The role of complex agroforestry systems in the conservation of forest tree diversity and structure in southeastern Ghana

The role of different agroforestry systems in the conservation of plant diversity and forest structure has not been directly compared in many agricultural dominated landscapes. In this study, we investigated tree diversity and forest structure in a complex agroforestry landscape traditionally grown for cocoa and mixed food crops and compared these to the natural forest in southeastern Ghana. The study was carried out using 36 25 m × 25 m plots. There was significant difference [95% Confidence Interval (95% CI)] in the native forest/non-crop tree species richness between the natural forest and the agroforest farmlands but species richness was similar between the cocoa and mixed food crops agroforests. The density of native forest/non-crop trees was significantly higher (P < 0.05) in the natural forest but similar between cocoa and mixed food crops agroforest. Similarly, the basal area of native forest/non-crop trees was significantly higher (P < 0.05) in the natural forest but comparable between cocoa and food crops agroforest. Of the 20 most abundant native forest/non-crop trees recorded, 12 of them showed significant responses (P < 0.05) to land use change with nine of the species significantly abundant in the natural forest relative to the agroforest systems. Eighteen native forest/non-crop trees species in the agroforestry systems were commonly recorded as being used; 100% of them being used as fuel wood with 83.3 and 77.8%, respectively, used as medicines and materials. The findings of this study suggests that although complex agroforestry systems are a poor substitute for the natural forest the heterogeneous mosaic landscape in which complex agroforestry forms part can be strategically managed to maximize the benefits of both sustainable agriculture production and conservation of plant diversity by acting as buffer between protected areas and intensively managed areas.     

Stress responses of <Emphasis Type="Italic">Salix gracilistyla</Emphasis> and <Emphasis Type="Italic">Salix subfragilis</Emphasis> cuttings to repeated flooding and drought

To compare the responses to repeated flooding and drought of Salix gracilistyla, which grows on coarse gravel substrates, and Salix subfragilis, which grows on fine silt or clay substrates, we measured pre-dawn leaf water potential (Ψw _pd), osmotic adjustment (Ψw _tlp, Ψo _sat), and biomass production of cuttings under greenhouse conditions. The experimental design involved a control and four treatments that crossed 1 or 3-week flooding (F) with 1 or 2-week droughts (D). Ψw _pd was reduced after 2 weeks of drought when preceded by 1 week of flooding. Neither species increased osmotic adjustment in response to increased duration of drought between repeated 3-week flooding. Moreover, a decrease in the ratio of leaf biomass to total biomass or an increase in the ratio of root biomass to total biomass with longer drought repetitions was not observed for either species. The root ratio of S. gracilistyla was more strongly inhibited by flooding than that of S. subfragilis. The shoot-to-root ratio of S. subfragilis was higher than that of S. gracilistyla in all F combinations. The hypertrophied lenticel ratio of S. gracilistyla after 1 week of flooding was nearly the same as that after 3 weeks of flooding, whereas values for S. subfragilis after 1 week of flooding were lower than those after 3 weeks of flooding. The low allocation to roots and the generation of hypertrophied lenticels by S. gracilistyla in response to flooding, as compared with S. subfragilis, seem to be related to the different habitat substrate conditions of the two species.     

Above- and below-ground biomass dynamics in a sole cropping and an alley cropping system withGliricidia sepium in the semi-deciduous rainforest zone of West Africa

A considerable amount of data is available about above-ground biomass production and turnover in tropical agroforestry systems, but quantitative information concerning root turnover is lacking. Above- and below-ground biomass dynamics were studied during one year in an alley cropping system withGliricidia sepium and a sole cropping system, on aPlinthic Lixisol in the semi-deciduous rainforest zone of the Côte d'Ivoire. Field crops were maize and groundnut. Live root mass was higher in agroforestry than in sole cropping during most of the study period. This was partly due to increased crop and weed root development and partly to the presence of the hedgerow roots. Fine root production was higher in the alleys and lower under the hedgerows compared to the sole cropping plots. Considering the whole plot area, root production in agroforestry and sole cropping systems was approximatly similar with 1000–1100 kg ha^–1 (dry matter with 45% C) in 0–50 cm depth; about 55% of this root production occured in the top 10 cm. Potential sources of error of the calculation method are discussed on the basis of the compartment flow model. Above-ground biomass production was 11.1 Mg ha^–1 in sole cropping and 13.6 Mg ha^–1 in alley cropping, of which 4.3 Mg ha^–1 were hedgerow prunings. The input of hedgerow root biomass into the soil was limited by the low root mass ofGliricidia as compared to other tree species, and by the decrease of live root mass of hedgerows and associated perennial weeds during the cropping season, presumably as a result of frequent shoot pruning.     

Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths

Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched ¹⁵N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual ¹⁵N in the soil remained close to the injection points due to the joint application with a carbon source which promoted ¹⁵N immobilization. Temporal ¹⁵N uptake patterns (two-weekly leaf sub-sampling) as well as total ¹⁵N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little ¹⁵N from any depth but obtained an estimated 44–58% of its N from atmospheric N₂-fixation. Gliricidia took up an estimated 21 kg N ha^–1 and Peltophorum an estimated 42 kg N ha^–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of ¹⁵N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments. This revised version was published online in June 2006 with corrections to the Cover Date.     

A strategy for tree-perennial crop productivity: nursery phase nutrient additions in cocoa-shade agroforestry systems

Shade tolerant species response to nutrient additions and light regulation by canopy trees in perennial agroforestry systems has been well documented. However, accelerated early growth, particularly in cocoa-shade systems, may be offset by competition for limited resources on nutrient poor sites. To date, few agroforestry management strategies focus on nutrient manipulation of the shade tree component or strategies for precision nutrient application. Our research objective was to diagnose interactions between nutrient supplied shade trees intercropped with cocoa. We established greenhouse trials in Kwadaso, Ghana cultivating Terminalia superba seedlings with four fertility treatment levels: conventional rate (current practices) under linear additions, and half, full and double conventional rate under exponential additions (steady-state nutrition) to determine maximal growth and nutrient uptake. After 4 months of additions in the nursery, pre-fertilized T. superba seedlings were then out-planted into field trials with cocoa seedlings. After 4 months of intercropping, cocoa associated with half rate exponentially supplied T. superba had significantly larger leaf area, greater leaf number, and higher nutrition (N and P uptake) than cocoa associated with full rate conventionally supplied T. superba. This may be attributed to (1) more favorable light conditions under these taller shade seedlings and (2) the internal use of nutrients associated with exponentially supplied T. superba seedlings, which lowered stress on native soil resources. The latter is corroborated with our findings on soil fertility status. This strategy focused on reducing fertilizer inputs and developing precise plant nutrition technology for on-farm use. Our findings suggest that shade seedlings under steady state nutrition can mitigate early growth competition in the field.     

Allometric models for predicting above- and belowground biomass of <Emphasis Type="Italic">Leucaena</Emphasis>-KX2 in a shaded coffee agroecosystem in Hawaii

We developed site-specific allometric models for Leucaena leucocephala × pallida var. KX2 trees in a shaded coffee agroecosystem in Hawaii to predict above- and belowground biomass and the regrowth potential of pollarded trees. Models were used to compare tree growth rates in an experimental agroforestry system with different pollarding frequencies and additions of tree pruning residues as mulch. For all allometric equations, a simple power model (Y = aX^b) provided the optimal prediction of biomass or regrowth after pollarding. For aboveground biomass components (stem, branches, leaves, and seed and pods), stem diameter alone was the best predictor variable. Stump diameter provided the best prediction of coarse root biomass and aboveground regrowth after pollarding. Predictions of biomass from generalized allometric models often fell outside the 95% confidence intervals of our site-specific models, especially as biomass increased. The combination of pollarding trees once per year plus the addition of tree mulch resulted in the greatest aboveground regrowth rates as well as accumulation of biomass and C in the stump plus coarse roots. Although optimal prediction required the development of site-specific allometric relationships, a simple power model using stem or stump diameter alone can provide an accurate assessment of above- and belowground tree biomass, as well as regrowth potential under specific management scenarios.     

Individual-based fine root biomass and its functional relationship with leaf for <Emphasis Type="Italic">Pinus tabuliformis</Emphasis> in northern China

Root biomass plays an essential role in carbon sequestration at both individual and ecosystem scales, yet few feasible methods for measuring root biomass of individual trees have been developed. We sampled 11 trees in a pure 20-year-old Pinus tabuliformis plantation to estimate total root, fine root and leaf biomass of individual trees using the nested regression method. The relationships between fine root biomass and surface area as well as leaf biomass and area were examined across tree sizes. Fine roots of P. tabuliformis were estimated to consume 40 % of the net primary production for turnover, and absorbed a total of 1364 g m^?2 year^?1 of major nutrients. A significant linear relationship was determined between roots and leaves in terms of both biomass and surface area. The findings added weight to the concept that the functional balance theory is applicable to even-aged mature trees of P. tabuliformis.     

