Does soil determine the boundaries of monodominant rain forest with adjacent mixed rain forest and maquis on ultramafic soils in New Caledonia?

Aim To determine the soil characteristics of Nothofagus‐dominated rain forests in an ultramafic region (i.e. soils having high concentrations of metals including Mg, Fe and Ni), and whether soil characteristics may explain the location of monodominant rain forest in relation to adjacent mixed rain forest and maquis (shrub‐dominated vegetation). Location New Caledonia. Methods Soil characteristics were compared among six Nothofagus‐dominated rain forests from a range of altitudes and topographic positions. At four of these sites, comparisons were made with soils of adjacent mixed rain forest and maquis. Results Soil characteristics varied among the monodominant Nothofagus forests, largely due to differences between ultramafic soils and soils influenced by non‐ultramafic intrusions. The soils of all vegetation types had low concentrations of nutrients, particularly P, K and Ca (both total and extractable/exchangeable), and high total concentrations of Ni, Fe, Cr and Mn. There were significant differences between the rain forests and adjacent maquis in soil concentrations of several elements (N, P, Ca, Mg and Mn), more so in surface soils than at depth, but much of this pattern may be caused by effects of vegetation on the soil, rather than of soil on the vegetation. However, there were no significant differences in soil concentrations of any mineral elements between Nothofagus forest and adjacent mixed rain forest. Main conclusions We found no evidence for soil mediation of boundaries of Nothofagus rain forest with mixed rain forest, and little evidence for the boundaries of either forest type with maquis. We suggest that the local abrupt boundaries of these monodominant Nothofagus forests are directly related to temporal factors, such as time since the last wildfire and frequency of wildfire, and that disturbance is therefore a major causal factor in the occurrence of these forests.     

Extractability of nickel and its concentration in cultivated plants in Ni rich ultramafic soils of New Caledonia

The presence of higher-than-normal quantities of nickel is one of the most general features of ultramafic soils and is often suspected as the reason for their infertility. This study on the bioavailability of Ni in ultramafic soils derived from peridotites in New Caledonia showed important variations depending on the position of the soil in the landscape. In piedmont and non hydromorphic colluvio-alluvial soils, Ni was poorly absorbed by cultivated plants. In contrast, crops species grown in the plain soils, especially those found in the colluvio-alluvial and plain soils subject to temporary reducing conditions, possessed very high and even toxic Ni concentrations. Extraction of Ni by DTPA 5 mM was an effective method of estimating Ni bioavailability in these soils. The regression equation developed with only DTPA-extractable ni explained 88% of the variability in tomato Ni concentration. Extractable Ni might originate from the association of Ni with primary alterable minerals, organic matter and goethite. ei]Section editor: L V Kochian     

Distribution, Habitat and Red List Status of the New Caledonian Endemic Tree Canacomyrica monticola (Myricaceae)

The monotypic genus Canacomyrica Guillaumin is a small tree endemic to the rare remaining fragments of primary forest growing on ultramafic geology in New Caledonia. In the rich flora of this island it is one of many endemics to be threatened by habitat loss due to a variety of factors, most significantly open-cast mining for nickel. Using field observations and data from herbarium specimens the extent of occurrence of Canacomyrica monticola is established to be approximately 1420 km². Within this area the distribution of C. monticola is very fragmented and limited to just 11 known localities. Six localities are outside protected areas; two of these may be imminently threatened by mining activity and another may be threatened by bush fires. It is recommended that the IUCN Red List status of Endangered (EN B1ab (i,ii,iv,v)) is assigned to this species.     

Release of Ni and Co by microbial activity in New Caledonian ultramafic soils

A high positive correlation was found between extractable Ni and Co contents and microbial activity of 40 ultramafic soil samples from New Caledonia, suggesting a possible role of microorganisms in the release of these two metals. A saprolite (ultramafic subsoil) and a hypermagnesian brown soil were incubated 9 months in different conditions. Ni and Co release, measured by their extractability, occurred without reduction of soil pH but did not occur when the native microflora was eliminated by heat treatment. However, when autoclaved soil was re-inoculated with a pinch of the same nonheated soil, the release of metals was recorded. The concentrations of extractable Ni and Co were much higher in soils amended with organic compounds in which microbial activity was enhanced, but only if the soil was not heat treated. The presence of Grevillea exul, a metal-tolerant plant, stimulated the metal release process, but the stimulation was less effective than it was in the compost-amended soil without plant. The influence of the plant in extractable Ni and Co contents in this amended soil was not significant. The release of the two metals therefore seemed to be induced by the activity of specialized organotrophic microorganisms.     

