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  • Publication
    Accès libre
    Transformation scenarios towards multifunctional landscapes: A multi-criteria land-use allocation model applied to Jambi Province, Indonesia
    (2024)
    Volker von Groß
    ;
    Kibrom T. Sibhatu
    ;
    Alexander Knohl
    ;
    Matin Qaim
    ;
    Edzo Veldkamp
    ;
    Dirk Hölscher
    ;
    Zemp, Clara 
    ;
    Marife D. Corre
    ;
    Ingo Grass
    ;
    Sebastian Fiedler
    ;
    Christian Stiegler
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Kai Husmann
    ;
    Carola Paul
    In tropical regions, shifting from forests and traditional agroforestry to intensive plantations generates conflicts between human welfare (farmers' demands and societal needs) and environmental protection. Achieving sustainability in this transformation will inevitably involve trade-offs between multiple ecological and socioeconomic functions. To address these trade-offs, our study used a new methodological approach allowing the identification of transformation scenarios, including theoretical landscape compositions that satisfy multiple ecological functions (i.e., structural complexity, microclimatic conditions, organic carbon in plant biomass, soil organic carbon and nutrient leaching losses), and farmers needs (i.e., labor and input requirements, total income to land, and return to land and labor) while accounting for the uncertain provision of these functions and having an actual potential for adoption by farmers. We combined a robust, multi-objective optimization approach with an iterative search algorithm allowing the identification of ecological and socioeconomic functions that best explain current land-use decisions. The model then optimized the theoretical land-use composition that satisfied multiple ecological and socioeconomic functions. Between these ends, we simulated transformation scenarios reflecting the transition from current land-use composition towards a normative multifunctional optimum. These transformation scenarios involve increasing the number of optimized socioeconomic or ecological functions, leading to higher functional richness (i.e., number of functions). We applied this method to smallholder farms in the Jambi Province, Indonesia, where traditional rubber agroforestry, rubber plantations, and oil palm plantations are the main land-use systems. Given the currently practiced land-use systems, our study revealed short-term returns to land as the principal factor in explaining current land-use decisions. Fostering an alternative composition that satisfies additional socioeconomic functions would require minor changes ("low-hanging fruits"). However, satisfying even a single ecological indicator (e.g., reduction of nutrient leaching losses) would demand substantial changes in the current land-use composition ("moonshot"). This would inevitably lead to a profit decline, underscoring the need for incentives if the societal goal is to establish multifunctional agricultural landscapes. With many oil palm plantations nearing the end of their production cycles in the Jambi province, there is a unique window of opportunity to transform agricultural landscapes.
  • Publication
    Accès libre
    Combining planting trees and natural regeneration promotes long-term structural complexity in oil palm landscapes
    (2024)
    Tatsuro Kikuchi
    ;
    Dominik Seidel
    ;
    Martin Ehbrecht
    ;
    Zemp, Clara 
    ;
    Fabian Brambach
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Dirk Hölscher
    ;
    Holger Kreft
    ;
    Gustavo Brant Paterno
    Vegetation structural complexity has been identified as a vital factor for forest ecosystem function, stability, and resilience. However, agricultural land with much reduced structural complexity has largely replaced natural forests in the tropics. Therefore, restoring structural complexity in large-scale plantation monocultures by introducing agroforestry systems may counteract the loss of biodiversity and ecosystem functions. However, we still have limited knowledge of how the structural complexity of agroforests develops under different restoration treatments. We established a large-scale biodiversity enrichment experiment in a conventional monoculture oil palm plantation in Sumatra, Indonesia. In this experiment, agroforests were implemented by planting clusters of native trees (“tree islands”) within the oil palm plantation, systematically varying initially planted tree richness ranging from 0–6 (0 corresponding to natural regeneration only) and plot area (25–1600 m2). We tested the effect of the experimental treatments on nine years of the development of local structural complexity using a stand structural complexity index (SSCI) derived from terrestrial laser scanning. We found that tree planting and natural regeneration treatments promoted structural complexity by creating denser and more complex vegetation structures. Plots with a tree planting treatment tended to show greater structural complexity than plots with natural regeneration only. However, during the study period, oil palms still dominated heights, and the temporal change in structural complexity among plots with or without a tree planting treatment did not differ. As for plot area, our results indicate that structural complexity looking from the center of plots did not necessarily depend on the area during the study period, and even small tree islands can increase local structural complexity in a monoculture oil palm plantation. Initially planted tree richness did not significantly affect the development of structural complexity. Nine years after establishment, not planted trees but regenerated woody plants strongly positively affected vegetation density and structural complexity. Our findings highlight that sustaining vegetation density below oil palm canopies is a key strategy to increase the structural complexity of oil palm landscapes.
