Invasion impact is conditioned by initial vegetation states

Abstract Biological invasion is a crucial problem in the world because of its negative consequences for protected areas. The degradation stage of vegetation might affect the success of invasion. One of the most abundant and threatening invasive species is the common milkweed (Asclepias syriaca L.) which has invaded already 23 countries of Europe and in several habitat types its further spreading is promoted by climate change. Pannonian sand grassland is one of the most threatened habitat by common milkweed invasion. Therefore, invasion in sand grassland vegetation is an important issue. However, the effects of the invasive plant in the open sand grassland are rather controversial. In order to clarify the existing contradictory results, the study was carried out in a strictly protected area, near Fülöpháza (Hungary) in a reserve core area in a UNESCO biosphere reserve. Microcoenological study was applied to determinate the fine-scale community characteristics of non-invaded and invaded stands in natural and seminatural vegetation and data were processed by Juhász-Nagy's information theory models. Shannon diversity of species combinations (compositional diversity) which describes the ways of the coexistence of species, and the number of realized species combinations were used for measuring beta diversity. Differences between stands were analyzed by two-way ANOVA. The maximum compositional diversity of species and main life-forms (annuals, perennials and cryptogams) did not differ significantly between the non-invaded and invaded stands. In contrast, significantly larger characteristic areas of compositional diversity were detected in the invaded stands. Based on these results, it could be concluded that diversity of species combinations did not change but those values have shifted to coarser scales in case of invaded stands. The direction of this change suggests a kind of impoverishment in the presence of Asclepias. Thus, it is worth mentioning from the invasion management point of view that protection of the habitats against disturbance is a more cost-effective and successful way than protection against the establishment or extirpation of invasive species, since disturbance facilitates the invasions throughout the impoverishment of the community

Can forest management based on natural disturbances maintain ecological resilience?

Given the increasingly global stresses on forests, many ecologists argue that managers must maintain ecological resilience: the capacity of ecosystems to absorb disturbances without undergoing fundamental change. In this review we ask: Can the emerging paradigm of natural-disturbance-based management (NDBM) maintain ecological resilience in managed forests? Applying resilience theory requires careful articulation of the ecosystem state under consideration, the disturbances and stresses that affect the persistence of possible alternative states, and the spatial and temporal scales of management relevance. Implementing NDBM while maintaining resilience means recognizing that (i) biodiversity is important for long-term ecosystem persistence, (ii) natural disturbances play a critical role as a generator of structural and compositional heterogeneity at multiple scales, and (iii) traditional management tends to produce forests more homogeneous than those disturbed naturally and increases the likelihood of unexpected catastrophic change by constraining variation of key environmental processes. NDBM may maintain resilience if silvicultural strategies retain the structures and processes that perpetuate desired states while reducing those that enhance resilience of undesirable states. Such strategies require an understanding of harvesting impacts on slow ecosystem processes, such as seed-bank or nutrient dynamics, which in the long term can lead to ecological surprises by altering the forest's capacity to reorganize after disturbance

The Western Australian regional forest agreement: economic rationalism and the normalisation of political closure

This article explores the constraints imposed by economic rationalism on environmental policy-making in light of Western Australia\u27s (WA) Regional Forest Agreement (RFA) experience. Data derived from interviews with WA RFA stakeholders shed light on their perceptions of the RFA process and its outcomes. The extent to which involvement of science and the public RFA management enabled is analysed. The findings point to a pervasive constrainedness of WA\u27s RFA owing to a closing of the process by the administrative decision-making structures. A dominant economic rationality is seen to have normalised and legitimised political closure, effectively excluding rationalities dissenting from an implicit economic orthodoxy. This article argues for the explication of invisible, economic constraints affecting environmental policy and for the public-cum-political negotiation of the points of closure within political processes

Adaptive management and adaptive governance in the everglades ecosystem

The Everglades is an intensively managed ecosystem where control of the water has allowed agricultural, urban and economic development, while struggling to meet biodiversity conservation goals. The over 100 year history of control began in response to a disastrous series of floods and droughts followed by environmental crises at an ecosystem scale. Each of these events precipitated technological fixes that extended control of water resources. Institutional structures have been continually reorganized over the last century to meet shifting social objectives, the latest of which is ecosystem restoration. However, the basic response, which employs engineering and technological solutions, is a type of social trap, where governmental mandates, planning-based paradigms and vested interests all interact to inhibit the resolution of chronic environmental issues. Experience from other resource systems indicates that in such an inherently complex system wrought with multiple uncertainties, restoration must be discovered through experimentation and learning embraced by adaptive management. Though minimal steps towards adaptive management have been made, we argue that adaptive forms of experimentation and governance are needed to resolve chronic resource issues and achieve restoration goals. Copyright Springer Science+Business Media, LLP 2006Water management, Adaptive management, Adaptive governance, Everglades,