Why Pine Barrens Restoration Should Favor Barrens Over Pine

Pine barrens include an assortment of pyrogenic plant communities occurring on glacial outwash or rocky outcrops scattered along the Atlantic coastal plain from New Jersey to Maine, and inward across New England, New York, Pennsylvania, and the northern Great Lakes region. At least historically, pine barrens provided some of the highest quality terrestrial shrublands and young forests in the eastern North American sub‐boreal and northern temperate region. However, the mosaic open‐canopy, sparse‐shrub, and grassland early successional state is generally lacking in contemporary pine barrens. Many sites in the northeastern United States have converted to overgrown scrub oak (Quercus ilicifolia, Quercus prinoides) thickets and closed canopied pitch pine (Pinus rigida)‐dominated forests. Thinning pitch pine is a contentious issue for the imperiled pitch pine‐scrub oak barrens community type (G2 Global Rarity Rank, 6–20 occurrences). Here we provide a historical, ecological, and resource management rationale for thinning pitch pine forest to restore savanna‐like open barrens with a mosaic of scrub oaks, heath shrubs, and prairie‐like vegetation. We postulate that the contemporary dominance of pitch pine forest is largely of recent anthropogenic origin, limits habitat opportunities for at‐risk shrubland fauna, and poses a serious wildfire hazard. We suggest maintaining pitch pine‐scrub oak barrens at 10–30% average pitch pine cover to simultaneously promote shrubland biodiversity and minimize fire danger.     

Tropical dry forests in New Caledonia

Tropical dry forest is the most endangered major vegetation type in the New Caledonia biodiversity hotspot. Vegetation surveys following a transect method used by Gentry were undertaken in two tropical dry forest sites, Ouen-Toro and Pindai, in order to compare species richness, floristic composition, and structure. Pindai contained significantly higher species richness than Ouen-Toro, although there was little difference in forest structure. Tropical dry forest sites in New Caledonia were compared to seven other biodiversity hotspots with tropical dry forest where Gentry's transect method was employed. New Caledonia and other tropical dry forests on islands contain significantly lower species richness than mainland tropical dry forests in biodiversity hotspots. However, New Caledonia contained the highest number of threatened species based on IUCN global conservation categories. Tropical dry forest in New Caledonia appears to be the world's most endangered tropical dry forest based on the extent of forest, number of reserves, and threatened species. Management of tropical dry forests on private and community lands is absolutely imperative to the long-term persistence of this ecosystem.     

Microbial communities of ultramafic soils in maquis and rainforest at Mont Do,New Caledonia

We analysed variation in microbial community richness and function in soils associated with a fire‐induced vegetation successional gradient from low maquis (shrubland) through tall maquis to rainforest on metal‐rich ultramafic soils at Mt Do, New Caledonia. Random amplified polymorphic DNA fingerprinting was used to determine the extent of genetic relatedness among the microbial communities and indicated that the open and tall maquis microbial communities were more similar to each other than they were to the rainforest community. Sole‐source carbon utilization indicated variation in the microbial communities, again with greater diversity in rainforest soils. Plate counts showed that both rainforest and maquis soils contained bacteria that can grow in the presence of up to 20 mmol L^?1 nickel and 10 mmol L^?1 chromium. Understanding microbial community composition and dynamics in these ultramafic soils may lead to a better understanding of the processes facilitating vegetation succession from shrubland to forest on these high‐metal substrates, and of approaches to successful revegetation following mining for metals including nickel, chromium and cobalt.     

Rainforest and savanna landscape dynamics in New Caledonia: Towards a mosaic of stable rainforest and savanna states?

Stable forested environments can be converted to savanna in response to changes in environmental disturbances. New Caledonia is a biodiversity hotspot; significant ecological and economic resources would be lost if forests were turned into savanna by anthropogenic environmental changes. On the landscape scale, systems that have undergone shifts of this kind are characterized by sharp forest–savanna boundaries and mosaic‐like distributions of savanna and forest. Understanding the locations and the dynamics of such boundaries is a challenge for ecologists and is critical for landscape management and biodiversity conservation. Using a time series of aerial photographs (1955–2000) and a forest habitat suitability map, we tested the hypothesis that topography and spatial processes, especially those relating to fire spread and seed dispersal, are the main determinants of the spatial distribution of rainforest and savanna in a New Caledonian landscape covering 24 km². Within the studied landscape, the overall forest coverage decreased by 24% between 1976 and 2000. This was primarily due to the contraction of forests on west‐facing slopes, which accounted for about 90% of the total loss. Conversely, the east‐facing forests seemed to have contracted extensively prior to the studied period, and were confined to refuges. A habitat suitability index calculated from the landscape's topographical features using generalized additive models accurately predicted both the presence of forests and the probability of forest expansion/contraction. We also provide evidence that spatial processes such as fire spread and seed dispersal limit the expansion and contraction of forests. Our results suggest that rainforests on west‐facing slopes in New Caledonia will be progressively destroyed by fire until they are restricted to refuges along thalwegs and creeks, as appears to have already happened for their east‐facing counterparts.     

