Roads are an increasingly important anthropogenic disturbance to tropical ecological systems. Although the ecological impacts of roads are now well recognised, there remains a lack of certainty regarding how roads in general and roads with different widths affect vital ecosystem services such as above‐ground biomass (AGB) in tropics. Using a non‐destructive sampling method, we investigated disturbance effects of roads on AGB and related attributes in Xishuangbanna, China. We surveyed woody plants in natural forests, rubber plantations, and tea plantations up to 100 m from the edge of three different road widths and estimated AGB using allometric equations at 10 m intervals. Two sample t‐test results confirmed that natural forests stored more AGB than rubber and tea plantations, and less AGB at edges of wider road than at edges of narrower road. Linear mixed effects models revealed that land use, road width, and distance from edge significantly explained 68% (both fixed and random factors) variation in AGB. We observed two results that indicated wider roads altered more AGB than narrower road types in natural forests. First, AGB declined at road edges; second, the disturbance effects on AGB by wider road types went deeper than narrower roads did in natural forests. Our results suggest that both widening the existing roads and construction of new roads will degrade ecosystem productivity. We recommend that impacts assessments of roads on AGB should be considered and taken serious while planning and designing roads to avoid serious damages to many ecosystem services that AGB provides.
Tag: biomass
Trends in tree growth and intrinsic water-use efficiency in the tropics under elevated CO2 and climate change
Global environmental changes affect tree growth and physiological behavior across the major biomes around the world. However, it is not yet clear how tree growth and physiology of tropical trees responded to global environmental changes in a long term, yet such information is critical to get insight into how tropical trees will respond to future global changes. The main objective of this review article is to explore the long-term trends in tree growth, carbon isotope discrimination (Δ13C), intercellular CO2 concentration (Ci), and intrinsic water-use efficiency (iWUE) across the tropics and subtropics. We distinguished between data generated on plot levels or on species or tree individual levels. Stand-level growth trends were not consistent across the studies and plots, although recent studies indicated a declining growth trend. Ci and iWUE consistently increased during the past decades, while Δ13C remained nearly constant. Increased iWUE either caused by higher photosynthetic capacity or reduced stomatal conductance did not translate into tree- and species-level radial growth, probably because assimilated carbon was allocated more to the root development to facilitate water absorption from moisture-limited soils rather than to basal area growth or xylem cell differentiation and maturation processess were impared by cavitation induced hydraulic limitations. Thus, higher temperature or drought-induced soil moisture deficit might have strongly impaired radial growth which has probably overridden the small positive effect of atmospheric CO2. Yet, disentangling the role of multiple drivers in explaining stem radial growth variation and their interactive effects on tropical trees under natural field conditions are not adequately studied and hence future research should focus on this aspect. Tree hydraulics should be taken into account in future research when predicting radial growth variability in tropical trees.
An Introduction to the Climate-Smart Agriculture Papers
Over the last decade, international concerns about climate change have stimulated broad investment in the pursuit of agriculture that is more climate-smart. These concerns are particularly pressing in Africa, where most farmers remain severely impoverished and dependent on rain-fed production systems. This volume collates some of the latest research from agricultural scientists working to speed up the development and adoption of more climate-smart farming systems in eastern and southern Africa. These 25 papers highlight ongoing efforts to better characterise climate risks, develop and disseminate climate-smart varieties and farm management practices, and integrate these technologies into well-functioning value chains. The papers emphasise the additional research efforts needed to improve the understanding and response to climate risk. The expert authors also make suggestions for strengthening the responsiveness of agricultural research and extension systems to future climate changes.
Cowpea water relations and growth on a toposequence water table gradient
Cowpea sown after wetland rice in tropical monsoon climates is frequently subjected to soil saturation and a high water table during early growth. We compared the effects of variation in water table regime on the shoot and root growth, and plant water relations of two medium-maturing (cv. TVX3236-01G and TVX3410-02J) and two early maturing (cv. BS6 and IT82D-889) cowpea [Vigna unquiculata (L.) Walp] cultivars in three water table depth regimes on a Typic Tropudalf toposequence. Our objective was to elucidate the possible mechanisms of differential cultivar adaptation to shallow water table conditions. The shallow water table regime (SWT) significantly reduced the total dry matter accumulation and harvest index for BS6, an early maturing cultivar (reductions in stems, leaves, pods, and total dry matter by 82, 77, 88, and 84% respectively), while the least reductions (reductions by 44, 3, 57 and 55%, respectively) was observed for TVX 3410-02J, a medium-maturing cultivar. Roots of the medium cultivars were more concentrated in the top 0.2m in the SWT Site than those of the early-maturing cultivars. Roots of the medium cultivars later penetrated to 0.8-m maximum depth compared to 0.6-m maximum depth for the early cultivars, and extracted soil water from 20 cm deeper in the soil profile than the early maturing cultivars. The medium-maturity cultivars maintained higher leaf water potentials and lower canopy temperatures throughout the season. This was associated with greater end-of-season total soil profile water extraction. The medium-maturing cultivars showed better adaptation to shallow water table conditions due to superior plant water status, rooting pattern, and biomass production and partitioning.
