Caledonian Rainforest Research Articles

Intensive cycling of nickel in a New Caledonian forest dominated by hyperaccumulator trees.

The hyperaccumulator Pycnandra acuminata is a New Caledonian rainforest tree known to have the highest concentration of nickel in any living organism, with 25wt% nickel in its latex. All trees (with a diameter of >10cm) and soil profiles in a 0.25-hectare permanent plot were sampled to assess the biogeochemical compartmentalisation of nickel in a dense stand of P.acuminata trees. Nickel stable isotope analysis permitted insights into the cycling of nickel in this ecosystem. The total tree biomass of the plot was calculated to be 281tonnesha-1 , which contained 0.44kg of cobalt, 49.1kg of manganese, 257kg of nickel and 6.76kg of zinc. Nickel stable isotope analysis identified the biotic origin of the nickel in the soil upper layers, with P.acuminata shoots enriched in lighter nickel isotopes. The δ60 Ni latex signature suggests that long-distance transport, radial xylem and phloem loading are at play in P.acuminata.

Host effects in high ectomycorrhizal diversity tropical rainforests on ultramafic soils in New Caledonia

Abstract Tropical rainforests have been thought to have low prevalence and diversity of ectomycorrhizal symbioses. However, to date, tropical regions have been poorly sampled for ectomycorrhizal fungi. Here, we investigated ectomycorrhizal fungal community diversity and the role of host plants in shaping this diversity in three main ultramafic rainforests in New Caledonia, an archipelago renowned for its exceptional plant diversity and recognized as a biodiversity hotspot. Sampling of ectomycorrhizal root tips and fruit bodies in Nothofagus aequilateralis-dominated, Arillastrum gummiferum-dominated and mixed rainforests showed high fungal diversity with, in total, 28 lineages and 311 operational taxonomic units (OTUs), of which 95% might be endemic. We also found that host preference and host density influenced ectomycorrhizal community composition and contributed to the high fungal diversity of New Caledonian rainforests. Finally, the /cortinarius lineage dominated the below- and above-ground communities, which suggests that this lineage plays a central role in ultramafic ecosystems functioning.

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.

Invasive rats strengthen predation pressure on bird eggs in a South Pacific island rainforest.

Invasive rats (Rattus spp.) are known to have pervasive impacts on island birds, particularly on their nesting success. To conserve or restore bird populations, numerous invasive rat control or eradication projects are undertaken on islands worldwide. However, such projects represent a huge investment and the decision-making process requires proper assessment of rat impacts. Here, we assessed the influence of two sympatric invasive rats (Rattus rattus and R. exulans) on native bird eggs in a New Caledonian rainforest, using artificial bird-nest monitoring. A total of 178 artificial nests containing two eggs of three different sizes were placed either on the ground or 1.5 m high and monitored at the start of the birds’ breeding season. Overall, 12.4% of the nests were depredated during the first 7 days. At site 1, where nests were monitored during 16 days, 41.8% of the nests were depredated. The main predator was the native crow Corvus moneduloides, responsible for 62.9% of the overall predation events. Rats were responsible for only 22.9% of the events, and ate only small and medium eggs at both heights. Our experiment suggests that in New Caledonia, predation pressure by rats strengthens overall bird-nest predation, adding to that by native predators. Experimental rat control operations may allow reduced predation pressure on nests as well as the recording of biodiversity responses after rat population reduction.

Puddle use by New Caledonian Rainforest Birds

Abstract The water requirements of birds in humid areas are not well understood. Even rainforests have dry seasons, during which birds might experience water shortages. We surveyed use of puddles as a water source for birds in a New Caledonian rainforest during the dry season using camera traps. We found that birds frequently used puddles, and that especially granivorous and omnivorous birds were frequent water users. Almost all bird species visited puddles for bathing, but granivorous birds drank water significantly more often than other bird species. Our results suggest that even in tropical rainforests, birds depend on surface water.