Pouzolzia saxophila sp. nov. (Urticaceae tribe Boehmerieae) from Bahia,Brazil

The paper supplements a taxonomic revision of the New World species of Pouzolzia by Wilmot‐Dear and Friis in 1996 and a supplement in 2011 with an additional new species. Here another new species of Pouzolzia, P. saxophila Friis, Wilmot‐Dear & A. K. Monro, is described from a restricted area of xerophytic scrub vegetation on rocky outcrops in the Boa Nova National Park, Bahia, Brazil. The new species is somewhat similar to P. pringlei, a Mexican endemic, and to P. amambaiensis from the Brazil–Paraguay border, but also to the widespread Asiatic P. zeylanica. However, the similarities with these species are probably due to adaptation to similar dry habitats on rocky outcrops.     

High-elevation rock outcrop vegetation of the Southern Appalachian Mountains

Abstract. Species composition patterns and vegetation-environment relationships were quantified for high-elevation rock outcrops of the Southern Appalachian Mountains, an infrequent and insular habitat in a forested landscape. Outcrops occur over a wide geographic range encompassing extensive variation in both geology and climate. Geographic-scale factors interact with site-scale factors to produce variation in vegetation among outcrops. Similarly, site-scale factors interact with micro-scale factors to produce variation in vegetation within outcrops. To provide a quantitatively-based classification of outcrop vegetation we used a TWINSPAN analysis of 154 100-m² plots. We recognized nine communities that primarily correspond to different combinations of elevation, bedrock type, geography, and moisture. Within outcrops of a single bedrock type, vegetation composition of 100-m² plots was consistently correlated with elevation and solar radiation, but relationships to soil nutrients varied with bedrock type. Both site-scale (100 m²) factors (e.g. elevation, slope, aspect, and bedrock type) and plot-scale (1-m²) microsite factors (e.g. soil depth, vegetation height, soil nutrients) were strongly correlated with species composition at the 1-m² level. Environment can be used to predict composition more effectively for 100-m² plots on a single bedrock type than either across bedrock types or at a 1-m² scale. Composition-environment relationships resemble those described for outcrop systems from other regions with pronounced topographic relief more than they do those described for the nearby but flatter and lower-elevation outcrops of the Southeastern Piedmont. There is strong spatial autocorrelation in this community, perhaps owing to dispersal limitation. Consequently, a comprehensive conservation strategy must include reservation of both a range of geologic types and a range of geographic locations.     

The diversity and radiation of the largest monophyletic animal group on New Caledonia (Trichoptera: Ecnomidae: Agmina)

In area, New Caledonia is the smallest of the world’s 25 official biodiversity hotspots, but in many taxonomic groups, the island has the highest concentration of species on earth, particularly so in the freshwater insect order Trichoptera. This study aims at applying molecular data and morphology for estimating the real species diversity of the genus Agmina on New Caledonia and investigating potential effects of ultramafic rock substrate on diversification. A dated molecular phylogeny was applied to study diversity and diversification related to geological substrate using the dispersal–extinction–cladogenesis model, diva and Bayesian ancestral character reconstruction. More than 47 species (> 63%) were unknown to science. Initial radiation occurred on ultramafic substrate followed by several independent dispersal events to nonultramafic substrate. The rate of shift from ultramafic to nonultramafic substrate was significantly higher than the rate of shift in the opposite direction, indicating a possible cost associated with living on ultramafic substrate.     

Soil seed bank characteristics in Cameroonian rainforests and implications for post-logging forest recovery

The soil seed bank is considered as an important component for resilience of climacic vegetation. Whereas several related studies have been conducted in Asian, American and some African tropical forests, no investigation has ever been conducted in Central African rainforests, especially in logged forests where the soil seed bank could contribute to regeneration of timber of trees species. We studied the soil seed bank characteristics in relation to the standing vegetation in three Cameroonian forest zones with different disturbance regimes. There was no significant difference between sites in terms of density of the seed bank; the average mean density was 87.6 seeds m⁻². But dissimilarities of the floristic compositions between sites were quite high. Overall, seeds came from 43 species including three commercial tree species. Whereas the seedlings emerging from soil samples mostly came from weedy and short-lived pioneer species, climax species predominated in the extant vegetation, leading to a very weak similarity between soil seed flora and the surrounding vegetation: Sorensen's index ranged from 3.5 to 7.6%. Canopy openness could significantly affect the species richness of soil seed stocks but not the seed density. These results show that the soil seed bank contribution to the resilience of mature tropical forests is low. In particular, very few timber tree species could benefit from soil seed stocks for their regeneration. Therefore, the development of enrichment techniques including use of the soil seed bank as a source of tree regeneration in such a context would be irrelevant.     

