Will Edwards

Putting plant resistance traits on the map: a test of the idea that plants are better defended at lower latitudes

• It has long been believed that plant species from the tropics have higher levels of traits associated with resistance to herbivores than do species from higher latitudes. A meta-analysis recently showed that the published literature does not support this theory. However, the idea has never been tested using data gathered with consistent methods from a wide range of latitudes. • We quantified the relationship between latitude and a broad range of chemical and physical traits across 301 species from 75 sites world-wide. • Six putative resistance traits, including tannins, the concentration of lipids (an indicator of oils, waxes and resins), and leaf toughness were greater in high-latitude species. Six traits, including cyanide production and the presence of spines, were unrelated to latitude. Only ash content (an indicator of inorganic substances such as calcium oxalates and phytoliths) and the properties of species with delayed greening were higher in the tropics. • Our results do not support the hypothesis that tropical plants have higher levels of resistance traits than do plants from higher latitudes. If anything, plants have higher resistance toward the poles. The greater resistance traits of high-latitude species might be explained by the greater cost of losing a given amount of leaf tissue in low-productivity environments.

Long-term changes in liana abundance and forest dynamics in undisturbed Amazonian forests

Lianas (climbing woody vines) are important structural parasites of tropical trees and may be increasing in abundance in response to global-change drivers. We assessed long-term (-14-year) changes in liana abundance and forest dynamics within 36 1-ha permanent plots spanning -600 km2 of undisturbed rainforest in central Amazonia. Within each plot, we counted each liana stem (> or = 2 cm diameter) and measured its diameter at 1.3 m height, and then used these data to estimate liana aboveground biomass. An initial liana survey was completed in 1997-1999 and then repeated in 2012, using identical methods. Liana abundance in the plots increased by an average of 1.00% +/- 0.88% per year, leading to a highly significant (t = 6.58, df = 35, P < 0.00001) increase in liana stem numbers. Liana biomass rose more slowly over time (0.32% +/- 1.37% per year) and the mean difference between the two sampling intervals was nonsignificant (t = 1.46, df = 35, P = 0.15; paired t tests). Liana size distributions shifted significantly (chi2 = 191, df = 8, P < 0.0001; Chi-square test for independence) between censuses, mainly as a result of a nearly 40% increase in the number of smaller (2-3 cm diameter) lianas, suggesting that lianas recruited rapidly during the study. We used long-term data on rainfall and forest dynamics from our study site to test hypotheses about potential drivers of change in liana communities. Lianas generally increase with rainfall seasonality, but we found no significant trends over time (1997-2012) in five rainfall parameters (total annual rainfall, dry-season rainfall, wet-season rainfall, number of very dry months, CV of monthly rainfall). However, rates of tree mortality and recruitment have increased significantly over time in our plots, and general linear mixed-effect models suggested that lianas were more abundant at sites with higher tree mortality and flatter topography. Rising concentrations of atmospheric CO2, which may stimulate liana growth, might also have promoted liana increases. Our findings clearly support the view that lianas are increasing in abundance in old-growth tropical forests, possibly in response to accelerating forest dynamics and rising CO2 concentrations. The aboveground biomass of trees was lowest in plots with abundant lianas, suggesting that lianas could reduce forest carbon storage and potentially alter forest dynamics if they continue to proliferate.

Feeding guild structure of beetles on Australian tropical rainforest trees reflects microhabitat resource availability

1. We tested the hypotheses that feeding guild structure of beetle assemblages changed with different arboreal microhabitats and that these differences were consistent across rainforest tree species. 2. Hand collection and beating techniques were used from the gondola of the Australian Canopy Crane to collect beetles from five microhabitats (mature leaves, flush leaves, flowers, fruit and suspended dead wood) within the rainforest canopy. A simple randomization procedure was implemented to test whether the abundances of each feeding guild on each microhabitat were different from that expected based on a null hypothesis of random distribution of individuals across microhabitats. 3. Beetles from different feeding guilds were not randomly distributed, but congregated on those microhabitats that are likely to provide the highest concentrations of their preferred food sources. Herbivorous beetles, in particular, were over-represented on flowers and flush foliage and under-represented on mature leaves and dead wood. Proportional numbers of species within each feeding guild were remarkably uniform across tree species for each microhabitat, but proportional abundances of feeding guilds were all significantly non-uniformly distributed between host tree species, regardless of microhabitat, confirming patterns previously found for arthropods in trees in temperate and tropical forests. 4. These results show that the canopy beetle community is partitioned into discrete assemblages between microhabitats and that this partitioning arises because of differences in feeding guild structure as a function of the diversity and the temporal and spatial availability of resources found on each microhabitat.

