Stephen B. Horsley

White-tailed deer impact on the vegetation dynamics of a northern hardwood forest

Considerable controversy has arisen over the management of white-tailed deer in eastern landscapes where there is evidence of damage to forest vegetation, crops, and wildlife habitat attributable to deer. We examined the impact of 4, 8, 15, and 25 deer/ km 2 on herbaceous layer abundance and tree seedling density, height development, species composition, and diversity for 10 yr in a repeated-measures randomized-complete-block experiment at four replicate cherry-maple forest sites in northwestern Pennsylvania, USA. At each 65-ha site, deer were placed in 13- or 26-ha fenced enclosures in which the landscape composition and forage production of a forest managed on a 100-yr rotation was simulated by clear-cutting 10% of each area and thinning 30%. Vegetation was sampled 0-1, 3, 5, and 10 yr after treatment (YAT). We analyzed vegetative treatment responses separately in each silvicultural treatment. Time was an important factor mediating responses at all deer densities. Rubus spp. abundance in all silvicultural treatments and the density of striped maple (STM) in clearcuts and birch (BI), American beech (AB), and red maple (RM) in thinnings showed negative trends with increasing deer density. As deer density increased, we found negative linear trends in the height of BI, RM, and AB in clearcuts; in the height of AB, RM, and STM in thinnings; and in the height of AB and RM in uncut stands. Species richness showed a negative linear trend with increasing deer density in all silvicultural treatments. Conversely, species avoided by deer or resilient to deer browsing increased with in- creasing deer density. Percent cover of ferns, grasses, and sedges showed positive linear trends with deer density in clearcuts and in thinnings. The percentage of plots dominated by black cherry (BC) increased with increasing deer density in cut and uncut stands. The net result of increased deer impact was an altered trajectory of vegetation development dominated by species avoided by deer or resilient to deer browsing. Negative effects on vegetation became significant at deer impact levels well below those observed in many eastern forests. Moreover, species not browsed or resilient to browsing may have indirect effects on vegetation development through plant-plant interactions and on wildlife habitat quality for small mammals, birds, and deer. Managing these impacts is important as pressures to harvest and fragment eastern forests accelerate.

Sugar maple growth in relation to nutrition and stress in the northeastern United States

Sugar maple, Acer saccharum, decline disease is incited by multiple disturbance factors when imbalanced calcium (Ca), magnesium (Mg), and manganese (Mn) act as predisposing stressors. Our objective in this study was to determine whether factors affecting sugar maple health also affect growth as estimated by basal area increment (BAI). We used 76 northern hardwood stands in northern Pennsylvania, New York, Vermont, and New Hampshire, USA, and found that sugar maple growth was positively related to foliar concentrations of Ca and Mg and stand level estimates of sugar maple crown health during a high stress period from 1987 to 1996. Foliar nutrient threshold values for Ca, Mg, and Mn were used to analyze long-term BAI trends from 1937 to 1996. Significant (P < or = 0.05) nutrient threshold-by-time interactions indicate changing growth in relation to nutrition during this period. Healthy sugar maples sampled in the 1990s had decreased growth in the 1970s, 10-20 years in advance of the 1980s and 1990s decline episode in Pennsylvania. Even apparently healthy stands that had no defoliation, but had below-threshold amounts of Ca or Mg and above-threshold Mn (from foliage samples taken in the mid 1990s), had decreasing growth by the 1970s. Co-occurring black cherry, Prunus serotina, in a subset of the Pennsylvania and New York stands, showed opposite growth responses with greater growth in stands with below-threshold Ca and Mg compared with above-threshold stands. Sugar maple growing on sites with the highest concentrations of foliar Ca and Mg show a general increase in growth from 1937 to 1996 while other stands with lower Ca and Mg concentrations show a stable or decreasing growth trend. We conclude that acid deposition induced changes in soil nutrient status that crossed a threshold necessary to sustain sugar maple growth during the 1970s on some sites. While nutrition of these elements has not been considered in forest management decisions, our research shows species specific responses to Ca and Mg that may reduce health and growth of sugar maple or change species composition, if not addressed.

Prescribing regeneration treatments for mixed-oak forests in the Mid-Atlantic region

Includes guidelines for using the SILVAH decision-support system to perpetuate oak forests in the Mid-Atlantic region. Six chapters provide information on values of oak forests, inventory methods, key decision variables, decision charts, and silvicultural prescriptions, as well as guidance on fostering young stands. Sample tally sheets and SILVAH computer printouts are included in the Appendix.

Glucose-1-benzoate and prunasin from Prunus serotina

Abstract β- d -Glucopyranose 1-benzoate and prunasin have been isolated from the leaves of Prunus serotina . Both can yield benzoic acid, a potential allelopathic inhibitor of Acer rubrum .

Role of allelopathy in hay-scented fern interference with black cherry regeneration.

Black cherry (Prunus serotina Ehrh.) seedlings survive and grow poorly under dense hay-scented fern (Dennstaedtia punctilobula Michx.) ground cover in the understory of partially cut Allegheny hardwood stands. Previous field studies showed that there were about 80% fewer black cherry seedlings where fern was present than where it was absent. Allelopathic interference with black cherry seed germination, seedling survival, and growth by hay-scented fern foliage leachates, root washings, and soil transformation products was evaluated in a series of field, greenhouse, and laboratory experiments. Black cherry seeds germinated as well in the presence of hay-scented fern or its leachates as when they were absent in both the laboratory and the field. Fern foliage leachates and root washings did not affect black cherry growth in sand or natural soil cores in the greenhouse. There also was no evidence that hay-scented fern natural products or their soil transformation products built up in the soil. A two-year manipulative field experiment to separate effects of hay-scented fern foliage shade from foliar leaching showed that foliage shade significantly reduced black cherry seedling survival and growth; foliage leachates had no effect. Results of the studies led to the conclusion that allelopathy does not play a direct role in hay-scented fern interference with black cherry seedling establishment in partially cut Allegheny hardwood stands.

Sampling to assess species diversity of herbaceous layer vegetation in Allegheny hardwood forests

The optimum frequency and time of sampling required to generate comprehensive diversity indices of herbaceous species in Allegheny hardwood forests was studied. Four 8-ha sites on the Allegheny National Forest were sampled monthly from May to August in 1992 and 1993 for herbaceous layer species composition and percent cover.

Analysis of forest health monitoring surveys on the Allegheny National Forest (1998-2001)

Describes forest vegetation and health conditions on the Allegheny National Forest (ANF). During the past 20 years, the ANF has experienced four severe droughts, several outbreaks of exotic and native insect defoliators, and the effects of other disturbance agents. An increase in tree mortality has raised concerns about forest health. Historical aerial surveys (1984-98), Forest Inventory and Analysis plot data collected in 1989, and FHM plot data collected 1998-2001 were analyzed to compare disturbed and undisturbed areas. Tree mortality and crown dieback levels were compared between undefoliated areas and areas defoliated by cherry scallopshell moth, elm spanworm, and gypsy moth. American beech mortality was compared inside and outside the beech bark disease killing front. This study illustrates the value of an intensified grid of P3 plots and demonstrates the integration of aerial survey and plot data.