Reforestation success can be enhanced by improving tree planting methods

Successful cost-effective reforestation plantings depend substantially on maximising sapling survival from the time of planting, yet in reforestation programs remarkably little attention is given to management of saplings at the planting stage and to planting methods used. Critical determinants of sapling survival include their vigour and condition when planted, the wetness of the soil into which saplings are planted, the trauma of transplant shock from nursery to natural field soils, and the method and care taken during planting. While some determinants are outside planters' control, careful management of specific elements associated with outplanting can significantly lessen transplanting shock and improve survival rates. Results from three reforestation experiments designed to examine cost-effective planting methods in the Australian wet tropics provided the opportunity to examine the effects of specific planting treatments, including (1) watering regime prior to planting, (2) method of planting and planter technique, and (3) site preparation and maintenance, on sapling survival and establishment. Focusing on sapling root moisture and physical protection during planting improved sapling survival by at least 10% (>91% versus 81%) at 4 months. Survival rates of saplings under different planting treatments were reflected in longer-term survival of trees at 18-20 months, differing from a low of 52% up to 76-88%. This survival effect was evident more than 6 years after planting. Watering saplings immediately prior to planting, careful planting using a forester's planting spade in moist soil and suppressing grass competition using appropriate herbicides were critical to improved plant survival.

Solutions to fire and shade: resprouting, growing tall and the origin of Eurasian temperate broadleaved forest

Tree species of Eurasian broadleaved forest possess two divergent trait syndromes with contrasting patterns of resource allocation adapted to different selection environments: short-stature basal resprouters that divert resources to a bud bank adapted to frequent and severe disturbances such as fire and herbivory, and tall trees that delay reproduction by investing in rapid height growth to escape shading. Drawing on theory developed in savanna ecosystems, we propose a conceptual framework showing that the possession of contrasting trait syndromes is essential for the persistence of broadleaved trees in an open ecosystem that burns. Consistent with this hypothesis, trees of modern Eurasian broadleaved forest bear a suite of traits that are adaptive to surface and crown-fire regimes. We contend that limited opportunities in grassland restricts recruitment to disturbance-free refugia, and en masse establishment creates a wooded environment where shade limits the growth of light-demanding savanna plants. Rapid height growth, which involves investment in structural support and the switch from a multi-stemmed to a monopodial growth form, is adaptive in this shaded environment. Although clustering reduces surface fuel loads, these establishment nuclei are vulnerable to high-intensity crown fires. The lethal effects of canopy fire are avoided by seasonal leaf shedding, and aerial resprouting enhances rapid post-fire recovery of photosynthetic capacity. While these woody formations satisfy the structural definition of forest, their constituents are clearly derived from savanna. Contrasting trait syndromes thus represent the shift from consumer to resource regulation in savanna ecosystems. Consistent with global trends, the diversification of most contemporary broadleaved taxa coincided with the spread of grasslands, a surge in fire activity and a decline in wooded ecosystems in the late Miocene-Pliocene. Recognition that Eurasian broadleaved forest has savanna origins and persists as an alternative state with adjacent grassy ecosystems has far-reaching management implications in accordance with functional rather than structural criteria. Shade is a severe constraint to the regeneration and growth of both woody and herbaceous growth forms in consumer-regulated ecosystems. However, these ecosystems are highly resilient to disturbance, an essential process that maintains diversity especially among the species-rich herbaceous component that is vulnerable to shading when consumer behaviour is altered.

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers.

The future of sub-Saharan Africa’s biodiversity in the face of climate and societal change

