Rerouting a major Indonesian mining road to spare nature and reduce development costs

Road-infrastructure projects are expanding rapidly worldwide while penetrating into previously undisturbed forests. In Sumatra, Indonesia, a planned 88-km-long mining road for transporting coal would imperil the Harapan Forest, the island's largest surviving tract of lowland rainforest. Such roads often lead to increased forest encroachment and illegal logging, fires, poaching, and mining. To evaluate the potential impact of the proposed road, we first manually mapped all existing roads inside and around the Harapan Forest using remote-sensing imagery. We then calculated the expected increase in forest loss from three proposed mining-road routes using a metric based on travel-time mapping. Finally, we used least-cost-path analyses to identify new routes for the road that would minimize forest disruption and road-construction costs. We found that road density inside and nearby the Harapan Forest is already 3-4 times higher than official data sources indicate. Based on our analyses, each of the three proposed mining-road routes would lead to 3,000-4,300 ha of additional forest loss from human encroachment plus another 424 ha lost from road construction itself. We propose new routes for the mining road that would result in up to 3,321 ha less forest loss with markedly lower construction costs than any other planned route. We recommend approaches such as ours, using least-cost-path analysis, to minimize the environmental and financial costs of major development projects

Rainforest trees respond to drought by modifying their hydraulic architecture

Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun‐exposed young canopy branches from target species, we found species‐specific systematic variation in hydraulic‐related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought‐affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought‐affected individuals also had lower leaf to twig dry mass ratios, thinner leaves, and more negative pre‐dawn or mid‐day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine‐tune predictions of how future climate changes will affect tropical forests globally

The variation of productivity and its allocation along a tropical elevation gradient: a whole carbon budget perspective

Why do forest productivity and biomass decline with elevation? To address this question, research to date generally has focused on correlative approaches describing changes in woody growth and biomass with elevation. We present a novel, mechanistic approach to this question by quantifying the autotrophic carbon budget in 16 forest plots along a 3300 m elevation transect in Peru. Low growth rates at high elevations appear primarily driven by low gross primary productivity (GPP), with little shift in either carbon use efficiency (CUE) or allocation of net primary productivity (NPP) between wood, fine roots and canopy. The lack of trend in CUE implies that the proportion of photosynthate allocated to autotrophic respiration is not sensitive to temperature. Rather than a gradual linear decline in productivity, there is some limited but nonconclusive evidence of a sharp transition in NPP between submontane and montane forests, which may be caused by cloud immersion effects within the cloud forest zone. Leaf-level photosynthetic parameters do not decline with elevation, implying that nutrient limitation does not restrict photosynthesis at high elevations. Our data demonstrate the potential of whole carbon budget perspectives to provide a deeper understanding of controls on ecosystem functioning and carbon cycling

Structural, physiognomic and above-ground biomass variation in savanna-forest transition zones on three continents - How different are co-occurring savanna and forest formations?

Through interpretations of remote-sensing data and/or theoretical propositions, the idea that forest and savanna represent "alternative stable states" is gaining increasing acceptance. Filling an observational gap, we present detailed stratified floristic and structural analyses for forest and savanna stands located mostly within zones of transition (where both vegetation types occur in close proximity) in Africa, South America and Australia. Woody plant leaf area index variation was related to tree canopy cover in a similar way for both savanna and forest with substantial overlap between the two vegetation types. As total woody plant canopy cover increased, so did the relative contribution of middle and lower strata of woody vegetation. Herbaceous layer cover declined as woody cover increased. This pattern of understorey grasses and herbs progressively replaced by shrubs as the canopy closes over was found for both savanna and forests and on all continents. Thus, once subordinate woody canopy layers are taken into account, a less marked transition in woody plant cover across the savanna-forest-species discontinuum is observed compared to that inferred when trees of a basal diameter > 0.1 m are considered in isolation. This is especially the case for shrub-dominated savannas and in taller savannas approaching canopy closure. An increased contribution of forest species to the total subordinate cover is also observed as savanna stand canopy closure occurs. Despite similarities in canopy-cover characteristics, woody vegetation in Africa and Australia attained greater heights and stored a greater amount of above-ground biomass than in South America. Up to three times as much above-ground biomass is stored in forests compared to savannas under equivalent climatic conditions. Savanna-forest transition zones were also found to typically occur at higher precipitation regimes for South America than for Africa. Nevertheless, consistent across all three continents coexistence was found to be confined to a well-defined edaphic-climate envelope with soil and climate the key determinants of the relative location of forest and savanna stands. Moreover, when considered in conjunction with the appropriate water availability metrics, it emerges that soil exchangeable cations exert considerable control on woody canopy-cover extent as measured in our pan-continental (forest + savanna) data set. Taken together these observations do not lend support to the notion of alternate stable states mediated through fire feedbacks as the prime force shaping the distribution of the two dominant vegetation types of the tropical lands

