Lyn Atkins

Fire-Related Dynamics of a Banksia Woodland in South-Western Western Australia

We studied the post-fire vegetation development of a low open woodland dominated by Banksia attenuata and B. menziesii near Perth, Western Australia. Two similar stands burned in autumn and spring displayed different regeneration patterns, with seedling regeneration occurring only in the autumn burn area. Vegetative regrowth was more rapid and post-fire species numbers were higher in the spring burn area. Introduced annuals increased significantly in the autumn fire area. Longer-term vegetation development was studied in a series of stands ranging in age since last fire from 1 to >44 years. Species richness was greatest in the 5-year-old stand, and many shrub species were most abundant 2-5 years after fire. Non-native annuals were found only in stands less than 5 years old since last fire. Dominance by the shrub Eremaea pauciflora increased with stand age, although shrub structure and total biomass did not vary greatly except in the oldest stand studied. The proportion of total shrub biomass accounted for by leaves declined with stand age. Both the two major Banksia species had mixed size structures with seedlings present in all stands, indicating that neither is dependent on fire for recruitment. The results indicate that while autumn burns promote seedling regeneration they may also increase invasion by non-natives, and spring burning may be preferable in these Banksia woodlands. Burning rotations longer than those required for fuel reduction purposes are necessary to maximise conservation values.

Interactions between annuals and woody perennials in a Western Australian nature reserve

We studied the interactions between woody peren- nial species and native and non-native annual species in a number of vegetation types within a nature reserve in the Western Australian wheatbelt. In particular, we examined the responses of annuals to perennial canopy removal, fire, soil disturbance and nutrient additions, and the effects of removal of annuals on perennial seedling regeneration. Experimental shrub removal significantly increased the abundance of annuals in a dense shrubland dominated by Allocasuarina campestris, but had no effect in a more open species-rich sandplain heath. Soil disturbance and nutrient addition in the heath area had no significant influence on annual abundance until three years after treatment. Fire had no clear effect on annual abundance in the heath within the

Faunal use of bluegum (Eucalyptus globulus) plantations in southwestern Australia

We examined the faunal use of Eucalyptus globulus plantations in southern Western Australia, and compared use of remnant vegetation, agricultural land and plantations in different positions relative to large tracts of remnant vegetation. In general, faunal use of plantations is less than in comparison with adjacent remnant vegetation, but more than in open pasture. For all faunal groups there were almost twice as many species recorded in the native vegetation than in any site in the plantations or on agricultural land and they were in greater abundance. Faunal use of plantation edges and interiors did not show consistent patterns. Generally, edges next to remnants were most frequently used, but individual species showed a wide range of patterns of use across the various habitat types studied. More species of bird identified as being “at risk” were found in plantation edges than in interiors. Adjacency to remnant vegetation increased plantation use by some species, but the overall differences between isolated plantations and those adjacent to remnant vegetation were relatively small. We conclude that plantations provide some value in terms of habitat for some species, including some of conservation concern, but that this value is limited by the lack of habitat complexity in the intensively-managed plantations.

The influence of local elevation on soil properties and tree health in remnant eucalypt woodlands affected by secondary salinity

More than 2 M ha of remnant vegetation in Australia is predicted to be at risk from shallow water tables by 2050. Currently, vegetation is considered to be at risk where the water table is predicted to be less than 2 m below the soil surface, yet casual observation of areas affected by secondary salinity in the Western Australian wheatbelt has suggested that small differences in elevation (< 0.5 m) are important in determining plant health. In this study, we investigated how small changes in elevation (and hence depth to the water table) affected soil Cl concentrations and water contents, and whether small changes in elevation were associated with major changes in tree health in two remnants of Eucalyptus wandoo Blakely woodland with secondary salinity. At one site there were strong dissimilarities between soil samples collected above or below relative elevations of 0.5 m in areas with a shallow (0.3 m deep in September 2001) and saline water table. This was reflected in almost complete tree mortality at relative elevations below 0.5 m. However, low rainfall in 2001 meant that it was unlikely that current soil conditions had caused tree death. When water table data for 1999 was overlaid over plots of tree health and transect topography, high levels of tree mortality corresponded with areas where the water table was at or above the ground surface. At the other site, there was no clear relationship between elevation, soil characteristics and tree health. Localised variation in abiotic conditions and ecosystem processes at a fine-scale may buffer, to some extent, the spatial impact of soil salinity and waterlogging in remnant vegetation. Collapses in tree health at some sites are likely to be related to extreme and episodic events, which we may have limited ability to predict.

The influence of local elevation on the effects of secondary salinity in remnant eucalypt woodlands: Changes in understorey communities

Increasing land salinization in Australia is predicted to lead to severe declines in species diversity in affected areas, and perhaps significant numbers of species extinctions. Much of the diversity that will be lost consists of understorey and mid-storey species, yet the overwhelming majority of research has focussed on salinity tolerance in tree species. We investigated how the presence of a shallow, saline water table affected the understorey species composition, species richness and species diversity in two remnant Eucalyptus wandoo Blakely woodlands in the Western Australian wheatbelt. Species richness and species diversity were significantly lower in areas with a shallow water table at elevations < 0.5 m above the lowest local elevation, compared with both higher elevations and with areas of low elevation without a shallow water table. Species composition (Bray-Curtis similarities) was also significantly different in low elevation, saline areas. At one site, saline areas were colonized by native and alien species that were not present in the surrounding vegetation, yet the community that has developed does not contain either the species or structural diversity of the surrounding system. At the other site, no colonisation of saline areas by new species occurred. Even though small differences in elevation (< 0.5 m) at our study sites were important in moderating the impacts of salinity in areas with a shallow water table, the loss of species diversity, species richness and structural complexity in low-lying elevations indicated that the ecological risk from secondary salinity to species associated only with drainage lines, seasonally wet flats and other low-lying areas is severe. The priority is to identify those vegetation communities that are restricted to only low relative elevations within the landscape and that only occur in remnants predicted to be at a high risk of developing a shallow and saline water table.