Climate anomalies provide opportunities for large-scale mapping of non-native plant abundance in desert grasslands

Aim Native plant communities are susceptible to climate anomalies, which would favour the invasion of non‐native species. However, climate anomalies may also provide opportunities for detecting non‐native plants at a regional scale using remote sensing. Based on this mechanism, we propose a direct and effective remote sensing approach to map the abundance of South African Eragrostis lehmanniana Nees (Lehmann lovegrass), a highly invasive, non‐native plant in the desert grasslands of southwestern North America. Location The desert grassland of Fort Huachuca Military Reservation (31°34′N, 110°26′W) in southern Arizona, USA. Methods Simple linear regression models were used to examine the relationships between additional (comparing to the normal level) remotely sensed greenness (delta Enhanced Vegetation Index (ΔEVI) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS)), and field actual (g m^?2) and percentage (%) biomass of E. lehmanniana in an abnormal wet, cool period in October 2000. Results There was a strong and positive agreement (P < 0.005) between ΔEVI and field observations (R² = 0.72 and 0.64 for actual and percentage biomass of E. lehmanniana, respectively). These relationships allowed us to estimate the abundance of E. lehmanniana in the desert grassland. Main conclusions Phenology of native grass communities is quite similar to systems dominated by E. lehmanniana but responses differ when there are substantial amounts of precipitation in cool seasons. Eragrostis lehmanniana can produce significant amount of new tissues and seeds with sufficient cool season moisture, while native grasses are still in senescence or dormancy. Therefore, amplitude of ΔEVI during wet, cool seasons would indicate the abundance of E. lehmanniana. Long‐term climate records denote an amplification of cool season precipitation in the southwestern USA. This regional climatic trend should allow us to monitor E. lehmanniana and possibly other non‐native species frequently in this vast arid region.     

Effects of invasive plants on fire regimes and postfire vegetation diversity in an arid ecosystem

We assessed the impacts of co‐occurring invasive plant species on fire regimes and postfire native communities in the Mojave Desert, western USA. We analyzed the distribution and co‐occurrence patterns of three invasive annual grasses (Bromus rubens, Bromus tectorum, and Schismus spp.) known to alter fuel conditions and community structure, and an invasive forb (Erodium cicutarium) which dominates postfire sites. We developed species distribution models (SDMs) for each of the four taxa and analyzed field plot data to assess the relationship between invasives and fire frequency, years postfire, and the impacts on postfire native herbaceous diversity. Most of the Mojave Desert is highly suitable for at least one of the four invasive species, and 76% of the ecoregion is predicted to have high or very high suitability for the joint occurrence of B. rubens and B. tectorum and 42% high or very high suitability for the joint occurrence of the two Bromus species and E. cicutarium. Analysis of cover from plot data indicated two or more of the species occurred in 77% of the plots, with their cover doubling with each additional species. We found invasive cover in burned plots increased for the first 20 years postfire and recorded two to five times more cover in burned than unburned plots. Analysis also indicated that native species diversity and evenness as negatively associated with higher levels of relative cover of the four invasive taxa. Our findings revealed overlapping distributions of the four invasives; a strong relationship between the invasives and fire frequency; and significant negative impacts of invasives on native herbaceous diversity in the Mojave. This suggests predicting the distributions of co‐occurring invasive species, especially transformer species, will provide a better understanding of where native‐dominated communities are most vulnerable to transformations following fire or other disturbances.     

