Native Perennial Shrubs Research Articles

Investigating the applicability of UAVs in characterizing desert shrub biomass and developing biological indicators for the selection of suitable revegetation sites

This study focused on evaluating factors influencing the growth of perennial shrubs by integrating field-based experiments and spatial analysis using unmanned aerial vehicles (UAVs) to identify ecological indicators that can help detect potential locations for restoration and revegetation of native plants. The experiment was implemented in the Al-Abduli protected area in Kuwait, which is mainly dominated by a Rhanterium epapposum community (desert shrub). Aerial imagery of the study site was acquired using UAVs during the growing season to estimate the desert shrub biomass and carbon stock. Then, soil samples were collected based on vegetation density to determine the impact of the soil's physical and chemical properties on vegetation biomass, growth, and distribution. It was found that shrub biomass was significantly correlated with crown area and shrub volume. We also observed that annual plants support the growth of perennial shrubs, as the mean shrub height and crown area (CA) are significantly higher, with averages of 0.7 m and 3 cm, respectively, in the presence of high annual plant density. However, shrubs in plots with low annual density had an average shrub height of 0.5 m and CA of 1.4 cm. Annual plants also enhance the soil by providing approximately 50% higher soil moisture, phosphorous (P), organic matter (OM), and carbon dioxide (CO2) sequestration. In addition, annual plants are mainly supported by loamy soils in the deeper soil layers. We concluded that locations covered with annual plants represent suitable soils and that this can be considered a biological indicator for convenient locations for restoration and revegetation of native perennial shrubs. Remote sensing technologies could be utilized for initial assessments to detect sites that may support annual plant growth over a large scale for classification as potential restoration and revegetation areas.

Rehabilitation effects on gully sediment yields and vegetation in a savanna rangeland

AbstractGully rehabilitation can contribute to catchment management by stabilizing erosion and reducing downstream sediment yields, yet the globally observed responses are variable. Developing the technical basis for gully rehabilitation and establishing guidelines for application requires studies that evaluate individual rehabilitation measures in specific environments. An eight‐year field experiment was undertaken to evaluate sediment yield and vegetation responses to several gully rehabilitation measures. The rehabilitation measures aimed to reduce surface runoff into gully head cuts, trap sediment on gully floors and increase vegetation cover on gully walls and floors. The study occurred in a savanna rangeland in northeast Australia. Two gullies were subject to treatments while four gullies were monitored as untreated controls. A runoff diversion structure reduced headcut erosion from 4.3 to 1.2 m2 yr−1. Small porous check dams and cattle exclusion reduced gully total sediment yields by more than 80%, equivalent to a reduction of 0.3 to 2.4 t ha−1 yr−1, but only at catchment areas less than 10 ha. Fine sediment yields (silt and clay) were reduced by 7 and 19% from the two treated gullies, respectively. The porous check dam deposits contained a lower percentage of the fine fraction than the parent soil. Significant regeneration of gully floor vegetation occurred, associated with trapping of organic litter and fine sediment. Increases in vegetation cover and biomass were comprised of native perennial grasses, trees and shrubs. In variable climates, long‐term gully rehabilitation will progress during wetter periods, and regress during droughts. Understanding linkages between rehabilitation measures, their hydrologic, hydraulic and vegetation effects and gully sediment yields is important to defining the conditions for their success.

GERMINATION OF MULTI-YEAR COLLECTIONS OF CALIFORNIA GRASSLAND AND SCRUB SEEDS

Successful restoration of California terrestrial ecosystems requires knowledge of seed germination rates for a diversity of native species. We quantified greenhouse germination of 25 native perennial forbs, shrubs, and grasses collected coastally near Santa Cruz, CA for restoration at the Younger Lagoon Reserve and nine annual forb species from interior grasslands at Pinnacles National Park. Seeds of most species were collected in multiple years. Twenty-seven of our 34 study species had at least 25% germination without complicated germination triggers. All but two of the 13 species that were collected in ≥3 years and germinated showed significant interannual variation in germination; seven species had a trend of decreasing percent germination with increasing age. These species- and collection-year specific results indicate a necessity to test seed stock when possible prior to seeding to increase restoration success, and highlight the importance of following best practices for seed collection and storage.

