John L. Vankat

Diminished Plant Richness and Abundance Below Lonicera maackii, an Invasive Shrub

Abstract The Asian shrub Lonicera maackii (Amur honeysuckle) is now common in many secondary forests in southwestern Ohio and adjacent states. We found lower species richness and abundance in plots (0.5 m2) placed below crowns of L. maackii than in plots placed away: all species (53% lower richness and 63% lower cover), tree seedlings with canopy potential (−41% richness and −68% density) and seed + bud bank (−34% richness and −33% density). Moreover, most individual taxa had lower abundance below L. maackii: 86% of herbs, 100% of trees and 56% of seed + bud bank taxa. In addition, richness of all species and richness and density of tree seedlings decreased in forests with longer residence time of L. maackii.

Species Removals From a First-Year Old-Field Plant Community

The three models of succession described by Connell and Slatyer (1977) were tested by removing selected species from a 1st—yr old field in southwestern Ohio. The facilitation model, which is a restatement of the traditional view of succession, was rejected as inapplicable to the community investigated. Evidence favored the tolerance model over the inhibition models; however, it was concluded that more than one model of succession may apply in the same field at the same time, reflecting the spatial heterogeneity which characterizes old—field communities. The observation that community richness and diversity decreased with species removal contrasts with previous studies and is related to time of field abandonment. See full-text article at JSTOR

Landscape structure and spread of the exotic shrub Lonicera maackii (Amur honeysuckle) in Southwestern Ohio forests.

Abstract The Asian shrub Lonicera maackii (Rupr.) Herder has been widely used as an ornamental in the eastern United States. First planted in Oxford, Ohio, around 1960, it has since spread into forest patches in the surrounding agricultural landscape. Despite its abundance, and its bird-dispersed fruits, the spread of Lonicera maackii has been unequal in different directions, with local distribution limits much farther N than W of Oxford. Our objective was to determine whether the distribution limits of L. maackii in these two directions were correlated with differences in landscape structure: percentage of forest land and degree of forest connectivity. Aerial surveys were used to determine the current distribution of L. maackii in forest patches in a belt transecting N and W from Oxford. The N transect, which had more extensive spread of L. maackii, had greater forest cover and connectivity. In both transects, L. maackii reached its distribution limit when forest cover dropped to <5% and forest connectivity was 0%. Large expanses of agricultural land apparently act as a barrier to the dispersal of this naturalized shrub.

Effects of patch connectivity and arrangement on animal metapopulation dynamics: a simulation study

Abstract We constructed a simulation model of metapopulation dynamics consisting of two or three habitat patches using STELLA. our simulations show that, given the assumptions of the deterministic model, the metapopulation is doomed to global extinction with or without interpatch immigration when all local populations are below minimum viable population (MVP) size. This suggests that for a cluster of scattered small populations, it is preferable to focus on augmenting individual population sizes rather than enhancing interpatch immigration. In the case when at least one of the subpopulations is above the MVP size, there is a critical size for that subpopulation above which the metapopulation persists and otherwise collapses. Also, when a metapopulation system is composed of more than two patches, the spatial configuration in terms of patch connection and the relative position of the above-MVP subpopulation will have significant effects on metapopulation dynamics and persitence. All simulation results from the three-patch animal metapopulation model suggest that both the number of interpatch connections and the magnitude represented by them are crucial for overall patch connectivity. The magnitude of interpatch immigration is positively related to the minimum size of the above-MVP subpopulation in both the two- and three-patch metapopulation systems due to population sink effect. The phenomenon is especially significant when subpopulations in sink patches are well below MVP. Appropriate introduction of stochastic components into the model may increase its realism especially for the cases where all subpopulations are well below MVP. Although the current version of the model involves no more than three patches, it may serve as a general conceptual framework and a specific simulator for modeling metapopulation dynamics incorporating a variety of spatial arrangements of habitat patches.

Trail corridors as habitat and conduits for movement of plant species in Rocky Mountain National Park, Colorado, USA

Ground-layer vegetation was sampled along selected trail corridors to determine whether corridors provide habitat for certain species and act as conduits for species movement. Patterns of plant species composition were analyzed in relation to distance from trail edge, level of trail use, and distance from trailheads, junctions, and campgrounds. Species composition was significantly affected by distance from trail edge and level of trail use, as species were favored or inhibited by the corridor, depending upon their growth habits. Species composition was also affected by distance from trailheads. These findings, along with the presence of exotic species, indicate that trail corridors in Rocky Mountain National Park function as habitat and conduits for movement of plant species.