Responses of fine root mass,length, production and turnover to soil nitrogen fertilization in <Emphasis Type="Italic">Larix gmelinii</Emphasis> and <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> forests in Northeastern China

The responses of fine root mass, length, production and turnover to the increase in soil N availability are not well understood in forest ecosystems. In this study, sequential soil core and ingrowth core methods were employed to examine the responses of fine root (≤1 mm) standing biomass, root length density (RLD), specific root length (SRL), biomass production and turnover rate to soil N fertilization (10 g N m⁻² year⁻¹) in Larix gmelinii (larch) and Fraxinus mandshurica (ash) plantations. N fertilization significantly reduced fine root standing biomass from 130.7 to 103.4 g m⁻² in ash, but had no significant influence in larch (81.5 g m⁻² in the control and 81.9 g m⁻² in the fertilized plots). Similarly, N fertilization reduced mean RLD from 6,857 to 5,822 m m⁻² in ash, but did not influence RLD in larch (1,875 m m⁻² in the control and 1,858 m m⁻² in the fertilized plots). In both species, N fertilization did not alter SRL. Additionally, N fertilization did not significantly alter root production and turnover rate estimated from sequential soil cores, but did reduce root production and turnover rate estimated from the ingrowth core method. These results suggested that N fertilization had a substantial influence on fine root standing biomass, RLD, biomass production and turnover rate, but the direction and magnitude of the influence depended on species and methods.     

Growing woody biomass for bioenergy in a tree-based intercropping system in southern Ontario, Canada

During the spring of 2006, three willow varieties (SV1, SX67 and 9882-41) were established on marginal land in an agroforestry tree-intercropping arrangement where plots of short rotation willows were planted between rows (spaced 15?m apart) of 21-year-old mixed tree species. As a control, the same varieties were established on an adjacent piece of land without established trees (conventional willow system). This study investigated the magnitude of carbon pools, fine root and leaf biomass inputs and clone yields in both the tree-based intercropping (agroforestry) and conventional monocropping systems. Willow biomass yield was significantly higher in the agroforestry field (4.86?odt?ha^?1?y^?1) compared to the conventional field (3.02?odt?ha^?1?y^?1). In both fields, varieties SV1 and SX67 produced higher yields than the variety 9882-41. Willow fine root biomass in the top 20?cm of soil was significantly higher in the intercropping system (3,062?kg?ha^?1) than in the conventional system (2,536?kg?ha^?1). Differences in fine root biomass between clones were similar to that observed for differences in biomass yield: SV1?>?SX67?>?9882-41. Leaf input was higher in the intercropping system (1,961?kg?ha^?1) than in the conventional system (1,673?kg?ha^?1). Clonal differences in leaf inputs followed the same trends as those for root biomass and yield: SV1?>?SX67?>?9882-41. Soil organic carbon was significantly higher in the agroforestry field (1.94?%) than in the conventional field (1.82?%). A significant difference in soil organic carbon was found between the three clones: soils under clone 9882-41 had the lowest soil organic carbon at 1.80?%.     

Fine roots refilling process in an artificial gap in a Picea mongolica forest

Picea mongolica is an endemic but endangered species in China. The spruce forest is only found in sandy forest-steppe ecotones. In this study, we examined the initial response of the quantity and refilling process of fine roots in an artificial canopy gap with a diameter of 36 m in a P. mongolica forest. Under the canopy, the fine root length densities of trees, shrubs and herbs were 2,622, 864 and 3,086 m·m–2, respectively. The fine root biomass of trees, shrubs and herbs were 148, 62 and 65 g·m–2, respect...     

