Growth of ten multipurpose tree species on acid soils in Sangmelima,Cameroon

Ten multipurpose tree species were planted both in monoculture and intercropped withArachis hypogea (groundnut) in a randomized complete block with three replications. The vigrou, biomass, nutrient content, and coppicing percentage of the trees were evaluated. Intercropping with groundnuts during the establishment phase did not affect subsequent growth and development of the species.Acacia mangium, Acacia auriculiformis, Cassia siamea, Calliandra calothyrsus andParaserianthes falcataria established well, when compared toGliricidia sepium, Leucaena leucocephala, Dialum guineense, Dubocia macrocarpa andMilicia excelsa. A. mangium, A. auriculiformis, C. calothyrsus, C. siamea andP. falcataria produced the highest leaf (4 to 20 t ha^–1) and wood (12 to 37 t ha^–1) biomass yield (primary growth) at one to three years after planting. Coppicing percentage ofA. mangium A. auriculiformis andP. falcataria were relatively low (35 to 50%).C. calothyrsus andC. siamea showed the highest coppicing percentage (95 to 100%) and produced the greatest coppice biomass (9 to 13 t ha^–1). Total nitrogen and organic matter percentage of soils from under the stands of these two species were also significantly higher than that of the rest. The two species may thus be considered for use in agroforestry technologies for soil improvement on acid soils, which are typical of the moist tropics.     

Integration and role of planted trees in a bush-fallow cultivation system in central Zambia

The purpose of natural fallow in bush-fallow cultivaton systems is to improve soil fertility following a phase of cultivation and to provide useful forest products, including livestock feed. When natural fallow fails to serve these purposes, it can be supplemented or replaced by planted trees. This paper describes the development and function ofAcacia fallow in the Soli tribal land of central Zambia and examines the supplementary role of planted trees.The 31 woody species at five fallow sample sites were dominated byAcacia polyacantha. Thirty-nine percent of the species are leguminous and N-fixing while 42% are fodder plants. These species make thisAcacia fallow suitable for regeneration of soil fertility and production of fodder. The dominant species,A. polyacantha, has an extensive lateral root system and may attain a mean maximum girth at breast height (BH) of 125 cm within 20 years. In the study areaAcacia fallow regenerates from seed and root-stocks and with a maximum annual stem basal area increment of 0.87 m²ha^–1 at BH can acumulate a total of 17.4 m²ha^–1 in 20 years.However,Acacia fallow is poor in edible wild fruits and durable construction wood. The scarcity of fruits in the study area has been compensated by widespread planting of exotic fruit trees. Ninety percent of households have fruit trees (mean 2.3 fruit species per household). However, in spite of the scarcity of good construction wood in the Soli tribal land, no local initiative has developed to plant timber trees. A clear opportunity therefore exists to promote timber tree planting. Such a tree planting programme was started in the study area during the 1985/86 planting season (December-February) when 25,100 seedlings ofEcualyptus grandis, Gmelina arborea andLeuceana leucocephala were distributed, free of charge and the programme will continue until 1988. A survey carried out five to seven months after planting revealed that the survival ofE. grandis, L. leucocephala andG. arborea seedlings was 65%, 90% and 92%, respectively. The high mortality ofE. grandis seedlings was due to termite damage.     

Tree and livestock productivity in relation to tree planting configuration in a silvopastoral system in North Wales, UK

Silvopastoral systems in Europe offer the potential of introducing environmental benefits while at the same time increasing the diversity of farm outputs. The establishment of new silvopastoral systems by planting young trees into existing pasture was investigated at a site in North Wales, UK. Two tree species, sycamore (Acer pseudo-platanus L.) and red alder(Alnus rubra Bong.), were planted into pasture at a range of densities and planting arrangements. Growth of trees planted in farm woodland blocks (2500 stems ha^–1) was compared with the growth of trees planted at 400 stems ha^–1 in clumps and dispersed throughout the plot and at 100 stems ha^–1 (dispersed). Over the first six years after planting, alder trees were significantly taller and larger in diameter than sycamore. Sycamore trees planted at close spacing in farm woodland or clumped arrangements were significantly larger in diameter than widely spaced sycamore at 100 and 400 stems ha^–1. Livestock productivity was unaffected by the presence of trees during the six-year establishment phase of the system. The planting of trees in a clumped pattern appears to combine silvicultural benefits to tree growth with agricultural benefits of maintaining livestock production while trees are established.This revised version was published online in November 2005 with corrections to the Cover Date.     

