The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or ''functional groups'' of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C 3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C 4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C 4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C 3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora.Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C 4 grasses enhanc...

Summary1. There is increasing awareness that similar suites of plant traits may govern foliage palatability and litter decomposability, but whether there is an association between the response of vegetation to herbivory and litter decomposition rates across plant species remains unexplored. 2. We collected 141 samples of litter from 59 understorey and 18 canopy tree species from a total of 28 sites under natural forest throughout New Zealand. We assessed whether variables related to decomposition and quality of litter of the understorey species showed a statistical relationship with the response of vegetation density (assessed using a pole-intercept method) of the same species at the same locations to browsing by deer and goats. Decomposition and nutrient-loss data from litter were obtained using standardized laboratory bioassays.3. There was a significant positive correlation between litter decomposition rate and the extent to which vegetation density was reduced by browsing mammals ( r = 0·488, P < 0·001). Further, decomposition rate and vegetation response to herbivory were both correlated with several of the same litter quality variables. 4. The proportion of total initial phosphorus and nitrogen released from litter during decomposition was correlated with litter decomposition rate, but not with vegetation density response to browsing. This suggests that effects of browsers on vegetation composition are more likely to influence ecosystem carbon flow than nitrogen or phosphorus flow. 5. Litter-mixing experiments showed that good quality litters produced by plant species reduced by browsers tended to promote the decomposition of other litters. Meanwhile, poor quality litters from species promoted by browsers tended to decompose more rapidly when mixed with other litter types than when by themselves. However, these effects were weak and likely to be less important than the more direct effects of browsing mammals on vegetation composition. 6. The relationships between litter decomposition and effect of herbivory on vegetation density were driven primarily by differences among the main plant functional groups, which showed the same decreasing rank order for both variables: large-leaved dicots, small-leaved dicots, Nothofagus , ferns, and monocots. 7. The implications of these results for understanding how herbivores affect the decomposer subsystem are considered. Because the results of this work are only partially consistent with those of an earlier study on how browsers affect decomposer organisms and processes, conducted at the same 28 field sites, other mechanisms through which browser effects are manifested below-ground must often override that investigated in this study.

This chapter reviews the taxonomy; habitat; morphology; mating, oviposition and fecundity; population dynamics and abundance; feeding behaviour; respiration; aestivation; temperature and salt tolerance; dispersal; distribution across South East Asia and other countries as a food item, aquarium animal and as a biological control agent of gastropods and weeds; importance as an agricultural pest of rice and other crops and as a vector of human pathogens; and chemical, biological (mainly predators) and cultural control of apple snails (Pomacea spp.).

Achatinidae are native to Africa. The family is represented by about 200 species in 13 genera. Several species have attained pest status within their native African range when the habitat is modified for human habitation and cropping. Furthermore, associated with the increased mobility of humans and globalization of travel and trade, several achatinids, the most notable of which is Achatina fulica Bowdich, have been accidentally or purposefully transported to areas outside their native range in Africa and further afield. In these new areas Achatinidae can cause significant economic and ecological impacts. This chapter provides a synopsis of Achatinidae as pests in tropical agriculture, focusing primarily on A. fulica, but also bringing together the relevant information on other pestiferous achatinid species.

