Margaret S. Devall

Dendroecological analysis of a longleaf pine Pinus palustris forest in Mississippi

A climate model with time varying parameters was fit to longleaf pine (Pinus palustris) tree rings collected from the proposed Harrison Research Natural Area of the De Soto National Forest in southern Mississippi. The purpose of the analysis was to determine if any unexpected disturbances had influenced the growth of the trees. Current September temperature, August rainfall and February Palmer Drought Severity Index (PDSI) were found jointly to be the best variables in the model to predict growth. August rain had a constant significant effect on growth and February PDSI was not significant except between the years 1968–1983. It was concluded that the Harrison area has been in equilibrium for the past 50 years since no apparent outside influences have caused the trees to become less sensitive to climate. Thus, the forest is a good candidate for a Research Natural Area.

Self-Incompatibility in Ipomoea pes-caprae (Convolvulaceae)

-The breeding system of Ipomoea pes-caprae, the goats foot or beach morning glory, was examined in two populations bordering the Gulf of Mexico in order to investigate the self-incompatibility mechanism of the species, especially the number of s alleles in two populations. Ipomoea pes-caprae possesses a sporophytic multi-allelic incompatibility system which is rare in flowering plants. The maximum likelihood estimates of the number of s alleles in the samples of plants from Grand Isle, Louisiana, and Progreso, Yucatan, are four and seven, respectively. Although self-incompatibility appears to be an incongruous feature of a pantropical colonizing species, long-range dispersal of pollen and water-dispersed seeds enhance the self-incompatibility system to promote genetic diversity and a widespread distribution.

Growth and intraspecific competitive abilities of the dioecious Lindera melissifolia (Lauraceae) in varied flooding regimes.

Abstract The contribution of sexual dimorphism to male-biased colony ratios observed in field populations of the federally endangered Lindera melissifolia was investigated. Growth characteristics and intraspecific relative competitive abilities were determined for first-year male and female L. melissifolia plants grown at varied densities and receiving three flooding treatments. In the no-flooding and 30-day-flooding treatments, stem height, stem diameter, and total leaf area for male plants were significantly greater than that of higher density male plantings and of female plants without respect to density. In both male and female plants, stem growth ceased and leaves were abscised in response to flooding. Although density effects in combination with hydrologic regime influenced intersexual competition, male-bias from competitive exclusion was not indicated. Growth characteristics for male plants grown alone suggest potential for greater interspecific competitive abilities than that of female plants. Therefore, male plants may be better adapted for colonizing suitable habitat, thus contributing to male-biased colony ratios observed in naturally occurring populations.

Hermit Thrush is the First Observed Dispersal Agent for Pondberry (Lindera melissifolia)

Abstract We investigated dispersal opportunities for the endangered pondberry, Lindera melissifolia (Lauraceae). In 199 hours of observation at 5 fruiting colonies in the Delta National Forest, Sharkey County, Mississippi, we recorded 82 bird species in the vicinity of a colony. Of these, 12 were observed on pondberry plants, and two consumed ripe pondberry fruits. Of these, the northern cardinal, Cardinalis cardinalis (Cardinalidae), was a seed predator. The other, hermit thrush, Catharus guttatus (Turdidae), was a dispersal agent for the plants. Numbers of fruits declined rapidly after hermit thrushes arrived in October and no fruits remained by January. Winter behavior of hermit thrushes constrains their dispersal of seeds to short distances. Without establishment of additional colonies, pondberry dispersal by birds to unoccupied patches of suitable forest is unlikely.

Bottomland Forests in the Lower Mississippi Alluvial Valley Associated with the Endangered Lindera melissifolia

Abstract Forest canopy and subcanopy data were collected from and compared among five disjunct bottomland hardwood forests in the Lower Mississippi Alluvial Valley, each with known occurrence of a population of the federally endangered shrub Lindera melissifolia. All study sites are cut-over forests, underlain by hydric soils, and have a seasonal high water table. Canopy and subcanopy species are similar among sites, but species differ in relative importance, and flood tolerant tree species exceed that of flood intolerant species. Distribution of L. melissifolia colonies within each study site was not associated with mean tree density or d.b.h. Forest composition and structure at each study site reflect hydrologic regime, topography, historical disturbance, and an absence of recent disturbance. Results of this study provide a quantitative description of bottomland forests that currently sustain L. melissifolia populations. This information may be utilized for development of forest management plans aimed at ensuring continued sustainability of existing L. melissifolia populations and assessing other bottomland hardwood forests for potential reintroduction of this endangered species.

Flooding Facility Helps Scientists Examine the Ecophysiology of Floodplain Species Used in Bottomland Hardwood Restorations

Bottomland hardwood ecosystems, important for their unique functions and values, have experienced considerable degradation since European settlement through deforestation, development, and drainage. Currently, considerable effort is underway to restore ecological functions on degraded bottomland sites. Restoration requires a better understanding of the biological components, especially plants, and their interactions with other biotic and abiotic components of the ecosystem. Previous experimental approaches have focused on the effects of stress on floodplain plant species in controlled, small-scale studies or large, uncontrolled ecosystem-scale studies. We describe a facility, named the Flooding Research Facility (FRF), where hydrologic regimes can be manipulated to study ecophysiology of floodplain species. Key features of the FRF include the ability to establish experiments on a scale larger than would be possible in a greenhouse, but small enough to control key abiotic variables, such as flood frequency, duration, and light availability on native bottomland soil. Design of the FRF allows for random and replicated treatment applications. Additionally, we provide an example of ongoing research on the effects of flooding and light availability on pondberry (Lindera melissifolia), a federally endangered shrub found in the southeastern United States.

