Suchergebnisse

Man's recent colonization of New Zealand has dramatically altered the resident biota and resulted in the introduction of numerous alien organisms to these once remote islands. In reverse, there is increasing evidence of a lesser known export of species to other regions of the world. This volume presents an in-depth review of the level and rate of such invasions, and investigates what controls the success of invaders and the consequences for ecosystems both on land and offshore. It provides invasion biologists everywhere with tests of current theories about those factors leading to the success of invaders as well as evaluating principles for understanding the nature of their impacts that form a solid basis for the effective management of biological invasions worldwide.

AbstractWe propose that XML should be used as an interchange language for system dynamics models and we have designed and implemented a demonstration that we call XMILE. We believe that there will be many benefits for the system dynamics community in developing a full‐scale interchange language. This paper discusses the motivation factors behind the idea of developing an interchange language for system dynamics models, and explains why XML is a good candidate framework. An initial implementation of XMILE is also presented along with initial findings about its applicability to models built on various system dynamics software platforms. Copyright © 2005 John Wiley & Sons, Ltd.

Context Feral pigs (Sus scrofa) have a wide global distribution that includes large parts of Australia and New Zealand. There is concern about the impacts of feral pigs on above- and below-ground flora and fauna, but little is known about their habitat use and feeding activity in temperate rainforests. Aims We evaluated the importance of abiotic and biotic variables hypothesised to influence seasonal and annual feral pig habitat use and feeding activity in a montane conifer–angiosperm rainforest in Te Urewera, North Island, New Zealand. Methods We used a grid of 25 remote-camera locations to collect feral pig images in a 100-ha area during the winters and summers of 2010 and 2011. Plant composition, solar radiation and soil fertility variables were determined for each camera-image area. Multiseason, multistate occupancy models and information-theoretic methods were used to evaluate how these variables related to feral pig occupancy and feeding. Key results Feral pigs occupied more camera locations in summer than in winter, and detection probabilities increased if piglets were present and with increasing soil phosphorus (P). Piglets were detected only in summer, and their detection probability increased with increasing soil P. The probability of detecting feral pigs feeding also increased with soil P and was higher in 2010 than 2011. Conclusions Feral pigs selected locations with high soil P, probably because those sites had more food than did locations with low soil P. Mast fruiting of tawa (Beilschmiedia tawa) has been hypothesised to increase feral pig recruitment, and the higher detection probability of piglets in summer 2010 followed a heavier tawa fruit fall. Implications Our study highlighted the usefulness of camera traps and occupancy models for understanding seasonal and annual dynamics of cryptic ungulate species in remote, rugged forests, and suggests that the impacts of feral pigs will be greatest in areas of high soil P following widespread tawa masting.

Context When environmental, economic and/or social effects of wildlife are considered undesirable and need to be reduced, managers require knowledge of the effectiveness of candidate control techniques, particularly the relationship between control effort and change in abundance. Aims We evaluated the effects of control on the abundances of introduced red deer (Cervus elaphus scoticus) and sika deer (Cervus nippon) at three New Zealand forest sites (two North Island, one South Island) in an 8-year adaptive-management experiment. Methods We identified paired areas of 3600 ha at each site that were as similar as possible in geology, physical environments and forest composition and applied deer control (helicopter- and/or ground-based hunting) to a randomly selected member of each pair. The abundances of deer were monitored in each treatment and non-treatment area for up to 7 years by using faecal pellet counts on 50 randomly located transects. Key results The difference between deer abundances in the treatment and non-treatment areas was significantly negative at one site, significantly positive at one site and indistinguishable at the other site. Faecal pellet abundances declined with increasing helicopter-based hunting effort but did not change with increasing ground-based hunting effort. There was evidence that aerially sown 1080 baits used for possum control in two treatment areas reduced deer abundances. Conclusions The substantial uncertainty surrounding the relationships between deer control effort and changes in deer abundance means that managers cannot assume that the environmental, economic and/or social problems caused by deer will be alleviated with the quantum of control effort applied in the present study. Implications Reducing the abundances of deer in forests may require substantially more control effort than is currently believed.

Abstract
Linking individual and stand-level dynamics during forest development reveals a scaling relationship between mean tree size and tree density in forest stands, which integrates forest structure and function. However, the nature of this so-called scaling law and its variation across broad spatial scales remain unquantified, and its linkage with forest demographic processes and carbon dynamics remains elusive. In this study, we develop a theoretical framework and compile a broad-scale dataset of long-term sample forest stands (n = 1,433) from largely undisturbed forests to examine the association of temporal mean tree size vs. density scaling trajectories (slopes) with biomass accumulation rates and the sensitivity of scaling slopes to environmental and demographic drivers. The results empirically demonstrate a large variation of scaling slopes, ranging from −4 to −0.2, across forest stands in tropical, temperate, and boreal forest biomes. Steeper scaling slopes are associated with higher rates of biomass accumulation, resulting from a lower offset of forest growth by biomass loss from mortality. In North America, scaling slopes are positively correlated with forest stand age and rainfall seasonality, thus suggesting a higher rate of biomass accumulation in younger forests with lower rainfall seasonality. These results demonstrate the strong association of the transient mean tree size vs. density scaling trajectories with forest demography and biomass accumulation rates, thus highlighting the potential of leveraging forest structure properties to predict forest demography, carbon fluxes, and dynamics at broad spatial scales.

Context
There is concern that deer are shifting forests towards undesirable trajectories, and culling of deer is often advocated to mitigate these impacts. However, culling deer is expensive and sometimes controversial. To reliably ascertain whether such action is beneficial, management-scale experiments are needed. We conducted a management experiment to evaluate the benefits of culling deer in four New Zealand forests.

Aims
Our experiment tested the predictions that culling deer should increase (1) canopy tree seedling height relative growth rate (SHRGR), and (2) the foliar biomass of understorey species palatable to deer (FBP).

Methods
Each forest was divided into two 3600-ha areas, with deer culling randomly assigned to one area. Deer abundances were indexed using faecal pellet counts, and forest variables were measured at the start and end of the 8-year experiment. Deer were already at low abundance in one forest and were not culled there. We used structural equation modelling (SEM) with Bayesian variable selection to update our a priori graphical forest–deer model with data from all four forests.

Key results
Deer abundances were significantly reduced in one forest but increased or did not change in the other two forests in which deer culling occurred. Culling deer did not increase seedling height relative growth rate (SHRGR) or the foliar biomass of understorey species palatable to deer (FBP) in the three areas subject to deer culling compared with the three areas not subject to deer culling. SEM revealed no significant relationships between local-scale deer abundance and either SHRGR or FBP. Rather, tree basal area and the foliar biomass of unpalatable understorey species were important predictors of FBP and SHRGR, respectively, in some forests.

Conclusions
Our study revealed that culling deer, as currently practiced by New Zealand land managers, did not generate the desired responses in New Zealand forests, possibly due to deer not being culled to sufficiently low densities and/or because forest dynamics and abiotic drivers determined plant growth more than deer.

Implications
Managers should consider actions other than ineffective deer culling (e.g. creating canopy gaps) to alter the dynamics of New Zealand forests. Alternatively, managers will need to substantially increase culling effort above what is currently practised for this activity to substantially reduce deer populations and thus potentially alter forest dynamics.