Can invasion patches of Acacia mearnsii serve as colonizing sites for native plant species on Réunion (Mascarene archipelago)?

There is need for documenting the long-term effects of plant invasions at the landscape scale. We investigated the possible catalytic effect of invasive Acacia mearnsii De Wild. on the colonization of rural landscapes by native plant species on Réunion Island (Mascarene Archipelago, Indian Ocean). Data were recorded from 182 circular plots of 50 m² within a set of 48 large invasion patches, aged from 1 to 48+ years. Only eighteen native plant species were present in the invaded patches and these in only 21 of the 48 patches. The Acacia invasion patches colonized by native flora were older and closer to the closest forest remnant. Most invasion patches colonized by native species were located <200 m from forest remnants. Results are consistent with studies on colonization rates of nonindigenous forest plantations, which increase with age and decrease with distance to seeds sources. Yet, the rate of Acacia invasion patches colonized by native flora remained very low compared to studies on the colonization of exotic plantations in other tropical countries. We conclude that invasion patches of Acacia mearnsii are poor colonizing sites for native plant species. Allelopathy is suspected as one of the strongest factors, which prevent this colonization.     

The perfect storm: Weed invasion and intense storms in tropical forests

Climate change scientists predict an increased intensity of storms (cyclones, hurricanes and typhoons) in the future. Intense storms facilitate plant invasion by increasing resource availability, reducing competition and increasing opportunities for propagule dispersal. We document here the state of current understanding about the response of invasive plant species to intense storms and suggest that the structure and function of forests in storm‐prone regions may be much altered in the future as a result of weed invasion. Intense storms provide a large spatial and temporal window of opportunity for invasion and empirical research demonstrates growth and recruitment rates of invasive species increase following such events, and they spread readily. In particular, lianas and woody invasive species that are shade tolerant and recruit from the seedling layer may constitute the greatest threat to tropical forests following storm events. Forests persisting in fragmented landscapes will be exposed to some of the most severe consequences of intense storms and subsequent weed invasion. In storm‐prone regions, forests of the future are likely to experience a decrease in diversity of native species and homogenization of communities at landscape and regional scales, slower rates of forest succession, increasing degradation of forest fragments and ultimately a decrease in ecosystem function.     

Rearing and release of Homichloda barkeri (Jacoby) (Coleoptera: Chrysomelidae: Alticinae) for the biological control of prickly acacia, Acacia nilotica ssp. indica (Mimosaceae) in Australia

Abstract Prickly acacia, Acacia nilotica ssp. indica , a major weed of the Mitchell Grass Downs of northern Queensland, has been the target of biological control projects since the 1980s. The striped leaf-feeding beetle, Homichloda barkeri (Coleoptera: Chrysomelidae: Alticinae), was the third insect approved for release for the control of this weed in Australia. However, mass rearing this insect under glasshouse conditions proved to be difficult and time consuming as there were problems associated with low egg-hatching rates and poor larval survival. Eggs in diapause were stimulated to hatch by repeated wetting and drying. Larvae were fed on potted prickly acacia plants in cages. Late-instar larvae were collected and transferred to a mix of sand, peat moss and vermiculite for pupation and adult emergence. Over 10 500 adults were released at 28 sites in north Queensland between November 1996 and December 1999. Initial releases of insects confined to gauze cages resulted in limited adult survival, oviposition and development of first-generation larvae. First-generation larvae were observed at two sites where cages were not used. However, later inspections of release sites, including those made in April and December 2000, April 2001 and late March 2002, failed to find any trace of the insect, which is assumed to have failed to establish. Possible reasons for this failure are discussed.     

Land use,rangeland degradation and ecological changes in the southern Kalahari,Botswana