Biomass production and root distribution of Gmelina arborea under an agrisilviculture system in subhumid tropics of Central India

A study of an agrisilviculture system comprising Gmelina arborea and soybean (Glycine max) was conducted in the subhumid region of Central India. Above- and below-ground biomass production and distribution of coarse and fine roots were studied in 4-year-old G. arborea, planted at a spacing of 2 × 2 m, 2 × 3 m, 2 × 4 m and 2 × 5 m. The total biomass varied from 10.89 Mg ha^–1 to 3.65 Mg ha^–1 depending on the tree density. Among the different tree components, stemwood contributed maximum biomass (54.3–79.4%), followed by branches and leaves. Root distribution pattern showed that most of the coarse roots were distributed in the top 40 cm of soil, whereas fine roots were concentrated in the top 20 cm. Coarse root biomass decreased with an increase in spacing. The spread of roots was asymmetrical in trees planted at 2 × 2 m and 2 × 3 m spacings, while it was symmetrical in trees planted at wide spacings. No significant difference was observed in the fine root biomass in different stands. The root:shoot ratio increased with an increase in spacing. Crop (soybean) growth and productivity varied significantly and it increased with a decrease in tree density. Soybean yield varied between 1.5 Mg ha^–1 to 2.1 Mg ha^–1. The role of root architecture of G. arborea trees on productivity of crops under agri-silviculture system is discussed.     

Growth and yield of maize alley cropped with Leucaena leucocephala and Faidherbia albida in Morogoro, Tanzania

This study examined the effect of alley cropping of Leucaena leucocephala and Faidherbia albida on wood biomass, maize grain yield and soil nitrogen status. The treatments were: trees planted alone at 1 × 5 m spacing; trees intercropped with maize and a sole maize crop. Mulch biomass averaged 6.18 and 0.97 t ha⁻¹ for L. leucocephala and F. albida, respectively. Corresponding wood production was 1.71 and 1.11 t ha⁻¹. Both total N and inorganic N (NO ₃ ⁻ –N plus ₄ ⁺ –N) were higher under F. albida and lowest under L. leucocephala. Similarly, foliar N concentration in maize was higher in plots intercropped with F. albida and least in L. leucocephala intercropping. Maize grain yield was little affected by the tree intercrop as competition for resources was reduced through periodic pruning and clean weeding. There was no gain in maize grain yield due to the presence of L. leucocephala and F. albida. These results suggest that alley cropping in Gario is justified for wood production but not for increasing maize grain yield. This revised version was published online in June 2006 with corrections to the Cover Date.     

Crop yields of rice and wheat grown in rotation as intercrops with three tree species in the outer hills of Western Himalaya