Physicochemical habitat association of a native and a non-native crayfish in the lower Flint river, Georgia: implications for invasion success

Invasive species must cope with a suite of environmental conditions that are different from those in their native ranges. We examine how the physicochemical environment contributes to the invasion success of Orconectes palmeri, a non-native crayfish, in the lower Flint River basin, Georgia, USA. We examined the distribution of Procambarus spiculifer, a native crayfish, and O. palmeri within the lower Flint River basin, and examined associations between species relative abundance and physicochemical variables. Within the lower Flint River, O. palmeri was found almost exclusively at upstream sites, while P. spiculifer was more abundant downstream. We did not detect small O. palmeri downstream, suggesting little recruitment in this area. Within tributaries, only native crayfish were observed. O. palmeri was more abundant at sites with warmer water temperatures, and P. spiculifer was more abundant at sites with cooler water temperatures, which were maintained by ground water seepage. P. spiculifer abundance was also positively associated with abundance of coarse wood. Laboratory studies demonstrated that O. palmeri selected warmer temperatures than P. spiculifer, suggesting that warmer temperatures in the upstream area favor O. palmeri. Water temperatures may have increased in recent years due to human withdrawals from the aquifer and the installation of upstream dams, creating a thermal regime that P. spiculifer has not historically encountered. Our findings suggest that the maintenance of groundwater inputs and a forested riparian buffer is crucial to protect populations of P. spiculifer and to prevent further spread by O. palmeri, especially if climatic changes result in warmer waters.     

Establishment of Native Semidesert Grasses into Existing Stands of Eragrostis lehmanniana in Southeastern Arizona

The semidesert grassland in southern Arizona has changed from a native grassland to a scattered Prosopis juliflora var. velutina (mesquite) woodland with an understory of African Eragrostis lehmanniana (Lehmann lovegrass) on many sites. To determine native grass restoration potential, seven species were direct seeded into E. lehmanniana stands that were left alive, burned, sprayed with an herbicide and then either left standing, or mowed. Initial native grass establishment was limited in the live standing treatment but was successful for all other treatments when either June or August sowing was followed by consistent summer precipitation and soil water availability. Four species, Bothriochloa barbinodis (cane beardgrass), Bouteloua curtipendula (sideoats grama), Digitaria californica (Arizona cottontop), and Leptochloa dubia (green spangletop) initially established most successfully, while only Muhlenbergia porteri (bush muhly) had consistently limited or no establishment. E. lehmanniana establishment from the seed bank was increased by canopy removal associated with burning. Densities of native grasses one year after successful initial establishment were much lower than that of E. lehmanniana. A possible revegetation strategy would be to spray emergent E. lehmanniana seedlings and surviving plants with an herbicide during the summer rainy season after spring burning. Native grasses could then be established by sowing in early August of that year or June and August of subsequent years until consistent precipitation produces a native grass stand.     

Comparative seed germination ecology of Austrostipa compressa and Ehrharta calycina (Poaceae) in a Western Australian Banksia woodland

Austrostipa compressa, a native ephemeral of southwest Western Australia was stimulated to germinate under a range of temperatures, in the presence of light, and exposure to smoke-water. This combination of environmental cues results in winter-maximum germination in immediate postfire and disturbed-soil environments of this Mediterranean-type climate. In contrast, Ehrharta calycina, an introduced perennial grass from southern Africa that has invaded Banksia woodlands, germinated under a wide range of temperature and light conditions, but showed no promotive response to smoke-water. Although A. compressa seeds tolerated heat shock better than E. calycina, the self-burial mechanism of A. compressa seeds ensures protection from fire. High-intensity fire could have a greater impact on E. calycina, as the seeds of this species tend to accumulate in the top of the soil profile where they are more susceptible to high temperatures. Although seeds of E. calycina are more susceptible to high temperatures, survival of mature individuals by postfire resprouting ensures continued survival in native woodlands. Estimates of soil seed bank densities showed extreme variability, but some recently burnt areas of the Yule Brook Botany Reserve contained up to 8000 seed m^?2 of A. compressa and nearly 75 000 seeds m^?2 of E. calycina. Viable soil seed bank densities of A. compressa are reduced with time-since-last fire, but areas of greater than 45 years since the last fire, still contained up to 119 seeds m^?2. In both species, only about half their soil seed bank germinates following fire, thus ensuring the potential for later recruitment. Massive soil seed populations of E. calycina in native Banksia woodlands pose a major problem to management of this plant community type.     

