Invasive exotic tree and shrub species (woody weeds) form dense, monospecific stands in many areas of New Zealand. At some sites, the weed dies out naturally and is replaced by native species as succession proceeds, but at others the weed persists indefinitely. The ability to distinguish between these different trajectories is critical to effective weed management, but the conditions that determine successional outcomes remain poorly understood.
Many of New Zealand’s natural and induced tussock grasslands are in a degraded low-biomass state due to a combination of fire, overgrazing and weed invasion. The capacity of degraded grasslands to recover biomass is uncertain because legacies of degradation can strongly influence the demographic processes controlling ecosystem recovery. We develop a conceptual framework for understanding biomass carbon (C) flux in degraded perennial grassland based on demographic processes of growth, mortality and recruitment.
The literature on wind damage in New Zealand forests is reviewed to investigate how abiotic and biotic factors influence damage severity, damage type, and forest recovery. Winds that damage forests tend to result from extra-tropical depressions or from topographically enhanced westerly air flows. Severe wind damage can occur when wind speeds exceed c. 0 km/hr, although investigating the relationship between damage and wind speeds is difficult, as gusts, for which speed is usually unrecorded, are important.
Nearly one quarter of New Zealands unique vascular plant flora is threatened, and weed invasion is implicated in the decline of more than half of these threatened species. However, there is little experimental evidence showing that invasive weeds have a direct impact on threatened native plants. This study experimentally tested the hypothesis that competition with invasive weeds threatens the rare outcrop plant Pachycladon cheesemanii (Brassicaceae).
Over five years from November 1982 to November 1987, we examined 395 mice collected from unlogged and logged native forest and from exotic forest at Pureora Forest Park, in the central North Island of New Zealand. Sex ratio, litter size, and breeding effort (pregnancy rate in females, proportion of males with visible tubules) were similar in all samples.
Translocation to island reserves is a common strategy in New Zealand and elsewhere for safeguarding species against introduced predators. When successful, however, the closed nature and relatively small size of many island sanctuaries can result in populations quickly reaching their carrying capacity, which in itself can present further challenges such as reduced productivity and population growth rates associated with density-dependent effects as well as increased rates of inbreeding.