SCHNURR, JACLYN, L.," CHARLES D. CANHAM,' and RICHARD S.OSTFELD.' 'Idaho State University, Pocatello, ID 83201 USA; 'Instituteof Ecosystem Studies, Millbrook, NY 12545 USA. Escape from seed pre-dation in temperate forests: The effects of interspecific variation in seedproduction.

Survival of tree seeds in temperate forests may vary as a function of theresponses of generalist rodent seed predators to spatial and temporalvariation in the numbers and composition of the seed rain. We examinedrelationships between tree seed rain, seed predation, and rodent densityfrom 1994-1996 in northwestern Connecticut. Red oak (Quercus rubra)masting in 1994 caused extremely high rodent populations during 1995.In 1995 there was a general seed crop failure by all tree species. Seedremoval rates of all species were high that fall. Rodent mortality was highin winter of 1995-96, leading to very low animal densities the next springand fall. Acorn production in 1996 was still extremely low (2 acorns/m2);however, white pine (Pinus strobes) had a modest seed crop (33 seeds/m2). The white pine seed crop failed to satiate consumption of white pineseeds (90-95% removal), but relieved predation pressure on a less abun-dant crop of acorns (resulting in 25-30% survival). Our results indicatethat the analyses of the role of predator satiation in systems with gener-alist predators must consider interspecific variation in food resource avail-ability.

SCHOENLY, KENNETH G.,* and K. L. HEONG. International Rice Re-search Institute, PO. Box . 933, 1099 Manila, PHILIPPINES. When doesan herbivore become a crop pest? Lessons from tropical rice ecosys-tems.

An agricultural pest is a species that causes economic loss ota human-valued resource. In tropical Asia, various reports claim that between 800to 1400 insect species worldwide are rice pests; however, at any onetime and place, only a few herbivore taxa, if any, may demonstrably causeyield loss due to containment by a large complex of natural enemies.Unfortunately, many national agricultural institutions in Asia that employrice entomologists consider most rice herbivores as pests. Moreover, re-searcher-conducted crop-loss assessments make untested assumptionsabout presumed associations between herbivore densities and grain yieldsthat can bias cause-and-effect perceptions and pest managementdecisionmaking of Asian rice farmers. Our farmer surveys and experi-mental studies in tropical Asia show that: a) insecticides account for over90% of the pesticides used by rice farmers and that most are unneces-sary, are applied at the wrong time, and are used against the wrong tar-get; b) insect injuries are better correlates of grain yield (per hill of 2-3rice plants) than insect densities per se; c) some insect-specific injuries(e.g., counts of whiteheads and folded leaves by stemborers andleaffolders, respectively), when used alone, give misleading indicators ofplant injury because compensation across a gradient of hill quality is ig-nored; d) farmers who can tolerate leaf damage by leaf feeding insectsand low whitehead incidence in their fields may enjoy small dividends incrop yields if insecticides are replaced by N-fertilizers, provided such in-puts are sufficient to augment plant compensation mechanisms; and e)the minority of farmers who can accept low herbivore densities and ap-preciate natural biological controls in their fields generally reduce theirinsecticide inputs.

SCHRADER, BARBARA A.," and THOMAS A. SPIES.' 'Oregon StateUniversity, Corvallis, OR 97331 USA; 'Forestry Sciences Lab, USDAForest Service, Corvallis, OR 97331 USA. Invasion of Douglas-fir forestsby western hemlock regeneration: Establishment and growth rates incoastal Oregon.

Western hemlock is an important component of structure in Pacific North-west old-growth forests, yet little is known of rates and patterns of hem-lock invasion in mature forests. In this study, age and size class distribu-tions of western hemlock were measured in six late successional standsin the Oregon Coast Range. Results indicated that establishment of west-ern hemlock occurred in pulse and continual patterns. Time between ini-tial establishment and subsequent pulses of establishment was approxi-mately 40-70 years. These patterns were observed in all stands fromcool, moist coastal sites to the seasonally hot and dry Willamette ValleyMargin. Regional and size class differences in substrate colonizationpatterns were observed. Eighty-four percent of all western hemlock atcoastal sites were rooted on decayed logs compared to 26% at the ValleyMargin. Seedlings were predominantly observed on decaying wood whiletrees were predominantly observed on forest floor substrates. Growthrates of seedlings and saplings were also measured and related to re-gional and stand-level variables. Highest growth rates were found in lowelevation coastal sites, in stands containing the highest levels of coarsewoody debris, and the highest level of canopy gaps.

SCHULZ, KURT E.," J. ROCKS,' J. ZASADA,' D. BUCKLEY,' and T.CROW.' ' Southern Illinois University at Edwardsville, Edwardsville, IL62026-1651 USA; 'Forestry Sciences Lab, North Central Forest Experi-ment Station, Rhinelander, WI 53706 USA. Effect of canopy manage-ment regime on the performance of two ferns with contrasting frond phe-nology.

