Monoculture Rubber Research Articles

Introduction of a leguminous shrub to a rubber plantation changed the soil carbon and nitrogen fractions and ameliorated soil environments

The conversion of monoculture rubber (Hevea brasiliensis) plantations into rubber-based agroforestry systems has become a common trend in forestry management in the past few decades. Rubber–Flemingia macrophylla (a leguminous shrub) systems are popular in southwestern China’s Xishuangbanna region. The biogeochemical cycles of soil carbon and nitrogen in forests are mainly affected by their fractions. This study investigated the effect of introducing Flemingia macrophylla to rubber plantations of different ages on soil carbon and nitrogen fractions. The experimental treatments included R1 (young rubber plantation), RF1 (young rubber–Flemingia macrophylla system), R2 (mature rubber plantation) and RF2 (mature rubber–Flemingia macrophylla system). The results showed that the introduction of Flemingia macrophylla to rubber plantations of different ages significantly changed soil carbon and nitrogen fractions, improved soil labile organic carbon and nitrogen contents, and ameliorated soil environments. The average soil microbial biomass organic carbon, nitrogen and nitrate-nitrogen in the 0–10 cm soil layer during the experimental period was 38.9%, 55.5%, and 214.7% higher in RF1 than R1, respectively, and 22.1%, 22.2%, and 652.2% higher in RF2 than R2, respectively. Therefore, Flemingia macrophylla can be used as an alternative interplanted tree species within rubber plantations in similar environments of southeastern Asia.

The effects of introducing Flemingia macrophylla to rubber plantations on soil water content and exchangeable cations

Rubber-based (Hevea brasiliensis) agroforestry systems are the best way to resolve the environmental problems caused by rubber monoculture. Rubber–Flemingia macrophylla (nitrogen-fixing plants) systems have become popular in Xishuangbanna, Southwest China. Soil water content and exchangeable cations (Ca2+, Mg2+, K+, and Na+) are important for sustainably managing forest ecosystems. In this study, we investigated the responses of soil water content and exchangeable cations in rubber and rubber–Flemingia macrophylla systems. Soil water content increased in the 0–90 cm soil layer as the rubber plantations aged, and the mature rubber plantations had similar soil water storage to rainforests. The rubber plantations use soil water in the 30–90 cm soil layer to avoid drought stress during the long, dry season. The introduction of Flemingia macrophylla to the young rubber plantations significantly increased soil water depletion in the 30–90 cm soil layer. The introduction of Flemingia macrophylla to the mature rubber plantations had no significant effects on soil water in the 0–90 cm soil layer. The introduction of Flemingia macrophylla to the differently aged rubber plantations mitigated soil acidification by decreasing nitrogen inputs. The total exchangeable cations in the 0–90 cm soil layer sharply decreased as the rubber plantations aged due to the acceleration of soil acidification. When soil pH was below 5.5, 7.85 cmol kg−1 of soil exchangeable cations were released when the pH decreased by one unit. However, the introduction of Flemingia macrophylla to the differently aged rubber plantations effectively reduced the release of soil exchangeable cations by mitigating soil acidification. In conclusion, rubber–Flemingia macrophylla systems can mitigate soil acidification and reduce the release of soil exchangeable cations relative to rubber monoculture.

Can intercropping with the cash crop help improve the soil physico-chemical properties of rubber plantations?

Although rubber-based (Hevea brasiliensis) agroforestry systems are regarded as the best approach to improving the sustainability of rubber agriculture and environmental conservation, soil physico-chemical properties and their related interactions have rarely been examined in such systems. The objective of this study was to examine the management and landscape effects on soil structure, soil moisture and soil nutrients in the Xishuangbanna region. The treatments were tropical rain forest (TRF), rubber monoculture (Rm), and two rubber-based agroforestry systems: H. brasiliensis–T. cacao (HTAs) and H. brasiliensis–F. macrophylla (HFAs). The results showed that after approximately three decades of the conversion from tropical rain forest to rubber monoculture, soils in the rubber plantations suffered serious degradation (poor soil physical properties, poor soil structure, limited soil moisture, unstable aggregates, depleted nutrients and serious soil erosion). However, the rubber-based agroforestry systems (both HTAs and HFAs) evidently improved the soil physical properties and enriched the soil nutrients in the rubber plantations. Compared to the corresponding values in rubber monoculture, the total soil porosity, initial soil moisture, soil mean weight diameter (MWD) and soil hydraulic conductivity (Ks) in rubber-based agroforestry systems increased, on average, by 13.3%, 54.7%, 31.5%, and 246.4%, respectively. In addition, the nutrients of C, N, P, Ca and Mg increased, on average, by 38.8%, 38.5%, 48.2%, 47.9% and 31.4%, respectively, after the transformation from rubber monoculture to agroforestry systems. Our results clearly indicated that the soil physico-chemical properties of rubber plantations were improved by interplanting, and the patterns of the intercropping system could play key roles in promoting the sustainable development of agriculture and the environment.