  • Publication
    Accès libre
    Comparing airborne and terrestrial LiDAR with ground-based inventory metrics of vegetation structural complexity in oil palm agroforests
    (2024)
    Montoya-Sánchez, Vannesa 
    ;
    Nicolò Camarretta
    ;
    Martin Ehbrecht
    ;
    Michael Schlund
    ;
    Gustavo Brant Paterno
    ;
    Dominik Seidel
    ;
    Nathaly Guerrero-Ramírez
    ;
    Fabian Brambach
    ;
    Dirk Hölscher
    ;
    Holger Kreft
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Zemp, Clara 
    Vegetation structural complexity is an important component of forest ecosystems, influencing biodiversity and functioning. Due to the heterogeneous distribution of vegetation elements, structural complexity underpins ecological dynamics, species composition, microclimate, and habitat diversity. Field measurements and Light Detection and Ranging (LiDAR) data, such as airborne (ALS) and terrestrial (TLS), can assess structural characteristics of forest and agroforestry systems at various spatial scales. This assessment is urgently needed for monitoring ecosystem restoration in degraded lands (e.g., in oil palm landscapes), where it is not well-known how structural measures derived from these different approaches relate to each other. Here, we compared the degree of correlation between individual and multivariate datasets of vegetation structural complexity metrics derived from ALS, TLS, and ground-based inventory approaches. The study was conducted in a 140 ha oil palm monoculture, enriched with 52 plots in the form of tree islands representing agroforestry systems of varying sizes and planted diversity levels in Sumatra, Indonesia. Our datasets comprised 25 ALS, five TLS, and nine ground-based inventory metrics. We studied correlations among metrics related to traditional stand summary, heterogeneity, and vertical and horizontal stand structure. We used principal component analysis for data dimensionality reduction, correlation analysis to quantify the strength of relationships between metrics, and Procrustes analysis to investigate the agreement between datasets. Significant correlations were found between ALS and TLS metrics for canopy density (r = 0.79) and maximum tree height (r = 0.58) and between ALS and ground-based inventory measures of stand heterogeneity and height diversity (r between 0.60 and −0.63). Further, we observed significant agreements between the ordinations of multivariate datasets (r = 0.56 for ALS − TLS; and r = 0.46 for ALS – ground-based inventory). Our findings underline the ability of ALS to capture structural complexity patterns, especially for canopy gap dynamics and vegetation height metrics, as captured by TLS, and for measures of heterogeneity and vertical structure as captured by ground-based inventories. Our study highlights the strength of each approach and underscores the potential of integrating ALS and TLS with ground-based inventories for a comprehensive characterization of vegetation structure in complex agroforestry systems, which can provide guidance for their management and support ecosystem restoration monitoring efforts.
