edge effects

Indigenous vegetation fragments in agricultural landscapes are vulnerable to creeping edge effects and stochastic extinctions on top of the effects of historic land use and disturbance which have already resulted in significant changes to baselines. Agricultural intensification can potentially increase these threats through spillover of nutrients, water, and weeds, especially in dryland ecosystems which are naturally low in nitrogen and soil moisture.

The distribution and prevalence in New Zealand of adventive detritivores in native forest remnants, and of native detritivores in pine plantations, are not well known. We investigated whether forest type (small urban native remnants, large remote native remnants, and pine) and plot location (edge plot vs centre plot) influenced the abundance and community composition of native and adventive detritivores (Diplopoda, Isopoda, and Amphipoda) in forests of a modified landscape in the lower North Island of New Zealand.

Positive effects of fragmentation on plant reproduction are uncommon; in a literature review we found significant negative effects on fruit or seed set for 50 plant species, compared to 26 species showing no effect, and only nine affected positively. One of these is the declining New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae), and here we investigate the mechanism of this positive effect. P. tetrapetala requires visits from native bird or bee pollinators to produce fruit.

Despite the importance of forest edges in ecology, only one study has previously been carried out in New Zealand on the modification of climate across forest edges. We measured light exposure, wind speed, air and soil temperature, and vapour pressure deficit (VPD) perpendicular to a north-south aligned, mature, edge of native broadleaf rainforest adjoining grazed pasture. At a point 80 m into the forest from the edge, light was only c. 0.7% and wind speed c. 20% of that in the open, and there was much less diurnal fluctuation in soil temperature, air temperature and VPD.

Fragments of kahikatea (Dacrycarpus dacrydioides) forest provide a major opportunity for conservation of indigenous biodiversity in the heavily deforested landscape of the Waikato Basin, New Zealand. However, there is little documented information on what indigenous fauna survives in these fragments.

Flower predators (florivores) may affect plant reproduction directly through loss of pollen and ovules, or indirectly by deterring pollinators which avoid damaged flowers. Caterpillars of the widespread endemic moth Zelleria maculata feed inside flower buds of the endemic mistletoes Peraxilla tetrapetala and P. colensoi in New Zealand. We measured flower predation rates between 1995 and 2007 at 24 sites throughout New Zealand and assessed Zelleria feeding impact on fruit set.

Recent work has shown that resource accumulation is important in allowing mast-seeding plants to display occasional intense reproductive efforts. Anecdotal reports suggest that Chionochloa tussocks (bunchgrasses) on patch edges flower more frequently, and it has been proposed that this is due to greater resource availability. This study aimed to quantify any edge effect in flowering effort in Chionochloa populations at Mt Hutt in the Southern Alps of New Zealand, and to look for correlations with available soil nutrients.