Lawrence R. Walker

Biological Invasion by Myrica faya Alters Ecosystem Development in Hawaii

The exotic nitrogen-fixing tree Myrica faya invades young volcanic sites where the growth of native plants is limited by a lack of nitrogen. Myrica quadruples the amount of nitrogen entering certain sites and increases the overall biological availability of nitrogen, thereby altering the nature of ecosystem development after volcanic eruptions.

Ecosystems of disturbed ground

Hardbound. As the human population inexorably grows, its cumulative impact on the Earths resources is hard to ignore. The ability of the Earth to support more humans is dependent on the ability of humans to manage natural resources wisely. Because disturbance alters resource levels, effective management requires understanding of the ecology of disturbance. This book is the first to take a global approach to the description of both natural and anthropogenic disturbance regimes that physically impact the ground. Natural disturbances such as erosion, volcanoes, wind, herbivory, flooding and drought plus anthropogenic disturbances such as foresty, grazing, mining, urbanization and military actions are considered. Both disturbance impacts and the biotic recovery are addressed as well as the interactions of different types of disturbance. Other chapters cover processes that are important to the understanding of disturbance of all types including soil proc

Tree damage and recovery from Hurricane Hugo in Luquillo Experimental Forest, Puerto Rico

Hurricane Hugo struck Puerto Rico on 18 September 1989 with maximum sustained winds of over 166 km/hr (Scatena & Larsen 1991) and caused severe defoliation of 56 percent of the trees in study plots at El Verde in the Luquillo Experimental Forest (LEF). Some trees were uprooted (9%) or had trunks that snapped (11%), but overall mortality was low (7%). Damage was patchy on twenty 300 m2 plots with most damage occurring on north-facing sites. Tall trees and trees with large diameters were most likely to be uprooted, but successional status of trees was not a good predictor of the amount of damage the trees sustained. Recovery patterns varied among species but refoliation was rapid. Widespread sprouting and minimal breakage of large branches will probably lead to the recovery of most trees.

Summary of the effects of Caribbean hurricanes on vegetation.

PAPERS IN THIS ISSUE OF BIOTROPICA treat the effects of hurricanes on forest vegetation in Puerto Rico, the Virgin Islands, South Carolina, Jamaica, and the Yucatan Peninsula. Using a diversity of research approaches, the authors studied hurricane damage to vegetation and recorded short-term (<2 yr) patterns of vegetation response. We summarize these papers and some other recent studies, and we discuss possible longer term patterns of vegetation recovery. Tanner et al. ( 1991) place these studies of hurricane damage in a broader context and suggest directions for future research.

Linking restoration and ecological succession

Preface Contributors List Glossary Forging a New Alliance Between Succession and Restoration.- Insights Gained from Succession for the Restoration of Landscape Structure and Function.- Aboveground-Belowground Linkages, Ecosystem Development and Ecosystem Restoration.- Retrogressive Succession and Restoration on Old Landscapes.- Succession and Restoration of Drained Fens: Perspectives from Northwestern Europe.- Manipulation of Succession.- Restoration as a Process of Assembly and Succession Mediated by Disturbance.- Integrating Restoration and Succession.- Index.

ECOSYSTEM DEVELOPMENT AND PLANT SUCCESSION ON LANDSLIDES IN THE CARIBBEAN

Landslides are common in mountainous regions of the Caribbean and are triggered by heavy rains and earthquakes, and often occur in association with human disturbances (e.g., roads). Spatially heterogeneous removal of both substrate and vegetation is responsible for a variety of patterns of ecosystem development and plant successional trajectories within Caribbean landslides. Soil nutrient pools in exposed mineral soils reach levels comparable to mature forest soils within 55 yr but soil organic matter recovers more slowly. Plant colonization of landslides depends on the availability of propagules and suitable sites for germination, soil stability, and the presence of residual or newly deposited soil organic matter and associated nutrients. Once initial colonization occurs, the rate and trajectory of plant succession on landslides is strongly affected by plant/plant interactions. We present two conceptual models of landslide succession that summarize the major processes and pathways of ecosystem development and plant succession on landslides. Additional work is needed to characterize interactions between spatially heterogeneous zones, controls over soil development, impacts of key plant species, and the role of animals on Caribbean landslides.

