Thomas R. Wentworth

Infaunal community development of artificially established salt marshes in North Carolina

In recent years, artificial establishment of Spartina alterniflora marshes has become a common method for mitigating impacts to salt marsh systems. The vegetative component of artificially established salt marshes has been examined in several studies, but relatively little is known about the other aspects of these systems. This study was undertaken to investigate the infaunal community of artificially established salt marshes. Infauna were sampled from pairs of artificially established (AE) salt marshes and nearby natural marshes at six sites along the North Carolina coast. The AE marshes ranged in age from 1 yr to 17 yr. Total infaunal density, density of dominant taxa, and community trophic structure (proportions of subsurface-deposit feeders, surface-deposit and suspension feeders, and carnivores) were compared between the two types of marsh to assess infaunal community development in AE marshes. Overall, the two marsh types had similar component organisms and proportions of trophic groups, but total density and densities within trophic groupings were lower in the AE marshes. Soil organic matter content of the natural marshes was nearly twice that of the AE marshes, and is a possible cause for the higher infaunal densities observed in the natural marshes, Using the same three criteria, comparisons of the natural and AE marshes at each of the six locations revealed varying degrees of similarity. Similarity of each AE marsh to its natural marsh control appeared to be influenced by differences in environmental factors between locations more than by AE marsh age. Functional infaunal habitat convergence of an AE marsh with a natural marsh somewhere within its biogeographical region is probable, but success in duplicating the infaunal community of a particular natural marsh is contingent upon the developmental age of the natural marsh and the presence and interaction, of site-specific factors.

CONNECTING FINE- AND BROAD-SCALE SPECIES-AREA RELATIONSHIPS OF SOUTHEASTERN U.S. FLORA

Although the rate that species accumulate with area has long been regarded as an important component of fine-scale community structure and several studies have examined this rate in meta-analyses, few if any studies have systematically examined fine- scale species-area relationships using a consistent survey protocol over a large region. We examined fine-scale species-area relationships using the extensive database of the Carolina Vegetation Survey (North Carolina, South Carolina, Georgia, and Tennessee, USA), in- cluding 1472 plots wherein vascular plant richness was recorded for each of six subplot sizes regularly spaced on a log10 scale, from 0.01 to 1000 m 2 . Contrary to prevailing theory, our data closely and consistently fit an Arrhenius (power law) species-area model, echoing broader-scale patterns. Species accumulation rate (Z) values fell within a narrow range (95% between 0.2 and 0.5) despite a 30-fold range in 1000-m 2 richness. When we added regional- and global-scale richness estimates to our results, a Preston-type triphasic curve emerged. We suggest that (1) fine-scale species-area relationships are remarkably consistent and (2) full-scale species-area curves reveal scale dependencies in diversity data that are not accounted for by current species-area theory.

Genetic discontinuity revealed by chloroplast microsatellites in eastern North American Abies (Pinaceae).

Development of conservation strategies for Fraser fir (Abies fraseri) in the southern Appalachian Mountains depends in part on recognition of the extent to which Fraser fir is genetically distinct from the closely related balsam (A. balsamea) and intermediate (A. balsamea var. phanerolepis) fir. These sibling species have exhibited intergrading, clinal variation in morphological, chemical, and genetic characteristics in prior research. Chloroplast microsatellite markers were polymerase chain reaction amplified from genomic DNA samples of 78 individuals representing the geographic ranges of Fraser, balsam, and intermediate fir. Gene diversity levels at two loci ranged among taxa from 0.65 to 0.84. Allele frequencies demonstrated significant differentiation among taxa, with R(ST) values of 0.36 and 0.10. Haplotype diversity and D(SH) were highest for balsam fir and lowest for intermediate fir. A haplotype network analysis based on allele size distribution for the two loci revealed two distinct clusters of haplotypes and population-specific haplotypes. Ninety-two percent of the haplotypes in one cluster were from balsam fir and intermediate fir, and 84% of the haplotypes in the other cluster were from Fraser fir and intermediate fir. The genetic differentiation of chloroplast DNA markers provides justification for the recognition of Fraser fir as a distinct Management Unit (MU) for conservation purposes, regardless of its taxonomic classification.

