Daniel J. Metcalfe

Land-use intensification reduces functional redundancy and response diversity in plant communities.

Ecosystem resilience depends on functional redundancy (the number of species contributing similarly to an ecosystem function) and response diversity (how functionally similar species respond differently to disturbance). Here, we explore how land-use change impacts these attributes in plant communities, using data from 18 land-use intensity gradients that represent five biomes and > 2800 species. We identify functional groups using multivariate analysis of plant traits which influence ecosystem processes. Functional redundancy is calculated as the species richness within each group, and response diversity as the multivariate within-group dispersion in response trait space, using traits that influence responses to disturbances. Meta-analysis across all datasets showed that land-use intensification significantly reduced both functional redundancy and response diversity, although specific relationships varied considerably among the different land-use gradients. These results indicate that intensified management of ecosystems for resource extraction can increase their vulnerability to future disturbances.

Leaf chemical and spectral diversity in Australian tropical forests

Leaf chemical and spectral properties of 162 canopy species were measured at 11 tropical forest sites along a 6024 mm precipitation/yr and 8.7 degrees C climate gradient in Queensland, Australia. We found that variations in foliar nitrogen, phosphorus, chlorophyll a and b, and carotenoid concentrations, as well as specific leaf area (SLA), were expressed more strongly among species within a site than along the entire climate gradient. Integrated chemical signatures consisting of all leaf properties did not aggregate well at the genus or family levels. Leaf chemical diversity was maximal in the lowland tropical forest sites with the highest temperatures and moderate precipitation levels. Cooler and wetter montane tropical forests contained species with measurably lower variation in their chemical signatures. Foliar optical properties measured from 400 to 2500 nm were also highly diverse at the species level, and were well correlated with an ensemble of leaf chemical properties and SLA (r2 = 0.54-0.83). A probabilistic diversity model amplified the leaf chemical differences among species, revealing that lowland tropical forests maintain a chemical diversity per unit richness far greater than that of higher elevation forests in Australia. Modeled patterns in spectral diversity and species richness paralleled those of chemical diversity, demonstrating a linkage between the taxonomic and remotely sensed properties of tropical forest canopies. We conclude that species are the taxonomic unit causing chemical variance in Australian tropical forest canopies, and thus ecological and remote sensing studies should consider the role that species play in defining the functional properties of these forests.

On the delineation of tropical vegetation types with an emphasis on forest/savanna transitions

Background: There is no generally agreed classification scheme for the many different vegetation formation types occurring in the tropics. This hinders cross-continental comparisons and causes confusion as words such as ‘forest’ and ‘savanna’ have different meanings to different people. Tropical vegetation formations are therefore usually imprecisely and/or ambiguously defined in modelling, remote sensing and ecological studies. Aims: To integrate observed variations in tropical vegetation structure and floristic composition into a single classification scheme. Methods: Using structural and floristic measurements made on three continents, discrete tropical vegetation groupings were defined on the basis of overstorey and understorey structure and species compositions by using clustering techniques. Results: Twelve structural groupings were identified based on height and canopy cover of the dominant upper stratum and the extent of lower-strata woody shrub cover and grass cover. Structural classifications did not, however, always agree with those based on floristic composition, especially for plots located in the forest–savanna transition zone. This duality is incorporated into a new tropical vegetation classification scheme. Conclusions: Both floristics and stand structure are important criteria for the meaningful delineation of tropical vegetation formations, especially in the forest/savanna transition zone. A new tropical vegetation classification scheme incorporating this information has been developed.

Monocot Leaves are Eaten Less than Dicot Leaves in Tropical Lowland Rain Forests: Correlations with Toughness and Leaf Presentation

BACKGROUND AND AIMS In tropical lowland rain forest (TLRF) the leaves of most monocots differ from those of most dicots in two ways that may reduce attack by herbivores. Firstly, they are tougher. Secondly, the immature leaves are tightly folded or rolled until 50-100 % of their final length. It was hypothesized that (a) losses of leaf area to herbivorous invertebrates are generally greatest during leaf expansion and smaller for monocots than for dicots, and (b) where losses after expansion are appreciable any difference between monocots and dicots then is smaller than that found during expansion. METHODS At six sites on four continents, estimates were made of lamina area loss from the four most recently mature leaves of focal monocots and of the nearest dicot shoot. Measurements of leaf mass per unit area, and the concentrations of water and nitrogen were made for many of the species. In Panama, the losses from monocots (palms) and dicots were also measured after placing fully expanded palm leaflets and whole dicot leaves on trails of leaf-cutter ants. KEY RESULTS At five of six sites monocots experienced significantly smaller leaf area loss than dicots. The results were not explicable in terms of leaf mass per unit area, or concentrations of water or nitrogen. At only one site was the increase in loss from first to fourth mature leaf significant (also large and the same in monocots and dicots), but the losses sustained during expansion were much smaller in the monocots. In the leaf-cutter ant experiment, losses were much smaller for palms than for dicots. CONCLUSIONS The relationship between toughness and herbivory is complex; despite the negative findings of some recent authors for dicots we hypothesize that either greater toughness or late folding can protect monocot leaves against herbivorous insects in tropical lowland rain forest, and that the relative importance varies widely with species. The difficulties of establishing unequivocally the roles of leaf toughness and leaf folding or rolling in a given case are discussed.