Characterisation of the complete mitochondrial genome and 13 microsatellite loci through next-generation sequencing for the New Caledonian spider-ant Leptomyrmex pallens

The complete mitochondrial genome and a set of polymorphic microsatellite markers were identified by 454 pyrosequencing (1/16th of a plate) for the New Caledonian rainforest spider-ant Leptomyrmex pallens. De novo genome assembly recovered the entire mitochondrial genome with mean coverage of 8.9-fold (range 1-27). The mitogenome consists of 15,591 base pairs including 13 protein-coding genes, 2 ribosomal subunit genes, 22 transfer RNAs, and a non-coding AT-rich region. The genome arrangement is typical of insect taxa and very similar to the only other published ant mitogenome from the Solenopsis genus, with the main differences consisting of translocations and inversions of tRNAs. A total of 13 polymorphic loci were also characterized using 41 individuals from a single population in the Aoupinié region, corresponding to workers from 21 nests and 16 foraging workers. We observed moderate genetic variation across most loci (mean number of alleles per locus=4.50; mean expected heterozygosity=0.53) with evidence of only two loci deviating significantly from Hardy-Weinberg equilibrium due to null alleles. Marker independence was confirmed with tests for linkage disequilibrium. Most loci cross amplified for three additional Leptomyrmex species. The annotation of the mitogenome and characterization of microsatellite markers will provide useful tools for assessing the colony structure, population genetic patterns, and dispersal strategy of L. pallens in the context of rainforest fragmentation in New Caledonia. Furthermore, this paper confirms a recent line of evidence that comprehensive mitochondrial data can be obtained relatively easily from small next-generation sequencing analyses. Greater synthesis of next-generation sequencing data will play a significant role in expanding the taxonomic representation of mitochondrial genome sequences.

Rat Control in New Caledonian “Mainland Island” Rainforests: Will the Game be Worth the Candle?

Author(s): Duron, Quiterie; Bourguet, Edouard; Franquet, Romain; Folger, Djaek; Teimpouene, Gabriel; Wanguene, Maurice; Cassan, Jean-Jerome; Rigault, Frederic; De Meringo, Helene; Millon, Alexandre; Vidal, Eric | Abstract: Due to its unique biodiversity and extreme endemism rates, New Caledonia archipelago is listed as one of Earth’s 35 biodiversity hotspots. New Caledonian biota is now threatened by invasive species, with introduced rats considered to be particularly damaging. At the initiative of local institutions and NGOs, an innovative scientific experiment has been launched to quantify the Response of Forest Ecosystems to Rodent and Cat Control (REFCOR) and to test the relevance of such control at a large spatial scale (200 ha) on a dense evergreen rainforest (Mont Panie Wilderness Nature Reserve). Rat control will begin mid-2014 with a short toxin knockdown, and will thereafter involve intensive trapping sessions over the next 6 years, together with biodiversity monitoring and experiments. Rat impact studies initiated in early 2013 also aim to identify possible biodiversity indicators that could be used for a rapid assessment of rat control efficiency and effects. One of the major impacts of invasive rats is the disruption caused to plant and bird reproduction processes, placing them at high risk. Pre-and post-control experiments include the assessment of palm fruit consumption rates and of predation risk to artificial bird nests. Initial surveys of both rat populations and palm fruits (2 species), as well as artificial bird nest predation experiments, were conducted in 2013. Rat abundance was high, fluctuating among study areas and seasons, with more individual reproducers in December than in May. Fruit predation was high for one of the two species, in line with the rat abundance pattern. Surprisingly, artificial bird nest predation by rats was far lower than expected. These first results corroborate the influence of rats on some taxa. Monitoring and experiments will be repeated after and throughout rat control. This “before-after-control-impact” project, conducted in close collaboration with local stakeholders (Dayu Biik NGO), offers a unique opportunity to evaluate 1) the feasibility of controlling rat populations in the New Caledonian rainforest by trapping as an alternative to long-term poisoning, and 2) the benefits of rat control for native biodiversity and rainforest ecosystem functioning.

Population dynamics of canopy trees in New Caledonian rain forests: are monodominantNothofagus(Nothofagaceae) forests successional to mixed rain forests?

