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The role of density dependence in the population dynamics of tropical trees has been a subject of considerable debate. Here, we present data on the demography of the edible palm Euterpe edulis, classified into seven size categories and monitored over three years. On average, each adult palm contributed 98 seedling recruits per year into the population. The pattern of mortality was similar to that of other palms, with mortality being highest among the smallest plants. Those plants with a diameter at soil level >20 mm had an annual mortality <7%. Density dependence was found to act only on the seedling stage of the life cycle. The probability of survival and transition of seedlings to the next size class were affected both by the density of seedlings and the presence of conspecific adults. Matrix modeling indicated that the true finite rate of population increase (λ) was 1.28 and that the observed reverse “J”‐shaped size distribution of plants was a consequence of the density dependence operating in the population. Elasticity analysis showed that the survival elements in the matrix contributed most to the value of λ, and that the position of the transition matrix in growth–survival–fecundity (G–L–F) space was influenced by density. The matrix model incorporating density dependence predicted size distributions and densities approximating the maximum observed in the field. Spatial simulations indicated that the predictions from the matrix model relating to the size structure of plants are robust, but that the predictions of densities are sensitive to the precise spatial dynamics of the population.

Summary1. Structured population models are used in a range of forms to predict the long-term behaviour of populations of economic or conservation interest. Such models rarely include density-dependence and do not account explicitly for the ordering of events within a generation. 2. We analysed a model for the harvesting of adults of the edible palm Euterpe edulis in which the role of density-dependence had been clearly defined. We modified the timing of harvesting in relation to the point in the life cycle at which populations were censused. 3. It is shown that the timing, form and intensity of harvesting are all important in determining asymptotic population behaviour. If harvesting affects only those individuals that were recorded as being adults at the start of a year, then the model predicts that all adults may be harvested without population eradication. In contrast, if harvesting also affects individuals moving from the next smaller size class during the course of a year then populations can, under some forms of harvesting, tolerate much lower levels of harvesting. 4. If density-dependence is not taken into consideration, predictions of population responses to harvesting may be erroneous. A review of transition matrices for woody plants indicates that many of these may have been derived from populations subject to strong population regulation. 5. Synthesis and applications. In the specific case of E. edulis our model shows that, although populations appear to be robust to very high levels of harvesting, when modelled as affecting only reproductive adults, this conclusion may be sensitive to varying the timing and form of harvest, and to the assumption that only reproductive individuals are removed. Structure population models used to determine levels of harvesting should account for the existence of density-dependence as well as its timing.

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The effect of the adjacent non-forested environment on the forest near the edge, edge influence (EI), is an important impact in fragmented landscapes and is believed to vary with factors such as forest structure and edge contrast. In order to improve our understanding of the factors governing the variability in EI, we studied microclimate and vegetation at cerrado edges surrounded by variable land uses in southeastern Brazil, a system with both forest and savanna fragments. We determined the significance, magnitude and distance of EI on microclimate, vegetation structure and grass biomass which we measured along five transects perpendicular to fourteen edges in forest or savanna next to different land uses. We introduce a quantitative measure of edge contrast that considers land uses at different distances from the same edge (e.g., a firebreak between a forest edge and a plantation) and verified whether edge contrast is correlated with EI in this system. Notwithstanding the large variation in EI among variables and study sites, there were some similarities in the patterns of EI between forest and savanna edges. Edge contrast was successfully quantified by our measure but was only correlated with EI on moisture and grass biomass. Our results point to the high variability in EI within a region. Our quantitative measure of edge contrast may be useful in explaining variability in EI. However, much unexplained variation remains in the highly fragmented cerrado system which is affected by EI in both forest and savanna fragments.