Strategies to persist in the community: Soil seed bank and above‐ground vegetation in Patagonian pine plantations

AbstractQuestionsIn terms of biodiversity conservation, forest plantations are often considered problematic because they usually have negative effects on natural ecosystems. Soil seed banks could play an important role in restoring vegetation that was originally present, by recruiting species that have disappeared above‐ground. We addressed this topic in plantations located in the Patagonian steppe by asking the following questions: Are richness, abundance and composition of steppe above‐ground vegetation and soil seed bank affected by plantations? Is species composition of the above‐ground vegetation and soil seed bank similar in plantations and in the steppe?LocationNW of Chubut Province, Patagonia, Argentina.MethodsWe selected three plantations located in the steppe, and delimited three sectors: steppe, plantation edge and plantation interior. We compared richness and abundance by species origin and growth form among sectors for the above‐ground vegetation and soil seed bank compartments, using generalized linear mixed models. We compared species composition for each compartment and between them using permutational multivariate analysis of variance and non‐metric multidimensional scaling.ResultsIn above‐ground vegetation, we found a decrease in richness and abundance, and changes in composition from the steppe to the plantation interior. Richness and abundance of the soil seed bank did not show differences among steppe and the plantation sectors, although composition was different among them. Above‐ground vegetation and soil seed bank species composition were always different; native perennial herbs and shrubs were predominant in the above‐ground vegetation while exotic annual herbs dominated the soil seed bank.ConclusionsOur findings suggest that plant recruitment from the soil seed bank would not be sufficient for restoring depleted species pools in the above‐ground vegetation of plantations. Therefore, actions promoting native species reestablishment and control of exotics should be considered to reach the aim of restoring biodiversity in former plantations.

The environmental and economic importance of Astragalus Spinosus in land restoration

ABSTRACT Astragalus spinous is a native perennial shrubs from Leguminosae family that widely distributed in severely degraded lands at northern Kuwait. A restoration program was applied via levelling and refilling the quarries and rehabilitation of the natural vegetation and wildlife to their original outward appearance before degradation. The existence of Astragalus shrubs indicated that soil after depth 40 cm was very hard and compacted. Therefore, A. spinosus is considered as one of the efficient native plants in the rehabilitation process for highly degraded lands affected by soil compaction and sealing. The A. spinosus formed a maximum volume of nabkha deposits up to 1.12 m3 which makes it one of the effective plants in controlling mobile sand and dust. Every single plant has the capability to save the Kuwait economy by USD 3.6 via trapping mobile sand and saving the infrastructures from sand encroachment as a major challenge.

Quad bike impacts on vegetation and soil physicochemical properties in an arid ecosystem

The increase use of Off-Road Vehicles (ORVs) coupled with the absence of control strategies have led to extensive use of natural areas for the creation of recreational trails. We assessed the effects of quad bikes on vegetation and soils in an arid ecosystem subjected to intensive quad bike use. We selected randomly eight traffic sites (disturbed sites) and eight adjacent control sites (undisturbed sites). Plant cover and composition were assessed with the point-intercept method and phytosociological census. In each site, we collected soil samples to assess soil physicochemical properties, including apparent specific weight (ASG), actual specific weight (RSG), porosity, texture, electric conductivity (EC) and pH. Soil compaction was measured at 30 spaces points per site. Plant cover and richness was significant lower in disturbed sites, with only four species present in areas subjected to disturbance. There were also changes in species dominance, with native perennial shrubs and grasses characterizing the undisturbed sites while the disturbed sites were mainly dominated by the invasive exotic herb Salsola kali. ORVs traffic also affected soil physicochemical properties including soil compaction, ASG, EC and soil pH. Soil compaction was more than double in disturbed sites and ASG tended to be higher under this condition. The EC was significantly higher and soil pH was significantly lower in the disturbed sites. Reduced vegetation cover and changes to soils physicochemical properties on quadbike trails highlights the impacts of ORVs in the landscape and the need to develop management strategies to minimize disturbance from ORVs on vegetation and soils.

