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 grass genus Chionochloa in New Zealand exhibits a high degree of mast seeding synchronised across species and habitats. Masting appears to be maintained by a predator satiation mechanism involving three pre-dispersal seed- and flower-feeding insects. It is not clear how important each of the three insects is in favouring the masting strategy. An undescribed cecidomyiid fly (Diptera: Cecidomyiidae) may be particularly important, since its conspicuous larvae are found throughout the South Island of New Zealand on many Chinochloa species.
Immediately before human settlement, dense tall podocarp- angiosperm forest dominated the moist Southland and southern coastal Otago districts. Open, discontinuous podocarp-angiosperm forest bordered the central Otago dry interior, extending along the north Otago coast. Grassland was mostly patchy within these woody ecosystems, occurring on limited areas of droughty or low-nutrient soils and wetlands, or temporarily after infrequent fire or other disturbance.
Chionochloa species vary in the degree to which they are grazed by introduced ruminants. This is presumed to reflect the relative nutritive value and/or palatability of the forage provided by these indigenous grasses. Data are presented here on silicon content, in vitro organic matter digestibility (OMD), metabolisable energy (ME), crude protein and total nutrient mineral (TNM) contents of mature leaves of eleven Chionochloa species in southern New Zealand.
Less than 4% of the non-bamboo grasses worldwide abscise old leaves, whereas some 18% of New Zealand native grasses do so. Retention of dead or senescing leaves within grass canopies reduces biomass production and encourages fire but also protects against mammalian herbivory. Recently it has been argued that elevated rates of leaf abscission in New Zealand’s native grasses are an evolutionary response to the absence of indigenous herbivorous mammals.
Leaf functional traits have been proposed as general indicators of plant palatability to ungulate herbivores, identifying which species are likely to be most at risk from ungulates, and how ungulate grazing may change ecosystem processes. However, few studies have tested whether leaf trait–palatability relationships are consistent across different ungulate species.
In New Zealand, alpine grasslands occur above the treeline of beech forest. Historically stoat control paradigms in New Zealand’s montane natural areas have assumed alpine grassland is a marginal habitat that limits dispersal between beech forest stoat populations. We compared the summer-to-autumn (January–April) density, weight, diet and winter survival of stoats between these two habitatsduring years of low beech seedfall.
Predation by introduced stoats is now considered a major threat to the population viability of several New Zealand endemic bird species. Historically stoat research and management has focused on beech forests and little is known about the ecology of stoats in the alpine grasslands occurring above the natural altitudinal limit of beech forest. Several stoat control operations in beech forest valley floors in southern New Zealand assume that adjacent montane areas act as a barrier to stoat immigration.