Donald J. Leopold

Pathogens, Patterns, and Processes in Forest EcosystemsPathogens influence and are influenced by forest development and landscape characteristics

lthough pathogens are regarded as agents responsible for the specific dynamics of natural forest communities (Dickman 1992, Dinoor and Eshed 1984, Haack and Byler 1993, van der Kamp 1991), they have received little attention at the landscape level, especially compared to catastrophic abiotic disturbances, such as fire and blowdowns (Foster and Boose 1992, Heinselman 1973). With so much emphasis today on ecosystem management and the maintenance of natural disturbance regimes, the role of pathogens deserves careful scrutiny. Pathogens (biotic agents that incite disease) differ from many abiotic disturbances by selectively eliminating the less vigorous or genetically unfit individuals of a population, yet the biotic and abiotic agents are similar in that both function to recycle essential elements and to alter forest development and landscape patterns. Pathogen interaction with abiotic disturbance to control the direction and rate of forest succession also has received minimal attention, although such

STRUCTURAL CHARACTERISTICS OF OLD-GROWTH, MATURING, AND PARTIALLY CUT NORTHERN HARDWOOD FORESTS

Live tree diameter distributions, and abundance and quality of standing and downed coarse woody debris (CWD), were compared among three northern hardwood stand types in the Adirondack Mountains of New York, USA: old growth; partially cut, uneven-aged with 40–50 cm maximum residual diameters; and maturing, even-aged, 90–100 yr old, postfire. Downed CWD (stumps ≤1 m tall and logs) volumes in the old-growth, partially cut, and maturing stands were 139, 69, and 61 m3/ha, respectively. Large (≥50 cm diameter) CWD comprised 17%, 13%, and 4% of the total downed CWD volume in the old-growth, partially cut, and maturing stands respectively. Approximately one-half the large CWD in the partially cut stands was in the form of cut stumps. Standing CWD (stumps >1 m tall and standing dead trees) basal areas averaged 8.6, 1.2, and 4.1 m2/ha in the old-growth, partially cut, and maturing stands, respectively. Basal area of large (≥50 cm diameter) standing CWD averaged 70%, 0%, and 5% of the total in the old-growth, partia...

Tree dynamics in an old-growth, deciduous forest.

Abstract In 1926, all trees (⩾ 10.2 cm dbh) were measured, tagged and mapped in a 20.6 ha, old-growth oak forest within the extensively farmed Tipton Till Plain of Indiana. All trees (⩾ 10.0 cm dbh) within the central 8.5 ha of this forest were measured, tagged and mapped again in 1976. Stand density and basal area increased by 93.9 and 30.8%, respectively, to 320 stems ha−1 and 31.0 m2 ha−1. Density of Ulmus americana and Acer saccharum increased most; the largest density decreases were of Quercus rubra and Fraxinus americana. Basal area increases were greatest for Q. rubra, A. saccharum, and Q. alba. The most important species in 1926 were (in order of decreasing importance value, IV) [IV = (relative density + relative basal area)/2] Q. rubra, F. americana, Q. alba, Q. macrocarpa and U. americana. In 1976, Q. rubra, U. americana, A. saccharum, Q. alba and F. americana were the most important. Nearly half (46.9%) of those trees measured in 1926 had died by 1976; however, mortality varied by species, size-class and size-class within a species. Species with low mortality (⩽ 25%) included A. saccharum, Aesculus glabra, Carya spp. (except C. cordiformis), Celtis occidentalis and Quercus spp. (except Q. rubra). Species with high mortality (⩾ 75%) included Fagus grandifolia, Ulmus americana, U. rubra, and Fraxinus nigra. The majority of ingrowth trees within a 5 m radius gap of dead dominant or codominant trees were U. americana (30% of total), followed by A. saccharum (20%). No species had greater than 50% of its ingrowth within a 5 m radius of the dead trees. Diameter growth of surviving trees varied greatly among species, size-class and size-class within a species. Q. rubra and F. americana had greatest average diameter increases after 50 years (21.8 and 18.4 cm dbh, respectively). Mortality was relatively low and diameter growth high in the 50.0–69.9 cm diameter class for all species combined. The rotated-sigmoid curve, rather than the negative exponential, appears to best describe the size-class distributions of all species in 1976. An analysis of the size-class distribution of all species suggests that early and mid-seral species such as Gleditsia triacanthos, Juglans nigra, and Quercus spp. are gradually being replaced by more tolerant, late seral and climax species such as Acer saccharum, Aesculus glabra, Carya ovata and others. Despite the old-growth appearance of this forest much structural and compositional changes have been taking place.

