The effects of vegetation removal by grass carp and herbicides on the water chemistry of four Florida lakes

SUMMARY.

• 1 Four lakes in central Florida each received a different weed control treatment consisting of herbicide and/or different stocking ratios of grass carp (Ctenopharyngodon idella Val.).
• 2 Submersed vegetation was eliminated by grass carp within 6 months In Lake Orienta and within 14 months in Clear Lake. Because Little Lake Fairview, treated with herbicide and a smaller stocking ratio of grass carp, retained abundant vegetation levels over the first two study years, grass carp which had been introduced initially were replaced with a greater number of fish at the beginning of the third year. Submersed vegetation was subsequently eliminated in this lake within LO months. Aquatic vegetation was reduced but not eliminated in Lake Mann which was treated with herbicide only.
• 3 Where macrophytes were removed there tended to be increased bottom dissolved oxygen, higher and more stable total alkalinity values, increased turbidity, lowered transparency, higher specific conductivity and increased chlorophyll levels. Significant increases in pH were probably due to low water levels resulting from a severe drought rather than weed control. Low water also affected specific conductivity. Annual means for nutrients did not differ significantly between years in the four lakes.

     

Bone-seed (

Bone-seed, Chrysanthemoides monilifera ssp. monilifera (L.), is an environmental weed of coastal vegetation communities scattered throughout New Zealand. To assess the long-term implications for native forest regeneration in sites where bone-seed is present, we selected four study sites around Wellington, New Zealand, where bone-seed was abundant. We compared seed bank composition in bone-seed-invaded sites with nearby native forest patches, and monitored bone-seed and native seedling recruitment with and without control of mature bone-seed plants. We also tested the potential effects of fire on bone-seed recruitment in these communities by heating seeds prior to germination. Bone-seed, gorse (Ulex europaeus), and native species emerged from seed bank samples taken from bone-seed-invaded sites, but only native species and (less) gorse emerged from seed bank samples taken from native forest patches. Gorse germination was strongly promoted by heat but bone-seed germination was less affected by heat. Bone-seed seedling abundance increased dramatically following canopy removal, whereas native seedling abundance decreased dramatically. This suggests that disturbance of any form is likely to favour recruitment of bone-seed (and gorse) over native species, although in the long term, native seedlings can establish beneath the canopy of mature bone-seed plants. It is not yet known if, in the absence of further disturbance, regenerating native vegetation will eventually replace bone-seed in New Zealand.     

Phytoplankton responses to reduction and elimination of submerged vegetation by herbicides and grass carp in four Florida lakes

Four central Florida lakes were monitored for 3 years to determine the effects of macrophyte reduction and elimination by grass carp and herbicide on phytoplankton populations. Clear Lake, in which grass carp were stocked after a year of baseline studies, had all macrophytes eliminated within 14 months. The density of phytoplankton increased significantly from an initial 24-month mean of 165 000 cells 1⁻¹ to a mean level of 787 900 cells 1⁻¹ in the third year. In Little Lake Fairview, stocked with grass carp in both the first and third years of study, vegetation was not eliminated until the 34th month. Phytoplankton density increased significantly from a 24-month mean of 64 200 cells 1⁻¹ to a mean of 370 200 cells 1⁻¹ in the third year. Lake Orienta, stocked with grass carp in the first year, had all vegetation eliminated within 6 months. Phytoplankton abundance did not change significantly over the course of the study (mean: 2 700 000 cells 1⁻¹). Lake Mann was treated with herbicide alone after an initial year of baseline data collection. Submerged vegetation was reduced in the second year but increased to near initial biomass levels in Year 3, with Nitella sp. replacing Hydrilla verticillata (L.f.) Royle as the dominant macrophyte. No significant yearly changes were noted in density of phytoplankton in this lake. Lake Orienta was the only lake in which the number of phytoplankton species collected differed significantly between years. Cyanophytes (notably species of Anacystis, Microcystis and Anabaena) and the diatom, Fragilaria sp., predominated in all lakes as macrophytes were removed. Most changes observed were in the direction of apparent increased trophic state. Major shifts in the phytoplankton assemblage (e.g., Shannon diversity indices and abundance) coincided with periods of maximal fluctuation in vegetation. Reversals of these tendencies were observed during prolonged stable periods of both high and low macrophute biomass.     

