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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 support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. The decreased ability of northern red oak (Quercus rubra) to regenerate throughout its range in the eastern United States has important ecological and economic implications. We studied regeneration of northern red oak in oak and pine stands on moderately productive sites in northern Lower Michigan. Our objectives were (1) to investigate the hypothesis that regeneration of northern red oak is more successful in pine than in oak stands and (2) to test whether removal of potential overstory and understory competitors increases regeneration success on moderately productive sites.Northern red oak acorns and 2-yr-old nursery seedlings were planted in spring 1991 in three natural oak stands and three red pine (Pinus resinosa) plantations on comparable, moderately productive sites. Each stand contained four canopy cover treatments: clearcut, 25% cover (50% the first year), 75% cover, and uncut. Each canopy cover treatment contained four understory treatments: herb-layer removal, shrub-layer removal, litter removal, and control. Seedling survival, performance, and damage due to deer and late spring frosts were quantified along with vegetation characteristics, light, soil moisture, air temperature, soil temperature, and precipitation during the 1991 and 1992 growing seasons. Survival of seedlings was significantly lower in the pine than in the oak stands; the pine stands had a higher incidence of white-tailed deer browsing and lower levels of belowground resources than the oak stands. Canopy cover treatments produced a gradient from high stress (low light and soil moisture) and low disturbance (slight browsing and frost damage) in uncut plots to low stress (high light and soil moisture) and high disturbance (high browsing and frost damage) in clear-cut plots. Understory vegetation developmentand soil temperature were low in uncut plots, high in clear-cut plots, and intermediate in plots with partial overstory removal. Despite poor growth, the mortality of seedlings planted in uncut plots was low. In contrast, mortality was high and surviving seedlings exhibited good growth in clearcuts. Understory treatment effects were slight compared with overstory treatment effects. Results on our sites (1) do not support the hypothesis that regeneration success of northern red oak may be greater in pine than in oak stands and (2) indicate that the positive effects of removing potential competitors on seedling growth and physiological status may be compromised by simultaneous negative effects of browsing and frost damage. Key words: competition; deer browsing; field experiment; frost; n...

. Kopp2, L.B. smart2, C.A. ~a~n a r d~, J.G. 1sebrands4, G.A. ~u s k a n~ and L.P. ~b r a h a m s o n~9Efforts aimed at genetic improvement of Salix are increasing in North America. Most of these are directed towards developing improved clones for biomass production, phytoremediation, nutrient filters, and stream bank stabilization in the Northeast and North-central United States. Native species are of primary interest, but a small number of clones containing non-native germplasm are also being used in the breeding program to provide valuable traits. Parent combinations for controlled crosses are being selected with the hope of maximizing the probability of producing clones exhibiting heterosis for traits of interest, such as rapid early growth, pest resistance, general adaptability, etc. The present strategy is to test as many parent clone combinations as possible, and then repeat the most promising crosses to produce large families from which the best clones will be selected for further testing. Molecular fingerprinting technology will be applied to accelerate the rate of improvement. National and international cooperation would facilitate regional clone development and promotion of willow as a bioenergy crop.Key words: Salix, biomass production, breeding, heterosis, molecular fingerprinting Les efforts destinks h l'amklioration gknttique du Salix croissent sans cesse en AmCrique du Nord. La majeure partie des efforts est concentrke sur le dkveloppement de clones amCliorks pour la production de biomass?, la phytoremkdiation, les fdtres d'k1Cments nutritifs et la stabilisation des rives des cours d'eau dans le nord-est et le centre-nord des Etats-Unis. L'intkret porte avant toute chose sur les espbces indigbnes, mais un petit nombre de clones contenant des cellules embryonnaires non indighnes sont Cgalement utilisCs dans le programme de reproduction afm d'apporter des caractCristiques intkressantes. Les combinaisons parentales pour obtenir des descendants de provenance conMl& sont choisies dans le but de maximiser la probabilitk de produire des clones dCmontrant une hCerogCnCit6 des caractCristiques intCressantes, comme la croissance initiale rapide, la rksistance aux ravageurs, l'adaptabilitk gCnCrale, etc. La stratCgie actuelle est de tester autant de combinaisons parentales de clones que possible, et de reproduire par la suite les descendants les plus prometteurs pour produire des grandes familles desquelles les meilleurs clones seront choisis pour poursuivre les tests. La technologic de l'empreinte digitale molCculaire sera utilisCe pour accklkrer le taux d'amklioration. La coopkration nationale et internationale faciliterait le d6veloppement de clones rkgionaux et la promotion du saule en tant que resource bioknergetique.

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