Rainforest Plots Research Articles

Flowers are essential to maintain high beetle diversity (Coleoptera) in a Neotropical rainforest canopy

ABSTRACT Many hypotheses have been proposed to explain the megadiversity of angiosperms and insects. Flowers and their pollinators represent the most common terrestrial mutualistic interaction today and this is thought to have driven the evolution of angiosperms and their visitors. Within the framework of that interaction, this paper develops and tests two new hypotheses: 1) megadiversity of canopy beetles in tropical rainforests is largely based on flower resources, and 2) the majority of adult canopy beetles are adapted to visit flowers. To test hypothesis 1, the beetle fauna associated with 23 canopy tree species (13 families, 45 individuals) in a 1.4 ha canopy plot of pristine lowland tropical rainforest in southern Venezuela was studied over one year. In total, 6698 adult beetles were collected and identified to 859 species in 44 families. Of these 859 species, 647 species (75.3%) were found with at least one individual on flowering trees, and 527 species (61.4%) were associated exclusively with flowering trees. The proportion of beetle species visiting exclusively small white flowers of the morphological generalist syndrome amounts to 36.6% of the entire canopy beetle community. Based on these findings, the second hypothesis was formulated that canopy beetles are specially adapted flower visitors. To test hypothesis 2, a sub-set study was conducted of the beetles visiting flowers of one tree species in the canopy plot, Hymenopus heteromorphus (Benth.) Sothers and Prance (Chrysobalanaceae). This is a mass-flowering tree with white flowers of a generalised morphology. A total of 440 adult beetles were collected in 20 days and identified to 138 species in 54 genera in 23 families. This assemblage was restricted to the flowering season of this tree. Data collected for H. heteromorphus and other mass-flowering tree species in the same plot indicates that a particular combination of flowering characteristics – massively flowering, white colour, and generalised morphology – attracts the highest diversity of beetles. These findings together suggest that the enormous diversity of canopy beetles in Amazonian tropical rainforests is due mainly to flowers and that mass-flowering trees with small white flowers of the generalist syndrome play a particularly crucial role in assembly and nourishment of this megadiverse beetle community.

Response of tree community composition, plant diversity and aboveground tree biomass in tropical rainforests of Sri Lanka to variation in altitude

Tropical rain forests (TRFs) are a major carbon sink and play an important role in regulating the global climate. Floristic composition, structure and carbon storage in biomass of TRFs could vary substantially with climatic and edaphic factors. Altitudinal transects represent an excellent setting for investigating the responses of TRFs to environmental change. Objectives of this study were to determine the variation patterns and possible inter-relationships between plant community composition, diversity and aboveground biomass (AGB) in TRFs across an altitudinal gradient from 134 m to 1,667 m above sea level in Sri Lanka. Five permanent sampling plots of 1 ha each, consisting of four plots in lowland rainforests in Kanneliya and Pitadeniya- Sinharaja Forest Reserves and one plot in the tropical montane forest in Rilagala, were established. Trees with DBH≥10 cm were measured and taxonomically identified. A total of 3,781 trees, belonging to 191 species from 106 genera and 53 families were recorded, with a total basal area of 203.68 m2. Floristic composition of sampling plots showed substantial variation with altitude. Tree density and numbers of species, genera and families and plant diversity indices (i.e. Shannon-Wiener and Simpson’s Indices, evenness and richness of tree species) showed negative curvilinear declines with increasing altitude. Mean DBH, tree basal area and AGB increased from low- (348 kg ha-1) to midaltitudes (762 kg ha-1) and decreased from mid- to highaltitudes (70 kg ha-1), thus showing second-order polynomial relationships with altitude. Similar trends were shown between AGB and tree species number and diversity indices, thus indicating that AGB is maximum at intermediate vegetation diversity.