An introduction to hurricanes in the Caribbean

THIS ISSUE OF BIOTROPICA brings together, for the first time, a collection of case studies that document the damage to natural ecosystems and the initial recovery process from three recent hurricanes in the Caribbean. The majority of papers address the impact of Hurricane Hugo (1989) and subsequent recovery during the year following the hurricane at three sites: St. John in the U.S. Virgin Islands, Puerto Rico, and South Carolina on the U.S. mainland (Fig. 1). Hurricane Hugo triggered a rapid increase in the level of hurricane research, in part because it passed over two Long-Term Ecological Research sites (Luquillo Experimental Forest, Puerto Rico and North Inlet, South Carolina) which had ecological data that allowed comparisons of prehurricane and posthurricane conditions. Benefits of such long-term studies include the ability to separate damage caused by the recent hurricane from previous damage; to not depend on reconstruction of damage scenarios from historical evidence; and, to begin studies of recovery immediately. Hurricane Hugo also provided an opportunity to contrast hurricane damage in different environments: tropical and temperate, humid and dry, island and continental. In addition to studies of Hurricane Hugo, we include studies of the effects of Hurricane Gilbert (1988) on Jamaica and Mexico, and Hurricane Joan (1988) on Nicaragua (Fig. 1). We have emphasized studies of terrestrial ecosystems; hurricane impacts on marine and coastal ecosystems have been examined elsewhere (Woodley et al. 1981, BenitoEspinal & Benito-Espinal 1991, Finkl & Pilkey 1991). Hurricanes are frequent, large-scale disturbances in the Caribbean. During the period 18711964, zero to eleven hurricanes per year (average = 4.6, median = 8) occurred in the Caribbean (Alaka 1976), resulting in, for example, a return time of 21 yr for the island of Puerto Rico (Salivia 1972). The strongest Caribbean hurricanes typically originate off the western coast of Africa, gain strength as they pass westward over the Atlantic Ocean, and rapidly deteriorate when they reach the mainland somewhere between Panama and New England. Weaker hurricanes and tropical storms (wind speeds 63-119 km/hr) have their origins throughout the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. With wind speeds of at least 119 km/hr and paths often tens of kilometers wide, hurricanes have a profound effect on plants, soils, animals, humans, and even landforms. Much attention is given to the destruction of property (Saffir 1991, Sparks 1991), and the loss of human lives in these storms. The effects of hurricanes on natural ecosystems (Fig. 2) have also been noted (e.g., Foster 1988) but are less understood. Studies in Puerto Rico suggest that hurricanes may have a major effect in structuring natural ecosystems in terms of age distribution of tropical forest trees (Doyle 1981, Weaver 1986, Lugo & Rivera-Batlle 1987), or biomass and species diversity (Crow 1980). These studies add to the accumulating evidence that suggests natural systems are largely organized by disturbance (Pickett & White 1985, Denslow 1987). The study of how natural ecosystems are altered by hurricanes and how they respond is essential to the understanding of how these systems are structured. Adding urgency to this study is the relationship between hurricanes and global climate change. Slight increases in surface water temperatures or periods of high rainfall in the I Received 28 July 1991, revision accepted 5 August 1991.

Differential Seedling Responses to Litter After Hurricane Hugo in the Luquillo Experimental Forest, Puerto Rico

We studied the dynamics of the seedling community in the Luquillo Experimental Forest during one year following Hurricane Hugo, to look at the effect of three litter treatments (continuous litter removal, unaltered litter quantity [controll and continuous litter addition), on seedling emergence, growth, density, and mortality. Total seedling densities (for both newly emerged and established seedlings) were highest in the litter removal treatment, suggesting that litter is a major constraint to recruitment of seedlings. However, species differed in their responses to the three treatments: species characteristic of early succession (Chionanthus domingensis and Cecropia schreberiana ex. C. peltata) were densest in the litter removal treatment, while densities of species characteristic of late succession either did not increase (Sloanea berteriana) or declined (Dacryodes excelsa) in the litter removal treatment. Height growth was lowest and mortality generally highest for seedlings in the litter removal treatment. Variability in species responses to litter after the hurricane may lead to changes in the species composition of the forest.

INTRODUCTION : DISTURBANCE AND CARIBBEAN ECOSYSTEMS

The fifteen articles in this special issue describe long-term (2 5 years) responses or perspectives on disturbance in Caribbean ecosystems. Most (1 1) of the articles describe the responses of Caribbean forests to hurricane disturbance, particularly the effects of Hurricane Hugo on wet forest in the Luquillo Experimental Forest (LEF), Puerro Rico. Ten articles discuss, alone or in addition to hurricanes, the effects of other types of disturbance including that due to humans, treefalls, drought, and landslides. In this introductory article we summarize the post-hurricane trajectories of various ecosystem components in the LEF. We also address how responses to other types of disturbance can be brought together to obtain a more thorough understanding of the comparative responses of Caribbean ecosystems to different disturbances. Finally, we identify those areas of disturbance ecology in the Caribbean that require further investigation.

Immediate Impact of Hurricance Hugo on a Puerto Rican Rain Forest

Tropical forests are subject to natural disturbances ranging from falling trees to landslides, forest fires, and hurricanes (Jordan 1986). Hurricane Hugo struck northeastern Puerto Rico on 18 September 1989 (Fig. 1) with maximum sustained winds of over 166 km/h and caused considerable damage to the Luquillo Experimental Forest (LEF). Hurricanes of this magnitude (category 4) pass over LEF at an estimated recurrence interval of 60 yr (Scatena 1989). Hugo was the first hurricane to pass directly over LEF since 1932. The path, wind velocities, and seasonality of this storm were typical of previous hurricanes, but rainfall associated with the storm was unusually low, 100-339 mm (USDC 1990) vs. 500-750 mm for all previous hurricanes since 1876 (Salivia 1972). Previous research at LEF (Brown et al. 1983) and sampling begun 1 yr prior to Hurricane Hugo have provided us with an exceptional opportunity to measure damage to previously marked trees, to evaluate whether damage to trees can be predicted by wood density, tree diameter, or the presence of buttresses, and to compare light levels before and after the hurricane. Our data on the immediate and short-term (2 mo) effects of Hurricane Hugo should assist later studies to place patterns of damage in the context of recovery.