Many of the world’s most biodiverse regions are found in the poorest and second most populous continent of Africa; a continent facing exceptional challenges. Africa is projected to quadruple its population by 2100 and experience increasingly severe climate change and environmental conflict—all of which will ravage biodiversity. Here we assess conservation threats facing Africa and consider how these threats will be affected by human population growth, economic expansion, and climate change. We then evaluate the current capacity and infrastructure available to conserve the continent’s biodiversity. We consider four key questions essential for the future of African conservation: (1) how to build societal support for conservation efforts within Africa; (2) how to build Africa’s education, research, and management capacity; (3) how to finance conservation efforts; and (4) is conservation through development the appropriate approach for Africa? While the challenges are great, ways forward are clear, and we present ideas on how progress can be made. Given Africa’s current modest capacity to address its biodiversity crisis, additional international funding is required, but estimates of the cost of conserving Africa’s biodiversity are within reach. The will to act must build on the sympathy for conservation that is evident in Africa, but this will require building the education capacity within the continent. Considering Africa’s rapidly growing population and the associated huge economic needs, options other than conservation through development need to be more effectively explored. Despite the gravity of the situation, we believe that concerted effort in the coming decades can successfully curb the loss of biodiversity in Africa.

Can I afford to publish? A dilemma for African scholars

With open-access publishing authors often pay an article processing charge and subsequently their article is freely available online. These charges are beyond the reach of most African academics. Thus, the trend towards open-access publishing will shift the business model from a pay-wall model, where access to literature is limited, to a pay-to-publish one, where African scholars cannot afford to publish. We explore the costs of publishing and the ability of African scholars to afford to publish via open access in top journals. Three-quarters of the 40 top ecology journals required payment for open-access publishing (average cost $3150). Paying such fees is a hardship for African scholars as grant funding is not available and it is not feasible to pay the fees themselves as salaries are low. We encourage funders and publishers to facilitate an equitable publishing model that allows African scholars to make their research available through open-access publishing.

Quantifying carbon in tree bark: The importance of bark morphology and tree size

Bark contributes approximately 20% to the total above-ground biomass of trees, yet bark is not properly accounted for when estimating carbon sequestered by trees. Current allometric functions estimate tree volume from diameter measured over the bark, and derive bark density and carbon content from estimates for wood. As the bark density of hardwood species is 40%-50% lower than the wood density, but nearly equivalent in conifers, bark carbon is overestimated for most species. The latter is further exacerbated by variation in bark volume with bark surface morphology.Fissured bark volume is overestimated by diameter over bark measurements by up to 40%. The vacant space in fissures can be accounted for by a bark fissure index (BFI). We calculate bark carbon for Australian species from a non-destructive and effective BFI using bark thickness measured in the field.Bark volume, and in turn bark carbon, scaled inversely with tree size (diameter) so that bark volume comprised 42% of small trees (10 cm diameter at breast height, DBH) but 23% of large trees (50 cm DBH). Our BFI method using a bark thickness gauge (BGM) yielded similar results than using the less time-efficient contour gauge method (CM) to estimate BFI (bias BGM-CM -1.3%, non-significant at p = 0.72). Both BGM and CM had an error of <4% compared to digitized BFI from destructive sampled stem disks. An average of 15 bark gauge measurements per tree estimated bark thickness (and inconsequence BFI) for both fissured and unfissured bark with <20% error relative to the exact value.Using the bark gauge method, BFI can be rapidly measured from large numbers of trees needed for estimating bark carbon at the community level and modelling carbon uptake, storage and cycling in woody biomes.

Cats are a key threatening factor to the survival of local populations of native small mammals in Australia’s tropical savannas: evidence from translocation trials with Rattus tunneyi

Abstract ContextInvasive predators are a key threat to biodiversity worldwide. In Australia, feral cats are likely to be responsible for many extinctions of native mammal species in the south and centre of the continent. AimsHere we examine the effect of feral cats on native rodent populations in the second of two translocation experiments. MethodsIn a wild-to-wild translocation, we introduced pale field rats, Rattus tunneyi, whose populations are declining in the wild, into two pairs of enclosures where accessibility by feral cats was manipulated. Key resultsIndividual rats translocated into enclosures accessible to cats were rapidly extirpated after cats were first detected visiting the enclosures. Rats in the enclosure not exposed to cats were 6.2 times more likely to survive than those exposed to cats. Two individual cats were responsible for the deaths of all but 1 of 18 cat-accessible rats. Rats in the site with denser ground cover persisted better than in the site with more open cover. ConclusionsThese results are consistent with our previous study of a different native rat species in the same experimental setup, and provide further evidence that, even at low densities, feral cats can drive local populations of small mammals to extinction. ImplicationsEffective feral cat control may be necessary to enable recovery of small mammals.