Studies on tree crop interaction under rainfed condition in Dehradun valley were conducted for 13 years during 1977 to 1990. Grewia optiva (Bhimal), Morus alba (Mulbery) and Eucalyptus hybrid were tried along with rice (CV: Akashi) — wheat (CV: RR-21) rotation. One-year-old tree seedlings of the above tree species were planted in line, 5 m apart in N-S direction, in July 1977, in the middle of the plot (size 20 m × 20 m). Eucalyptus was first harvested in 1987. Grewia optiva, Morus alba and coppice of Eucalyptus were harvested in 1990. All tree species had depressing effect on crop yields. Eucalyptus had maximum effect in depressing crop yield till the first harvest and had least effect thereafter. From 1987 onwards, Morus alba affected rice most, while wheat was mostly affected by Grewia optiva. The depressing effect on an average varied from 28 to 34% depending upon the species.Distance of tree line from the crop significantly affected the crop yield upto a distance of 5 m and there was 39% decrease in crop yield upto 1 m, 33% from 1–2 m, 25% from 2–3 m and 12% from 3–5 m distance. Annual removal of lops and tops from trees partly compensated the deficit. Grewia optiva could produce 1.08 t ha^–1 yr^–1 of branches and 0.26 t ha^–1 yr^–1 of leaves (air dry) and 1.28 t ha^–1 yr^–1 of branches and 0.28 t ha^–1 yr^–1 of leaves were obtained from Morus alba. Wood (ADT) produced by the trees was 33.6 t ha^–1 from Eucalyptus, 9.5 t ha^–1 from Grewia optiva and 11.6 t ha^–1 from Morus alba.     

Pasture production under different tree species and densities in an Atlantic silvopastoral system

We studied the effect of six tree species planted at six different densities on pasture production seven years after establishment. Annual and seasonal pasture production was studied every six months, over three years. Pasture production was lower under conifer trees (Pseudotsuga menziesii (Mirb.) Franco, Pinus pinaster Aiton, Pinus radiata D. Don) than under broadleaved trees (Betula alba L., Quercus rubra L. and Castanea sativa Mill.). Annual pasture production under Pseudotsuga menziesii and Pinus pinaster decreased progressively starting from 952 trees ha⁻¹, while decline in herbage production under Pinus radiata began to occur at 427 trees ha⁻¹. Tree density effect on pasture production was detected at 2,000 trees ha⁻¹ for all of the deciduous species studied. This effect on pasture production was more important in the first six months of the year (June sampling), while from June to December herbage production was less affected by tree density. The tree effect became more noticeable over time, with the last sampling showing the inverse relationship between tree density and herbage production most clearly. Seven years after tree establishment, pasture production was quite consistent under tree densities between 190 trees ha⁻¹ and 556 trees ha⁻¹ and declined remarkably from 556 trees ha⁻¹ to 2,500 trees ha⁻¹. The study also indicated that by the sixth growing season, annual pasture production under different tree species is inversely correlated with tree leaf area index.     

Rotational woodlot technology in northwestern Tanzania: Tree species and crop performance

Growing of trees as woodlots on farms for five to seven years in rotation with crops was considered as a potential technology to overcome the shortage of wood, which is a common problem to many parts of sub-Saharan Africa. The paper summarizes the results of trials conducted at Tabora and Shinyanga in northwestern Tanzania on rotational woodlots, to evaluate tree species for wood production and yields of maize grown in association with and after harvest of trees. On acid sandy soils at Tabora, Acacia crassicarpa A. Cunn. ex Benth. grew fast and produced 24 to 77 Mg ha⁻¹ of wood in four to five years. On alkaline Vertisols at Shinyanga, seven years old woodlots of Acacia polyacantha Willd. and Leucaena leucocephala (Lam.) De Wit. produced 71 and 89 Mg ha⁻¹ of wood, respectively. Intercropping of maize between trees was possible for two years without sacrificing its yield. The first maize crop following A. crassicarpa woodlots gave 29 to 113% greater yield than the crop after natural fallow. Acacia polyacantha and L. leucocephala woodlots also increased the subsequent maize yields over a three-year period. The increase in crop yields after woodlots was attributed partly to accumulation of greater amounts of inorganic N in the topsoil compared to the traditional fallow, and partly to other effects. Thus medium-term rotational woodlots are likely to contribute to meet the wood requirements of rural people and thereby help protect the natural woodlands in sub-Saharan Africa. This revised version was published online in June 2006 with corrections to the Cover Date.     