Seeding native species increases resistance to annual grass invasion following prescribed burning of semiarid woodlands

Exotic grass invasions are often facilitated by disturbances, which provide opportunities for invasion by releasing pulses of resources available to invaders. Where disturbances such as prescribed fire are used as a management tool, there is a pressing need to identify ecosystem attributes associated with susceptibility to disturbance-induced invasion. In the Great Basin of the western United States, expansion of the exotic annual grass Bromus tectorum is transforming native ecosystems. In this study we examined long-term understory plant community responses to experimental prescribed fire and post-fire seeding treatments in Great Basin pinyon-juniper woodlands. We asked (1) how long-term ecosystem resistance to fire-induced B. tectorum invasion varies along major abiotic and biotic gradients, and (2) whether post-fire seeding of perennial species promotes perennial plant establishment and increases resistance to invasion. Fourteen years after burning, we found that resistance to invasion was high on relatively cool and moist sites (higher elevation), but that the warmer and drier (low- to mid-elevation) burned sites had become heavily invaded by B. tectorum. Post-fire B. tectorum dominance was highest in sites with high pre-fire tree cover, where residual and newly established native perennial plant cover was limited following fire. We found that seeding perennial species after burning decreased invasibility in sites with low resistance. Seeding a mix of native perennial shrubs, forbs, and grasses was more effective at increasing perennial cover and inhibiting B. tectorum invasion than seeding a mix of non-native perennial grasses. Our results highlight the need for long-term studies to evaluate plant community responses to prescribed fire, as important treatment differences were not captured in a shorter (3–4 year) post-fire monitoring period.

Invasive grass affects seed viability of native perennial shrubs in arid woodlands

It is often assumed that declines in native vegetation associated with alien plant invasion are driven by competition between plants for limited resources. However, invasion can also impact native plants through recruitment limitation mechanisms. We examined the effects of Cenchrus ciliaris L. (buffel grass, an alien pasture species) on the seed viability and germination of two native perennial shrubs (Acacia tetragonophylla and A. victoriae) in arid woodlands of central Australia. Dormancy, germination rate and seed viability were assessed using laboratory-based germination assays on seeds collected from the soil and mature shrubs in: (1) woodland invaded by buffel grass and (2) areas in which buffel grass had been removed and reinvasion prevented for at least 7 years. There was a twofold increase in viability of A. victoriae seeds in buffel grass-removed compared with invaded sites, and a faster germination rate (T50) for A. tetragonophylla in buffel grass-removed sites. Acacia victoriae seed mass was reduced by approximately 25% in invaded areas, associated with decomposed or absent embryos. Invasion may limit native recruitment by reducing the viability and germination rate of native seeds prior to dispersal from parent plants. Reduced seed viability would reduce seed bank accumulation and total available seed for A. victoriae, while slower germination rates would minimise the efficiency by which A. tetragonophylla responds to sporadic rainfall events. Both mechanisms could lead to long term declines in native plant populations. Reduced seed viability would compound interference of buffel grass on recruiting plants.

The Bet-Hedging Strategies for Seedling Emergence of Calligonum mongolicum to Adapt to the Extreme Desert Environments in Northwestern China.

Calligonum mongolicum is a dominant native perennial shrub on sand dunes in arid deserts of northwestern China, and is therefore widely used in sand dune stabilization in these regions. However, it remains largely unknown how seedling emergence of C. mongolicum has adapted to unpredictable sand movement and extreme drought. Here we examined effects of seed burial depth, light intensity, and seed age on seedling emergence, and considered seed germination and seedling emergence strategies for the shrub’s adaption to the desert environment. In our pot experiment, the optimum seeding depth for emergence of C. mongolicum was 2 cm, indicating that for germination and seedling emergence only moderate sand burial is required. Light intensity at the surface soil (0 cm) was important for seedling emergence, while there was no significant difference between 50 and 20% light flux density, at burial depths of 1 and 2 cm, indicating that C. mongolicum seeds had adapted to sand burial, while not exposure from sand erosion. We also found C. mongolicum seedlings emerged in spring and in late summer to early autumn. Meanwhile, seedling emergence percentage for 3-year-old seeds was similar to that of 1-year-old seeds, which meant that C. mongolicum seeds were well preserved under normal sand dune conditions, thus were capable of developing a persistent, but shallow soil seed-bank. These results indicated that germination and seedling emergence take a bet-hedging strategies to adapt to variable desert environments. Our study confirmed that C. mongolicum desert shrubs combine strategies in its adaption to arid and variable sand environments.

