Dirk Hölscher's research while affiliated with Georg-August-Universität Göttingen and other places

Publications (156)

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How to enhance biodiversity in monoculture-dominated landscapes is a key sustainability question that requires considering the spatial organization of ecological communities (beta diversity). Here, we experimentally tested if increasing landscape heterogeneity - through tree islands - is a suitable landscape restoration strategy when aiming to enha...
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Rubber monoculture plantations are expanding but may cause environmental problems, and rubber-based agroforestry can provide ways of more environmentally friendly rubber cultivation. The general objective of this study was to investigate plant soil water uptake in different rubber agroforestry systems with water stable isotopes (δ²H and δ¹⁸O), and...
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Resolving ecological-economic trade-offs between biodiversity and yields is a key challenge when addressing the biodiversity crisis in tropical agricultural landscapes. Here, we focused on the relation between seven different taxa (trees, herbaceous plants, birds, amphibians, reptiles, butterflies, and ants) and yields in vanilla agroforests in Mad...
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Trees in agroforestry systems provide multiple ecological and economic functions. Smallholder vanilla agroforests include shade trees common across agroforestry systems, and small-statured support trees carrying the vanilla vine. Support trees have received little scientific attention so far. The objectives of our study were to assess the diversity...
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Significance Finding entry points where policy has strong leverage to transform land systems for people and nature is pivotal. We develop an innovative framework to identify and evaluate such leverage points along land-use trajectories that account for path dependency. Applied to the biodiversity hotspot Madagascar, the framework reveals three leve...
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In India, short-rotation plantations have increasingly been promoted over the last decades in response to altered forest management policy and increased wood demand. Understanding how short-rotation forest species coordinate fast growth with water demand and carbon investment will help improving management decisions. We investigated the intra-speci...
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1In India, short-rotation plantations have increasingly been promoted over the last decades in 2 response to altered forest management policy and increased wood demand. Understanding how 3 short-rotation forest species coordinate fast growth with water demand and carbon investment 4 will help improving management decisions. 5
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Farmland tree cultivation is considered an important option for enhancing wood production. In South India, the native leaf-deciduous tree species Melia dubia is popular for short-rotation plantations. Across a rainfall gradient from 420 to 2170 mm year-1 , we studied 186 farmland wood-lots between one and nine years in age. The objectives were to i...
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Microclimate and Land Surface Temperature (LST) are important analytical variables used to understand complex oil palm agroforestry systems and their effects on biodiversity and ecosystem functions. In order to examine experimental effects of tree species richness (0, 1, 2, 3 or 6), plot size (25 m², 100 m², 400 m², 1600 m²) and stand structural co...
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Agroforestry options such as mixed-species tree planting and natural regeneration in oil palm plantations may alleviate negative effects of forest loss on biodiversity and ecosystem functioning. The effects of agroforestry on microclimate and land surface temperatures (LST) remain largely unknown despite their central role in controlling abiotic an...
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Forests and tree-dominated land uses store large amounts of carbon stocks in plant biomass. However, anthropogenic changes in land use and land cover decrease tree cover and associated carbon stocks. Agroforestry has the potential to maintain or restore carbon in plant biomass but the amount will be influenced by various factors that may include la...
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Leaf stoichiometry and its biogeography play vital roles in nutrient cycling of plant communities. To understand the potential drivers of leaf stoichiometry in karst ecosystems, we measured leaf morphological traits (dry mass content (DM), specific leaf area (SLA)), and biochemical traits (C, N, P, K and Ca stoichiometry) of 53 species of different...
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Premise: Leaf mass (M) and lamina surface area (A) are important functional traits reported to obey a scaling relationship called "diminishing returns" (i.e., M ∝ Aα>1 ). Previous studies have focused primarily on eudicots and ignored whether the age of leaves affects the numerical value of the scaling exponent (i.e., α). Methods: The effect of...