Vegetation management for the maintenance and conservation of butterfly habitats in temperate human-dominated landscapes

Abstract Many temperate butterfly species occur in habitats where human activities have altered the natural or long-term disturbance regime, and current activities modify the structure and availability of butterfly habitats over several spatial and temporal scales. Indeed, human activities modify key ecological processes sufficiently that the maintenance of some butterfly populations depends on human intervention to provide suitable habitat. Combined changes in historic and current disturbance regimes and human land-use practices necessitate active vegetation and habitat management to conserve and expand many butterfly populations. Efforts to protect temperate butterfly habitats often have resulted in successional changes that reduce habitat suitability. Butterfly habitats commonly deteriorate through a reduced intensity and frequency of long-term disturbance or management patterns that result in smaller and fragmented patches of early successional habitat. Fragmentation of otherwise continuous habitats can result in the forced dependence of a metapopulation structure. Because some butterfly larvae require one or a few host plants or adults are selective for nectar or oviposition sites, habitat management plans that include selection of an appropriate site for subsequent vegetation management activities may enhance conservation efforts. Vegetation management activities within an area can be coordinated to provide a mosaic landscape with habitats suitable for numerous species. Recommended vegetation management strategies vary with plant community type, historic disturbance regime, desired vegetation structure and composition, spatial pattern of habitat patches, land ownership patterns, and economic constraints. Because butterflies respond directly and indirectly to vegetation management and to the mosaic nature of habitat patches within the landscape, management plans must accommodate the constraints of the regional landscape and the spatial and temporal dynamics of the prescribed disturbance or management regime. We review efforts to manage temperate plant communities for butterfly habitat, and discuss general strategies for developing a vegetation management program for butterfly habitats in human-dominated landscapes. A case study of Karner blue butterfly habitat conservation efforts is provided.

Community characteristics and vegetation management of Karner blue butterfly (Lycaeides melissa samuelis) habitats on rights-of-way in east-central New York, USA

Lupinus perennis L. (blue lupine) and associated nectar species represent critical habitat for the endangered, federally listed Lycaeides melissa samuelis Nabokov (Karner blue butterfly), and exist on transmission line rights-of-way in New York, USA. While rights-of-way provide habitat and may represent a potential corridor for butterfly dispersal among sites, few data are available to quantify habitat characteristics. We investigated rights-of-way in east-central New York to: characterize L. perennis populations and associated plant communities; quantify the relationship between L. perennis and both environmental characteristics and management schemes; and assess the relationship between butterfly population size and habitat characteristics. Lupinus perennis individuals were robust in communities with Comptonia peregrina, species in the Poaceae, and Daucus carota. Lupinus perennis and L. m. samuelis abundance were correlated positively with high relative light intensity and large patch areas, and inversely correlated with the number of years since the last management activity. There was no clear relationship between vegetation patterns and the different types of recent rights-of-way vegetation management schemes. To enhance L. perennis and L, m. samuelis populations, vegetation management on rights-of-way should reduce trees and shrubs, and increase light intensity to a level of photosynthetically active radiation that exceeds 65% of the maximum possible light intensity. Other manageable conditions associated with a larger index of L. m. samuelis population size include larger habitat areas and more frequent vegetation management that reduces the cover and density of woody species. The relationship between both L. perennis clump size and L. m. samuelis population size with the distance to the warm edge of the right-of-way suggests a potential influence of microclimate and merits further attention. Vegetation management based on infrequent mechanical removal of woody stems (e.g. handcutting, mowing, brush-hogging) was associated with increased woody plant density. A more frequent mechanical treatment or a seasonally timed application of an appropriate herbicide would be more effective at controlling the woody vegetation that competes with L. perennis.

Understory response to springtime prescribed fire in two New York transition oak forests

Abstract Portions of two south-central New York transition oak stands received 0, 1 or 2 springtime prescribed fires between 1980/1981 and 1984. Observations 8–12 years later showed that forb richness, forb and shrub cover, and the importance values of forbs relative to shrubs increased in areas receiving one or two fires. Fagus grandifolia, Dennstaedtia punctilobula, Gaultheria procumbens and Trientalis borealis exhibited small, but detectable increases in importance values in burned areas. The importance values of Quercus rubra, Kalmia latifolia and Viburnum acerifolium decreased in burned areas. Areas receiving greater intensity fires contained taller tree regeneration and greater shrub cover, but no important changes in community composition could be attributed to fire intensity. An apparent relationship between rhizome depth and post-fire competitiveness of dominant perennial forbs and shrubs suggests the importance of below-ground morphological traits on survival and recovery following fire. Overall, the 12-year, post-burn cover and density of understory vegetation increased in burned areas and in areas receiving greater intensity fires, however, community composition remained largely unaffected by these springtime prescribed fires.