Dual‐scale analyses assessing farm‐scale patterns of ecological change and landscape‐scale patterns of change in vegetation cover and animal distribution are presented from ecological transect studies away from waterpoints, regional remotely sensed analysis of vegetation cover and animal numbers across the southern Kalahari, Botswana. Bush encroachment is prevalent in semi‐arid sites where Acacia mellifera Benth. is widespread in communal areas and private ranches, showing that land tenure changes over the last 40 years have not avoided rangeland degradation. Herbaceous cover is dominated in intensively grazed areas by the annual grass Schmidtia kalahariensis Stent and in moderately grazed areas by the perennial grass Eragrostis lehmanniana Nees. Nutritious perennial grass species including Eragrostis pallens Hack. Ex Schinz remain prevalent in Wildlife Management Areas. Other ecological changes include the invasion of the exotic Prosopis glandulosa Torr. and dense stands of Rhigozum trichotomum Kuntze. in the arid southwest. Regional patterns of wildlife species show that the expansion of cattleposts and fenced ranches has led to large areas of low wildlife conservation value even in areas where cattle production is not practiced. Findings show the need for integrated landscape‐scale planning of land use if the ecological value and biodiversity of the southern Kalahari is to be retained.     

The host range and biology of <Emphasis Type="Italic">Cometaster pyrula</Emphasis>; a biocontrol agent for <Emphasis Type="Italic">Acacia nilotica</Emphasis> subsp. <Emphasis Type="Italic">indica</Emphasis> in Australia

Prickly acacia, Acacia nilotica subsp. indica (Benth.) Brenan, a major weed of the Mitchell Grass Downs of northern Queensland, Australia, has been the target of biological control projects since the 1980s. The leaf-feeding caterpillar Cometaster pyrula (Hopffer) was collected from Acacia nilotica subsp. kraussiana (Benth.) Brenan during surveys in South Africa to find suitable biological control agents, recognised as a potential agent, and shipped into a quarantine facility in Australia. Cometaster pyrula has a life cycle of approximately 2 months during which time the larvae feed voraciously and reach 6 cm in length. Female moths oviposit a mean of 339 eggs. When presented with cut foliage of 77 plant species, unfed neonates survived for 7 days on only Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana. When unfed neonates were placed on potted plants of 14 plant species, all larvae except those on Acacia nilotica subsp. indica and Acacia nilotica subsp. kraussiana died within 10 days of placement. Cometaster pyrula was considered to be highly host specific and safe to release in Australia. Permission to release C. pyrula in Australia was obtained and the insect was first released in north Queensland in October 2004. The ecoclimatic model CLIMEX indicated that coastal Queensland was climatically suitable for this insect but that inland areas were only marginally suitable.     

Evaluation of major Acacia species in the nursery towards apicultural landscape restoration around Southwestern Saudi Arabia

Southwestern Saudi Arabia is described by a unique ecosystem and composed of apicultural landscapes where nearly 70% of the beekeeping activities are concentrated. However, this economically important resource is under continuous degradation threat urging restoration. Besides, profound information on the possible major biological components of future restoration; nursery level performances of the native plants, Acacia species is lacking. Hence, the study was aimed at evaluating performances of selected native Acacia species at nursery level as candidate biological tool for apicultural landscape restoration. For this, nine native Acacia species’ seedlings were prepared in accordance to appropriate techniques of nursery operations recommended for arid areas. Meanwhile, species were evaluated and compared based on some performance parameters. Accordingly, significant (P < 0.005) variations were observed among the species in shoot height, collar diameter, height to collar diameter ratio, number of leaves and seedling survival. Acacia origena Hunde, A. gerrardii Benth., and A. johnwoodii Boulos. were superior over the others in most parameters while A. etbaica Schiweinf. and A. asak (Forssk.) willd. were less vulnerable to chanced pathogens. Generally, nursery level performances of all Acacia species under experimentation were within the acceptable range and showed a remarkable score which may lead them to be considered as competent biological tools in the incorporation of the genotypes in apicultural landscape restoration efforts.     

Are environmental factors important facilitators of pompom weed (<Emphasis Type="Italic">Campuloclinium macrocephalum</Emphasis>) invasion in South African rangelands?