Response of semi-desert grasslands invaded by non-native grasses to altered disturbance regimes

Aim Using a long‐term data set we investigated the response of semi‐desert grasslands to altered disturbance regimes in conjunction with climate patterns. Specifically, we were interested in the response of a non‐native grass (Eragrostis lehmanniana), mesquite (Prosopis velutina), and native species to the reintroduction of fire and removal of livestock. Location The study site is located on the 45,360‐ha Buenos Aires National Wildlife Refuge (31°32′ N, 110°30′ W) in southern Arizona, USA. In 1985, livestock were removed and prescribed fires were reintroduced to this semi‐desert grassland dominated by non‐native grasses and encroaching mesquite trees. Methods Plant species cover was monitored along 38, 30‐m transects five times over a period of 15 years. Data were analysed using principal components analysis on the variance–covariance and correlation matrix, multivariate analysis of variance for changes over time in relation to environmental data, and analysis of variance for altered disturbance regimes. Results Reintroduction of fire and removal of livestock have not led to an increase in native species diversity or a decrease in non‐native grasses or mesquite. The cover of non‐native grass was influenced by soil type in 1993. Main conclusions Variability of plant community richness, diversity, and cover over time appear to be most closely linked to fluctuations in precipitation rather than human‐altered disturbance regimes. The effects of altered grazing and fire regimes are likely confounded by complex interactions with climatic factors in systems significantly altered from their original physiognomy.     

Patterns of abundance of fire ants and native ants in a native ecosystem

Abstract 1. This correlational study examines the relationship between the red imported fire ant (Solenopsis invicta) and native ants in a longleaf pine savanna. Fire ants are frequently associated with a decline in native ants throughout the invaded range, but fire ant invasion is often coupled with habitat disturbance. Invasion of fire ants into the longleaf pine savanna provides an opportunity to examine the structure of the ant community in the absence of habitat disturbance. 2. Pitfall trapping was conducted within the longleaf pine savanna as well as across a naturally occurring soil moisture gradient, in plots that had been artificially watered. 3. Species richness did not vary as a function of fire ant density. There was an inverse relationship between native ant density and fire ant density, but this abundance pattern does not necessarily imply a causal link between fire ant invasion and native ant decline. For individual species, fire ant densities were negatively correlated with the densities of only two native ant species, including Solenopsis carolinensis, a native species that potentially limits the invasion of fire ants. Additionally, fire ants and native ants respond differently to soil moisture, with native ants favouring drier conditions than fire ants. 4. The possible exclusion of fire ants by some native ants, as well as differences in habitat preferences, provide alternative explanations for the frequently observed negative correlation between fire ants and native ants.     

The impact of fire regimes on populations of an endangered lizard in montane south‐eastern Australia

The Blue Mountains water skink (Eulamprus leuraensis; Scincidae) is restricted to less than 40 fragmented swamp sites, all within the Blue Mountains and Newnes Plateau areas of New South Wales, Australia. Climate change is expected to increase fire frequency in the area, potentially degrading habitat quality for this endangered reptile. We quantified lizard abundances in 12 swamps using standardized surveys, and constructed a Global Information System (GIS) database to determine fire‐histories for each swamp since 1967. The abundance of Blue Mountains water skinks was negatively correlated with fire frequency, but not with time since fire. Indirect impacts of fire (mediated via shifts in vegetation density, moisture levels, prey availability and post‐fire predation) may be more important than direct effects in these cool, moist habitats. Although lizards were less common in swamps close to urban areas, and less common in frequently burnt areas, viable populations of this endangered reptile still persist even in anthropogenically disturbed swamps and in swamps that have experienced up to four fires in 20 years. Future research could usefully extend these analyses to other swamps in the locality, and explore the broader impacts of fire regimes on the distinctive flora and fauna of this threatened ecological community.     