What causes the vegetation types on Mount Bloomfield,a coastal tropical mountain of the western Philippines?

Mount Bloomfield has been shown to have several vegetation types, including medium stature forest on greywacke, small stature forest on serpentinized peridotite, and scrub and Gymnostoma woodland on dunite. The causes of the large physiognomic and floristic differences among these vegetation types have been investigated by soil chemical analyses, soil physical studies, and by a phytometer experiment involving the crop plant Zea mays. There was no relationship between maximum tree height and the soil chemical factors analysed (P, K, Ca, Mg, Ni) but there was a directly proportional relationship between maximum tree height and soil water retention. The phytometer experiment supported the idea that there is no acute soil toxicity in spite of the high soil Ni and Mg/Ca quotients recorded in this study. It is concluded that soil water retention, perhaps in combination with fire, is the major cause of stature differences among the vegetation types and together with soil chemistry is an important determinant of floristic composition.     

Metal accumulation by the ultramafic flora of Kosovo

The largest serpentine outcrops in Europe occur in the Balkan Peninsula. Kosovo, as a part of this region, hosts an ultramafic area of 487 km² within its territory. This work reports the first systematic biogeochemical survey on the significant and most representative ultramafic massifs of Kosovo. The aim of this study was (i) to detail the geochemical composition of 12 ultramafic pedons obtained from 10 selected sites chosen as representative for Kosovo, (ii) to inventoriate the flora occurring on these sites and (iii) to identify plant species with potential for use in phytostabilization or phytoextraction purposes. Twelve representative pedons from 10 different sites across the country were excavated and 27 horizon samples were collected. Regarding the serpentine flora, a total of 162 plant taxa located at the ultramafic sites were collected. Soils samples were characterized for basic physico-chemical characteristics and both plant and soil samples were analyzed for chemical composition. The serpentine soils samples displayed a vast array of physico-chemical characteristics which reflected the geochemistry of the bedrock, the degree of weathering and the horizon characteristics. However there appeared to be a relationship between edaphic properties and the occurrence of several plant species. Although most of the plants’ species did not show metal concentrations above 1000 mg kg^?1, Odontarrhena muralis (syn. Alyssum murale Waldst. and Kit). and Noccaea ochroleuca (Boiss and Heldr.) F.K.Mey. (syn.Thlaspi ochroleucum), did, thus meeting the criterion of Ni hyperaccumulating plants. Given the aforementioned, the resilience of these plants to both tolerate and accumulate heavy metals may prove useful for phytostabilization,     

Wildfire risk for main vegetation units in a biodiversity hotspot: modeling approach in New Caledonia,South Pacific

Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modeling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behavior simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one‐off event model and a multi‐event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramafic substrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic‐free areas decreases drastically the risk. A one‐off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one‐off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires.     

Nickel bioavailability in an ultramafic toposequence in the Vosges Mountains (France)

A serpentinised harzburgite outcrop located in the Vosges Mountains hosts a population of the Ni-hyperaccumulator Thlaspi caerulescens J. & C. Presl. A complete study was undertaken to relate the variability of Ni availability along the ultramafic toposequence to pedogenesis, soil mineralogy and functioning with X-Ray Diffraction, Transmission Electron Microscope observations coupled with Isotopic Exchange Kinetics and diethylenetriamine pentaacetic acid extraction of Ni. The soil profiles ranging from Dystric Cambisol to Hypermagnesic Hypereutric Cambisol were distributed unevenly along the toposequence probably due to geochemical variability of the bedrock and also complex quaternary erosion features. The richest soils were characterised by slight mineral weathering leading to Ni, Cr and Fe accumulation in the B horizons whereas the lowest saturated soils had very low-metal contents. Most soil minerals were inherited from the parent materials and there were only few traces of formation of secondary minerals. Primary minerals (e.g. serpentine, chlorite) contained low Ni concentrations (0.2%) whereas neoformed goethite, mainly in the B horizons of the richest soils, contained up to 4.3% Ni. Ni was probably sorbed onto amorphous Fe oxy−hydroxide particles (oxalate extraction) rather than incorporated within the crystal lattice of goethite. Ni availability in the B horizon of Hypereutric Cambisols was extremely high and so was the oxalate extractable Fe. At the toposequence level, there was a high level of Ni availability in the least weathered soils and a very low-availability level in the more intensively weathered soils (strongly acidic pH). Ni availability was unexpectedly positively correlated to pH and was controlled by soil mineralogy and Ni-bearing mineral phases. Ni hyperaccumulation (above 1,000 mg kg⁻¹) by native T. caerulescens was only reached in the Ni-rich soils as a consequence of the local edaphic factors. Ni uptake by T. caerulescens is strongly regulated by Ni availability in soils and therefore related to pedogenesis.