Spatial heterogeneity of element and litter turnover in a Bornean rain forest.

The spatial heterogeneity of element fluxes was quantified by measuring litterfall, throughfall and litter decomposition for 1 y in 30 randomly located sampling areas in a lowland dipterocarp rain forest. The idea tested was that turnover of elements is more variable than turnover of dry matter in a forest with extremely high tree species diversity. In spite of the low fertility of the soil (an ultisol), total litter production (leaves, trash, and wood <2 cm in diameter) was high (1105 g

Soil Carbon Pool and Carbon Fluxes Estimation in 26 Years after Selective Logging Tropical Forest at Sabah, Malaysia

The soil carbon pool holds an enormous amount of carbon, making it the largest reservoir in the terrestrial ecosystem. However, there is growing concern that unsustainable logging methods damage the soil ecosystem, thus triggering the release of soil carbon into the atmosphere hence contributing to ongoing climate change. This study uses a replicated (n = 4) logging experiment to examine the impact of supervised logging with climber cutting (SLCC) and conventional logging (CL) on basic soil characteristics, litter input to soils, soil carbon pools, and soil respiration in a mixed dipterocarp forest 26 years after logging. This study found that there was no significant difference observed in the soil physicochemical properties and total carbon pools between the logging treatments and the virgin forest. Soil carbon pools dominated the total carbon pools, and the highest mean value was recorded in SLCC (87.95 +/- 13.67 Mg C ha(-1)). Conventional logging had a lower mean value (71.17 +/- 12.09 Mg C ha(-1)) than virgin forest (83.20 +/- 11.97 Mg C ha(-1)). SLCC also shows a higher value of soil respiration rate (161.75 +/- 21.67 mg C m(-2) h(-1)) than CL (140.54 +/- 12.54 mg C m(-2) h(-1)). These findings highlight the importance of accurate quantification of the effect of different logging methods on the forest's carbon pools

Ecological responses of a Bornean heath forest (kerangas) to experimental lime and nitrogen addition

Heath forests are a rare but widespread forest type found across the tropics that have low productivity and relatively low plant species diversity but with high endemism. These forests develop on strongly weathered spodosols that are acidic soils with low nutrients, which is generally believed to explain heath forest distribution. In this study, I tested whether tropical heath forest productivity is limited by low soil nitrogen (N) availability, soil acidity or an interaction between the two, with a factorial N and CaCO3 addition experiment in a Bornean heath forest. I also assessed the susceptibility of this forest type to the predicted increases of N deposition in tropical areas. I recorded the highest wet inorganic N deposition rate measured in Malaysia (7.45 kg N ha-1 yr-1) that was dominated by NH4+-N and most likely derived from agro-industrial fertilization. Prior to the experimental treatments of my plots, I correlated edaphic and topographical differences among plots with species diversity, distribution and stand structure. Soil acidity had the greatest influence on species distribution and forest structure but the subsequent experimental liming did not affect tree performance, only soil acidity and the decomposer community. On the other hand, N addition increased tree relative growth rates, and foliar N concentration after only two years of treatment, but no effect of N addition was detectable on litterfall mass during one year of fertilisation. Overall, both the correlational study on habitat filtering and N addition found most effect on trees 5-10 cm DBH but both acquisitive and conservative species reacted equally to N addition. My results show that heath forest productivity is N limited; moreover, increased N deposition is likely to further acidify this forests’ soil – as seen in soil leachate after one year of N fertilization - possibly increasing the amount of undecomposed organic matter and reducing the availability of soil nutrients to forest trees. Our results from litterfall, fresh leaves and soil leachate also present further hypotheses to be tested suggesting that soil phosphorus (P) and iron (Fe) could be limiting in this forest typology. In conclusion, I show that tropical heath forest are sensitive to N availability. To conserve this unique forest type, local governments should develop policies to limit atmospheric N input

