The Assessment of Ecological Condition in South-East Queensland
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The assessment of ecological condition in South-East Queensland, Australia: An evaluation of reliability across variable environments and surrogate efficacy for biodiversity values David Ian Tucker B. App. Sc. (Hons) School of Earth, Environmental and Biological Sciences Science and Engineering Faculty Queensland University of Technology This dissertation is submitted in fulfilment of requirements for the degree of Doctor of Philosophy 2016 Abstract As comprehensive biodiversity assessment is often costly and difficult to complete, ecological surrogates are employed to address gaps in taxonomic information. Whereas some surrogates are represented by the presence, absence or abundance of indicator species, others take the form of easily mapped environmental components such as land classes or vegetation types. One form of environmental surrogate involves the measurement of terrestrial ecological condition or integrity. Ecological condition surrogates are often multimetric indices and are represented by easily measured spatial, compositional, structural and functional attributes of native vegetation. Ecological condition is generally assessed by comparing attributes against benchmarks derived from reference sites that typify relatively unmodified examples of the same vegetation type. The utility of ecological condition approaches has seen them adopted by a number of Australian government agencies as part of a broader framework to measure impacts on terrestrial ecosystems, monitor ecological health and calculate vegetation offsets. The BioCondition framework of Queensland is a typical Australian multimetric condition approach. BioCondition quantifies how well terrestrial ecosystems are functioning for biodiversity values by measuring a number of vegetation and landscape condition attributes. Important management decisions are based on the outcomes of ecological condition metrics and must therefore be repeatable, reliable and scientifically rigorous. Attributes must be applicable across multiple systems and scales and demonstrate significant associations with ecological patterns and processes. Since its inception, the BioCondition framework has been tested for attribute suitability, observer variability and appropriate reference site identification. However, the robustness of BioCondition and other multimetric condition approaches to variability linked to environmental gradients and disturbance regimes has not been assessed. The effects of variability may impair surrogate efficacy and potentially result in poorly informed conservation policy and planning. Therefore, this study is the first to consider the reliability of vegetation-based ecological condition assessment across variable environments, and the implications this variability may have for surrogate efficacy. Metric reliability was tested by measuring the influence of climatic, environmental and disturbance variables on selected vegetation communities, and on BioCondition attributes derived from condition assessments within these communities. In addition, the capacity for multimetric condition approaches to represent biodiversity values with respect to this variability was tested through comparative measurements of BioCondition and an independent acoustic index of ecological health. The study focused on two ecological communities located in South-East Queensland, Australia. The two communities were defined by spotted gum (Corymbia citriodora ssp. variegata) open forest and scribbly gum (Eucalyptus racemosa ssp. racemosa) woodland and categorised under the regional ecosystem vegetation mapping framework as RE 12.11.5e and RE 12.5.3 respectively. A total of 62 sites were surveyed across the South-East Queensland study area, with each site subjected to a full floristic survey, ecological condition assessment, and a measurement of disturbance. In addition, acoustic recordings were taken within ten selected RE 12.11.5e sites and nine selected RE 12.5.3 sites. Changes in vegetation composition and abundance, and vegetation condition attributes for RE 12.11.5e and RE 12.5.3 were related to latitudinal effects. Where these effects were explicitly tested across two distinct subregions for RE 12.11.5e there was a general trend of decreasing importance for latitudinally-related climatic gradients with progression from tree to ground layers. The influence of non-climatic environmental attributes and disturbance regimes were increasingly important for shrub and ground strata. Where the same environmental and disturbance variables were examined for RE 12.5.3 it was shown that latitudinal variation was attributed to the geographical disjunction between two vegetation types and geographically- related disturbance processes linked to fire regimes and landscape fragmentation. It was demonstrated that there was a significant relationship between BioCondition and the Normalised Difference Soundscape Index (NDSI) of ecological health. This relationship indicated that multimetric condition approaches can effectively measure biodiversity values with regard to the effects of environmental variability through comparisons with an independent index of similar purpose. Much of the variation in the soundscape as measured by NDSI was underpinned by landscape attributes, including patch size, context and connectivity. Although NDSI was related to a range of BioCondition vegetation attributes it was determined that their effects were likely connected to fragmentation processes. The findings of this study have management implications for multimetric condition assessments. The strategic location of reference sites for benchmarking was fundamental to mitigating the effects of climate, environmental gradients and disturbance processes. Landscape-level variability was found to have an inordinate effect on vegetation composition and structure, vegetation condition attributes, bird species richness and composition, and the soundscape as measured by NDSI, suggesting that heavily weighted landscape attributes are important for metric efficacy. In addition, results suggest that multimetric design may be altered through the removal of vegetation species richness estimates, improving usability for non- specialists without compromising surrogacy potential. It was shown that BioCondition scores remained unaffected once adjusted, effectively providing the same measurement of ecological condition. Finally, it was concluded that multimetric condition approaches can be augmented with novel metrics of ecological health derived from acoustic recordings. This study has shown that multimetric ecological condition indices can account for environmental variability through strategic application and design. Government agencies use ecological condition measurements to inform policy, and therefore it is essential that they operate effectively. If used in conjunction with other assessment methods, and if trialled and tested over multiple ecosystems, environmental gradients and disturbance regimes, then multimetric condition approaches may continue to serve as useful and scientifically rigorous tools for biodiversity management and conservation planning. Keywords Australia, benchmarks, biodiversity assessment, disturbance regimes, ecological condition, ecological surrogates, environmental gradients, eucalypt forest, , landscape fragmentation, metric efficacy, multimetric indices, normalised difference soundscape index, reference conditions, soundscape, South-East Queensland, vegetation attributes Contents Statement of Original Authorship ................................................................................ 1 Acknowledgements ...................................................................................................... 2 Chapter 1: General introduction—biodiversity assessment and the utility of ecological condition metrics as ecological surrogates ................................................. 3 1.1 Introduction ........................................................................................................ 5 1.2 Research problems and project aims ............................................................... 13 Chapter 2: General methods—an introduction to the study area, experimental design and vegetation survey approaches ................................................................ 17 2.1 Broad study area .............................................................................................. 19 2.2 RE 12.11.5e study areas ................................................................................... 21 2.3 RE 12.5.3 study area ......................................................................................... 23 2.4 Site selection .................................................................................................... 25 2.5 Ecological condition surveys............................................................................. 30 2.6 Vegetation composition and abundance surveys ............................................ 33 2.7 Disturbance survey ........................................................................................... 34 2.8 Environmental and land use datasets .............................................................. 36 Chapter 3: The study system—baseline analyses of vegetation patterns across environmental gradients and disturbance regimes in spotted gum open forest (RE 12.11.5e) and scribbly gum woodland (RE 12.5.3) .................................................... 39 3.1 Introduction .....................................................................................................