A global review of rubber plantations: Impacts on ecosystem functions, mitigations, future directions, and policies for sustainable cultivation

Carbon (C) losses due to the conversion of natural forests adversely affect the biotic and abiotic components of terrestrial ecosystems. In tropical China, rubber cultivation often extends from its traditional range to elevations of up to 1400 m. However, C stock in rubber plantations along elevation gradients is poorly understood. In this study, we investigated biomass and C stock along elevation gradients in two age groups (8- and 12-year-old) of rubber monoculture plantations in Xishuangbanna, Southwest China. The C distribution across various tree sections, ranging from aboveground biomass (AGB) to belowground biomass (BGB), including litter, big dead branches, and different soil depths were measured. A significant negative correlation was observed between AGB, BGB, litter, and total ecosystem C stocks and elevation gradients in both age groups. However, no correlation was observed between the total soil C stock and elevation gradients in 8-year-old rubber plantations, while significant decline was detected in 12-year-old rubber plantations. The highest ecosystem C stock of 197.90 Mg C ha−1 was recorded at 900 m in 8-year-old plantations; whereas, in 12-year-old rubber plantations, the highest value of 183.12 Mg C ha−1 was found at 700 m. The total ecosystem C stock decreased to their lowest level at 1000 m in both the 8-year-old and 12-year-old plantations, ranging between 113.05 Mg C ha−1 and 125.75 Mg C ha−1, respectively. Moreover, total ecosystem C stock significantly decreased from 51.55% to 8.05% and from 42.96% to 11.46% between 700 m and 1100 m, in both 8-year-old and 12-year-old plantations, respectively. Regardless of elevation gradients, the total ecosystem C stock of 12-year-old rubber plantations was 1.98% greater than that of 8-year-old rubber plantations. Biomass was the second largest contributor, while soil accounted for 82% to 90%, and the other components contributed less than 2% of the total ecosystem C stock in both age groups. These fluctuations in C stock along elevation gradients in both 8- and 12-year-old plantations suggested that rubber growth, biomass, and C stock capacity decreased above 900 m, and that age and elevation are key factors for biomass and C stock in rubber monoculture plantations.

Carbon balance of rubber (Hevea brasiliensis) plantations: A review of uncertainties at plot, landscape and production level

Review of allometric equations for major land covers in SE Asia: Uncertainty and implications for above- and below-ground carbon estimates

Diversified land conversion deepens understanding of impacts of rapid rubber plantation expansion on plant diversity in the tropics

Flooding drives plant diversity-biomass relationships in riparian zones of the three Gorges reservoir area.

The expansion of rubber (Hevea brasiliensis) cultivation plantation over the past few decades has been significantly explosive in Xishuangbanna, southwest China. More and more evidences concerning the expansion of rubber plantations lead to the negative influence to local regional hydrology. It is vital to explore the impact of climate change and rubber (Hevea brasiliensis) plantation expansion on reference evapotranspiration (ET0) for the sustainable and efficient use of regional water resources. In this study, the spatiotemporal variation of ET0 as well as its relationship in rubber plantations area in Xishuangbanna from 1970–2017 were analyzed by using trend, correlation and contribution analysis. The results showed that the rubber plantation was 12,768 ha yr–1 from 1990 to 2017 in Xishuangbanna, and nearly 40.8% of new rubber plantations expanded above 900 m in altitude from 2000 to 2017. Sunshine duration and average relative humidity were the key meteorological factors that affect ET0 in Xishuangbanna, with the sensitivity coefficient of 0.51 and 0.35, respectively. The multiyear relative change of ET0 in Xishuangbanna was 9.18%, and the total contribution of major climate factors was 7.87% during 1970 and 2017. The average relative humidity in the plantation area decreases, which directly leads to the increase of ET0. The amount of ET0 change from 2000 to 2017 affected by climate change increased at 3.13 mm/10a, whereas it was 2.17 mm/10a affected by the expansion of rubber plantations by quantitative separation. ET0 was significantly affected by climate change but intensified by the expansion of rubber plantation.