Positive feedbacks between plant invasions and fire regimes: <Emphasis Type="Italic">Teline monspessulana</Emphasis> (L.) K. Koch (Fabaceae) in central Chile

Invasive species can increase fire frequency and intensity, generating favorable conditions for their self-perpetuation. Mediterranean south-central Chile may be especially prone to the effects of invasive species on fire regimes because it is less adapted to fire and it contains a highly endemic flora. Teline monspessulana (L.) K. Koch (syn. Cytisus monspessulanus L.; Genista monspessulana (L.) L.A.S. Johnson) is an introduced shrub that forms monotypic stands or is present as an understory species in native forests as well as in forestry plantations. Dense T. monspessulana stands are completely destroyed by fire, generating the conditions for it seeds to germinate and establish an abundant regeneration, with up to 900 plants/m². We report key evidence on abundance and biomass in adult stands, and patterns of seed bank and regeneration after fire in stands of T. monspessulana around the city of Concepción, Chile. We estimated living biomass in pure stands and underneath Eucalyptus plantations. In burned areas, we assessed T. monspessulana seed bank and studied regeneration patterns. We found that T. monspessulana densities reaches 52,778 plants/ha and 8.92 ton/ha in pure stands and 34,223 plants/ha and 2.31 ton/ha underneath Eucalyptus plantations. T. monspessulana generates small caliper fuel and acts as a ladder-fuel. Large soil seed banks allow for abundant regeneration after fire, with mean densities of 877,111 plants/ha, but an overall mortality of 37.2% in the first year after the fire. The high values of regeneration compared to final densities in adult stands suggest that density-dependent mortality. Our results indicate that T. monspessulana regeneration is not only favored by fires, but also that the species creates favorable conditions for intense and continuous fires, both under pure conditions, but also associated to exotic tree plantations. To understand the implications of positive feedbacks between invaders and fire, we recommend focusing in the mechanisms by which they increases fuel accumulation and fuel flammability, and how higher fire frequency and intensity favors invasive species recruitment over native species. Comprehension of this dynamics will allow for better management and control of these invasions which have major ecological, economical and social implications.     

Fire frequency and time‐since‐fire effects on the open‐forest and woodland flora of Girraween National Park,south‐east Queensland,Australia

Abstract The effects of recent fire frequency and time‐since‐fire on plant community composition and species abundance in open‐forest and woodland vegetation in Girraween National Park, south‐east Queensland, Australia, were examined. Cover‐abundance data were collected for shrub and vine species in at least 10 400‐m² plots in each of four study areas. Study areas were within one community type and had burnt most recently either 4 or 9 years previously. Variations in fire frequency allowed us to compare areas that had burnt at least three times in the previous 25 years with less frequently burnt areas, and also woodlands that had experienced a 28‐year interfire interval with more frequently burnt areas. Although species richness did not differ significantly with either time‐since‐fire or fire frequency, both these factors affected community composition, fire frequency being the more powerful. Moisture availability also influenced floristics. Of the 67 species found in five or more plots, six were significantly associated with time‐since‐fire, whereas 11 showed a significant difference between more and less frequently burnt plots in each of the two fire‐frequency variables. Most species, however, did not vary in cover‐abundance with the fire regime parameters examined. Even those species that showed a marked drop in cover‐abundance when exposed to a particular fire regime generally maintained some presence in the community. Five species with the capacity to resprout after fire were considered potentially at risk of local extinction under regimes of frequent fire, whereas two species were relatively uncommon in long‐unburnt areas. Variable fire regimes, which include interfire intervals of at least 15 years, could be necessary for the continuity of all species in the community.     

An unfortunate alliance: Native shrubs increase the abundance,performance, and apparent impacts of Bromus tectorum across a regional aridity gradient

