Grazing in remnant woodland vegetation: changes in species composition and life form groups

Grazing by domestic livestock in native woodlands can have major effects on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in floristics in a large group of remnants of native woodland left after agricultural clearing in southwestern Australia. Species richness and diversity were significantly reduced in remnants and the proportion of exotic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and identified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that normally influence floristic patterns. Floristic characteristics of sites that were influencing the position of plots on the ordination diagram included proportion of exotic species and proportion of native perennial shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form groups such as native perennial grasses and geophytes were not significantly affected by grazing. Reproductive strategies of perennial species showed a significant decrease in numbers of resprouters and a significant increase in numbers of facultative seeder/sprouters. Exclosure plots showed increases in number and cover of perennial shrubs and herbs after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of exclosure plots in grazed sites became closer to that of the ungrazed sites

Vegetation patterns and plant response to gradients of soil salinity and innundation

Inundation and edaphic factors are considered to be the primary factors controlling the distribution of tree species at Lake Toolibin, an ephemeral freshwater lake situated in the Central Wheatbelt of Western Australia. Clearing of the catchment surrounding the lake for agriculture has led to changes in the hydrology, causing increased runoff, higher groundwater levels and mobilization of sub-soil salt stores. Thus higher groundwater and subsequent salt accumulation in surface soil during periods of lake dryness (NARWRC 1978). Both prolonged flooding and increased soil salinity are believed to affect tree vigour at Lake Toolibin. The aims of this study were to determine vegetation patterns and their relationships to soil salinity and inundation, and to elucidate possible causes of recent tree mortality

Distribution, productivity and reproductive phenology of emergent macrophytes in relation to water regimes at wetlands of south-western Australia

Variability in the response of Baumea articulata and Typha orientalis to water regime was assessed at eight urban wetland lakes on the Swan Coastal Plain, south-western Australia. Distribution, productivity and reproduction along water regime gradients were assessed, and the importance of wetland nutrient status in altering plant response to water regime was also considered. The overall range in distribution observed across the lakes was similar for both species, but there was significant between-lake variation in distribution relative to mean water depth. Neither species occupied its full 'potential' distribution range, relative to water regime, at any one wetland. Standing biomass and ramet and inflorescence densities varied along the water regime gradient, with peak values generally occurring at intermediate water depths. There was a shift in phenology (ramet emergence, new leaf growth, flowering and seed production) with increasing mean water depth and nutrient status. Seasonal values of aboveground productivity changed along the water regime gradient for both species. Comparison of productivity at sampling points of different nutrlent status but similar water regime showed a significantly greater growth response in T. orientalis compared with B. articulata. The significance of these results to urban wetland management is discussed

Responses of emergent macrophytes to altered water level regimes in urban wetlands of Western Australia

On the sandy Swan Coastal Plain the distribution of the two most common emergent macrophytes, Baumea articulata and Typha angustifolia is similar along transects in different wetlands. Their biomass distribution is a reflection of measured productivity. Their response is similar to different stable water levels under controlled conditions, maximum productivity for both being achieved where the water level is at the sediment surface. The conclusion that water regime explains distribution is modified in the field, where different productivities were found in wetlands with the same water regimes, but different sediment nutrient concentrations and soil types. Typha fared better than Baumea when the two were grown in the same containers. In the field Typha replaced Baumea when Baumea had been eliminated by altered water levels

Remote sensing methods for wetlands: report to Water Authority of Western Australia and Department of Conservation and Land Management

Landsat MSS imagery was evaluated for its accuracy in delineating, mapping and classifying wetlands, catchment areas and land cover types. A comparison was made between results from Landsat MSS imagery, 1:25000 scale colour aerial photography and ground truth data, for the same area in the Coobidge Creek Catchment, Western Australia. Landsat MSS was found to be useful in identifying lakes as small as 0.4 ha with differing water chemistry. A comparison was made between the aerial photography based inventory (1988) and satellite image derived inventory (1984-1986). Analysis of the satellite based inventory helped to confirm high fluctuations in the water table of many wetlands in the catchment. Change detection images and bivariate plots of the image data indicate that the physical size of the wetland and a rainfall pattern are only some of the factors influencing wetlands appearance in the satellite image. Lakes of similar size, depth, of close proximity (eg. Lake Carbul, Kubitch and Gidong), varied significantly in the water volume between seasons. Very large lakes, such as Lake Gore fluctuate in their boundaries by as much as 400 m. Wetland water quality parameters could only be established in qualitative terms. For quantitative assessment, field checks coinciding with the satellite overpass would have to be arranged. Hence, it was not possible to establish water salinity in this study. Relative water turbidity, water depth and fringing vegetation were possible to compare using bivariate scatter plots. Changes within the same water body between the seasons were observable on the same plots overlayed for different dates. Limiting factors in water quality detection were water depth and size of the water body relative to the resolution of the sensor. Due to the limited time, a detailed comparison of the wetland classification scheme based on a unitemporal and multitemporal data set were not completed. Preliminary assessment indicates that the classification accuracy will improve if a separate training (image sampling) procedure is followed for each of the dates. This is primarily due to large radiance changes between the seasons of the same surfaces. It was hoped that some time would be saved if a common training data set could be used for classifying each image