How does a rubber plantation affect the spatial variability and temporal stability of throughfall?

Abstract In Xishuangbanna, southwest China, the large-scale monoculture rubber plantation replaced the primary tropical forest, which changed the regional hydrology processes and biogeochemical cycles. As throughfall was an important component of the forest ecosystem water input, we researched the spatial variability and temporal stability of throughfall in the rubber plantation. We recorded 30 rainfall events by using 90 rain gauges during 2015–2016. We found a highly significant linear relationship between rainfall and throughfall, and a strong power correlation between the peak 30 min rainfall intensity and throughfall. The coefficient of variation for throughfall was significant and negatively correlated with rainfall and rainfall intensity. We also observed that throughfall had a strong spatial autocorrelation that would decrease during heavy rainfall events. The results indicate that the leaf area index did not have a significant relationship with throughfall. However, the lateral translocation of the throughfall in the canopy significantly affected the spatial distribution of the throughfall. Generally, the lower throughfall positions were close to the nearest rubber trunk, and the higher throughfall positions were mostly below the slope. This study contributes to the knowledge of the spatiotemporal heterogeneity of throughfall and helps elucidate the interception processes in the rubber plantation.

NERACA KARBON, EMISI DAN SERAPAN HISTORIS CO2 KARENA PERUBAHAN PENGGUNAAN LAHAN DI KABUPATEN BANYUASIN, SUMATERA SELATAN

Land use change is the cause of carbon loss from land. The loss of this carbon becomes a source of carbon dioxide (CO 2 ) in the atmosphere that can cause global warming. Intensive land use and land cover occurred in Kabupaten Banyuasin from 2004-2014. The purpose of this study. to create carbon balance, emissions and sequestration of CO 2 during the period of 2004 - 2014 in Banyuasin Regency caused by land use change and land cover change. The method used to create carbon balance using land use change matrix, carbon calculation of each carbon pool by allometric method, destructive sample and organic C by Walkley and Black method. Stock diference method for analysis of changes in carbon storage, CO 2 emissions and CO 2 sequestration. The results of this study indicate that the 2004-2014 carbon balance in Banyuasin Regency is negative, with a carbon loss of 22,033,277 tons with an average annual carbon loss of 2,203,327 tons. CO 2 sequestration of 29,298,966 tons and CO 2 emissions 118,044,141 tons, while net emissions 88,745,175 tons. Average net CO 2 emissions from above ground carbon pools, carbon necromassa pools, litter carbon pools and underground carbon pools are 7 tonnes ha -1 year -1 , whereas CO 2 emissions from organic soil C 0.61 tonnes ha - 1 year -1 . The largest contributor of CO 2 emissions in Banyuasin Regency are sequentially caused by changes in peat swamp forests, secondary mangrove forests, primary mangrove forests and secondary swamp forests. While the source of sequestration is the change of monoculture rubber peat, oil palm, rubber monoculture and shrubs.

Effects of forest transition on litterfall, standing litter and related nutrient returns: Implications for forest management in tropical China