Fine root dynamics across pantropical rainforest ecosystems

Fine roots constitute a significant component of the net primary productivity (NPP) of forest ecosystems but are much less studied than above-ground NPP. Comparisons across sites and regions are also hampered by inconsistent methodologies, especially in tropical areas. Here, we present a novel dataset of fine root biomass, productivity, residence time, and allocation in tropical old-growth rainforest sites worldwide, measured using consistent methods, and examine how these variables are related to consistently determined soil and climatic characteristics. Our pantropical dataset spans intensive monitoring plots in lowland (wet, semi-deciduous, deciduous) and montane tropical forests in South America, Africa, and Southeast Asia (n=47). Large spatial variation in fine root dynamics was observed across montane and lowland forest types. In lowland forests, we found a strong positive linear relationship between fine root productivity and sand content, this relationship was even stronger when we considered the fractional allocation of total NPP to fine roots, demonstrating that understanding allocation adds explanatory power to understanding fine root productivity and total NPP. Fine root residence time was a function of multiple factors: soil sand content, soil pH, and maximum water deficit, with longest residence times in acidic, sandy, and water-stressed soils. In tropical montane forests, on the other hand, a different set of relationships prevailed, highlighting the very different nature of montane and lowland forest biomes. Root productivity was a strong positive linear function of mean annual temperature, root residence time was a strong positive function of soil nitrogen content in montane forests, and lastly decreasing soil P content increased allocation of productivity to fine roots. In contrast to the lowlands, environmental conditions were a better predictor for fine root productivity than for fractional allocation of total NPP to fine roots, suggesting that root productivity is a particularly strong driver of NPP allocation in tropical mountain regions.Output Status: Forthcoming/Available Online Additional co-authors: Christopher E. Doughty, Imma Oliveras, Darcy F. Galiano Cabrera, Liliana Durand Baca, Filio Farfán Amézquita, Javier E. Silva Espejo, Antonio C.L. da Costa, Erick Oblitas Mendoza, Carlos Alberto Quesada, Fidele Evouna Ondo, Josué Edzang Ndong, Vianet Mihindou, Natacha N’ssi Bengone, Forzia Ibrahim, Shalom D. Addo-Danso, Akwasi Duah-Gyamfi, Gloria Djaney Djagbletey, Kennedy Owusu-Afriyie, Lucy Amissah, Armel T. Mbou, Toby R. Marthews, Daniel B. Metcalfe, Luiz E.O. Aragão, Ben H. Marimon-Junior, Beatriz S. Marimon, Noreen Majalap, Stephen Adu-Bredu, Miles Silman, Robert M. Ewers, Patrick Meir, Yadvinder Malh

Carbon declines along tropical forest edges correspond to heterogeneous effects on canopy structure and function

Nearly 20% of tropical forests are within 100 m of a nonforest edge, a consequence of rapid deforestation for agriculture. Despite widespread conversion, roughly 1.2 billion ha of tropical forest remain, constituting the largest terrestrial component of the global carbon budget. Effects of deforestation on carbon dynamics in remnant forests, and spatial variation in underlying changes in structure and function at the plant scale, remain highly uncertain. Using airborne imaging spectroscopy and light detection and ranging (LiDAR) data, we mapped and quantified changes in forest structure and foliar characteristics along forest/oil palm boundaries in Malaysian Borneo to understand spatial and temporal variation in the influence of edges on aboveground carbon and associated changes in ecosystem structure and function. We uncovered declines in aboveground carbon averaging 22% along edges that extended over 100 m into the forest. Aboveground carbon losses were correlated with significant reductions in canopy height and leaf mass per area and increased foliar phosphorus, three plant traits related to light capture and growth. Carbon declines amplified with edge age. Our results indicate that carbon losses along forest edges can arise from multiple, distinct effects on canopy structure and function that vary with edge age and environmental conditions, pointing to a need for consideration of differences in ecosystem sensitivity when developing land-use and conservation strategies. Our findings reveal that, although edge effects on ecosystem structure and function vary, forests neighboring agricultural plantations are consistently vulnerable to long-lasting negative effects on fundamental ecosystem characteristics controlling primary productivity and carbon storage

Influence of species functional strategy on leaf stoichiometric responses to fertilizer in a Bornean heath forest