Does rapid utilization of elevated nutrient availability allow eucalypts to dominate in the tropical savannas of Australia?

Northern Australia's savannas are among the most fire-prone biomes on Earth and are dominated by eucalypts (Eucalyptus and Corymbia spp.). It is not clear what processes allow this group to dominate under such extreme fire frequencies and whether a superior ability to compete for nutrients and water might play a role. There is evidence that eucalypts are adapted to frequent fires; juvenile eucalypts escape the fire trap by growing rapidly in height between fires. However, non-eucalypts are less able to escape the fire trap and tend to have stand structures strongly skewed toward suppressed juveniles. The mechanisms that drive these contrasting fire responses are not well understood. Here, we describe the results of a controlled glasshouse seedling experiment that evaluated the relative importance of nutrient and water availability in determining height growth and biomass growth of two eucalypt and one noneucalypt tree species, common in northern Australian savannas. We demonstrate that growth of eucalypt seedlings is particularly responsive to nutrient addition. Eucalypt seedlings are able to rapidly utilize soil nutrients and accumulate biomass at a much greater rate than noneucalypt seedlings. We suggest that a seasonal spike in nutrient availability creates a nutrient-rich microsite that allows eucalypt seedlings to rapidly gain height and biomass, increasing their likelihood of establishing successfully and reaching a fire-resistant size. Our results extend our understanding of how eucalypts dominate northern Australian savannas under extremely high fire frequencies.

Ants as ecological indicators of rainforest restoration: Community convergence and the development of an Ant Forest Indicator Index in the Australian wet tropics

Ecosystem restoration can help reverse biodiversity loss, but whether faunal communities of forests undergoing restoration converge with those of primary forest over time remains contentious. There is a need to develop faunal indicators of restoration success that more comprehensively reflect changes in biodiversity and ecosystem function. Ants are an ecologically dominant faunal group and are widely advocated as ecological indicators. We examine ant species and functional group responses on a chronosequence of rainforest restoration in northern Australia, and develop a novel method for selecting and using indicator species. Four sampling techniques were used to survey ants at 48 sites, from grassland, through various ages (1–24 years) of restoration plantings, to mature forest. From principal components analysis of seven vegetation metrics, we derived a Forest Development Index (FDI) of vegetation change along the chronosequence. A novel Ant Forest Indicator Index (AFII), based on the occurrences of ten key indicator species associated with either grassland or mature forest, was used to assess ant community change with forest restoration. Grasslands and mature forests supported compositionally distinct ant communities at both species and functional levels. The AFII was strongly correlated with forest development (FDI). At forest restoration sites older than 5–10 years that had a relatively closed canopy, ant communities converged on those of mature rainforest, indicating a promising restoration trajectory for fauna as well as plants. Our findings reinforce the utility of ants as ecological indicators and emphasize the importance of restoration methods that achieve rapid closed‐canopy conditions. The novel AFII assessed restoration status from diverse and patchily distributed species, closely tracking ant community succession using comprehensive species‐level data. It has wide applicability for assessing forest restoration in a way that is relatively independent of sampling methodology and intensity, and without a need for new comparative data from reference sites.

Small fire refugia in the grassy matrix and the persistence of Afrotemperate forest in the Drakensberg mountains

Afrotemperate forests situated in the Drakensberg mountains of South Africa are characteristically small (1–10 s ha) and widely dispersed in a vast fire-prone grassland. Compared with lowland forests, they are typically species poor with low levels of endemism and species turnover, patterns that are to date unexplained. Here we show that the richness, composition and functional traits of tree species distributed on extremely small (10–100 s m²) rocky fire-refugia situated in grassland are indistinguishable from that in forest. Afrotemperate forest tree species in the Drakensberg are widely dispersed and conform to the habitat generalist strategy. Most forest trees are bird dispersed; wind dispersal is rare and is associated only with species that resprout in response to fire. We present the ‘matrix refuge hypothesis’, which proposes that fire and extreme conditions associated with exposed rocky outcrops have filtered the Afrotemperate forest tree composition resulting in convergence in functional traits essential for trees to arrive, establish and persist on fire refugia in the grassland matrix. Most Afrotemperate forest tree diversity in the Drakensberg thus resides in the matrix where it may function as a recolonisation reservoir during climatic bottlenecks.