The absence of natural enemies being keystone to the success of invasive alien plants (IAPs) can only be accepted once all the factors governing the invader and the ecosystems it invades have been established. Few studies have attempted this approach. This study reports on the relations between the invasive alien forb Campuloclinium macrocephalum (Less.) DC. (pompom weed), herbivory and the ecology of the rangelands invaded in South Africa. Eighty invaded rangelands in Gauteng Province were studied. Pompom weed herbivory was insignificant with the greatest damage being caused by native grasshoppers. Rainfall, topography and soil texture were the primary drivers of vegetation pattern. Pompom weed exhibited disturbance-mediated invasion strategies, favouring rangelands affected by non-sustainable commercial grazing practices, abandoned agricultural fields and drained wetlands. It invaded vegetation in poor condition with sward basal cover <19%. Weed density was exacerbated by high fire frequency. Vegetation susceptible to pompom weed was also invaded by other alien and native pasture weeds. The absence of natural enemies could give pompom weed a competitive advantage over native pioneer cohorts in disturbed rangelands, but is unlikely to increase fitness enabling its establishment in vegetation in good condition. Grazing strategies that promote the dominance of grass species adapted to frequent non-selective defoliation appear to restrict pompom weed better than degraded rangelands that are not utilised. Biotic resistance of rangelands to pompom weed invasion will be greatest in vegetation in good condition and under good management. The low abundance of pompom weed in rangelands in communal areas and fence-line contrasts in invaded and un-invaded road reserves warrants further investigation.     

Fire does not facilitate invasion by alien annual grasses in an infertile Australian agricultural landscape

Plant invasions are a significant threat to fragmented native plant communities in many agricultural regions. Fire potentially facilitates invasions, but in landscapes historically subject to recurrent fires, exclusion of fire is also likely to result in loss of biodiversity. We investigated the relationship between fire, fragmentation and alien plant invasion in mallee communities of the Western Australian wheatbelt. We hypothesized that invasion is limited by lack of propagules and the low soil nutrient levels of this old, infertile landscape, but that fire and/or fragmentation disrupt these limits. We tested the effects of three factors on establishment and abundance of alien annuals: ± fire, ± post-fire seeding with the locally invasive Avena barbata (propagule availability) and three landscape contexts. The three landscape contexts, exploring site limitations, were reserve interiors, perimeter edges adjacent to agricultural land and internal reserve roadside edges. Our first hypothesis was supported: Avena establishment was consistently greater in seeded plots, but away from perimeter edges, growth was poor. Our second hypothesis was supported only for perimeter edges: neither fire nor fragmentation by interior roads enhanced invasive plant establishment or biomass. At perimeter edges, invasive plant biomass was significantly greater. This was associated with higher propagule availability and elevated soil nutrient levels but was not enhanced by fire. We conclude that fire is unlikely to promote invasion by alien annuals in low-nutrient ecosystems such as mallee, hence is a viable disturbance strategy for biodiversity conservation away from nutrient-enriched edges.     

Effects of resource availability and social parasite invasion on field colonies of Bombus terrestris

Abstract.  1. The survival, growth and fecundity of bumblebee colonies are affected by the availability of food resources and presence of natural enemies. Social parasites (cuckoo bumblebees and other bumblebees) can invade colonies and reduce or halt successful reproduction; however, little is known about the frequency of invasion or what environmental factors determine their success in the field.
2. We used 48 experimental colonies of the bumblebee Bombus terrestris , and manipulated both resource availability at the landscape scale and date of colony founding, to explore invasion rates of social parasites and their effect on the performance of host colonies.
3. Proximity to abundant forage resources (fields of flowering oilseed rape) and early colony founding significantly increased the probability of parasite invasion and thus offset the potential positive effects of these factors on bumblebee colony performance.
4. The study concludes that optimal colony location may be among intermediate levels of resources and supports schemes designed to increase the heterogeneity of forage resources for bumblebees across agricultural landscapes.     

Effect of method of processing foliage of Acacia mangium and inclusion of bamboo charcoal in the diet on performance of growing goats

Two experiments were conducted to examine the effect of including charcoal and of different processing methods of foliage from Acacia mangium in the diet on intake and performance of goats. In experiment 1, four male goats were used in a Latin square arrangement. The treatments were: control, no bamboo charcoal, and 0.5, 1.0 or 1.5 g bamboo charcoal per kg body weight (BW). The diet consisted of 10 g/kg initial BW dry matter (DM) of concentrate and Para grass, respectively. Acacia was fed ad libitum at a level of 130% of the individual fresh intake the previous day. The time for each period was 21 days with the last seven days for data collection. Adding bamboo charcoal to the diet did not increase DM intake of Acacia, total DM intake or neutral detergent fiber or acid detergent fiber digestibilities, but had a significant effect on DM, organic matter (OM) and crude protein (CP) digestibilities and nitrogen (N) retention higher values being obtained in treatments 0.5 and 1.0, significantly higher than in the control or 1.5 treatments.