Effects of restoration on tree communities and carbon storage in rainforest fragments of the Western Ghats, India

AbstractEcological restoration is a leading strategy for reversing biodiversity losses and enhancing terrestrial carbon sequestration in degraded tropical forests. There have been few comprehensive assessments of recovery following restoration in fragmented forest landscapes, and the efficacy of active versus passive (i.e., natural regeneration) restoration remains unclear. We examined 11 indicators of forest structure, tree diversity and composition (adult and sapling), and aboveground carbon storage in 25 pairs of actively restored (AR; 7–15 yr after weed removal and mixed‐native tree species planting) and naturally regenerating (NR) plots within degraded rainforest fragments, and in 17 less‐disturbed benchmark (BM) rainforest plots in the Western Ghats, India. We assessed the effects of active restoration on the 11 indicators and tested the hypothesis that the effects of active restoration increase with isolation from contiguous and relatively intact rainforests. Active restoration significantly increased canopy cover, adult tree and sapling density, adult and sapling species density (overall and late‐successional), compositional similarity to benchmarks, and aboveground carbon storage, which recovered 14–82% toward BM targets relative to NR baselines. By contrast, tree height–diameter ratios and the proportion of native saplings did not recover consistently in actively restored forests. The effects of active restoration on canopy cover, species density (adult), late‐successional species density (adult and sapling), and species composition, but not carbon storage, increased with isolation across the fragmented landscape. Our findings show that active restoration can promote recovery of forest structure, composition, and carbon storage within 7–15 yr of restoration in degraded tropical rainforest fragments, although the benefits of active over passive restoration across fragmented landscapes would depend on indicator type and may increase with site isolation. These findings on early stages of recovery suggest that active restoration in ubiquitous fragmented landscapes of the tropics could complement passive restoration of degraded forests in less fragmented landscapes, and protection of intact forests, as a key strategy for conserving biodiversity and mitigating climate change.

Drivers of tropical rainforest composition and alpha diversity patterns over a 2,520 m altitudinal gradient.

AimWe sought to determine the relationship of forest composition and alpha diversity (the species diversity of a local assemblage) to altitude, soil, and spatial factors over a 440–2,950 m a.s.l gradient.LocationAltitudinal gradient on the Caribbean slope of the Talamanca Cordillera, Costa Rica.TaxonAngiosperm and gymnosperm trees, palms, and tree ferns.MethodsWe measured and identified all stems ≥10 cm dbh in 32 0.25‐ha undisturbed rain forest plots over the gradient. We determined compositional patterns using Non‐Metric Multidimensional Scaling (NMS) ordination, and used linear regressions to explore the relationship between four alpha diversity metrics and altitude. With variation partitioning (VARPART), we determined the compositional variation explained by altitude, soil, and spatial variables quantified using Principle Components of Neighbor matrices.ResultsWe identified 425 species. NMS axis 1 separated a lowland zone (440–1,120 m asl) from a transitional one dominated by holarctic Oreomunnea mexicana (1,400–1,600 m asl) and Quercus‐dominated forests at altitudes >2,100 m asl. The lowland zone was separated into two clusters of plots on NMS axis 2, the first in the 430–620 m asl range and the second at 1,000–1,120 masl. Regressions showed that all alpha diversity metrics were strongly negatively related to altitude (R 2 > 0.78). Overall, adjusted R 2 from VARPART was 0.43, with 0.30, 0.21, and 0.17 for altitude, soil, and space respectively. The respective adjusted R 2 of individual matrices, on controlling for the other two, was 0.06, 0.05 and 0.09 (p < 0.001).Main conclusionsThere are two well‐defined forest compositional zones on this gradient—lowlands 430–1,120 m asl and montane forests >2,150 m asl—with a transitional zone at 1,400–1,600 m asl, where lowland tropical and montane holarctic species are found together. Montane forests are very distinct in their composition and low alpha diversity. Vegetation and soil respond to altitude, and therefore temperature, as an integrated system, a model that goes beyond niche assembly as shown by the significant effect of space in the VARPART.