Disturbance-dependent invasion of the woody weed, Calotropis procera, in Australian rangelands

Plant invasions are threats to biodiversity and ecosystem processes that have far reaching ecological and economic impacts. Understanding the mechanisms of invasion essentially helps in developing effective management strategies. Rubber bush (Calotropis procera) is an introduced milkweed that invades Australian beef production rangelands. Its establishment is often associated with disturbances caused by pastoral management practices. We examined whether or not rubber bush (1) outcompetes native grasses, (2) can invade intact rangeland, and (3) if disturbance facilitates rubber bush establishment and spread in grassy rangelands. We measured the competitive response of different densities of Mitchell grass (Astrebla pectinata) individuals and the competitive effects of associate rubber bush seedlings in an additive common garden experiment. Replicated field exclosure experiments, under grass-dominated and tropical savanna woodland conditions examined the effect of increasing levels of disturbance on rubber bush seedling emergence. The dominant native Mitchell grass was a stronger competitor than rubber bush when grown together under greenhouse conditions, whereby root and shoot biomass yields were more restricted in rubber bush compared with Mitchell grass. This finding was corroborated in the field exclosure experiments at both sites, where seedling emergence increased 5-fold in seeded and highly disturbed plots where superficial soils were turned over by treatments simulating heavy grazing and trampling by cattle or machinery. Emergence of rubber bush seedlings in seeded plots that were undisturbed, clipped and grazed was minimal and rubber bush seedlings did not survive the seedling stage in these plots. These results demonstrate that disturbance to the superficial soil stratum affects the ability of rubber bush seeds to successfully establish in a microsite, and high levels of soil disturbance substantially increase establishment. Thus, rubber bush is a poor competitor of Mitchell grass and does not invade intact grassland. Consequently, rubber bush invasion is disturbance-dependent in the vast Australian rangelands. The spread of this weed may be arrested by management practices that minimise disturbances to grass cover.

Frequent fires reduce the nutritional quality of Sorghum stipoideum seed, a keystone food resource for the Gouldian finch (Erythrura gouldiae)

Fire is a pervasive feature of the tropical savannas of northern Australia. Increasingly extensive and intensive fires have had an adverse effect on grass layer diversity. Reduced grass species diversity and abundance are important correlates of the decline of granivores in these tropical savannas. The Gouldian finch (Erythrura gouldiae), an endangered species that is endemic to northern Australia, is particularly vulnerable to changes to the grass layer as its diet comprises only grass seed, and it relies mostly on Sorghum stipoideum during the breeding season. Although this annual grass species is abundant at breeding sites, the finches do not always choose to breed at these sites, raising the possibility that seed quality may vary from year to year. This study examines the effect of fire (time since last fire; fire frequency) on soil fertility and seed nutritional quality. We hypothesise that recently burnt sites produce a flush of soil nutrients and Sorghum stipoideum seed at these sites is of higher nutritional quality. Furthermore, we posit that frequently burnt sites become depleted of soil nutrients and their seeds are of lower nutritional quality. There was a significant increase in inorganic nitrogen in soils following a fire, but no notable change in other soil nutrients. Contingent on this increase in soil inorganic nitrogen, seed nutrient levels, particularly essential proteins, were greater at sites that were recently, but infrequently burnt. Fires appear to affect soil nitrogen and in turn seed nutrition, providing a plausible explanation for why Gouldian finches choose recently, but infrequently burnt breeding sites.