Interspecific facilitation contributes to the assembly of desert plant communities. However, we know little of how desert communities invaded by exotic species respond to facilitation along regional-scale aridity gradients. These measures are essential for predicting how desert plant communities might respond to concomitant plant invasion and environmental change. Here, we evaluated the potential for Bromus tectorum (a dominant invasive plant species) and the broader herbaceous plant community to form positive associations with native shrubs along a substantial aridity gradient across the Great Basin, Mojave, and San Joaquin Deserts in North America. Along this gradient, we sampled metrics of abundance and performance for B. tectorum, all native herbaceous species combined, all exotic herbaceous species combined, and the total herbaceous community using 180 pairs of shrub and open microsites. Across the gradient, B. tectorum formed strong positive associations with native shrubs, achieving 1.6–2.2 times greater abundance, biomass, and reproductive output under native shrubs than away from shrubs, regardless of relative aridity. In contrast, the broader herbaceous community was not positively associated with native shrubs. Interestingly, increasing B. tectorum abundance corresponded to decreasing native abundance, native species richness, exotic species richness, and total species richness under but not away from shrubs. Taken together, these findings suggest that native shrubs have considerable potential to directly (by increasing abundance and performance) and indirectly (by increasing competitive effects on neighbors) facilitate B. tectorum invasion across a large portion of the non-native range.     

Plant architecture,growth and biomass allocation effects of the invasive pathogen myrtle rust (Austropuccinia psidii) on Australian Myrtaceae species after fire

In 2010, the parasitic fungus Austropuccinia psidii (myrtle rust) was detected in Australia. Austropuccinia psidii infects immature growth of myrtaceous species. Many of Australia’s myrtaceous species occur within fire‐prone vegetation communities and have the capacity to resprout after fire. Therefore, it is likely that new post‐fire growth may be vulnerable to A. psidii infection, causing subsequent flow‐on effects to species’ persistence and community dynamics. The aim of this study was to test the impacts of A. psidii on native Australian Myrtaceae species after fire. We grew eight native susceptible species in a glasshouse experiment before burning them and inoculating the resprouting new growth of half the plants with A. psidii. We assessed the effect of A. psidii on the architecture, growth and biomass allocation of our study species. Although general patterns were observed across species, results were found to be species‐specific. Austropuccinia psidii significantly reduced the height of two of the eight species (Callistemon citrinus and Eucalyptus moluccana), but none of the species had increased branching. As expected, specific leaf area was lower (9%) in inoculated plants – although only significant for C. citrinus and E. dalrympleana – and leaf biomass was greater (15%), but significant for Angophora costata only. Finally, biomass allocation did not significantly differ between infection treatments. We can conclude that the effect of A. psidii infection on fire‐damaged plants has significant impacts on plants at the species level, which may have flow‐on effects at the community level, especially after repeated infections. Furthermore, these impacts may be exacerbated in the future under climate change, as the predicted increase in frequency and intensity of fires across Australia will result in more frequent new growth availability, providing more opportunities for A. psidii infection.     

Rare but not lost: Endemic mountain lizard occupancy following megafire and grazing disturbances

Wildfire and grazing by invasive herbivores can influence habitat suitability for ground-dwelling fauna, such as reptiles. Australia has a large and diverse reptile fauna, with the Australian Alps bioregion in the southeast of the continent supporting a disproportionately high number of threatened species. In this bioregion, many species are threatened by fire, habitat loss or modification, and invasive species. The range of one such threatened endemic lizard, Cyclodomorphus praealtus (family Scincidae), was impacted by the 2019–20 megafires and is also subject to widespread grazing by invasive species. We investigated the relationship between C. praealtus site occupancy and fire and grazing. We completed 2045 surveys across 120 sites over 4 years, detecting the species at 43% of sites and increasing the species' known geographic range. Using single season detection occupancy models, we found C. praealtus occupancy was not associated with elevation, vegetation height or whether the site was burnt, but was positively associated with grazing activity. Our results indicate that C. praealtus has the capacity to persist following a single fire in some cases, and that habitats with high occupancy probabilities are subject to high grazing pressure. However, our results do not rule out more nuanced impacts associated with these disturbances, which affect a large proportion of C. praealtus' habitat. Our cumulative detection probability calculations revealed that considerable survey effort is often required to determine C. praealtus site occupancy. We therefore recommend that impact assessments assume species presence within areas of suitable habitat within the species' range. Our study improves our understanding of disturbance impacts on C. praealtus' occupancy, while demonstrating the need for sufficiently resourced impact assessments for cryptic and threatened species.     