Liana cover in the canopies of rainforest trees is not predicted by local ground‐based measures

AbstractLianas (woody climbers) are structural parasites of trees that compete with them for light and below‐ground resources. Most studies of liana–tree interactions are based on ground‐level observations of liana stem density and size, with these assessments generally assumed to reflect the amount of liana canopy cover and overall burden to the tree. We tested this assumption in a 1‐ha plot of lowland rainforest in tropical Australia. We recorded 1072 liana stems (≥1 cm diameter at breast height {dbh}) ha−1 across all trees (≥10 cm dbh) on the plot and selected 58 trees for detailed study. We estimated liana canopy cover on selected trees that hosted 0–15 liana individuals, using a 47‐m‐tall canopy crane. Notably, we found no significant correlations between liana canopy cover and three commonly used ground‐based measurements of liana abundance as follows: liana stem counts per tree, liana above‐ground biomass per tree and liana basal area per tree. We also explored the role of tree size and liana infestation and found that larger trees (≥20 cm dbh) were more likely to support lianas and to host more liana stems than smaller trees (≤20 cm dbh). This pattern of liana stem density, however, did not correlate with greater liana coverage in the canopy. Tree family was also found to have a significant effect on likelihood of hosting lianas, with trees in some families 3–4 times more likely to host a liana than other families. We suggest that local ground‐based measures of liana–tree infestation may not accurately reflect liana canopy cover for individual trees because they were frequently observed spreading through neighbouring trees at our site. We believe that future liana research will benefit from new technologies such as high‐quality aerial photography taken from drones when the aim is to detect the relative burden of lianas on individual trees.

Patterns of local species richness and their associations with functional traits in a 60‐ha tropical forest dynamics plot

AbstractUnderstanding the underlying mechanisms of diversity maintenance in tropics remains a challenge for ecologists. To reveal the underlying mechanism from a plant‐eye‐view perspective, we examined the patterns of local species richness which was defined as the number of species around individuals of a target species within circles of different radii and their correlations with major plant functional traits in a tropical montane rainforest. In 2012, we established a 60‐ha forest dynamics plot (FDP) in tropical montane rainforest on Hainan Island, China. In 2013, we measured eight functional traits (specific leaf area [SLA], leaf dry matter content [LDMC], wood density, potential maximum height, leaf carbon content [LCC], leaf nitrogen content [LNC], leaf phosphorus content [LPC], and leaf potassium content) of all the species in the FDP. Based on all the mapped individuals that had a diameter at breast height ≥10 cm, we utilized individual species–area relationships function (ISARs(r)) combined with the heterogeneous Poisson null model to quantify the patterns of local species richness at scales from 1 to 50 m. Regression analysis was used to determine which functional traits could influence the local diversity pattern. Results showed that the 123 ISARs(r) curves were relatively similar and no species seemed to be extremely higher or lower than the average of all the ISARs(r) curves. The percentage of species that behaved predominantly as accumulators or repellers or neutrally was 42.23%, 13.82%, and 43.9% at scale of &lt;30 m, respectively. But at scales ≥30 m, more than 70% of all species behaved neutrally suggesting that facilitative interactions probably occurred when neighborhoods were &lt;30 m apart. Among the eight measured traits, the SLA, LNC, and LPC were negatively associated with local species richness. Our results indicated that (1) the spatial community structure was not controlled by key species; (2) facilitative interactions played an important role in local diversity maintenance; (3) species with conservative functional trait syndromes were more likely to have relatively high local species richness in the tropical montane rainforest on Hainan Island, China.

Rate of forest recovery after fire exclusion on anthropogenic savannas in the Democratic Republic of Congo

Deforestation in the tropics is often followed by the creation of anthropogenic savannas used for animal husbandry. By discontinuing burning regimes, forests may recolonize the savanna and carbon stocks may recover. However, little is known about the success and speed of tropical forest recovery, while such information is vital for a better quantification of efforts to reduce emissions from deforestation and forest degradation (REDD+) as well as supporting Forest Landscape Restoration (FLR) practices. Therefore, we designed a forest regeneration experiment within a savanna patch in the Mayombe hills (Democratic Republic of Congo), by discontinuing the annual burning regime in an 88 ha exclosure since 2005. 101 permanent inventory plots (40.4 ha) were installed in 2010 and remeasured in 2014. Tree species were classified as savanna or forest specialists. We estimate a forest specialist encroachment rate of 9 stems ha−1 yr−1 and a savanna specialist disappearance rate of 16 stems ha−1 yr−1. Average diameter of forest specialists did not change due to an increasing influx of recruits, while average diameter of savanna trees increased due to decreasing recruitment. Carbon stored by forest specialists increased from 3.12 to 5.60 Mg C ha−1, suggesting a forest carbon recovery rate of 0.62 Mg C ha−1 yr−1. Using the average carbon stock of 19 nearby mature rainforest plots as a reference, we estimate a total forest carbon recovery time of at least 150 years. The Manzonzi exclosure may potentially become an important reference experiment to quantify REDD+ schemes in Central Africa. Furthermore, this natural regeneration experiment demonstrates how carbon sequestration and biodiversity conservation can go hand-in-hand. However, more censuses are needed to better quantify the long-term carbon recovery trajectory within the protected area.