Land-use change is widespread throughout the tropics where large areas of natural forests being converted to secondary forests and tree plantations. In order to search for appropriate forest management, it is necessary to evaluate litter production, its temporal variation, and nutrient return of these ecosystems. In this study therefore, we investigated litterfall production, standing litter and litter quality for 5 years in a tropical seasonal rainforest (TSR), tropical secondary forest (TSF), tropical anthropogenic forest (TAF), and a rubber monoculture (RM) in Xishuangbanna, SW China. Results showed that the annual mean litterfall was significantly higher in TSF (14.83 Mg ha−1 year−1), followed by TAF (12.69 Mg ha−1 year−1), TSR (11.20 Mg ha−1 year−1) and RM (9.21 Mg ha−1 year−1). Both precipitation and temperature exerted greater impacts on litterfall amount in TSR and TSF than that in TAF and RM. The peak litterfall occurred in the cool and dry season for all four forest sites. Average standing litter for 5 years followed the order of TAF (3.08 Mg ha−1) > RM (2.91 Mg ha−1) > TSR (2.52 Mg ha−1) > TSF (2.04 Mg ha−1). Total returns of C, N, P, and K to mineral soil showed a decreasing trend of TSF > TAF > TSR > RM, which had a variation pattern similar to that for litter production. Nutrient-use efficiency varied with the mineral elements involved, and they differed significantly across the four forest types. Overall, litter production and nutrient returns increased after conversion of tropical primary forest to secondary forest and anthropogenic forest, but both responses decreased after conversion to the rubber monoculture. Therefore, establishing a multilayered community on degraded tropical land or introducing native species into ageing rubber forest offers a promising way to maintain the sustainable use and management of local forest resources.

Natural forests maintain a greater soil microbial diversity than that in rubber plantations in Southwest China

The conversion of tropical forests to monoculture rubber plantations throughout Southeast Asia threatens to have widespread negative impacts on ecosystem services. The aim of this study was to identify the impacts of forest conversion to rubber plantations on soil microorganisms, using a space for time substitution design. Soil microbial communities from natural forests, young rubber and mature rubber plantations were investigated using phospholipid fatty acid (PLFA) analysis. Microbial PLFA biomass of all functional groups including actinomycete, arbuscular mycorrhiza, fungi, bacteria and protozoa was lower in rubber plantations as compared to natural forests. This was true for young rubber and mature rubber plantations tested in both dry and wet seasons. The composition of microbial communities differed between natural forests, young rubber and mature rubber plantations. Changes in microbial community composition were strongly correlated with pH, which was lower in mature rubber plantations than in natural forests and young rubber plantations. In addition, our results showed that the variation in soil microbial community composition was strongly affected by seasonality, with higher PLFA biomass recorded in the dry season than in the wet season. The low soil microbial biomass in rubber plantations has long term implications regarding the soil health of rubber plantations.

Effectiveness of protected areas in preventing rubber expansion and deforestation in Xishuangbanna, Southwest China

AbstractProtected areas (PAs) are supposedly key refuges for the world's remaining biodiversity. Our study site, Xishuangbanna, harbors a high proportion of China's biodiversity but is threatened by rapid deforestation and expansion of monoculture rubber. We quantified the success of Xishuangbanna's PAs in preventing deforestation. Most previous analyses of PA effectiveness have insufficiently accounted for biases arising from PA location and establishment, because they overlooked the importance of site‐matching in accounting for landscape change. We used matching methods to minimize such biases in comparing land use conversion rates inside and outside‐PAs. By 2010, Xishuangbanna had 3,455.5 km2 (~18%) designated as PAs. However, rubber occupied 22% of its land area and was expanding at a rate of 153.4 km2/year. Between 1988 and 2010, conventional analysis showed a deforestation rate of 9.3 km2/year. However, matching analysis showed a significantly higher rate of deforestation, 10.7 km2/year, which resulted in the deforestation of ~11% of PA's land. We argue that PAs were less effective than had previously been thought. The situation worsened from 2002 to 2010, when the deforestation rate within PAs was actually higher than that of outside PAs, although this difference was not significant. The designated higher levels of protection in ‘core’ zones were also unsuccessful in preventing deforestation. At current rates, within the next 50 years, a further 16% of PAs would be deforested in Xishuangbanna. This could even be an underestimate, as without intervention, drivers of deforestation tend to accelerate. Therefore, reviewing and strengthening current PA management policies is essential.

Expansion dynamics of deciduous rubber plantations in Xishuangbanna, China during 2000–2010

