Carolina Murcia

Edge effects in fragmented forests: implications for conservation.

Edges are presumed to have deleterious consequences for the organisms that remain in forest fragments. However, there is substantial discrepancy among recent studies about the existence and intensity of edge effects. Most studies have focused on seeking simplistic and static patterns. Very few have tested mechanistic hypotheses or explored the factors that modulate edge effects. Consequently,studies are very site-specifci and their results cannot be generalized to produce a universal theory of edges. Although estimates of the intensity and impact of edge effects in fragmented forests are urgently required, little can be done to ameliorate edge effects unless their mechanics are better understood.

Effect of Floral Morphology and Temperature on Pollen Receipt and Removal in Ipomoea Trichocarpa

In Gainesville, Florida, the coastal morning glory Ipomoea trichocarpa varies considerably in flower size, shape, and stigma-anther separation. I studied some of the causes and reproductive consequences of this variation by exploring its effect on pollen receipt and removal. Variation in flower size was caused by variation within genets and, more drastically, by temperature fluctuations. While several insect taxa visited I. trichocarpa flowers, I concentrated on one hawk moth species (Enyo lugubris) and the bumble bee Bombus pennsylvanicus. Hawk moths visited the flowers from the time of anthesis until sunrise, when bumble bees arrived. Stepwise regression analyses indicated that flower morphology affected pollen deposition during single hawk moth visits, single bumble bee visits, or unlimited hawk moth and bumble bee visits. The morphological variables with strongest effects differed in each case, and could be related to the foraging technique of each pollinator. Floral morphology affected pollen removal from flowers more than it influenced pollen receipt. The morphological variables that best explained variation in the amount of pollen removed from the anthers during a single bumble bee visit differed from those influencing pollen receipt. In the field, hawk moths could potentially fully pollinate I. trichocarpa before pollen from later rising bumble bees could send tubes to ovules. However, tube growth rate increased with rising morning temperatures. Thus, ovules could potentially have been fertilized by a mixture of pollen deposited by hawk moths and by bumble bees. Furthermore, low morning temperatures excluded hawk moths entirely from I. trichocarpa pollination, by delaying anthesis. On cool mornings, flowers opened in time to receive bumble bee visits only. The effect of temperature on flower size and pollinator type, coupled with the physical interaction between flower and pollinator morphologies, determined the amount of pollen removed from and received by I. trichocarpa.

Evaluation of Andean alder as a catalyst for the recovery of tropical cloud forests in Colombia

Abstract Andean alder (Alnus acuminata) is a tree species often used in revegetation programs in the Colombian Andes, because it is native to the area and grows rapidly even in nitrogen-poor soils. Previous work implied that Andean alder plantings might not lead to as rich a diversity of native vegetation as would natural regeneration. At Ucumari Regional Park in the Central Andes of Colombia, 30-year-old alder plantations are juxtaposed to naturally regenerated forests of the same age. This study quantifies the impact of Andean alder on plant species composition and forest structure, compared to natural regeneration. Plantations and naturally regenerated forests differed in physiognomy, species composition and in some structural aspects. Alder plantations produced an even 20 m tall canopy. The foliage was vertically stratified into two distinct strata separated by a gap that exposed the boles. The naturally regenerated forest had an uneven 16–18 m tall canopy, vertically continuous foliage cover and significantly higher canopy cover. In both forest types, basal area and stem density were equivalent and distributed among size classes in the same way. Snags in naturally regenerated forests were thicker, perhaps offering a better resource base to organisms using this resource. Plantations had up to one-third fewer species per unit than naturally regenerated forests. Plantations showed a low alpha and beta diversity, with lower species turnover from plot to plot. Qualitatively, the vegetation in the plantations was distinct from that in naturally regenerated forests, as it was composed of a particular subset of species. Approximately one-fourth of species in plantations were exclusive to that forest type. The same patterns were found in the understorey vegetation (1.3–10 m high), where alder is not recruited. This suggests that these patterns are not an artifact of numerical abundance of alder, but rather that alder actually has an effect on species composition. Although alder may create a forest cover in a shorter time, natural regeneration might be a better strategy for the recovery and conservation of biodiversity as long as a propagule source is available. Presence of both forest types, however, may increase species richness and spatial heterogeneity at the landscape level.

A Review and Synthesis of Conceptual Frameworks for the Study of Forest Fragmentation

Forest fragmentation is the large-scale transformation of a forested landscape to one in which remnant forest patches are isolated in a matrix of anthropogenic habitats. Forest fragmentation is a major cause of loss of biological diversity, in particular in the species-rich wet tropics, where landscape transformation is an ongoing process (Whitmore 1997; Vina and Cavelier 1999). A large body of literature gives evidence of the negative effects of fragmentation, which include changes in the physical environment, and regional and local extirpation of populations of many species of plants and animals (Saunders et al. 1991; Schelhas and Greenberg 1996; Turner 1996; Laurance and Bierregaard 1997).