Portrayal of sustainability principles in the mission statements and on home pages of the world's largest organizations

Conservation can be achieved only if sustainability is embraced as core to organizational cultures. To test the extent to which the related concepts of sustainability, conservation, response to climate change, poverty alleviation, and gender equity have been incorporated into organizational culture, we compared mission statements published from 1990 to 2000 with those published in 2014 for 150 organizations, including conservation nongovernmental organizations (NGOs), aid NGOs, government development agencies, resource extraction companies, and retailers (30 in each category). We also analyzed the 2014 home web pages of each organization. Relative to the earlier period, the frequency with which mission statements mentioned poverty alleviation, biodiversity conservation, and a range of sustainable practices increased only slightly by 2014, particularly among resource extractors and retail companies. Few organizations in any sector had embedded either climate change or gender equity into their mission statements. In addition, the proportional intensity with which any of the aspirations were expressed did not change between periods. For current home pages, conservation NGOs, resource extractors, and government agencies were significantly more likely to acknowledge the importance of matters that were not part of their core business, but few aid agencies or retail companies promoted goals beyond alleviation of crises and profit maximization, respectively. Overall, there has been some progress in recognizing poverty alleviation, biodiversity conservation, and sustainable practices, but gender equity and a determination to reduce impacts on climate change are still rarely promoted as central institutional concerns. Sustainability in general, and biodiversity conservation in particular, will not be achieved unless their importance is more widely apparent in core communication products of organizations.

The potential distribution of the woody weed Calotropis procera (Aiton) W.T. Aiton (Asclepiadaceae) in Australia

The potential spread of any invasive plant is a central concern in weed risk assessment. Calotropis procera is wind dispersed and forms extensive monospecific stands that reduce the productivity of pastoral land, but its potential distribution and drivers of its spread are not well known. Using maximum entropy methodology, we modelled current and future potential distributions of C. procera in Australia. Occurrence data (n = 5976 presence records) were collated from regional databases and a field survey. Of a set of ‘independent’ environmental correlates, those that best accounted for the observed distribution of C. procera in Australia were distance (km) to roads, average annual rainfall (mm), mean temperature (°C), average wind speed (km/h), beef density and vegetation type, in that order of importance. Current and potential distribution of C. procera was best explained by interactions between anthropogenic disturbance and climatic factors, all underpinned by species characteristics. Models were based on a grid cell size of 5 km × 5 km and model performance was good (mean AUC = 0.916; s.d. = 0.014; AUC = area under the curve; perfect fit = 1). The model showed that C. procera has not saturated its current potential distribution. Models of future spread derived from climate change projections, based on global circulation models in the ‘Representative Concentration Pathway 4.5 emissions scenario for 2035’, show the area suitable for C. procera will increase, increasing the risk the weed poses. Range expansion will occur into all three states surrounding the Northern Territory, but mostly into the north-eastern border regions of Western Australia and north-western Queensland. Joint management of rubber bush at a regional scale across jurisdictions, is urgently advised to avoid future spread of rubber bush and further reductions in pastoral productivity.

Deriving Multiple Benefits from Carbon Market-Based Savanna Fire Management: An Australian Example

Carbon markets afford potentially useful opportunities for supporting socially and environmentally sustainable land management programs but, to date, have been little applied in globally significant fire-prone savanna settings. While fire is intrinsic to regulating the composition, structure and dynamics of savanna systems, in north Australian savannas frequent and extensive late dry season wildfires incur significant environmental, production and social impacts. Here we assess the potential of market-based savanna burning greenhouse gas emissions abatement and allied carbon biosequestration projects to deliver compatible environmental and broader socio-economic benefits in a highly biodiverse north Australian setting. Drawing on extensive regional ecological knowledge of fire regime effects on fire-vulnerable taxa and communities, we compare three fire regime metrics (seasonal fire frequency, proportion of long-unburnt vegetation, fire patch-size distribution) over a 15-year period for three national parks with an indigenously (Aboriginal) owned and managed market-based emissions abatement enterprise. Our assessment indicates improved fire management outcomes under the emissions abatement program, and mostly little change or declining outcomes on the parks. We attribute improved outcomes and putative biodiversity benefits under the abatement program to enhanced strategic management made possible by the market-based mitigation arrangement. For these same sites we estimate quanta of carbon credits that could be delivered under realistic enhanced fire management practice, using currently available and developing accredited Australian savanna burning accounting methods. We conclude that, in appropriate situations, market-based savanna burning activities can provide transformative climate change mitigation, ecosystem health, and community benefits in northern Australia, and, despite significant challenges, potentially in other fire-prone savanna settings.