The tolerance of grass carp, Ctenopharyngodon idella Val., to aquatic herbicides

Because grass carp may feed selectively on water plants, additional conventional methods may be necessary for effective control of aquatic vegetation. For economic reasons aquatic herbicides are most likely to be used in conjunction with grass carp within an integrated aquatic weed control programme. The acutely lethal toxicities of ten herbicides to grass carp were measured. A preliminary evaluation of the risk to these fish showed that, when used at the recommended rate, the maximum herbicide concentration likely to be found in water should cause little harm to the fish, although attention should be given to the possible inhibition of feeding.     

新西兰霍克湾普卡瓦湖岩芯植硅体分析所揭示的火山喷发事件后的植被变化

含火山灰层沉积的植硅体分析为了解植被对从空中下降的火山灰的反应提供新的信息。新西兰霍克湾的一个深197m钻孔的上部50m样品,提供了距今约50ka以来连续的植被记录。植硅体组合在4个主要的火山灰层都发生了明显的变化,表现在树木和灌木的急剧下降及禾草类和莎草科的繁盛。在每次火山灰降落后,都会有一系宁继后变化,木本类最早死亡,禾草类和莎草科取而代之,并很快占据裸露的地表。经过一个相当长的滞后时间,树木和／或灌木重新替代草本和莎草科。     

Influence of hydrophyte abundance on the spatial distribution of zooplankton in selected lakes in Greece

Submerged hydrophyte vegetation consists of a highly important biotic component of maintaining lake ecosystems towards a “clear water” ecological status. Aquatic macrophytes are well known to play a significant multidimensional role in lakes by competing with phytoplankton growth, stabilising sediment and offering refuge to fishes, macro-invertebrates and littoral zooplankton, amongst others. Zooplanktons that are associated with macrophyte beds, in particular, may act as a positive feedback mechanism that contributes to maintaining a clear-water state. Although there are several studies investigating the relationships between macrophytes and zooplankton in European lakes, few have yet been carried out in Greek lakes. Seasonal field sampling was conducted from spring 2006 to autumn 2008 in four lakes of northwestern Greece. Zooplankton samples were collected from within hydrophyte beds in each lake to estimate their relative abundance and species density. Hydrophyte abundance and composition was recorded on a five-point scale. Moreover, water samples were analysed to determine nutrient and chlorophyll-a concentration. Pearson correlations between zooplankton density and key physicochemical variables were conducted to distinguish significant abiotic variables related with major zooplankton groups. Kruskal–Wallis non-parametric analysis was used to test for significant differences in zooplankton composition and environmental variables amongst the five hydrophyte abundance classes. In addition, Canonical correspondence analysis was used to distinguish possible correlations amongst the macrophyte and zooplankton species. Zooplankton density was significantly higher in dense macrophyte vegetation. Small-sized species (e.g. Rotifera) dominated the zooplankton community, indicating the eutrophic nature of the lakes. Large Cladocera were present in low abundance and were mostly littoral. The current research contributes to a better understanding of relationships between biotic groups in selected Greek lakes.     

Impacts of introduced brown and rainbow trout on benthic invertebrate communities in shallow New Zealand lakes

1. Brown and rainbow trout have been introduced to many inland waters in New Zealand, but research on the impacts on native communities has focused mainly on streams. The purpose of this study was to compare the benthic communities of trout and troutless lakes. Based on previous studies in North America and Europe, we predicted that the benthic biomass, and especially the abundance of large invertebrates, would be lower in lakes with trout as compared to those without. We surveyed the invertebrate fauna of 43 shallow, high‐elevation lakes (26 with and 17 without trout) in four geographic clusters on the central South Island and then conducted a detailed quantitative study of invertebrate biomass and community structure in 12 of these lakes. 2. Benthic community composition and diversity of lakes with and without trout were nearly identical and biomass was as high or higher in the lakes with as without trout. There was no evidence that trout have caused local extinctions of benthic invertebrates. Although the proportional abundance of large‐bodied aquatic was slightly lower in lakes with than without trout, the abundance of several groups of large‐bodied benthic taxa (dragonflies, caddisflies and water bugs) did not differ. 3. Our findings are in contrast to those in North American and Europe where trout introductions into previously troutless lakes have led to declines in the abundance of benthic invertebrates, especially large‐bodied taxa. We propose that the modest effects of trout in New Zealand could be explained by (i) the high areal extent of submergent vegetation that acts as a benthic refuge, (ii) low intensity of trout predation on benthic communities and/or (iii) characteristics of the benthic invertebrates that make them relatively invulnerable to fish predation. 4. Regardless of the relative importance of these hypotheses, our results emphasise that the same invertebrates occurred in all of the lakes, regardless of size, elevation and presence of trout, suggesting habitat generalists dominate the benthic fauna in shallow New Zealand lakes.     