The distribution of Bornean heath forest on white sand soils is believed to be due to element limitation and soil acidity. To determine the impact of both element limitation and soil acidity on tropical heath forest, we established a soil fertilization experiment to investigate the impact that increased soil N availability and reduced soil pH (using lime/CaCO3) had on a range of elements in tree leaves. We hypothesized that alterations in soil resource availability would cause changes in the tree leaf N:P ratio and concentrations of other elements and these changes would be influenced by species' functional strategies. The experiment was carried out in a Bornean heath forest on infertile soil over a 2-year period. We selected 10 common tree species, spanning acquisitive to conservative strategies and tested whether tree species functional strategies influenced tree leaf elemental concentrations after the fertilization. Leaf N:P ratios showed considerable differences among co-occurring species. Overall, we found that soil N addition treatments increased leaf N concentration, although leaf N:P ratios were not affected. Changes in leaf Al, Fe and S concentrations were correlated with species functional strategy: conservative species showed a greater increase in leaf Fe compared with acquisitive species, whereas acquisitive species showed a greater increase in leaf Al but a decrease in leaf S compared with conservative species. Synthesis. We show that soil elements uptake differs between acquisitive and conservative species and that acquisitive species may not take up soil elemental resources more effectively than conservative species. We suggest that the greater Fe acquisition by conservative species, in comparison to acquisitive species, might be due to a stress tolerance strategy. The overall increase in leaf N showed that, in this nutrient-poor forest, N is a fundamental requirement irrespective of species functional strategies. Given the increased leaf Al and Fe concentration after liming, we also suggest that these elements are important, and possibly limiting (Fe), in this heath forest

Ecosystem carbon dynamics in logged forest of Malaysian Borneo

The tropical rainforest of Borneo is heavily disturbed by logging, to date less than half of the original forest cover remains. To counteract such development logged forest is rehabilitated to regenerate its natural protective function. In this thesis we consider the carbon budget of logged forest and the ecology of the trees that are planted for rehabilitation. We show that the logged forest under study differs from unlogged forest due to the lack of the dominant trees and hence the organic carbon that is stored in their biomass. Besides this difference our results indicate that logged forest can maintain its protective function for carbon storage and is therefore worth preserving. The dominant trees, known as dipterocarps, belong to the Dipterocarpaceae family and are keystone species of the lowland forests of Borneo. On the basis of experimental work we study the carbon dynamics of selected dipterocarp species at the seedling stage. With plant physiological measurements of the carbohydrate stores we demonstrate how seedlings adapt to a changing light environment. Our results show that photosynthates are invested into growth or carbohydrate reserves, irrespective of the tree species under study. Further, experimental evidence suggests that the ectomycorrhizal association (plant-fungi-symbiosis) is crucial for the growth of seedlings and should therefore be considered for forest rehabilitation measures. In contrast we could not find evidence for a complex ectomycorrhiza-network between dipterocarp trees and seedlings in logged forest

Soils and topography drive large and predictable shifts in canopy dynamics across tropical forest landscapes

Summary Tropical forests can vary enormously in their 3D structure and dynamics across surprisingly small spatial scales. However, the drivers that underpin this local‐scale variation in forest structure and dynamics remain poorly understood. We acquired repeat airborne laser scanning data across an old‐growth tropical forest landscape in Malaysian Borneo, characterized by a steep gradient in soil fertility and topography that gives rise to large variability in canopy 3D structure. Using this unique dataset, we explored how local‐scale variation in topography and forest structure shapes rates of gap formation, closure, and canopy growth across the landscape. We found that both canopy gains and losses were 2.5–4.7 times greater in low‐lying alluvial forests on fertile soils than in nearby nutrient‐depleted kerangas forests on hilltops. Moreover, we found that variation in canopy 3D structure and dynamics was tightly coupled across the landscape, with taller and more structurally heterogeneous canopies also experiencing faster rates of gap dynamics. Our study highlights the key role that soils and topography play in shaping the structural complexity and dynamics of tropical forest landscapes. </jats:p