Litter and biomass production from planted and natural fallows on a degraded soil in southwestern Nigeria

To rehabilitate a degraded Alfisol at Ibadan, southwestern Nigeria, Senna siamea (non-N-fixing legume tree), Leucaena leucocephala, and Acacia leptocarpa (N-fixing legume trees) were planted in 1989, and Acacia auriculiformis (N-fixing legume tree) in 1990. Pueraria phaseoloides (a cover crop) and natural fallow were included as treatments. Litterfall and climatic variables were measured in 1992/1993 and 1996/1997 while biomass production and nutrient concentrations were measured in 1993 and 1995. Total litter production from the natural and planted fallows was similar, with means ranging from 10.0 (L. leucocephala) to 13.6 t ha⁻¹ y⁻¹ (natural fallow) during the 1996/1997 collection. Leaves constituted 73% (L. leucocephala) to 96% (A. auriculiformis) of total litterfall. Acacia auriculiformis grew most quickly but S. siamea produced the highest aboveground biomass which was 127 t ha⁻¹ accumulated over four years, and 156 t ha⁻¹ accumulated over six years of establishment. The aboveground biomass of P. phaseoloides and natural fallow was only 6 to 9 t ha⁻¹ at six years after planting. Nitrogen concentration in the leaves/twigs of was 2.5% for L. leucocephala, and 2% for other planted species and natural fallow. Pueraria phaseoloides had concentrations of P, K, Ca and Mg comparable to levels in the leaves/twigs of the tree species. Through PATH analysis, it was found that maximum temperature and minimum relative humidity had pronounced direct and indirect effects on litterfall. The effects of these climatic variables in triggering litterfall were enhanced by other variables, such as evaporation, wind, radiation, and minimum temperature. Improvement in chemical properties by fallows was observed in the degraded soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparative performance of seventeen upperstorey tree species associated with crops in the highlands of Uganda

Trials were established at three sites in Uganda to test the suitability of multipurpose trees (MPTs) as upperstorey in crop lands to provide poles, small timber and fuelwood. The three sites were Kachwekano District Farm Institute (1°16 S, 29°57 E, 2000 m.a.s.l.) in Kabale District, Kabanyolo University Farm (0°28 N, 32°27 E, 1250 m.a.s.l.) in Mpigi District and Bushenyi District Farm Institute (0°34 S, 30°13 E, 1610 m.a.s.l.) in Bushenyi District. The MPTs were planted in single rows at intra spacing of 2 m and each plot contained seven or nine trees. On both sides of the tree row, crops were raised. Data on crop yields were collected every season, while data on the growth of the trees were collected four times each year.In terms of tree growth,Grevillea robusta, Casuarina cunninghamiana andAlnus acuminata performed well with height growth of 1.8–2.4 m per year at Kachwekano, while at BushenyiGrevillea robusta, Casuarina junghuhniana, Cupressus lusitanica andCedrela serrulata averaged 1.6–2.0 m height per year. At Kabanyolo,Melia azedarach, Cassia siamea, Jacaranda mimosifolia, Grevillea robusta andMaesopsis eminii had height increments ranging from 1.8–2.7 m annually. Crop yields were affected by the presence of the MPTs, withMaesopsis eminii being the most competitive (averaging 60% reduction, over five seasons). The crop rows nearest to the tree line were the most affected. OnlyAlnus acuminata seems to have had a positive effect on crop yields. The installation of a root mesh to reduce tree root competition for nutrients and water in four species increased yields in plots with MPTs by 5% (Melia azedarach) to 152% (Maesopsis eminii), but the control plot still had significantly higher bean yields, suggesting that shading could also be important. In the case of maize, suppression seems to be due mainly to root competition because after its elimination yields obtained thereafter did not differ significantly from those of the control except for the Maesopsis plots. The negative influence of the MPTs could, therefore, be minimized by periodically pruning the tree crowns and roots.     

