Edaphic Specialization in Tropical Trees: Physiological Correlates and Responses to Reciprocal Transplantation

Recent research has documented the importance of edaphic factors in determining the habitat associations of tree species in many tropical rain forests, but the underlying mechanisms for edaphic associations are unclear. At Sepilok Forest Reserve, Sabah, Malaysian Borneo, two main soil types derived from sandstone (ridges) and alluvium (valleys) differ in nutrient and water availability and are characterized by forests differing markedly in species composition, structure, and understory light availability. We use both survey and reciprocal transplants to examine physiological adaptations to differences in light, nutrient, and water availability between these soil types, and test for the importance of resource-use efficiency in determining edaphic specialization. Photosynthetic surveys for congeneric and confamilial pairs (one species per soil type) of edaphic specialists and for generalists common to both soil types show that species specializing on sandstone derived soil had lower stomatal conductance at a given assimilation rate than those occurring on alluvial soil and also had greater instantaneous and integrated water-use efficiencies. Foliar dark respiration rates per unit photosynthesis were higher for sandstone ridge than alluvial lowland specialists. We suggest that these higher respiration rates are likely due to increases in photosynthetic enzyme concentrations to compensate for lower internal CO2 concentrations resulting from increased stomatal closure. This is supported by lower photosynthetic nitrogen-use efficiencies in the sandstone ridge specialists. Generalist species had lower water-use efficiencies than sandstone ridge specialists when growing on the drier, sandy ridgetops, but their nitrogen-use efficiencies did not differ from the species specialized to the more resource-rich alluvial valleys. We varied light environment and soil nutrient availability in a reciprocal transplant experiment involving two specialist species from each soil type. Edaphic specialist species, when grown on the soil type for which they were not specialized, were not capable of acclimatory shifts to achieve similar resource-use efficiencies as species specialized to that soil type. We conclude that divergent water-use strategies are an important mechanism underlying differences in edaphic associations and thus contributing to maintenance of high local tree species diversity in Bornean rain forests

Insect diversity of Bukit Hampuan Forest Reserve, Sabah, Malaysia

An insect diversity survey was carried out at Bukit Hampuan Forest Reserve, adjacent to Kinabalu Park in Sabah, Malaysia. The nocturnal insect diversity was very high, with a mean of 113 species recorded from one square metre of light-trapping cloth. Diurnal insects were sampled using sweep nets and fine forceps. A total of 19 Bornean endemic insect species were recorded, comprising 15 moth and four beetle species. A few of the endemic moths are confined to Sabah, namely Buzara saikehi, Cyana saulia and Lyclene mesilaulinea. Forty-two butterfly species were recorded. Endemic insect species sampled from this survey indicate the significance of protecting and conserving this forest reserve. Such findings provide important data to enhance the need and effort in biodiversity conservation. The recent gazettement of Bukit Hampuan Forest Reserve is appropriate, and it is also recommended that Bukit Hampuan Forest Reserve be connected to the adjacent Kinabalu Park, i.e. to gazette the connecting state land area into a forest reserve. Forest fires, illegal hunting for wild animals and orchids, and agricultural activities are among the threats to Bukit Hampuan Forest Reserve which directly affect its insect diversity. To mitigate these threats, it is important to adopt a multi-disciplinary and participatory approach in a smart partnership involving relevant stakeholders and the local communities in monitoring, enforcement and promoting environmental awareness

