Letteratura scientifica selezionata sul tema "Chionochloa spp"

Snow tussocks (Chionochloa spp.) in New Zealand exhibit extreme mast (episodic) seeding which has important implications for plant ecology and plant–insect interactions. Heavy flowering appears to be triggered by very warm/dry summers in the preceding year. In order to investigate the physiological basis for mast flowering, mature snow tussock plants in the field and younger plants in a glasshouse and shadehouse were subjected to a range of manipulative treatments. Field treatments included combinations of warming, root pruning and applications of two native gibberellins (GAs) GA3, which is known to be highly floral inductive and GA4, which is associated with continued floral apex development in another long-day grass. Warming, GA3 alone and especially warming + GA3, significantly promoted flowering, as did applications of GA4 alone and GA4 + CCC (2-chloroethyltrimethylammonium chloride, which is a known synergist of GA3-induced flowering in the annual grass, Lolium temulentum L.). Our results provide support for the concept that mast flowering events in tussock species are causally related to high temperature-induced increases in endogenous gibberellin levels. It is likely that GAs (endogenous or applied) promote the continued development of a previously long-day induced floral apex. In addition to the promotion of flowering, applied GA3 also disturbed the plant’s innate resource threshold requirements, as shown by the death, over winter, of many non-flowering tillers. Applied GA4 did not show this effect, likely due to its rapid catabolic metabolism to an inactive form. High temperature-induced flowering mediated by elevated levels of endogenous floral-promotive GAs could have important implications for regulating the evolutionary interaction between these masting plants and their seed predators.

Context. Rodent populations in many parts of the world fluctuate in response to resource pulses generated by periodic high seed production (masting) by forest trees, with cascading effects on predation risk to other forest species. In New Zealand forests, populations of exotic house mice (Mus musculus) irrupt after periodic heavy beech (Nothofagus spp.) seedfall. However, in alpine grasslands, where snow tussock grasses (Chionochloa spp.) also flower and set seeds periodically, little is known about house mouse population dynamics. Aims. Our primary objective was to test for an increase in alpine mouse density following a summer when snow tussocks flowered profusely. We also estimated mouse density in adjacent montane forest over 2 years, and assessed mouse diet, to predict their potential impacts on native species. Methods. Flowering intensity of Chionochloa was assessed by counting flowering tillers on permanent transects (2003–06). Mouse density was estimated with capture–mark–recapture trapping in alpine (2003–07) and forest (2003–04) habitats. Mice were also collected and their stomach contents analysed. Flowering or fruiting of alpine shrubs and herbs, and beech seedfall at forest sites, were also measured. Key results. Chionochloa flowered profusely in austral summer 2005/06. Between autumn (May) and spring (November) 2006, mean alpine mouse density increased from 4 ha–1 to 39 ha–1, then declined to 8 ha–1 by autumn (May 2007). No mice were captured in 768 trap-nights during the following spring (November 2007). Prior to the mouse irruption, mouse density was consistently higher at alpine (0.4–4.0 mice ha–1) than at montane forest (0.02–1.8 mice ha–1) sites (in 2003–04). Alpine mouse diet was dominated by arthropods before mast flowering, and by seeds during it. Conclusions. The density and dynamics of alpine mice in relation to intensive snow-tussock flowering were similar to those in New Zealand beech forest in relation to beech masts. Implications. We predict the timing and duration of periods of heightened predation risk to native alpine fauna, as the result of pulses in mouse density and likely associated pulses in the density of stoats (Mustela erminea), a key exotic predator.

Three new genera and six new species of felt scale insects (Eriococcidae) are described, including the first record for the genus Kuwanina from New Zealand. The genera, species and their habitats are: Alpinococcus elongatus gen. et sp. nov. from basal sheaths of Schoenus pauciflorus (Cyperaceae) in subalpine to penalpine wetlands; Bryococcus hippodamus gen. et sp. nov. from mossy wood in Fiordland; Kuwanina kiwiana sp. nov., on Nothofagus menziesii (Nothofagaceae) in montane forest; Montanococcus gen. nov. with three new species: M. graemei, M. petrobius and M. thriaticus, from basal sheaths of Schoenus pauciflorus and Chionochloa spp. (Poaceae) in subalpine to penalpine wetlands and damp grassland. Keys are provided to the New Zealand genera of Eriococcidae, and to species of Kuwanina and Montanococcus.

Porina (Wiseana spp) has become a major pasture pest in New Zealand over the past century in response to natural forest and grasslands being converted into pastures for livestock Limited information is available on the growth and survival of porina larvae on native host species Field collected porina larvae were fed on 5 selected native plants (Festuca actae Aciphylla squarrosa Poa cita Chionochloa rubra and Phormium tenax) one exotic (Lolium multiflorum cv Manawa) and mixed species over 5 months and the fitness response of porina to each of these grasses was measured The most rapid growth of larvae was observed on L multiflorum while the slowest was on P tenax A squarrosa and P cita The largest weight gain was on L multiflorum There was a significant difference in larval growth between L multiflorum and P tenax (P0019) Percentage mortality was lowest on L multiflorum (125) with the larvae surviving for 177 days The highest mortality of 75 was recorded on P cita which also had the lowest survival of 77 days This study provided useful information on the development of porina on native hosts which provide a habitat for its expansion on to pasture

