Net woody vegetation increase confined to seasonally inundated lowlands in an Australian tropical savanna,Victoria River District,Northern Territory

Abstract Georeferenced digital aerial photographs were used to assess changes in overstorey vegetation cover since 1948 in the Victoria River District, Northern Territory, Australia, across a range of lowland tropical savanna habitats and with explicit consideration of known and variable site‐specific grazing and fire management histories. Vegetation surveys at corresponding locations on the ground identified five distinct woody vegetation communities defined primarily by water drainage and secondarily by soil characteristics. Air‐photo analyses revealed that, contrary to popular perceptions and in contrast to results from other habitats, there has been no generalized net increase in overstorey woody vegetation cover across the full range of lowland savanna habitats. Rather, different habitats exhibited distinctly different vegetation change mechanisms: low‐lying seasonally inundated ‘wet’ habitats have experienced woody vegetation increase since 1948, whereas well‐drained ‘dry’ habitats have experienced overstorey vegetation stability or loss. In almost every instance woody vegetation increase could be attributed to the invasion or proliferation of a single species, Melaleuca minutifolia F.Muell. The extent of M. minutifolia increase was unrelated to historical grazing/fire regime. Demographic analyses for this species revealed that recruitment was often episodic and that synchronized recruitment events occurred uniformly across the full range of historical management treatments, most likely as a consequence of favourable climatic conditions in years with an extended wet season. Heavy grazing facilitated juvenile survival and/or recruitment, most likely by reducing grassy fuel loads and eliminating landscape fire. We conclude that while there has been no generalized net increase in overstorey woody vegetation cover in lowland environments, savanna dynamics are complex, and multiple change mechanisms have occurred simultaneously in different habitats, some of which have been significantly transformed since 1948. Where net woody vegetation increase has occurred it is primarily a natural consequence of episodic M. minutifolia establishment in climatically favourable years, but the extent and magnitude of this effect is likely mediated by fire/grazing regime.     

How the west was once: vegetation change in south-west Queensland from 1930 to 1995

Aim Conflicting perceptions of past and present rangeland condition and limited historical data have led to debate regarding the management of vegetation in pastoral landscapes both internationally and in Australia. In light of this controversy we have sought to provide empirical evidence to determine the trajectory of vegetational change in a semi‐arid rangeland for a significant portion of the 20th century using a suite of proxy measures. Location Ambathala Station, approximately 780 km west of Brisbane, in the semi‐arid rangelands of south‐western Queensland, Australia. Methods We excavated stratified deposits of sheep manure which had accumulated beneath a shearing shed between the years 1930 and 1995. Multi‐proxy data, including pollen and leaf cuticle analyses and analysis of historical aerial photography were coupled with a fine resolution radiocarbon chronology to generate a near annual history of vegetation on the property and local area. Results Aerial photography indicates that minor (< 5%) increases in the density of woody vegetation took place between 1951 and 1994 in two thirds of the study area not subjected to clearing. Areas that were selectively or entirely cleared prior to the 1950s (approximately 16% of the study area) had recovered to almost 60% of their original cover by the 1994 photo period. This slight thickening is only partially evident from pollen and leaf cuticle analyses of sheep faeces. Very little change in vegetation is revealed over the nearly 65 years based on the relative abundances of pollen taxonomic groups. Microhistological examination of sheep faeces provides evidence of dramatic changes in sheep diet. The majority of dietary changes are associated with climatic events of sustained above‐average rainfall or persistent drought. Most notable in the dietary analysis is the absence of grass during the first two decades of the record. Main conclusions In contrast to prevailing perceptions and limited research into long‐term vegetation change in the semi‐arid areas of eastern Australia, the record of vegetation change at the Ambathala shearing shed indicates only a minor increase in woody vegetation cover and no decrease in grass cover on the property over the 65 years of pastoral activity covered by the study. However, there are marked changes in the abundance of grass cuticles in sheep faeces. The appearance and persistence of grass in sheep diets from the late 1940s can be attributed to the effects of periods of high rainfall and possibly some clearing and thinning of vegetation. Lower stock numbers may have allowed grass to persist through later drought years. The relative abundances of major groups of plant pollen have not changed significantly over the past 65 years.     