In experiment 2, 42 goats were randomly allotted to 6 different treatment groups. The treatments were three different methods of processing Acacia: fresh foliage, wilted foliage or dried foliage. Each method was tested with or without adding bamboo charcoal (0.5 g charcoal/kg BW). The diet was the same as in Exp. 1. The experimental time was 12 weeks. The goats fed the diet with bamboo charcoal consumed similar amounts of total DM and DM of Acacia as the goats fed the diet without bamboo charcoal and grew significantly faster (53 and 44 g/day, respectively, with and without charcoal). The processing method of Acacia foliage had a significant effect on total DM intake and DM intake of Acacia. The highest total DM intake was obtained by goats fed wilted Acacia, significantly different from fresh and dried Acacia. The weight gain of goats fed wilted or dried Acacia was higher than that of goats fed fresh Acacia, but this difference was not significant. In conclusion, the value of Acacia mangium as a feed for goats can be improved by wilting the foliage and feeding 0.5 to 1 g/kg BW of bamboo charcoal per day     

A typical browser, the roe deer, may consume substantial quantities of grasses in open landscapes

In open landscapes, grass leaves provide an abundant resource for ruminants, with potentially high nutritional value. However, their extensive digestion requires a long fermentation time, achieved through large rumen and the stratification of the rumen content. Due to anatomical and physiological differences, ruminants differ in their ability to process grass leaves. Particularly, the small roe deer, with its viscous saliva and unstratified rumen content, is generally classified as a strict browser. We hypothesised that roe deer may be able to use grass leaves in some circumstances, notably when the availability of other resources declines and when the quality of grass leaves is high. We expected that (1) grass leave consumption should be higher in open landscapes than in forest habitat because grasses are more widely available and more nutritious in open landscapes and (2) grass leave consumption should increase in winter when the availability of other resources declines. We assessed grass consumption by microscopic analysis of roe deer faecal pellets collected monthly both in forest habitat and in the surrounding open landscape. We found that both the occurrence and the proportion of grass leaves in the faeces were higher in the open landscape (predicted mean proportion 0.31) than in the forest (predicted mean proportion 0.05). In addition, the proportion of grass leaves in the faeces was higher in winter and lower in spring in both forest and open landscape. We suggest that roe deer are able to use grass leaves with unusually high nutritional quality in winter in this mild climate area. This involves a certain level of digestive plasticity to efficiently digest high quality grasses and may confer nutritional benefit to individuals feeding in an open landscape.     

Weed Diversity and Uses: a Case Study from Tea Plantations in Northern Thailand

Based on concerns that useful weed diversity in agroecosystems as well as associated traditional knowledge may be declining due to agricultural intensification and indiscriminate eradication of weeds, we studied weed diversity and use by local ethnic groups in tea plantations in northern Thailand under different agricultural intensities and landscape complexities, namely agroforestry, organic, and Good Agricultural Practice (GAP) based conventional system. In each system, we sampled five tea plantations using belt-transects of 25 m². Use data were collected through interviews with specialist informants. We recorded 214 weed species (gamma-diversity) of which 66 were useful. Agroforestry system had the highest alpha- and beta-weed diversity, suggesting that the low agricultural intensity and high landscape complexity in this system is associated with higher weed diversity in tea plantations. The common weed species were clearly different in the three systems and only a small fraction (22 species) of widespread weeds was shared among them, resulting in low weed similarity between systems. The 66 useful species of weeds were mostly for food and medicine. Uses of some weeds were shared between systems. Many of the useful weeds are invasive species, suggesting that they are prevalent and inexpensive plant resources for rural people and could represent alternative resources in the future. Because the occurrence of invasive weeds may affect the natural habitats of the native flora, integrating the exploitation of weeds into weed management strategies may reduce the weed population while sustaining agrobiodiversity and conserving associated traditional knowledge in the long term.     