A synthesis of postfire recovery traits of woody plants in Australian ecosystems

Postfire resprouting and recruitment from seed are key plant life-history traits that influence population dynamics, community composition and ecosystem function. Species can have one or both of these mechanisms. They confer resilience, which may determine community composition through differential species persistence after fire. To predict ecosystem level responses to changes in climate and fire conditions, we examined the proportions of these plant fire-adaptive traits among woody growth forms of 2880 taxa, in eight fire-prone ecosystems comprising ~87% of Australia's land area. Shrubs comprised 64% of the taxa. More tree (>84%) than shrub (~50%) taxa resprouted. Basal, epicormic and apical resprouting occurred in 71%, 22% and 3% of the taxa, respectively. Most rainforest taxa (91%) were basal resprouters. Many trees (59%) in frequently-burnt eucalypt forest and savanna resprouted epicormically. Although crown fire killed many mallee (62%) and heathland (48%) taxa, fire-cued seeding was common in these systems. Postfire seeding was uncommon in rainforest and in arid Acacia communities that burnt infrequently at low intensity. Resprouting was positively associated with ecosystem productivity, but resprouting type (e.g. basal or epicormic) was associated with local scale fire activity, especially fire frequency. Although rainforest trees can resprout they cannot recruit after intense fires and may decline under future fires. Semi-arid Acacia communities would be susceptible to increasing fire frequencies because they contain few postfire seeders. Ecosystems dominated by obligate seeders (mallee, heath) are also susceptible because predicted shorter inter-fire intervals will prevent seed bank accumulation. Savanna may be resilient to future fires because of the adaptive advantage of epicormic resprouting among the eucalypts. The substantial non-resprouting shrub component of shrublands may decline, but resilient Eucalyptus spp. will continue to dominate under future fire regimes. These patterns of resprouting and postfire seeding provide new insights to ecosystem assembly, resilience and vulnerability to changing fire regimes on this fire-prone continent.

Functional and environmental determinants of bark thickness in fire-free temperate rain forest communities

PREMISE OF THE STUDY

In fire-prone ecosystems, variation in bark thickness among species and communities has been explained by fire frequency; thick bark is necessary to protect cambium from lethal temperatures. Elsewhere this investment is deemed unnecessary, and thin bark is thought to prevail. However, in rain forest ecosystems where fire is rare, bark thickness varies widely among species and communities, and the causes of this variation remain enigmatic. We tested for functional explanations of bark thickness variation in temperate rain forest species and communities.

METHODS

We measured bark thickness in 82 tree species throughout New Zealand temperate rain forests that historically have experienced little fire and applied two complementary analyses. First, we examined correlations between bark traits and leaf habit, and leaf and stem traits. Second, we calculated community-weighted mean (CWM) bark thickness for 272 plots distributed throughout New Zealand to identify the environments in which thicker-barked communities occur.

KEY RESULTS

Conifers had higher size-independent bark thickness than evergreen angiosperms. Species with thicker bark or higher bark allocation coefficients were not associated with "slow economic" plant traits. Across 272 forest plots, communities with thicker bark occurred on infertile soils, and communities with thicker bark and higher bark allocation coefficients occurred in cooler, drier climates.

CONCLUSIONS

In non-fire-prone temperate rain forest ecosystems, investment in bark is driven by soil resources, cool minimum temperatures, and seasonal moisture stress. The role of these factors in fire-prone ecosystems warrants testing.