Multi‐decadal stability of woody cover in a mesic eucalypt savanna in the Australian monsoon tropics

Previous analyses of historical aerial photography and satellite imagery have shown thickening of woody cover in Australian tropical savannas, despite increasing fire frequency. The thickening has been attributed to increasing precipitation and atmospheric CO₂ enrichment. These analyses involved labour‐intensive, manual classification of vegetation, and hence were limited in the extent of the areas and the number of measurement times used. Object‐based, semi‐automated classification of historical sequences of aerial photography and satellite imagery has enabled the spatio‐temporal analysis of woody cover over entire landscapes, thus facilitating measurement, monitoring and attribution of drivers of change. Using this approach, we investigated woody cover change in 4000 ha of intact mesic savanna in the Ranger uranium lease and surrounding Kakadu National Park, using imagery acquired on 10 occasions between 1950 and 2016. Unlike previous studies, we detected no overall trend in woody cover through time. Some variation in cover was related to rainfall in the previous 12 months, and there were weak effects of fire in the year of image acquisition and the antecedent 4 years. Our local‐scale study showed a mesic eucalypt savanna in northern Australia has been resilient to short‐term variation in rainfall and fire activity; however, changes in canopy cover could have occurred in other settings. When applying this semi‐automated approach to similar studies of savanna dynamics, we recommend maximising the time depth and number of measurement years, standardising the time of year for image acquisition and using many plots of 1 ha in area, rather than fewer, larger plots.     

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

Aim Encroachment or densification by woody plants affects natural ecosystems around the world. Many studies have reported encroachment in temperate Australia, particularly in coastal ecosystems and grassy woodlands. However, the degree to which published studies reflect broad-scale changes is unknown because most studies intentionally sampled areas with conspicuous densification. We aimed to estimate changes in woody vegetation cover within lowland grassy woodland and coastal ecosystems in Victoria from 1989 to 2005 to determine whether published reports of recent encroachment are representative of broad-scale ecosystem changes. Location All lowland grassy woodland and coastal ecosystems (c. 6.11 × 10⁵ ha) in Victoria, Australia. Four major ecosystems were analysed: Plains woodlands, Herb-rich woodlands, Riverine woodlands and Coastal vegetation. Methods Changes in woody vegetation cover from 1989 to 2005 were assessed based on state-wide vegetation maps and Landsat analyses of woody vegetation cover conducted by the Australian Greenhouse Office’s National Carbon Accounting System. The results show changes in woody cover within mapped patches of native vegetation, rather than changes in the extent of woody vegetation resulting from clearing and revegetation. Results When pooled across all ecosystems, woody vegetation increased by 18,730 ha from 1989 to 2005. Woody cover within Riverine woodlands and within Plains woodlands each increased by >7000 ha. At the patch scale, the mean percentage cover of woody vegetation in each polygon increased by >5% in all four ecosystems: Riverine woodlands (+9.2% on average), Herb-rich woodlands (+7.6%), Plains woodlands (+6.7%) and Coastal vegetation (+5.9%). Regression models relating degree of encroachment to geographic and climatic variables were extremely weak (r² ≤ 0.026), indicating that most variation occurred at local scales rather than across broad geographic gradients. Main conclusions At the scale of observation, woody vegetation cover increased in all lowland woodland and coastal ecosystems over the 16-year period. Thus, published examples of encroachment in selected coastal and woodland patches do appear to reflect widespread increases in woody vegetation cover in these ecosystems. This densification appears to be associated with changes in land management rather than with post-fire vegetation recovery and is likely to be ongoing and long-lasting, with substantial implications for biodiversity conservation and ecosystem services.     