Improvements in Soil Carbon and Nitrogen Capacities after Shrub Planting to Stabilize Sand Dunes in China’s Horqin Sandy Land

Caragana microphylla, a native perennial leguminous shrub, is widely used for desertification control in China’s Horqin Sandy Land. We investigated the effects of afforestation using C. microphylla in areas with fixed and active dunes on soil carbon (C) and nitrogen (N) storage in the soil total and light-fraction (LF) organic matter. Compared to the values in the control areas, soil organic carbon (SOC) storage to a depth of 100 cm increased by 88%, 74%, and 145% at 9, 15, and 31 years after shrub planting, respectively; the corresponding values were 68%, 61%, and 195% for total nitrogen (TN) storage, 109%, 199%, and 202% for LF organic carbon storage, and 203%, 337%, and 342% for LF nitrogen storage. The soil light-fraction (LF) organic matter contributed significantly to total SOC and TN storage, despite the low proportion of total soil mass accounted for by the LF dry matter. Thus, afforestation using C. microphylla was an effective way to sequester C and to restore degraded soils, but the process was slow; it would take more than 100 years to fully restore SOC storage in active dunes through afforestation with C. microphylla in the Horqin Sandy Land.

Soil free-living nematodes as bio-indicators for assaying the invasive effect of the alien plant Heterotheca subaxillaris in a coastal dune ecosystem

The Israeli Mediterranean coastal dunes are considered to be a center of floral and faunal speciation and a natural habitat for rare endemic plants, with an extremely sensitive area for alien species invasion. The soil free-living nematode communities are one of the most important groups of soil biota, constituting an essential trophic link between primary decomposers, such as the soil microflora, and larger animals. Despite the fact that soil free-living nematodes play an important role in fundamental ecological processes and are sensitive bio-indicators for understanding processes of succession and nutrient flow in different ecosystems, little is known about the impact of invasive plant species on the soil free-living nematode communities. The present study was designed to fill this gap and evaluate the invasive effect of Heterotheca subaxillaris on the soil free-living nematode communities inhabiting the Mediterranean coastal dunes. Soil samples were collected from the upper (0–10cm) soil layer under H. subaxillaris (invasive perennial shrub) and Artemisia monosperma (native perennial shrub) at two different sites in the sea-sand ecosystem during the winter and summer seasons. Molecular analysis using the 18S rRNA gene for species determination, along with the traditional method, was a useful tool for evaluation of ecological conditions under the plant associations. The nematode communities, trophic diversity, and taxon composition were affected by the invasive plant at the study sites. Furthermore, this study showed that unfavorable seasonal conditions can also exacerbate the harmful effects of the invasive plants on nematode abundance and trophic and species diversity.

The Influence of Host Plant Extrafloral Nectaries on Multitrophic Interactions: An Experimental Investigation.

A field experiment was conducted with outplantings of the native perennial shrub Senna mexicana var. chapmanii in a semi-natural area adjacent to native pine rockland habitat in southern Florida. The presence of ants and the availability of extrafloral nectar were manipulated in a stratified random design. Insect communities were monitored and recorded over a period of six months with a view to addressing three main questions. Do ants provide biotic defense against key herbivores on S. chapmanii? Is the presence of ants on S. chapmanii mediated by EFN? Finally, are there ecological costs associated with the presence of ants on S. chapmanii, such as a reduction in alternative predator or parasitoid numbers? Herbivores on S. chapmanii included immature stages of three pierid butterflies, and adult weevils. Eight species of ants were associated with the plants, and other predators included spiders, ladybugs, wasps, and hemipterans. Parasitic, haemolymph-sucking midges (Ceratopogonidae) and parasitoid flies were also associated with the caterpillar herbivores, and possibly the extrafloral nectaries of the plants. The presence of ants did not appear to influence oviposition by butterflies, as numbers of lepidopterans of all developmental stages did not differ among treatments. Significantly more late instar caterpillars, however, were observed on plants with ants excluded, indicating that ants remove small caterpillars from plants. Substantially more alternative predators (spiders, ladybugs, and wasps) were observed on plants with ants excluded. Rates of parasitization did not differ among the treatments, but there were substantially fewer caterpillars succumbing to virus among those collected from control plants.We provide a rare look at facultative ant-plant mutualisms in the context of the many other interactions with which they overlap. We conclude that ants provide some biotic defense against herbivores on S. chapmanii, and plants benefit overall from the presence of ants, despite negative impacts on non-ant predators.

