Aim The impact of fragmentation on a eucalypt forest was investigated by examining the effects of fragment size, time since fragmentation, degree of anthropogenic disturbance to fragment interiors, and time since fire, on native and exotic plant species richness per unit area. Location Two areas of dry open‐forest were studied on the central coast of New South Wales in south‐eastern Australia. Fifty forest fragments were located at Tomago, an area progressively fragmented over the last 60 years, most recently by clearing for sand‐mining. Also at Tomago were six very large blocks of forest that were used as reference sites. The second area at Myall Lakes National Park (50 km north of Tomago) had four very large areas of intact forest that were also used as reference sites. Methods Fragments were allocated into (1) three size classes: small (<1 ha), medium (1 to <10 ha) and large (10 to <100 ha); (2) two classes of age since fragmentation: young (up to 10 years) and old (10 years or more); (3) two classes of disturbance (minor, major) based on the degree and extent of human‐induced disturbance to the fragment interior; and (4) two classes of time since fire (between 5 and 6 years; 10 years or more). Reference sites belonged to a very large size class (>100 ha). Mean plant species richness per 25 m2 area was determined for each fragment and analysed separately for native and exotic species. Results The most significant effects observed resulted from anthropogenic disturbance. In fragments with major disturbance, native species richness per unit area was significantly reduced in small‐sized young and medium‐sized old fragments. A significant increase was also observed for exotic species richness in fragments with major disturbance. With minor disturbance, native species richness in small fragments declined significantly with time since fragmentation, in contrast to medium and large fragments. Among recently created fragments, those recently burned had significantly more native species per unit area than those burned 10 or more years ago. Main conclusions Anthropogenic disturbance coupled with fragmentation had a stronger and more immediate effect in reducing native species richness and increasing exotic species richness than did fragmentation alone. In the absence of major disturbance, small fragments had fewer native species than larger size classes, but only after 10 or more years since fragmentation, confirming the importance of controlling for age of fragments when examining species–area relationships. This study has not tested whether differences in area were the direct cause of this loss of species over time; other factors that are correlated with area (such as edge effects) may also be involved. The increase in native species richness following fire was consistent with other studies of fire in unfragmented eucalypt forest. This study thus shows that in addition to the factors emphasized in classical island biogeography models, fragment age, disturbance and fire history are important in explaining species richn...

For over three decades the equilibrium theory of island biogeography has galvanized studies in ecological biogeography. Studies of oceanic islands and of natural habitat islands share some similarities to continental studies, particularly in developed regions where habitat fragmentation results from many land uses. Increasingly, remnant habitat is in the form of isolates created by the clearing and destruction of natural areas. Future evolution of a theory to predict patterns of species abundance may well come from the application of island biogeography to habitat fragments or isolates. In this paper we consider four factors other than area and isolation that influence the number and type of mammal species coexisting in one place: habitat diversity, habitat disturbance, species interactions and guild assembly rules. In all examples our data derive from mainland habitat, fragmented to differing degrees, with different levels of isolation. Habitat diversity is seen to be a good predictor of species richness. Increased levels of disturbance produce a relatively greater decrease in species richness on smaller than on larger isolates. Species interactions in the recolonization of highly disturbed sites, such as regenerating mined sites, is analogous to island colonization. Species replacement sequences in secondary successions indicate not just how many, but which species are included. Lastly, the complement of species established on islands, or in insular habitats, may be governed by guild assembly rules. These contributions may assist in taking a renewed theory into the new millennium.

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We have begun a long-term ecological research project to address questions about the impact of multiple disturbances on the species richness of communities and whether multiple disturbances are additive or interactive. A protected water catchment area was chosen, which is subjected to fires, sand mining and clearing, and for which detailed records are available. The study area, at Tomago (32°52'S, 151°45'E), has forest, woodland, shrubland and swamp on a sand substrate, with the vegetated dunes forming part of a coastal embayment. Forty-four sites were located in forested areas that had undergone disturbance by either fire, sand mining or clearing. Sites of each disturbance type were grouped into four age classes: less than 1 year since disturbance, nominally 1991; 5 years, nominally 1986; 11 years, nominally 1980; and 17 years, nominally 1974. A set of burned sites, with the time of the last fire matched to the times of the other disturbances, was used as the control response. In this paper we describe the study area and sites, then examine the effects of each single disturbance on vegetation structure. Canopy cover increased with time and type of disturbance, with 17 year old cleared or mined sites similar to the cover of 11 year old burned sites. In the first two years after disturbance, burned sites had significantly more understorey vegetation than cleared or mined sites, but by 5 years all three were similar. The data presented here show that regeneration of mined sites at Tomago is substantially slower than regeneration following disturbance by fire, with the regeneration of cleared sites intermediate but closer to mining than fire. After 17 years regeneration, cleared and sand mined sites had not returned to the vegetation structure of the pre-disturbance state. Understorey height and the amount of vegetation on cleared or mined sites have not achieved the levels in the original forest, although canopy cover did seem to have reached pre-disturbance levels. Current rehabilitation techniques are more sophisticated than those used 17 years ago and continued monitoring of sites currently being rehabilitated may show a faster return to pre-disturbance states. Having established the hierarchy and nature of the response to each single disturbance here, we are now in a position to investigate the impact of multiple disturbances.