Nicholas Brokaw

Gap-phase regeneration in a tropical forest.

Gap-phase regeneration of trees was described for the first 5-6 yr of regrowth in 30 treefall gaps (20-705 m2) in tropical moist forest on Barro Colorado Island, Panama. Trees were classified as pioneers (saplings found only in gaps) or primary species (saplings found in gaps and in the understory of mature forest). In most of the gaps studied, stem densities rose rapidly after gap formation, then levelled offor declined by years 3-6. This pattern was particularly marked in some large gaps (> 150 m2), where pioneers attained high densities, then experienced heavy mortality. Stem density of primary species did not vary with gap size. In large gaps the mean rate of growth in height was greater for pioneers than for primary species, size-class distribution broadened more for pioneers than for primary species, and early recruits of both regeneration types grew faster than later ones. Gap formation fosters regeneration of pioneer and primary species and, in this forest, produces patches that differ markedly in tree population dynamics, species composition, and growth rate.

Forest damage and recovery from catastrophic wind

The literature on the effects of catastrophic wind disturbance (windstorms, gales, cyclones, hurricanes, tornadoes) on forest vegetation is reviewed to examine factors controlling the severity of damage and the dynamics of recovery.Wind damage has been quantified in a variety of ways that lead to differing conclusions regarding severity of disturbance. Measuring damage as structural loss (percent stems damaged) and as compositional loss (percent stems dead) is suggested as a standard for quantifying severity. Catastrophic wind produces a range of gaps from the size caused by individual treefalls to much larger areas. The spatial pattern of damage is influenced by both biotic and abiotic factors. Biotic factors that influence severity of damage include stem size, species, stand conditions (canopy structure, density), and the presence of pathogens. Abiotic factors that influence severity of damage include the intensity of the wind, previous disturbance, topography, and soil characteristics.Recovery from catastrophic wind disturbance follows one of four paths: regrowth, recruitment, release, or repression. The path of recovery for a given site is controlled both by the severity of disturbance and by environmental gradients of resources. Recovery is influenced also by frequency of wind disturbance, which varies across geographical regions.To develop robust theories regarding catastrophic wind disturbance, the relative roles of different abiotic and biotic factors in controlling the patterns of severity of damage must be determined. These patterns of severity and environmental gradients must then be tied to long-term dynamics of recovery.ResumenLa literatura sobre los efectos de disturbios catastróficos del viento (tormentas, ventarrones, ciclones, huracánes, tornados) sobre la vegetatión de bosque es revisada para examinar los factores que controlan la severidad del daño y la dinámica de recuperación.El daño del viento puede ser cuantificado en varias formas, lo cualo conlleva a diferir en las conclusiones en cuanto a la severidad del disturbio. Medir daños como la pérdida estructural (por ciento de tallos dañados) y la pérdida compositional (porcentaje de tallos muertos) son normas sugeridas para cuantificar la severidad. Los vientos catastróficos producen una extensión de aperturas de gran tamaño causados por árboles caídos sobre muchas otras áreas mayores. El patrón espacial de daño es influenciado por factores abióticos y bióticos. Factores bióticos que influyen severamente al daño pueden ser tamaño del tallo, especie, conditión de tolerancia (estructura del dosel, densidad), y la presencia de patogénos. Factores abióticos que influyen severamente sobre el daño incluyen la intensidad del viento, disturbios anteriores, topografía, y las características del suelo.La recuperatión de las catástrofes causados por el viento siguen uno de cuatro patrones: crecimiento, reclutaje, liberar o reprimir. La trayectoria de recuperatión para un lugar es controlado por ambos: por lo severo del disturbio y por los gradientes ambientales del recurso. La recuperatión es influenciada también por la frecuencia del disturbio por viento, el cual varia sobre el globo.Para desarrollar una fuerte teoría en cuanto a disturbios catastróficos por viento, los roles relativos de los factores abióticos y bióticos en el control de modelos de severidad de daño tienen que ser determinados. Estos modelos de severidad y gradientes ambientales tienen que ser enlazados para una dinámica de recobro a largo plazo.РЕФЕРАТОбзор литературы о во здействии катастроф ических ветров (штормов, цикло нов, ураганов, смерчей) на лесную растительность с цел ью выявления факторо в, влияющих на величину ущерба и на д инамику рекомпенсац ии.Ущерб от ветра оценив ается различными мет одами, приводящими к разным выводам. Измерение ущ ерба как структурного воздей ствия (процент повреж денных стволов) и как композиционног о воздействия (процен т погибших стволов) предложено в качестве стандарта. Катастрофический ве тер образует серию пр оплешин, размер которых колеблется в широком диапазоне. Пространственная конфигурация ущерба находится под воздей ствием как биотических, так и аби отических факторов. Б иотические факторы величины уще рба включают: размер с твола, особенности особи, ус ловия древостоя (стру ктура и плотность листвы) и пр исутствие патогенов. Абиотические факторы величины уще рба включают интенси вность ветра, предшествующие атмо сферные возмущения, т опографию и характеристики почв ы.Рекомпенсация после катастрофического в етрового воздействия следует по одному из четырех п утей: спонтанное возобнов ление, спонтанное зам ещение другими древесными особями, п одавление нижних яру сов древостоя (нуждающееся в их “выс вобождении” от листв ы верхнего яруса), нашествие сорн яковой растительнос ти. Какой из путей рекомпенсации возобладает, зависит от масштаба атмосферного возмущ ения и от целого ряда с редовых градиентов. Рекомпен сация также зависит о т глобально изменчивой частоты в етровых возмущений.Для создания продукт ивных теорий измерен ия ветрового ущерба нео бходима оценка разли чных биотических и абиотических факто ров, влияющих на велич ину и конфигурацию ущерба. Последняя, а также сре довые градиенты должны быт ь увязаны с долгосроч ной динамикой рекомпенсации.