Abstract:In New Caledonia, rain forests with an upper canopy dominated by single species ofNothofagusoccur next to mixed-canopy forests, without discernible environmental cause. A potential explanation is that they are different successional stages. To test this hypothesis and predict long-term change in canopy dominance, population size structures of 61 canopy species were analysed in sixNothofagus-dominated forests and three adjacent mixed rain forests. Weibull analysis suggests that theseNothofagusforests are secondary forests, with recruitment insufficient to maintain monodominance, except at a high-altitude site. At low- to mid-altitudes theNothofaguscanopy is predicted to develop into a mixed canopy, unless moderate to severe disturbance occurs within its reproductive lifespan. However, adjacent mixed rain forests are also secondary, with 85% of analysed species showing no evidence of continuous regeneration. Fifteen species from both forest types showed reverse-J curves suggesting continuous regeneration, but onlyCalophyllum caledonicumdid so consistently. Since few canopy species showed evidence of high shade tolerance and persistence, a small number of shade-tolerant species is predicted to dominate both forests in the long term, in the hypothetical absence of disturbance. Hence, temporal factors associated with disturbances play a key role in determining dominance in these forests.

Wood properties and trunk allometry of co‐occurring rainforest canopy trees in a cyclone‐prone environment

New Caledonia commonly experiences cyclones, so trees there are expected to have enhanced wood traits and trunk allometry that confer resistance to wind damage. We ask whether there is evidence of a trade-off between these traits and growth rate among species. Wood traits, including density, microfibril angle (MFA), and modulus of elasticity (MOE), ratio of tree height to stem diameter, and growth rate were investigated in mature trees of 15 co-occurring canopy species in a New Caledonian rainforest. In contrast to some studies, wood density did not correlate negatively with growth increment. Among angiosperms, wood density and MOE correlated positively with diameter-adjusted tree height, and MOE correlated positively with stem-diameter growth increment. Tall slender trees achieved high stiffness with high efficiency with respect to wood density, in part by low MFA, and with a higher diameter growth increment but a lower buckling safety factor. However, some tree species of a similar niche differed in whole-tree resistance to wind damage and achieved wood stiffness in different ways. There was no evidence of a growth-safety trade-off in these trees. In forests that regularly experience cyclones, there may be stronger selection for high wood density and/or stiffness in fast-growing trees of the upper canopy, with the potential growth trade-off amortized by access to the upper canopy and by other plant traits. Furthermore, decreasing wood density does not necessarily decrease resistance to wind damage, resistance being influenced by other characteristics including cell-level traits (e.g., MFA) and whole-plant architecture.

Protein kinase inhibitors from the New Caledonian rainforest

Some interesting features can be drawn from these chemical series. All the active compounds possess a polycyclic ring system and at least one phenol ring. The location of the hydroxy groups seems to be important for the expression of a strong inhibition. In the phenanthrenes series, the most active compound possess the hydroxy group at position C-1, whereas compounds with an hydroxyl at C-2 are less active. A hydroxyl at position C-4’ in the flavone series and at position C-6, or to a lesser extent at C-8, in the aristolactam series are essential for a strong binding affinity; only velutin (7), aristolactam AIIIa (11) and velutinam (12) possess a strong activity. In addition, the Goniothalamus species contain a second type of inhibitor with the presence of medioresinol (13), a lignan previously isolated from Eucommia ulmoides.(5) The kinase inhibiting property could explain the cytotoxicity found on KB cells for most of the active compounds, except for medioresinol (13), which is not active on KB cells at 10 μg/mL. Results Appendicula reflexa is an endemic plant growing in the South Pacific region. The genus Appendicula has never been studied but Orchidaceae have been widely investigated. Two new (1 and 6) and 4 known phenanthrenes have been isolated from the aerial part after bioassay-guided purification. Phenanthrenes are fairly distributed in higher plants, but mainly in the Orchidaceae family. The new compounds exhibited a strong inhibiting activity on the CDK1/cyclin B kinase.

