Lindsay Banin

Tropical forest wood production: a cross-continental comparison

Summary: Tropical forest above-ground wood production (AGWP) varies substantially along environmental gradients. Some evidence suggests that AGWP may vary between regions and specifically that Asian forests have particularly high AGWP. However, comparisons across biogeographic regions using standardized methods are lacking, limiting our assessment of pan-tropical variation in AGWP and potential causes. We sampled AGWP in NW Amazon (17 long-term forest plots) and N Borneo (11 plots), both with abundant year-round precipitation. Within each region, forests growing on a broad range of edaphic conditions were sampled using standardized soil and forest measurement techniques. Plot-level AGWP was 49% greater in Borneo than in Amazonia (9.73 ± 0.56 vs. 6.53 ± 0.34 Mg dry mass ha -1 a -1 , respectively; regional mean ± 1 SE). AGWP was positively associated with soil fertility (PCA axes, sum of bases and total P). After controlling for the edaphic environment, AGWP remained significantly higher in Bornean plots. Differences in AGWP were largely attributable to differing height-diameter allometry in the two regions and the abundance of large trees in Borneo. This may be explained, in part, by the greater solar radiation in Borneo compared with NW Amazonia. Trees belonging to the dominant SE Asian family, Dipterocarpaceae, gained woody biomass faster than otherwise equivalent, neighbouring non-dipterocarps, implying that the exceptional production of Bornean forests may be driven by floristic elements. This dominant SE Asian family may partition biomass differently or be more efficient at harvesting resources and in converting them to woody biomass. Synthesis. N Bornean forests have much greater AGWP rates than those in NW Amazon when soil conditions and rainfall are controlled for. Greater resource availability and the highly productive dipterocarps may, in combination, explain why Asian forests produce wood half as fast again as comparable forests in the Amazon. Our results also suggest that taxonomic groups differ in their fundamental ability to capture carbon and that different tropical regions may therefore have different carbon uptake capacities due to biogeographic history. North Bornean forests have much greater AGWP rates than those in north-western Amazon when soil conditions and rainfall are controlled for. Greater resource availability and the highly productive dipterocarps may, in combination, explain why these Asian forests produce wood half as fast again as comparable forests in the Amazon. Our results also suggest that taxonomic groups differ in their fundamental ability to capture carbon and that different tropical regions may therefore have different carbon uptake capacities due to biogeographic history.

Tree Nutrient Status and Nutrient Cycling in Tropical Forest—Lessons from Fertilization Experiments

Highly productive tropical forests often occur on nutrient-poor soils . The apparent lack of a relationship between tree growth and site fertility has generated decades of research into which nutrients, if any, limit tropical forest productivity. This chapter looks at the lessons we have learned from several decades of fertilization experiments, which investigate nutrient limitation by measuring changes in growth and productivity in response to the addition of specific nutrients. The enormous diversity of tropical forest ecosystems often confounds attempts to measure a clear ecosystem response to fertilization because tree species’ nutrient requirements differ according to life history strategy , adaptation to site fertility, and the life stage of the individuals under study. Importantly, other limiting resources, such as light and water, constrain individual responses to nutrient availability, whereas species interactions such as competition, herbivory , and symbioses can mask growth responses to nutrient amendments. Finally, fertilization changes the timing and balance of nutrient inputs to the forest, whereas litter manipulation studies demonstrate that the combined addition of many different nutrients and organic carbon minimizes nutrient losses. Most fertilization studies have investigated responses to nitrogen and phosphorus additions but there is still no general consensus on nutrient limitation in tropical forests. Future experiments will need to evaluate how the balance of multiple macro- and micronutrients affects tropical forest growth and ecosystem dynamics.

Long-term carbon sink in Borneo's forests halted by drought and vulnerable to edge effects

Less than half of anthropogenic carbon dioxide emissions remain in the atmosphere. While carbon balance models imply large carbon uptake in tropical forests, direct on-the-ground observations are still lacking in Southeast Asia. Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 per year (95% CI 0.14–0.72, mean period 1988–2010) in above-ground live biomass carbon. These results closely match those from African and Amazonian plot networks, suggesting that the world’s remaining intact tropical forests are now en masse out-of-equilibrium. Although both pan-tropical and long-term, the sink in remaining intact forests appears vulnerable to climate and land use changes. Across Borneo the 1997–1998 El Niño drought temporarily halted the carbon sink by increasing tree mortality, while fragmentation persistently offset the sink and turned many edge-affected forests into a carbon source to the atmosphere.The existence of a pan-tropical forest carbon sink remains uncertain due to the lack of data from Asia. Here, using direct on-the-ground observations, the authors confirm remaining intact forests in Borneo have provided a long-term carbon sink, but carbon net gains are vulnerable to drought and edge effects.