Comparative habitat susceptibility to invasion by Chinese ash (Fraxinus chinensis: Oleaceae) in a tropical Andean landscape

Chinese ash (Fraxinus chinensis) is an exotic tree species that has been used in non-commercial monospecific plantations for revegetation programs in the Central Andes of Colombia. At the Otún river watershed, these plantations occur in patches intermixed with old pastures, oak forests, and successional forests. In this heterogeneous landscape, the ash has been able to invade some of its surrounding habitats. This study evaluates the invasion patterns of ash to each of these habitats and experimentally quantifies seed and seedling survivorship and seedling growth as three processes that could determine ash establishment. Of the four habitats examined, old pastures were the most vulnerable to invasion, followed by oak plantations, and successional forest. Ash plantations exhibited recruitment levels intermediate between pastures and oak plantations. Abandoned pastures showed the highest seed germination, seedling survivorship, and seedling growth. In the ash plantations, recruitment seemed negatively affected by the low number of germinated seeds, high mortality of seedlings, and low growth. Invasion in oak plantations was constrained by high seed mortality and burial of seedlings by leaf litter, although the seedlings that did survive grew fast and produced a high number of leaves. Within the successional forest, Chinese ash seeds germinated but establishment was constrained by a reduced seedling survivorship and low growth. This research offers new evidence of how different processes affecting the establishment of an invader may differ among landscape elements, and it also yields important information for the management and control of ash in these Andean landscapes.

The road to confusion is paved with novel ecosystem labels: a reply to Hobbs et al.

Responding to our critique of the novel ecosystem concept [1], Hobbs et al. [2] misrepresent our points of view, so we begin by clarifying our position. First, we do not deny the existence of anthropogenically transformed ecosystems; cities, pastures, agricultural fields, or open-pit mines are real and have accompanied humans for millennia. We agree: society must deal with these ecosystems in sensible and effective ways, as part of the much larger effort to transition toward sustainability, maintain biodiversity, and provide ecosystem services to humans and habitat to other species.

Tree Responses to Edge Effects and Canopy Openness in a Tropical Montane Forest Fragment in Southern Costa Rica

Tropical forests frequently experience the opening and closing of canopy gaps as part of their natural dynamics. When fragmented, the forests are also exposed to edges, which (at least in the lowlands) cause increased mortality on the fragments periphery and—depending on the fragment size—also on the forest interior. Here we explore if the presence of edges increase the rate at which the canopy opens in a montane forest and if and how that interaction affects the vegetation composition and structure. At Las Cruces Biological Station (SW Costa Rica), we surveyed four 150 m edge-to-interior transects to evaluate changes in vegetation structure (stem density and basal area for all plants with DBH > 5 cm) and species richness and composition as a function of both distance to the edge and canopy openness. Edge proximity did not increase canopy openness. Canopy openness, however, did affect stem density, species richness, and composition. Consequently, heterogeneity in forest structure, diversity, or composition could not be attributed to indirect edge effects. Forest edges, however, had a direct effect on species composition, but with a negligible effect on species diversity and forest structure. Overall, these results reveal that the structure, diversity, and composition of tree communities in this tropical premontane forest fragment are more strongly influenced by canopy openness than by the proximity of edges.

APPLICATION OF SCIENCE TO PROTECTED AREA MANAGEMENT: OVERCOMING THE BARRIERS1

Abstract No other line of practice requires application of science more urgently than conservation. Here we explore several elements that must be put in place to establish lines of communication between scientists and managers of protected areas. First, it is necessary that scientists are aware of the information needs of managers, that they produce the relevant information, and that this information is available to managers. Second, it is necessary that managers not only know how to access, process, and incorporate the information, but that they also internalize their need for that science and the clear advantages of incorporating it into their practice. We propose several mechanisms to ensure an adequate flow of information between the two groups: active dialogue between the parties, translators of science located both in academia and government and nongovernmental organizations (NGOs), and execution of joint projects. In particular, we argue that science-oriented NGOs can play a major role in bridging the gap between basic science and on-the-ground conservation. We finish by describing three case studies in which some of these models have been explored in Colombia and how science has been applied to address conservation and management concerns.

An Evaluation of Bess Beetles (Passalidae) and Their Resource Base in a Restored Andean Forest

Degraded lands in the Colombian Andes have been restored by means of monospecific tree plantations of native and exotic species, and by abandoning lands to natural regeneration. Both methods rapidly produce a vegetation cover that helps to stabilize soils, but the value of resulting ecosystems for wildlife needs to be evaluated. We assessed the effects of these two restoration methods on the diversity and abundance of bess beetles (Passalidae), which are important deadwood recyclers. We quantified coarse woody debris (logs and branches >10 cm diameter) and associated passalid beetle fauna in 40-year-old Andean alder (Alnus acuminata) plantations, adjacent natural regeneration and old-forest remnants, at 2430 m of elevation in the Central Andes. The three forest types contained the same number of logs per unit area, but wood volume was lower in alder stands than in natural forest types. Old-forest remnants contained a higher number of occupied logs and individual beetles per transect and per unit wood volume than the two other habitats. We found six species of beetle, three of which were found in the three habitats and the other three in one habitat each. Forest remnants and natural regeneration had four species each, whereas alder plantations had three species. Although beetle abundance was lower in alder stands, in the small-scale mosaic found at this site alder plantations behaved similarly to secondary forest and merged as part of the local habitat heterogeneity. Whether these results apply to larger and more isolated plantations remains to be established.

“Reading the Minds” for Quantitative Sustainability: Assessing Stakeholder Mental Models via Probabilistic Text Analysis

Management of complex ecosystems is a difficult process that involves multiple factors and stakeholders. In most cases, the interactions of these factors and stakeholders’ trade-offs are not considered quantitatively in the design and management of ecosystems. To address these issues mental modeling is useful for eliciting stakeholder objectives and preferences in order to evaluate preliminary knowledge about structure and function of complex ecosystems. This is advantageous for ecosystem analysis, modeling, and management.