Monoculture rubber plantations have been replacing tropical rain forests substantially in Southern China and Southeast Asia over the past several decades, which have affected human wellbeing and ecosystem services. However, to the best of our knowledge on the extent of rubber plantation expansion and their stand ages is limited. We tracked the spatiotemporal dynamics of deciduous rubber plantations in Xishuangbanna, the second largest natural rubber production region in China, from 2000 to 2010 using time-series data from the Phased Array type L-band Synthetic Aperture Radar (PALSAR), Landsat, and Moderate Resolution Imaging Spectroradiometer (MODIS). We found that rubber plantations have been expanding across a gradient from the low-elevation plains to the high elevation mountains. The areas of deciduous rubber plantations with stand ages ≤5, 6–10, and ≥11-year old were ~1.2 × 105 ha, ~0.8 × 105 ha, and ~2.9 × 105 ha, respectively. Older rubber plantations were mainly located in low-elevation and species-rich regions (500–900 m) and younger rubber trees were distributed in areas of relative high-elevation with fragile ecosystems. Economic and market factors have driven the expansion of rubber plantations, which is not only a threat to biodiversity and environmental sustainability, but also a trigger for climatic disasters. This study illustrates that the integration of microwave, optical, and thermal data is an effective method for mapping deciduous rubber plantations in tropical mountainous regions and determining their stand ages. Our results demonstrate the spatiotemporal pattern of rubber expansions over the first decade of this century.

Dung beetles and their ecological functions in three agroforestry systems in the Lacandona rainforest of Mexico

There is growing interest in evaluating the impact that management intensity of agroecosystems has on animal communities and their ecological functions. Dung beetles are a highly used focal taxon for assessing the effects of anthropogenic disturbances and management practices on biodiversity. In the Lacandona rainforest region in southern Mexico, we quantified several metrics of the dung beetle community (number of species, number of individuals, total biomass, mean beetle size) and four of their ecological functions (dung removal, soil excavation, seed dispersal, seed exhumation) in conserved rainforest and three agroforestry systems with different management intensities: rustic cocoa, polyculture cocoa, and rubber monoculture. We also assessed the correlation between dung removal and the other functions, as well as the relationships between functions and community metrics. Land-use type affected the dung beetle communities as well as their functions, with negative effects on response variables in the most intensely managed agroecosystems (polyculture cocoa and rubber). Rustic cocoa had values similar to those of the conserved forest for all functions and community metrics, except the mean number of species per trap. Dung removal was correlated with the other ecological functions. The mean number of species per trap was significantly associated with all four functions. In our study region rustic cocoa plantations favor the maintenance of a high proportion of dung beetle species and maintain their ecological functions. Our findings corroborate that agroecosystems with less intense management may contribute to buffering the effects of landscape homogenization caused by more intensely managed agroecosystems, such as rubber plantations.

Impact of forest conversion to oil palm and rubber plantations on microclimate and the role of the 2015 ENSO event

Oil palm and rubber expansion is a main driver of the widespread deforestation of tropical rainforests taking place in South-East Asia, particularly in Indonesia. The replacement of forests with monoculture plantations of rubber and oil palm reduces biodiversity and carbon pools but also modifies canopy structure, which is an important determinant of microclimate. There is, however, a lack of quantitative information characterizing the effect of such land transformation on microclimate. We report the first medium-term observations of below-canopy microclimatic conditions (air temperature, relative humidity, vapour pressure deficit and soil temperature) across forest, jungle rubber agroforest, oil palm and rubber monoculture plantations in Sumatra/Indonesia. The data set covers a period of approximately three years (2013–2016) and includes one of the strongest El Niño-Southern Oscillations (ENSO) of the last decades. Forests were up to 2.3 and 2.2 °C cooler than oil palm and rubber monocultures respectively. The monocultures were also drier (11.9% and 12.8% less in oil palm and rubber respectively) and had higher vapour pressure deficit (632 Pa and 665 Pa higher in oil palm and rubber respectively) than the forest, while differences in soil temperature were less pronounced. Conversion from forest to other land uses, especially to monocultures, also amplified the diurnal range of all microclimatic variables studied. Jungle rubber stands out as the transformed land-use system that maintains more stable microclimatic conditions. Our results indicate that canopy openness is a key driver of below-canopy microclimate, and hence could be used in climate models to better evaluate climatic feedbacks of land-use change to rubber and oil palm. The ENSO event of 2015 led to warmer and drier conditions than in the previous two years in all four land-use systems, especially in the forest (up to 2.3 °C warmer, 8.9% drier and up to 351 Pa more during ENSO). The relative effect of ENSO was lower in the monoculture plantations, where below-canopy microclimate is generally more similar to open areas. Forests exhibited the largest differences with the pre-ENSO years, but still maintained more stable microclimatic conditions (lower temperatures and vapour pressure deficit and higher relative humidity) due to their higher climate regulation capacity. During ENSO, microclimatic conditions in jungle rubber were comparable to those in the monocultures, suggesting that while forests buffered the increase of temperature, jungle rubber might have surpassed its buffering capacity to extreme events. This capacity of buffering extreme climatic events should be considered when assessing the effects of land-use change.

