Proefschrift--Utrecht. / "Stellingen": 2 l. laid in. "Literatuur": p. [358]-367.

Proefschrift--Utrecht. / "Stellingen": 2 l. laid in. "Literatuur": p. [358]-367.

Akademisk avhandling--Uppsala. / "Literaturverzeichnis": p. [423]-434.

The plant pathogen, Phytophthora dnnamomi, is a cause of dieback disease observed in sclerophyll vegetation in Australia, The effects of P. dnnamomi on flora and fauna were studied at two locations in heathland vegetation near the coastal town of Anglesea, Victoria. The pathogen was isolated from soils beneath diseased heathland plants. The extent of diseased vegetation was assessed by the presence and absence of highly sensitive indicator species, Xanthorrhoea australis and hopogon ceratophyllus. The characteristics of heathland vegetation exhibiting dieback disease associated with the presence of P. dnnamomi were investigated. Plant species richness was similar between diseased and non-diseased areas however diseased areas were characterised by significant declines in the cover and frequency of susceptible species, increases in resistant species and increases in percent cover of open ground. Compared to non-diseased areas, diseased areas exhibited fewer shrub species and decreased shrub cover. The percentage cover and number of species of sedges, lilies and grasses were higher in diseased areas. Structural differences were significant between 0-0.6 m with decreased cover of vegetation in diseased areas. Differences in structure between diseased and non-diseased areas were not as great as expected due to increases in the cover of resistant species. A number of regenerating X australis were observed in post-disease areas. Cluster analysis of floristic data could clearly separate diseased and non-diseased trap stations. The population dynamics and habitat use of eight small mammal species present were compared in diseased and non-diseased areas using trapping and radio-tracking techniques. The number of small mammal species captured in post-disease areas was significantly lower than non-diseased areas. Mean captures of Antechinus stuartii and Rattus fiisdpes were significantly lower in diseased areas on Grid B. Mean captures of Rattus lutreolus were significantly lower in diseased areas on both study grids. Significant differences were not observed in every season over the two year study period. Radio tracking revealed more observations of Sminthopsis leucopus in non-diseased vegetation than in diseased. Cercartetus nanus was frequently observed to utilise the disease susceptible X. australis for nesting. At one location, the recovery of vegetation and small mammal communities in non-diseased and diseased vegetation after fuel reduction burning was monitored for three years post-fire. Return of plant species after fire in both disease classes were similar, reaching 75% of pre-fire richness after three years. Vegetation cover was slower to return after fire in diseased areas. Of the seven small mammal species captured pre-fire, five were regularly captured in the three years after fire. General linear model analysis revealed a significant influence of disease on capture rates for total small mammals before fire and a significant influence of fire on capture rates for total small mammals after fire. After three years, the influence of fire on capture rates was reduced no significant difference was detected between disease classes. Measurements of microclimate indicate that diseased, burnt heathland was likely to experience greater extremes of temperature and wind speed. Seeding of diseased heathland with X. australis resulted in the establishment of seedlings of this sensitive species. The reported distributions of the mamma] species in Victoria were analysed to determine which species were associated with the reported distribution of dieback disease. Twenty-two species have more than 20% of their known distribution in diseased areas. Five of these species, Pseudomys novaehollandiae, Pseudomys fumeust Pseudomys shortridgei, Potorous longipes and Petrogale pencillata are rare or endangered in Victoria. Four of the twenty-two species, Sminthopsis leucopus, Isoodon obesulus, Cercartetus nanus and Rottus lutreolus am observed in Victorian heathlands. Phytophthora cinnamomi changes both the structure and floristics of heathland vegetation in the eastern Qtway Ranges. Small mammals respond to these changes through decreased utilisation of diseased heathland. The pathogen threatens the diversity of species present and future research efforts should be directed towards limiting its spread and rehabilitating diseased areas.