Correlates of Recent Declines of Rodents in Northern and Southern Australia: Habitat Structure Is Critical

Australia has experienced dramatic declines and extinctions of its native rodent species over the last 200 years, particularly in southern Australia. In the tropical savanna of northern Australia significant declines have occurred only in recent decades. The later onset of these declines suggests that the causes may differ from earlier declines in the south. We examine potential regional effects (northern versus southern Australia) on biological and ecological correlates of range decline in Australian rodents. We demonstrate that rodent declines have been greater in the south than in the tropical north, are strongly influenced by phylogeny, and are consistently greater for species inhabiting relatively open or sparsely vegetated habitat. Unlike in marsupials, where some species have much larger body size than rodents, body mass was not an important predictor of decline in rodents. All Australian rodent species are within the prey-size range of cats (throughout the continent) and red foxes (in the south). Contrary to the hypothesis that mammal declines are related directly to ecosystem productivity (annual rainfall), our results are consistent with the hypothesis that disturbances such as fire and grazing, which occur in non-rainforest habitats and remove cover used by rodents for shelter, nesting and foraging, increase predation risk. We agree with calls to introduce conservation management that limits the size and intensity of fires, increases fire patchiness and reduces grazing impacts at ecological scales appropriate for rodents. Controlling feral predators, even creating predator-free reserves in relatively sparsely-vegetated habitats, is urgently required to ensure the survival of rodent species, particularly in northern Australia where declines are not yet as severe as those in the south.

Testing the Shifting Persistence Niche Concept: Plant Resprouting along Gradients of Disturbance

Plant resprouting after disturbance confers community resilience because individuals persist through trade-offs in resources for buds versus those required to produce seeds. However, repeated disturbance may deplete bud banks, and population persistence may become increasingly reliant on regeneration from seed. Theory predicts a shift in community assemblage from species with a strategy of persistence by resprouting (persistence niche) to one of regeneration from seed (regeneration niche) as the disturbance frequency increases. We tested, for the first time, the shifting persistence niche concept in a model system at local and regional community scales using a phylogenetically diverse floristic assemblage. Persistence traits of vascular plants were modeled as a function of dry-down frequency in wetlands. Resprouting species occupying the persistence niche were more common in stable wetlands than in those more frequently disturbed by dry downs. The patterns of resprouting species in standing vegetation and in seed banks provide strong support for the shifting persistence niche model involving trade-offs between resprouting (clonality) and sexual reproduction.

Predator satiation and recruitment in a mast fruiting monocarpic forest herb

BACKGROUND AND AIMS

Cross-pollination and satiation of seed predators are often invoked to explain synchronous mast reproduction in long-lived plants. However, explanations for the synchronous death of parent plants are elusive. The roles of synchronous seeding and post-reproductive mortality were investigated in a perennial monocarpic herb (Isoglossa woodii) in coastal dune forest in South Africa.

METHODS

Pre-dispersal seed predation and seed production were assessed by measuring fruit and seed set of inflorescences sprayed with insecticide or water and with no spray treatments. Seed predation was measured at different densities of I. woodii plants by monitoring removal rates of seed from the forest floor. The influence of adult plants on establishment of I. woodii seedlings was assessed by monitoring growth and survivorship of seedlings in caged and uncaged 1 × 1 m plots in understorey gaps and thickets.

KEY RESULTS

Fruit and seed set were similar between spray treatments. An I. woodii stem produced 767·8 ± 160·8 seeds (mean ± s.e.) on dune crests and 1359·0 ± 234·4 seeds on the foredune. Seed rain was greater on the foredune than in other topographic locations. Seed predation rates were 32 and 54 % on dune crests and in dune slacks, respectively, and decreased with seed abundance, number of inflorescences per stem and plant height. Seedling recruitment was greater beneath synchronously dying adult plants than in natural understorey gaps (no I. woodii). However, seedling growth rate beneath I. woodii mid-way through its life-cycle was less than in gaps, although survivorship was similar.

CONCLUSIONS

The selective advantage of masting in I. woodii derives from satiation of both pre- and post-dispersal seed predators. In addition, post-seeding mortality of adult plants facilitates seedling establishment. Satiation of seed predators and the benefits of seedling establishment are strong drivers of the evolution of synchronous monocarpy in I. woodii.