The influence of macrophyte beds on plankton communities and their export from fluvial lakes in the St Lawrence River

1. To determine the influence of macrophyte beds on plankton abundance within fluvial lakes of the St Lawrence River, planktonic components (macrozooplankton, heterotrophic bacteria, and phytoplankton as chlorophyll- a [Chl- a ]) were sampled in Lake St Francis and Lake St Pierre during summer 1998. We tested the hypothesis that the abundance of planktonic components was higher within macrophyte beds in comparison to the more rapidly flushed open water areas of the fluvial lakes.
2. The large cross channel variation in zooplankton biomass was indeed correlated with the presence of dense beds of submerged macrophytes. Total macrozooplankton biomass was nine-fold greater within the beds (mean=180 μg L−1 dry mass) than in either the open water or areas with only sparse vegetation (mean=20 μg L−1 dry mass).
3. Chl- a and heterotrophic bacterial abundance were also higher in the beds, but only slightly so. There was no difference in total phosphorus or dissolved organic carbon concentrations between areas of dense vegetation, sparse vegetation or open water.
4. Macrophyte beds on the margins of the fluvial lakes allow the development of high planktonic abundance relative to the fast flowing central channel. Macrozooplankton biomass was much higher at the outflows of the lakes (∼50 μg L−1 dry mass) in comparison to the inflows (<20 μg L−1 dry mass). The increase is due to the transfer of organisms from submerged macrophyte beds into the central channel in the downstream quarter of the two lakes where the marginal littoral waters enter central channel waters.
5. Along rivers, shallow fluvial lakes appear to act as sources of plankton which is exported downstream during years of extensive littoral macrophyte development.     

Biodiversity impacts of an invasive grass: ant community responses to <Emphasis Type="Italic">Cenchrus ciliaris</Emphasis> in arid Australia

Buffel grass (Cenchrus ciliaris) is a highly invasive species that thrives in semi-arid environments and has the capacity to transform native vegetation outside its native range. However, there is limited information on the effects of buffel grass invasion on native fauna. We used an experimental approach to investigate the impact of buffel grass on the native ant fauna near Alice Springs in semi-arid central Australia. A series of plots where buffel grass was removed and native vegetation had regenerated (B?), paired with adjacent control plots heavily invaded by buffel grass (B+), were used to assess the impact of buffel grass on ant diversity and composition, and on rates of seed dispersal by ants. Differences in ant diversity were also compared between two microhabitat types: bare ground and under cover, to examine the extent to which any impacts were a simple function of change in vegetation cover. Ant abundance and richness were approximately 50 % higher in B? compared with B+ plots, and higher abundance was especially pronounced for the very thermophilic Hot-Climate Specialists. Ant species composition varied significantly between plot types. B? plots supported more species and individuals in both bare and covered microhabitats, which suggests that the differences in ant diversity was not simply through changes in vegetation cover. Rates of seed removal by ants were marginally higher in B? plots. Our findings indicate that buffel grass has a major impact on a dominant faunal group of arid Australia, and possibly reduces the delivery of an important ecosystem service. In addition, our study demonstrates the potential for ecosystem recovery following effective buffel grass management.     

Relationships between zooplankton abundance and trophic state in seven New Zealand lakes

The zooplankton communities of seven Rotorua, New Zealand, lakes of different trophic status were studied in 1977–78. They were generally dominated by the calanoid copepod, Calamoecia lucasi. Bosmina meridionalis occurred in all the lakes and Ceriodaphnia dubia in most. Only small numbers of Macrocyclops albidus ever occurred. Rotifers were not studied in detail. Community composition was similar to that in other northern New Zealand lakes. No well defined patterns of seasonal change in abundance were found and the timing of changes, which were of low magnitude, was different in each lake. Clutch sizes in all species were small. Calamoecia population parameters were analysed using multivariate methods and shown to be related to lake trophic level. Population densities were higher in more productive lakes whereas breeding levels were inversely related to indices of trophic status and population abundance. It is suggested that the populations, as in other northern New Zealand lakes, are food-limited, probably as a consequence of a lack of marked climatic seasonality and the absence of major predation pressures. Groupings of the lakes based on the Calamoecia data are in general agreement with those derived from parallel studies of water chemistry, phytoplankton and macrobenthos.     

