Survival and growth data for tree species planted to reforest degraded tropical peat swamp forests and functional trait data for peat swamp forest species across Southeast Asia
Zenodo (CERN European Organization for Nuclear Research), May 10, 2022
Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree ... more Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations 1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories 7 , we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.
The use of fertilizers in agriculture is vital for crop growth and yield particularly in nutrient... more The use of fertilizers in agriculture is vital for crop growth and yield particularly in nutrient-limited soils. However, fertilizer application has been found to increase heavy metal (HM) contents which could affect the crop and soil quality. This study aimed to determine selected HMs concentrations in 11 commercially available fertilizers in Brunei Darussalam, comprising of organic (poultry manure, sheep manure and compost) and inorganic (seven NPK fertilizers and urea) fertilizers using an inductively coupled plasma-optical emission spectroscopy. All fertilizers had metal concentrations that were mostly below the standard safety limits. The highest average metal concentration in all fertilizers was Al, particularly in sheep manure but there are no standard safety limits set for Al. The Cd contents in inorganic fertilizers (NPK ? Mg ? TE 12:12:17:02, NPK ? TE 15:15:15 and NPK 13:13:21) were above the permissible safety limits of China and Japan (8 mg kg-1) but below the safety guidelines set by Australia, Canada and European Commission. The Cd, Co, Cr, Mn, Ni and Pb levels were found to be the highest in NPK ? Mg ? TE 12:12:17:02 than all the other fertilizers while the highest levels of Fe and Al, and Cu and Zn were observed in the sheep manure and poultry manure, respectively, relative to other fertilizers. Almost all HMs analyzed was highly correlated with each other, suggesting that the HMs could be present as a complex from similar sources. Hence, continuous and repeated monitoring of HM concentrations in fertilizers is recommended to assess potential health risks in plants and humans towards achieving food security.
A method for the vegetative propagation of Dillenia suffruticosa with important cultural, medicin... more A method for the vegetative propagation of Dillenia suffruticosa with important cultural, medicinal and ecological values was developed. Juvenile stem cuttings were collected from wild populations in Brunei Darussalam. The cuttings with or without leaves were treated with Indole Butyric Acid (IBA), Naphthaleneacetic acid (NAA), or Indole Acetic Acid (IAA) at 0, 0.01, 0.05, 0.10, or 0.20% (w/v) using a quick-dip method, planted in rooting media and kept in a misted greenhouse. The survival and rooting percentages, number and length of new roots produced, number and area of leaves and Relative Growth Rate (RGR) based on stem length and stem diameter were assessed at a 4-week interval for 24 weeks. The leafless cuttings and leafy cuttings treated with distilled water after week 4 and 16, respectively, did not survive. All of the leafy stem cuttings treated with 0.10 and 0.20% NAA and 0.20% IAA survived for 24 weeks. Leafy stem cuttings treated with 0.10 and 0.20% NAA and not ABA had formed significantly more and longer roots than cuttings in the other treatments at week 8. Leafy stem cuttings treated with 0.10% IAA had more new leaves and greater leaf area, than cuttings in the other treatments at week 8. There were no significant differences in the RGR of leafy stem cuttings among the different treatments at week 8. This study demonstrates that treatments with 0.10-0.20% NAA and 0.10% IAA and not IBA resulted in the development roots and shoots from leafy stem cuttings and can be used for the mass production of D. suffruticosa plantlets, which will prevent the over exploitation of wild stocks.
Tropical peatlands are estimated to hold carbon stocks of 70 Pg C or more as partly-decomposed or... more Tropical peatlands are estimated to hold carbon stocks of 70 Pg C or more as partly-decomposed organic matter, or peat. Peat may accumulate over thousands of years into gently mounded deposits called peat domes with a relief of several meters over distances of kilometers. The curved shape of peat domes accounts for much of the carbon storage in these landscapes, but their subtle topographic signal is difficult to measure. As many of the world's tropical peatlands are remote and inaccessible, spaceborne laser altimetry data from missions such as NASA's Global Ecosystem Dynamics Investigation (GEDI) and the Advanced Topographic Laser Altimeter System (ATLAS) instrument on the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) observatory could help to describe these deposits. However, for better and for worse, tropical peatlands may also support forests with high above-ground biomass-averages of over 200 Mg C / ha have been reported-which increases their carbon stocks but further complicates determination of their surface topography using laser altimetry. In this work, we evaluate retrieval of ground elevations and canopy metrics derived from GEDI waveform data, as well as single-photon data from ATLAS, with reference to an airborne laser scanning dataset covering an area of over 100 kmˆ2 in the Belait District of Brunei Darussalam. We find that despite infrequent ground retrievals, with regularization these spaceborne platforms can provide useful data for tropical peatland surface altimetry.