Development of utility and location indices for classifying agroforestry species: the case of Rwanda

In a study of farmer knowledge and experimentation of trees and tree cultivation, two categories of farmer consultants were identified, tree experts (n = 44) and control farmers (n = 70), via a two stage process of knowledge ranking and community interviews conducted in three communes in southern Rwanda in 1992. A detailed inventory of tree species was conducted revealing two key characteristics for on-farm trees: multiple utility and high locational flexibility. In order to logically organize the species inventory, two indices, a utility index (UI) and a locational flexibility index (LFI), were developed. The two indices were calculated for each species and then plotted as the axes on a bivariate grid. While few species had both high utility and flexibility indices, the majority that did were indigenous species long used in agroforestry systems (e.g., Euphorbia tirucalli, Vernonia amygdalina, Erythrina abyssinica, etc.). A few naturalized exotics introduced in the 1930s (e.g., Grevillea robusta, Eucalyptus camaldulensis, E. saligna, E. maideni, Cupressus lusitanica and Persea gratissima) were also appreciated for their multiple utility and locational flexibility. Farm sizes varied, averaging 1.27 ha among tree experts and 0.18 ha in the control group. The mean number of species cultivated was significantly higher on tree expert farms (P < 0.01). However, tree density was much lower on tree expert farms (731 trees · ha^–1) than on control farms (1,689 trees · ha^–1). Competitive species were found primarily on larger farms, whereas smaller farms were associated with species of greater UI and LFI. Farmers demonstrated deliberate and rational choices about which trees to plant in accordance with each species utility and flexibility in relation to land availability.     

Optimising the management of maize — Grevillea robusta fields in Kenya

The study optimised the management of a Grevillea robusta (A. Cunn.) stand growing in the central highlands of Kenya. The optimisations were conducted separately for even-aged and uneven-aged management system of trees. The management was also optimised with the requirement that maize production under the tree cover must be profitable every year. Technically, the optimisation problems were solved by linking a simulation program with the non-linear optimisation algorithm of Hooke and Jeeves. The simulation program calculated the tree growth, volumes of harvested trees, and maize yields with a given set of management parameters (decision variables). The maize yield predictions and simulated timber yields were converted into gross incomes of which the production costs were subtracted. In even-aged management the objective variable was the soil expectation value with 5% discounting rate. In uneven-aged management the mean annual net income was maximised. The optimal solutions indicated that with both management systems it is optimal to concentrate on wood production. The optimal stand densities were so high that profitable maize production was not possible under the tree cover. The mean annual wood production of the optimal management schedule was more than 50m³ ha^–1. Forcing profitable maize production in the solution decreased the wood production by 57% (even-aged forestry) or 27% (uneven-aged forestry) and net income by 45% (even-aged forestry) or 24% (uneven-aged forestry).This revised version was published online in November 2005 with corrections to the Cover Date.     

The framework tree species approach to conserve medicinal trees in Uganda

Framework species are indigenous tree species planted in a mixed stand to accelerate natural regeneration of forest and encourage biodiversity regeneration. In this study we used the framework species method to make multipurpose tree gardens to provide traditional healers with woody species used for medicine and other needs like food and firewood. We specifically determined the phenology, germination behaviour, survival and growth after planting 19 indigenous and 8 introduced woody species. The species were planted in a mixed stand together at a density of 3125 ha⁻¹. Field performance was assessed by monitoring survival, height and crown width once every month for 13 months after planting. Eleven species (Artocarpus heterophyllus, Calliandra calothyrsus, Callistemon citrinus, Carica papaya, Carissa spinarum, Leucaena leucocephala, Markhamia lutea, Sarcocephalus latifolius, Senna siamea, S. spectabilis and Terminalia schimperiana) proved to be excellent framework species. Eight species qualified as ‘acceptable’ FWS (Albizia coriaria, Ceiba pentranta, Entada abyssinica, Erythrina abyssinica, Eugenia jambos, Ficus sycomorus, Maesopsis eminii and Milicia excelsa), while seven species were ranked as ‘marginally acceptable’ (Acacia macrothyrsa, Calpurnia aurea, Canarium schweinfurthii, Capparis tomentosa, Ficus natalensis, Senna sp. and Warburgia salutaris). Annona squamosa was the only species rejected since both germination and survival was low. Trees with good reforestation traits could be recommended for planting while the species that were marginally acceptable or rejected require extra research since some of them are important medicinal woody species of conservation concern.     

