich et al., 1990), which could be due to a 1995). Conversely, ®re may deplete foliar nutrients post-®re increase in available soil nutrients, and which and enhance production of defensive compounds. This may manifest itself as increased seedling growth rates is particularly relevant to the gypsy moth, which is 5Adams and Rieske, 2001), or increased growth of responsive to enhanced nutritional substrate 5Roth overstory trees 5Boerner et al., 1988). Defensive et al., 1994; Rieske and Raffa, 1998) and alterations in phenolic compounds may also be affected by the defensive phenolic compounds 5Baldwin and Schultz, increase in soil nutrients 5Hunter and Schultz, 1995) 1983; Schultz, 1988). or increased sunlight 5Dudt and Shure, 1994). Given Regeneration of oak stands and suppression of the potential effects of ®re on oak phytochemistry, invasive native and non-native plants and animals are foliar nutritional suitability and susceptibility to mam- emerging issues in deciduous forest management. The malian and arthropod herbivores may be drastically objectives of our study were to characterize the effects altered. of ®re on foliar chemistry of canopy oaks and red The gypsy moth 5Lymantria dispar L., Lepidoptera: maple, to determine the effects of any ®re-induced Lymantriidae) is an introduced defoliator with out- phytochemical changes on preferred and non-preferred break potential that has become established through- host suitability to an insect folivore, and to assess how out the northeastern US. The successful expansion of these potential changes may impact deciduous forest the geographic range of the gypsy moth into the composition. central hardwood forests of the Appalachian Cumber- land Plateau is assured by an abundance of several oak species, which are the insects' preferred host plants 2. Methods 5USDA Forest Service, 1991; Leibhold et al., 1995). The impacts of gypsy moth outbreaks can be devasta- We assessed the impacts of a prescribed burn on ting, and include shifts in forest stand composition the foliar chemistry and vigor of canopy chestnut oak away from oak dominance 5Campbell and Sloan, 5Q. prinus L.), and scarlet oak 5Q. coccinea Muenchh.), 1977; Gottschalk, 1993; Fajvan and Wood, 1996; both preferred hosts of the gypsy moth, and red maple, Davidson et al., 1999), similar to shifts in stand a non-preferred gypsy moth host. We also assessed the composition due to ®re suppression. suitability of the burned and non-burned scarlet oak Natural resource managers are increasingly turning and red maple foliage for the development of gypsy to silvicultural techniques to mitigate the effects of moth caterpillars. L.K. Rieske et al. / Forest Ecology and Management 160 72002) 177±187 179 2.1. Study sites and sampling shotgun to remove terminal branches on 6 May 1998, corresponding to leaf-out, and on 20 and 28May, 3 This study was conducted in the Red River Gorge and 17 June. On the ®rst, second, fourth, and ®fth Geological Area of the Daniel Boone National Forest sample dates, foliage was designated for phytochem- in eastern Kentucky 5USA), in conjunction with the ical analysis, including foliar non-structural carbohy- prescribed burn management program implemented drates, tannins, nutrients, and ®ber. On the third 528 by the US Forest Service. The Red River Gorge is May) sample date only, a smaller set of foliar samples located in the Cliff Section of the Cumberland Plateau N 16 from scarlet oak and red maple were dedi- and is characterized by xeric ridge tops supporting a cated to gypsy moth feeding trials. diverse suite of oaks, including scarlet oak, chestnut oak, white oak 5Q. alba L.), and black oak 5Q. velutina 2.2. Phytochemical analysis Lam.), several species of pines 5Pinus rigida Mill., P. echinata Mill., and P. virginiana Mill.), red maple, Leaves from each branch were removed at the base and mesic coves of beech 5Fagus grandifolia Ehrh.), and divided into two groups; one was ¯ash frozen in Magnolia spp., Rhododendron spp., and hemlock liquid nitrogen for analysis of carbohydrates and 5Tsuga canadensis L.) 5Braun, 1950). tannins, and the other was oven dried for nutrient and Our experiment was conducted on a single ridge ®ber