Estimating oil-palm Si storage, Si return to soils and Si losses through harvest in smallholder oil-palm plantations of Sumatra, Indonesia

Silicon (Si) is known to have multiple beneficial effects on crops. Most plant-available Si in soils is provided through litter decomposition and subsequent phytolith dissolution, especially in strongly desilicated tropical soils. The importance of Si cycling in tropical soil-plant systems raised the question if oil-palm cultivation, the oil palm being a Si-accumulating crop, alters Si cycling. As Si accumulates in plant tissue, we hypothesized that i) Si is stored in the aboveground biomass of oil palms with time, and that ii) the system might lose considerable amounts of Si every year through fruit-bunch harvest. To test these hypotheses, we sampled leaflets, the rachis, fruit-bunch stalk, fruit pulp, kernels and frond bases from mature oil palms planted on well-drained and temporarily flooded riparian smallholder oil-palm plantations (n = 4 each) in lowland Sumatra, Indonesia. We quantified Si concentrations of these oil-palm parts by NaCO3 extraction. We further estimated Si storage in the total above-ground biomass of the oil palms, Si return to soils through decomposing pruned palm fronds, and Si losses from the system through harvest, to assess if Si return to soils via pruned palm fronds sufficed for maintaining Si cycling in the system, or if any measures are needed to compensate for Si export through fruit-bunch harvest. At all sites, leaflets of oil-palm fronds had a significantly higher (p &le; 0.05) mean Si concentration (&ge; 1 wt. %) than the rachis, frond base, fruit-bunch stalk, fruit pulp and kernel (&le; 0.5 wt. %). All analysed oil-palm parts had a Si/Ca weight ratio &ge; 1, except for the rachis. At well-drained sites, mean Si concentrations in leaflets increased with palm-frond age (R&sup2; = 0.98). Estimates of Si storage in the total above-ground biomass of oil palms, Si return to soils through decomposing pruned palm fronds, and Si losses through harvest were similar at well-drained and riparian sites: a single palm tree could store about 4&ndash;5 kg of Si in its total above-ground biomass, a smallholder oil-palm plantation of 1 hectare could store about 550 kg of Si in the palm trees&rsquo; above-ground biomass. Pruned palm fronds were estimated to return 110&ndash;131 kg of Si per hectare to topsoils each year. Fruit-bunch harvest corresponded to an annual Si export of 32&ndash;72 kg Si per hectare in 2015 and 2018. Thus, on smallholder plantations in our study area, more Si can be returned to soils through pruned palm fronds than is lost through fruit-bunch harvest. Greater Si losses would occur if oil-palm stems were removed from plantations prior to replanting. Therefore, it is advisable to leave oil-palm stems on the plantations e.g., by distributing chipped stem parts across the plantation at the end of a plantation cycle (~25 years). This would return about 550 kg ha-1 Si stored in the palm trees&rsquo; above-ground biomass to the soils.</p

Diverse and larger tree islands promote native tree diversity in oil palm landscapes

In monoculture-dominated landscapes, recovering biodiversity is a priority, but effective restoration strategies have yet to be identified. In this study, we experimentally tested passive and active restoration strategies to recover taxonomic, phylogenetic, and functional diversity of woody plants within 52 tree islands established in an oil palm landscape. Large tree islands and higher initial planted diversity catalyzed diversity recovery, particularly functional diversity at the landscape level. At the local scale, results demonstrated that greater initial planting diversity begets greater diversity of native recruits, overcoming limitations of natural recruitment in highly modified landscapes. Establishing large and diverse tree islands is crucial for safeguarding rare, endemic, and forest-associated species in oil palm landscapes

From earthquakes to island area: multi‐scale effects upon local diversity

Tropical forests occupy small coral atolls to the vast Amazon basin. They occur across bioregions with different geological and climatic history. Differences in area and bioregional history shape species immigration, extinction and diversification. How this effects local diversity is unclear. The Indonesian archipelago hosts thousands of tree species whose coexistence should depend upon these factors. Using a novel dataset of 215 Indonesian forest plots, across fifteen islands ranging in area from 120 to 785 000 km$^{2}$, we apply Gaussian mixed effects models to examine the simultaneous effects of environment, earthquake proximity, island area and bioregion upon tree diversity for trees ≥ 10 cm diameter at breast height. We find that tree diversity declines with precipitation seasonality and increases with island area. Accounting for the effects of environment and island area we show that the westernmost bioregion Sunda has greater local diversity than Wallacea, which in turn has greater local diversity than easternmost Sahul. However, when the model includes geological activity (here proximity to major earthquakes), bioregion differences are reduced. Overall, results indicate that multi‐scale, current and historic effects dictate tree diversity. These multi‐scale drivers should not be ignored when studying biodiversity gradients and their impacts upon ecosystem function