Net changes in regional woody vegetation cover and carbon storage in Texas Drylands, 1937–1999

Although local increases in woody plant cover have been documented in arid and semiarid ecosystems worldwide, there have been few long‐term, large‐scale analyses of changes in woody plant cover and aboveground carbon (C) stocks. We used historical aerial photography, contemporary Landsat satellite data, field observations, and image analysis techniques to assess spatially specific changes in woody vegetation cover and aboveground C stocks between 1937 and 1999 in a 400‐km² region of northern Texas, USA. Changes in land cover were then related to topo‐edaphic setting and historical land‐use practices. Mechanical or chemical brush management occurred over much of the region in the 1940–1950s. Rangelands not targeted for brush management experienced woody cover increases of up to 500% in 63 years. Areas managed with herbicides, mechanical treatments or fire exhibited a wide range of woody cover changes relative to 1937 (?75% to + 280%), depending on soil type and time since last management action. At the integrated regional scale, there was a net 30% increase in woody plant cover over the 63‐year period. Regional increases were greatest in riparian corridors (33%) and shallow clay uplands (26%) and least on upland clay loams (15%). Allometric relationships between canopy cover and aboveground biomass were used to estimate net aboveground C storage changes in upland (nonriparian) portions of regional landscapes. Carbon stocks increased from 380 g C m^?2 in 1937 to 500 g C m^?2 in 1999, a 32% net increase across the 400 km² region over the 63‐year period. These plant C storage change estimates are highly conservative in that they did not include the substantial increases in woody plant cover observed within riparian landscape elements. Results are discussed in terms of implications for ‘carbon accounting’ and the global C cycle.     

The eco-hydrology of partly cleared,native ecosystems in southern Australia: a review

Water use by the native vegetation that existed in southern Australia prior to European settlement was largely in balance with rainfall. European settlers altered the landscape by clearing land to grow agricultural crops and pastures, and with the introduction of livestock to graze the partly cleared, native ecosystems. The aim of this review is to contrast the hydrology of grazed, partly cleared ecosystems, intact indigenous ecosystems, and entirely cleared agricultural systems in the intensive land-use zone (350–1000 mm annual rainfall zone) of southern Australia. Since European settlement, the areas of forests and woodlands in the Murray–Darling Basin have declined by approximately 64% to make way for agricultural enterprises. Modern-day vegetation surveys estimate between 52 and 58% of the intensive land-use zone of the Murray–Darling Basin has been entirely cleared, while about 40% is in the partly cleared state (disturbed ecosystems with canopy cover exceeding 5%). The replacement of native vegetation by agricultural crops and pastures has disturbed the water cycle that existed prior to European settlement, and has markedly elevated the amount of water leaking beyond the root zone of introduced species, and contributing to groundwater systems. Estimates of annual leakage beneath the root zone of annual crops range from 0 to 63 mm per annum; however, no estimates of leakage for partly cleared woodlands exist. Yet, because the groundwater beneath partly cleared woodlands rises considerably more slowly than under entirely cleared landscapes, it is likely that less water leaks beneath the roots of grazed woody ecosystem. However, aging of these systems by livestock grazing will reduce the numbers of woody individuals and will impact on groundwater recharge.     

A Comparison of Remote Sensing and Ground-Based Methods for Monitoring Wetland Restoration Success

Abstract Efficient and accurate vegetation sampling techniques are essential for the assessment of wetland restoration success. Remotely acquired data, used extensively in many locations, have not been widely used to monitor restored wetlands. We compared three different vegetation sampling techniques to determine the accuracy associated with each method when used to determine species composition and cover in restored Pacific coast wetlands dominated by Salicornia virginica (perennial pickleweed). Two ground‐based techniques, using quadrat and line intercept sampling, and a remote sensing technique, using low altitude, high resolution, color and color infrared photographs, were applied to estimate cover in three small restoration sites. The remote technique provided an accurate and efficient means of sampling vegetation cover, but individual species could not be identified, precluding estimates of species density and distribution. Aerial photography was determined to be an effective tool for vegetation monitoring of simple (i.e., single‐species) habitat types or when species identities are not important (e.g., when vegetation is developing on a new restoration site). The efficiency associated with these vegetation sampling techniques was dependent on the scale of the assessment, with aerial photography more efficient than ground‐based sampling methods for assessing large areas. However, the inability of aerial photography to identify individual species, especially mixed‐species stands common in southern California salt marshes, limits its usefulness for monitoring restoration success. A combination of aerial photography and ground‐based methods may be the most effective means of monitoring the success of large wetland restoration projects.     

