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Large trees are keystone structures in many terrestrial ecosystems. They contribute disproportionately to reproduction, recruitment and succession, and influence the structure, dynamics and diversity of forests. Recently, researchers have become concerned about evidence showing rapid declines in large, old trees in a range of ecosystems across the globe. We used ≥10 cm diameter at breast height (DBH) stem inventory data from 20, 0.5 ha forest plots spanning the wet tropical rainforest of Queensland, Australia to examine the contribution of large-diameter trees to above ground biomass (AGB), richness, dominance, mortality and recruitment. We show consistencies with tropical rainforest globally in that large-diameter trees (≥70 cm DBH) contribute much of the biomass (33%) from few trees (2.4% of stems ≥10 cm DBH) with the density of the largest trees explaining much of the variation (62%) in AGB across plots. Measurement of AGB in the largest 5% of trees allows plot biomass to be predicted with ~85% precision. In contrast to rainforest in Africa and America, we show that a high proportion of tree species are capable of reaching a large-diameter in Australian wet tropical rainforest resulting in weak biomass hyperdominance (~10% of species account for 50% of the biomass) leading to high potential resilience to regional disturbances and global environmental change. We show that the high AGB in Australian tropical forests is driven primarily by the high density of large trees coupled with contributions from high densities of medium size trees. Australian wet tropical rainforests are well positioned to maintain the current densities of large-diameter trees and high AGB into the future due to the species richness of large trees and a high density of replacement smaller trees.

Plant species show considerable leaf trait variability that should be accounted for in dynamic global vegetation models (DGVMs). In particular, differences in the acclimation of leaf traits during periods more and less favourable to growth have rarely been examined. We conducted a field study of leaf trait variation at seven sites spanning a range of climates and latitudes across the Australian continent; 80 native plant species were included. We measured key traits associated with leaf structure, chemistry and metabolism during the favourable and unfavourable growing seasons. Leaf traits differed widely in the degree of seasonal variation displayed. Leaf mass per unit area (Ma) showed none. At the other extreme, seasonal variation accounted for nearly a third of total variability in dark respiration (Rdark). At the non‐tropical sites, carboxylation capacity (Vcmax) at the prevailing growth temperature was typically higher in summer than in winter. When Vcmax was normalized to a common reference temperature (25°C), however, the opposite pattern was observed for about 30% of the species. This suggests that metabolic acclimation is possible, but far from universal. Intraspecific variation—combining measurements of individual plants repeated at contrasting seasons, different leaves from the same individual, and multiple conspecific plants at a given site—dominated total variation for leaf metabolic traits Vcmax and Rdark. By contrast, site location was the major source of variation (53%) for Ma. Interspecific trait variation ranged from only 13% of total variation for Vcmax up to 43% for nitrogen content per unit leaf area. These findings do not support a common practice in DGVMs of assigning fixed leaf trait values to plant functional types. Trait‐based models should allow for interspecific differences, together with spatial and temporal plasticity in leaf structural, chemical and metabolic traits. A plain language summary is available for this article. Plain Language Summary

Big trees and abundant species dominate forest structure and composition. As a result, their spatial distribution and interactions with other species and individuals may contribute disproportionately to the emergence of spatial heterogeneity in richness patterns. We tested scale‐dependent spatial patterning and species richness structures to understand the role of individual trees (big trees) and species (abundant species) in driving spatial richness patterns on a 25 ha plot in a diverse tropical forest of Australia. The individual species area relationship (ISAR) was used to assess species richness in neighborhoods ranging from 1 to 50 m radii around all big trees (≥70 cm dbh, n = 296) and all species with more than 100 individuals in the plot (n = 53). A crossed ISAR function was also used to compute species richness around big trees for trees of different size classes. Big individuals exert some spatial structuring on other big and mid‐sized trees in local neighborhoods (up to 30 m and 16 m respectively), but not on small trees. While most abundant species were neutral with respect to richness patterns, we identified consistent species‐specific signatures on spatial patterns of richness for 14 of the 53 species. Seven species consistently had higher than expected species richness in their neighborhood (species “accumulators”), and seven had lower than expected (species “repellers”) across all spatial scales. Common traits of accumulators and repeller species suggest that niche partitioning along disturbance gradients is a primary mechanism driving spatial richness patterns, which is then manifested in large‐scale spatial heterogeneity in species distributions across the plot. Most big trees and abundant species in a diverse tropical forest in Australia leave no strong spatial signature on tree species diversity in their surrounding neighbourhood. However, a small number of abundant species leave a consistent spatial fingerprint of higher or lower than expected tree species diversity across scales of up to 50 m radius.

Most research on boundaries between vegetation types emphasizes the contrasts and similarities between conditions on either side of a boundary, but does not compare boundary to non-boundary vegetation. That is, most previous studies lack suitable controls, and may therefore overlook underlying aspects of landscape variability at a regional scale and underestimate the effects that the vegetation itself has on the soil. We compared 25 soil chemistry variables in rainforest, sclerophyll vegetation and across rainforest-sclerophyll boundaries in north-eastern Queensland, Australia. Like previous studies, we did find some contrasts in soil chemistry across vegetation boundaries. However we did not find greater variation in chemical parameters across boundary transects than in transects set in either rainforest or woodland. We also found that soil on both sides of the boundary is more similar to “rainforest soil” than to “woodland soil”. Transects in wet sclerophyll forests with increasing degrees of rainforest invasion showed that as rainforest invades wet sclerophyll forest, the soil beneath wet sclerophyll forest becomes increasingly similar to rainforest soil. Our results have implications for understanding regional vegetation dynamics. Considering soil-vegetation feedbacks and the differences between soil at boundaries and in non-boundary sites may hold clues to some of the processes that occur across and between vegetation types in a wide range of ecosystems. Finally, we suggest that including appropriate controls should become standard practice for studies of vegetation boundaries and edge effects worldwide.