bioRxiv (Cold Spring Harbor Laboratory), Jan 8, 2023
Speciation can result from both neutral and adaptive processes, but their relative importance and... more Speciation can result from both neutral and adaptive processes, but their relative importance and the factors exerting selective pressures are incompletely understood. In theory, interspecific gene flow could suffice to reverse speciation, or else erode neutral divergence and expose traits and underlying genes whose divergence is due to selection. Hence, introgression can shed light on selection during the speciation process. Here we study mixed assemblages of carnivorous Nepenthes pitcher plants, which frequently produce natural hybrids yet maintain distinct phenotypes. Using ddRAD-seq markers, we characterize divergence and introgression for eight Nepenthes species that grow sympatrically in communities of three to seven species at four locations in Southeast Asia, totalling 22 populations. The sympatric species fell into two discrete classes of high and low divergence. Five lineages with high divergence displayed little recent introgression in tests of locationdependent allele sharing (ABBA-BABA) despite the presence of some natural hybrids. However, all five lineages appear to have introgressed in the more distant past, as revealed by coalescent models with Approximate Bayesian Computation. In the same locations occur three further sympatric species with low genetic divergence. These incipient species also showed some natural hybrids, but in addition both ABBA-BABA tests and ABC suggested very recent or ongoing introgression, raising the question how divergence is maintained in these hybrid zones. One trait possibly involved in maintenance of divergence against gene flow might be the carnivorous pitcher traps, whose morphology showed greater divergence than expected under neutral evolution (Pst-Fst) in the introgressing species pair N. hemsleyana and N. rafflesiana t.f..
The genus Epirixanthes Blume is revised for Brunei Darussalam. Four species are recognised for th... more The genus Epirixanthes Blume is revised for Brunei Darussalam. Four species are recognised for the country: Epirixanthes cylindrica Blume, E. elongata Blume, E. kinabaluensis T.Wendt and E. papuana J.J.Sm., with the two latter species being newly recorded for the Brunei flora. A single collection from Brunei that was formerly identified as Epirixanthes pallida T.Wendt is now confirmed as E. papuana. A revised key for the genus is included.
Southeast Asia supports high biodiversity, in a mosaic of forest types formed by the expansion an... more Southeast Asia supports high biodiversity, in a mosaic of forest types formed by the expansion and contraction of habitats through past climate changes. Among the region's forest types, the geographical distribution of peat swamp forests has fluctuated intensely over the past 120,000 years. Most peat swamp forests in Southeast Asia are found in coastal regions and formed within the last 7,000 years after a decline in sea level. However, some peat swamps were initiated earlier on substrates of slightly higher elevation, and these peat swamps might have been refugia for peat swamp species in the last glacial period and the high sea level period. We assessed genetic diversity, genetic structure and divergence time of current genetic groups for Shorea albida in Brunei, an endemic tree species of Bornean peat swamp forests, using 18 microsatellite markers. Genetic diversity was not lower than has been found in other Shorea species, possibly because of the high density of S. albida in Brunei. Although overall genetic divergence between populations was low, two populations (Ingei and Labi Road 3) were distinct from the other populations. Analysis using DIYABC estimated that three genetic groups (Ingei, Labi Road 3 and others) diverged simultaneously from their ancestral population, whose effective size was very small, about 7,500 years ago, corresponding to a recent sea level peak in the Belait-Baram river basin. In that high sea level period, some higher-elevation lands remained, and peat formation had already started in this region. We propose that the current genetic structure of S. albida in Brunei was formed from small refugial populations that survived the period of higher sea level in these higher-elevation areas. Because of their relatively high genetic diversity, Brunei's S. albida populations should become an important genetic resource for the recovery of genetically healthy populations in other parts of northwest Borneo.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The varying roles of environmental drivers of fine-scale diversity in a hyperdiverse tropical rainforest