Mixed planted-fallows using coppicing and non-coppicing tree species for degraded acrisols in Zambia
The widespread planting of Sesbania sesban fallows for replenishing soil fertility in eastern Zambia has the potential of causing pest outbreaks in the future. The pure S. sesban fallows may not produce enough biomass needed for replenishing soil fertility in degraded soils. Therefore, an experiment was conducted at Kagoro in Katete district in the Eastern Province of Zambia from 1997 to 2002 to test whether multi-species fallows, combining non-coppicing with coppicing tree species, are better than mono-species fallows of either species for soil improvement and increasing subsequent maize yields. Mono-species fallows of S. sesban (non-coppicing), Gliricidia sepium, Leucaena leucocephala and Acacia angustissima (all three coppicing), and mixed fallows of G. sepium + S. sesban, L. leucocephala + S. sesban, A. angustissima + S. sesban and natural fallow were compared over a three-year period. Two maize (Zea mays) crops were grown subsequent to the fallows. The results established that S. sesban is poorly adapted and G. sepiumis superior to other species for degraded soils. At the end of three years, sole G. sepium fallow produced the greatest total biomass of 22.1 Mg ha1 and added 27 kg ha1 more N to soil than G. sepium + S. sesban mixture. During the first post-fallow year, the mixed fallow at 3.8 Mg ha1 produced 77% more coppice biomass than sole G. sepium, whereas in the second year both sole G. sepium and the mixture produced similar amounts of biomass (1.6 to 1.8 Mg ha1). The G. sepium + S. sesban mixture increased water infiltration rate more than sole G. sepium, but both these systems had similar effects in reducing soil resistance to penetration compared with continuous maize without fertilizer. Although sole G. sepium produced high biomass, it was G. sepium + S. sesban mixed fallow which resulted in 33% greater maize yield in the first post-fallow maize. However, both these G. sepium-based fallows had similar effects on the second post-fallow maize. Thus the results are not conclusive on the beneficial effects of G. sepium + S. sesban mixture over sole G. sepium
Tephrosia species and provenances for improved fallows in southern Africa
Seeking an alternative to Sesbania spp. tree fallows, a Tephrosia species and provenance trial was conducted at Msekera Research Station, Chipata (Zambia) to evaluate eleven Tephrosia vogelii and three Tephrosia candida provenances. They were tested for biomass production, quality of biomass, resistance to root-knot nematodes, nitrogen release, and for their effects on soil nitrogen dynamics. At the end of 1.5 years, the T. candida provenances 02970, 02971 and 02972 from Madagascar produced two times greater amount of aboveground biomass than the T. vogelii provenances. There was little variability among the T. vogelii provenances in terms of litter and biomass production. Weed growth was significantly greater under T. vogelii than T. candida provenances. While Tephrosia vogelii provenance 98/02 from Zambia and T. candida 02972 were highly tolerant to the Meloidogyne incognita nematodes, T. vogelii provenances 02977, 98/03, 02973 from Kenya, Zambia and Malawi, respectively, were highly susceptible to the nematodes. The Tephrosia species and provenances showed a wide variability in terms of N, lignin and polyphenol concentration in their foliage. Mineralization of N in the foliage of T. candida provenances 02970 and 02971 and T. vogelii provenances 98/04 and 02974 from Malawi occurred rapidly within 14 weeks of incubation. At the end of the 2-year growth period, there was significantly greater total inorganic N under T. candida provenance 02972 (12.5 mg kg1) than T. vogelii (5 mg kg1) provenance Mungwi 98/02. Maize (Zea mays L.) yields after T. candida provenances were greater than those after T. vogelii provenances. Further testing of the most promising provenances is needed for their effects on subsequent maize yields under a range of farm conditions.
