facilitation

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.

Recruitment failure of native plants is common in dryland ecosystems in New Zealand. We investigated whether herbicide control of invasive grasses or restoration of either shrub cover or the natural disturbance regime (river gravel deposition after flooding) can promote seedling establishment of the critically endangered shrub Olearia adenocarpa and two common species also found in river floodplain ecosystems (Carmichaelia australis and Sophora microphylla).

The species composition of the understory can be a key indicator of successional trajectories in the absence of disturbance at forested sites. We surveyed species composition and percent cover in the understory of 132 closed-canopy stands of 41 woody weed species throughout New Zealand as a first step in understanding potential successional trajectories in these weed populations. Twenty-seven weed species had zero, or very few, conspecific seedlings or saplings present beneath their own canopy.

It is common practice in New Zealand dryland areas to chemically or mechanically control invasive woody weeds, including Scotch broom (Cytisus scoparius). Such weed control is not always effective in achieving the often implicit aim of advancing the restoration of indigenous woody vegetation. We used a field experiment on a braided river terrace on the Canterbury Plains to test how five different management treatments of broom cover affected the germination, survival and growth of six indigenous tree and shrub species in a dryland setting.

Establishment of Nothofagus spp. into grasslands can be limited by a lack of ectomycorrhizal inoculum, but the degree of mycorrhizal inoculum limitation and how far mycorrhizal inoculum spreads from forest edges has not been quantified. Further, it has been hypothesised, but not confirmed, that established Kunzea ericoides (a native Myrtaceae tree with both ectomycorrhizal and arbuscular mycorrhizal associations) could serve as an alternative host for ectomycorrhizal fungi and thus facilitate mycorrhizal infection of Nothofagus.

The introduced brushtail possum (Trichosurus vulpecula) is a major environmental and agricultural pest in New Zealand but little information is available on the ecology of possums in drylands, which cover c. 19% of the country. Here, we describe a temporal snapshot of the diet and feeding preferences of possums in a dryland habitat in New Zealand's South Island, as well as movement patterns and survival rates. We also briefly explore spatial patterns in capture rates. We trapped 279 possums at an average capture rate of 9 possums per 100 trap nights.