Mapping the structure of Borneo's tropical forests across a degradation gradient

South East Asia has the highest rate of lowland forest loss of any tropical region, with logging and deforestation for conversion to plantation agriculture being flagged as the most urgent threats. Detecting and mapping logging impacts on forest structure is a primary conservation concern, as these impacts feed through to changes in biodiversity and ecosystem functions. Here, we test whether high-spatial resolution satellite remote sensing can be used to map the responses of aboveground live tree biomass (AGB), canopy leaf area index (LAI) and fractional vegetation cover (FCover) to selective logging and deforestation in Malaysian Borneo. We measured these attributes in permanent vegetation plots in rainforest and oil palm plantations across the degradation landscape of the Stability of Altered Forest Ecosystems project. We found significant mathematical relationships between field-measured structure and satellite-derived spectral and texture information, explaining up to 62% of variation in biophysical structure across forest and oil palm plots. These relationships held at different aggregation levels from plots to forest disturbance types and oil palms allowing us to map aboveground biomass and canopy structure across the degradation landscape. The maps reveal considerable spatial variation in the impacts of previous logging, a pattern that was less clear when considering field data alone. Up-scaled maps revealed a pronounced decline in aboveground live tree biomass with increasing disturbance, impacts which are also clearly visible in the field data even a decade after logging. Field data demonstrate a rapid recovery in forest canopy structure with the canopy recovering to pre-disturbance levels a decade after logging. Yet, up-scaled maps show that both LAI and FCover are still reduced in logged compared to primary forest stands and markedly lower in oil palm stands. While uncertainties remain, these maps can now be utilised to identify conservation win–wins, especially when combining them with ongoing biodiversity surveys and measurements of carbon sequestration, hydrological cycles and microclimate

Differences in soil properties among contrasting soil types in Northern Borneo

Soil in the tropics is high in diversity, and despite the diversity of Borneo's forest-soil associations, there is a paucity of data on its soil properties. We investigated the differences between three soil types in the Kabili-Sepilok Forest Reserve, Sabah, Malaysia, encompassing the contrasting alluvial, sandstone and heath forest typologies. We examined the distribution of nutrients between soil types and through soil depths, and assessed the extent of spatial autocorrelation in the three soil types. We confirmed the fertility gradient from alluvial to heath forest soil found by others. Soil elemental concentrations declined in deeper horizons with the exception of exchangeable sodium and aluminium that remained constant through alluvial and sandstone soil profiles. Spatial autocorrelation was present in all three soil types and strongest in the sandstone soil. Overall, we show how bedrock, erosion, leaching and topography influence soil properties across this mosaic of soil types and note their importance in influencing tree communities and their ecological functioning

Reconciling the contribution of environmental and stochastic structuring of tropical forest diversity through the lens of imaging spectroscopy.

Both niche and stochastic dispersal processes structure the extraordinary diversity of tropical plants, but determining their relative contributions has proven challenging. We address this question using airborne imaging spectroscopy to estimate canopy β-diversity for an extensive region of a Bornean rainforest and challenge these data with models incorporating niches and dispersal. We show that remotely sensed and field-derived estimates of pairwise dissimilarity in community composition are closely matched, proving the applicability of imaging spectroscopy to provide β-diversity data for entire landscapes of over 1000 ha containing contrasting forest types. Our model reproduces the empirical data well and shows that the ecological processes maintaining tropical forest diversity are scale dependent. Patterns of β-diversity are shaped by stochastic dispersal processes acting locally whilst environmental processes act over a wider range of scales

Three decades of post-logging tree community recovery in naturally regenerating and actively restored dipterocarp forest in Borneo