Recognizing the Rapid Expansion of Rubber Plantation – A Threat to Native Forest in Parts of Northeast India

With the current trend of land use/land cover (LULC) change taking place globally, several parts of northeast India are also showing signs of change in LULC pattern leading to forest loss. This study focusses on the expansion of monoculture rubber plantation ( Hevea brasiliensis ) in selected sub-watersheds in north-east India, and distributed in parts of north Tripura, Mizoram and a major portion in the Karimganj district of Assam. Remote sensing and GIS technique has been used to map and analyse the extent of rubber plantation using temporal IRS LISS III satellite data from 1997 to 2013. It has been observed that rubber plantation increased from 4.47 sq. km to 28.42 sq. km in various parts of the study area. The expansion was more rapid during recent times, i.e. during 2010 to 2013. The plantation took place in dense forest, open forest and degraded forest areas. The spread of the plantation was also observed in one reserved forest located within the study area. There are several instances of negative impacts of rubber plantation expansion in Southeast Asia. Similar expansion of rubber plantation has been observed in northeast India as well. Further spread of rubber plantations in the region needs to be regulated to avoid conversion of dense and reserved forest areas by fostering use of mixed cropping methods instead of rubber monocultures, and by adopting more sustainable land use and management practices.

Forest gardens management under traditional ecological knowledge in West Kalimantan, Indonesia

Winarni B, Lahjie AM, Simarangkir B.D.A.S., Yusuf S, Ruslim Y. 2018. Forest gardens management under traditional ecological knowledge in West Kalimantan, Indonesia. Biodiversitas 19: 77-84. Local wisdom of Dayak Kodatn people in West Kalimantan in forest management shows that human and nature are in one beneficial ecological unity known as Traditional Ecological Knowledge (TEK). Former cultivation forest areas are managed in various ways, including planting forest trees, fruit-producing plants, and rubber trees until they transform into the forest garden. This research used three models, monoculture rubber cultivation (Model 1), combined rubber and camphor cultivation (Model 2), and combined rubber and durian cultivation (Model 3). This research intended to: (i) analyze the production of rubber latex and durian fruit; (ii) analyze the growth increment of camphor and durian trees; (iii) analyze the financial feasibility of rubber tree plantation, combined rubber and camphor tree plantation, and combined rubber and durian trees plantation; (iv) formulate the model of rubber cultivation. This research also used measurement methods other than field measurement, which were tree diameter and height, rubber latex and durian fruit weight, and questionnaire interviews. The maximum productions of rubber latex from three models were achieved at the age of 17 years, while maximum production of durian fruits was achieved at the age of 55 years. The maximum growth increment of camphor and durian trees were achieved at the age of 40 years. Based on NPV analysis and IRR, those three models were worthy of being cultivated. Financially, the combined rubber and durian cultivation (Model 3) was the most profitable, followed by monoculture rubber cultivation (Model 1), and lastly the combined rubber and camphor cultivation (Model 2).

The use of a mixed rubber landscape by tufted-ear marmosets.

With the loss and fragmentation of tropical forests, the survival of primates depends on their ability to adapt to human-introduced modifications in their habitat. Marmosets are known for their ecological and behavioral plasticity and have been registered in various agricultural landscapes. Our goal was to describe the ecology of tufted-ear marmosets (Callithrix sp.) in a rubber/forest landscape, monitoring their use of habitat and diet. We followed two groups using radio telemetry and visual observations for nine months at the Michelin plantation Ltd. in Bahia, Brazil. Both groups used mainly pioneer forest and rubber with pioneer vegetation more than expected according to availability, even though they explored all types of vegetation. Rubber monocultures act as corridors for marmoset locomotion among more suitable habitats. Feeding, gummivory and socialization were mainly performed in the pioneer forest (with or without rubber), in which most sleeping sites and food sources were found. Groups of marmosets can incorporate agroforest matrixes to their area of use and activity patterns. Maintenance of marmosets in fragmented landscapes might be favored by their diet flexibility, with the use of resources such as gum and fruit, including exotic plants. Although known for their ecological flexibility, marmosets do require certain resources to be present in native habitat to adapt to agricultural landscapes. Patches of forest within a rubber landscape and pioneer vegetation in the rubber inter-rows should be considered to maintain populations of Callithrix in rubber landscapes.