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Agroforestry can contribute to an increase in tree cover in historically forested tropical landscapes with associated gains in biodiversity and ecosystem functioning, but only if established on open land instead of underneath a forest canopy. However, declines in yields with increasing shade are common across agroforestry crops, driving shade-tree...
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In tropical landscapes dominated by oil palm monocultures, scattered trees can contribute to biodiversity, regulate diverse ecosystem functions and deliver goods and services. However, basic quantitative information about such trees is often lacking. The objectives of our study were to identify the landscape-wide density and distribution patterns o...
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Forests and tree-dominated land uses store large amounts of carbon stocks in plant biomass. However, anthropogenic changes in land use and land cover decrease tree cover and associated carbon stocks. Agroforestry has the potential to maintain or restore carbon in plant biomass but the amount will be influenced by various factors that may include la...
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Question: In human-modified tropical landscapes, agroforestry is considered a promising land use to reconcile biodiversity conservation with production goals. The role of agroforests regarding conservation may be strongly influenced by land-use history; however, few studies have explicitly investigated this. We therefore tested the importance of la...
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For the assessment of evapotranspiration, near-surface airborne thermography offers new opportunities for studies with high numbers of spatial replicates and in a fine spatial resolution. We tested drone-based thermography and the subsequent application of the DATTUTDUT energy balance model using the widely accepted eddy covariance technique as a r...
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The efficiency of the water transport system in trees sets physical limits to their productivity and water use. Although the coordination of carbon assimilation and hydraulic functions has long been documented, the mutual inter-relationships between wood anatomy, water use and productivity have not yet been jointly addressed in comprehensive field...
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Plant transpiration is a key element in the hydrological cycle. Widely used methods for its assessment comprise sap flux techniques for whole-plant transpiration and porometry for leaf stomatal conductance. Recently emerging approaches based on surface temperatures and a wide range of machine learning techniques offer new possibilities to quantify...
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The scaling relationship between either leaf dry or fresh mass (M) and surface area (A) can reflect the photosynthetic potential and efficiency of light harvesting in different broad-leaved plants. In growing leaves, lamina area expansion is typically finished before the completion of leaf biomass accumulation, thereby affecting the M vs. A scaling...
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The rapid expansion of rubber and oil palm plantations in Jambi Province, Sumatra, Indonesia, is associated with large-scale deforestation and the impairment of many ecosystem services. According to villagers' observations, this land use change has, together with climate change, led to an increase in the magnitude and frequency of river flood event...
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Agroforestry can contribute to an increase in tree cover in historically forested tropical landscapes with associated gains in biodiversity and ecosystem functioning, but only if established on open land instead of inside forest. However, trade-offs between shade and crop yields are common across many agroforestry crops, driving shade-tree loss in...
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Agroforestry is widely promoted as a potential solution to address multiple UN Sustainable Development Goals, including Zero Hunger, Responsible Consumption and Production, Climate Action, and Life on Land. Nonetheless, agroforests in the tropics often result from direct forest conversions, displacing rapidly vanishing and highly biodiverse forests...
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Moso bamboo is widespread in natural forests and is cultivated over large areas in China. This study investigated how climate controls its distribution, about which little is known. We collected moso bamboo presence-absence data from 674 sites with long-term climate data in Mainland China. Generalized additive models that included location and clim...
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Abstract. For the assessment of evapotranspiration, near-surface airborne thermography offers new opportunities for studies with high numbers of spatial replicates and in a fine spatial resolution. We tested drone-based thermography and the subsequent application of three energy balance models (DATTUTDUT, TSEB-PT, DTD) using the widely accepted edd...
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As the most widely distributed giant running bamboo species in China, Moso bamboo (Phyllostachys edulis) can accomplish both development of newly sprouted culms and leaf renewal of odd-year-old culms within a few months in spring. The two phenological events in spring may together change water distribution among culms in different age categories wi...
