Pattern and Diversity in Swamp and Dune Vegetation, North Stradbroke Island

Abstract

The pattern of plant species distribution, the richness of species composition, the distribution of resources among species and the manner of change in these parameters across landscapes are examined in three habitats on North Stradbroke Island. The closed-heath vegetation of a freshwater swamp, the grassland and low closed-forest of a frontal low dune sequence and the closed sclerophyllous forests of inland high dunes are studied by a variety of statistical techniques, including a new method for determining the degree and scale of microcommunity pattern. Of the three vege- tation types, the floristic diversity and complexity of spatial patterning within a small area is highest in the freshwater swamp vegetation. Not only is the scale of spatial variation smallest in this habitat, but the scale of patterning and co-association also becomes smaller as one proceeds into the swamp. The complexity of the vegetation is enhanced by a remarkably high species richness, a very low concentration of dominance and a high degree of intermingling of species. The floristic diversity and complexity of spatial patterning within such a small area of vegetation bears comparison with that of complex tropical rain-forest. The swamp vegetation appears to have undergone a high degree of speciation; at the same time, intermixture of species and the small scale of patterning have served as a means of minimizing intraspecific competition. If, like the tropical rain-forest, the ecosystem has evolved characteristics of rigid stability the system is likely to recover only slowly from major perturbation.

Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

“…These aspects are significant since the natural patterns of vegetation establishment on the dunes of eastern Australia have been closely correlated with the soil's nutrient bioavailability and associated podzolization status (Thompson 1981(Thompson , 1992. In these coastal environments, the intended mixed-Eucalypt communities typically populate high dune environments having intermediate-to late-stage podzol soils (Westman 1975;Westman and Rogers 1977). By contrast, pioneer and/or facilitator species such as black sheoak often populate the adjacent fore-dunes, which have early-stage podzol soils (Lunt 1998b).…”

“…Recalling that this latter species was directly seeded as part of the rehabilitation strategy (albeit at different seeding intensities depending on the period of rehabilitation), it is suspected that the loss of soil fertility and its reversion to an early podzol status would have facilitated initial growth conditions conducive to the species' opportunistic colonisation due to its general 'ruderal' adaptations to nutrient-poor conditions (Crowley 1984;Diem et al 2000). Conversely, such postdisturbance soil conditions could have been disadvantageous for the desired and relatively slowergrowing mixed-Eucalypts that are typically only sparsely distributed among the fore-dunes (Westman 1975). For these reasons, we suspect that altered edaphic conditions associated with the management of post-disturbance soils along with the seeding of pioneer species likely contributed the primary first steps leading to the divergence of older rehabilitated sites away from the intended natural analogues-unlike younger sites where soil conditions are believed to have been more carefully managed.…”

Quantification of landform heterogeneity and its relationship with ecological patterns in broad-scale post-mine rehabilitation

“…The flora diversity decreases with dune-age while the swamps display highest flora diversity (Westman, 1975). Apart from dune-leaching, the topography and ground-water table, climate and rainfall, wind intensity and gradients in salt spray are some of the influences on vegetation on the island (Westman, 1975). NSI has total 760 species recorded with high proportion (up to 30%) of weedy species (Stephens, 2011).…”

“…NSI vegetation can thus be broadly classified into vegetation on ancient dunes, vegetation on recent dunes and the fringe wetland vegetation (Westman, 1975). The flora diversity decreases with dune-age while the swamps display highest flora diversity (Westman, 1975). Apart from dune-leaching, the topography and ground-water table, climate and rainfall, wind intensity and gradients in salt spray are some of the influences on vegetation on the island (Westman, 1975).…”

“…NSI vegetation can thus be broadly classified into vegetation on ancient dunes, vegetation on recent dunes and the fringe wetland vegetation (Westman, 1975). The flora diversity decreases with dune-age while the swamps display highest flora diversity (Westman, 1975).…”