Stephen M. Turton

Immediate impacts of a severe tropical cyclone on the microclimate of a rain-forest canopy in north-east Australia

Tropical cyclones, which are frequent along the north-eastern Australian coast, can result in severe disturbances to rain forests in the region (Grove et al. 2000, Webb 1958). Branch breakages and tree falls result in high levels of light penetration to the forest floor, which is normally heavily shaded (Turton 1992). This change in microclimate stimulates the growth of normally suppressed seedlings, the germination of seeds that are triggered by sunlight (Chazdon 1988), and often, invasion by weeds. Fragmented rain forests, that are common in the region, are particularly vulnerable to impacts of cyclones because of their large edge to forest area ratio. Appropriate management of such rain forests, following catastrophic disturbance, requires a thorough understanding of recovery processes at a number of temporal and spatial scales (Grove et al. 2000).

Understorey light environments in a north-east Australian rain forest before and after a tropical cyclone

This paper describes estimates of canopy openness and associated light availability in the understorey of a north-east Australian rain forest before and immediately after a tropical cyclone. On the basis of 20 hemispherical (fisheye) canopy photographs it was shown that direct, diffuse and total site factors increased significantly as a result of the slight-to-moderate canopy disturbance caused by the cyclone. In the understorey, median total site factors ranged from 2.5–3.4% before the cyclone and from 6.0–8.6% after the cyclone, representing a 2- to 3-fold increase in potential light availability. Following the cyclone, mean relative gap frequencies increased substantially at all altitudes but particularly at canopy positions more than 70° above the horizon. Cyclone-induced canopy disturbance not only reduced the complexity of the understorey light regime but may have also increased the seasonal variability of light within the understorey of the forest during the interval of canopy recovery. The implications of these results for the ecophysiology of understorey tree seedlings and saplings at several temporal scales are discussed.

Trampling resistance of tropical rainforest soils and vegetation in the wet tropics of north east Australia

Controlled trampling was conducted to investigate the trampling resistance of contrasting high fertility basaltic and low fertility rhyolitic soils and their associated highland tropical rainforest vegetation in north east Australias Wet Tropics. Although this approach has been taken in numerous studies of trampling in a variety of ecosystem types (temperate and subtropical forest, alpine shrubland, coral reef and seagrass beds), the experimental method does not appear to have been previously applied in a tropical rainforest context. Ground vegetation cover and soil penetration resistance demonstrated variable responses to trampling. Trampling, most noticeably after 200 and 500 passes reduced organic litter cover. Bulk density increased with trampling intensity, particularly on basalt soils as rhyolite soils appeared somewhat resistant to the impacts of trampling. The permeability of the basalt and rhyolite soils decreased markedly with increased trampling intensity, even after only 75 passes. These findings suggest physical and hydrological changes may occur rapidly in tropical rainforest soils following low levels of trampling, particularly on basalt soils.

LONG-TERM SURVIVORSHIP AND CROWN AREA DYNAMICS OF TROPICAL RAIN FOREST CANOPY TREES

Lateral shading of direct-beam irradiation among neighboring canopy tree crowns in a nonequatorial tropical rain forest canopy was modeled as a function of solar position using a photogrammetric database derived from large-scale color aerial stereopairs (1:1500–1:3000 scale) acquired in 1976. The interception of direct-beam irradiation by the orthogonally projected crown area of each tree was computed at hourly intervals over a full calendar year using a Parameterization model of cloud-attenuated direct-beam availability. The annual totals of intercepted direct-beam irradiation (Ib) ranged from 1.81 to 4.13 GJ·m−2·yr−1. Expressed as a percentage of the available incident direct-beam irradiation, these values ranged from 44% to 100%. Approximately 20% of the sample population intercepted <70% of the available annual direct-beam irradiation. The long-term effects of lateral shading and the intertree differences in Ib were assessed using repeat aerial stereophotography of the same section of forest 18 yr later in 1994 for the determination of the mortality, survivorship, and crown growth of the canopy trees delimited in the 1976 stereopairs. Mortality over the 18-yr period amounted to 27.2%. Based on the lateral shading simulations, the mean annual Ib totals of the survivors and those that died were significantly different (P < 0.001). Approximately 40% of the survivors experienced crown area reductions. Although there was no significant difference in the Ib of survivors with crown growth and those with crown reductions, a relationship was established between Ib and the extent of crown area change. Canopy trees that intercept the most direct-beam irradiation and experience the least lateral shading have higher probabilities of survivorship and significant crown area changes that may be in the form of crown growth or crown reduction. Their laterally shaded neighbors have a lower survivorship probability, and those that survive persist in an inhibited state with limited crown area change. We conclude that the effects of lateral shading are not limited to the margins of treefall gaps and that lateral shading determined by crown position in the uneven upper canopies of nonequatorial tropical rain forests has a detectable effect on the long-term fates of neighboring canopy trees.