Rapid Recovery of an Urban Remnant Reptile Community following Summer Wildfire

Reptiles in urban remnants are threatened with extinction by increased fire frequency, habitat fragmentation caused by urban development, and competition and predation from exotic species. Understanding how urban reptiles respond to and recover from such disturbances is key to their conservation. We monitored the recovery of an urban reptile community for five years following a summer wildfire at Kings Park in Perth, Western Australia, using pitfall trapping at five burnt and five unburnt sites. The reptile community recovered rapidly following the fire. Unburnt sites initially had higher species richness and total abundance, but burnt sites rapidly converged, recording a similar total abundance to unburnt areas within two years, and a similar richness within three years. The leaf-litter inhabiting skink Hemiergis quadrilineata was strongly associated with longer unburnt sites and may be responding to the loss of leaf litter following the fire. Six rarely-captured species were also strongly associated with unburnt areas and were rarely or never recorded at burnt sites, whereas two other rarely-captured species were associated with burnt sites. We also found that one lizard species, Ctenotus fallens, had a smaller average body length in burnt sites compared to unburnt sites for four out of the five years of monitoring. Our study indicates that fire management that homogenises large areas of habitat through frequent burning may threaten some species due to their preference for longer unburnt habitat. Careful management of fire may be needed to maximise habitat suitability within the urban landscape.     

Abundance,species richness and feeding preferences of introduced molluscs in native grasslands of Victoria,Australia

Abstract Introduced molluscs have invaded endangered, remnant native grasslands of south‐eastern Australia, but few studies have investigated their distribution, abundance or potential impact. Molluscs were surveyed in grassland sites across an urban to rural transect west of Melbourne, Australia. It was confirmed that several introduced mollusc species have invaded these areas. Three snail and five slug species were identified, none of which was native to Australia. The most common species was the brown field slug (Deroceras panormitanum). Mollusc capture and species richness were positively related to the degree of urbanization in the surrounding landscape. There was also a negative relationship with fire frequency. Feeding trials revealed selective herbivory by the black‐keeled slug (Milax gagates) among native plants. Anecdotal evidence that variable glycine (Glycine tabacina) and button wrinklewort (Rutidosis leptorrhynchoides) are palatable to molluscs was supported. Mollusc herbivory may potentially lead to reduced fitness of palatable species, and changes in community composition and structure.     

Pine invasion decreases density and changes native tree communities in woodland Cerrado

ABSTRACT

Background: Invasive plants can negatively impact native communities, but the majority of the effects of these invasions have been demonstrated only for temperate ecosystems. Tropical ecosystems, including the Cerrado, a biodiversity hotspot, are known to be invaded by numerous non-native species, but studies of their impacts are largely lacking.

Aims: Our research aimed at quantifying how Pinus spp. presence and density affected Cerrado plant communities.

Methods: We sampled areas invaded and non-invaded by Pinus spp. to determine if pine invasion affected native tree richness, diversity, evenness, and density. We also evaluated if community composition differed between invaded and non-invaded sites.

Results: We found invaded plots had lower native tree densities than non-invaded plots and that Pinus spp. invasions changed native tree communities by reducing native species abundances.

Conclusion: Invasive pines had negative impacts on the native Cerrado tree community by reducing native plant density and changing species abundances. Reduced density and abundance at early invasion stages can result in reduction in biodiversity in the long term.     

Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in Hawaii

The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non‐indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass‐fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there.     

Vertebrate browsing impacts in a threatened montane plant community and implications for management