Habitat filtering of six coexistingHeliconiaspecies in a lowland tropical rain forest in Amazonian Ecuador

AbstractHerbaceous plants are often under-studied in tropical forests, despite their high density and diversity, and little is known about the factors that influence their distribution at microscales. In a 25-ha plot in lowland Amazonian rain forest in Yasuní National Park, Ecuador, we censused six species ofHeliconia(Heliconiaceae) in a stratified random manner across three topographic habitat types. We observed distribution patterns consistent with habitat filtering. Overall, more individuals occurred in the valley (N = 979) and slope (N = 847) compared with the ridge (N = 571) habitat. At the species level,Heliconia stricta(N = 1135),H.spathocircinata(N = 309) andH.ortotricha(N = 36) all had higher abundance in the valley and slope than ridge. Further,H. vellerigera(N = 20) was completely absent from the ridge. Conversely,H. velutina(N = 903) was most common in the drier ridge habitat. The two most common species (H.strictaandH.velutina) had a reciprocal or negative co-occurrence pattern and occurred preferentially in valley versus ridge habitats. These results suggest that taxa within this family have different adaptations to the wetter valley versus the drier ridge and that habitat partitioning contributes to coexistence.

Numerical characteristics of plant sexual system of the woody plants in the 60 ha plot in the tropical rain forest in Jianfengling, Hainan Island

Numerical characteristics of plant sexual system of the woody plants in the 60 ha plot in the tropical rain forest in Jianfengling, Hainan Island

Ants Response to Human-Induced Disturbance in a Rain Tropical Forest

A high rate of human-induced disturbance of tropical ecosystems results in enormous loss of biodiversity due to local extinctions. Yet, mechanisms at the population level that lead to the extinction are still poorly understood. Here we tested the hypothesis that human-induced disturbance results in smaller amount of nesting sites for wood-dwelling arthropods that leads to smaller population size and diminished reproduction, and therefore, may promote local extinctions. We completed censuses in less-disturbed and human-disturbed secondary rain forest plots in Puerto Rico. We measured population size and brood production in wood-nesting ants and examined whether these parameters differ between less-disturbed and more-disturbed habitats. In addition, we measured volume of wood parts of all inhabited and potential nesting sites to assess nest site availability. We found that more human-disturbed forests furnish smaller nest sites, resulting in diminished population size and lowered brood production. Our study shows that human-induced disturbance decreases volume of available nesting sites that leads to decreased population size and lowered reproduction. Thus, in addition to the well-documented loss of species richness in human-disturbed tropical habitats, we demonstrated the direct effect of the disturbance that may promote vulnerability of local populations.

Topography and neighborhood crowding can interact to shape species growth and distribution in a diverse Amazonian forest.

Abiotic constraints and biotic interactions act simultaneously to shape communities. However, these community assembly mechanisms are often studied independently, which can limit understanding of how they interact to affect species dynamics and distributions. We develop a hierarchical Bayesian neighborhood modeling approach to quantify the simultaneous effects of topography and crowding by neighbors on the growth of 124,704 individual stems ≥1cm DBH for 1,047 tropical tree species in a 25-ha mapped rainforest plot in Amazonian Ecuador. We build multi-level regression models to evaluate how four key functional traits (specific leaf area, maximum tree size, wood specific gravity and seed mass) mediate tree growth response to topography and neighborhood crowding. Tree growth is faster in valleys than on ridges and is reduced by neighborhood crowding. Topography and crowding interact to influence tree growth in ~10% of the species. Specific leaf area, maximum tree size and seed mass are associated with growth responses to topography, but not with responses to neighborhood crowding or with the interaction between topography and crowding. In sum, our study reveals that topography and neighborhood crowding each influence tree growth in tropical forests, but act largely independently in shaping species distributions. While traits were associated with species response to topography, their role in species response to neighborhood crowding was less clear, which suggests that trait effects on neighborhood dynamics may depend on the direction (negative/positive) and degree of symmetry of biotic interactions. Our study emphasizes the importance of simultaneously assessing the individual and interactive role of multiple mechanisms in shaping species dynamics in high diversity tropical systems.