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Evapotranspiration (ET) is a central flux in the hydrological cycle. Various approaches to compute ET via energy balance models exist, but their handling is often complex and challenging. We developed QWaterModel as an easy-to-use tool to make ET predictions available to broader audiences. QWaterModel is based on the DATTUTDUT energy balance model...
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Land-use transitions can enhance the livelihoods of smallholder farmers but potential economic-ecological trade-offs remain poorly understood. Here, we present an interdisciplinary study of the environmental, social and economic consequences of land-use transitions in a tropical smallholder landscape on Sumatra, Indonesia. We find widespread biodiv...
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Key message A highly significant and positive scaling relationship between bamboo leaf dry mass and leaf surface area was observed; leaf shape (here, represented by the quotient of leaf width and length) had a significant influence on the scaling exponent of leaf dry mass vs. area. ContextThe scaling of leaf dry mass vs. leaf area is important for...
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The leaves of vines exhibit a high degree of variability in shape, from simple oval to highly dissected palmatifid leaves. However, little is known about the extent of leaf bilateral symmetry in vines, how leaf perimeter scales with leaf surface area, and how this relationship depends on leaf shape. We studied 15 species of vines and calculated (i)...
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Tropical rainforests comprise complex 3D structures and encompass heterogeneous site conditions; their transpiration contributes to climate regulation. The objectives of our study were to test the relationship between tree water use and crown metrics and to predict spatial variability of canopy transpiration across sites. In a lowland rainforest of...
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Complementary use of resources is considered a strong driver of enhanced performance in mixed-species assemblages. In income-producing agroforestry systems, economically valuable species will ideally benefit from resource partitioning. In agroforests in southern India, we assessed soil water uptake depths of coffee and different shade tree species...
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Oil palm plantations are intensively managed agricultural systems that increasingly dominate certain tropical regions. Oil palm monocultures have been criticized because of their reduced biodiversity compared to the forests they historically replaced, and because of their negative impact on soils, water, and climate. We experimentally test whether...
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Bamboo water transport comprises the pathway rhizomes-culms-leaves as well as transfer among culms via connected rhizomes. We assessed bamboo water transport in three big clumpy bamboo species by deuterium tracing. The tracer was injected into the base of established culms, and water samples were collected from leaves of the labeled culms and from...
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Bamboo culms are connected to neighboring culms via rhizomes, which enable resource exchange between culms. We assessed water transfer between established and neighboring, freshly sprouted culms by thermal dissipation probes (TDP) inserted into culms and the connecting rhizome. During the early phase of sprouting, highest sap flux densities in fres...
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1.Large‐scale conversion of tropical forests into oil palm monocultures has led to dramatic losses of biodiversity and ecosystem functions. While ecological restoration is urgently needed in many oil palm landscapes, there is a lack of scientific knowledge of sustainable management strategies. 2.We established experimental tree islands of varying s...
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Transpiration at the stand level is often estimated from water use measurements on a limited number of plants and then scaled up by predicting the remaining plants of a stand by plant size related variables. Today, drone‐based methods offer new opportunities for plant size assessments. We tested crown variables derived from drone‐based photogrammet...
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Aboveground tree architecture is neither fully deterministic nor random. It is likely the result of mechanisms that balance static requirements and light‐capturing efficiency. Here, we used terrestrial laser scanning data to investigate the relationship between tree architecture, here addressed using the box‐dimension (Db), and the architectural be...
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Since water balance is considered as a major constituent in the environmental issue for sustainability of oil palm production system, particularly as significant biomass contributor, runoff water as water loss and infiltrated water for oil palm consumption play the most significant role for the explanation of water status and should be exposed comp...
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Oil palm monocultures are highly productive, but there are widespread negative impacts on biodiversity and ecosystem functions. Some of these negative impacts might be mitigated by mixed-species tree interplanting to create agroforestry systems, but there is little experience with the performance of trees planted in oil palm plantations. We studied...