Dendroecological analysis of a Fitzroya cupressoides and a Nothofagus nitida stand in the Cordillera Pelada, Chile

Abstract Lumbering of Fitzroya cupressoides in Chile began in 1599 and continued until 1976, when the species was declared a national monument and cutting of live trees was prohibited. Today, F . cupressoides is threatened; many of the remaining stands in the coastal range appear to be declining, with a predominance of standing dead stems and patchy, sparse regeneration. We performed tree-ring analysis on a F . cupressoides stand and a nearby Nothofagus nitida stand, in the Cordillera Pelada, of coastal Chile (40°S) in order to examine the ecological history of two stands in the montane forest. Our analysis demonstrates that the F . cupressoides stand has undergone several periods of growth release and disturbance; the last 34 years of the chronology show a trend of increasing growth. In contrast, after 1865 radial growth of the N . nitida stand is fairly constant and steady. Radial growth of these two species is highly correlated with spring rainfall. November rainfall of the current growing season proved to be the best growth predictor of F . cupressoides , whereas current June and December rain, and December rain of the past growing season best predicted growth of N . nitida . Although episodic disturbances have occurred, the chronologies demonstrated that these stands are vigorous, despite the presence of dead stands nearby. These results do not support the idea that climatic deterioration is responsible for the decline of F . cupressoides during the past 77 years. La tala de F. cupressoides en Chile empezo en 1599 y continuo hasta 1976, cuando la especie fue declarada monumento nacional y la corta de arboles vivos fue prohibida. Esta especie es hoy considerada vulnerable. Muchos rodales que subsisten en las cumbres de la cordillera de la costa (40–42°S) parecen estar en declinacion con una predominancia de individuos muertos en pie. La regeneracion de F . cupressoides esta limitada a algunos rodales intervenidos. En este estudio se llevo a cabo un analisis de anillos de crecimiento de F . cupressoides y de N. nitida en dos rodales de la Cordillera Pelada (800–900 m), en la costa de Chile a 40°S, con el proposito de reconstruir la historia de estos bosques montanos en la cordillera de la costa. El analisis sugirio que el rodal de F . cupressoides ha sufrido varios periodos de liberacion de crecimiento y perturbacion. Los ultimos 34 anos de la cronologia demuestran una tendencia de crecimiento alto. Por otra parte, despues de 1865, el crecimiento del rodal de N . nitida es medianamente constante. El crecimiento de las dos especies se correlaciona fuertemente con las precipitaciones de primavera registradas en una estacion al sureste del area de estudio. La lluvia del mes de noviembre del ano anterior fue el mejor predictor de la cronologia de F . cupressoides , mientras que las lluvias de junio y diciembre del ano actual y la lluvia de diciembre de los dos anos anteriores predicen la cronologia de N . nitida . A pesar de la presencia de disturbios ocasionales, y la existencia de rodales vecinos compuestos de arboles muertos y de alta mortandad en rodales maduros, las cronologias demuestran que los rodales estudiados de F . cupressoides y de N . nitida estan saludables. Estos resultados no apoyan la idea de que el deterioro del clima podria ser responsable por la reduccion de F . cupressoides durante los ultimos 77 anos.

Effects of global climate change on biodiversity in forests of the Southern United States

Climate has not been stable in the past. Fluctuations of pine (Pinus) pollen in a 50,000-year sequence from Lake Tulane in Florida indicate that major vegetation shifts occurred during the last glacial cycle. Phases of pollen dominated by pine (indicating a wet climate) were interspersed with periods with plentiful oak (Quercus), ragweed, and marsh elder (Ambrosia type) populations (Grim et al., 1993). During the Holocene (i.e., the last 12,000 years), climate has fluctuated with periods of cooler, warmer, wetter or drier weather than at present. The greatest changes in climate probably occurred during deglaciation, approxiamtely 12,500 to 11,000 years ago. However in parts of the United States great shifts in plant distribution and composition occurred during the past 120 years, mainly resulting from anthropogenic factors (Miller and Wigand, 1994). From 1550 to 1850 a small ice age caused widespread starvation in Europe. Living things have been able to adapt to the warming since then, but widespread, rapid warming could be disastrous (Fajer and Bazzaz, 1992).

Cat Island Swamp: window to a fading Louisiana ecology.

Abstract The structure and composition of a Louisiana swamp bordering the Mississippi River were investigated; twenty species of trees were encountered in six communities. Hackberry (Celtis laevigata) had the highest importance value for the entire tract, followed by cypress (Taxodium distichum), green ash (Fraxinus pennsylvanica), and tupelo gum (Nyssa aquatica). The understory was sparse, and saplings were not represented in the same frequency as the trees. Herbs were monitored in 1-m2 quadrats to determine their frequency and density. Soil was tested for pH and for extractable nutrients, and a texture analysis was carried out. Discriminant-function analysis was performed to determine which environmental variables influences tree distribution.

Inland occurrence of the strand plant Ipomeoa pes-caprae (Convolvulaceae) around Lake Nicaragua

Abstract Ipomoea pescaprae (L.) Roth (railroad vine, Convolvulaceae) is a pantropical, perennial beach plant that forms large patches just above the high tide line on coastal beaches and dunes throughout tropical and subtropical areas of the world. In spite of its wide distribution, only rare occurrences of I. pescaprae have been documented in inland habitats. Here we report on an extensive population of I. pescaprae growing on the shores of Lake Nicaragua in the interior of Nicaragua.