Mechanical Land Clearing to Promote Establishment of Coastal Sandplain Grassland and Shrubland Communities

The decline in grasslands and other species‐rich early successional habitats on the coastal sandplains of the northeastern United States has spurred management to increase the area of these declining plant communities. We mechanically removed overstory oak and applied seed from a nearby sandplain grassland on the island of Martha’s Vineyard, Massachusetts, to evaluate this technique for creating an open oak community able to support sandplain herbaceous species. We compared vegetation structure and composition before and after clearing in an area of total tree removal (clearcutting), an area where 85% of tree basal area was removed (savanna cutting), and in adjacent coastal oak forest. Plant responses to clearcutting and savanna cutting were similar. Sandplain herbs colonized at high frequencies after seeding and increased herbaceous cover from less than 7% before clearing to 22–38% three growing seasons later. Pennsylvania sedge (Carex pensylvanica) increased in cover approximately 6‐fold, accounting for 84–90% of the increased herbaceous cover. Other native ruderals and exotic herbs reached 2 and less than or equal to 1%, cover, respectively, after three years. Species richness across cleared treatments increased from 30 to 79 species. All forest species were retained. Forest shrubs and trees initially declined from their dominant cover but rebounded after three years. Tree clearing plus seeding appeared to be a viable management practice for increasing cover of herbaceous sandplain species while causing minimal increases in exotic herbaceous cover. The long‐term persistence of sandplain herbs may require periodic disturbances that limit woody regrowth.     

Cascading biodiversity and functional consequences of a global change–induced biome switch

Aim At a regional scale, across southern Africa, woody thickening of savannas is becoming increasingly widespread. Using coupled vegetation and faunal responses (ants), we explore whether major changes in woody cover in savannas represent an increase in the density of savanna trees (C₄ grass layer remains intact) or a ‘regime shift’ in system state from savanna to thicket (=dry forest) where broad‐leaved, forest‐associated trees shade out C₄ grasses. Location Hluhluwe Game Reserve, South Africa. Methods We sampled paired open (low woody cover) and closed (high cover that have undergone an increase in tree density) sites. Vegetation was sampled using belt transects, and a combination of pitfall trapping and Winkler sampling was used for ants. Results Closed habitats did not simply contain a higher density of woody savanna species, but differed significantly in structure, functional composition (high prevalence of broad‐leaved trees, discontinuous C₄ grasses) and system properties (e.g. low flammability). Ant assemblage composition reflected this difference in habitat. The trophic structure of ant assemblages in the two habitats revealed a functional shift with much higher abundances of predatory species in the closed habitat. Main conclusions The predominance of species with forest‐associated traits and concomitant reduction of C₄ grasses in closed sites indicate that vegetation has undergone a shift in fundamental system state (to thicket), rather than simply savanna thickening. This biome shift has cascading functional consequences and implications for biodiversity conservation. The potential loss of many specialist savanna plant species is especially concerning, given the spatial extent and speed of this vegetation switch. Although it is not clear how easily the habitat switch can be reversed and how stable the thicket habitats are, it is likely in the not‐too‐distant future that conservation managers will be forced to make decisions on whether to actively maintain savannas.     

The importance of canopy complexity in shaping seasonal spider and beetle assemblages in saltmarsh habitats

1. Habitat structure, including vegetation structural complexity, largely determines invertebrate assemblages in semi‐natural grasslands. The importance of structural complexity to the saltmarsh invertebrate community, where the interplay between vegetation characteristics and tidal inundation is key, is less well known. 2. It was hypothesised that canopy complexity would be a more important predictor of spider and beetle assemblages than simple vegetation attributes (e.g. height, community type) and environmental variables (e.g. elevation) alone, measured in two saltmarsh regions, south‐east (Essex) and north‐west (Morecambe Bay) U.K. Canopy complexity (number of non‐vegetated ‘gaps’ in canopy ≥ 1 mm wide) was assessed using side‐on photography. Over 1500 spiders and beetles were sampled via suction sampling, winter and summer combined. 3. In summer, saltmarshes with abundant spider and beetle populations were characterised by high scores for canopy complexity often associated with tussocky grass or shrub cover. Simple vegetation attributes (plant cover, height) accounted for 26% of variation in spider abundance and 14% in spider diversity, rising to 46% and 41%, respectively, with the addition of canopy complexity score. Overwintering spider assemblages were associated with elevation and vegetation biomass. Summer beetle abundance, in particular the predatory and zoophagous group, and diversity were best explained by elevation and plant species richness. 4. Summer canopy complexity was identified as a positive habitat feature for saltmarsh spider communities (ground‐running hunters and sheet weavers) with significant ‘added value’ over more commonly measured attributes of vegetation structure.     