Ecosystem service indicators: data sources and conceptual frameworks for sustainable management

Purpose – The purpose of this paper is to review, from a sustainable management perspective, a range of conceptual frameworks; determine the efficacy and utility of three different data sources in generating indicators collectively; and consider the utility of a single index of total ecosystem services (TESI). The ecosystem service (ES) concept has been discussed as an important model to aid sustainable land-use management. Design/methodology/approach – The historical development and the relative merits of sustainable management frameworks which can be implemented in a decision-making context were examined. The efficacy of a single index TESI was examined considering three data sources for 11 contrasting sites within the UK. Findings – The choice of conceptual framework and data source depends on the specific question and scale being addressed. Publicly available data through the Eurostat route is primarily limited to the assessment of the provisioning services. Research limitations/implications – Limitat...

Field methods for sampling tree height for tropical forest biomass estimation

Abstract Quantifying the relationship between tree diameter and height is a key component of efforts to estimate biomass and carbon stocks in tropical forests. Although substantial site‐to‐site variation in height–diameter allometries has been documented, the time consuming nature of measuring all tree heights in an inventory plot means that most studies do not include height, or else use generic pan‐tropical or regional allometric equations to estimate height. Using a pan‐tropical dataset of 73 plots where at least 150 trees had in‐field ground‐based height measurements, we examined how the number of trees sampled affects the performance of locally derived height–diameter allometries, and evaluated the performance of different methods for sampling trees for height measurement. Using cross‐validation, we found that allometries constructed with just 20 locally measured values could often predict tree height with lower error than regional or climate‐based allometries (mean reduction in prediction error = 0.46 m). The predictive performance of locally derived allometries improved with sample size, but with diminishing returns in performance gains when more than 40 trees were sampled. Estimates of stand‐level biomass produced using local allometries to estimate tree height show no over‐ or under‐estimation bias when compared with biomass estimates using field measured heights. We evaluated five strategies to sample trees for height measurement, and found that sampling strategies that included measuring the heights of the ten largest diameter trees in a plot outperformed (in terms of resulting in local height–diameter models with low height prediction error) entirely random or diameter size‐class stratified approaches. Our results indicate that even limited sampling of heights can be used to refine height–diameter allometries. We recommend aiming for a conservative threshold of sampling 50 trees per location for height measurement, and including the ten trees with the largest diameter in this sample.

Height-diameter input data and R-code to fit and assess height-diameter models, from 'Field methods for sampling tree height for tropical forest biomass estimation' in Methods in Ecology and Evolution

1. Quantifying the relationship between tree diameter and height is a key component of efforts to estimate biomass and carbon stocks in tropical forests. Although substantial site-to-site variation in height-diameter allometries has been documented, the time consuming nature of measuring all tree heights in an inventory plot means that most studies do not include height, or else use generic pan-tropical or regional allometric equations to estimate height. 2. Using a pan-tropical dataset of 73 plots where at least 150 trees had in-field ground-based height measurements, we examined how the number of trees sampled affects the performance of locally-derived height-diameter allometries, and evaluated the performance of different methods for sampling trees for height measurement. 3. Using cross-validation, we found that allometries constructed with just 20 locally measured values could often predict tree height with lower error than regional or climate-based allometries (mean reduction in prediction error = 0.46 m). The predictive performance of locally-derived allometries improved with sample size, but with diminishing returns in performance gains when more than 40 trees were sampled. Estimates of stand-level biomass produced using local allometries to estimate tree height show no over- or under-estimation bias when compared with estimates using measured heights. We evaluated five strategies to sample trees for height measurement, and found that sampling strategies that included measuring the heights of the ten largest diameter trees in a plot outperformed (in terms of resulting in local height-diameter models with low height prediction error) entirely random or diameter size-class stratified approaches. 4. Our results indicate that even remarkably limited sampling of heights can be used to refine height-diameter allometries. We recommend aiming for a conservative threshold of sampling 50 trees per location for height measurement, and including the ten trees with the largest diameter in this sample.

Author Correction: Long-term carbon sink in Borneo’s forests halted by drought and vulnerable to edge effects

The original version of this Article contained an error in the third sentence of the abstract and incorrectly read “Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 year−1 (95% CI 0.14–0.72, mean period 1988–2010) above-ground live biomass”, rather than the correct “Here, using long-term plot monitoring records of up to half a century, we find that intact forests in Borneo gained 0.43 Mg C ha−1 year−1 (95% CI 0.14–0.72, mean period 1988–2010) in above-ground live biomass carbon”. This has now been corrected in both the PDF and HTML versions of the Article.

