Shem Kuyah

How does biomass distribution change with size and differ among species? An analysis for 1200 plant species from five continents

Summary We compiled a global database for leaf, stem and root biomass representing c. 11 000 records for c. 1200 herbaceous and woody species grown under either controlled or field conditions. We used this data set to analyse allometric relationships and fractional biomass distribution to leaves, stems and roots. We tested whether allometric scaling exponents are generally constant across plant sizes as predicted by metabolic scaling theory, or whether instead they change dynamically with plant size. We also quantified interspecific variation in biomass distribution among plant families and functional groups. Across all species combined, leaf vs stem and leaf vs root scaling exponents decreased from c. 1.00 for small plants to c. 0.60 for the largest trees considered. Evergreens had substantially higher leaf mass fractions (LMFs) than deciduous species, whereas graminoids maintained higher root mass fractions (RMFs) than eudicotyledonous herbs. These patterns do not support the hypothesis of fixed allometric exponents. Rather, continuous shifts in allometric exponents with plant size during ontogeny and evolution are the norm. Across seed plants, variation in biomass distribution among species is related more to function than phylogeny. We propose that the higher LMF of evergreens at least partly compensates for their relatively low leaf area : leaf mass ratio.

Evaluating a non-destructive method for calibrating tree biomass equations derived from tree branching architecture

Key messageFunctional branch analysis (FBA) is a promising non-destructive method that can produce accurate tree biomass equations when applied to trees which exhibit fractal branching architecture.AbstractFunctional branch analysis (FBA) is a promising non-destructive alternative to the standard destructive method of tree biomass equation development. In FBA, a theoretical model of tree branching architecture is calibrated with measurements of tree stems and branches to estimate the coefficients of the biomass equation. In this study, species-specific and mixed-species tree biomass equations were derived from destructive sampling of trees in Western Kenya and compared to tree biomass equations derived non-destructively from FBA. The results indicated that the non-destructive FBA method can produce biomass equations that are similar to, but less accurate than, those derived from standard methods. FBA biomass prediction bias was attributed to the fact that real trees diverged from fractal branching architecture due to highly variable length–diameter relationships of stems and branches and inaccurate scaling relationships for the lengths of tree crowns and trunks assumed under the FBA model.

Trees in agricultural landscapes enhance provision of ecosystem services in Sub-Saharan Africa

ABSTRACT The recent interest in multi-functional agricultural landscapes has not been matched with formal assessment of the roles that trees play across the spectrum of ecosystem services (ESs) provided in Sub-Saharan Africa (SSA). A structured literature review (1995–2014) assessed 350 journal articles about provision of one or more ESs by trees on farms and in agricultural landscapes in SSA. This revealed information on 15 ESs from studies in 23 countries covering arid (1% of studies), semi-arid (49%), sub-humid (26%) and humid (24%) agro-ecological zones. The majority of the studies reported provisioning (39%) and supporting (35%) followed by regulating (26%) ESs while studies on cultural services were scarce. Beneficial impacts of trees were dominating (58%), in particular in semi-arid zones where they were associated with enhancing water and nutrient cycling. A decline in some ESs was reported in 15% of the studies, while 28% found no effect of trees. Although the effects of trees were mainly positive, a decline in crop production was noted as a key trade-off against the provisions of ESs, such as modification of microclimate. This highlights the need to manage trade-offs among impacts of trees on ES provision to reduce competition and increase complementarity between trees and crops.

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.

Regulating Ecosystem Services Delivered in Agroforestry Systems

Regulating ecosystem services are the benefits obtained from the regulation of ecosystem processes. The multifunctional role of trees makes agroforestry interventions ideal management practices to supply a variety of regulating ecosystem services. This chapter reviews seven regulating ecosystem services (carbon sequestration, soil fertility enhancement, prevention of soil erosion, water regulation, wind regulation, pest regulation, and pollination) for which research in tropical and/or temperate regions have shown evidence that introduction of agroforestry practices on crop or pasture land can provide significant benefits. In each case, we provide a general description of the ecosystem service and evidence of whether this service increases or not by agroforestry practices and discuss the factors that affect the provision of the ecosystem service in agroforestry. We also discuss the multifunctionality with synergies and trade-offs among regulating ecosystem services and provide suggestions on how modifications of tree-based systems may increase ecosystem service provision. Generally, agroforestry increases delivery of regulating ecosystem services within the landscape, leading to increased growth and yields from crops and animals. However, there are situations where agroforestry may lead to a reduction in certain ecosystem services, leading to trade-offs. Trade-offs among regulating services and between regulating services and other ecosystem services are, for example, brought about by competition for water and other resources and increases in certain pests. We discuss how agroforestry practices can be designed in a way that reduces ecosystem service trade-offs while increasing the productivity of crops and livestock.

Diversity and importance of local fodder tree and shrub resources in mixed farming systems of central Kenya

Abstract Locally available tree fodder resources are seldom considered in livestock feeding strategies despite their nutritional potential to supplement grass forages. Knowledge gaps on species availability and utilization may be the cause. This study surveyed 117 random farms locatedin humid (Githunguri and Lari) and drier parts (Kayatta) of central Kenya to identify fodder trees and shrubs diversity available to supplement existing livestock feeding options. Major forage and feed types used by farmers include napier grass (98.2%); maize and bean stover (85.7%); banana stover (60.5%), dairy meal (60.1%), hay (58.3%) and fodder trees (57.7%). A total of 60 fodder tree and shrub species were found on farm. Indigenous species comprised 65% of total richness but only 12% of the total abundance. The most common exotic and indigenous trees were Grevillea robusta and Persea americana, and Acacia tortilis and Terminalia brownii, respectively. Mean species richness per farm was 6.8 with significantly higher richness in Kayatta (10) compared to Lari and Githunguri (both 5.4, p < 0.05). Land size had a positive influence on total indigenous species richness and abundance on farms while the number of dairy cows had a negative influence. Findings confirm availability of diverse tree fodder trees to supplement current feeding options. However, where farms are small, farmers may require external feed sources as limited tree richness and abundance may not support profitable dairy farming.