  • Publication
    Accès libre
    Tree islands enhance biodiversity and functioning in oil palm landscapes
    (2023)
    Zemp, Clara 
    ;
    Nathaly Guerrero-Ramirez
    ;
    Fabian Brambach
    ;
    Kevin Darras
    ;
    Ingo Grass
    ;
    Anton Potapov
    ;
    Alexander Röll
    ;
    Isabelle Arimond
    ;
    Johannes Ballauff
    ;
    Hermann Behling
    ;
    Dirk Berkelmann
    ;
    Siria Biagioni
    ;
    Damayanti Buchori
    ;
    Dylan Craven
    ;
    Rolf Daniel
    ;
    Oliver Gailing
    ;
    Florian Ellsäßer
    ;
    Riko Fardiansah
    ;
    Nina Hennings
    ;
    Bambang Irawan
    ;
    Watit Khokthong
    ;
    Valentyna Krashevska
    ;
    Alena Krause
    ;
    Johanna Kückes
    ;
    Kevin Li
    ;
    Hendrik Lorenz
    ;
    Mark Maraun
    ;
    Miryam Sarah Merk
    ;
    Carina C. M. Moura
    ;
    Yeni A. Mulyani
    ;
    Gustavo B. Paterno
    ;
    Herni Dwinta Pebrianti
    ;
    Andrea Polle
    ;
    Di Ajeng Prameswari
    ;
    Lena Sachsenmaier
    ;
    Stefan Scheu
    ;
    Dominik Schneider
    ;
    Fitta Setiajiati
    ;
    Christina Ani Setyaningsih
    ;
    Leti Sundawati
    ;
    Teja Tscharntke
    ;
    Meike Wollni
    ;
    Dirk Hölscher
    ;
    Holger Kreft
    In the United Nations Decade on Ecosystem Restoration1, large knowledge gaps persist on how to increase biodiversity and ecosystem functioning in cash crop-dominated tropical landscapes2. Here, we present findings from a large-scale, 5-year ecosystem restoration experiment in an oil palm landscape enriched with 52 tree islands, encompassing assessments of ten indicators of biodiversity and 19 indicators of ecosystem functioning. Overall, indicators of biodiversity and ecosystem functioning, as well as multidiversity and ecosystem multifunctionality, were higher in tree islands compared to conventionally managed oil palm. Larger tree islands led to larger gains in multidiversity through changes in vegetation structure. Furthermore, tree enrichment did not decrease landscape-scale oil palm yield. Our results demonstrate that enriching oil palm-dominated landscapes with tree islands is a promising ecological restoration strategy, yet should not replace the protection of remaining forests.
  • Publication
    Accès libre
    Landscape heterogeneity and soil biota are central to multi-taxa diversity for oil palm landscape restoration
    (2023)
    Montoya-Sánchez, Vannesa 
    ;
    Holger Kreft
    ;
    Isabelle Arimond
    ;
    Johannes Ballauff
    ;
    Dirk Berkelmann
    ;
    Fabian Brambach
    ;
    Rolf Daniel
    ;
    Ingo Grass
    ;
    Jes Hines
    ;
    Dirk Hölscher
    ;
    Bambang Irawan
    ;
    Alena Krause
    ;
    Andrea Polle
    ;
    Anton Potapov
    ;
    Lena Sachsenmaier
    ;
    Stefan Scheu
    ;
    Leti Sundawati
    ;
    Teja Tscharntke
    ;
    Zemp, Clara 
    ;
    Nathaly Guerrero-Ramírez
    Enhancing biodiversity in monoculture-dominated landscapes is a key sustainability challenge that requires considering the spatial organization of ecological communities (beta diversity). Here, we tested whether increasing landscape heterogeneity, through establishing 52 tree islands in an oil-palm landscape, is a suitable restoration strategy to enhance the diversity of six taxa (multi-taxa diversity). Further, we elucidated whether patterns in the spatial distribution of above- and below-ground taxa are related, and their role in shaping multi-taxa beta diversity. After five years, islands enhanced diversity at the landscape scale by fostering unique species (turnover). Partial correlation networks revealed that dissimilarity, in vegetation structural complexity and soil conditions, impacts multi-taxa beta diversity and turnover. In addition, soil fauna, bacteria, and fungi were more strongly associated with the overall community than aboveground taxa. Thus, strategies aiming to enhance multi-taxa diversity should consider the central role of landscape heterogeneity and soil biota.