The overlooked biodiversity of flower-visiting invertebrates.

Estimates suggest that perhaps 40% of all invertebrate species are found in tropical rainforest canopies. Extrapolations of total diversity and food web analyses have been based almost exclusively on species inhabiting the foliage, under the assumption that foliage samples are representative of the entire canopy. We examined the validity of this assumption by comparing the density of invertebrates and the species richness of beetles across three canopy microhabitats (mature leaves, new leaves and flowers) on a one hectare plot in an Australian tropical rainforest. Specifically, we tested two hypotheses: 1) canopy invertebrate density and species richness are directly proportional to the amount of resource available; and 2) canopy microhabitats represent discrete resources that are utilised by their own specialised invertebrate communities. We show that flowers in the canopy support invertebrate densities that are ten to ten thousand times greater than on the nearby foliage when expressed on a per-unit resource biomass basis. Furthermore, species-level analyses of the beetle fauna revealed that flowers support a unique and remarkably rich fauna compared to foliage, with very little species overlap between microhabitats. We reject the hypothesis that the insect fauna on mature foliage is representative of the greater canopy community even though mature foliage comprises a very large proportion of canopy plant biomass. Although the significance of the evolutionary relationship between flowers and insects is well known with respect to plant reproduction, less is known about the importance of flowers as resources for tropical insects. Consequently, we suggest that this constitutes a more important piece of the ‘diversity jigsaw puzzle’ than has been previously recognised and could alter our understanding of the evolution of plant-herbivore interactions and food web dynamics, and provide a better foundation for accurately estimating global species richness.

Apparent environmental synergism drives the dynamics of Amazonian forest fragments

Many contemporary ecosystems are likely to be affected by multiple environmental drivers, complicating efforts to predict future changes in those ecosystems. We studied long-term changes (1980–2012) in forest dynamics and liana (woody vine) abundance and biomass in fragmented and intact forests of the central Amazon. We did so by contrasting trends in 33 permanent 1-ha plots near forest edges (plot center <100 m from the nearest edge) with those in 36 1-ha plots in intact-forest interiors (150–3300 m from nearest edge). In fragmented and edge-affected forests, rates of tree (≥10 cm diameter at breast height) mortality and recruitment were often sharply elevated, especially in the first 10–15 years after fragmentation. Lianas (≥2 cm stem diameter) also increased markedly in abundance (mean ± SD = 1.78 ± 1.23% per yr) and biomass (1.30 ± 1.39% per yr) over time, especially in plots with high edge-related tree mortality. However, plots in undisturbed forest interiors, which were originally established as experimental controls, also experienced long-term changes. In these plots, tree mortality and recruitment rose significantly over time, as did liana abundance (1.00 ± 0.88% per yr) and biomass (0.32 ± 1.37% per yr). These changes were smaller in magnitude than those in fragments but were nonetheless concerted in nature and highly statistically significant. The causes of these changes in forest interiors are unknown, but are broadly consistent with those expected from rising atmospheric CO2 or regional climate drivers that influence forest dynamics. Hence, the dynamics of Amazonian forest fragments cannot be understood simply as a consequence of forest fragmentation. Rather, the changes we observed appear to arise from an interaction of fragmentation with one or more global- or regional-scale drivers affecting forest dynamics. Both sets of phenomena are evidently increasing forest dynamics and liana abundances in fragmented forests, changes that could reduce carbon storage and alter many aspects of forest ecology.

Variation in beetle community structure across five microhabitats in Australian tropical rainforest trees

Beetles (Coleoptera) are the most species‐rich and ecologically diverse group of organisms in tropical rainforest canopies. This study reports on the distribution of the beetle community on five discrete canopy microhabitats (mature leaves, new leaves, flowers, fruit, and suspended dead wood) on 23 tree species in an Australian tropical rainforest. We tested the hypothesis that the beetle fauna will vary in community structure between microhabitats based on differences in the quantity, quality as a food source and availability of different canopy microhabitats. There was substantial variation in dominant beetle families in terms of abundance between microhabitats. All assemblages contained a high number of rare species, with flowers supporting most of the more abundant species. Consequently, the flower‐visitor assemblage was more heterogeneous than expected by chance, whereas the mature leaf assemblage was more even in the proportional abundances of species than expected. The distribution of singletons was also non‐random and flowers, which are spatially and temporally restricted, supported fewer singletons than expected by chance, whereas mature leaves and dead wood supported more. These differences were insensitive to beetle feeding guild, and are most likely related to variation in microhabitat distribution and availability, which influenced relative sampling efforts and the probability of random microhabitat/beetle associations. High dissimilarity in species overlap between microhabitats suggests that each microhabitat attracts a unique beetle assemblage, which has an additive effect on canopy‐wide species richness patterns. Consequently, biodiversity studies that focus on single microhabitats may inadvertently omit a large proportion of canopy species.