In contrast to trees, a considerable part of plant biodiversity of tropical rainforests is still ... more In contrast to trees, a considerable part of plant biodiversity of tropical rainforests is still largely unexplored. We examined the fine-scale drivers of ground herb species richness and composition in one of the world’s most species-rich plant communities. Using 200 subplots of two 1-ha permanent plots in Brunei Darussalam, Borneo, a complete composition of ground herbs was sampled and assigned to 5 frequently occurring functional-taxonomic groups, i.e. ferns, aroids, gingers, mycoheterotrophs and orchids. In total, 157 species of ground herbs were recorded, most of them belonging to the families Zingiberaceae and Araceae. We analyzed the relationship between sets of three key environmental factors and i) species composition, ii) total species richness, iii) each group’s species richness. The most important factor was topography. It had a strong impact on the total species richness as well as species richness of aroids and ferns. The role of soil chemistry was also important, but less pronounced. The taxonomic-functional species groups responded differently to environment. Gingers and aroids responded to the light conditions, while ferns showed the closest association to local topography due to their preference for shady humid microhabitats and easy dispersal. On the other hand, mycoheterotrophs and orchids showed no links to environmental conditions. Given their dependence on heterotrophy or mixotrophy, these two groups mostly utilize other resources than the rest of the studied groups. The present study emphasizes the role of microhabitat conditions on the patterns of functional diversity in tropical rainforest plant communities, calling for further research regarding various functional groups and spatiotemporal resolutions.
Tree species that ‘live slow, die older’ enhance tropical peat swamp restoration: Evidence from a systematic review
Journal of Applied Ecology
Degraded tropical peatlands lack tree cover and are often subject to seasonal flooding and repeat... more Degraded tropical peatlands lack tree cover and are often subject to seasonal flooding and repeated burning. These harsh environments for tree seedlings to survive and grow are therefore challenging to revegetate. Knowledge on species performance from previous plantings represents an important evidence base to help guide future tropical peat swamp forest (TPSF) restoration efforts. We conducted a systematic review of the survival and growth of tree species planted in degraded peatlands across Southeast Asia to examine (1) species differences, (2) the impact of seedling and site treatments on survival and growth and (3) the potential use of plant functional traits to predict seedling survival and growth rates. Planted seedling monitoring data were compiled through a systematic review of journal articles, conference proceedings, reports, theses and unpublished datasets. In total, 94 study‐sites were included, spanning three decades from 1988 to 2019, and including 141 indigenous peatl...
Data from Sullivan et al. (2020) Long-term thermal sensitivity of Earth's tropical forests. Science. DOI: 10.1126/science.aaw7578
ABSTRACT: The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting... more ABSTRACT: The sensitivity of tropical forest carbon to climate is a key uncertainty in predicting global climate change. Although short-term drying and warming are known to affect forests, it is unknown if such effects translate into long-term responses. Here, we analyze 590 permanent plots measured across the tropics to derive the equilibrium climate controls on forest carbon. Maximum temperature is the most important predictor of aboveground biomass (−9.1 megagrams of carbon per hectare per degree Celsius), primarily by reducing woody productivity, and has a greater rate of decline in the hottest forests (>32.2°C). Our results nevertheless reveal greater thermal resilience than observations of short-term variation imply. To realize the long-term climate adaptation potential of tropical forests requires both protecting them and stabilizing Earth's climate.
Terrestrial and epiphytic herbaceous forest species have different ecology and leaf stoichiometry... more Terrestrial and epiphytic herbaceous forest species have different ecology and leaf stoichiometry. In tropical regions, a great component of herbaceous forest species is represented by ferns with different lifeforms. However, little is known about the differences in leaf stoichiometry between the lifeforms. We account for the concentrations of leaf elements (N, P, K, Ca and Mg) between terrestrial and epiphyte lifeforms and evolutionary clades. The fern species were sampled from the forest of Brunei Darussalam. Five leaves were collected from 5 individuals from 16 terrestrial and 4 epiphytic ferns. The leaves were then acid-digested and analyzed. Epiphytic species had higher concentration of most of the leaf elements. The N:P ratio showed that the epiphytic species being much more nutrient-limited, relying on stochastic events, compared to the terrestrial species which have a constant availability of soil elements. Epiphytes showed a higher concentration of P, which could be explain...
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