Incorporating invasive weeds into a plant indicator method (LakeSPI) to assess lake ecological condition

The use of lake macrophytes for ecological quality assessments usually seeks to indicate the degree of anthropogenic impact, but few of these schemes implicitly consider impacts of alien weeds. LakeSPI (submerged plant indicators) uses indicators of habitat degradation for macrophytes but also incorporates the degree of impact from alien weeds. Application of LakeSPI to 195 New Zealand lakes provided a dataset to examine how component metrics responded over gradients of anthropogenic pressures, and consider whether weed invasion was merely a ‘passenger’ of habitat degradation, or represented an additional pressure. As expected, metrics measuring depth, and diversity of native vegetation negatively correlated with independent measures of lake eutrophy and were also relatively well explained (69–78% variation) by multiple regression with lake and catchment attributes that included proxies for anthropogenic pressure. In contrast, metrics for invasive impact were largely de-coupled from eutrophication, and poorly explained (31%) by the multiple regression. The response of native vegetation metrics to invasive impact measures varied, with the strongest detected interaction relating to native displacement by increased weed occupation of the vegetated zone. Interactions between invasion and lake trophic status were also discerned, with the extent of weed occupation having a more substantial outcome for the presence of charophyte meadows in low productivity lakes than in more productive lakes. These results suggest weed invasion should be considered as an additional source of anthropogenic pressure, and incorporated in macrophyte bioassessment schemes for a more complete differentiation of lake ecological condition.     

Responses of invertebrates to herbicide in Salix cinerea invaded wetlands: Restoration implications

The use of herbicides to control weeds, particularly large invasions, has now become an essential management tool in many ecological restoration projects. The herbicide glyphosate is routinely used to control the invasive weed, Grey Willow (Salix cinerea), within New Zealand wetlands. However, little is known about the effects of glyphosate on invertebrates. We determine the short‐term effects of glyphosate on the abundance and composition of the nontarget canopy invertebrate community in wetlands invaded by Grey Willow in New Zealand. Initially, the application of glyphosate and a surfactant showed no detectable effect on the canopy invertebrates examined in this study. However, 27 days after herbicide application, significant Grey Willow canopy loss caused dramatic decreases in the abundance of invertebrates in the glyphosate‐treated plots compared with the unsprayed plots. Invertebrates appeared to be sensitive to changes in vegetation structure, such as canopy loss. These results agree with previous studies that have shown that the negative impacts of glyphosate on invertebrate communities are related to indirect effects via habitat modification as the herbicide‐treated vegetation dies. From a terrestrial invertebrate perspective, this study suggests that the use of glyphosate herbicide is suitable for the control of invasive weeds within wetland restoration projects as it appears to have negligible impact on the canopy invertebrate assemblage.     

Somatic mutation-mediated evolution of herbicide resistance in the nonindigenous invasive plant hydrilla (Hydrilla verticillata)

Hydrilla (Hydrilla verticillata L.f. Royle) was introduced to the surface water of Florida in the 1950s and is today one of the most serious aquatic weed problems in the USA. As a result of concerns associated with the applications of pesticides to aquatic systems, fluridone is the only USEPA-approved chemical that provides systemic control of hydrilla. After a decrease in fluridone's efficacy at controlling hydrilla, 200 Florida water bodies were sampled to determine the extent of the problem and the biological basis for the reduced efficacy. Our studies revealed that hydrilla phenotypes with two- to six-fold higher fluridone resistance were present in 20 water bodies. Since fluridone is an inhibitor of the enzyme phytoene desaturase (PDS), the gene for PDS (pds) was cloned from herbicide-susceptible and -resistant hydrilla plants. We report for the first time in higher plants three independent herbicide-resistant hydrilla biotypes arising from the selection of somatic mutations at the arginine 304 codon of pds. The three PDS variants had specific activities similar to the wild-type enzyme but were two to five times less sensitive to fluridone. In vitro activity levels of the enzymes correlated with in vivo resistance of the corresponding biotypes. As hydrilla spread rapidly to lakes across the southern United States in the past, the expansion of resistant biotypes is likely to pose significant environmental challenges in the future.     