Genotypic variation and phenotypic plasticity in the drought response of fine roots of European beech

How temperate trees respond to drier summers, as predicted by climate change models for parts of Europe and eastern North America, will depend on the drought susceptibility of the root systems. We investigated the importance of the genetic constitution for the belowground drought response of European beech (Fagus sylvatica L.), in four populations from regions differing in precipitation (520-970 mm year(-1)). Saplings were grown at ample (10 vol.%; well-watered) or reduced (5 vol.%; drought treatment) soil water content in the G?ttingen Rhizolab Facility for two consecutive summers, and the responses of fine root biomass, root morphology, root depth distribution, and fine root production and turnover were investigated by a combined mini-rhizotron and harvest technique approach. In the drought treatment, total root mass per plant was reduced by 30-40% as a result of: (1) a reduction in median fine root lifespan by roughly 50% and hence an increase in fine root turnover; and (2) a 10-fold reduction in relative fine root growth rate (productivity per standing root biomass). The root:shoot ratio did not increase with drought. Although beech plants originating from drier climates tended to reduce their root biomass in response to drought less than those from wetter climates, analyses of variance revealed no significant influence of genotype on root mass, morphology, growth rate or turnover. However, most fine root traits showed marked differences between the well-watered and drought treatments. We conclude that beech saplings respond to summer drought primarily by shortening root lifespan, whereas root system structure and root:shoot carbon partitioning pattern are unaltered. Beech fine root growth and turnover exhibited high phenotypic plasticity, but genotypic variation was of minor importance. In contrast, genotype had a strong influence on leaf and shoot morphogenesis and growth.     

Organic matter contribution to soil fertility improvement and maintenance in red Alder （Alnus rubra） silvopastoral systems

An investigation was conducted to quantify fine roots and roots nodules over the four seasons in forestry and agroforestry alder (Alnus rubra) stands in North Wales. Soil samples collected in each season were excavated at three sampling points (0.30 m, 0.57 m and 1.00 m distance from the base of each tree) from nine trees of the agroforestry and forestry plots. Result showed that the density of live fine root had significant differences in between seasons and treatments (P ＜ 0.001). The mean weight density of live fine root over the four seasons in agroforestry and forestry was 0.27±0.01 kg·m-3 and 0.54±0.03 kg·m-3, respectively. Weight density of dead root in each system remained constant throughout the year. The mean weight density of dead root was also significantly different (P ＜ 0.01) between forestry and agroforestry systems. Weight density of live and dead root nodule was both constant throughout the year and between the different sampling distances. The mean weight densities of live and dead root nodule over the four seasons were 0.09±0.03 kg·m-3 and 0.05±0.03 kg·m-3 in agroforestry and 0.08±0.02 kg·m-3 and 0.03±0.01 kg·m-3 in the forestry plots, respectively.     

Root biomass and distribution of a <Emphasis Type="Italic">Picea–Abies</Emphasis> stand and a <Emphasis Type="Italic">Larix–Betula</Emphasis> stand in pumiceous Entisols in Japan

Root biomass and root distribution were studied in Entisols derived from the thick deposition of volcanic pumice on Hokkaido Island, Japan, to examine the effect of soil conditions on tree root development. The soil had a thin (<10 cm) A horizon and thick coarse pumiceous gravel layers with low levels of available nutrients and water. Two stands were studied: a Picea glehnii–Abies sachalinensis stand (PA stand) and a Larix kaempferi–Betula platyphylla var. japonica stand (LB stand). The allometric relationships between diameter at breast height (DBH) and aboveground and belowground biomass of these species were obtained to estimate stand biomass. The belowground biomass was small: 30.6 Mg ha₋₁ for the PA stand and 24.3 Mg ha₋₁ for the LB stand. The trunk/root ratios of study stands were 4.8 for the PA stand and 4.3 for the LB stand, which were higher than those from previous studies in boreal and temperate forests. All species developed shallow root systems, and fine roots were spread densely in the shallow A horizon, suggesting that physical obstruction by the pumiceous layers and their low levels of available water and nutrients restricted downward root elongation. The high trunk/root ratios of the trees may also have resulted from the limited available rooting space in the study sites.     

Root distribution of under-planted European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) below the canopy of a mature Norway spruce stand as a function of light

Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings (Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm) soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech with increasing light intensity for both fine and coarse roots.     