Redefining the ecological niche of a tropical rain forest canopy tree species using airborne imagery: long-term crown dynamics of Toona ciliata

Past controlled growth experiments indicate that the seedling and sapling responses of the tropical rainforest canopy tree species Toona ciliata are most consistent with a light-demanding, early successional pioneer. This ecological niche assignment was tested in the mature stage of its life cycle after it achieves a position in the upper canopy. Mortality, survivorship and crown growth rates over the 18-y period 1976-1994 were measured using co-registered repeat airborne stereophotographic coverage of a representative forest stand in northeast Queensland, Australia, where T. ciliata had the fourth highest relative importance in a population of 46 co-occurring canopy tree species. The airborne re-inventory was conducted in a 3.6-ha sample area and limited to only canopy trees. The results were compared with a ground-based inventory of both canopy and subcan- opy trees l10 cm dbh in a 0.5-ha permanent plot. Over the period 1976-1994, there was no mortality and no evidence of decline among T. ciliata conspecifics having crown areas >60 m2 and trunk diameters >30 cm. In the 3.6-ha airborne sample area, more than 85% of T. ciliata survivors experienced positive crown growth, in contrast to only 57% of the other co-occurring canopy trees. Toona ciliatas crown growth rates were highest in the 60-80-m2 crown size class. Upon reaching an upper canopy position, T. ciliata not only persisted as a dominant canopy tree species, but it also achieved some of the largest crown areas (> 100 m2). Toona ciliata mortality in the ground-based plot involved mainly subcanopy trees of 10-30 cm dbh that had not yet assumed a canopy position and were not detectable in the aerial stereopairs. Both the crown and dbh growth rates of T. ciliata indicate enhanced vigour in the later stage of its life cycle. Its long-term survivorship and growth patterns are indicative of a persistent canopy tree species

Ecosystem services capacity across heterogeneous forest types: understanding the interactions and suggesting pathways for sustaining multiple ecosystem services

As ecosystem services supply from tropical forests is declining due to deforestation and forest degradation, much effort is essential to sustain ecosystem services supply from tropical forested landscapes, because tropical forests provide the largest flow of multiple ecosystem services among the terrestrial ecosystems. In order to sustain multiple ecosystem services, understanding ecosystem services capacity across heterogeneous forest types and identifying certain ecosystem services that could be managed to leverage positive effects across the wider bundle of ecosystem services are required. We sampled three forest types, tropical rainforests, sclerophyll forests, and rehabilitated plantation forests, over an area of 32,000m(2) from Wet Tropics bioregion, Australia, aiming to compare supply and evaluate interactions and patterns of eight ecosystem services (global climate regulation, air quality regulation, erosion regulation, nutrient regulation, cyclone protection, habitat provision, energy provision, and timber provision). On average, multiple ecosystem services were highest in the rainforests, lowest in sclerophyll forests, and intermediate in rehabilitated plantation forests. However, a wide variation was apparent among the plots across the three forest types. Global climate regulation service had a synergistic impact on the supply of multiple ecosystem services, while nutrient regulation service was found to have a trade-off impact. Considering multiple ecosystem services, most of the rehabilitated plantation forest plots shared the same ordination space with rainforest plots in the ordination analysis, indicating that rehabilitated plantation forests may supply certain ecosystem services nearly equivalent to rainforests. Two synergy groups and one trade-off group were identified. Apart from conserving rainforests and sclerophyll forests, our findings suggest two additional integrated pathways to sustain the supply of multiple ecosystem services from a heterogeneous tropical forest landscape: (i) rehabilitation of degraded forests aiming to provide global climate regulation and habitat provision ecosystem services and (ii) management intervention to sustain global climate regulation and habitat provision ecosystem services.

A review of ecosystem services research in Australia reveals a gap in integrating climate change and impacts on ecosystem services

Ecosystem services (ES) are the benefits people obtain from ecosystems. A substantial part of human well-being is dependent on the sustainable flow of ES. Climate change, economic growth and an increasing human population has placed greater pressures on global ES. Australia’s ecosystems are among the most vulnerable sectors to climate change. Hence, a comprehensive review is necessary to explore ES research that integrates climate change impacts. Our review reveals that ES research in Australia, stimulated in the early 2000s, has continued to increase consistently after the Millennium Ecosystem Assessment. Australian ES research has primarily focused on the impact of land-use change and management, policy and governance issues, but less on the impact of climate change on ES. Climate change models show that climate will threaten most of the main ES in Australia by 2050. For the sustainable management of these ES – incorporating climate change – ecosystem and ES specific adaptations are suggested as the best sustainable policy tools for the future. Therefore, further research needs to incorporate climate change and ES for evidence-based sustainable management of Australia’s ES. We provide the following recommendations for future ES research: (i) evaluating the extent and trend of climate change impacts on ES through consideration of different climate change scenarios; (ii) preparing vulnerability maps of important ES that are likely to be sensitive to climate change and (iii) developing ecosystem and ES specific adaptations to climate change that involve key stakeholders.