Vegetation on Limestone and Granite in the Mule Mountains, Arizona

Gradient analysis was employed to determine vegetation pattern in relation to environment on limestone and granite in the Mule Mountains, Cochise County, Arizona, USA, using data obtained from 175 0.1—ha (20 x 50 m) quadrats located over ranges of elevation and topographic position. Sequences of major community types from mesic to xeric positions on the mountain slopes were pygmy conifer—oak scrub, open oak woodland, and desert grassland on granite and Cercocarpus breviflorus scrub, mesic phase Chihuahuan desertscrub, and xeric phase Chihuahuan desertscrub on limestone. Calcareous bajadas (alluvial plains) southwest of the Mule Mountains support a disturbed Chihuahuan desertscrub type. An environmental scalar was developed to quantify site position along complex—gradients of elevation and topographic position. The scalar was correlated with indirect ordination axes from reciprocal averaging, principal components analysis, and Wisconsin polar ordination. Over similar ranges of elevation and topographic position, granitic sites have higher species richness, greater importance of herbaceous and arborescent species, and lower importance of shrubby species than limestone sites. Both rock types support vegetation rich in widely distributed southwestern species but the vegetation on limestone has a distinctly Chihuahuan character, while that on granite is Madrean. Investigation of species distributions indicated a modal shift toward more mesic environments on limestone as compared to granite. This shift complemented other observations which suggested more xeric conditions on limestone. The low—elevation plant communities on limestone represent the northwesternmost occurrence of the Chihuahuan Desert formation. This may be due to three factors: (1) limestone habitats are arid (as judged from observations of vegetation); (2) increased aridity favors desert species, but the local climate (particularly cool winter temperatures) selects for Chihuahuan, rather than Sonoran, species; and (3) among desert species the Chihuahuan are better adapted to calcerous soils, which occur widely in the Chihuahuan Desert.

Influence of Fire and Southern Pine Beetle on Pine-Dominated Forests in The Linville Gorge Wilderness, North Carolina

ABSTRACT Historically, fire and the southern pine beetle (Dendroctonus frontalis) have interacted in a manner that maintains the stability of pine-dominated forests in the southern Appalachians. Fire suppression has recently been implicated in the disruption of the integrity of these forests and their shift toward hardwood dominance. This study examined the influences of fire and southern pine beetle infestation on stand structure and resin flow of pines in pine-dominated forests in the Linville Gorge Wilderness of North Carolina. Resin flow in most pine species increases in response to various types of wounding and is a pine trees primary defense against insect pathogens. Pine-dominated stands in this study decreased in both basal area and density after exposure to fire and/or southern pine beetle infestation. Decreases in basal area and density of Pinus pungens were strongly associated with infestation, while decreases in Pinus rigida were influenced primarily by exposure to fire. Resin flow was substantially higher in trees that were exposed to fire, but not infested, than in trees experiencing any other combination of fire exposure and infestation (including trees that were neither exposed to fire nor infested). This elevated resin flow was still present 18 mo after burning. Since resin flow is the primary means of host defense against southern pine beetle, it is suspected that fire could confer an acquired resistance to future southern pine beetle infestations through elevated resin flow.

Distributions of C4 plants along environmental and compositional gradients in southeastern Arizona

Distributional patterns of C4 plants were investigated in 4 study areas located in se Arizona: granite slopes in the M ule M ountains, limestone slopes in the M ule M ountains, calcareous bajada (alluvial plain) below the M ule M ountains, and limestone slopes in the H uachuca M ountains. Cover data for all vascular species were obtained from 238 0.1 ha (20 × 50 m) sample quadrats located over ranges of elevation and topographic position within the study areas. Overall, 69 C4 species representing 6 angiosperm families were encountered. C4 species accounted for 13.5% to 22.3% of vascular species within the study areas. C4 species frequency in quadrats (on the basis of all species or of grasses only) increased from mesic to xeric community types in all study areas except the calcareous bajada. Similar, but less consistent, trends were evident in the relative cover contributed by C4 species. I n two of the study areas (granite slopes in the Mule Mountains, limestone slopes in the Huachuca Mountains) regression analyses revealed statistically significant trends of C4 species frequency and relative cover along environmental (elevation/solar-irradiation scalar) and compositional (reciprocal averaging ordination) gradients. A lack of consistent trends on limestone slopes in the Mule Mountains may be the result of grazing and/or recent invasion of low-elevation limestone areas by a Chihuahuan Desert flora dominated by C3 dicot shrubs. The calcareous bajada below the Mule Mountains was studied less intensively, but its flora was found to contain the highest frequency of C4 species of the 4 study areas. In contrast, C4 cover on the bajada was low, presumably as a consequence of heavy grazing pressure on the grasses. The results of the present investigation support the prediction that C4 species should be proportionally more successful in habitats characterized by high temperatures, high irradiance and low moisture.

Recent vicariance and the origin of the rare, edaphically specialized Sandhills lily, Lilium pyrophilum (Liliaceae): evidence from phylogenetic and coalescent analyses

Establishing the phylogenetic and demographic history of rare plants improves our understanding of mechanisms that have led to their origin and can lead to valuable insights that inform conservation decisions. The Atlantic coastal plain of eastern North America harbours many rare and endemic species, yet their evolution is poorly understood. We investigate the rare Sandhills lily (Lilium pyrophilum), which is endemic to seepage slopes in a restricted area of the Atlantic coastal plain of eastern North America. Using phylogenetic evidence from chloroplast, nuclear internal transcribed spacer and two low‐copy nuclear genes, we establish a close relationship between L. pyrophilum and the widespread Turk’s cap lily, L. superbum. Isolation‐with‐migration and coalescent simulation analyses suggest that (i) the divergence between these two species falls in the late Pleistocene or Holocene and almost certainly post‐dates the establishment of the edaphic conditions to which L. pyrophilum is presently restricted, (ii) vicariance is responsible for the present range disjunction between the two species, and that subsequent gene flow has been asymmetrical and (iii) L. pyrophilum harbours substantial genetic diversity in spite of its present rarity. This system provides an example of the role of edaphic specialization and climate change in promoting diversification in the Atlantic coastal plain.