Defaunation is causing declines of large-seeded animal-dispersed trees in tropical forests worldwide, but whether and how these declines will affect carbon storage across this biome is unclear. Here we show, using a pan-tropical data set, that simulated declines of large-seeded animal-dispersed trees have contrasting effects on aboveground carbon stocks across Earth’s tropical forests. In our simulations, African, American and South Asian forests, which have high proportions of animal-dispersed species, consistently show carbon losses (2–12%), but Southeast Asian and Australian forests, where there are more abiotically dispersed species, show little to no carbon losses or marginal gains (±1%). These patterns result primarily from changes in wood volume, and are underlain by consistent relationships in our empirical data (∼2,100 species), wherein, large-seeded animal-dispersed species are larger as adults than small-seeded animal-dispersed species, but are smaller than abiotically dispersed species. Thus, floristic differences and distinct dispersal mode–seed size–adult size combinations can drive contrasting regional responses to defaunation. Defaunation is linked to the decline of tree species that depend on large animals for seed dispersal, but it is unclear if this affects carbon storage. Here the authors show that defaunation effects on carbon storage vary across continents, driven by relationships between seed dispersal strategies and adult tree size.

The processes determining where seeds fall relative to their parent plant influence the spatial structure and dynamics of plant populations and communities. For animal dispersed species the factors influencing seed shadows are poorly understood. In this paper we test the hypothesis that the daily temporal distribution of disperser behaviours, for example, foraging and movement, influences dispersal outcomes, in particular the shape and scale of dispersal curves. To do this, we describe frugivory and the dispersal curves produced by the southern cassowary, Casuarius casuarius, the only large-bodied disperser in Australia's rainforests. We found C. casuarius consumed fruits of 238 species and of all fleshy-fruit types. In feeding trials, seeds of 11 species were retained on average for 309 min (± 256 SD). Sampling radio-telemetry data randomly, that is, assuming foraging occurs at random times during the day, gives an estimated average dispersal distance of 239 m (± 207 SD) for seeds consumed by C. casuarius. Approximately 4% of seeds were dispersed further than 1,000 m. However, observation of wild birds indicated that foraging and movement occur more frequently early and late in the day. Seeds consumed early in the day were estimated to receive dispersal distances 1.4 times the 'random' average estimate, while afternoon consumed seeds received estimated mean dispersal distances of 0.46 times the 'random' estimate. Sampling movement data according to the daily distribution of C. casuarius foraging gives an estimated mean dispersal distance of 337 m (± 194 SD). Most animals' behaviour has a non-random temporal distribution. Consequently such effects should be common and need to be incorporated into seed shadow estimation. Our results point to dispersal curves being an emergent property of the plant--disperser interaction rather than being a property of a plant or species.

1. 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. 2. 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. 3. 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. 4. 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. 5. 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.

We report measurements characterizing the performance of a kinetic inductance detector array designed for a wavelength of 25 microns and very low optical background level suitable for applications such as a far-infrared instrument on a cryogenically cooled space telescope. In a pulse-counting mode of operation at low optical flux, the detectors can resolve individual 25-micron photons. In an integrating mode, the detectors remain photon noise limited over more than 6 orders of magnitude in absorbed power from 70 zW to 200 fW, with a limiting noise equivalent power of 4.6 × 10 − 20     W   Hz − 1 at 1 Hz. In addition, the detectors are highly stable with flat power spectra under optical load down to 1 mHz. Operational parameters of the detector are determined including the efficiency of conversion of the incident optical power into quasiparticles in the aluminum absorbing element and the quasiparticle self-recombination constant.

The Universe has never been seen like this before. The window into the infrared opens only above Earth's atmosphere, and humanity has barely glimpsed outside. About half of the light emitted by stars, planets, and galaxies over the lifetime of the Universe emerges in the infrared. With an unparalleled sensitivity increase — up to a factor of 1,000 more than any previous or planned mission — the advance offered by the Origins Space Telescope (OST) is akin to that from the naked eye to humanity's first telescope, or from Galileo's first telescope to the first telescope in space. While key path-finding missions have glimpsed a rich infrared cosmos, extraordinary discovery space awaits; the time for a far-infrared revolution has begun.Are we alone or is life common in the Universe? OST will directly address this long-standing question by searching for signs of life in the atmospheres of potentially habitable terrestrial planets transiting M dwarf stars. How do planets become habitable? OST will trace the trail of cold water from the interstellar medium, through protoplanetary disks and into the outer reaches of our own Solar System. How do stars, galaxies, black holes and the elements of life form, from the cosmic dawn to today? With broad wavelength coverage and fast mapping speeds, OST will map millions of galaxies, simultaneously measuring star formation rates and black hole growth across cosmic time, peering deeper into the far reaches of the Universe than ever before.OST will be maintained at a temperature of 4 K, enabling its tremendous sensitivity gain, and will operate from 5 m to 600 m, encompassing the mid- and far-infrared. OST has two Mission Concepts: Concept 1 with a 9.1-m deployed off-axis primary, and Concept 2, described here, a non-deployed 5.9-m on-axis telescope with the equivalent collecting area of the James Webb Space Telescope (JWST). Concept 2 includes four instruments with capabilities for imaging (large surveys and pointed), spectroscopy (survey and high-resolution modes) and polarimetry, as well as an instrument for high-precision spectroscopy of transiting exoplanets. Concept 2 is optimized for maximum science return and minimal complexity, and offers fast mapping (approximately 60 arcseconds per second). We describe here the three key science themes for OST and the basic mission specifications.

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 m 2 /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.