Using landscape context to map invasive species with medium‐resolution satellite imagery

The spread of invasive species is a global problem of major ecological and economic concern. Landscape level assessment of invasive spread is critical, but remote sensing (RS) analyses are often complicated by the spectral similarity of species and the need to balance spatial resolution with data storage and analysis complexity. One example is the ridge and slough landscape (RSL) of the Florida Everglades, where inflowing nutrients have facilitated large‐scale cattail invasions. Hand delineation of aerial imagery has been successful in mapping cattail spread, but this technique requires considerable time and effort. Computerized classification of medium‐resolution imagery would increase the ability of scientists to provide up‐to‐date data for water management decisions. Advances in RS technologies have created opportunities that were not previously available in landscapes such as the RSL—to automatically classify sawgrass and cattail communities with medium‐resolution satellite imagery using knowledge of the invasion ecology of cattail and landscape context. We developed a computer‐classification technique that provided measure of cattail expansion that matched ground‐truthed data and show an increase in cattail area (similar to previous estimates), but a reduction in the rate of expansion over time. Although this technique can miss small patches of plants that might indicated new invasions, its rapid mapping can improve tracking of invasion fronts in the Everglades and other landscapes.     

Landscape genetics of the widespread ground-beetle Carabus auratus in an agricultural region

The brachypterous carabid beetle Carabus auratus was chosen as an indicator organism for analysing the relationship between landscape composition and population genetic structure (AFLP) in an agricultural region. We selected eight landscape sections with different landscape composition. The landscapes were analysed in 7 radii ranging from 500 to 2000 m (step size: 250 m). It is shown that the population as a whole exhibits a moderate genetic differentiation with geographically restricted genetic exchange. Genetic diversity of local populations is high. It is positively associated with increasing numbers of migrants estimated from the molecular data. This indicates that even widespread species with a presumed low dispersal capacity may exhibit high levels of genetic exchange at larger spatial scales. The availability of grassland within the landscape sections enhanced genetic diversity of local populations at larger spatial scales and explained over 50% of the observed genetic diversity. Thus, the unexpectedly high genetic exchange of C. auratus critically depends on the availability of suitable landscape features. Our results emphasise the need to take into account the adverse effects of ongoing changes in landscape composition on the genetic diversity even of widespread species when aiming at conserving genetic and functional diversity in agricultural landscapes.     

The fauna of dynamic riverine landscapes

1.  Riverine landscapes are heterogeneous in space (complex mosaic of habitat types) and time (expansion and contraction cycles, landscape legacies). They are inhabited by a diverse and abundant fauna of aquatic, terrestrial and amphibious species.
2.  Faunal distribution patterns are determined by interactive processes that reflect the landscape mosaic and complex environmental gradients. The life cycles of many riverine species rely upon a shifting landscape mosaic and other species have become adapted to exploit the characteristically high turn-over of habitats.
3.  The complex landscape structure provides a diversity of habitats that sustains various successional stages of faunal assemblages. A dynamic riverine landscape sustains biodiversity by providing a variety of refugia and through ecological feedbacks from the organisms themselves (ecosystem engineering).
4.  The migration of many species, aquatic and terrestrial, is tightly coupled with the temporal and spatial dynamics of the shifting landscape mosaic. Alternation of landscape use by terrestrial and aquatic fauna corresponds to the rise and fall of the flood. Complex ecological processes inherent to intact riverine landscapes are reflected in their biodiversity, with important implications for the restoration and management of river corridors.     

The host specificity of Anomalococcus indicus Ayyar (Hemiptera: Lecanodiaspididae), a potential biological control agent for prickly acacia (Vachellia nilotica ssp. indica) in Australia

ABSTRACT

Prickly acacia, Vachellia nilotica ssp. indica (Benth.) Kyal. & Boatwr, is a significant weed of northern Australia and has been a target of weed biological control in Australia since the 1980s. Following native range surveys in India, the scale insect Anomalococcus indicus Ayyar was identified as the most promising agent and was imported into Australia for further research. A. indicus is a major pest of prickly acacia on the Indian subcontinent, where it causes shoot tip dieback and plant death. Despite field observations suggesting the species was specific to V. nilotica, A. indicus completed development on 17 of the 84 non-target plant species tested during no-choice host specificity trials under quarantine conditions. Of these, Acacia falcata, V. bidwillii, V. sutherlandii and Neptunia major supported high numbers of mature females in all replicates. All of these species were utilised in choice trials. Combined risk scores indicate that V. sutherlandii, N. major and A. falcata may be attacked in the field. Due to the limited ability of scale insects to disperse, only those non-target species that occur on the Mitchell grass downs (i.e. V. sutherlandii) are considered to be at risk. Nevertheless, in view of the disparity between quarantine test results and the observed field host specificity of A. indicus in India, field trials are currently being conducted in India using Australian native species on which complete development has occurred. The future of A. indicus as a biological control agent for prickly acacia in Australia will be determined once results from these field trials are known.     