The impact of habitat fragmentation and the success of habitat restoration were studied through a multi-taxonomic approach. The response to landscape structure and/or habitat quality of three taxonomic groups was explored, in (semi-)natural habitats. The three taxonomic groups were complementary, both in terms of their specific life history traits and their place in the food chain. We considered autotrophic species (vascular plants), herbivores (butterflies) and predators (spiders). Life-history traits and species specialization for target habitat were used to refine the analysis. Target habitat was a complex of wet heathlands, poor fens and bogs. Patches of this complex of habitats were sampled on two high plateaus in the Belgian Ardenne, the Plateau de Saint-Hubert and the Plateau des Tailles. Over the last 250 years, two jointly acting habitat dynamics were observed in these areas: a loss of area (and connectivity) on the one hand but also the creation of new habitat patches. It is precisely this double dynamics that enabled us to analyze and develop concepts linked to the response of species faced with spatio-temporal modifications of their habitat. Specifically, in this work we focused on the comprehension of two unbalanced situations, affecting the relationships between species richness and patch characteristics. A first unbalanced situation, the extinction debt, was observed for vascular plant communities. On the opposite, a colonization credit, the second unbalanced situation, was noted for butterflies and seemed to mainly affect specialist species. Specialist species of the three taxonomic groups showed relatively contrasted responses compared to generalist species. However, the life-history traits we studied only slightly influenced the response of species at the community level, excepted for pioneer communities in habitat patches less than 5 years old.

This thesis examines community structure of cliff-top coastal heathlands in Botany Bay National Park, Sydney. Community properties of floristic composition, structure and species richness are investigated. This investigation is made in order to assess the justification for contemporary pre-emphasis in local studies on individual community properties. It is also made in order to assess the relative and independent contributions of individual properties to variance in overall community structure. It is also made in order to assess the relative utility of multi-property classifications in summarising community structure of cliff-top coastal heathlands. First, the presence of determinable structure in each property is assessed through multivariate classification of respective data sets. Secondly, a new model of community structure is developed in which the hypothesis that community structure is a function of common (shared) and independent (unique) variance in each of the three properties is assessed. This is achieved through application of variance partitioning using correspondence analysis techniques. Thirdly, a matrix combining variance in all three properties is classified. This classification is compared with those of individual properties in order to assess the hypothesis that more ecologically cohesive classifications than those of single properties are obtainable. The ecological significance (environmental relativity) of all classifications and variance components is assessed through examination of relationships with variance in 20 environmental factors which encompass variation in maritime factors, soil physical factors, soil nutrition factors and effects of time since fire. Classifications of individual properties showed the presence of determinable structure in each. Eleven floristic complexes, nine structural complexes and eighteen species richness complexes were recognised. Nineteen community complexes were recognised from the classification of the combined property matrix. All complexes were shown to differ significantly with respect to multiple environmental factors. Variance partitioning showed the presence of both independent and common variance components with respect to properties compared pairwise. These were all shown to differ in magnitude. Examination of environmental correlates showed ecological differentiation of all properties and most variance components. Maritime and fire factors provide a major axis of environmental differentiation for most properties and variance components. A second major axis was resolved with respect to physical soil factors. With the exception of variance in species richness, major soil nutrients were generally of secondary importance to community structure. Low soil nutrients may demarcate heathlands from other vegetation types. However, this study shows elevated importance of other major areas of environment for community structure within cliff-top coastal heathlands. Comparisons of environmental homogeneity characteristics between all classification systems showed the classification of the combined property matrix to be more ecologically robust than those of structure or species richness. Homogeneity characteristics of the combined classification remained statistically inseparable from that of floristic composition. However, studies provided some evidence suggesting greater robustness of the combined classification with regard to fine-scale variance in community structure. This thesis shows that variance in all major community properties of the studied vegetation to be of ecological significance. It also shows that this significance is differential with respect to properties and their variance components. Pre-emphasis on individual properties in syntheses of local systems thus involves the loss of ecological information. I thus conclude that if adequate ecological syntheses of cliff-top coastal heathlands are to be obtained which are appropriate to their scale of distribution and functioning in the Sydney area then inclusion of attributes of multiple properties is required. Equally, multiple sources of environmental variation need to be examined.