Protists, abundant but enigmatic single-celled eukaryotes, are important soil microbiota providing numerous ecosystem functions. We employed high-throughput sequencing of environmental DNA, targeting the V4 region of the 18S rRNA gene, to characterize changes in their abundance, species richness, and community structure with conversion of lowland rainforest into rubber agroforest (jungle rubber), and rubber and oil palm plantations; typical agricultural systems in Sumatra, Indonesia. We identified 5,204 operational taxonomic units (OTUs) at 97% identity threshold of protists from 32 sites. Protists species richness was similar in rainforest, jungle rubber and oil palm plantations but significantly lower in rubber plantations. After standardization, 4,219 OTUs were assigned to five trophic groups, and inspected for effects of land-use change, and potential biotic and abiotic driving factors. The most abundant trophic group was phagotrophs (52%), followed by animal parasites (29%), photoautotrophs (12%), plant parasites (1%), and symbionts (<1%). However, the relative abundance and OTU richness of phagotrophs and photoautotrophs increased significantly with increasing land-use intensity. This was similar, but less pronounced, for the relative abundance of symbionts. Animal and plant parasites decreased significantly in abundance and species richness with increasing land-use intensity. Community compositions and factors affecting the structure of individual trophic groups differed between land-use systems. Parasites were presumably mainly driven by the abundance and species richness of their hosts, while phagotrophs by changes in soil pH and increase in Gram-positive bacteria, and photoautotrophs by light availability. Overall, the results show that relative species richness, relative abundance, and community composition of individual trophic groups of protists in tropical lowland rainforest significantly differ from that in converted ecosystems. This is likely associated with changes in ecosystem functioning. The study provides novel insight into protist communities and their changes with land-use intensity in tropical lowland ecosystems. We show, that trophic groups of protists are powerful indicators reflecting changes in the functioning of ecosystems with conversion of rainforest into monoculture plantations.

Introduction The rapid expansion of rubber (Hevea brasiliensis) plantations in Southwestern China has transformed forest-dominated landscapes. However, the hydrological consequences of this land-use change have not been comprehensively quantified. Methods This study reconstructed the long-term actual evapotranspiration (ET a_reconstructed ) of rubber plantations using the "Kc-ET0" method, which integrates meteorological data and actual crop coefficients (Kc,actual). The coefficient of variation (CV) and the Random Forest (RF) algorithm were employed to identify the key drivers and analyze the spatiotemporal patterns of the reconstructed ET a_reconstructed . Furthermore, we quantitatively evaluated the influence of ET a_reconstructed on major ecosystem service values (ESVs). Results Our results showed that rubber plantations expanded at a rate of 12.49 × 10⁴ ha per decade between 2000 and 2022. The annual average ETa_reconstructed was 952 mm, showing an increasing trend of 12 mm per decade since 1970. The ETa_reconstructed exhibited stable interannual variability (CV range: 0.04–0.11) and was significantly positively correlated with maximum temperature, sunshine duration (SSD), and rubber plantation area, but negatively correlated with relative humidity. SSD (28.5%–38.4%) and rubber plantation area (11.4%–20.3%) were identified as the crucial drivers. The optimal ESVs for rubber plantations were achieved at a multi-year average SSD of 4.17 hours, where the reconstructed ETa ranged between 2.0 and 3.0 mm/day, and carbon sequestration and oxygen release reached their peak values. Discussion In conclusion, the ETa_reconstructed of rubber plantations, primarily driven by increased sunshine duration, significantly affects their ecosystem service values in Southwestern China. The identified optimal ETa_reconstructed range provides a scientific basis for precise water management in tropical rubber plantations in the context of climate change.