Changes over 46 years in plant community structure in a cleared brigalow (Acacia harpophylla) forest

Plant succession theory underpins the development of strategies for the conservation and regeneration of native communities. Current theory has been based largely on space‐for‐time rather than long‐term monitoring data, which have known limitations. There is general consensus that more site‐specific studies are needed to corroborate existing hypotheses. The target vegetation is a brigalow (Acacia harpophylla, Mimosaceae) forest in one of Australia's most endangered ecosystems, which was cleared and burnt in 1963. Forty quadrats were placed systematically within each of six 20 m × 20 m permanent plots. Presence, density and per cent canopy cover data were recorded for each species at 18 times over 46 years. Brigalow dominated the original vegetation, assumed dominance soon after clearing through massive root suckering and remained dominant throughout the study. It achieved maximum density within two years when severe intraspecific competition led to self‐thinning. After approximately 30 years, vacant niches appeared. Woody understorey species were slow to recolonise. Species richness and other diversity indices increased rapidly to a maximum after 2–4 years, declined until the 30th year when they again increased. This was the pattern of the species‐rich herbaceous layer; woody species showed a steady monotonic increase. The ‘hump‐shaped’ relationship between cover (biomass) and species richness was confirmed. This example fits the inhibition model for which few examples have been described. While the long‐term successional pattern is slightly confounded by climatic variability preceding sample surveys, this space‐for‐time study not only supports a bimodal pattern of diversity over time but also indicates that the relative species richness of the herbaceous and woody layers may explain the extreme variability reported in the literature.     

Composition of grazed and cleared temperate grassy woodlands in eastern Australia: patterns in space and inferences in time

Abstract. A regional vegetation survey of the temperate grassy woodlands (temperate savanna) in Australia was designed to assess the effects of clearing and grazing on the composition of vegetation remnants and the adjacent pasture matrix. Vegetation was sampled across a range of habitats using 77 0.1024‐ha quadrats; the relative abundance of species was recorded. Classification analysis clustered the sites into three main groups that corresponded to intensity of grazing/clearing followed by groups based on underlying lithology (basalt, metasediment, granites). Using Canonical Correspondence Analysis, exogenous disturbance and environmental variables were related to the relative abundance of species; grazing intensity had the highest eigenvalue (0.27) followed by tree canopy cover (0.25), lithology (0.18), altitude (0.17) and slope (0.10). Based on two‐dimensional ordination scores, six species response groups were defined relating to intensity of pastoralism and nutrient status of the landscape. Abundance and dominance of native shrubs, sub‐shrubs, twiners and geophytes were strongly associated with areas of less‐intense pastoralism on low‐nutrient soils. The strongest effects on species richness were grazing followed by canopy cover. Continuously grazed sites had lower native species richness across all growth forms except native grasses. There was no indication that intermediate grazing intensities enhanced forb richness as a result of competitive release. Species richness for all native plants was lowest where trees were absent especially under grazed conditions. Canopy cover in ungrazed sites appeared to promote the co‐existence of shrubs with the herbaceous layer. Predicted declines in forb richness in treeless, ungrazed, sites were not detected. The lack of a disturbance‐mediated enhancement of the herbaceous layer was attributed to habitat heterogeneity at 0.1 ha sampling scale.     