Niche versus chance and tree diversity in forest gaps

Studies that are unprecedented in scale, detail or approach show that niche partitioning contributes less, and chance events more, than expected to maintaining tree species richness via gap dynamics in tropical and temperate forests. Some tree species are differentially adapted for regeneration in different gap microenvironments. However, the stochastic availability of gaps, and limited recruitment of juveniles, mean that gaps are filled mostly by chance occupants rather than by best adapted species. This chance survival can slow competitive exclusion and maintain tree diversity. Gap dynamics do not explain the latitudinal gradient in tree richness.

Responses of Tree Species to Hurricane Winds in Subtropical Wet Forest in Puerto Rico: Implications for Tropical Tree Life Histories

JESS K. ZIMMERMAN,* EDWIN M. EVERHAM III,t ROBERT B. WAIDE,* D. JEAN LODGE,*? CHARLOTTE M. TAYLOR,t** and NICHOLAS V. L. BROKAW? *Terrestrial Ecology Division, University of Puerto Rico, PO Box 363682, San Juan, PR 00936, tSUNY College of Environmental Science and Forestry, Syracuse, NY 13210, USA, IDepartment of Biology, University of Puerto Rico, Rio Piedras, PR 00931, ?Manomet Observatory, Box 1770, Manomet, MA 02345, USA

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.

Sprouting of Broken Trees on Barro Colorado Island, Panama

The perception of mature forests as homogeneous stands of large trees has given way to the more dynamic idea that, due to natural disturbances, forests consist of mosaics of areas in different stages of regeneration (for recent reviews see Brokaw 1985a, Denslow 1987). Much attention has focused on canopy gaps formed by the death of large trees and the response of previously suppressed plants and buried seeds to canopy opening. Although several researchers have recognized the importance of vegetative recovery of seedlings damaged when gaps form (e.g., Spurr 1956, Nicholson 1965, Platt and Hermann 1986), sprouting of large broken trees in natural forests has not been well studied. The goal of the research reported here was to assess the ecological importance of sprouting of naturally broken trees > 10 cm dbh (stem diameter at 1.4 m) in gapphase regeneration of a moist tropical forest in Panama. Sprouting is a well-recognized mode of regeneration where trees are cut down and where their above-ground portions are killed by fire (for a review see Blake 1983). Stump sprouts contribute greatly to vegetative regrowth in logged temperate (e.g., Zahner et al. 1985) and tropical forests (e.g., Webb et al. 1972, Knight 1975, Uhl et al. 1981). Management of coppice stands for firewood and small dimension timber probably represents the most ancient form of silviculture (Smith 1986). Stems of sprout origin make use of at least part of the root system of the original tree and thus are capable of extremely rapid growth rates (e.g., Wilson 1968). Due to frequent incidence of heart rots (e.g., Leffelman and Hawley 1925, Roth and Hepting 1943, but see Zahner et al. 1985), coppiced stands are generally managed on a short rotation basis for poles, firewood, and charcoal (e.g., Troup 1928, Smith 1986). In a study of treefalls on Barro Colorado Island, Panama, Putz et al. (1983) reported that of trees suffering complete stem breakage between 1976 and 1980, approximately half sprouted. Trees smaller than the median size (dbh = 22 cm) had a higher propensity to sprout than larger trees. They also observed that the height of stem breakage was fairly evenly distributed

Valuation of consumption and sale of forest goods from a Central American rain forest.

Researchers recognize that society needs accurate and comprehensive estimates of the economic value of rain forests to assess conservation and management options. Valuation of forests can help us to decide whether to implement policies that reconcile the value different groups attach to forests. Here we have measured the value of the rain forest to local populations by monitoring the foods, construction and craft materials, and medicines consumed or sold from the forest by 32 Indian households in two villages in Honduras over 2.5 years. We have directly measured the detailed, comprehensive consumption patterns of rain forest products by an indigenous population and the value of that consumption in local markets. The combined value of consumption and sale of forest goods ranged from US

Household determinants of deforestation by amerindians in honduras

17.79 to US

The Effect of Income on the Extraction of Non-Timber Tropical Forest Products: Model, Hypotheses, and Preliminary Findings from the Sumu Indians of Nicaragua

23.72 per hectare per year, at the lower end of previous estimates (between US

An introduction to hurricanes in the Caribbean

49 and US