Survival and growth of drought hardened <Emphasis Type="Italic">Eucalyptus pilularis</Emphasis> Sm. seedlings and vegetative cuttings

Forestry requires low mortality of transplanted seedlings. Mortality shortly after planting is often associated with inadequate hydration of transplants. Seedlings can be hardened to the drought conditions they may experience after transplanting by exposing them to controlled drought conditions in the nursery. Eucalyptus pilularis Sm. seedlings were drought hardened by providing nil (severe treatment) or half (mild treatment) the daily irrigation routinely received (control treatment) for up to two non-consecutive days per week during the last 4 weeks of growth in the nursery. Drought hardening reduced stem diameter, seedling leaf area, leaf area per root biomass and seedling quality measured by the Dickson quality index, but increased root:shoot ratio. Hardened seedlings had lower stomatal conductance and leaf water potential on the days they received less irrigation that the control treatment. Hardened seedlings had greater stomatal conductance and were less water stressed than seedlings experiencing drought for the first time indicating hardened seedlings had adjusted physiologically to drought. Survival after transplanting in the controlled drought environment in a glasshouse was enhanced by the hardening treatments. Non hardened seedlings that had had their upper leaves manually removed immediately prior to transplanting to reduce leaf area (top-clipped) had similar survival to hardened seedlings. Stomatal conductance and leaf water potential after transplanting were higher in hardened and top-clipped seedlings than unhardened control seedlings or vegetative cuttings. Survival in the field trial was over 95% for all treatments, possibly as rain fell within 4 days of planting and follow-up rain occurred in the subsequent weeks. Neither the hardened or top-clipped seedlings planted in the field trial had reduced growth, increased propensity to form double leaders or worse stem form than control seedlings when measured at age 3 years.     

Fine root and nodule dynamics of Erythrina poeppigiana in an alley cropping system in Costa Rica

Fine root and nodule production and turnover in pruned 2- and 8-yr-old Erythrina poeppigiana (Walp.) O.F. Cook trees were estimated under humid tropical conditions by applying the compartment flow model (CFM) to fine root and nodule biomass and necromass measured in sequentially taken core samples. Shoot pruning intensities compared were complete pruning (i.e., complete removal of shoots) and partial pruning (i.e., retention of one branch on the pruned stump). The CFM provided reasonable estimates of nodule dynamics but did not apply to fine root data. Over a five-month observation period, nodule production in completely and partially pruned 2-yr-old trees was 58.2 and 115 g tree^–1, respectively, and the corresponding values in 8-yr-old trees were 26.8 and 26.4 g tree^–1. Senescent nodules and fine roots pass to soil organic matter via decomposition. Partially and completely pruned 2-yr-old trees added 95.4 and 50.4 g tree^–1 decomposed nodules to soil, respectively. The respective value for 8-yr-old trees were 26.7 and 36.5g tree^–1. Nodule and fine root turnover was compensated for by new production at 10–14 weeks after pruning. The retention of a branch on the pruned E. poeppigiana tree stump allows better fine root and nodule survival, and enhances tree biomass production.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effects of <Emphasis Type="Italic">Inga densiflora</Emphasis> on the microclimate of coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) and overall biomass under optimal growing conditions in Costa Rica

The advantages of associating shade trees in coffee agroforestry systems (AFS) are generally thought to be restricted mostly to poor soil and sub-optimal ecological conditions for coffee cultivation whereas their role in optimal conditions remains controversial. Thus, the objective of this study was to investigate, under the optimal coffee cultivation conditions of the Central Valley of Costa Rica, the impact of Inga densiflora, a very common shade tree in Central America, on the microclimate, yield and vegetative development of shaded coffee in comparison to coffee monoculture (MC). Maximum temperature of shaded coffee leaves was reduced by up to 5°C relative to coffee leaf temperature in MC. The minimum air temperature at night was 0.5°C higher in AFS than air temperature in MC demonstrating the buffering effects of shade trees. As judged by the lower relative extractable water (REW) in the deep soil layers during the dry season, water use in AFS was higher than in MC. Nevertheless, competition for water between coffee and associated trees was assumed to be limited as REW in the 0–150 cm soil layer was always higher than 0.3 in shaded coffee compared to 0.4 in monoculture. Coffee production was quite similar in both systems during the establishment of shade trees, however a yield decrease of 30% was observed in AFS compared to MC with a decrease in radiation transmittance to less than 40% during the latter years in the absence of an adequate shade tree pruning. As a result of the high contribution (60%) of shade trees to overall biomass, permanent aerial biomass accumulation in AFS amounted to two times the biomass accumulated in MC after 7 years. Thus provided an adequate pruning, Inga-shaded plantations appeared more advantageous than MC in optimal conditions, especially considering the fact that coffee AFS provides high quality coffee, farmers’ revenue diversification and environmental benefits.     