Remote sensing of wetland vegetation degradation

The suitability of Landsat Thematic Mapper (TM) data in mapping vegetation and detecting vegetation degradation was assessed. Four TM images from February 1991, September 1990, March 1990 and August 1989, of an area west of Esperance, Western Australia, were examined to detect remnant vegetation degradation caused by waterlogging, flooding, fires and salinization. Moreover, several change detection techniques were tested to determine their usefulness in analysing TM data. Overall, the high classification accuracy obtained using a single and a multitemporal data set, indicate that Landsat TM data is suitable for detecting plant damage. However, the linear and visual change detection techniques and the vegetation indices tested, were found to be only of a limited use in examining changes in Western Australian remnant vegetation. Mapping of vegetation degradation using more powerful software and hardware is still continuing, and is due to be completed in November 1993 as a part of an honours project at Murdoch University

Biodiversity and management of riparian vegetation in Western Australia

This paper considers the nature of riparian vegetation in south west Western Australia and issues relevant to its management. Riparian forests and vegetation in Western Australia are generally less species rich than adjacent upland communities. This correlates with the few studies in other parts of Australia and South Africa, but is in contrast with the situation in Europe. Structurally, the vegetation is usually more complex than that of upland areas. Riparian vegetation has been severely degraded in many parts of Western Australia and plant species biodiversity is threatened by a number of environmental problems. Foremost among these are clearing, grazing, salinization, weed invasion, urbanisation and frequent burning. The relative importance of these problems is related to the geographical area in question. Management practices to maintain biodiversity need to be tailored to the conditions of each particular area. In relatively undegraded areas an integrated management approach, especially in relation to weeds, is likely to provide the best outcome. In more degraded areas, biodiversity is greatly decreased from that of natural systems. The priority in these areas should be to enhance the value of the system through revegetation and moderation of degrading influences. A primary need in this area is a data-bank of recruitment requirements of suitable riparian plant species to enable their re-establishment on riverbanks

Effects of salinity and waterlogging on the vegetation of Lake Toolibin, Western Australia

Increased rates of tree senescence and mortality in and adjacent to an ephemeral lake in the Western Australian wheatbelt have been attributed to increased levels of soil salinity and inundation following agricultural clearing. Winter lake salinities approximate freshwater lake values, but during periods when the lake is dry, capillary rise of groundwater is thought to increase surface soil salinity. An undescribed species of Melaleuca and Casuarina obesa dominated the seasonally inundated regions of the lake bed. Aeolian deposits of higher elevation were dominated by Eucalyptus loxophleba, Allocasuarina huegeliana or species of Banksia. Woodland of E. oleosa var. longicornis and E. salmonophloia occurred predominantly on upland fluviatile deposits of sand and sandy clays. Measurements of soil salinity and the calculation of percentage inundation from tree elevations and observations of tree vigour and xylem pressure potential response indicated that tree deaths in Melaleuca sp. and C. obesa were due to increased levels of salinity. Deaths and low vigours in E. rudis were attributed to both increasing salinities and prolonged inundation. We believe control of ground water levels should be a major consideration in the preservation of this ephemeral lake and the water fowl populations it supports

What happens when you add salt: Predicting impacts of secondary salinisation on shallow aquatic ecosystems by using an alternative-states model

Alternative-states theory commonly applied, for aquatic systems, to shallow lakes that may be dominated alternately by macrophytes and phytoplankton, under clear-water and enriched conditions, respectively, has been used in this study as a basis to define different states that may occur with changes in wetland salinity. Many wetlands of the south-west of Western Australia are threatened by rapidly increasing levels of salinity as well as greater water depths and permanency of water regime. We identified contrasting aquatic vegetation states that were closely associated with different salinities. Salinisation results in the loss of freshwater species of submerged macrophytes and the dominance of a small number of more salt-tolerant species. With increasing salinity, these systems may undergo further change to microbial mat-dominated systems composed mostly of cyanobacteria and halophilic bacteria. The effect of other environmental influences in mediating switches of vegetation was also examined. Colour and turbidity may play important roles at low to intermediate salinities [concentration of total dissolved solids (TDS) 10 000 mg L–1 TDS). The role of nutrients remains largely unquantified in saline systems. We propose that alternative-states theory provides the basis of a conceptual framework for predicting impacts on wetlands affected by secondary salinisation. The ability to recognise and predict a change in state with changes in salinity adds a further tool to decision-making processes. A change in state represents a fundamental change in ecosystem function and may be difficult to reverse. This information is also important for the development of restoration strategies. Further work is required to better understand the influence of temporal variation in salinity on vegetation states and probable hysteresis effects

Subcontinental heat wave triggers terrestrial and marine, multi-taxa responses

Heat waves have profoundly impacted biota globally over the past decade, especially where their ecological impacts are rapid, diverse, and broad-scale. Although usually considered in isolation for either terrestrial or marine ecosystems, heat waves can straddle ecosystems of both types at subcontinental scales, potentially impacting larger areas and taxonomic breadth than previously envisioned. Using climatic and multi-species demographic data collected in Western Australia, we show that a massive heat wave event straddling terrestrial and maritime ecosystems triggered abrupt, synchronous, and multi-trophic ecological disruptions, including mortality, demographic shifts and altered species distributions. Tree die-off and coral bleaching occurred concurrently in response to the heat wave, and were accompanied by terrestrial plant mortality, seagrass and kelp loss, population crash of an endangered terrestrial bird species, plummeting breeding success in marine penguins, and outbreaks of terrestrial wood-boring insects. These multiple taxa and trophic-level impacts spanned >300,000 km2—comparable to the size of California—encompassing one terrestrial Global Biodiversity Hotspot and two marine World Heritage Areas. The subcontinental multi-taxa context documented here reveals that terrestrial and marine biotic responses to heat waves do not occur in isolation, implying that the extent of ecological vulnerability to projected increases in heat waves is underestimated