Evidence for range stasis during the latter Pleistocene for the Atlantic Coastal Plain endemic genus, Pyxidanthera Michaux

The general phylogeographical paradigm for eastern North America (ENA) is that many plant and animal species retreated into southern refugia during the last glacial period, then expanded northward after the last glacial maximum (LGM). However, some taxa of the Gulf and Atlantic Coastal Plain (GACP) demonstrate complex yet recurrent distributional patterns that cannot be explained by this model. For example, eight co‐occurring endemic plant taxa with ranges from New York to South Carolina exhibit a large disjunction separating northern and southern populations by >300 km. Pyxidanthera (Diapensiaceae), a plant genus that exhibits this pattern, consists of two taxa recognized as either species or varieties. We investigated the taxonomy and phylogeography of Pyxidanthera using morphological data, cpDNA sequences, and amplified fragment length polymorphism markers. Morphological characters thought to be important in distinguishing Pyxidanthera barbulata and P. brevifolia demonstrate substantial overlap with no clear discontinuities. Genetic differentiation is minimal and diversity estimates for northern and southern populations of Pxyidanthera are similar, with no decrease in rare alleles in northern populations. In addition, the northern populations harbour several unique cpDNA haplotypes. Pyxidanthera appears to consist of one morphologically variable species that persisted in or near its present range at least through the latter Pleistocene, while the vicariance of the northern and southern populations may be comparatively recent. This work demonstrates that the refugial paradigm is not always appropriate and GACP endemic plants, in particular, may exhibit phylogeographical patterns qualitatively different from those of other ENA plant species.

Intercontinental comparison of habitat levels of invasion between temperate North America and Europe

Several studies have demonstrated that floras of the New World contain larger proportions of alien species than those of the Old World; however, the differences in fine-scale invasion patterns are poorly known. We compared the levels of invasion in analogous habitats of two environmentally similar regions in temperate North America and Europe (the Carolinas and the Czech Republic), using comprehensive vegetation-plot databases. Native and alien vascular plant species were identified within 4165 vegetation plots assigned to 12 habitats occurring in both areas. The level of invasion was calculated for each habitat (1) as the proportion of aliens recorded cumulatively across multiple plots (habitat scale) and (2) as the mean proportion of aliens per plot (plot scale), both separately for all alien species and for the subgroup of aliens originating in one region and invading the other. The proportions of species native on one continent and invading the other were also calculated for each habitat to compare the alien species exchange between continents. Habitat levels of invasion showed remarkably similar patterns on the two continents. There were significant positive relationships for the levels of invasion, both for all alien species (habitat-scale R2 = 0.907; plot-scale R2 = 0.676) and for those that originated on the opposite continent (habitat-scale R2 = 0.624; plot-scale R2 = 0.708). In both regions, the most and the least invaded habitats were the same, but on average, North American habitats showed higher habitat-scale levels of invasion than their European counterparts. At the same time, a larger proportion of alien species was provided by European habitats for invasion to North America than vice versa. The consistent intercontinental pattern of habitat levels of invasion suggests that these levels are driven by similar mechanisms in distant regions. Habitat conditions are likely to have stronger effect on the level of invasion than the identity of alien species, as shown by similar levels of invasion in analogous habitats despite different geographical origins of alien species. The higher flux of alien species from Europe to North America is consistent with a generally higher level of invasion of North American habitats.

Demographic effects of fire on two endemic plant species in the longleaf pine-wiregrass ecosystem

Fire can have dramatic effects on the vital rates of plant species and has been used successfully for management in a number of ecosystems. However, the demographic response of species to fire in fire-dependent ecosystems is variable, making it important to study the effects of fire on rare and threatened species. We quantified the effects of fire on Astragalus michauxii and Pyxidanthera brevifolia, two rare endemics of the longleaf pine-wiregrass ecosystem of the southeastern USA, by means of periodic matrix models to project the effect of fire frequency on population growth. In contrast to many species in the longleaf pine-wiregrass ecosystem, fire had short-term negative effects on both species, causing reductions in survival, size, flowering, and fruit production. Relative to the three-year fire intervals to which the study populations are currently exposed, more frequent burning is projected to cause population decline, with the most dramatic effects under annual burning. Although the current longleaf pine-wiregrass ecosystem is fire dependent and has experienced frequent fire for at least several thousand years, we propose that the two endemic species may be remnants from a past vegetation assemblage that experienced less frequent fire and thus may be adapted to longer fire-return intervals compared to other species currently in the ecosystem. Despite the short-term negative effects of fire on the vital rates of these species, longer-term benefits such as reduction of woody encroachment and litter removal may be important for the ultimate success of the species.