Tree pruning, zone and fertiliser interactions determine maize productivity in the Faidherbia albida (Delile) A. Chev parkland agroforestry system of Ethiopia
Faidherbia albida is an important tree species in the parkland agroforestry system of the Rift Valley region, central and south-eastern Ethiopia. Positive effects of F. albida on crop production are widely recognised. However, the effects of tree pruning, zone and fertiliser interactions on crop growth have not been addressed in earlier studies. A field experiment containing three levels of tree pruning (100% pruned, 50% pruned, and unpruned) as main plots, and application of recommended rates of N and P fertilisers as sub-plots, was conducted during the 2015 and 2016 growing seasons. Maize grain yield and biomass, light intensity, and soil nutrients and moisture were measured at different positions from each F. albida tree trunk (0–2, 2–4 and 4–6 m) and in crop-only plots. Biomass and yield of maize were significantly greater under tree canopies compared to crop-only plots in both the 2015 and 2016 growing seasons, regardless of pruning levels. Fertilisation significantly increased yields under tree canopies compared to crop-only plots in both years. Light intensity increased with distance from trees and with greater pruning levels. Soil carbon and nutrient concentrations and moisture content decreased with increasing distance from tree and with soil depth. These results suggest that maize production and profitability could be maintained or improved through only partial pruning of F. albida rather than pollarding, and by preferentially applying fertilisers in normal and wet years. Recommendations need to be evaluated in a total system context including other rotational crops, fuel, livestock and socio-economic factors.
Agroforestry and firewood production
The increasing recognition of the potential role of agroforestry as an integrated, sustainable and multiple-output land use system, and of the productive and protective value of trees on farmlands, is discussed. An overview is given of the types of agroforestry system found (with tables indicating various classifications and arrangements) and of the role of agroforestry in the production of biomass energy, particularly the use of multipurpose trees for fuelwood production in agroforestry systems. Examples of suitable species are given for different ecological regions and countries. Different management systems and programme options are discussed (in the light of recent forestry initiatives such as farm and community forestry, and woodlots) with a consideration of socioeconomic factors
Quantifying tree biomass carbon stocks and fluxes in agricultural landscapes
This chapter presents methods to quantify carbon stocks and carbon stock changes in biomass of trees in agricultural landscapes. Specifically it assesses approaches for their applicability to smallholder farms and other tree enterprises in agricultural landscapes. Measurement techniques are evaluated across three criteria: accuracy, cost, and scale. We then recommend techniques appropriate for users looking to quantify carbon in tree biomass at the whole-farm and landscape scales. A basic understanding of the carbon cycle and the concepts of biomass assessment is assumed.
Adoption of Agroforestry technologies in Zambia: synthesis of key findings and implications for policy
Due to a mix of agro-ecological factors (incessant drought, low soil fertility, environmental degradation) and other man-made problems (illiteracy, unfavorable development policies), southern Africa region faces several challenges including worsening poverty, food insecurity, low income base and more recently HIV/AIDS pandemic. Low soil fertility is identified as one of the greatest biophysical constraints to increasing agricultural productivity (Bekunda et al., 1997, Sanchez, 1999). The degradation of soils is caused by a breakdown of the traditional production systems resulting from shortening of fallow periods due to population pressure (Kwesiga et al., 1999). With the collapse of the erstwhile government support for the use of mineral fertilizer (e.g. through subsidies and distribution channels), in the 1990s, the ability of most smallholder farmers to purchase the same level of mineral fertilizers was reduced because the input became unaffordable to them. In addition, many countries in southern Africa are landlocked thus increasing the cost of transporting fertilizer from the ports. Howard and Mungoma (1996) estimated that the use of mineral fertilizer fell by 70% following an increase in the cost of the inputs. The sub-region also faces a rapid degradation of the miombo woodland, shortage of fodder and decreasing access to fuelwood supplies (Kwesiga and Beniest, 1998). For example, Chidumayo (1997) estimated that Zambia alone loses about 200 000 ha of forests per year. Some of the key avenues for overcoming food insecurity and rural poverty in southern Africa include reversing soil fertility depletion, intensifying and diversifying land use with introduction of high value products, and facilitating an appropriate policy environment for the smallholder farming sector. While mineral fertilizer is still one of the best options for overcoming land depletion and increasing food production, the majority of the smallholder farmers are unable to afford and apply the fertilizers at the recommended rates and at the appropriate time because of high cost and delivery delays (Kwesiga et al, 2003; Akinnifesi et al, 2006). Low-cost technologies are needed on a scale wide enough to improve the livelihood of these farmers. This will require the adoption of new approaches to agriculture and rural development (Pretty, 1995). Agroforestry has proven to be one of such approaches. For the past fifteen years, farmers and researchers from different national and international institutions led by the International Centre for Research in Agroforestry (ICRAF), otherwise known as the World Agroforestry Centre have been combining their expertise and resources to develop agroforestry technologies and options to address some of these challenges facing smallholder agricultural production and the environment in the sub-region. The different types of agroforestry technologies address specific human and environmental needs in southern Africa. These include fertilizer tree systems for replenishing soil fertility, rotational woodlots for solving fuel wood problems, fodder banks to supplement feed for livestock and indigenous fruit trees for improving nutrition during the seasonal hunger periods and enhance the preservation of indigenous plant genetic materials.