The influence of grass carp on habitat structure and its subsequent effect on the diet of tench

Ecological studies were carried out in shallow experimental sites in the Lancaster Canal to evaluate potential interactions between grass carp and feeding habits of tench.
Grass carp, through moderate weed consumption, produced better conditions for the exploitation of benthic organisms by the benthophagous tench, because tench (>35 cm fork length) were able to search for food in the open areas created. This also enabled the fish to make use of zooplankton, mainly the large species Eurycercus lamellatus whose restricted phytophilic habitat made it vulnerable to predation. Epibenthic animals, in particular gastropods and Asellus aquaticus , suffered principally from the predation, which caused severe reduction of them in the site totally depleted of vegetation. In this site, tench utilized a diet in which red chironomids were the dominant prey group together with a large amount of fine detritus.
It is suggested that a moderate control of vegetation in temperate climates, using the grass carp as the biological agent, could be a satisfactory management technique for the improvement of aquatic habitats.     

Factors affecting the cost of weed biocontrol programs in New Zealand

Many national schemes for setting priorities for invasive weed management have emphasized the current or future impacts of the weed more than the cost or feasibility of control, perhaps because the latter may be difficult to estimate. As part of a project to improve prioritization of weed biocontrol targets in New Zealand, we investigated factors that were hypothesized to influence the cost of conducting weed biological control, using data from New Zealand programs. Taxonomic isolation of the target weed, relative to commercially important plants and native flora was not a significant influence on program cost, although we present evidence that disease, which to date has only affected agents released against taxonomically isolated weed targets, has masked the importance of taxonomic isolation in New Zealand. Opposition to biocontrol has caused delays, but has not had a major influence on the cost of biocontrol in New Zealand, probably because weed species with the greatest potential for opposition were identified during feasibility studies and avoided, or because conflicts were resolved by conducting cost-benefit analyses that were minor components of the total program costs. Only two factors explained virtually all the variance in program cost: program type (repeat programs were cheaper than novel/pioneering programs); and the number of agent species released. The predicted cost of future weed biocontrol programs can now be incorporated into decision-making tools ranking New Zealand weed biocontrol targets. Efficiencies in future programs are most likely to be gained by better agent selection so that fewer agents are released. For repeat programs this could be achieved by waiting until monitoring has been conducted overseas, so that the best agents or combination of agents can be selected for any particular weed. This reiterates the need for better post-release evaluation of weed biocontrol agent effectiveness worldwide.     

Effects of a rapidly increasing population of common carp on vegetative cover and waterfowl in a recently restored Midwestern shallow lake

Although the common carp (Cyprinus carpio), an invasive benthic fish from Eurasia, has long been strongly implicated in the disappearance of vegetative cover and reduced waterfowl abundance in North American shallow lakes, the details of this relationship are obscure. This study documented ecological changes in a recently restored shallow lake (Hennepin and Hopper Lakes, IL, USA) at a time that it was experiencing a large increase in its carp population. We estimated the abundance and biomass of carp 7 years after this lake had been restored and then back-calculated carp population size across time while examining changes in the lake’s plant and waterfowl communities. We found that the biomass of carp remained below ~30 kg/ha for 5 years following restoration, but then increased to ~100 kg/ha in the sixth year following a strong recruitment event. Although a carp biomass of <30 kg/ha had no discernible effects on vegetative cover (which exceeded 90%) or waterfowl (which exceeded 150,000 individuals during fall censuses), the increase to 100 kg/ha was associated with a ~50% decrease in both vegetative cover and waterfowl. A further increase in carp biomass to over 250 kg/ha during the seventh year coincided with a decrease in the vegetative cover to 17% of the lake’s surface and a decline in waterfowl use to ~10% of its original value. These data suggest that the common carp is extremely damaging to the ecological integrity of shallow lakes when its density exceeds ~100 kg/ha. Since the biomass of carp in Midwestern shallow lakes commonly exceeds this value by 3–4 times, it seems likely that carp are responsible for the large-scale habitat deterioration described in many of these ecosystems. Handling editor: J. Cambray     