Application of QuickBird and aerial imagery to detect Pinus radiata in remnant vegetation

The invasion of Pinus radiata from long‐term established plantations is contributing to the degradation of fragmented and isolated remnants of native vegetation. Within the south‐east of South Australia, the 20 vegetation communities that occur within 500 m of a plantation edge are at risk, including nine state threatened communities. To plan effective mitigation strategies, the current extent and distribution of P. radiata needs to be ascertained. High spatial resolution, multispectral QuickBird imagery and aerial photography were used to classify P. radiata within eucalypt and acacia woodlands, melaleuca shrubland, modified pasture and an Eucalyptus globulus plantation. Unsupervised classification of aerial photography gave the best result showing reasonable conformity with the observed distribution of P. radiata at the site scale. However, the 9.4 ± 13.5 (SD) cover classified in the quadrats sampled for the accuracy assessment exceeded the 1.4 ± 2.4 (SD) P. radiata cover determined from an independent dataset. Only 30.1 ± 37.9% (SD) of trees within the quadrats and 9.40 ± 13.49% (SD) of their foliage cover were classified. Trees detected by partial classification of canopy were positively correlated with both tree height and canopy diameter. Overall, the low detection rates were attributed to insufficient spectral resolution. Using higher resolution imagery, together with an object‐based image analysis or combination of multispectral and airborne digital image classification, restricted to large emergent adult trees using LiDAR analysis, is likely to improve adult P. radiata detection accuracy.     

Savanna woody encroachment is widespread across three continents

Tropical savannas are a globally extensive biome prone to rapid vegetation change in response to changing environmental conditions. Via a meta‐analysis, we quantified savanna woody vegetation change spanning the last century. We found a global trend of woody encroachment that was established prior the 1980s. However, there is critical regional variation in the magnitude of encroachment. Woody cover is increasing most rapidly in the remaining uncleared savannas of South America, most likely due to fire suppression and land fragmentation. In contrast, Australia has experienced low rates of encroachment. When accounting for land use, African savannas have a mean rate annual woody cover increase two and a half times that of Australian savannas. In Africa, encroachment occurs across multiple land uses and is accelerating over time. In Africa and Australia, rising atmospheric CO₂, changing land management and rainfall are likely causes. We argue that the functional traits of each woody flora, specifically the N‐fixing ability and architecture of woody plants, are critical to predicting encroachment over the next century and that African savannas are at high risk of widespread vegetation change.     

The irreversible cattle-driven transformation of a seasonally flooded Australian savanna

Aim Anecdotal historical and photographic evidence suggests that woody vegetation is increasing dramatically in some northern Australian savanna habitats. Vegetation change in savannas has important implications for pastoral land‐use, conservation management, and landscape‐scale carbon storage, and informs theoretical debates about ecosystem function. This study seeks to determine the nature, extent and cause(s) of woody vegetation change in a seasonally flooded alluvial savanna habitat. Location The study area is located within the seasonally inundated alluvial zone of the tidal portion of the Victoria River, Northern Territory, Australia. The study area has been grazed by domestic stock since c. 1900, prior to which the area was inhabited and more likely regularly burnt by Aboriginal people for thousands of years. Methods Digital georeferenced aerial photographic coverages were used to examine and quantify woody vegetation change between 1948 and 1993. Transect surveys of woody and herbaceous vegetation were carried out to ground‐truth air‐photo results and determine the nature and causes of observed vegetation changes. Results There has been a dramatic increase in woody vegetation cover throughout the study area. Vegetation change patterns are roughly uniform across the full range of edaphic habitat variation and are unrelated to the depositional age of fluvial sediments. Two woody species, Eucalyptus microtheca and Excoecaria parvifolia, are predominantly responsible for observed increases. Demographic analyses reveal that woody invasions have been episodic and indicate that in most locations peak woody species establishment occurred in the mid‐1970s. Grasses are almost absent in a majority of habitats within the study area. Instead, large areas are covered by scalded soil, dense invasive weed populations, and unpalatable forbs and sedges. What grasses do occur are predominantly of very low value for grazing. The condition of the herbaceous layer renders most of the study area almost completely non‐flammable; what fires do burn are small and of low intensity. Main conclusions Multiple working hypotheses explaining observed patterns of woody vegetation increase were considered and rejected in turn. The only hypothesis consistent with the evidence is as follows: (1) observed changes are a direct consequence of extreme overgrazing by cattle, most likely when stocking rates peaked in the mid‐1970s; (2) prolonged heavy grazing effected the complete transformation of much of the herbaceous vegetation to a new state that is not flammable; and (3) in the absence of regular fire mortality, woody vegetation increased rapidly. The relatively treeless system that existed in 1948 was apparently stable and resilient to moderate grazing levels, and perhaps also to episodic heavy grazing events. However, grazing intensity in excess of a sustainable threshold has forced a transition that is irreversible in the foreseeable future. Stable‐state transitions such as this one inform debates at the heart of ecological theory, such as the nature of stability, resilience, equilibrium and carrying capacity in dynamic savanna ecosystems.     