Immediate impactxs of invasion by Wasmannia auropunctata (Hymenoptera: Formicidae) on native litter ant fauna in a New Caledonian rainforest

Immediate impactxs of invasion by Wasmannia auropunctata (Hymenoptera: Formicidae) on native litter ant fauna in a New Caledonian rainforest

Niche opportunity and ant invasion: the case of Wasmannia auropunctata in a New Caledonian rain forest

Due to the unbalanced distribution of their fauna and flora, which leads to the creation of a niche opportunities, it is generally accepted that island communities offer weak biotic resistance to biological invasion. In order to empirically test this statement, we compared resource use by ants in the understorey of an undisturbed New Caledonian rain forest recently invaded by the little fire ant, Wasmannia auropunctata. We tested the exploitation of: (1) food sources by placing baits on all trees with trunks greater than 5 cm in diameter; and (2) nesting sites on two tree species likely to shelter ant colonies. In non-invaded areas, the native ants occupied only 44.6% of the baits after 2 h of exposure, while in invaded areas all the baits were occupied by numerous W. auropunctata workers. Similarly, in non-invaded areas only 48.9% of Meryta coriacea (Araliaceae) trees and 64.5% of Basselinia pancheri (Arecaceae) sheltered ants, while in invaded areas W. auropunctata nested in 92.6–98.3% of these trees. Also, workers attended native Margarodidae (Hemiptera) for which they promoted the development of populations significantly larger than those attended by native ants. Thus native ants appear unable to efficiently exploit and defend several of the available food sources and nesting sites, providing a niche opportunity for an invader like W. auropunctata.

Immediate impacts of invasion by Wasmannia auropunctata (Hymenoptera: Formicidae) on native litter ant fauna in a New Caledonian rainforest

Abstract For the last 30 years, Wasmannia auropunctata (the little fire ant) has spread throughout the Pacific and represents a severe threat to fragile island habitats. This invader has often been described as a disturbance specialist. Here we present data on its spread in a dense native rainforest in New Caledonia. We monitored by pitfall trapping the litter ant fauna along an invasive gradient from the edge to the inner forest in July 1999 and March 2000. When W. auropunctata was present, the abundance and richness of native ants drops dramatically. In invaded plots, W. auropunctata represented more than 92% of all trapped ant fauna. Among the 23 native species described, only four cryptic species survived. Wasmannia auropunctata appears to be a highly competitive ant that dominates the litter by eliminating native ants. Mechanisms involved in this invasive success may include predation as well as competitive interactions (exploitation and interference). The invasive success of W. auropunctata is similar to that of other tramp ants and reinforces the idea of common evolutionary traits leading to higher competitiveness in a new environment.

Foliar mineral content of Nothofagus species on ultramafic soils in New Caledonia and non-ultramafic soils in Papua New Guinea

Nothofagus species dominate the upper canopy of some New Caledonian rainforests on ultramafic soils. The characteristics of Nothofagus that facilitate its dominance of these forests are uncertain, but may include a superior capacity to resist the severe soil conditions. In this study, we compared foliar concentrations of macronutrients and heavy metals of Nothofagus species from ultramafic soils in New Caledonia with those from non-ultramafic soils in New Guinea. The concentrations of N and P were significantly lower (4–5-fold difference) and Fe, Cr and Ni significantly higher (140–600-fold difference) in the New Caledonian soils than in the New Guinean soils. The magnitude of difference between the two regions in mean foliar mineral concentrations was considerably less. Analysis of the full leaf data set indicated significant differences between the five New Caledonian and five New Guinea species only in P (c. 2.5-fold higher in New Guinean species) and Cr (c. 6-fold higher in New Caledonian species). The absence of significant differences between regions for most foliar elements is associated with leaf : soil ratios (foliar concentration : soil concentration) that show negative correlations with soil mineral-element concentrations. The highest leaf : soil ratios were recorded in New Caledonian species in K and Ca : Mg. The lowest ratios were recorded in the New Caledonian species in Cr, Ni and Fe. There is no evidence of accumulation of heavy metals in the New Caledonian species, with foliar concentrations similar to those of other New Caledonian species growing on non-ultramafic soils. Instead, the limited evidence suggests they are 'excluders'. In general, the New Caledonian Nothofagus species appear to have relatively low foliar concentrations of macronutrients compared with other New Caledonian rainforest species, suggesting that canopy dominance may be in part due to high nutrient efficiency in terms of growth rate per unit nutrient uptake.

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