Post-fire vegetation dynamics of a sagebrush steppe community change significantly over time

Sagebrush steppe ecosystems of the Intermountain West have experienced a decline over the past 150 years due to changing fire regimes, invasive species and conifer encroachment. Prescribed fire is a common and cost-effective tool used in sagebrush restoration and fuels management. We examined the post-fire succession of a sagebrush steppe community over a nearly 30-year period at two study sites in northeastern California. The long-term nature of this study was particularly significant, as invasive annual grasses dominated the plant community in the years immediately following fire, but native perennial grasses and shrubs successfully out-competed them in the long term. Shrubs were slow to recover but had returned to pre-fire levels by the end of the study period. There was also notable increase in western juniper throughout the study sites, particularly in areas that had not been burned. Our results indicate that mean fire return intervals of 50 years or less would help reduce western juniper encroachment and preserve sagebrush habitat, especially for potentially threatened species such as the sage grouse.

Australian perennial shrub species add value to the feed base of grazing livestock in low- to medium-rainfall zones

Australian native perennial shrubs that are adapted to drought and infertile soils contribute nutrients to grazing systems that would otherwise support limited ruminant productivity. In this study, we report the nutritive value of 39 Australian shrub species of the genera Atriplex, Rhagodia, Maireana, Chenopodium, Enchylaena, Acacia, Eremophila, and Kennedia. Edible foliage was sampled in winter and summer, and there was little difference in nutritive value between seasons. The in vitro organic matter digestibility of most shrub species was 40–70%. Most species contained medium to high levels of crude protein (12–22% of dry matter, DM) and high concentrations of sulfur (2–8 g/kg DM). In an 8-week grazing experiment in which Merino wethers grazed a ‘shrub system’ containing four shrub species and a sown inter-row of annual pasture, the sheep gained weight during autumn without supplementary feeding. By comparison, sheep fed senesced volunteer pasture and supplementary cereal grain only maintained weight. The forage shrubs provided up to 50% of the total DM intake of sheep grazing the ‘shrub system’ and made a modest contribution to the digestible energy intake of the animals and a large contribution to their crude protein and mineral intake. Considering the timely and predictable provision of limiting nutrients and benefits such as gut health and the provision of shade and shelter, we suggest that Australian shrub species can make a valuable addition to the feed base of low- to medium-rainfall zones in southern Australia.

Postfire Seeding and Plant Community Recovery in the Great Basin

As wildland fire frequency increases around the globe, a better understanding of the patterns of plant community recovery in burned landscapes is needed to improve rehabilitation efforts. We measured establishment of seeded species, colonization of Bromus tectorum and other nonnative annual plants, and recovery of nonseeded native species in topographically distinct areas within five fires that burned Great Basin shrub-steppe communities in Elko County, Nevada. Plant density, frequency, and cover data were collected annually for 4 yr postfire. Vegetation composition varied among flat areas and north- and south-facing aspects, and changed over the course of the sampling period; recovery varied among sites. In general, B. tectorum densities were higher on south aspects, particularly 3 and 4 yr after fire, when densities increased dramatically relative to prefire conditions. Nonseeded native perennial grasses, forbs, and shrubs were abundant in three of the five fire sites, and were more likely to be present on north aspects and flat areas. Over time, nonseeded perennial grass densities remained relatively constant, and nonseeded forbs and shrubs increased. Seeded species were most likely to establish in flat areas, and the density of seeded perennial grasses, forbs, and shrubs decreased over time. Frequency and density measurements were highly correlated, especially for perennial species. Our results emphasize the value of considering site aspect and the potential for native regrowth when planning and monitoring restorations. For example, effective rehabilitation of south aspects may require the development of new restoration methods, whereas north aspects and flat areas in sites with a strong native component were not improved by the addition of seeded species, and may require weed control treatments, rather than reseeding, to improve recovery. Tailoring revegetation objectives, seed mixes, seeding rates, and monitoring efforts to conditions that vary within sites may lead to more cost effective and successful restoration.