Supplementary pollination in the production of custard apple (Annona sp.) - the effect of pollen source

Summary Low natural pollination rates produce few and poorly formed fruits in commercial orchards of the custard apple (Annona squamosa A. cherimola) cultivar ‘Hillary White’ on the Atherton Tablelands, North Queensland, Australia. To overcome this limitation, conventional practice is to hand-pollinate with pollen from either cv. ‘Hillary White’ or cv. ‘African Pride’. Supplementary pollination, using either pollen type, significantly increased overall fruit production and fruit quality above natural levels. However, pollen sourced from cv. ‘African Pride’ trees produced significantly larger and more symmetrical fruits than pollen from cv. ‘Hillary White’. Increased quality was not at the expense of quantity. There was no difference in mean fruit yield between flowers treated with pollen from either variety. These results indicate that using cv. ‘African Pride’ pollen should result in greater economic returns for growers through the production of a higher proportion of ‘best’ quality fruits.

The impacts of oil palm agriculture on Colombia's biodiversity: what we know and still need to know.

The inexorable expansion of oil palm plantations has been a major driver of biodiversity loss in the tropics. This is particularly evident in Malaysia and Indonesia, where the majority of the worlds oil palm is cultivated. In Latin America oil palm acreage has also been steadily increasing, especially in countries such as Colombia, the largest producer by far. However, information on the biological implications of rapid land conversion to oil palm in the region remains scarce. Here, we review the state of knowledge about the impacts of oil palm on biodiversity in Colombia. We also discuss the conservation strategies that have been implemented in the country, and propose research that we need to develop best management practices. The vast majority of research has focused on biotechnology, soils, biological pest control, carbon stock and reduction of greenhouse gases emission, but research on biodiversity is very scarce, or is not published yet. However, important investment and research on this topic are being developed. The most threatened ecosystems are the savannas in the Orinoquia region, where most of the expansion is predicted. The demands for green markets and certification are slowly encouraging oil palm corporations to mitigate their ‘biological footprint‘. However, applied research on the possible impacts of oil palm on biodiversity are urgently needed to support conservation efforts in the oil-palm-dominated landscapes of Colombia, along with commitments by the government and companies to adopt the resulting recommendations.

Multiple resprouting from diaspores and single cotyledons in the Australian tropical tree species Idiospermum australiense

[Extract] In 1999, Dalling & Harms simulated 100% above-ground herbivory on seedlings of Gustavia superba, a large-seeded species from Barro Colorado Island, Panama, and showed the remarkable ability for cotyledons to regenerate up to eight new shoots. They used this evidence to propose that cotyledon size (at least in this species)was adaptive in surviving pre- and early post-germination hazards (Dalling & Harms 1999). In this note we describe the first record of multiple resprouting in an Australian tropical plant species. Idiospermum australiense (Diels) S. T. Blake (Calycanthaceae) exhibits characteristics similar (but not identical) to G. superba that support the contention of Dalling & Harms (1999).

Dynamics of Logging in Solomon Islands: The Need for Restoration and Conservation Alternatives

Forests of Asia-Pacific islands have undergone degradation by some of the worst-known selective logging practices in the tropics. It is unclear whether severely damaged forests can return to a pre-logging state via natural regeneration, or whether active restoration is required. In this review, we highlight how the socioeconomic dynamics in the Solomon Islands promote excessive logging, resulting in highly degraded forests. We detail seven key elements currently promoting excessive logging in this region: (i) economic interests, (ii) corruption, (iii) poor employment conditions in the logging sector, (iv) high forest accessibility, (v) resource limitations for forest monitoring, (vi) contention over logging benefits, and (vii) a paucity of information for policy development. Though research on the regeneration capacity of logged forests in the Solomon Islands remains extremely limited, we suggest that some logged forests in the country may require active restoration—especially those that have been most heavily damaged. Our argument is based on previous tree planting initiatives in logged forest in the 1970s and 1980s. We propose three broad restoration techniques—enrichment planting, direct seeding, and the use of artificial perches—as viable options to help restore logged forests in the Solomon Islands. Lastly, we recommend the conservation-concession model to aid forest restoration, given its recent success in the region.