  • Publication
    Accès libre
    Microclimate and land surface temperature in a biodiversity enriched oil palm plantation
    (2021)
    Laura Somenguem Donfack
    ;
    Alexander Röll
    ;
    Florian Ellsäßer
    ;
    Martin Ehbrecht
    ;
    Bambang Irawan
    ;
    Dirk Hölscher
    ;
    Alexander Knohl
    ;
    Holger Kreft
    ;
    Eduard J. Siahaan
    ;
    Leti Sundawati
    ;
    Christian Stiegler
    ;
    Zemp, Clara 
    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 and biotic factors and in buffering climate at a larger scale. We assessed spatial and temporal microclimate and LST variability in a biodiversity enrichment experiment, in which tree islands have been planted in an oil palm plantation in Sumatra (Indonesia). Four years after establishment of the experiment, we measured microclimate and LST using mini microclimate sensors and drone-recorded thermal images. We examined 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 complexity on microclimate and LST. Diurnal patterns showed ambient air temperature peaks and relative humidity (RH) minima at 3 pm, whereas diurnal soil temperatures peaked around 6 pm. The lowest LST were observed from oil palm canopy leaves and the highest from bare soils and understorey vegetation (including trees). Spatial and temporal ranges of ambient air temperature were smaller than LST ranges, and average ambient air temperature and LST were positively correlated. Tree species diversity had no overall significant effect neither on microclimate nor LST, but humidity was higher in planted tree islands compared to natural regeneration only. Smaller plots were characterized by higher mean air, soil and LST, compared to larger plots. Structurally complex plots were associated with low mean and maximum values of ambient air temperature, soil temperature and LST and high mean and minimum RH. Still, conditions were hotter and drier in several experimental plots compared to conventional oil palm plantations, considering a higher transpiration in the latest. We conclude that stand structural complexity and tree island size control microclimate and LST in the experimental oil palm agroforests, but alleviating the harsh microclimate conditions in oil palm plantations might take longer to occur.
  • Publication
    Accès libre
    Dataset on microclimate and drone-based thermal patterns within an oil palm agroforestry system
    (2021)
    Laura Somenguem Donfack
    ;
    Alexander Röll
    ;
    Florian Ellsäßer
    ;
    Martin Ehbrecht
    ;
    Bambang Irawan
    ;
    Dirk Hölscher
    ;
    Alexander Knohl
    ;
    Holger Kreft
    ;
    Eduard J. Siahaan
    ;
    Leti Sundawati
    ;
    Christian Stiegler
    ;
    Zemp, Clara 
    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 complexity on microclimate and Land Surface Temperature, related data were collected following a strict design. The experiment was carried out in the Jambi province, in Sumatra (Indonesia), as part of the collaborative project EFForTS [Ecological and Socioeconomic Functions of Tropical Lowland Rainforest Transformation Systems]. Microclimate data collected using miniaturized data loggers combined with drone-based thermal data were considered within an oil palm plantation enriched with six target tree species. The timeframe considered for data analysis was 20th September 2017 to 26th September 2017. The experiment data can be used for comparison with data from conventional oil palm agroforestry systems in the tropics. They can more specifically be used as reference to assess microclimate and Land Surface Temperature patterns within similar agroforestry systems.
  • Publication
    Accès libre
    Mixed-species tree plantings enhance structural complexity in oil palm plantations
    (2019)
    Zemp, Clara 
    ;
    Martin Ehbrecht
    ;
    Dominik Seidel
    ;
    Christian Ammer
    ;
    Dylan Craven
    ;
    Joshua Erkelenz
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Dirk Hölscher
    ;
    Holger Kreft
    Conversion of structurally complex rainforests into simplified oil palm monocultures leads to dramatic losses of biodiversity and ecosystem functioning. To alleviate negative ecological impacts, enrichment with native tree species may rapidly restore structural complexity in existing oil palm plantations. However, the mechanisms underlying the recovery of structural complexity in mixed-species tree plantings remain poorly understood. We measured structural complexity from terrestrial laser scanning in a biodiversity enrichment experiment with multiple tree species planted in an oil palm monoculture, forming agroforestry plots of varying tree species diversity and plot size. We find that three years after tree planting, structural complexity in oil palm increased by one third, representing 25% of the increase needed to restore the structural complexity of tropical forests. Changes in structural complexity were associated with denser and more complex filling of three-dimensional space, whereas vertical stratification was mainly influenced by oil palm. Furthermore, structural complexity increased with tree species diversity in the agroforestry plots. This relationship was mainly due the presence of well-performing species that contributed to higher levels of structural complexity. However, interactions among multiple species independently from the species identity were also detected. Finally, increasing plot size had a positive effect on a scale-independent measure of structural complexity. Our results provide evidence that planting multiple tree species in large agroforestry plots is a suitable strategy to rapidly enhance structural complexity in oil palm plantations.