A direct benefit of native saltbush revegetation for an endemic lizard (Tiliqua rugosa) in southern Australia

Land alteration for intensive agriculture has been a major cause of species decline and extinction globally. In marginal grazing regions of southern Australia, native perennial shrubs are increasingly being planted to supplement pasture feeding of stock. Such revegetation has the benefits of reducing erosion and salinity, and importantly, the potential provision of habitat for native fauna. We explored the use of revegetated native saltbush by the sleepy lizard (Tiliqua rugosa) an endemic Australian species common in the region. We repeatedly sampled revegetated saltbush throughout 2010 and 2011 for adults (n = 55) and juveniles (n = 26). Using genotypes from eight microsatellite loci, parents were assigned to half of all juveniles with high statistical confidence. Parents were sampled in the same patch of revegetated saltbush as their offspring, thus supporting the observation that juvenile sleepy lizards remain within the home range of their parents before dispersal. Most importantly, our findings indicate that revegetated saltbush provides important habitat for T. rugosa at significant life stages – before and during breeding for adults, and before dispersal for juveniles. We conclude that revegetation using simple, monoculture plantations provides beneficial habitat for T. rugosa and may also be beneficial habitat for other native species in human-altered agricultural landscapes.

Native herbivores and plant facilitation mediate the performance and distribution of an invasive exotic grass

Summary1. Exotic plant species have become increasingly prominent features of ecological landscapes throughout the world, and their interactions with native and exotic taxa in these novel environments may play critical roles in mediating the dynamics of such invasions.2. Here, we summarize results from comparative and experimental studies that explore the effects of two factors – herbivory and facilitation – on the performance and distribution of an invasive South African grass,Ehrharta calycina, in a coastal foredune system in northern California, USA.3. Using a 2‐year exclosure experiment, we show that a native herbivore, black‐tailed jackrabbits (Lepus californicus), significantly reduced the height, shoot production, fecundity and above‐ground biomass of this exotic grass.4. Data from two comparative studies and a neighbour‐removal experiment revealed thatEhrhartafrequently escaped herbivores by associating with three neighbouring plant species – an exotic perennial grass,Ammophila arenaria, an exotic perennial succulent,Carpobrotus edulis, and a native perennial shrub,Baccharis pilularis.Ehrhartagrowing in association with neighbours was taller, had fewer grazed shoots, produced greater numbers of spikelets and had greater above‐ground biomass than unassociated individuals. Furthermore, removing neighbours generally eliminated these benefits in 7 months, although effects differed among neighbour species.5. An additional neighbour‐removal experiment conducted in the absence of jackrabbits indicated that neighbour removals did not have significant impacts onEhrhartaheight, shoot production, spikelet production or above‐ground dry biomass. These results suggest that the primary means by whichEhrhartabenefits from neighbouring plants is protection from herbivores – either because they are less apparent to herbivores or less accessible – and thatEhrhartalikely incurred minimal costs from associating with neighbours.6. Ehrhartawas more frequently associated with neighbours than expected due to chance, and less frequently found in open dune habitat. These results are consistent with the hypothesis that the effects of herbivory and facilitation have been sufficiently strong to shape the local distribution of this invader in the landscape.7. Synthesis. Our research has demonstrated that herbivory and facilitation have jointly influenced the dynamics of a biological invasion, and highlights the importance of evaluating the effects of multiple interactions on invasions in a single system.

Individual plant species responses to phosphorus and livestock grazing

Livestock grazing and fertilisation are primary management activities that determine variation in plant species composition within grazed temperate grassy ecosystems of Australia. The present paper provides an extensive catalogue of the responses of individual species to grazing and fertilisation that can be used to guide management and restoration in differing situations. A hierarchical model that links plant species identities, simple plant traits and two continuous predictive variables (livestock density and available phosphorus) was used to estimate probability of occurrence of plant species across grazing and phosphorus gradients. Certain species and groups of species, particularly native perennial geophytes, ferns and shrubs, were especially sensitive to increases in each of these management gradients, whereas a small group of exotic plants were most tolerant. In the moderately intensive livestock production landscapes sampled, most native plant species preferred ungrazed areas with low available phosphorus. Many non-native plant species also tolerated or preferred such habitats. Less than 1% of all observed species are predicted to occur at high levels of available phosphorus (75 mg kg–1) and heavy stocking (9 dry sheep equivalents ha–1). There is, however, a suite of native species that persist at moderate livestock densities, but only if soils are not phosphorus-enriched. These data can be used to guide options for restoration including ranking of potential sites or selection of species for reintroduction. In most cases, livestock grazing intensity is thought to be the primary factor influencing plant species composition in grazed woodlands. These data, however, highlight the great importance of fertilisation history in limiting ground-layer plant diversity and determining options for management.