Bark and Ambrosia Beetle (Curculionidae: Scolytinae) Diversity Found in Agricultural and Fragmented Forests in Piracicaba-SP, Brazil.

Land use changes and forest fragmentation result in biodiversity loss and displacement, with insects among the most affected groups. Among these, bark beetles (Curculionidae: Scolytinae) occupy a prominent position due to their close ties to food resources, i.e., trees, and importance as primary decomposers in forest ecosystems. Therefore, our study aimed to document scolytine biodiversity associated with landscape components that vary based on their physical or botanical composition. Bark beetle diversity was sampled monthly for 12 mo in an Atlantic forest remnant and five adjacent vegetation plots (mixed Agroforestry System-AFS, of native trees and fruit species; AFS of rubber trees and coffee plants; coffee monoculture; rubber monoculture; and pasture). In total, 1,833 individuals were sampled from 38 species of which 24 (63%) were detected in very low abundance. The remaining 14 species were more abundant and widespread almost in all areas. Hypothenemus hampei (Westwood), Premnobius cavipennis (Eichhoff), Hypothenemus sp1., and Xyleborus volvulus (Fabricius) were the most abundant. The greatest abundance and richness of bark beetles were found in the dry and cold season. The varied microclimatic conditions of the vegetation plots greatly affected the diversity of the Scolytinae. Solar radiation presented a significant negative effect on abundance in almost all the studied areas. The greatest scolytine diversity was found in anthropic areas with tree canopy structure. Open areas (pasture and coffee monocrop) had a lower species diversity. Similarly, a lower abundance and species richness were found for the Atlantic forest remnant.

Impact of tropical forest conversion on soil bacterial diversity in tropical region of China

In Xishuangbanna, a China's tropical region, monoculture rubber plantations have expanded dramatically over the past two decades. However, the effect of conversion of tropical forests to rubber plantations on the soil microbial compositions and diversity remains poorly understood. This study investigated the bacterial diversity and biomass in rubber plantations, secondary tropical forest and tropical seasonal rainforest in Xishuangbanna, southwest China, based on an analyses of PCR-amplified 16S rRNA genes. Our findings revealed that soil of rubber plantation was different from secondary tropical forest and tropical seasonal rainforest in bacterial compositions at phylum, family as well as OTU (Operational Taxonomic Units) levels. The most abundant phylum in rubber plantations was Firmicutes, however, in secondary tropical forest and tropical seasonal rainforest it was Proteobacteria. In both dry season and rainy season, diversity indices of rubber plantations were significantly higher than those of secondary tropical forest and tropical seasonal rainforest, indicating that bacterial diversity increased after conversion. However, the total microbial biomass carbon (MBC) decreased after conversion. RDA results showed that soil pH and total phosphorus maybe the two most important factors controlling bacterial communities, and explained 49.2% and 38.1% of total variance of phylum compositions, respectively. Management practices, especially the application of fertilizers with phosphorous would thus probably influence the taxonomic composition and diversity of bacterial communities in this region.

Throughfall kinetic energy and its spatial characteristics under rubber-based agroforestry systems

Rubber is usually grown as a monoculture but there have been recent attempts to encourage rubber-based agroforestry systems to reduce adverse environmental impacts, including the reduction of soil erosion in Xishuangbanna, SW China. To estimate the influence of different types of rubber-based agroforestry systems on soil erosion processes, we measured the throughfall kinetic energy (TKE) under different vegetation types by using 640 sand-filled Tübingen splash cups. This study was conducted in Xishuangbanna Tropical Botanical Gardens under natural rainfall conditions. Our results indicated that in both rubber-based agroforestry systems and rubber monocultures, a significant linear positive correlation exists between TKE and rainfall amount. Rainfall amount is a critical factor that contributes to soil detachment in rubber plantations in this region. TKE under rubber plantation conditions was found to be notably higher than under open field conditions (ranging from 1.84 to 2.32 times greater). However, there was no significant difference under multiple canopies compared to monoculture. TKE values under the different rubber-based agroforestry systems were closely related to the canopy structure, and TKE and leaf area index were significantly negatively correlated. The spatial variability of TKE was higher in rubber-based agroforestry systems than in rubber monocultures. In addition, TKE was usually concentrated in 3–4m bands that did not have the protection of a sub-canopy. The fact that the erosion by TKE under rubber-based agroforestry was still high highlights the importance of selecting intercrops when constructing rubber-based agroforestry systems and of improving planting patterns.