Ecological filtering by a dominant herb selects for shade tolerance in the tree seedling community of coastal dune forest

The regeneration niche is commonly partitioned along a gradient from shade-tolerant to shade-intolerant species to explain plant community assembly in forests. We examined the shade tolerance of tree seedlings in a subtropical coastal forest to determine whether the ecological filtering effect of a dominant, synchronously monocarpic herb (Isoglossa woodii) selects for species at either end of the light response continuum during the herb's vegetative and reproductive phases. Photosynthetic characteristics of seedlings of 20 common tree species and the herb were measured. Seedlings were grown in the greenhouse at 12-14% irradiance, and their light compensation points measured using an open-flow gas exchange system. The light compensation points for the tree species were low, falling within a narrow range from 2.1 ± 0.8 μmol m(-2) s(-1) in Celtis africana to 6.4 ± 0.7 μmol m(-2) s(-1) in Allophylus natalensis, indicating general shade tolerance, consistent with a high and narrow range of apparent quantum yield among species (0.078 ± 0.002 mol CO(2) mol(-1) photon). Rates of dark respiration were significantly lower in a generalist pioneer species (Acacia karroo) than in a forest pioneer (C. africana), or in late successional phase forest species. We argue that the general shade tolerance, and phenotypic clustering of shade tolerance, in many tree species from several families in this system, is a result of ecological filtering by the prevailing low light levels beneath the I. woodii understorey, which excludes most light-demanding species from the seedling community.

Pollination ecology of Isoglossa woodii, a long-lived, synchronously monocarpic herb from coastal forests in South Africa

Synchronous monocarpy in long-lived plants is often associated with pollination by wind, in part because infrequent mass flowering may satiate pollinators. Selfing in synchronous monocarps may provide reproductive assurance but conflict with the benefits of outcrossing, a key evolutionary driver of synchrony. We predicted that animal-pollinated species with synchronous flowering would have unspecialised flowers and attract abundant generalised pollinators, but predictions for selfing and outcrossing frequencies were not obvious. We examined the pollination biology of Isoglossa woodii (Acanthaceae), an insect-pollinated, monocarpic herb that flowers synchronously at 4-7-year intervals. The most frequent visitor to I. woodii flowers was the African honeybee, Apis mellifera adansonii. Hand-pollination failed to enhance seed production, indicating that the pollinators were not saturated. No seed was set in the absence of pollinators. Seed set was similar among selfed and outcrossed flowers, demonstrating a geitonogamous mixed-mating strategy with no direct evidence of preferential outcrossing. Flowers contained four ovules, but most fruits only developed one seed, raising the possibility that preferential outcrossing occurs by post-pollination processes. We argue that a number of the theoretical concerns about geitonogamous selfing as a form of reproductive assurance do not apply to a long-lived synchronous monocarp such as I. woodii.

Pollinators, "mustard oil" volatiles, and fruit production in flowers of the dioecious tree Drypetes natalensis (Putranjivaceae)

The Putranjivaceae is an enigmatic family, notable for being the only lineage outside the Capparales to possess the glucosinolate biochemical pathway, which forms the basis of an induced chemical defense system against herbivores (the "mustard oil bomb"). We investigated the pollination biology and floral scent chemistry of Drypetes natalensis (Putranjivaceae), a dioecious subcanopy tree with flowers borne on the stem (cauliflory). Flowering male trees were more abundant than female ones and produced about 10-fold more flowers. Flowers of both sexes produce copious amounts of nectar on disc-like nectaries accessible to short-tongued insects. The main flower visitors observed were cetoniid beetles, bees, and vespid wasps. Pollen load analysis indicated that these insects exhibit a high degree of fidelity to D. natalensis flowers. Insects effectively transfer pollen from male to female plants resulting in about 31% of female flowers developing fruits with viable seeds. Cetoniid beetles showed significant orientation toward the scent of D. natalensis flowers in a Y-maze olfactometer. The scents of male and female flowers are similar in chemical composition and dominated by fatty acid derivatives and isothiocyanates from the glucosinolate pathway. The apparent constitutive emission of isothiocyanates raises interesting new questions about their functional role in flowers.

Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird

Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).