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  • Publication
    Accès libre
    Land-use trajectories for sustainable land system transformations: Identifying leverage points in a global biodiversity hotspot
    (2022)
    Dominic Andreas Martin
    ;
    Fanilo Andrianisaina
    ;
    Thio Rosin Fulgence
    ;
    Kristina Osen
    ;
    Anjaharinony Andry Ny Aina Rakotomalala
    ;
    Estelle Raveloaritiana
    ;
    Marie Rolande Soazafy
    ;
    Annemarie Wurz
    ;
    Rouvah Andriafanomezantsoa
    ;
    Harilala Andriamaniraka
    ;
    Aristide Andrianarimisa
    ;
    Jan Barkmann
    ;
    Saskia Dröge
    ;
    Ingo Grass
    ;
    Nathaly Guerrero-Ramirez
    ;
    Hendrik Hänke
    ;
    Dirk Hölscher
    ;
    Bakolimalala Rakouth
    ;
    Hery Lisy Tiana Ranarijaona
    ;
    Romual Randriamanantena
    ;
    Fanomezana Mihaja Ratsoavina
    ;
    Lala Harivelo Raveloson Ravaomanarivo
    ;
    Dominik Schwab
    ;
    Teja Tscharntke
    ;
    Zemp, Clara 
    ;
    Holger Kreft
    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 leverage points: Two leverage points are associated with trade-offs between biodiversity, ecosystem services, and agricultural productivity, while the third entails cobenefits. Swift policy action is required, as path dependency caused by forest loss may soon put two leverage points out of reach. We argue that such closing windows of opportunity may be common, but often overlooked, calling for a wider consideration of path dependency in land-system science.
  • 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.