Cyclone Effects on the Structure and Production of a Tropical Upland Rainforest: Implications for Life-History Tradeoffs

Wind is known to alter the structure and functioning of forest ecosystems. Because the intensity and frequency of severe wind events are likely to increase, it is important to understand the species- and substrate-specific effects of these disturbances. We assessed the structure and production among 63 species of trees in an Australian tropical rainforest before and after Cyclone Larry (March 2006). We assessed forest occurring on two different substrates: nutrient-poor schist and relatively nutrient-rich basalt. Leaf area reduction and stem breakage were markedly variable among species, but were more evident on basalt soils than schist soils, and were positively correlated with leaf N and P. In the 18-month period following the cyclone, litterfall, stem biomass increment, and ANPP were 44, 20, and 27% of pre-cyclone measurements and did not differ between soils. More severe modification of leaves, branches, and stems on basalt soils, relative to schist soils, suggests that trees/species growing on nutrient-limited soils are less susceptible to high winds. Disturbance regime and resource availability are likely to interact, creating potential plant strategies that increase fitness either by enhanced investments in carbon or enhanced investments in nitrogen and phosphorus.

The impact of fire on habitat use by the short-snouted elephant shrew ('Elephantulus brachyrhynchus') in North West Province, South Africa

ABSTRACT Several studies have investigated the response of small mammal populations to fire, but few have investigated behavioural responses to habitat modification. In this study we investigated the impact of fire on home range, habitat use and activity patterns of the short-snouted elephant shrew (Elephantulus brachyrhynchus) by radio-tracking individuals before and after a fire event. All animals survived the passage of fire in termite mound refugia. Before the fire, grassland was used more than thickets, but habitat utilization shifted to thickets after fire had removed the grass cover. Thickets were an important refuge both pre- and post-fire, but the proportion of thicket within the home range was greater post-fire. We conclude that fire-induced habitat modification resulted in a restriction of E. brachyrhynchus movements to patches of unburned vegetation. This may be a behavioural response to an increase in predation pressure associated with a reduction in cover, rather than a lack of food. This study highlights the importance of considering the landscape mosaic in fire management and allowing sufficient island patches to remain post-fire ensures the persistence of the small mammal fauna.

Identifying Priority Areas for Conservation and Management in Diverse Tropical Forests

The high concentration of the world’s species in tropical forests endows these systems with particular importance for retaining global biodiversity, yet it also presents significant challenges for ecology and conservation science. The vast number of rare and yet to be discovered species restricts the applicability of species-level modelling for tropical forests, while the capacity of community classification approaches to identify priorities for conservation and management is also limited. Here we assessed the degree to which macroecological modelling can overcome shortfalls in our knowledge of biodiversity in tropical forests and help identify priority areas for their conservation and management. We used 527 plant community survey plots in the Australian Wet Tropics to generate models and predictions of species richness, compositional dissimilarity, and community composition for all the 4,313 vascular plant species recorded across the region (>1.3 million communities (grid cells)). We then applied these predictions to identify areas of tropical forest likely to contain the greatest concentration of species, rare species, endemic species and primitive angiosperm families. Synthesising these alternative attributes of diversity into a single index of conservation value, we identified two areas within the Australian wet tropics that should be a high priority for future conservation actions: the Atherton Tablelands and Daintree rainforest. Our findings demonstrate the value of macroecological modelling in identifying priority areas for conservation and management actions within highly diverse systems, such as tropical forests.