Distribution and spread of environmental weeds along New?Zealand roadsides

Most non-native weeds and other naturalised plants are in the early stages of invasion into New Zealand landscapes. For this invasion to be controlled, even partially, it is important to understand the dominant routes, mechanisms, and rates of weed spread across landscapes. With their linear corridors of disturbed habitats, roadsides are thought to play a large role in the spread of some weeds. We used both new surveys and existing data to assess which of the 328 environmental weeds listed by the Department of Conservation are most frequently found and where on roadsides, and whether distribution patterns are consistent with linear dispersal. We also analysed historical survey data for relationships between reserve weediness and proximity to roads. We surveyed 340 plots of 100-m-long stretches of roadside across four regions and found between 2 and 19 environmental weeds per plot; 128 species in total (Chao estimate 148). Especially abundant were agricultural (weeds and cultivated) species, species that have been naturalised for well over 50 years, and species that disperse externally attached to vertebrates. While we purposefully sampled within 10 km of town limits, we found no strong effect of distance from town on roadside weed richness, including richness of just ornamentally sourced weeds. Instead, number of houses within 250?m and presence of an adjacent house or other residential structure were both important, as was presence of woody vegetation on and adjacent to roadsides. Reserves adjacent to roads had significantly higher weed richness than reserves further from roads, although the causal mechanisms are unclear. Our results suggest that while roadsides include suitable habitats for most environmental weeds, distributions are patchy and roads show little sign of acting as linear dispersal corridors, instead they largely reflect neighbouring land uses. As such, roadside weeds should best be managed as part of the wider landscape.     

Habitat quality and connectivity in agricultural landscapes: The role of land use systems at various scales in time

Connectivity is a key concept of landscape ecology as it relates to flows and movements of organisms as driven by landscape structure. More and more aspects of landscape heterogeneity are considered in measuring connectivity, as the diversity of crops in agricultural landscapes. In this paper, we explored the value of considering changes and cumulated effects of connectivity over time. As an example, we analysed connectivity among patches influenced by maize over 7 years in an agricultural landscape in Brittany, France.Clear temporal patterns appeared: maize is concentrated in certain parts of the landscape, but over the period the whole area, 70% of the landscape, used for maize was connected. Instead of discrete patches, maize may produce large clusters allowing movement from patch to patch from year to year. This reinforces the importance of understanding land use allocation rules within farms and landscapes to evaluate the ecological effects of agriculture.     

Temporal variability of aphid biological control in contrasting landscape contexts

Landscape complexity may provide ecosystem services to agriculture through the provision of natural enemies of agricultural pests. Strong positive effect of adjacent semi-natural habitats on natural enemies in croplands has been evidenced, but the resulting impact on biological control remains unclear. Taking into account the temporal dynamics of pest and natural enemies in agricultural landscapes provides better resolution to the studies and better understanding of the biological control service.In this study, the population dynamics of aphids and two groups of predators (coccinellid and carabid beetles) were examined. Insects were sampled in 20 wheat fields, surrounded by structurally simple and complex landscapes in Chilean central valley. Considering the whole sampling period, the diversity of aphids and natural enemies were similar in wheat crops surrounded by both types of landscapes, and the abundance of ladybirds was higher in crops in the complex landscapes. The dynamics of predators was more advanced in complex landscapes than in the simple ones, whereas the dynamics of aphids were similar in both types of landscape. Negative correlation between abundance of predators and aphid population growth rate in both landscape contexts were observed suggesting a control of the pest population by the predators. Different temporal patterns were observed in these correlations in the two landscape contexts, which suggests differences in the biological control related to the landscape composition.The present study shows that colonization of crops by natural enemies occurs sooner in structurally complex landscapes and suggests that this early colonization may facilitate an early and efficient control of aphid populations, nevertheless the biological control efficiency seems to be higher in structurally simple landscapes later in the season.