Land Degradation Controlled and Mitigated by Rubber‐based Agroforestry Systems through Optimizing Soil Physical Conditions and Water Supply Mechanisms: A Case Study in Xishuangbanna, China

AbstractDifferent rubber‐based agroforestry systems are adopted to control and mitigate land degradation. However, the soil physical conditions and soil hydrological processes of different agroforestry systems are still unclear. Thus, in this study, rubber (Hevea brasiliensis) monoculture, rubber and Clerodendranthus spicatus agroforestry system (RCS) and rubber and Amomum villosum agroforestry system (RAV) were developed from a degraded land that had similar backgrounds of terrain and management measures for 50 years. Conventional methods were applied, and dye tracer experiments were conducted to measure the soil physical conditions and determine the water movement in soil. After 5 years' growth, both RCS and RAV could effectively promote the soil physical conditions and optimize soil structure by improving the proportion of the three soil phases. Favourable soil properties, multiple‐layered canopies and ground cover in agroforestry systems could promote the formation of three‐dimensional hydraulic redistribution in soil profile. The infiltration of rainfall into the soil was enhanced; meanwhile, surface runoff and soil erosion were mitigated, and then more water was transported, redistributed and stored into the different soil layers by the more dominant preferential flow, water exchange and lateral flow in soil profiles. These water supply mechanisms could allow planting intercrops with rubber trees to uptake water from different water sources and coexist in an agroforestry system. Our results highlighted that rubber‐based agroforestry systems are a useful management practice to maximize the utilization of land and water resources. Copyright © 2017 John Wiley & Sons, Ltd.

Tree soil water uptake and transpiration in mono-cultural and jungle rubber stands of Sumatra

Rubber tree mono-cultural plantations are expanding. Also, there is an increasing search for ‘green’ rubber production. Rubber tree cultivation in stands with admixed, spontaneously established native trees, referred to as jungle rubber, has a long tradition on Sumatra. For rubber tree monocultures on mainland Asia, concerns have been raised because of potentially very high tree transpiration rates. The objectives of our study were to analyze tree water use rates and tree soil water uptake depths in mono-cultural and jungle rubber stands with a focus on the role of tree diameter. Sap flux measurements suggest similar water use rates for rubber trees in the two cultivation systems. Stand-level transpiration in jungle rubber was 27% higher than in rubber monocultures, which was related to higher stand densities in jungle rubber stands. A water stable isotope (δ18O and δD) approach suggests different soil water uptake depths for the rubber trees in the two cultivation systems. In a relatively dry period, the main tree water uptake in the monoculture was relatively close to the soil surface, whereas rubber trees in jungle rubber stands mainly took up water from deeper soil strata; here the native trees had their main uptake depth relatively close to the soil surface. This pattern indicates plasticity in rubber tree water uptake and points to competitive displacement. Across rubber trees in both cultivation systems and also among the native trees, there was a clear relationship between tree diameter and soil water uptake depth: bigger trees tended to take up soil water closer to the soil surface. Diameter and density regulation by thinning of big native trees thus appears as a potential management option for influencing water uptake in jungle rubber stands in favor of rubber trees.

Adoption of intercropping among smallholder rubber farmers in Xishuangbanna, China

ABSTRACTWhile the expansion of rubber plantations in the mountainous areas of Southern China has contributed to poverty reduction among the indigenous ethnic groups, the concerns about the associated negatives on ecosystems and sustainable development of livelihoods is rising. One of the measures suggested to reduce environmental and economic risks is rubber intercropping. This study uses cross-section data of some 600 rubber farmers in Xishuangbanna, as a basis to develop four empirical models in order to analyse adoption of intercropping at farm and at plot level. Our study shows that only a small proportion of rubber farmers have adopted intercropping, with tea being the most frequently adopted intercrop. However, we also find that intercropping is an important source of income for the household in the lower income category. Intercropping adoption is affected by ethnicity, household wealth and family labour. The choice of intercrops depends on the nature of rubber plots, the age of rubber trees and geography. This study contributes to a better understanding of the transformation path from rubber monoculture to more diversified, rubber-based agroforestry systems and thus can provide important information for agricultural extension services charged with the promotion of sustainable rubber-based livelihood systems in the Mekong area.