Remote sensing of upland vegetation: the potential of high spatial resolution satellite sensors

Aim Traditional methodologies of mapping vegetation, as carried out by ecologists, consist primarily of field surveying or mapping from aerial photography. Previous applications of satellite imagery for this task (e.g. Landsat TM and SPOT HRV) have been unsuccessful, as such imagery proved to have insufficient spatial resolution for mapping vegetation. This paper reports on a study to assess the capabilities of the recently launched remote sensing satellite sensor Ikonos, with improved capabilities, for mapping and monitoring upland vegetation using traditional image classification methods. Location The location is Northumberland National Park, UK. Methods Traditional remote sensing classification methodologies were applied to the Ikonos data and the outputs compared to ground data sets. This enabled an assessment of the value of the improved spatial resolution of satellite imagery for mapping upland vegetation. Post‐classification methods were applied to remove noise and misclassified pixels and to create maps that were more in keeping with the information requirements of the NNPA for current management processes. Results The approach adopted herein for quick and inexpensive land cover mapping was found to be capable of higher accuracy than achieved with previous approaches, highlighting the benefits of remote sensing for providing land cover maps. Main conclusions Ikonos imagery proved to be a useful tool for mapping upland vegetation across large areas and at fine spatial resolution, providing accuracies comparable to traditional mapping methods of ground surveys and aerial photography.     

Reconstructing pre-impact vegetation cover in modified landscapes using environmental modelling, historical surveys and remnant vegetation data: a case study in the Fleurieu Peninsula, South Australia

Aim To investigate the application of environmental modelling to reconstructive mapping of pre‐impact vegetation using historical survey records and remnant vegetation data. Location The higher elevation regions of the Fleurieu Peninsula region in South Australia were selected as a case study. The Fleurieu Peninsula is an area typical of many agricultural regions in temperate Australia that have undergone massive environmental transformation since European settlement. Around 9% of the present land cover is remnant vegetation and historical survey records from the ad 1880s exist. It is a region with strong gradients in climate and topography. Methods Records of pre‐impact vegetation distribution made in surveyors’ field notebooks were transcribed into a geographical information system and the spatial and classificatory accuracy of these records was assessed. Maps of remnant vegetation distribution were obtained. Analysis was undertaken to quantify the environmental domains of historical survey record and remnant vegetation data to selected meso‐scaled climatic parameters and topo‐scaled terrain‐related indices at a 20 m resolution. An exploratory analytical procedure was used to quantify the probability of occurrence of vegetation types in environmental domains. Probability models spatially extended to geographical space produce maps of the probability of occurrence of vegetation types. Individual probability maps were combined to produce a pre‐impact vegetation map of the region. Results Surveyors’ field notebook records provide reliable information that is accurately locatable to levels of resolution such that the vegetation data can be spatially correlated with environmental variables generated on 20 m resolution environmental data sets. Historical survey records of vegetation were weakly correlated with the topo‐scaled environmental variables but were correlated with meso‐scaled climate. Remnant vegetation records similarly not only correlated to climate but also displayed stronger relationships with the topo‐scaled environmental variables, particularly slope. Main conclusions A major conclusion of this study is that multiple sources of evidence are required to reconstruct past vegetation patterns in heavily transformed region. Neither the remnant vegetation data nor historical survey records provided adequate data sets on their own to reconstruct the pre‐impact vegetation of the Fleurieu Peninsula. Multiple sources of evidence provide the only means of assessing the environmental and historical representativeness of data sets. The spatial distribution of historical survey records was more environmentally representative than remnant vegetation data, which reflect biases due to land clearance. Historical survey records were also shown to be classificatory and spatially accurate, thus are suitable for quantitative spatial analyses. Analysis of different spatial vegetation data sets in an environmental modelling framework provided a rigorous means of assessing and comparing respective data sets as well as mapping their predicted distributions based on quantitative correlations. The method could be usefully applied to other regions where predictions of pre‐impact vegetation cover are required.     

