We tested the Walker and Syers (1976) conceptual model of soil development and its ecological implications by analyzing changes in soil P, vegetation, and other ecosystem properties on a soil chronosequence with six sites ranging in age from 300 yr to 4.1 x 106 yr. Climate, dominant vegetation, slope, and parent material of all of the sites were similar. As fractions of total P, the various pools of soil phosphorus behaved very much as predicted by Walker and Syers. HCI—extractable P (presumably primary mineral phosphates) comprised 82% of total P at the 300—yr—old site, and then decreased to 1% at the 20,000—yr—old site. Organic phosphorus increased from the youngest site to a maximum at the 150 000 yr site, and then declined to the 4.1 x 106 yr site. Occluded (residual) P increased steadily with soil age. In contrast to the Walker and Syers model, we found the highest total P at the 150 000—yr—old site, rather than at the onset of soil development, and we found that the non—occluded, inorganic P fraction persisted through to the oldest chronosequence site. Total soil N and C increased substantially from early to middle soil development in parallel with organic P, and then declined through to the oldest site. Readily available soil P, NH4+, and NO3— were measured using anion and cation exchange resin bags. P availability increased and decreased unimodally across the chronosequence. NH4+ and NO3— pools increased through early soil development, but did not systematically decline late in soil development. In situ decomposition rates of Metrosideros polymorpha litter were highest at two intermediate—aged sites with soil fertility (20 000 yr and 150 000 yr), and lowest at the less—fertile beginning (300 yr) and endpoint (4.1 x 106 yr) of the chronosequence. M. polymorpha leaves collected from these same four sites, and decomposed in a common site, suggested that leaves from intermediate—aged sites were inherently more decomposable than those from the youngest and oldest sites. Both litter tissue quality and the soil environment appeared to influence rates of decomposition directly. The highest mean soil N2O emissions (809 mg°m—2°d—1) were measured at the 20 000—yr—old site, which also had the highest soil nitrogen fertility status. Plant communities at all six chronosequence sites were dominated primarily by M. Polymorpha, and to a lesser extent by several other genera of trees and shrubs. There were, however, differences in overall vegetation community composition among the sites. Using a detrended correspondence analysis (DECORANA), we found that a high proportion of species variance among the sites (eigenvalue = 0.71) can be explained by site age and thus soil developmental stage. Overall, long—term soil development across the chronosequence largely coincides with the conceptual model of Walker and Syers (1976). How P is distributed among different organic and inorganic fractions at a given stage of soil development provides a useful context of evaluating contemporary cycling of P and other nutrients, and for deter...

Summary 1We measured above-ground net primary productivity (ANPP) and ecosystem structure and processes in eight rain forest stands at four elevations (700, 1700, 2700 and 3100 m) and on two geological substrates (sedimentary vs. ultrabasic rock) on Mount Kinabalu, Borneo. 2 All ultrabasic sites had smaller pools of total soil phosphorus (P) and of labile inorganic P than did the sedimentary sites at the same altitudes. We predicted that the magnitude of altitudinal changes in ANPP would be less on ultrabasic than on sedimentary substrates, reflecting lower temperature dependency of ANPP under stronger P limitation. 3 Although ANPP declined with increasing altitude on both substrates, the slopes of the two regression lines were similar. The intercept was, however, marginally greater on sedimentary than on ultrabasic substrate. 4 Stand-level nutrient-use efficiencies (the ratio of litterfall mass to nutrient return) for N and P were only affected by altitude on ultrabasic substrate where they increased exponentially. Mean foliar N and P contents per unit leaf area of the canopy species increased with altitude on both substrates, but differed between substrates at the same altitude only for P (lower on ultrabasic). 5 Leaf area index (LAI) decreased upslope on both substrates. We assumed that half of primary production was allocated below-ground in order to evaluate stand level net assimilation rate (NAR). This was nearly constant on sedimentary substrate, but declined linearly with increasing altitude on ultrabasic substrate, where it may have to be added to LAI to explain ANPP patterns. 6 We suggest that on sedimentary substrate trees may be able to maintain NAR under colder environments by increasing foliar N and P per unit leaf area, but P deficiency prevents them from adjusting on ultrabasic substrate.Key-words : air temperature, carbon sequestration, foliar nutrients, leaf area index, nutrient and quantum use efficiency

A quantitative transect analysis of altitudinal sequences of forest canopy species from 600 to 3400 m asl on Mt. Kinabalu (4101 m), Borneo, resulted in four discrete altitudinal vegetation zones. These were made up of mutually exclusive species groups for lowland ( < 1200 m asl), lower montane (1200 to 2000-2350 m asl), upper montane (2000-2350 to 2800 m asl), and subalpine (2800 to the forest line, 3400 m asl) zones. Zonal soil types were correlated with the vegetation zones. In upslope sequence, these were: lowland Oxisols, montane Histosol/Spodosol complex, and subalpine Inceptisols. The highest contents of organic carbon, extractable phosphorus, and exchangeable magnesium and potassium were recorded in the lower and upper montane zones. The upper boundaries of the lowland, upper montane and subalpine zones coincided with thermal thresholds of latitudinal bioclimatic zones: 18 °C T M I N (K6ppen's tropical), WI 85 (Kira's warm temperate), and WI 45 (Kira's cool temperate), respectively. The upper limit of the lower montane zone was correlated with an abrupt increase of water surplus estimated from the annual rainfall minus annual potential evaporation. These climatic characteristics appear to define ecological altitudinal turnover points, so called 'critical altitudes', where groups of associated species are displaced by other groups. Abbreviations: asl= above sea level, D B H =diameter at breast height, P H Q = Park headquarters, TMAX = Mean daily maximum air temperature, T M I N = Mean daily minimum air temperature, T W I N S P A N = Two-way indicator species analysis, WI = Warmth index. Nomenclature: Nomenclature follows the index of the herbarium, Sepilok Forest Research Center (SAN), Sabah, Malaysia.

Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity.

Aim Tropical forests have been recognized as important global carbon sinks and sources. However, many uncertainties about the spatial distribution of live tree above-ground biomass (AGB) remain, mostly due to limited availability of AGB field data. Recent studies in the Amazon have already shown the importance of large sample size for accurate AGB gradient analysis. Here we use a large stem density, basal area, community wood density and AGB dataset to study and explain their spatial patterns in an Asian tropical forest.Location Borneo, Southeast Asia. MethodsWe combined stem density, basal area, community wood density and AGB data from 83 locations in Borneo with an environmental database containing elevation, climate and soil variables. The Akaike information criterion was used to select models and environmental variables that best explained the observed values of stem density, basal area, community wood density and AGB. These models were used to extrapolate these parameters across Borneo. ResultsWe found that wood density, stem density, basal area and AGB respond significantly, but differentially, to the environment. AGB was only correlated with basal area, but not with stem density and community wood specific gravity. Main conclusionsUnlike results from Amazonian forests, soil fertility was an important positive correlate for AGB in Borneo while community wood density, which is a main driver of AGB in the Neotropics, did not correlate with AGB in Borneo. Also, Borneo's average AGB of 457.1 Mg ha -1 was c. 60% higher than the Amazonian average of 288.6 Mg ha -1 . We find evidence that this difference might be partly explained by the high density of large wind-dispersed Dipterocarpaceae in Borneo, which need to be tall and emergent to disperse their seeds. Our results emphasize the importance of Bornean forests as carbon sinks and sources due to their high carbon storage capacity.