The caterpillar stage of the endemic Wiseana spp complex commonly known as porina are foliage feeders Research indicates that porina will feed on harakeke (Phormium tenax) red tussock (Chionochloa rubra) and hard tussock (Festuca novae zealandiae) In 1952 Miller reported that porina were abundant in kumara plantations and caused damage to the plants The accuracy of this observation is uncertain due to taxonomic changes and the ambiguous nature of Millers identification Feeding bioassays were undertaken to determine if porina caterpillars would feed on the leaves stems or tuber of the Owairaka kumara plant (Ipomoea batatas) using white clover foliage (Trifolium repens) as a control Over a 6week Porina provided with tuber had a weight increase of >01 g within the first two weeks which was a 122 gain (compared to clover) The leaves and stems supported less weight gain over the two week period (92 and 85 compared to clover respectively) These results suggest that porina can feed on kumara plants but further field testing will be required to support this claim

The upland (800-2000 m) snow tussock (Chionochloa spp.) rangelands of South Island, New Zealand have a long history of burning that pre-dates human occupation during the last millennium. Their present extent in part reflects their ability to displace a range of woody vegetation, including forest, through tolerance of periodic fne. Research has confirmed the general tolerance of these grasslands to fire, though recovery of some features (e.g. biomass and flowering potential) may take more than 14 years. Mammalian grazing, by contrast, is a recent phenomenon, associated with European settlement and pastoralism over the last 150 years, on these mostly Crown (i.e. public-owned) lands. Such grazing, particularly when combined with regular burning, has usually resulted in prolonged reductions in tussock biomass, vigour and stability, as well as in the control and yield of water, potentially the most valuable product for humans from the upland grasslands. Fire promotes vegetative growth, flowering and seed germination within 2 years of burning. It also increases the palatability of these long-lived dominant grasses which are vulnerable to severe grazing by introduced ruminants, especially in the immediate post-fire recovery period when nutrients are reallocated from roots to leaf tissue. Management constraints, particularly restriction of grazing during the post-fie recovery period, have been inadequate to prevent continued degradation of the grasslands through weakening or displacement of the dominant tussock grass cover and a consequent loss of stability in many areas. Under pastoralism, the productive potential of the grasslands, together with their water, soil and nature conservation values have generally declined. Existing pastoral practices in many areas clearly represent non-sustainable utilisation of the rangelands for pastoralism. Recovery will be difficult and costly, both economically and socially. Some representative areas have been formally reserved and are being monitored to serve as baseline references.

New Zealand's South Island tussock grasslands have been highly modified by human activities, including burning, grazing and introductions of exotic plants for pastoralism. Studies suggest that tussock grasslands are degraded, in that native species have declined, and exotic species have increased in both diversity and abundance. These trends are primarily thought to be related to the impacts of grazing and subsequent grazing removal. Few studies have assessed long-term changes that have occurred in tussock grasslands, and those that have are generally limited to one particular location. This thesis aimed to investigate temporal changes in community structure in tussock grasslands, and relate these changes to environmental variables and land tenure. Data were used from 90 permanently-marked vegetation transects, which were set up on 19 geographically widespread properties in areas of tussock grassland across Canterbury and Otago in the South Island of New Zealand. The transects were on land in both conservation and pastoral tenure. Each transect was 100 m, and consisted of 50 0.25 m² quadrats. The transects were measured between 1982 and 1986 (first measurement), were re-measured between 1993 and 1999 (second measurement) and again between 2005 and 2006 (third measurement). A total of 347 vascular species were observed over the 90 transects and three measurement times. Species richness declined between the first and second measurements (first time interval), and increased between the second and third measurements (second time interval), at both the small (quadrat) and large (transect) scales. Both native and exotic species declined in mean quadrat species richness during the first time interval, and then increased during the second time interval. Changes in mean quadrat species richness were similar on transects in both conservation and pastoral tenure. Multivariate analysis of species' occurrences in quadrats identified a long gradient in species composition for these 90 transects. Four key plant communities were identifed along this gradient and differed in their mean elevation: (1) Highly-modified pastoral community, (2) Short-tussock grassland community, (3) Tall-tussock grassland community, (4) Alpine mat-forming species community. A detailed investigation into temporal changes that occurred on 53 transects that occurred in short- and tall-tussock grassland communities showed that changes in species composition were not consistent over time. Transects on different properties changed in species composition by different amounts. Specifically, in ordination space, transects on two properties changed in composition significantly more than transects on one other property. The property that a transect was on also affected the way that it changed in composition, i.e. native species were more likely to have increased on transects on some properties. Transects in conservation tenure did not change in species richness or composition differently from those in pastoral tenure. Considering that many native plants in tussock grasslands are relatively slow-growing, and that these areas have been grazed and burned for more than a century, we may expect it to be some time before we can detect differences in vegetation dynamics on conservation land from that on pastoral land. The changes in the community structure of these tussock grasslands were related to a combination of environmental factors, such as soil chemistry, climate, and management factors. This study has allowed greater understanding of vegetation change in tussock grasslands, and demonstrates the importance of long-term ecological monitoring in making reliable and accurate predictions about landscape-scale changes in tussock grassland community structure.