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Aims: To detect changes in area and vegetation dynamics of monsoon rain forests in relation to disturbance and an observed wetting trend. Location: The Mitchell Plateau and the Bougainville Peninsula (north Kimberley, Australia). Methods: Geo-rectified aerial photographs acquired in 1949 and 1969 and a preexisting map from 2005 were used to detect changes in rain forest boundaries. To ground-truth rain forest expansion, we established 20 transects running across rain forest-savanna boundaries and recorded plant species, stand basal area, grass and rock cover, cattle impact, and canopy cover. Generalised linear models and Akaike's information criterion were used to detect differences in these variables between locations. Results: On the Bougainville Peninsula average fire frequency was low (0.11 per year) and cattle entirely absent, while on the Mitchell Plateau average fire frequency was high (0.58 per year), and cattle were common and associated with lower seedling density in savannas. Rain forests expanded more on the Bougainville Peninsula (69%),where patches were bigger and more convoluted, than on the Mitchell Plateau (9%).Rain forest expansion was positively associated with rainfall and topographic complexity, and on level terrain it occurred only on the Bougainville Peninsula. Rain forests were floristically and structurally similar in the two locations, while savannas on the Bougainville Peninsula had denser vegetation and more abundant rain forest elements.The frequency distribution of canopy cover was bimodal on the Mitchell Plateau, signalling the presence of two distinct vegetation states, and unimodal on the Bougainville Peninsula, consistent with the blending of the two states.Main conclusions: Wetting trends are likely strong drivers of rain forest expansion, but at a landscape scale their effect is probably modulated by fire activity and the presence of mega-herbivores, which may also be pivotal in maintaining sharp floristic and structural distinctions between rain forests and savannas. K E Y W O R D SAustralian tropics, cattle impact, climate change, fire, historical aerial photography, monsoon rain forests, tropical savannas

Indigenous groups are increasingly combining traditional ecological knowledge and Western scientific approaches to inform the management of their lands. We report the outcomes of a collaborative research project focused on key ecological questions associated with monsoon vine thickets in Wunambal Gaambera country (Kimberley region, Western Australia). The study mapped monsoon rainforests and analysed the environmental correlates of their current distribution, as well as the historical drivers of patch dynamics since 1949. Remote sensing was used to chart the effectiveness of an intervention designed to re-instate Aboriginal fire regimes according to customary principles. We identified the most vulnerable patches based on size, distance from neighbouring patches, and fire frequency. More than 6000 rainforest patches were mapped. Most were small (<1 ha), occurring predominantly on nutrient-rich substrates (e.g., basalt) and fire-sheltered topographic settings (e.g., slopes and valleys). Rainforests with low fire frequency and no cattle were more likely to expand into surrounding long-unburnt savannas. Frequent fires and cattle did not cause substantial contraction, although the latter affected rainforest understories through trampling. Fire management performed by Aboriginal rangers effectively shifted fire regimes from high-intensity late dry season fires to early dry season fires, particularly in areas with clusters of vulnerable rainforests. The remote sensing methods developed in this project are applicable to the long-term monitoring of rainforest patches on Aboriginal-managed land in North Kimberley, providing tools to evaluate the impacts of fire management, feral animal control, and climate change. The study confirmed the importance of the cattle-free and rarely burnt Bougainville Peninsula as one of the most important rainforest areas in Western Australia.

Abstract:The study of treefall and its after-effects is a common theme in studies of forest structure and local dynamics, yet its value as descriptor of broader-scale ecological dynamics is rarely explored. Here we synthesize the most highly cited literature on treefalls, from 1985 to 2016 (in three-year blocks), highlighting the importance of the causes, characteristics and consequences of such events. We then ask how this knowledge might contribute to the broader conceptual model of forest dynamics, and develop two conceptual models, which we use to illustrate both the classic and alternative views of how forests 'work'. Treefalls are one of the few 'integrating' attributes of forests, because of their ubiquity and longevity, and therefore can inform a variety of processes (e.g., tree mortality, turnover rates, structural impacts, recruitment, and fire frequency) due to their impacts occurring simultaneously over space (patterns), and time (legacy effects). The substantial knowledge that already exists on localized treefall dynamics should be combined with more integrative approaches to studying forest ecosystems, to investigate landscape-scale patterns of treefall and reconstruct past disturbance events.

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