  • Publication
    Accès libre
    Drone-Based Assessment of Canopy Cover for Analyzing Tree Mortality in an Oil Palm Agroforest
    (2019)
    Watit Khokthong
    ;
    Zemp, Clara 
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Holger Kreft
    ;
    Dirk Hölscher
    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 a biodiversity enrichment experiment in the lowlands of Sumatra that was established in a 6- to 12-year-old oil palm plantation by planting six tree species in different mixtures on 48 plots. Three years after tree planting, canopy cover was assessed by drone-based photogrammetry using the structure-from-motion technique. Drone-derived canopy cover estimates were highly correlated with traditional ground-based hemispherical photography along the equality line, indicating the usefulness and comparability of the approach. Canopy cover was further partitioned between oil palm and tree canopies. Thinning of oil palms before tree planting created a more open and heterogeneous canopy cover. Oil palm canopy cover was then extracted at the level of oil palms and individual trees and combined with ground-based mortality assessment for all 3,819 planted trees. For three tree species (Archidendron pauciflorum, Durio zibethinus, and Shorea leprosula), the probability of mortality during the year of the study was dependent on the amount of oil palm canopy cover. We regard the drone-based method for deriving and partitioning spatially explicit information as a promising way for many questions addressing canopy cover in ecological applications and the management of agroforestry systems.
  • Publication
    Accès libre
    Tree performance in a biodiversity enrichment experiment in an oil palm landscape
    (2019)
    Zemp, Clara 
    ;
    Anne Gérard
    ;
    Dirk Hölscher
    ;
    Christian Ammer
    ;
    Bambang Irawan
    ;
    Leti Sundawati
    ;
    Miriam Teuscher
    ;
    Holger Kreft
    ;
    Marney Isaac
    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 sizes (25 m2 to 1,600 m2) and diversity levels (1, 2, 3 and 6 species) in an oil palm plantation in Sumatra, Indonesia. Six native multi‐purpose tree species including Archidendron pauciflorum (Jengkol), Durio zibethinus (Durian), Parkia speciosa (Petai), Shorea leprosula (Meranti), Peronema canescens (Sungkai) and Dyera polyphylla (Jelutung) were planted between living and felled oil palms. Here, we analyse the controlling factors of tree growth and survival during the first 4 years at the level of local neighbourhood and tree island. 3. We found a significant effect of diversity levels on tree productivity, that is, basal area was higher in multi‐species than in single‐species tree islands. This overyielding was attributed to enhanced tree growth, while mortality had no effect. In the local neighbourhood, tree species richness had a positive effect on tree growth during the first year only, indicating that selection and dominance of well‐performing species at high level of diversity are most likely driving overyielding. 4. Trees grew better away from living oil palms, suggesting tree‐palm competition. Proximity to felled oil palms increased growth especially during the first years, during which the planted trees might have benefited from the additional available space and resources. Despite positive edge effects from the conventional oil palm management in the surrounding, tree island size had an overall positive effect on tree growth. 5. Synthesis and applications. We planted native trees in an oil palm landscape following a tree island pattern. The establishment success differed widely among the six planted species. The selection of particular species is a decisive factor to foster a positive relationship between diversity and tree growth. Planting larger tree islands (e.g. 1,600 square metres) is a better option to enhance tree growth, but tree‐palm competition implies a trade‐off between tree growth and palm oil production in the tree islands.