Syzygium (Myrtaceae): Monographing a taxonomic giant via 22 coordinated regional revisions

Syzygium Gaertn. is the largest woody genus of flowering plants in the world. Unpublished but extensive recent herbarium surveys suggest 1200‒1800 species distributed throughout the Old-World tropics and subtropics (Table 1). Until recently, Syzygium exemplified a recurring taxonomic impediment among megadiverse genera, wherein few taxonomists worked on the group in any sustained manner, a majority of the herbarium specimens remained undetermined or misidentified, few if any attempts were made to look at the genus globally and limited or no molecular studies were available to provide a predictive phylogenetic context of the genus. The situation with Syzygium has slowly begun to change as allied genera have been absorbed into the genus (Biffin et al., 2006; Craven & Biffin, 2010), and predictive phylogenetically based infrageneric classifications are emerging. Taxonomic outputs on Syzygium also have been increasing across its range with the description of new species, resolution of nomenclatural and typification issues, and some regional revisions being initiated or updated. However, virtually all regional treatments (which some areas lack) need urgent revision because they are severely outdated, have limited molecular sampling and are error-ridden. We are coordinating a genus-wide taxonomic update of Syzygium through a series of 22 regional revisions, including 9 in the Flora Malesiana region (Figure 1). Each treatment will include a phylogenetic framework with species descriptions, type information, synonymy, distributions, ecological notes, and keys. Field images (Figure 2) and/or line drawings will be included with the goal of every species being illustrated. This working group has been formed to encourage a coordinated effort to document this unwieldy taxonomic giant and regional botanists working on the group are encouraged to be involved. A robust taxonomy of the genus is a prerequisite for testing the many complex questions about evolution and ecology that Syzygium could help address

Balancing economic and ecological functions in smallholder and industrial oil palm plantations

The expansion of the oil palm industry in Indonesia has improved livelihoods in rural communities, but comes at the cost of biodiversity and ecosystem degradation. Here, we investigated ways to balance ecological and economic outcomes of oil palm cultivation. We compared a wide range of production systems, including smallholder plantations, industrialized company estates, estates with improved agronomic management, and estates with native tree enrichment. Across all management types, we assessed multiple indicators of biodiversity, ecosystem functions, management, and landscape structure to identify factors that facilitate economic-ecological win-wins, using palm yields as measure of economic performance. Although, we found that yields in industrialized estates were, on average, twice as high as those in smallholder plantations, ecological indicators displayed substantial variability across systems, regardless of yield variations, highlighting potential for economic-ecological win-wins. Reducing management intensity (e.g., mechanical weeding instead of herbicide application) did not lower yields but improved ecological outcomes at moderate costs, making it a potential measure for balancing economic and ecological demands. Additionally, maintaining forest cover in the landscape generally enhanced local biodiversity and ecosystem functioning within plantations. Enriching plantations with native trees is also a promising strategy to increase ecological value without reducing productivity. Overall, we recommend closing yield gaps in smallholder cultivation through careful intensification, whereas conventional plantations could reduce management intensity without sacrificing yield. Our study highlights various pathways to reconcile the economics and ecology of palm oil production and identifies management practices for a more sustainable future of oil palm cultivation.</p

Reducing Fertilizer and Avoiding Herbicides in Oil Palm Plantations—Ecological and Economic Valuations

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 less intensive management schemes may enhance biodiversity and lessen detrimental effects on the environment while maintaining high yields. We compare reduced vs. conventional fertilization, as well as mechanical vs. chemical weed control (with herbicides) in a long-term, full-factorial, multidisciplinary experiment. We conducted the experiment in an oil palm company estate in Sumatra, Indonesia, and report the results of the first 2 years. We measured soil nutrients and functions, surveyed above- and below-ground organisms, tracked oil palm condition and productivity, and calculated plantation gross margins. Plants, aboveground arthropods, and belowground animals were positively affected by mechanical vs. chemical weed control, but we could not detect effects on birds and bats. There were no detectable negative effects of reduced fertilization or mechanical weeding on oil palm yields, fine roots, or leaf area index. Also, we could not detect detrimental effects of the reduced fertilization and mechanical weeding on soil nutrients and functions (mineral nitrogen, bulk density, and litter decomposition), but water infiltration and base saturation tended to be higher under mechanical weeding, while soil moisture, and microbial biomass varied with treatment. Economic performance, measured as gross margins, was higher under reduced fertilization. There might be a delayed response of oil palm to the different management schemes applied, so results of future years may confirm whether this is a sustainable management strategy. Nevertheless, the initial effects of the experiment are encouraging to consider less intensive management practices as economically and ecologically viable options for oil palm plantations

The global abundance of tree palms

Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees.Publisher PDFPeer reviewe