No evidence for long‐term increases in biomass and stem density in the tropical rain forests of Australia

Summary Pervasive increases in biomass and stem density of tropical forests have been recorded in recent decades, potentially having significant implications for carbon storage, biodiversity and ecosystem function. This trend is widely considered to be the result of multidecadal and global scale growth stimulation arising from increases in atmospheric CO2 and temperatures. However, contrasting patterns have been recorded across the tropics, and the role of disturbance in driving biomass and stem dynamics has been highlighted as an alternative explanation. Australian tropical forests have rarely been assessed in pan-tropical analyses of long-term dynamics. We have measured recruitment, mortality and growth in 20 permanent plots in tropical forest across north-eastern Australia since 1971. We assess changes in plot level above-ground live biomass (AGB) and stem density, and compare our results with those documented over a similar time frame in the neo-tropics. No significant increase in AGB was found over the 40-year time period. Above-ground biomass tended to increase over the first two decades of the monitoring period and decrease in the final two with gain terms (growth and recruitment) lower than loss terms (mortality) by the final decade (2000s). Stem density significantly decreased over the monitoring period with recruitment consistently lower than mortality. There was large variation in individual plots in their pattern of AGB and stem density changes over time which was consistent with the response of each plot to known disturbance events, including cyclones, pathogen outbreaks and drought. Our results are in contrast to those described for neo-tropical plots which appear to show a widespread pattern of increasing growth and stem density. Synthesis. The trend towards increasing biomass and stem density of tropical forests described for the neo-tropics does not necessarily reflect patterns in areas of the tropics where large-scale natural disturbances are relatively frequent. Australian tropical rain forests are either not increasing in productivity in response to global change, or cyclones and other regional and local mechanisms of change mask any evidence of larger-scale patterns.

The Australian SuperSite Network: A continental, long-term terrestrial ecosystem observatory

Ecosystem monitoring networks aim to collect data on physical, chemical and biological systems and their interactions that shape the biosphere. Here we introduce the Australian SuperSite Network that, along with complementary facilities of Australias Terrestrial Ecosystem Research Network (TERN), delivers field infrastructure and diverse, ecosystem-related datasets for use by researchers, educators and policy makers. The SuperSite Network uses infrastructure replicated across research sites in different biomes, to allow comparisons across ecosystems and improve scalability of findings to regional, continental and global scales. This conforms with the approaches of other ecosystem monitoring networks such as Critical Zone Observatories, the U.S. National Ecological Observatory Network; Analysis and Experimentation on Ecosystems, Europe; Chinese Ecosystem Research Network; International Long Term Ecological Research network and the United States Long Term Ecological Research Network. The Australian SuperSite Network currently involves 10 SuperSites across a diverse range of biomes, including tropical rainforest, grassland and savanna; wet and dry sclerophyll forest and woodland; and semi-arid grassland, woodland and savanna. The focus of the SuperSite Network is on using vegetation, faunal and biophysical monitoring to develop a process-based understanding of ecosystem function and change in Australian biomes; and to link this with data streams provided by the series of flux towers across the network. The Australian SuperSite Network is also intended to support a range of auxiliary researchers who contribute to the growing body of knowledge within and across the SuperSite Network, public outreach and education to promote environmental awareness and the role of ecosystem monitoring in the management of Australian environments.

Long‐term stem inventory data from tropical rain forest plots in Australia

We present repeated stem measurement data from 20 0.5-ha (100 × 50 m) permanent rain forest plots in northern Queensland, Australia, from 1971 to 2013. The plots have a rainfall range of 1200 to 3500 mm, represent 11 vegetation types, six parent materials, and range from 15 to 1200 m above sea level. Except for minor disturbances associated with selective logging on two plots, the plots were established in old growth forest and all plots have thereafter been protected. Plots were regularly censused and at each census the diameter at breast height (DBH) of all stems ≥10 cm DBH were recorded. Data is presented for 10 998 individual stems with plot stem densities at establishment ranging from 476 to 1104 stems/ha. Due to the wide geographical range of the plots, no species dominate, although the families Lauraceae, Rutaceae, and Myrtaceae contribute a large number of species. Basal area values at establishment ranged from 28.6 to 63.3 m2/ha and showed no trend of increasing or decreasing over time due mainly to regular disturbance and recovery from natural events such as cyclones. In addition to stems ≥10 cm DBH data, we present height data, floristic data from understory stems (≥50 cm height to <10 cm DBH), an auxiliary species list (including vines, epiphytes, ferns, grasses, herbs, and other life forms), and a list of voucher specimens lodged in herbaria. The data collected from the 20 plots provides an insight into the floristics, structure, and long-term forest dynamics of Australian tropical rain forests and allows direct comparisons to be made with long-term monitoring plots at a global scale.