Montane ecosystems are vulnerable to the removal of vegetation cover through browsing by feral or native vertebrate fauna. The highest elevated peaks of the Stirling Range in Western Australia provide habitat for an endemic plant community, Critically Endangered due to plant disease, frequent fire and an emerging threat of browsing by vertebrate fauna. Survey and camera trapping confirmed the herbivorous feral Rabbit (Oryctolagus cuniculus) and native Quokka (Setonix brachyurus) are present. Dietary analysis through faecal examination revealed contrasting diets and implicates native rather than feral species as responsible for impacts on dicotyledonous species, and in particular those of conservation significance. Exclosure experiments conducted over 1 year revealed significant changes in abundance, cover and height of perennial herbs and an increase in growth and/or reproduction of four threatened endemic plants. Detrimental impacts caused by native browsing fauna are not unprecedented and may be attributed to disequilibria in ecosystem processes due to multiple interacting threats. Montane ecosystems may be particularly vulnerable to browsing due to their naturally slow recovery after disturbance and browsing may also create environmental conditions more conducive to plant disease. For plant species with critically low population numbers, the impact of browsing poses a threat to population persistence and undermines investment into other conservation recovery actions. For effective management, it is critical to determine the relative impact of browsing species present. Where native species are implicated, the physical protection of high value assets in wire exclosures is warranted to complement other recovery actions and ensure effective species and community recovery.     

Feral horse impacts on threatened plants and animals in sub‐alpine and montane environments in Victoria,Australia

Feral herbivores are a major driver of biodiversity loss globally and can alter the structure, composition and functioning of ecosystems. The direct impacts of feral herbivores on plant communities are well studied, but the direct and indirect effect they have on wildlife is not well understood. In Victoria (south‐eastern Australia), a large feral Horse (Equus caballus) population coincides with highly sensitive and nationally endangered Alpine Sphagnum Bogs and Associated Fens communities, and several threatened animal species. We assessed the impact of feral horses on this ecological community and the Alpine Water Skink (Eulamprus kosciuskoi) and the Broad‐toothed Rat (Mastacomys fuscus) at 20 sites with varying levels of horse disturbance. We used scat counts to determine an index of feral horse abundance and quantified impacts associated with their presence in the landscape. Active searches were used for Alpine Water Skink and scat and runway surveys for Broad‐toothed Rat. We also measured the vegetation structure and the abundance of different vegetation types (life forms). Our results suggest that feral horses are associated with vegetation types and characteristics that negatively influence the presence or abundance of Alpine Water Skink and Broad‐toothed Rat. Sites with high horse activity had more low‐growing forbs, and the abundance of Alpine Water Skink was negatively related to this vegetation type. Grasses, sedges, rushes and shrubs were also less dense and lower in height in high horse activity sites, and Broad‐toothed Rat was less likely to be present in areas with these habitat attributes. We recommend that feral horses are controlled to protect these threatened vertebrate species and their Sphagnum bog habitat.     

Leaf gas exchange and water status responses of a native and non-native grass to precipitation across contrasting soil surfaces in the Sonoran Desert

Arid and semi-arid ecosystems of the southwestern US are undergoing changes in vegetation composition and are predicted to experience shifts in climate. To understand implications of these current and predicted changes, we conducted a precipitation manipulation experiment on the Santa Rita Experimental Range in southeastern Arizona. The objectives of our study were to determine how soil surface and seasonal timing of rainfall events mediate the dynamics of leaf-level photosynthesis and plant water status of a native and non-native grass species in response to precipitation pulse events. We followed a simulated precipitation event (pulse) that occurred prior to the onset of the North American monsoon (in June) and at the peak of the monsoon (in August) for 2002 and 2003. We measured responses of pre-dawn water potential, photosynthetic rate, and stomatal conductance of native (Heteropogon contortus) and non-native (Eragrostis lehmanniana) C₄ bunchgrasses on sandy and clay-rich soil surfaces. Soil surface did not always amplify differences in plant response to a pulse event. A June pulse event lead to an increase in plant water status and photosynthesis. Whereas the August pulse did not lead to an increase in plant water status and photosynthesis, due to favorable soil moisture conditions facilitating high plant performance during this period. E. lehmanniana did not demonstrate heightened photosynthetic performance over the native species in response to pulses across both soil surfaces. Overall accumulated leaf-level CO₂ response to a pulse event was dependent on antecedent soil moisture during the August pulse event, but not during the June pulse event. This work highlights the need to understand how desert species respond to pulse events across contrasting soil surfaces in water-limited systems that are predicted to experience changes in climate.