Human-modified forested landscapes are prevalent in the tropics, and the role of complex mosaics of diverse vegetation types in biodiversity conservation remains poorly understood. Demographic traits and the spatial pattern of biodiversity are essential information when considering proper forest management and land use strategies. We compared the tree community structure (stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and species composition) and the forest dynamics (mortality, recruitment rate, and increments of basal area, and above- and below-ground biomass) of 39–46 plots among five dominant forest types: young and old fallows, rubber plantations, and fragmented and old-growth forests in Sarawak, Malaysia. We also explored how tree diversity was distributed across different spatial scales using additive partitioning of diversity. Swidden cultivation and rubber plantations showed decreased stem density, basal area, tree diversity, abundance of rare, endemic, and upper-layer trees, and increments of above- and below-ground biomass, which affected tree mortality, dominant trees, and species composition. Little distinction in species composition was observed among young and old fallows and rubber plantations, indicating a relatively quick recovery of the tree community in the early stages. The highest diversity was found among forest types, indicating that the whole forested landscape comprises a suitable scale for tree biodiversity conservation in the region. Our results suggest that although fragmented and old-growth forests have an irreplaceable role and a high priority in conserving biodiversity and sustaining the function of the forest ecosystem, secondary forests may also have a reinforcing role in maintaining tree diversity in the region, especially under the current circumstances in which a large portion of the landscape is human-modified and faces an increasing threat from the expansion of oil palm plantations.

&lt;p&gt;Establishment of cover crop has been a standard scientific agronomic intervention in rubber (&lt;em&gt;Hevea brasiliensis&lt;/em&gt;) plantations. Natural leaf fall in rubber plantations is an unaccounted phenomenon which also improves the physicochemical properties and biological activities of soil. A comparison of the decomposition of leaf litter from different sources in soil and the release of utrients from them has been attempted in this study through a field experiment. Studies indicated that the degradation and release of nutrients to the soil pool was mainly decided by the leaf chemistry and degradability of the litter. Rubber litter had its own edge over other leguminous cover crop litter, in providing a sustained release of potassium, calcium and magnesium owing to its slow and steady mineralization rate compared to cover crops. Higher content of nutrients was recorded in degraded litter in comparison to fresh sources. Legume cover crops are capable of enhancing the bacterial and fungal populations in soil compared to nonleguminous crops in rubber plantations.&lt;/p&gt;

Precipitation-induced biomass enhancement and differential allocation in Inner Mongolia's herbaceous and shrub communities

We investigated the effects of soil resources on species composition, plant diversity, and plant biomass in four alpine Kobresia meadow communities. Species diversity was lower in the Kobresia tibetica swamp meadow community than in the other three communities, but this community was characterized by the highest aboveground and belowground biomass and soil nutrients. Aboveground biomass was positively correlated with soil organic matter and soil total nitrogen in all four alpine meadow communities. The proportion of light fraction organic carbon (LFOC) was positively correlated with soil total organic carbon in all types of grassland. In alpine meadows, belowground biomass mostly occurred at 0-10 cm soil, as did soil nutrients. Community differences in plant species composition were reflected in biomass distribution. The highest total biomass (13,759 ± 497 g/m2) including above- and belowground biomass appeared in the sedge-dominated Kobresia tibetica swamp meadow community. Intermediate biomass (3,235 ± 142 g/m2, 2,645 ± 16 g/m2) was found in the Kobresia pygmaea swamp meadow and Potentilla fruticosa shrubs meadow community, dominated by forbs, sedges, and woody plants. The lowest biomass (2,433 ± 162 g/m2) was observed in the Kobresia humilis meadow, mainly dominated by forbs and grasses. The results indicated that fertility of the vegetation caused a decrease in plant species, increase in plant biomass, and also changes in species composition. Species traits (such as ability to respond to higher nutrient levels) as well as competitive interaction may determine ecosystem function (e.g., productivity). Plants with higher competitive ability would then have access to a greater proportion of available resources, leading to increased total resource uptake by roots, lower nutrient losses from the ecosystems, and increased aboveground and belowground biomass. The distribution of aboveground and belowground biomass is largely influenced by the plant species and growth forms within spatial gradients in soil moisture and edaphic conditions.