Density-dependent and distance-dependent effects in a 60-ha tropical mountain rain forest in the Jianfengling mountains, Hainan Island, China: Spatial pattern analysis

To understand the density-dependent and distance-dependent effects on the spatial patterns of trees in tropical mountain rain forest, we used the recent developed O-ring statistic, which is a point pattern analysis method, to explore spatial distribution patterns and spatial associations of trees of different size-classes in a 60-ha tropical mountain rain forest plot in the Jianfengling Nature Reserve, Hainan Island, China. We describe four main findings. (1) As the size-classes of live trees increased, the live trees became more regular. (2) Densities of saplings, small trees, and dead trees tended to decrease with increasing distances, while densities of medium trees, big trees, and old-growth trees initially increased and then decreased at greater distances, showing a skewed inverted V-shaped pattern. (3) Densities of saplings, small trees, and medium trees first increased rapidly from 0 m to 5 m to 7 m radius (distance from old-growth trees) and then decreased continuously away from old-growth trees, showing consistent patterns expect from the distance-dependent effect. (4) Mortality was non-random, and dead trees were significantly aggregated with live trees at scales <2 m, showing clustering of dead (or surviving) trees and clear density dependence where stems with more neighbors had a higher risk of mortality. We concluded that size and spacing effects play important roles in determining spatial distribution patterns of the trees in the Jianfengling tropical mountain rain forest plot.

Do N‐fixing legumes promote neighbouring diversity in the tropics?

Abstract1. Although nitrogen‐fixing plants play a crucial role in maintaining high ecosystem productivity, their effects on forest diversity are greatly debated. Legumes can reduce local diversity because of the fertilization effect; however, they can also facilitate species coexistence through complementary resource utilization.2. In natural forests, nitrogen requirements and biological nitrogen fixation (BNF) vary widely among legumes. We used leaf nitrogen isotopic composition to differentiate the level of BNF activity among seven legumes across a steep gradient of soil available nitrogen within a 60‐ha stem‐mapping plot in a montane tropical rainforest in Hainan Island, China, and we evaluated their spatial distribution and neighbourhood diversity.3. Results show that the levels of BNF activity are tightly correlated with legume association to available soil nitrogen, where legumes associated with nitrogen‐rich habitats exhibit surprisingly greater BNF activity and a more diverse neighbourhood.4. Synthesis. These findings indicate that legumes satisfy their nitrogen‐demanding metabolism through a synergy of habitat preference and BNF activity. High BNF activity drives local diversity by promoting complementary resource utilization rather than intensifying above‐ground competition. This may be achieved by improving litter quality and stimulating mycorrhizal and microbial diversity. The abundance of nitrogen fixers in nitrogen‐rich habitats also explains how legumes contribute to maintaining high levels of soil nitrogen in tropical forests.

Flowering and Fruiting Phenology of Woody Trees in the Tropical-Seasonal Rainforest, Southwestern China

The reproductive phenology of tropical plants is potentially driven by a number of abiotic and biotic factors. However, it is still unclear as to which climatic factors and biotic interactions drive the reproductive phenology of woody trees in the tropical seasonal rainforest of Xishuangbanna region in Southwest China. We conducted observations on woody plants (including trees and shrubs) phenology between November 2004 and October 2007 at bi-weekly intervals in the one hectare permanent plot of tropical seasonal rainforest in Southwest China. A total of 357 individuals of 76 species (70 genera, 37 families),comprising of 59 (78%) woody trees and 17(22%) shrub species were observed. Our results demonstrate that flowering an fruiting frequencies show slight temporal variation between years. Flowering was significantly correlated with day-length, temperature and rainfall and fruiting was significantly correlated with rainfall and temperature. This finding indicates that woody tree reproductive phenology was primarily associated with temperature and rainfall and to a lesser extent with day-length. Reproductive phenology is also linked to seasonal patterns with flowering peaking in the late dry season and fruiting peaking in the late wet season. Moreover, reproductive phenology is also significantly associated with reproductive ecological guilds such as pollination types and dispersal modes. Community reproductive phenology is associated with climatic seasonality and biotic interactions. It also suggests that seasonal phenology patterns may play a fundamental role in community reproductive success in the tropical seasonal rainforest of Xishuangbanna region of South-west China.