This thesis examines community structure of cliff-top coastal heathlands in Botany Bay National Park, Sydney. Community properties of floristic composition, structure and species richness are investigated. This investigation is made in order to assess the justification for contemporary pre-emphasis in local studies on individual community properties. It is also made in order to assess the relative and independent contributions of individual properties to variance in overall community structure. It is also made in order to assess the relative utility of multi-property classifications in summarising community structure of cliff-top coastal heathlands. First, the presence of determinable structure in each property is assessed through multivariate classification of respective data sets. Secondly, a new model of community structure is developed in which the hypothesis that community structure is a function of common (shared) and independent (unique) variance in each of the three properties is assessed. This is achieved through application of variance partitioning using correspondence analysis techniques. Thirdly, a matrix combining variance in all three properties is classified. This classification is compared with those of individual properties in order to assess the hypothesis that more ecologically cohesive classifications than those of single properties are obtainable. The ecological significance (environmental relativity) of all classifications and variance components is assessed through examination of relationships with variance in 20 environmental factors which encompass variation in maritime factors, soil physical factors, soil nutrition factors and effects of time since fire. Classifications of individual properties showed the presence of determinable structure in each. Eleven floristic complexes, nine structural complexes and eighteen species richness complexes were recognised. Nineteen community complexes were recognised from the classification of the combined property matrix. All complexes were shown to differ significantly with respect to multiple environmental factors. Variance partitioning showed the presence of both independent and common variance components with respect to properties compared pairwise. These were all shown to differ in magnitude. Examination of environmental correlates showed ecological differentiation of all properties and most variance components. Maritime and fire factors provide a major axis of environmental differentiation for most properties and variance components. A second major axis was resolved with respect to physical soil factors. With the exception of variance in species richness, major soil nutrients were generally of secondary importance to community structure. Low soil nutrients may demarcate heathlands from other vegetation types. However, this study shows elevated importance of other major areas of environment for community structure within cliff-top coastal heathlands. Comparisons of environmental homogeneity characteristics between all classification systems showed the classification of the combined property matrix to be more ecologically robust than those of structure or species richness. Homogeneity characteristics of the combined classification remained statistically inseparable from that of floristic composition. However, studies provided some evidence suggesting greater robustness of the combined classification with regard to fine-scale variance in community structure. This thesis shows that variance in all major community properties of the studied vegetation to be of ecological significance. It also shows that this significance is differential with respect to properties and their variance components. Pre-emphasis on individual properties in syntheses of local systems thus involves the loss of ecological information. I thus conclude that if adequate ecological syntheses of cliff-top coastal heathlands are to be obtained which are appropriate to their scale of distribution and functioning in the Sydney area then inclusion of attributes of multiple properties is required. Equally, multiple sources of environmental variation need to be examined.

Abstract not available

No description available.

Heathlands typically experience regimes consisting of frequent and intense fires. These fire regimes play important roles in the lifecycles and population dynamics of all species in these communities. Prescribed fire is commonly applied to heathlands to minimise the risk of wildfires as well as to promote biodiversity. Ignitions in heathlands tend to either be unsustainable, or quickly develop into rapidly spreading intense fires. This presents a major problem for the application of prescribed fire and is the primary focus of this thesis. Heathland ignition has been investigated in three sections; litter ignition; vertical development of fire into the shrub layer; and horizontal spread through the shrub layer. These were studied in laboratory experiments using miniature versions of field fuels. Ignition success in litter layers was related to the dead fuel moisture content. Litter type, ignition source, and presence of wind were found to affect the range of ignitable fuel moisture contents of a litter bed. The effect of litter type was best explained by density. Dense litter beds required drier conditions for ignition than low density litter beds. The vertical development of fire into shrubs was mostly dependent on live fuel moisture content, but crown base height, presence of wind, ignition source, shrub height and the percentage of dead elevated fuel were also important. Horizontal spread of fires through shrub layers was most affected by the presence of a litter layer, with nearly all ignitions successful when there was an underlying litter fire. Fire spread would only occur in shrubs without a litter layer when the shrub layer was dense and dry, or had a substantial dead fuel component. Spread was more likely to be sustained when there was wind. Models predicting the moisture content of dead fuels were tested in heathlands, and as would be expected those that can be calibrated for different fuel types were found to have the best performance. Fuel moisture content and fuel load models were reviewed for heathlands, and a number of recommendations for future research were made.