Forest dwelling browsing mammals, notably feral goats and deer, have been introduced to New Zealand over the past 220 years; prior to this such mammals were absent from New Zealand. The New Zealand forested landscape, therefore, presents an almost unique opportunity to determine the impacts of introduction of an entire functional group of alien animals to a habitat from which that group was previously absent. We sampled 30 long-term fenced exclosure plots in indigenous forests throughout New Zealand to evaluate community-and ecosystem-level impacts of introduced browsing mammals, emphasizing the decomposer subsystem.Browsing mammals often significantly altered plant community composition, reducing palatable broad-leaved species and promoting other less palatable types. Vegetation density in the browse layer was also usually reduced. Although there were some small but statistically significant effects of browsing on some measures of soil quality across the 30 locations, there were no consistent effects on components of the soil microfood web (comprising microflora and nematodes, and spanning three consumer trophic levels); while there were clear multitrophic effects of browsing on this food web for several locations, comparable numbers of locations showed stimulation and inhibition of biomasses or populations of food web components. In contrast, all microarthropod and macrofaunal groups were consistently adversely affected by browsing, irrespective of trophic position. Across the 30 locations, the magnitude of response of the dominant soil biotic groups to browsing mammals (and hence their resistance to browsers) was not correlated with the magnitude of vegetation response to browsing but was often strongly related to a range of other variables, including macroclimatic, soil nutrient, and tree stand properties.There were often strong significant effects of browsing mammals on species composition of the plant community, species composition of leaf litter in the litter layer, and composition of various litter-dwelling faunal groups. Across the 30 locations, the magnitude of browsing mammal effects on faunal community composition was often correlated with browser effects on litter layer leaf species composition but never with browser effects on plant community composition. Browsing mammals usually reduced browse layer plant diversity and often also altered habitat diversity in the litter layer and diversity of various soil faunal groups. Across the 30 locations, the magnitude of browser effects on diversity of only one faunal group, humus-dwelling nematodes, was correlated with browser effects on plant diversity. However, browser effects on diversity of diplopods and gastropods were correlated with browser effects on habitat diversity of the litter layer. Reasons for the lack of unidirectional relationships across locations between effects of browsers on vegetation community attributes and on soil invertebrate community attributes are discussed.Browsing mammals generally did not have strong effects on C mineralizatio...

Summary 0The development of general principles regarding biotic interactions involving plants\ or plant species e}ects in ecosystems\ is best achieved through simultaneous evaluation of several species[ We utilized a comparative approach involving 19 dicotyledonous herbaceous species\ to explore possible relationships between several plant eco! physiological traits and plant litter decomposition\ interactions involving competition and herbivory\ and plant species e}ects on soil properties[ 1 Decomposition rates of plant stem and leaf litter were negatively related to plant mass\ time until~owering and vegetative growth rate\ and positively related to stem nitrogen content[ Root decomposition was also related to several traits[ Multiple regression relationships showed that 63) and 73) of the variation across species for stem and root litter decomposition\ respectively\ could be predicted by plant traitst his suggests that plant traits may be powerful predictors of decomposition and have potential as alternative predictors to the litter quality characteristics that previous studies have concentrated on[ 2 Palatability of both seedlings and leaf discs by the invertebrate herbivores Deroceras reticulatum and Listronotus bonariensis were frequently related to plant traits[ Those traits that showed the strongest relationships with the palatability data included various vegetative growth characteristics and "for the leaf disc data# nitrogen con! centrations of~owering plant stems[ 3 Competitive e}ects of the dicotyledonous species against a phytometer species\ the grass Lolium perenne\ were negatively related to leaf nitrogen concentration\ and multiple regression relationships involving this trait in combination with others explai! ned over 49) of the variation across species[ The competitive response of both plant mass and total seed production to L[ perenne was poorly related to plant traits[ 4 The e}ects of plant species on soil properties including microbial biomass and activity\ pH\ nitrate concentration and total nitrogen were often closely related to various plant traits[ Multiple regression relationships revealed that combinations of several traits were often important in determining these e}ects^the strongest relationships found were for e}ects of senescent plants on soil respiration and for the e}ects of~owering plants on soil nitrate[ Plant traits were therefore clearly important in determining plant species e}ects on soils[ 5 Our study emphasizes the importance of plant traits in understanding "and pre! dicting# species interactions and e}ects in communities and ecosystems\ and shows that properties considered at the whole plant level have the potential to manifest

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3‐yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot‐to‐root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe‐feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe‐feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community‐level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil‐associated herbivorous arthropods and microbial‐feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced dive...

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