Endemic trees in a tropical biodiversity hotspot imperilled by an invasive tree

Non-native plants invade some tropical forests but there are few long-term studies of these invasions, and the consequences for plant richness and diversity are unclear. Repeated measurements of permanent plots in tropical montane rain forests in the Blue and John Crow Mountains National Park in Jamaica over 24 to 40years coincided with invasion by a non-native tree, Pittosporum undulatum. By 2014, P. undulatum comprised, on average, 11.9% of stems≥3cm diameter and 10.4% of the basal area across 16 widespread plots within c. 250ha of the forests. Across these plots, the more P. undulatum increased in basal area over 24years, the greater the decline in local, plot-scale tree species richness, and the greater the reduction in the percentage of stems of endemic tree species. Plot-scale tree diversity (Shannon and Fisher's alpha) also declined the more P. undulatum basal area increased, but beta diversity across the plots was not reduced. Declines in local-scale tree species diversity and richness as the invasion progresses is especially concerning because Jamaica is a global biodiversity hotspot. Native birds disperse P. undulatum seeds widely, and future hurricanes will probably further increase its invasion by reducing canopy cover and therefore promoting growth rates of its established shade-tolerant seedlings. Remedial action is needed now to identify forest communities with greatest endemism, and to protect them through a continuing programme of control and removal of P. undulatum.

High endemism and stem density distinguish New Caledonian from other high-diversity rainforests in the Southwest Pacific.

The biodiversity hotspot of New Caledonia is globally renowned for the diversity and endemism of its flora. New Caledonia's tropical rainforests have been reported to have higher stem densities, higher concentrations of relictual lineages and higher endemism than other rainforests. This study investigates whether these aspects differ in New Caledonian rainforests compared to other high-diversity rainforests in the Southwest Pacific. Plants (with a diameter at breast height ≥10 cm) were surveyed in nine 1-ha rainforest plots across the main island of New Caledonia and compared with 14 1-ha plots in high-diversity rainforests of the Southwest Pacific (in Australia, Fiji, Papua New Guinea and the Solomon Islands). This facilitated a comparison of stem densities, taxonomic composition and diversity, and species turnover among plots and countries. The study inventoried 11 280 stems belonging to 335 species (93 species ha-1 on average) in New Caledonia. In comparison with other rainforests in the Southwest Pacific, New Caledonian rainforests exhibited higher stem density (1253 stems ha-1 on average) including abundant palms and tree ferns, with the high abundance of the latter being unparalleled outside New Caledonia. In all plots, the density of relictual species was ≥10 % for both stems and species, with no discernible differences among countries. Species endemism, reaching 89 % on average, was significantly higher in New Caledonia. Overall, species turnover increased with geographical distance, but not among New Caledonian plots. High stem density, high endemism and a high abundance of tree ferns with stem diameters ≥10 cm are therefore unique characteristics of New Caledonian rainforests. High endemism and high spatial species turnover imply that the current system consisting of a few protected areas is inadequate, and that the spatial distribution of plant species needs to be considered to adequately protect the exceptional flora of New Caledonian rainforests.