A conceptual model of plant community changes following cessation of cultivation in semi‐arid grassland

AbstractQuestion: Can vegetation changes that occur following cessation of cultivation for cereal crop production in semi‐arid native grasslands be described using a conceptual model that explains plant community dynamics following disturbance?Location: Eighteen native grasslands with varying time‐since‐last cultivation across northern Victoria, Australia.Methods: We examined recovery of native grasslands after cessation of cultivation along a space for‐ time chronosequence. By documenting floristic composition and soil properties of grasslands with known cultivation histories, we established a conceptual model of the vegetation states that occur following cessation of cultivation and inferred transition pathways for community recovery.Results: Succession from an exotic‐dominated grassland to native grassland followed a linear trajectory. These changes represent an increase in richness and cover of native forbs, a decrease in cover of exotic annual species and little change in native perennial graminoids and exotic perennial forbs. Using a state‐and‐transition model, two distinct vegetation states were evident: (1) an unstable, recently cultivated state, dominated by exotic annuals, and (2) a more diverse, stable state. The last‐mentioned state can be divided into two further states based on species composition: (1) a never‐cultivated state dominated by native perennial shrubs and grasses, and (2) a long‐uncultivated state dominated by a small number of native perennial and native and exotic annual species that is best described as a subset of the never‐cultivated state. Transitions between these states are hypothesized to be dependent upon landscape context, seed availability and soil recovery.Conclusions: Legacies of past land use on soils and vegetation of semi‐arid grasslands are not as persistent as in other Australian communities. Recovery appears to follow a linear, directional model of post‐disturbance regeneration which may be advanced by overcoming dispersal barriers hypothesised to restrict recovery.

The effects of browsing by feral and re-introduced native herbivores on seedling survivorship in the Australian rangelands

Browsing by introduced cattle (Bos taurus) and rabbits (Oryctolagus cuniculus) can limit the recruitment of some arid zone tree and shrub species. In a study conducted at the Arid Recovery Reserve, Roxby Downs, SA, we aimed to quantify initial recruitment changes in shrubs after the removal of cattle and rabbits and the re-introduction of locally extinct fauna. The presence and abundance of seedlings was measured at groves of seven native perennial shrubs over 6 years under four browsing treatments: (1) ‘reserve-reintroductions’ [re-introduced greater stick-nest rats (Leporillus conditor), burrowing bettongs (Bettongia lesueur) and greater bilbies (Macrotis lagotis)], (2) ‘reserve-no browsers’, (3) ‘pastoral-stocked’ (rabbits and cattle), and (4) ‘pastoral-destocked’ (rabbits). Recruitment of mulga (Acacia aneura F.Muell. ex Benth.), silver cassia (Senna artemisioides subsp. petiolaris Randell) and sandhill wattle (Acacia ligulata A.Cunn. ex Benth.) was significantly greater in the two browsing regimes inside the Reserve than in the two pastoral regimes. The number of recruits of these three species declined at ‘pastoral-destocked’ and ‘pastoral-stocked’ sites but increased at ‘reserve-reintroductions’ and ‘reserve-no browsers’ sites from 2001 to 2006. Narrow-leaf hopbush (Dodonaea viscose (L.) Jacq.) showed a trend towards increased recruitment at sites in both browsing regimes inside the Reserve, but decreased recruitment at sites in both pastoral regimes. Native plum (Santalum lanceolatum R.Br.), native apricot (Pittosporum phylliraeoides orth. var. DC.) and bullock bush (Alectryon oleifolius (Desf.) S.T.Reynolds) exhibited no significant difference in recruitment between the four browsing regimes within the study timeframe. These results suggest that excluding rabbits and stock may benefit the germination and survival of mulga, silver cassia and sandhill wattle. To date, re-introduced native herbivores at low numbers have not been found to negatively affect the recruitment or growth rate of the seven perennial plant species studied.