A test of the 'one-point method' for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis

Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (Vcmax). Estimating this parameter using A–Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration (Asat) measurements, from which Vcmax can be extracted using a 'one-point method'.\ud \ud We used a global dataset of A–Ci curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate Vcmax from Asat via this 'one-point method'.\ud \ud If leaf respiration during the day (Rday) is known exactly, Vcmax can be estimated with an r2 value of 0.98 and a root-mean-squared error (RMSE) of 8.19 μmol m−2 s−1. However, Rday typically must be estimated. Estimating Rday as 1.5% of Vcmax, we found that Vcmax could be estimated with an r2 of 0.95 and an RMSE of 17.1 μmol m−2 s−1.\ud \ud The one-point method provides a robust means to expand current databases of field-measured Vcmax, giving new potential to improve vegetation models and quantify the environmental drivers of Vcmax variation

Global variability in leaf respiration in relation to climate, plant functional types and leaf traits

• Leaf dark respiration (Rdark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. • Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in Rdark. • Area-based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8–28°C). By contrast, Rdark at a standard T (25°C, Rdark25) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark25 at a given photosynthetic capacity (Vcmax25) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark25 values at any given Vcmax25 or [N] were higher in herbs than in woody plants. • The results highlight variation in Rdark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of Rdark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs)

Hidden challenges for conservation and development along the Trans-Papuan economic corridor

The island of New Guinea harbours one of the world’s largest tracts of intact tropical forest, with 41% of its land area in Indonesian Papua (Papua and Papua Barat Provinces). Within Papua, the advent of a 4000-km ‘development corridor’ reflects a national agenda promoting primary-resource extraction and economic integration. Papua, a resource frontier containing vast forest and mineral resources, increasingly exhibits new conservation and development dynamics suggestive of the earlier frontier development phases of other Indonesian regions. Local environmental and social considerations have been discounted in the headlong rush to establish the corridor and secure access to natural resources. Peatland and forest conversion are increasingly extensive within the epicentres of economic development. Deforestation frontiers are emerging along parts of the expanding development corridor, including within the Lorentz World Heritage Site. Customary land rights for Papua’s indigenous people remain an afterthought to resource development, fomenting conditions contrary to conservation and sustainable development. A centralised development agenda within Indonesia underlies virtually all of these changes. We recommend specific actions to address the environmental, economic, and socio-political challenges of frontier development along the Papuan corridor

Dissolved organic carbon concentration and its relationship to electrical conductivity in the waters of a stream in a forested Amazonian blackwater catchment

Background: Dissolved organic carbon (DOC) is a major component of the total carbon in headstreams in Amazonia. Long-term measurements of DOC concentration are difficult to obtain in remote areas of Amazonia. Aims: To take measurements of electrical conductivity (EC) and DOC concentration in a blackwater stream and to determine whether it is possible to make predictions of the DOC concentration in such streams using continuous measurements of EC alone. Methods: In a forested area, DOC concentration and EC were measured in groundwater along a topographic gradient at weekly intervals over a period of 8 months, and in stream water at half-hourly intervals over 2 years. Results: Strong and positive relationships between EC and DOC concentration were found in stream water in wet (r 2 = 0.99) and dry periods (r 2 = 0.97). It was thus possible to produce two equations that could be used to derive DOC concentration values from continuous measurements of EC. Both DOC concentration and EC varied according to the discharge, indicating that the largest amounts of DOC are transported during the wet season. The amount of carbon exported annually was estimated to be between 2.5% and 5% of the sink estimated by the eddy covariance method. Conclusions: The relationship found offers an opportunity for a comprehensive assessment of DOC concentration in blackwater catchments based on low-cost and simple EC measurements, rather than on expensive and complex estimates of DOC concentration. © 2014 Copyright 2013 Botanical Society of Scotland and Taylor & Francis

Rainforest trees respond to drought by modifying their hydraulic architecture

Increased drought is forecasted for tropical regions, with severe implications for the health and function of forest ecosystems. How mature forest trees will respond to water deficit is poorly known. We investigated wood anatomy and leaf traits in lowland tropical forest trees after 24 months of experimental rainfall exclusion. Sampling sun-exposed young canopy branches from target species, we found species-specific systematic variation in hydraulic-related wood anatomy and leaf traits in response to drought stress. Relative to controls, drought-affected individuals of different tree species variously exhibited trait measures consistent with increasing hydraulic safety. These included narrower or less vessels, reduced vessel groupings, lower theoretical water conductivities, less water storage tissue and more abundant fiber in their wood, and more occluded vessels. Drought-affected individuals also had thinner leaves, and more negative pre-dawn or mid-day leaf water potentials. Future studies examining both wood and leaf hydraulic traits should improve the representation of plant hydraulics within terrestrial ecosystem and biosphere models, and help fine-tune predictions of how future climate changes will affect tropical forests globally