Nitrogen-fixing trees inhibit growth of regenerating Costa Rican rainforests

More than half of the world's tropical forests are currently recovering from human land use, and this regenerating biomass now represents the largest carbon (C)-capturing potential on Earth. How quickly these forests regenerate is now a central concern for both conservation and global climate-modeling efforts. Symbiotic nitrogen-fixing trees are thought to provide much of the nitrogen (N) required to fuel tropical secondary regrowth and therefore to drive the rate of forest regeneration, yet we have a poor understanding of how these N fixers influence the trees around them. Do they promote forest growth, as expected if the new N they fix facilitates neighboring trees? Or do they suppress growth, as expected if competitive inhibition of their neighbors is strong? Using 17 consecutive years of data from tropical rainforest plots in Costa Rica that range from 10 y since abandonment to old-growth forest, we assessed how N fixers influenced the growth of forest stands and the demographic rates of neighboring trees. Surprisingly, we found no evidence that N fixers facilitate biomass regeneration in these forests. At the hectare scale, plots with more N-fixing trees grew slower. At the individual scale, N fixers inhibited their neighbors even more strongly than did nonfixing trees. These results provide strong evidence that N-fixing trees do not always serve the facilitative role to neighboring trees during tropical forest regeneration that is expected given their N inputs into these systems.

Comparison of two monodominant species in New Caledonia: floristic diversity and ecological strategies of Arillastrum gummiferum (Myrtaceae) and Nothofagus aequilateralis (Nothofagaceae) rainforests

Mechanisms leading to monodominance in rainforests are still commonly discussed within the framework of forest succession. Here, we focused on the comparison of two monodominant species, Arillastrum gummiferum (Myrtaceae) and Nothofagus aequilateralis (Nothofagaceae), to try to better understand the underlying ecological mechanisms. Those two species are known to dominate the upper canopy of some rainforests on ultramafic substrates in New Caledonia. We investigated the structure, diversity and composition of Arillastrum-dominated plots and compared them with adjacent Nothofagus-dominated and mixed rainforest plots. We found that the dominance of Arillastrum was more pronounced in terms of basal area, whereas for Nothofagus the dominance was mainly in terms of stem density. Species richness and diversities in the two dominated forests were not lower than those observed in mixed rainforests, suggesting that monodominance would not lead to a limitation of diversity. Finally, our observations were consistent with a transient dominance for the two species. We suggest that resistance of Arillastrum to some wildfire regimes would allow the species to survive and regenerate, whereas Nothofagus may have a supportive strategy towards their seedlings through mycorrhizal networks. Both competitive advantages would contribute to the maintenance of monodominance.

A combined field survey and molecular identification protocol for comparing forest arthropod biodiversity across spatial scales.

Obtaining fundamental biodiversity metrics such as alpha, beta and gamma diversity for arthropods is often complicated by a lack of prior taxonomic information and/or taxonomic expertise, which can result in unreliable morphologically based estimates. We provide a set of standardized ecological and molecular sampling protocols that can be employed by researchers whose taxonomic skills may be limited, and where there may be a lack of robust a priori information regarding the regional pool of species. These protocols combine mass sampling of arthropods, classification of samples into parataxonomic units (PUs) and selective sampling of individuals for mtDNA sequencing to infer biological species. We sampled ten lowland rainforest plots located on the volcanic oceanic island of Réunion (Mascarene archipelago) for spiders, a group with limited taxonomic and distributional data for this region. We classified adults and juveniles into PUs and then demonstrated the reconciliation of these units with presumed biological species using mtDNA sequence data, ecological data and distributional data. Because our species assignment protocol is not reliant upon prior taxonomic information, or taxonomic expertise, it minimizes the problem of the Linnean shortfall to yield diversity estimates that can be directly compared across independent studies. Field sampling can be extended to other arthropod groups and habitats by adapting our field sampling protocol accordingly.

Phylogenetic analysis of Ganoderma australe complex in a Bornean tropical rainforest and implications for mechanism of coexistence of various phylogenetic types

We hypothesized that different phylogenetic types of the Ganoderma australe complex can coexist and that their coexistence is promoted by resource partitioning among them. Our field survey and phylogenetic analysis revealed six phylogenetic types coexisting within a 3 ha primary forest plot in a Bornean tropical rainforest. Two of the six have been reported previously, whereas the remaining four are new. Fruit bodies of all dominant phylogenetic types appeared more frequently from fresh coarse woody debris than expected. Comparison of resource use patterns between the observed fungal community and the null community did not provide significant evidence of niche partitioning. Although we found high genetic diversity within the plot, the phylogenetic types at the site share resources. Resource partitioning on phylogenetic types of host trees or stochastic processes during colonization of pieces of coarse woody debris might play an important role in forming the community structure of phylogenetic types of G. australe.