Mapping deciduous rubber plantations through integration of PALSAR and multi-temporal Landsat imagery

In the last decades, lowland tropical rainforest has been converted in large into plantation systems. Despite the evident changes above ground, the effect of rainforest conversion on the channeling of energy in soil food webs was not studied. Here, we investigated community‐level neutral lipid fatty acid profiles in dominant soil fauna to track energy channels in rainforest, rubber, and oil palm plantations in Sumatra, Indonesia. Abundant macrofauna including Araneae, Chilopoda, and Diplopoda contained high amounts of plant and fungal biomarker fatty acids (FAs). Lumbricina had the lowest amount of plant, but the highest amount of animal‐synthesized C20 polyunsaturated FAs as compared to other soil taxa. Mesofauna detritivores (Collembola and Oribatida) contained high amounts of algal biomarker FAs. The differences in FA profiles between taxa were evident if data were analyzed across land‐use systems, suggesting that soil fauna of different size (macro‐ and mesofauna) are associated with different energy channels. Despite that, rainforest conversion changed the biomarker FA composition of soil fauna at the community level. Conversion of rainforest into oil palm plantations enhanced the plant energy channel in soil food webs and reduced the bacterial energy channel; conversion into rubber plantations reduced the AMF‐based energy channel. The changes in energy distribution within soil food webs may have significant implications for the functioning of tropical ecosystems and their response to environmental changes. At present, these responses are hard to predict considering the poor knowledge on structure and functioning of tropical soil food webs.

Grazing is one of the main human disturbance factors in alpine grassland on the Qinghai-Tibet Plateau (QTP), which can directly or indirectly influence the community structures and ecological functions of grassland ecosystems. However, despite extensive field grazing experiments, there is currently no consensus on how different grazing management approaches affect alpine grassland diversity, soil carbon (C), and nitrogen (N). Here, we conducted a meta-analysis of 70 peer-reviewed publications to evaluate the general response of 11 variables related to alpine grassland ecosystems plant diversity and ecological functions to grazing. Overall, the results showed that grazing significantly increased the species richness, Shannon–Wiener index, and Pielou evenness index values by 9.89% (95% CI: 2.75–17.09%), 7.28% (95% CI: 1.68–13.62%), and 3.74% (95% CI: 1.40–6.52%), respectively. Aboveground biomass (AGB) and belowground biomass (BGB) decreased, respectively, by 41.91% (95% CI: −50.91 to −32.88%) and 17.68% (95% CI: −26.94 to −8.52%). Soil organic carbon (SOC), soil total nitrogen (TN), soil C:N ratio, and soil moisture decreased by 13.06% (95% CI: −15.88 to −10.15%), 12.62% (95% CI: −13.35 to −8.61%), 3.27% (95% CI: −4.25 to −2.09%), and 20.75% (95% CI: −27.89 to −13.61%), respectively, whereas, soil bulk density and soil pH increased by 17.46% (95% CI: 11.88–24.53%) and 2.24% (95% CI: 1.01–3.64%), respectively. Specifically, moderate grazing, long-durations (>5 years), and winter grazing contributed to increases in the species richness, Shannon–Wiener index, and Pielou evenness index. However, AGB, BGB, SOC, TN, and soil C:N ratios showed a decrease with enhanced grazing intensity. The response ratio of SOC was positively associated with AGB and BGB but was negatively related to the Shannon–Wiener index and Pielou evenness index. Furthermore, the effects of grazing on plant diversity, AGB, BGB, SOC, and TN in alpine grassland varied with grazing duration, grazing season, livestock type, and grassland type. The findings suggest that grazing should synthesize other appropriate grazing patterns, such as seasonal and rotation grazing, and, furthermore, additional research on grazing management of alpine grassland on the QTP is needed in the future.