The ecology of the Asian dipterocarps

The Dipterocarpaceae is the emblematic family of South-east Asian tropical rain forests and many of the seasonally dry forests of continental South and South-east Asia. Whilst dipterocarps are pantropical, with two subfamilies Monotoideae and Pakaraimoideae found in Africa and South America (Maury-Lechon and Curtet 1998), Asian forests that can be dominated by dipterocarps occur from southern India throughout Malesia to New Guinea (Figures 1 and 2). In South-east Asia, the dominance of dipterocarps is evident in most mature forest communities, comprising around 20% of all trees (Slik et al. 2003) and a greater proportion of the larger forest trees; the majority are lowland species rarely found above 1200 m above sea level (Whitmore 1984). In the drier continental forests, dipterocarps make up a greater proportion of the trees but with reduced species diversity (Smitinand et al. 1980; Ashton 2014; Figure 2). Given this ecological predominance, advancing our knowledge of the ecologyof dipterocarp species yields a better understanding of the forests of South and Southeast Asia as a whole (Ashton 1988, 2014; Ghazoul 2016). Dipterocarp trees are influential in the structure and function of Asian forests. They are amongst the tallest trees found in the tropics (Banin et al. 2012; Mongabay 2016a, 2016b), making them important stores of aboveground carbon (Slik et al. 2013), and they are highly productive (Banin et al. 2014). These features, combined with their commercially favourable wood properties, clear straight boles and high stem density in accessible lowland forests meant they became widely exploited for timber in the twentieth century (Sodhi et al. 2004). Indeed, many of the earliest studies of dipterocarps were by silviculturalists (e.g. Brandis 1895; Foxworthy 1932; Symington 1943). The forests of South-east Asia have therefore been shaped by a long management and disturbance history, with slightly less than half of the original forest area now remaining (Stibig et al. 2014). Whilst logging has declined in some parts of Asia, agriculture and the fragmentation associated with land conversion pose further threats to the ecological functioning of remaining forest stands (Wilcove et al. 2013). Nonetheless, in recent years, there has been an increased commitment to restoring forest cover in tropical Asia, and new scientific understanding is required to determine how this might be done successfully (Chazdon 2008; Kettle 2010; Tuck et al. 2016). Evidently, forest restoration in much of Asia will have to rely on successful establishment of dipterocarp communities facilitated by a deeper understanding of their ecology. The Asian dipterocarps are found in India (Antin et al. 2016), Bangladesh, Nepal, Sri Lanka and the Andaman Islands, in the seasonal forests of Thailand (Disyatat et al. 2016), Cambodia (Kenzo et al. 2016b), Vietnam (Nguyen and Baker 2016; Dong et al. 2016a, 2016b), Myanmar, Laos and into southern China. These drier forests are more open, shorter and have markedly lower diversity (Figures 1 and 2). Dipterocarps are found acrossMalesia, throughout theMalay peninsula (Chong et al. 2016; Ng et al. 2016; Yamada et al. 2016; Kenzo et al. 2016a), Sumatra, Java, and in Borneo (Ang et al. 2016; Brearley et al. 2016; Dent and Burslem 2016; Nutt et al. 2016; Saner et al. 2016), they reach their highest species diversity (Figure 2). East of Wallace’s line, in neighbouring Sulawesi, diversity decreases markedly and although dipterocarp ranges extend to New Guinea (Figure 2), dipterocarp species constitute a much smaller component of the forest canopy. The family-level dominance of the dipterocarps in the forests of South and South-east Asia has longfascinated ecologists; the closest tropical ecological equivalents are the stands of Caesalpinioideae subfamily of the Leguminosae found in West Africa and SouthAmerica (Henkel 2003; Peh et al. 2011; Newbery et al. 2013). Dipterocarps have a number of ecological characteristics that all likely contribute, in some way, to their dominance, which play out at various points during their life cycle (Figure 3). These include their non-pioneering yet often fast-growing lifestyle (Thomas and Bazzaz 1999; Banin et al. 2014), mast fruiting (Ashton et al. 1988; Brearley et al. 2007; Numata et al. 2013), wind-dispersed winged fruits (Suzuki and Ashton 1996; Smith et al. 2015) and symbiotic ectomycorrhizal associations (Brearley 2011, 2012) (Figure 3). Under conditions relatively free from exogenous disturbance, these family-wide traits and underlying mechanisms could