Effects of Submerged Vegetation on Water Clarity Across Climates

A positive feedback between submerged vegetation and water clarity forms the backbone of the alternative state theory in shallow lakes. The water clearing effect of aquatic vegetation may be caused by different physical, chemical, and biological mechanisms and has been studied mainly in temperate lakes. Recent work suggests differences in biotic interactions between (sub)tropical and cooler lakes might result in a less pronounced clearing effect in the (sub)tropics. To assess whether the effect of submerged vegetation changes with climate, we sampled 83 lakes over a gradient ranging from the tundra to the tropics in South America. Judged from a comparison of water clarity inside and outside vegetation beds, the vegetation appeared to have a similar positive effect on the water clarity across all climatic regions studied. However, the local clearing effect of vegetation decreased steeply with the contribution of humic substances to the underwater light attenuation. Looking at turbidity on a whole-lake scale, results were more difficult to interpret. Although lakes with abundant vegetation (>30%) were generally clear, sparsely vegetated lakes differed widely in clarity. Overall, the effect of vegetation on water clarity in our lakes appears to be smaller than that found in various Northern hemisphere studies. This might be explained by differences in fish communities and their relation to vegetation. For instance, unlike in Northern hemisphere studies, we find no clear relation between vegetation coverage and fish abundance or their diet preference. High densities of omnivorous fish and coinciding low grazing pressures on phytoplankton in the (sub)tropics may, furthermore, weaken the effect of vegetation on water clarity.     

Plant/pathogen interactions observed during host range testing of the rust fungus Uromyces pencanus,a classical biological control agent for Chilean needle grass (Nassella neesiana) in Australia and New Zealand

Nassella neesiana (Chilean needle grass) is a South American grass species that is a serious weed in Australia and New Zealand. The rust fungus Uromyces pencanus is a promising biocontrol agent that could be used to control the weed in both countries. Extensive host range testing has been conducted to explore the specificity of the rust. In this paper we discuss the different degrees of invasion by the rust of the tissues of target and non-target species; the plant defences elicited by such invasion at the cellular level; and their relevance to the biological control of Chilean needle grass.     

甘南高寒草甸退化对植物功能群多样性与物种多度分布的影响

为分析甘南高寒草甸植物功能群多样性及其物种多度分布对退化的响应,探讨其多样性的形成与维持机制,采用样地调查法收集数据,并使用物种多度模型对其进行拟合分析。结果表明:随着退化程度的加深,植被优势种以禾草科和莎草科植物为主,逐渐变为杂草功能群植物为主,杂草功能群在群落多样性分布中起着主导作用;全部物种多度分布随着退化程度的加深发生变化,其中,无退化草甸的最优拟合模型是VOLKOV,轻度退化草甸的最优拟合模型是GEO,中度退化草甸和重度退化草甸的最优拟合模型为BRO,资源分配模式由随机分配转向固定分配的分配模式;禾草功能群的最优拟合模型以生态位模型为主,资源分配方式由固定分配和随机分配共同主导,豆科功能群的最优拟合模型是BRO,资源分配方式以固定分配为主,杂草功能群的最优拟合模型从中性模型向生态位模型转变,与全部物种多度分布的最优模型基本一致,且资源分配由随机分配向固定分配转变,可以认为杂草功能群是影响群落物种多度分布的主要原因,但是禾草和豆科功能群的贡献也不可忽视。     

Impacts on invertebrate fungivores: a predictable consequence of ground-cover weed invasion?

Empirical impact evidence exists for few of New Zealand’s environmental weeds. Financial constraints prevent managers examining all impacts of all weeds. Therefore it is useful to seek generalisable rules which allow managers to predict impacts of new invasions. Invasive weeds may indirectly affect fungivorous invertebrates through mechanisms such as altered litter-fall, decomposition rates, and microclimate, all of which may alter fungal activity. I tested the hypothesis that fungivorous invertebrates would be consistently affected by three invasive weeds, and that this effect would be more pronounced than for other invertebrate functional groups. Using pitfall traps, I compared invertebrates beneath climbing asparagus, tradescantia and ginger with invertebrates of uninvaded lowland forest. Five out of six Coleoptera taxa which differed in abundance between invaded and uninvaded sites were fungivores; the remaining taxon was a saprophage. At least two taxa of fungivorous Coleoptera responded to each of the three weed species. Acari (mainly Oribatids, some of which are fungivores), Isopoda and Amphipoda (decomposers) were the only taxa to respond to the presence of all three weed species. These results provide some support for the hypothesis that fungivores are particularly responsive to ground-cover weed invasion, but suggest this could be extended to include decomposers as well. However, the direction of effect differed among weed species. Therefore, while changes in fungivore and decomposer abundance may be predicted as one of the more likely consequences of ground-cover weed invasion in New Zealand low-land forest, site- and taxa-specific effects make it difficult to predict the direction of effect.