Southwestern Association of Naturalists Variable Budbreak and Insect Folivory of Gambel Oak (Quercus gambelii: Fagaceae) Author(s): Stanley H. Faeth and Robert F. Rooney, III Source: The Southwestern Naturalist, Vol. 38, No. 1 (Mar., 1993), pp. 1-8 Published by: Southwestern Association of Naturalists Stable URL: http://www.jstor.org/stable/3671636 Accessed: 07/05/2010 20:37 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=swan. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Southwestern Association of Naturalists is collaborating with JSTOR to digitize, preserve and extend access to The Southwestern Naturalist. http://www.jstor.org THE SOUTHWESTERN NATURALIST 38(1):1-838(1): 1 -8 MARCH 1993 VARIABLE BUDBREAK AND INSECT FOLIVORY OF GAMBEL OAK (QUERCUS GAMBELH: FAGACEAE) STANLEY H. FAETH AND ROBERT F. ROONEY, III Department of Zoology, Arizona State University, Tempe, Arizona 85287-1501 ABSTRACT-Budbreakof individualramets of clonal Gambeloak (Quercusgambelii: Fagaceae) was advancedexperimentally to test the effects of altered timing of budbreakand hence, leaf age, on patternsof folivory.Early-season folivory by leaf-chewinginsects was significantlygreater on younger leaves of controlramets than older leaves of experimentalramets. However, differences in cumulative folivory between control and experimentalramets disappearedby the end of the growing season. Colonization by three species of late-season leafminers was also unaffected by altered budbreak, indicatingthe impact of altered budbreakon folivoresis concentratedearly in the growing season. Analyses of nutritionaland allelochemicalcontent of experimentaland controlramets correspond to the patternsof folivory;leaves of experimentalramets were significantlyhigher in gallotannincontent than leaves of controlramets, but these differencesalso waned by the middle of the growing season. Our resultssuggest that variablebudbreak can alter degreeof folivoryon Gambeloak, but only early in the growing season.The evolutionaryimplications of, and constraintson, variationin budbreakin woody plants are discussed. Many folivorous insect species that feed on trition, and morphology (Haukioja et al., 1985; deciduous or semi-evergreen trees prefer and per- Tuomi et al., 1989). Despite the potential of vari- form better on younger leaves than old ones (e.g., able budbreak in altering folivore abundances on Feeny, 1970; Rockwood, 1974; Schweitzer, 1979; trees, relatively few studies of herbivore-plant in- Cates, 1980; Rauscher, 1981; Kraft and Denno, teractions have focused on this plant trait. Those 1982; Coley, 1980; Niemela and Haukioja, 1982; studies that have, have produced conflicting re- Niemela et al., 1982; Fowler and Lawton, 1984). sults. Feeny (1976) concluded that early or late As leaves age, they change in surface area, water flushing oaks harbor fewer insects than the pop- content, toughness, thickness, chemical compo- ulation in general. Defoliated branches of moun- sition and nutritional quality (Feeny, 1970; tain birch (Betula pubescens ssp. tortuosa) break Crawley, 1983; Raupp and Denno, 1983; Coley, bud later in the following year, and Tuomi et al. 1980; Faeth, 1985a). Therefore, the synchrony (1989) hypothesized that these branches should between budbreak of host trees and folivore emer- have less herbivory than branches that flush leaves gence from overwintering stages is critical to foli- earlier. Similarly, late breaking holly oaks (Quer- vore success. Insects that emerge too early may cus ilex) had less herbivory from the folivore Tor- starve (Futuyma and Wasserman, 1980; Hunter, trix viridana than early breaking trees (Du Merle, 1990), while insects that emerge too late may 1988). In contrast, experimentally retarded, encounter a suboptimal food source (Embree, younger foliage of Betula pubescens had more her- 1965; Feeny, 1970, 1976). bivory than older, control foliage (Fowler and Variation in timing of budbreak often occurs Lawton, 1984). Also, tropical plants with late, within populations of trees. For example, pedun- asynchronous leaf flush typically have higher rates culate oak (Quercus robur) trees vary in timing of herbivory (Rockwood, 1974; Lieberman and of budbreak by as much as two weeks within a Lieberman, 1984; Aide, 1988). given locality (Feeny, 1970). Because timing of We tested the influence of variable budbreak budbreak is at least partly determined by genetic on folivory by advancing the timing of budbreak factors (Kramer and Kozlowski, 1979), variation experimentally within clones of Gambel's oak in time of budbreak has been considered a plant (Quercus gambelii Nutt.). Since spring folivores defense against folivores, similar to other variable generally prefer and perform better on younger plant characteristics such as allelochemistry, nu- leaves than older leaves, presumably because of 2 The Southwestern Naturalist vol. 38. no. 1 TABLE 1-Budbreak phenology of experimental (E) Typical leaf flush of Gambel's oak at Aztec Peak and control (C) ramets. occurs in late April to early May. Most leaves remain on trees until late September to early November. No leaf flush occurred on the dur- Expo- Differ- secondary study genets the course of this Most leaves abscise Tree sure (E) (C) ence ing study. by mid-November, although some senesced leaves remain 1 N 16 April 30 April 14 days on the ramet until budbreak in the following spring. 1 S 16 April 30 April 14 days Gambel oak exists in clones (genets) composed of many 1 E 16 April 30 April 14 days individual shoots (ramets), connected to the same root 30 14 1 W 16 April April days system. By using clones, we could manipulate budbreak of adult trees in the while for 2 N 26 April 5 May 9 days field, controlling genetic treatment and control ramets in 2 S 30 April 5 May 5 days variability between to 2 E 26 April 5 May 9 days resistance folivory. To of Gambel's oak 2 W 26 April 5 May 9 days advance budbreak, four genets were selected on the basis of similar size (approxi- 3 N 30 15 May 15 days April mately 10 m in height and 10 m in diameter) and 3 S 30 15 May 15 days April exposure (level ground in full sunlight). All genets were 3 E 30 15 15 days April May apparently healthy and located within a 300-m radius. 3 W 30 15 15 days April May Clonal Gambel's oak in this area grows as large, dis- 4 N 26 April 12 May 16 days tinct genets composed of 10-50 ramets, which range 4 S 30 April 12 May 12 days from less than 1 m to over 10 m in height. Study genets 4 Eb were divided into four quadrants corresponding to the 4 W 26 April 12 May 16 days four cardinal compass points to account for variation in budbreak within clones due to different sun expo- a Mean difference in budbreak between experiment sure. One experimental and one control ramet were (E) and control (C) ramets = 12.8 ? 3.28 days. selected from the pool of ramets within quad- b Ramet 4EX was snow on 17 randomly destroyed by April, rants of 1.5-3 m in and not more 1988. approximately height than 2 m from the outermost ramets, giving a total of 16 control and 16 experimental ramets. lower amounts of allelochemicals and degree of On 29 March 1988, all experimental ramets were and amounts of nutrients (Feeny, toughness higher enclosed in 1 m x 2 m bags of 2.5 mm thick polyeth- we that older leaves 1970), predicted produced ylene to increase temperatures sufficiently to induce leaf flush should have lower rates of by early early budbreak. All enclosed and control ramets were folivory than control (normal budbreak) leaves. inspected twice weekly for time of budbreak. Bags were We monitored nutrition (protein) and allelo- removed from experimental ramets when the control chemistry (tannins) to determine phytochemical ramet from paired controls broke bud, so that exposure differences between advanced and control leaves time to folivores was equivalent on experimental and control ramets. The ramets broke bud an that might explain any differences in folivory. experimental of 12.8 earlier than the control We also examined the distribution of late-season average (+3.28) days ramets (Table 1). Some frost damage was recorded on leaf-mining insects to determine whether differ the experimental ramets of Trees 1 and 2 on 12 May, ences in the advanced leaves and experimental resulting in the loss of some leaves. A late snowstorm the control leaves for late-season younger persist on 17 April resulted in the loss of ramet 4EX due to folivores. breakage caused by accumulation of snow on the bag. Ramet 4EX was therefore treated as a missing value MATERIALS AND METHODS-Experiments and ob- in all statistical analyses. The frost damage to Trees 1 servations were conducted on clones of Gambel oak and 2 was ignored since loss of leaves was minimal. (Quercus gambelii) at Aztec Peak (2,225 m elevation), Leaves were scored for leaf-chewing insect damage Tonto National Forest, Gila County, Arizona, from on 29 May, 7 July, and 5 August 1988.