Evaluating the impact of biodiversity offsetting on native vegetation

Biodiversity offsetting is a globally influential policy mechanism for reconciling trade-offs between development and biodiversity loss. However, there is little robust evidence of its effectiveness. We evaluated the outcomes of a jurisdictional offsetting policy (Victoria, Australia). Offsets under Victoria's Native Vegetation Framework (2002–2013) aimed to prevent loss and degradation of remnant vegetation, and generate gains in vegetation extent and quality. We categorised offsets into those with near-complete baseline woody vegetation cover (“avoided loss”, 2702 ha) and with incomplete cover (“regeneration”, 501 ha), and evaluated impacts on woody vegetation extent from 2008 to 2018. We used two approaches to estimate the counterfactual. First, we used statistical matching on biophysical covariates: a common approach in conservation impact evaluation, but which risks ignoring potentially important psychosocial confounders. Second, we compared changes in offsets with changes in sites that were not offsets for the study duration but were later enrolled as offsets, to partially account for self-selection bias (where landholders enrolling land may have shared characteristics affecting how they manage land). Matching on biophysical covariates, we estimated that regeneration offsets increased woody vegetation extent by 1.9%–3.6%/year more than non-offset sites (138–180 ha from 2008 to 2018) but this effect weakened with the second approach (0.3%–1.9%/year more than non-offset sites; 19–97 ha from 2008 to 2018) and disappeared when a single outlier land parcel was removed. Neither approach detected any impact of avoided loss offsets. We cannot conclusively demonstrate whether the policy goal of ‘net gain’ (NG) was achieved because of data limitations. However, given our evidence that the majority of increases in woody vegetation extent were not additional (would have happened without the scheme), a NG outcome seems unlikely. The results highlight the importance of considering self-selection bias in the design and evaluation of regulatory biodiversity offsetting policy, and the challenges of conducting robust impact evaluations of jurisdictional biodiversity offsetting policies.     

Vegetation succession and recovery of ecological values in the southern Queensland Brigalow Belt

Summary Broadscale land‐clearing in the Queensland Brigalow Belt has resulted in widespread decline in ecological values including biodiversity loss and impairment of ecosystem processes and functions. More than 90% of brigalow ecological communities, i.e. those that have Acacia harpophylla, F. Muell. ex Benth (Brigalow) as a dominant and co‐dominant, have been entirely cleared or severely degraded in recent decades. In spite of this wide‐ranging disturbance, partial ecological recovery may be possible in the Queensland Brigalow Belt through the retention of regrowth brigalow stands. Few studies, however, have quantitatively examined brigalow vegetation succession, particularly in the context of cost‐effective ecological restoration. This study used a chronosequence approach to examine how species richness, abundance and structure change in brigalow woodlands with years since clearing. Floristic and structural characteristics were surveyed in 18 brigalow stands, of varying years since clearing, in the southern Queensland Brigalow Belt. Linear models were fitted for years since clearing versus total number of woody species, tree cover, shrub cover, herbaceous cover and litter cover. Regrowth brigalow communities were found to follow the inhibition model of succession, with Acacia harpophylla assuming dominance. The linear models suggested that at least 90 years of recovery would be required post‐clearing, before regrowth woodlands regained 90% of the species richness and structural characteristics of mature woodlands. Management practices such as thinning the dominant species and allowing for the accumulation of logs and litter may be necessary for promoting recovery of vegetation diversity and structural heterogeneity.