Selective logging has affected large areas of tropical forests and there is increasing interest in how to manage selectively logged forests to enhance recovery. However, the impacts of logging and active restoration, by liberation cutting and enrichment planting, on tree community composition are poorly understood compared to trajectories of biomass recovery. Here, we assess the long-term impacts of selective logging and active restoration for biomass recovery on tree species diversity, community composition, and forest structure. We censused all stems ≥2 cm diameter at breast height (DBH) on 46 permanent plots in unlogged, primary forest in the Danum Valley Conservation Area (DVCA; 12 plots, totalling 0.6 ha) and in sites logged 23–35 years prior to the census in the Ulu Segama Forest Reserve adjacent to DVCA (34 plots, totalling 1.7 ha) in Sabah, Malaysian Borneo. Active restoration treatments, including enrichment planting and climber cutting, were implemented on 17 of the logged forest plots 12–24 years prior to the census. Total plot-level basal area and pole (5–10 cm DBH) stem density were lower in logged than unlogged forests, however no difference was found in stem density amongst saplings (2–5 cm DBH) or established trees (≥10 cm DBH). Neither basal area, nor plot-level stem density varied with time since logging at any size class, although sapling and pole stem densities were lower in actively restored than naturally regenerating logged forest. Sapling species diversity was lower in logged than unlogged forest, however there were no other significant effects of logging on tree species richness or diversity indices. Tree species composition, however, differed between logged and unlogged forests across all stem size classes (PERMANOVA), reflected by 23 significant indicator species that were only present in unlogged forest. PERMANOVA tests revealed no evidence that overall species composition changed with time since logging or with active restoration treatments at any size class. However, when naturally regenerating and actively restored communities were compared, two indicator species were identified in naturally regenerating forest and three in actively restored forests. Together our results suggest that selective logging has a lasting effect on tree community composition regardless of active restoration treatments and, even when species richness and diversity are stable, species composition remains distinct from unlogged forest for more than two decades post-harvest. Active restoration efforts should be targeted, monitored, and refined to try to ensure positive outcomes for multiple metrics of forest recovery

Timonius kinabaluensis

Timonius kinabaluensis is only known from Ranau district, Sabah. The estimated area of occupancy (AOO) and extent of occurrence (EOO) are both 8 km2. The species is threatened by forest fire (Bukit hampuan forest reserve) with recurring fires occurring especially in the dry season. If these were to occur it could drive the species towards Critically Endangered or Extinct in the near future. Hence, it is assessed as Vulnerable. Timonius kinabaluensis is endemic to Sabah, Malaysia. It is restricted to the western and southern part of Kinabalu Park

Timonius tambuyukonensis

Timonius kinabaluensis is only known from Ranau district, Sabah. The estimated area of occupancy (AOO) and extent of occurrence (EOO) are both 8 km2. The species is threatened by forest fire (Bukit hampuan forest reserve) with recurring fires occurring especially in the dry season. If these were to occur it could drive the species towards Critically Endangered or Extinct in the near future. Hence, it is assessed as Vulnerable. Timonius kinabaluensis is endemic to Sabah, Malaysia. It is restricted to the western and southern part of Kinabalu Park

Polyalthia lasioclada

Polyalthia lasioclada is restricted to the montane area in Kinabalu Park and Mensalong Forest Reserve, Sabah. The estimated area of occupancy (AOO) and extent of occurrence (EOO) are 16 km2 and 29 km2, respectively. Due to land use change, estimated past loss of the species' AOO and EOO has been about 20% and 22%, respectively. Decline has now ceased as the species is protected in situ in at least two Totally Protected Areas. However, the species is at risk from potential threats such as climate change and forest fire which if they occur could drastically change its conservation status to Critically Endangered or Extinct. Hence, it is assessed as Vulnerable. Polyalthia lasioclada is endemic to Sabah, Malaysia. It is only known from Mount Kinabalu and vicinity. It is estimated that at least 20% of the species' area of occupancy (AOO) and 22% of its extent of occurrence (EOO) has been lost (based on GeoCAT reduction analysis). However as the remaining individuals are in protected areas decline is not continuing. The species has a small remaining AOO and EOO of 16 km2 and 29 km2, respectively

Borneodendron aenigmaticum

The species is endemic to Sabah. It is found growing in primary forest that occurs on ultramafic substrates. The estimated area of occupancy (AOO) and extent of occurrence (EOO) are 56 km2 and 8,777.8 km2 respectively. Although the AOO is calculated from known existing records, it is considered that the actual AOO may be considerably larger than this due to under sampling. There are no records of habitat decline for the species as ultramific areas are protected in Sabah. Therefore, the species occurs in nine Totally Protected Areas and no direct threats impact the species. Hence, it is assessed as Least Concerned. The species is endemic to Sabah, it is known to occur on ultramafic substrates