Tree performance in a biodiversity enrichment experiment in an oil palm landscape

Abstract

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. 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. 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. 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. 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.

Legacy Effects Overshadow Tree Diversity Effects on Soil Fungal Communities in Oil Palm-Enrichment Plantations

“…The relative importance of tree richness, tree species identity, and plot size was quantified using a linear model for random partition design [46] that was adapted to the design of EFForTS-BEE [42,44]. This design includes terms for tree species richness treated as a continuous variable (i.e., 0, 1, 2, 3, or 6), a numeric matrix indicating the presence or absence of each tree species, the number of planted tree species as a discrete variable ("nonlinear species richness"), and plot size.…”

“…This study was conducted in the framework of the biodiversity enrichment experiment EFForTS-BEE of the Collaborative Research Center 990 [42,44]. The research site is located in a commercial oil palm plantation (PT Humusindo Makmur Sejati, 01.95 south (S) and 103.25 east (E), 47 ± 11 m above sea level (a.s.l.))…”

“…Three years after establishment of the experiment, tree diversity significantly enhanced stand structural complexity [43]. The fastest growing tree species reached a height of approximately 6 m with a stem basal area of more than 20 cm 2 , while slow-growing species were well below the canopy with heights of 2.3 m and stem basal areas of only 2.7 cm 2 [44].…”

Physiological responses to light explain competition and facilitation in a tree diversity experiment

“…Experimental and observational research alike has shown that biodiversity often promotes ecosystem functions such as productivity (Tilman et al 2014). In forests, this trend has been shown in both experimental (Potvin & Gotelli 2008;Tobner et al 2016;Grossman et al 2017;Williams et al 2017;Huang et al 2018;Zemp et al 2019) and observational (Gamfeldt et al 2013;Liang et al 2016;Oehri et al 2017) data, across temperate (Tobner et al 2016;Grossman et al 2017;Williams et al 2017), subtropical (Huang et al 2018), and tropical (Potvin & Gotelli 2008;Zemp et al 2019) biomes. These positive relationships are robust to variation in climate, successional stage, and other factors (reviewed in Grossman et al 2018;Ammer 2018).…”

Complexity within an oil palm monoculture: The effects of habitat variability and rainfall on adult dragonfly (Odonata) communities

“…The majority of studies have largely focused on comparing oil palm with natural habitats, with fewer studies that have specifically tested the effects of plantation management strategies on environmental conditions, biodiversity, or ecosystem functions (Savilaakso et al, ). Although recent research efforts have given more attention to the effects of possible management strategies (e.g., Ashraf et al, ; Azhar et al, ; Darras et al, ; Ghazali et al, ; Teuscher et al, ; Zemp et al, in a smallholder context), given the huge global coverage of the crop, there is an urgent need to further investigate management techniques that can support biodiversity within plantations without reducing yield. This is particularly the case for taxa that contribute toward important ecosystem services associated with crop production, therefore, potentially benefitting both biodiversity and yield.…”