Long-term Spatiotemporal Dynamics Research Articles

Intervention Analysis of Hurricane Effects on Snail Abundance in a Tropical Forest Using Long-Term Spatiotemporal Data

Large-scale natural disturbances, such as hurricanes, have profound effects on populations, either directly by causing mortality, or indirectly by altering ecological conditions or the quantity, quality, and spatial distribution of resources. In the last 20 years, two major disturbances, Hurricane Hugo in 1989 and Hurricane Georges in 1998, struck the Luquillo Mountains of Puerto Rico, providing an unique opportunity to understand the long-term effects of recurrent disturbances on the abundance of species. Nenia tridens is one of the most abundant and pervasive terrestrial gastropods in the Luquillo Mountains. Estimates of yearly abundance of N. tridens from 40 sites on the Luquillo Forest Dynamics Plot from 1991 to 2007 facilitate the development of a spatiotemporal model with intervention effects on the mean abundance over time in response to each hurricane. Intervention effects characteristically decay over time, similar to those in a time series analysis. Model parameters were estimated in a Bayesian framework. Model comparison and diagnostics suggest that our intervention model provides a plausible description of hurricanes effects on the abundances of N. tridens and may be useful for studying long-term spatiotemporal dynamics from the perspective of disturbance and succession.

The effects of disturbance based management on the dynamics of Mediterranean vegetation: A hierarchical and spatially explicit modeling approach

The eastern Mediterranean region has been subjected to intensive human disturbance in the past 10,000 years, mainly in the forms of agro-pastoral activities such as grazing, shrub clearing, and prescribed burning. This disturbance history resulted in the formation of highly heterogeneous landscapes, characterized by high biodiversity. Recent changes in human activities have resulted in a decrease of landscape heterogeneity, leading to decreasing biodiversity and increasing fire risk. To conserve heterogeneity, land managers apply disturbance based management practices, using the same activities that created and maintained landscape heterogeneity in the past. However, the long-term and large-scale outcomes of these disturbances are often unknown, due to the complex response of Mediterranean vegetation to disturbance. Here we report on a spatially explicit, hybrid, and spatially hierarchical ecological model developed by us. The model attempts to predict the outcome of various disturbance based management activities on the long-term spatio-temporal dynamics of five common Mediterranean vegetation types. The model uses a spatially explicit state and transition formulation, with continuous transition functions. Model simulations were conducted on a Mediterranean landscape in Northern Israel, incorporating various disturbance practices that are common in the region. Simulation results highlight the potential of disturbance based management as a tool for conserving landscape heterogeneity, as well as the complex interactions between disturbances and the spatial structure of the landscape in Mediterranean regions.

Long-term spatiotemporal dynamics of solid-state lasers and vertical-cavity surface-emitting lasers

The number of Maxwell-Bloch equations describing the spatiotemporal evolution of solid-state and semiconductor-based lasers can be reduced when the temporal scales of the fields and atomic variables are very different. We demonstrate the existence of slow (center) manifolds for models of solid-state lasers (such as Nd:YAG) and vertical-cavity surface-emitting lasers and determine reduced equations in the presence of both diffraction and carrier diffusion. Two separate methods of obtaining the reduced equations are presented. Excellent agreement between the reduced models and the original equations is obtained when the slow manifolds are expanded in a perturbative series. Since stiffness is removed, the computational time for the long-term spatiotemporal dynamics of these devices can be strongly reduced, typically by 2 orders of magnitude.

Long-term spatio-temporal dynamics and historical continuity of European aspen (Populus tremula L.) stands in the Koli National Park, eastern Finland

Summary Although the European aspen ( Populus tremula L.) is regarded as a keystone species for the biodiversity of northern Europe, its mechanisms of regeneration and persistence under old-growth conditions without large-scale disturbances have remained obscure. The aim of this paper is to describe the long-term dynamics and regeneration of European aspen in the old-growth forests of the Koli National Park, eastern Finland, in order to gain a better understanding of the occurrence of this species under natural forest conditions. The park includes both natural forests and forests that were previously managed. The long-term occurrence of aspen populations was determined on the basis of inventory data available for the years 1910, 1936 and 2004. Aspen is shown to have occurred at least temporarily over 34 per cent of the total forest area (840 ha). In addition, 13 per cent of the forest area continuously supported stands that contained large aspen trees between 1910 and 2004. In areas where no management took place (6.4 per cent of the area), about one-third of all the aspen stands contained large trees and persisted throughout the period. The results show that aspen can maintain long-term occurrence in old-growth forests and that the species is not only transient or confi ned to young successional stages. Areas where aspen regeneration is possible, as deduced from its long-term occurrence should be regarded as highly valuable for biodiversity because they offer long-term habitats for several threatened species that are associated with aspen trees. Recent changes in ecological conditions, however, may affect this in the future. Most notably, the increased population of large mammalian browsers may make aspen regeneration more diffi cult and should be taken into account when restoration and management measures are planned.