Several studies have documented that fires are widespread in the tropics. Because fire in the Atlantic Rain Forest is rare, fire events and their consequences at the community level have not been evaluated. This study describes the composition of different seed banks in areas of Atlantic Forest. The study was carried out in the National Park of Tijuca in the state of Rio de Janeiro. Four different areas were chosen considering their differences on fire history. Fifteen soil surface samples (23 cm (centimeter) diameter ·7 cm height at 5 cm deep) were obtained from random locations within each site. The dominant family at all study sites except in the most preserved one were Dennstaetiaceae, followed by Melastomataceae and Poaceae. The family Dennstaetiaceae was exclusively represented by Pteridium aquilinum (Klf.) Herter. There were no significant differences among areas when comparing the number of seedlings excluding P. aquilinum. However, the number of P. aquilinum was higher in the most disturbed area, while Melastomataceae and Rubiaceae were more frequent in a less impacted area. Our results suggest that the seed bank in disturbed areas of the Atlantic Forest possibly will not contribute for forest restoration after disturbance.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. The role of density dependence in the population dynamics of tropical trees has been a subject of considerable debate. Here, we present data on the demography of the edible palm Euterpe edulis, classified into seven size categories and monitored over three years. On average, each adult palm contributed 98 seedling recruits per year into the population. The pattern of mortality was similar to that of other palms, with mortality being highest among the smallest plants. Those plants with a diameter at soil level >20 mm had an annual mortality <7%. Density dependence was found to act only on the seedling stage of the life cycle. The probability of survival and transition of seedlings to the next size class were affected both by the density of seedlings and the presence of conspecific adults. Matrix modeling indicated that the true finite rate of population increase (X) was 1.28 and that the observed reverse "J"-shaped size distribution of plants was a consequence of the density dependence operating in the population. Elasticity analysis showed that the survival elements in the matrix contributed most to the value of X, and that the position of the transition matrix in growth-survival-fecundity (G-L-F) space was influenced by density. The matrix model incorporating density dependence predicted size distributions and densities approximating the maximum observed in the field. Spatial simulations indicated that the predictions from the matrix model relating to the size structure of plants are robust, but that the predictions of densities are sensitive to the precise spatial dynamics of the population.1979, Hubbell and Foster 1986), known as the community drift model. In contrast to this nonequilibrium model, it has been argued at the other extreme that density-dependent and distance-related recruitment may be responsible for the low mean densities of many tropical trees and the consequent high species diversity (Janzen 1970, Connell 1971. In this latter case, specialist herbivores, seed predators, and pathogens are envisaged as maintaining populations around low densities and high species diversity. Critics of the Janzen-Connell model have suggested that the strength of density dependence is insufficient to remove the clumped distributions of seedlings beneath parents (Hubbell 1980). The community drift model of tropical forest dynamics, on the other hand, has also been criticized on the basis that it fails to take into account high levels of compositional similarity in disjunct samples of forest (Terborgh et al. 1996). Moreover, Wills et al. (1997) have found that int...

Large areas of the Brazilian savanna (cerrado) have been converted into farmland in recent years; however, little attention has been paid to the consequences of this land use and land cover change on groundwater recharge. Here, we assessed groundwater recharge in different physiognomies of the cerrado located in an outcrop area of the Guarani Aquifer System. Water table fluctuations were measured from October 2011 through August 2013, by 58 monitoring wells distributed on four physiognomies of the undisturbed cerrado. We used multiple monitoring wells located in “campo limpo” (cerrado grassland), “campo sujo” (shrub cerrado), “campo cerrado” (open wooded cerrado), and “cerrado sensu stricto” (wooded cerrado), cover types. Recharge rates were computed for each well using the water table fluctuation method. The measured precipitation for hydrological years 2011–2012 and 2012–2013 were 1247 and 1194 mm, respectively. We found values of average annual recharge of 363 ± 87 mm, 354 ± 85 mm, 324 ± 78 mm, and 315 ± 76 mm for “campo limpo,” “campo sujo,” “campo cerrado,” and “cerrado sensu stricto,” respectively. Our results suggest that recharge tends to decrease with the increase in the density of vegetation (grassland to woodland). These results indicate that water table depth may have an influence on the cerrado physiognomies or vice versa. Furthermore, replacement of undisturbed dense cerrado with croplands will likely alter recharge dynamics. Therefore, sound management of land use and land cover is needed to ensure future groundwater quantity and quality.