Concern over biodiversity losses caused by forest management regimeshas stimulated survey studies, but little work on species which might actas models of understory response. The winter-deciduous lady fern(Athyrium felix-femina) and evergreen shield fern (Dtyopteris spinulosa)are mid-summer dominants of maple-hemlock-yellow birch forests on theMichigan Upper Peninsula. Frond size and abundance were evaluated in1996 and 1997 in stands managed for even-aged and uneven-aged sizedistribution, 90 year-old second growth, and virgin forest (3 replicateseach). Lady fern ramets had greater frond size and abundance undereven-aged and uneven-aged management; shield fern showed no re-sponse. Even-aged sites showed significantly higher transmitted PAR(9.4% vs. ca . 4.3%). Replicate sites within management treatmentsshowed significant differences in lady fern performance, light availability,canopy cover, and microtopography. The undetectable response of shieldfern may be caused by its reliance on the late spring light window forphotosynthesis. Consideration of individual sites, with their uniquemicrotopography and history, as opposed to canopy harvest regime alone,may yield better predictions of understory species response to harvest.

SCHUUR, EDWARD A. G.," and PAMELA A. MATSON.' 'University ofCalifornia, Berkeley CA 94720 USA; 'Stanford University, Stanford CA94305 USA. The effect of water on litter decay dynamics in uplandrainforest ecosystems.

In mesic to wet ecosystems, the effect of moisture availability on ecosys-tem carbon cycling is often overlooked because water is not in limitedsupply. We tested the assumption that water is a neutral factor in deter-mining patterns of decomposition within humid ecosystems by measur-ing litter decay dynamics across a natural gradient of rainfall. We decom-posed leaves and roots at six sites in Hawaiian montane rainforests simi-lar in temperature regime, species composition, substrate age, and par-ent material, while mean annual precipitation ranged from 2200 to 5100mm/yr. We found a negative relationship between the decay rate con-stant and mean annual precipitation with a 6-fold change in leaf decayrate and a 4-fold change in root decay rate. Results from decompositionof common substrates and reciprocal transplants show that litter qualityhad a stronger effect on the relationship between the leaf litter decayconstant and mean annual precipitation while the reverse was true forroot litter decay. These data suggest that increasing mean annual pre-cipitation has a negative effect on carbon outputs from upland rainforestecosystems and that changes in litter quality can have as strong an effecton decomposition rate as changes in environmental conditions.

SCHUURMAN, GREGOR W. University of Minnesota, St. Paul, MN 55108USA. The relative roles of biotic and abiotic factors in regulating ecosys-tem functioning: Termites and decomposition in the semi-arid savannasof the Okavango Delta, Africa.

Understanding how communities contribute to biogeochemical processesis difficult because in most ecosystems much of mineralization, immobili-zation, and decomposition is mediated by complex mesofaunal and mi-crobial communities. In semi-arid African savannas, however, decompo-sition is carried out primarily by the termite community which is com-posed of readily identified and manipulated species, particularly the sub-family Macrotermitinae and their fungal symbionts (Termitomyces spp.).This relatively "simple" decomposer community permits investigation ofthe role of the community in the ecosystem functioning of the decom-poser subsystem. I experimentally examined how biotic factors (interac-tions among termite species) and abiotic factors (fire and soil moisture)regulate decomposition. These experiments showed that the dominant,mound-building species, Macrotermes michaelseni, displaces non-Macrotermes species from regions near mounds, yet decomposes litterat lower rates. Results also showed that fire had little effect on commu-nity composition or decomposition, whereas higher moisture increasedtermite community activity and decomposition rates. Collectively, thesestudies suggest that variation in decomposer community composition cansignificantly alter ecosystem functioning, that biotic effects may be equalto or stronger than abiotic effects, and that abiotic and biotic processesinteract to determine ecosystem response to environmental variation.

Oral Presentation Abstracts 117

ECOLOGICAL EXCHANGES BETWEEN MAJOR ECOSYSTEMS

GOVERNINGPresident: James A. MacMahon, Biology Department, UttaPresident-Elect: Katherine L Gross, Kellogg Biological Ste00ii,MilthtlftStatePast-President: James H. Brown, Department of Biology University of New NexiCAAlbiittuergiltiVice President for Science: Steward T A. Pickett Institute of Ecosystem StiidieS.fiCoAa, Millbrotk WIt3415Vice President for Finance: William H. Schlesinger, Duke University Dui-MAIM UM.Vice President for Public Affairs: Ann M. Bartuska, USDA Forest Service,RattalC40-' t1in$ton, DC 20090Vice President for Education and Human Resources: Alan R. Berkowitz, Institute Of "Itic,e-fT7-•Route 44A, Millbrook, NY 12545Secretary: Nancy J. Huntly, Department of Biological Sciences, Idaho State University, Pocatello,letiaMember-at-Large: Jill S. Baron, USGS-BRD, Natural Resource Ecology Laboratory, Colorado State Oftly it fort Collins,

CO 80523Member-at-Large: Nelson G. Hairston,Jr., Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853Member-at-Large: Laura F Huenneke, Biology Department, New Mexico State University, Las Cruces, NM 88003

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