Middle and high elevation coniferous forest communities of the North Rim region of Grand Canyon National Park, Arizona, USA

We examined the composition and structure of forest communities in a 3700 ha watershed in relation to environmental gradients and changes in land management practices. We identified four mixed-conifer forest types dominated by different combinations of Abies concolor, Picea pungens, Pinus ponderosa, Populus tremuloides, and Pseudotsuga menziesii, and a spruce-fir type dominated by Picea engelmannii and Abies lasiocarpa. The forest types occur in a complex pattern related to elevation and topographicmoisture gradients and variations in past fire regimes. However, widespread regeneration of A. concolor following possible changes in the fire regime in the late 19th century and continuing with institution of a fire suppression policy early in the 20th century is producing a more homogenous mixed-conifer forest with greater horizontal and vertical continuity of fuel. This shift toward landscape homogeneity not only may adversely affect biodiversity, but also may be perpetuated as the probability of large, high-severity fires increases with continued fire suppression.

Forest Colonization and Developmental Growth of the Invasive Shrub Lonicera maackii

Abstract The invasive shrub Lonicera maackii (Rupr.) Herder (Amur honeysuckle) dominates the understory of many deciduous forests in southwestern Ohio and other areas. Extensive sampling of an isolated population of L. maackii was used to elucidate its colonization of a forest woodlot and subsequent growth and development. The current population age structure indicated that colonization likely occurred by a series of small dispersal events. The population remained small for about ten years and then increased dramatically, presumably due to the seed reproduction of the early colonizers. Young prereproductive shrubs are characterized by rapid height growth and high stem recruitment. After shrubs become reproductive at age 5–8, height growth continues but basal stem recruitment is reduced and radial growth increases shrub basal area. Allocation of primary production apparently shifts from stem recruitment and height growth in young shrubs to a balance of height growth, radial expansion and reproduction in older shrubs.

Temporal variation in the woody understory of an old-growth Fagus-Acer forest and implications for overstory recruitment

Abstract. Changes in woody vegetation were examined over eight years, using a 1.05-ha permanent plot in which the location of every shrub and tree > 1m height was mapped. There was little change in the overstory vegetation, as expected for an old-growth forest. Much greater change occurred in the understory, primarily related to a 40 % increase in density. Differences occurred among species in the under-story, as Acer saccharum and Prunus serotina increased and Fraxinus americana and Fagus grandifolia decreased. Canopy gap dynamics are implicated in differences among species in the establishment and growth of individuals in the understory and their recruitment into the overstory. It is concluded that because understory is temporally variable, overstory recruitment from the understory may take different courses at different times in the same forest.

AN AREA-BASED MODEL OF SPECIES RICHNESS DYNAMICS OF FOREST ISLANDS

Abstract Landscape fragmentation results in forest islands surrounded by a matrix of agricultural species, at least above the minimum size necessary for the interior species. The species richness dynamics of these forest islands can be predicted by using mathematical modelling. Our area-based model describes the temporal dynamics of species richness of forest islands and depicts relationships between species richness and the edge, interior, and total area of forest islands. The mathematical model consists of a group of differential equations, and we also present results of a STELLA simulation model on woody species of deciduous forest islands. Simulations show that changes in species richness occur only when the area of forest islands is smaller than some threshold level which is different for the edge and interior species groups, that edge and interior species respond differently to the changes in island area, and that time delays embedded in community level responses may be important to understanding species richness dynamics of forest islands. The STELLA model is capable of simulating the dynamics of edge, interior, and total species richness with a variety of additional scenarios involving the change in area of forest islands.

The importance of environment vs. disturbance in the vegetation mosaic of Central Arizona

Abstract The vegetation of central Arizona is a mosaic of four vegetation types: chaparral, chaparral grassland, woodland, and woodland grassland. We analysed ten environmental variables, three disturbance variables, and five disturbance indicators to answer the question: What is the relative importance of environment and disturbance in explaining the vegetation pattern of our study area? We found that chaparral, chaparral grassland, and woodland are differentiated primarily by environmental factors and have high stability in the landscape. In contrast, woodland grassland is differentiated primarily by disturbance and is likely an early-successional stage of woodlands. Although other researchers have indicated that semi-arid vegetation is generally unstable, the vegetation of central Arizona is composed of two systems: those with a more stable landscape position determined primarily by environmental factors and those with a less stable landscape position determined primarily by disturbance factors. Nomenclature: Kearney & Peebles (1960) and McDougall (1973). Abbreviations: A = Grazing allotment size and chance corrected within-agreement; C = Number of permitted domestic grazing animals; CCA = Canonical Correspondence Analysis; DCA = Detrended Correspondence Analysis; MRPP = Multi-Response Permutation Procedure; NMS = Non-Metric Multi-dimensional Scaling; S = Fire size class; T = Grazing period; W = Probability that fire burned a stand or a conversion event took place.