Fine root dynamics in three central Himalayan high elevation forests ranging from closed canopied to open-canopied treeline vegetation

Fine root biomass, rates of dry matter production and nutrients dynamics were estimated for 1 year in three high elevation forests of the Indian central Himalaya. Fine root biomass and productivity were higher in closed canopied cappadocian maple forest (9.92 Mg ha⁻¹ and 6.34 Mg ha⁻¹ year⁻¹, respectively), followed by Himalayan birch forest (6.35 Mg ha⁻¹ and 4.44 Mg ha⁻¹ year⁻¹) and Bell rhododendron forest (6.23 Mg ha⁻¹ and 2.94 Mg ha⁻¹ year⁻¹). Both fine root biomass and productivity declined with an increase in elevation. Across the sites, fine root biomass was maximal in fall and minimal in summer. In all sites, maximum nutrient concentration in fine roots was in the rainy season and minimum in winter. Fine root biomass per unit basal area was positively related with elevation, Bell rhododendron forest having the largest fine root biomass per unit of basal area (0.53 Mg m⁻²) and cappadocian maple the least (0.18 Mg m⁻²). The production efficiency of fine roots per unit of leaf biomass also increased with elevation and ranged from 1.13 g g⁻¹ leaf mass year⁻¹ in cappadocian maple forest to 1.28 g g⁻¹ leaf mass year⁻¹ in Bell rhododendron forest. Present fine root turnover estimates showed a decline towards higher elevations (0.72 year⁻¹ in cappadocian maple and 0.58 year⁻¹ in Bell rhododendron forest) and are higher than global estimates (0.52).     

Exploring below ground complementarity in agroforestry using sap flow and root fractal techniques

Indices of shallow rootedness and fractal methods of root system study were combined with sapflow monitoring to determine whether these ‘short-cut’ methods could be used to predict tree competition with crops and complementarity of below ground resource use in an agroforestry trial in semi-arid Kenya. These methods were applied to Grevillea robusta Cunn., Gliricidia sepium (Jacq.) Walp., Melia volkensii Gürke and Senna spectabilis syn. Cassia spectabilis aged two and four years which were grown in simultaneous linear agroforestry plots with maize as the crop species. Indices of competition (shallow rootedness) differed substantially according to tree age and did not accurately predict tree:crop competition in plots containing trees aged four years. Predicted competition by trees on crops was improved by multiplying the sum of proximal diameters squared for shallow roots by diameter at breast height², thus taking tree size into account. Fractal methods for the quantification of total length of tree root systems worked well with the permanent structural root system of trees but seriously underestimated the length of fine roots (less than 2 mm diameter). Sap flow measurements of individual roots showed that as expected, deep tap roots provided most of the water used by the trees during the dry season. Following rainfall, substantial water uptake by shallow lateral roots occurred more or less immediately, suggesting that existing roots were functioning in the recently wetted soil and that there was no need for new fine roots to be produced to enable water uptake following rainfall. This revised version was published online in June 2006 with corrections to the Cover Date.     

Contrasting rooting patterns of some arid-zone fruit tree species from Botswana – I. Fine root distribution

To assess the possible degree of root competition from fruit trees which could potentially be used in agroforestry systems, fine root density of fruit trees Strychnos cocculoides Bak., Strychnos spinosa Lam. (Loganiaceae) and Vangueria infausta Burch. (Rubiaceae), as well as from the shrubby species, Grewia flava DC. (Tiliaceae) was investigated. Vangueria infausta had the highest fine root densities in both vertical and horizontal extensions. In Vangueria infausta fine root density decreased with increasing soil depth. For the other species in the 80 cm soil profile investigated, no significant changes in fine root density with soil depth were found. For Strychnos cocculoides almost no fine roots were detected in the upper soil horizon (0–20 cm). Using fine root surface area densities, exploration and exploitation indices were calculated. Vangueria infausta had the highest value of the exploration index compared to the other species. For use in agroforestry systems Vangueria infausta was estimated to be the most competitive of the investigated species, whereas Strychnos cocculoides seems to be the less competitive. Strychnos cocculoides has additionally spatial arrangements of fine roots favourable for agroforestry, slowly increasing with depth and additionally low concentrations in upper soil layers.