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Land conversion due to human activities produces distinctive spatial patterns across the landscape. It remains unclear, however, how particular spatial arrangements of remnant habitat patches influence species persistence. We present a conceptual model of landscape change that focuses explicitly on habitat spatial arrangement. Four sequences, characterized as shrinkage, bisection, fragmentation, and perforation, differ qualitatively in the spatial arrangement of intact habitat and differ quantitatively in boundary length, amount of interior area, and connectivity. We tested the predictions of this conversion sequence model in a \"microlandscape\" field experiment with insects in a native grassland habitat. The four conversion sequences significantly influenced the species composition of the above-ground insect community, and insect species groups varied in their responses. Four patterns were evident from the field experiment: (1) as habitat decreased, insect density rose sharply on small dispersed patches of the bisection and fragmentation sequences, an effect less evident in the large remnant patch of the shrinkage sequence; (2) species richness declined only in the case of shrinkage, whereas richness increased in the fragmentation sequence; (3) most individual species examined responded similarly to the community as a whole; and (4) large rare species were concentrated in remaining habitat of the shrinkage and fragmentation sequences. Overall, the shrinkage and perforation sequences, which had high connectivity, were similar to one another in species composition, while the bisection and fragmentation sequences, which had low connectivity, were similar to one another. Based on these results, we conclude that a spatial pattern of land conversion that maintains one or more large, closely spaced remnant patches of native vegetation is essential for species persistence.

A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15-20% of the United States is ecologically impacted by roads.

Woody plants and evidence of browsing were measured on eight reclaimed strip mines in Maryland and West Virginia to see whether revegetation patterns differed adjacent to concave, straight, and convex forest boundaries. Two clonal species predominated (Rubus allegheniensis and Robinia pseudoacacia), followed in abundance by three wind-dispersed species (Fraxinus americana, Acer rubrum, Betula lenta), and a variety of animal-dispersed species. Mine transects adjacent to concave forest boundaries had 2.5 times as many colonizing stems as those next to convex boundaries. Stems of colonizing species extended >61 m from concave boundaries, but rarely > 13 m from convex boundaries. Stem density of all the common animal-dispersed species was correlated with their abundance in the adjacent forest edge, whereas no relationship existed for Robinia or the wind-dispersed species. Evidence of browsing was greater adjacent to concave boundaries than opposite convex boundaries. These strikingly different colonization patterns appear to be primarily the result of the immigration process interacting directly with shape as a spatial characteristic. Through time, a @'concave-convex reversal@' in boundary form is evident. This results from a @'cove concentration effect@' where the greatest boundary expansion rate is in coves being colonized. Almost all patterns next to straight boundaries were intermediate between those opposite concave and convex boundaries. We conclude that boundary form may exert a powerful control over adjacent ecosystems in a landscape. This presents significant opportunities for planning and managing surface mines and other colonizing areas.

The role of herbs in affecting tree seedling patterns was investigated in an old-growth hemlock-hardwood forest in Cathedral State Park, West Virginia. Herb species cover, tree seedling density, and overhead foliage were sampled along with midsummer soil pH, soil moisture, and light intensity in 20 selected herb patches and 440 30 x 30 cm plots. Analyses of the patch data showed significant correlations of seedlings of major tree species: Prunus serotina, Acer rubrum, Tsuga canadensis, and Betula spp., with leading herb species (Dennstaedtia, Mitchella, Lycopodium, and Oxalis). Each tree species had few seedlings in some herb species patches, but was independent of or concentrated in other patches. Herb species were spatially related to other herb species, but showed little correspondence to soil pH, soil moisture, and light intensity patterns. Analyses of plot samples supported each of the above results. In addition, total tree seedling density was inversely correlated with total herb cover, but neither total seedling density nor number of seedlings of leading tree species was correlated with the abiotic factors. Seedling density and herb cover varied with the height and composition of the overhead canopy foliage. Based on the data from the two sampling approaches in this old mesic woods, we conclude that herb patches play a major role in determining the density and distribution of seedlings of leading tree species, and that the distribution of herb patches is significantly affected by both tree canopy foliage and other herb patches. Dynamic models of forest growth, species diversity, and composition must include herbs.