Linking landscape properties to local hydrogeologic gradients and plant species occurrence in minerotrophic fens of New York State, USA: A Hydrogeologic Setting (HGS) framework

We present a Hydrogeologic Setting (HGS) framework and the results of subsequent field evaluation for minerotrophic fens throughout New York State, USA. HGS uses a hierarchical approach to link landscape properties to local environmental gradient and, therefore, the plant communities that are associated with calcareous wetlands. This framework was organized into three general classes (i.e., chemical, physical, and spatial), which cumulatively represent the primary top-down factors driving fen occurrence. For 45 fen sites in the New York Natural Heritage Program (NYNHP) database, landscape setting was inferred based on review of published materials (e.g., geologic, topographic, soils maps, and reports). To examine the relationship between HGS and local environmental gradients, nested observation well clusters were placed in 30 of the fen sites. Environmental gradients were quantified in the field (e.g., water depth, pore water pH, temperature, and specific conductivity) and laboratory (e.g., dominant ion and major limiting nutrients concentrations). Statistical analyses were used to relate HGS to local environmental gradients, ecological community, and fen indicator species occurrence. Results suggest that known New York fens occupy distinct hydrogeologic settings, that HGS is significantly correlated to local environmental gradients, and that HGS and local environmental gradients are significantly related to fen ecological community and indicator species occurrence. We used this HGS framework for fens, but the rationale provided may be applied more broadly or narrowly to a range of ecosystem types.

The role of canopy gaps in maintaining vascular plant diversity at a forested wetland in New York State1

conifer swamp. Our study site, Nelson Swamp, has high documented species richness and supports a large number of state-protected species. Understory cover and species richness at both the quadrat and gap scale were compared among closed canopy areas and gaps in three size classes. To assess differences in the understory environment among the three size classes, we compared light, hydrology, and microtopography. We also tested for correlations between gap species richness and light, wetness, and microsite heterogeneity to determine which aspects of the gap environment might influence vascular plant diversity therein. There was higher quadrat- and gap-level species richness in gaps than in closed canopy areas. Small gaps did not appear to offer a physical environment substantially different from non-gaps, as no differences in their understory communities were apparent. Mid-sized and large gaps had higher species richness, substrate heterogeneity, and water table fluctuation than small gaps. Based on the correlations, the individual factors influencing species richness at the gap scale were depth to water, water level fluctuation, and microtopographic variability, indicating the importance of hydrology over light as a species control. Although gaps and non-gaps shared many of the same species, there were distinct subsets of species that were more important in either type of community. Based on these subsets, closed canopy areas and large gaps can be viewed as two ends of a continuum corresponding to light and hydrology gradients. Out of all the species encountered, 10 percent were found exclusively in gaps, and none were found only under closed canopy. Thus, these gaps are not only sites of higher overall plant growth, but also areas that allow rare species to persist.

Vascular plant species richness and rarity across a minerotrophic gradient in wetlands of St. Lawrence County, New York, USA

Thirteen wetlands in St. Lawrence County, NY were sampled to examine the effect of a minerotrophic gradient on vascular plant species richness and rarity. Wetlands ranged from organic soil based poor fens (average conductivity 46.40 microsemens, average Ca 3.55 ppm) to mineral soil based rich fens (average conductivity 342.10 microsemens, Ca 23.00 ppm). Vascular plant species richness was sampled during 1990 in randomly located 1.0 m2 quadrats. Specific conductivity, presence or absence of hummocks, and water depth predicted 62% of the variation in richness. Richness increased as conductivity increased until 413 microsemens at which a down trend became obvious. The negative curvilinear relation between conductivity and richness is in accordance with the hump-backed model of Grime but occurs at high rather than intermediate conductivity values. State-listed rare species were found in species-rich wetlands only and had a mean associated richness value of 14.50 species m-2. This relationship should be taken into consideration when selecting wetlands for protection or managing wetlands for maximum plant diversity.

EFFECTS OF DRAINAGE DITCHES ON VEGETATION PATTERNS IN ABANDONED AGRICULTURAL PEATLANDS IN CENTRAL NEW YORK

Drainage ditches and ground-water gradients in abandoned agricultural sapric peatlands (mucklands) produce distinctive vegetation patterns. Ditches in abandoned mucklands were ineffective in creating ground-water depression in adjacent soil, while ditches in a newly-cleared muckland were effective in doing so. Upon abandonment, drainage ditches are subject to bank erosion and sedimentation. Coupled with years of soil subsidence and an altered hydrologic regime, ditches lose effectiveness in draining and function merely as small-scale topographic depressions, providing linear zones of seasonally high water levels. Species are distributed on abandoned mucklands in association with soil moisture conditions induced by topographic variation at both small (i.e., ditches) and larger (i.e., site-wide) spatial scales. Vegetation that is usually restricted to moist or saturated soils had greater cover closer to or within drainage ditches or in other topographically low areas, while species with low fidelity to saturated soil dominated the remaining drier areas. Some shrub species had slightly greater stem densities either within or immediately adjacent to ditches, resulting in a “parallel” distribution (i.e., illustrating ditch fidelity). Species having higher affinity to lower soil moisture conditions, such as quaking aspen (Populus tremuloides), showed significantly greater stem density in areas farther away from ditches. Ground-water levels are of primary importance in affecting distribution patterns on naturally revegetating, abandoned agricultural mucklands. The accuracy of the wetland indicator status for woody and herbaceous species encountered on these abandoned mucklands is supported quantitatively by direct gradient analysis. The functioning of existing drainage ditch systems should be assessed prior to any mitigation or restoration activities.