Presentation
Cash crops farmed in agroforestry systems can be an economically attractive opportunity for farmers that are potentially ecologically sustainable alleviating negative impacts on biodiversity and ecosystem functions. Whether such a win-win situation can be realised is, however, highly context-dependent. Here, we study the impacts of vanilla agrofore...
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Land-use change has a strong impact on carbon, energy and water fluxes and its effect is particularly pronounced in tropical regions. Uncertainties exist in the prediction of future land-use change impacts on these fluxes by land surface models due to scarcity of suitable measured data for parametrization and poor representation of key biogeochemic...
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Trees providing non-timber forest products (NTFPs) are valuable forest resources, and their management can support conservation objectives. We analyzed the abundance of tree species providing NTFPs, recognized by local H’mong people, in both the strictly protected core zone and the low-intensity forest use buffer zone in north-western Vietnam. We i...
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Tropical dry forests are composed of tree species with different drought coping strategies and encompass heterogeneous site conditions. Actual water use will be controlled by soil moisture availability. In a premontane dry forest of southern Ecuador, tree water use patterns of four tree species of different phenologies were studied along an elevati...
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TreeDivNet is the largest network of biodiversity experiments worldwide, but needs to expand. We encourage colleagues to establish new experiments on the relation between tree species diversity and forest ecosystem functioning, and to make use of the platform for collaborative research.
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Key message Water content fluctuations in bamboo culms significantly influence sap flux measurements with thermal dissipation probes, as indicated and quantified by experimental, monitoring and model analyses. Abstract Bamboos and other plants may substantially rely on stem water storage for transpiration. Fluctuations in wood water content (θwood...
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Background and Aims To increase yield, cacao is planted increasingly in unshaded monocultures, replacing a more traditional cultivation under shade. We investigated how shade tree cover and species diversity affect the root system and its dynamics. Methods In a replicated study in Sulawesi (Indonesia), we studied the fine and coarse root system do...
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Cocoa is a major trade commodity that is seeing increasing demand, but also climate-related yield declines1 . There has been an ongoing discussion whether both, the effective adaptation of plantations to climate change and a long term increase of cocoa yields, can only be achieved with shaded agroforestry or also with full-sun monocultures2 . Abdul...
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Background Fujian cypress (Fokienia hodginsii) is a highly valued but endangered tree species. The Ta Xua Nature Reserve in Vietnam is one of its main conservation centers. This nature reserve consists of a fully protected core zone, a buffer zone in which low intensity forest use is permitted, and a forest restoration zone in which forest regenera...
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Rubber tree mono-cultural plantations are expanding. Also, there is an increasing search for 'green' rubber production. Rubber tree cultivation in stands with admixed, spontaneously established native trees, referred to as jungle rubber, has a long tradition on Sumatra. For rubber tree monocultures on mainland Asia, concerns have been raised becaus...
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The expansion of rubber cultivation in Southeast Asia raises concerns about the integrity of the hydrological cycle. From mainland Asia, high evapotranspiration from rubber plantations was reported. Our study was conducted in the Sumatran lowlands (Indonesia), where rubber is grown by small-holders under maritime climate. We assessed patterns of wa...
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Oil palm is rapidly expanding, particularly in Indonesia, but there is still very limited information on water and energy fluxes in oil palm plantations, and on how those are affected by varying environmental conditions or plantation age. In our study, we measured turbulent fluxes of sensible (H) and latent (LE) heat and gross primary productivity...
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Oil palm and rubber plantations extend over large areas and encompass heterogeneous site conditions. In periods of high rainfall, plants in valleys and at riparian sites are more prone to flooding than plants at elevated topographic positions. We asked to what extent topographic position and flooding affect oil palm and rubber tree water use patter...
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Oil palm cultivation is expanding rapidly across the globe. Current discussions on ecological impacts focus on the destruction of forests, greenhouse gas emissions and biodiversity loss. Little attention has been paid to concerns that oil palm expansion has severe impacts on local water resources.