Mosses of the coastal dune ecosystem were studied to determine whether a tolerance to chronic salt spray had evolved, if so, whether it was a species or population level trait, and whether it is important in the dune moss community. Ceratodon purpureus (Hedw.) Brid., Aulacomnium palustre (Hedw.) Schwaegr., and Polytrichum commune Hedw. from three different New Jersey habitats were misted with salt spray to simulate the secondary dune environment. No species survived salt spray alone. When rain was added however, Ceratodon did exhibit some salt tolerance. The results suggest that salt spray is sufficient to severely restrict the dune moss community, and that of the possible strategies, Ceratodon has evolved a salt tolerance, Aulacomnium and Polytrichum depend on salt dilution, and that recovery following salt stress is of secondary importance. There were no significant differences noted in response to salt spray among populations within a species, and this result was not affected by varying the substrate. Therefore salt tolerance is a species level trait, not a population level trait, suggesting that ecotypic differentiation has not taken place in response to salt spray.

State fire records and literature citations were examined to estimate both regional fire frequency and point fire frequency. The number of annual wild-fires in the 550,000 hectare Pine Barrens has remained at approximately 1100 since 1940 when fire control became effective. The total area burned annually dropped sharply from about 22,000 ha during 1906-1939 to 8,000 ha in the past four decades. Extensive wildfires of 8,000-16,000 ha each are common. Since 1838, about every two decades on the average, 10% or more of the predominant pine and oak forest burns in a single year (50,000 ha). An average point in the pine and oak forest burns currently at about 65 year intervals, compared with 20 year intervals earlier this century. The number of wildfires in the region correlates linearly with the number of dry months in a year. However, the area burned annually is constant with up to four dry months during the January-to-September period; both average and variability of area burned increases with five or more dry months. The results suggest the upland Pine Barrens are a mosaic of fire-caused patches at two levels of scale: a fine-grained scale of small (averaging 6 ha) young patches imprinted on a coarse-grained scale of large (several tens of ha), variable-sized patches more than four decades old. The drop in point fire frequency favors (a) non fire-adapted populations, (b) hardwoods swamp replacing cedar swamp, and (c) loss of the coarsegrained landscape mosaic.

Lichens containing blue-green algae are abundant (13,600/ha; total biomass 5.7 kg/ha) in a Colombian montane rain forest. These noncrustose lichens grow mainly on 3-12 cm diam twigs and small branches, 12-25 m high at the top of the crowns of canopy and subcanopy trees. They are rare below 4 m. Eighty-six% of the lichens contain Nostoc and, based on published laboratory nitrogen-fixation studies of lichenized Nostoc, these lichens fix an estimated 1.5-8 kg N/ha@?yr, equivalent to the estimated range of total nitrogen input in precipitation. This lichen phenomenon is probably widespread in rain forests of the American tropics. These results reemphasize the importance of the epiphyte community in the canopy layer of the rain forest ecosystem.

Lichens containing blue-green algae were measured by transects and reconnaissance in six major temperate vegetation types to estimate possible significance in annual nitrogen budgets and patch dynamics within ecosystems, and to estimate how a functional ecosystem attribute, i.e. nitrogen fixation, correlates with vegetation structure. Lichen cover was negligible in sagebrush desert, pinyon-juniper woodland, ponderosa pine forest and alpine tundra, but averaged 72 m2ha-1in Douglas fir forest and 33 m2ha-1in spruce-fir forest. North slopes of Douglas fir forest had the highest average cover, 130 m2ha-1. All macrolichens were terrestrial species of Peltigera with P. canina the overwhelming dominant. Based on published laboratory nitrogen fixation rates, lichens probably provide a significant input to the total annual nitrogen budget in the Douglas fir north slope forests and possibly in the spruce-fir forests. A feedback loop relating the role of nitrogen fixing lichens to patchiness within ecosystems is hypothesized. Nitrogen fixing lichens correlate poorly with vegetation structure. Excluding the cold alpine tundra, moisture is considered the primary determinant of nitrogen fixing lichen abundance.

One hundred five species of bryophytes and 159 of lichens are reported from four areas of the Shenandoah National Park in Page and Madison Counties, Virginia.