Status and Threats in the Dynamic Landscapes of Northern Australia’s Tropical Rainforest Biodiversity Hotspot: The Wet Tropics

Tropical rainforests throughout the world are highly contested landscapes as governments and the commercial sector seek to increase economic benefits from them. Major threats include logging, both legal and illegal, fire and general encroachment through increased access. Australia’s rainforests comprise a miniscule proportion of this total but are vitally important for their unique biodiversity. The largest fragment of tropical rainforest in Australia occurs as a narrow strip along the east coast from 15°30′S to almost 19°25′S and covers approximately two million hectares. Such is the biological significance of the largest section of rainforest, the so called Wet Tropics, that it was inscribed as the Wet Tropics of Queensland World Heritage Area in 1988. This area forms a small part of the recently recognised Forests of East Australia biodiversity hotspot. European settlement has brought about radical change to the Wet Tropics, displacing traditional management by Indigenous Australians. In the last 50 years, our understanding of the region and the threats to it has increased enormously. Logging has ceased, yet threats from invasive species, internal fragmentation and linear infrastructure are still apparent. Climate change looms as a source of a range of threats that the Wet Tropics is ill prepared to face.

Degraded tropical rain forests possess valuable carbon storage opportunities in a complex, forested landscape.

Tropical forests are major contributors to the terrestrial global carbon pool, but this pool is being reduced via deforestation and forest degradation. Relatively few studies have assessed carbon storage in degraded tropical forests. We sampled 37,000 m2 of intact rainforest, degraded rainforest and sclerophyll forest across the greater Wet Tropics bioregion of northeast Australia. We compared aboveground biomass and carbon storage of the three forest types, and the effects of forest structural attributes and environmental factors that influence carbon storage. Some degraded forests were found to store much less aboveground carbon than intact rainforests, whereas others sites had similar carbon storage to primary forest. Sclerophyll forests had lower carbon storage, comparable to the most heavily degraded rainforests. Our findings indicate that under certain situations, degraded forest may store as much carbon as intact rainforests. Strategic rehabilitation of degraded forests could enhance regional carbon storage and have positive benefits for tropical biodiversity.

Are less vocal rainforest mammals susceptible to impacts from traffic noise

Abstract Context. Traffic noise is believed to cause road avoidance and other barrier effects in a variety of wildlife species, and to force changes to call pitch or loudness in others; however, this has never been tested in the absence of other road impacts. Noise impacts on species that do not frequently vocalise are also poorly understood. We investigated traffic-noise impacts on the following three rainforest mammals that do not often vocalise: Hypsiprymnodon moschatus, Uromys caudimaculatus and Perameles nasuta. These species have previously been observed to exhibit varying levels of road avoidance. Aims. To determine whether traffic noise affects movement and behaviour of medium-sized, ground-dwelling rainforest mammals in the absence of other road-associated variables and potential impacts. We hypothesised that noise impacts would be greatest for species previously shown to avoid roads. Noise impacts on these less vocal species compared with more vocal species is also discussed. Methods. In north-eastern Queensland, Australia, mammals captured at least 500 m from any road were tracked after fitting with spool-and-line equipment. On noisy nights, traffic noise at levels similar to a busy highway was played continuously throughout the night from a line of 12 speakers mounted on trees. Speakers were silent on quiet nights. Key results. Traffic noise caused no increase in avoidance of the speaker line and was not a barrier to movements across the line. Overall, movement paths on noisy nights appeared similar in pattern (tortuosity) to those of quiet nights. At a finer scale, movements of H. moschatus and P. nasuta became more tortuous later in the track, suggesting a return to normal foraging behaviour and possible habituation to the noise. Conclusions. These three species with varying levels of previously recorded road avoidance, did not respond negatively to traffic noise. There was, however, a suggestion of habituation by H. moschatus and P. nasuta in response to the noise. Implications. The demonstrated lack of response to traffic noise in these less vocal species means that traffic noise is unlikely to cause road avoidance or barrier effects. Instead, lack of response and possible habituation to traffic noise may increase vulnerability to road mortality.