Effect of tree spacing on growth and wood density of 38-year-old Cariniana legalis trees in Brazil

Average wood density of 38-year-old Cariniana legalis (Mart.) Kuntze, a Brazilian native forest species, was found to increase with faster growth and lower stocking, while decreasing from pith to bark. A complete randomised block design was planted with five blocks. Ten trees were harvested in each of three spacing treatments. We hypothesised that the stand stemwood production would not significantly differ depending on tree spacing. However, tree growth would be higher in the wider spacing and wood density would be higher in the narrower spacing. The diameter growth of trees was higher at 3 m × 2.5 m than at 3 m × 2 m and 3 m × 1.5 m. Nevertheless, this higher individual tree growth at 3 m × 2.5 m did not compensate for the greater tree stock density at 3 m × 1.5 m with stand stemwood production at 38 years of 530 m3 ha^?1 and 649 m³ ha^?1, respectively. These results suggest that C. legalis, which can produce up to 17 m³ ha^?1 y^?1 of medium-to high-density timber – about 800 kg m^?3 – is a promising native species for forest plantations in Brazil.     

A comparison of cold tolerance and biomass production in Leucaena leucocephala L. pulverulenta and L. retusa

Expansion of leucaena into temperate regions of the world will require additional tolerance to freezing stress. Leucaena leucocephala may be the most widely tested woody legume in the last 15 years. Leucaena pulverulenta and Leucaena retusa are two species with more cold tolerance than L. leucocephala. A screening trial with 38 accessions of L. pulverulenta, 26 of L. leucocephala, and 1 of L. retusa was begun in 1983 at Kingsville, Texas where freezing temperatures may occur every year. A biomass production trial using L. leucocephala (K-8) was planted in 1982 to evaluate the biomass production of this widely used strain under semi-arid conditions with minimum fertilizer inputs and no irrigation. Biomass estimations were made with regression equations that predicted weight from log₁₀ basal stem diameter measurements. The trees in both trials were harvested after a − 12°C freeze in December 1983 killed all trees except L. retusa to ground level. Less severe freezes in 1984–1985 of − 7°C and − 9°C killed all L. leucocephala to ground level whereas less than 2% of the L. pulverulenta were killed to ground level, thus demonstrating the difference in cold tolerance between these two species. Dry wood production in the screening trial of the L. leucocephala after 10 months' coppice growth ranged from 654 to 3602 g dry biomass per tree and that of the L. pulverulenta during the same period ranged from 437 to 2505 g dry biomass per tree. Dry wood productivity of L. leucocephala (K-8) 1-year coppice growth ranged from 1.4 t ha⁻¹ on a poorly drained soil to 10 t ha⁻¹ on a moderately drained soil.     

Pine needle consumption and bark stripping by sheep grazing annual pastures in young stands of widely spaced Pinus radiata and P. pinaster

The consumption of the pine needles and the stripping of bark by sheep grazing annual pastures in three open stands of P. radiata and one of P. pinaster were measured. The P. radiata were four years old and the densities were 250, 500 and 750 trees ha^-1. The P. pinaster included two, three and four year-old trees and the density was 440 trees ha^–1.Needles were eaten immediately after the sheep were admitted and this continued throughout the year. Within ten weeks of the start of winter grazing, sheep stocked at 7–10 ha^–1 had eaten about half of the accessible needles on both species where densities were less than500 trees ha^–1. The estimated consumption was about 260 g sheep^–1 day^–1 for the P. radiata. Bark stripping then commenced and continued throughout spring and summer on most plots. In some plots at low tree density, bark was stripped from more than 35% of the trees. In denser stands, needle consumption per tree was less and bark was stripped from less than 5% of the trees.Bark damage was most common on the smaller trees, and severity of stripping was negatively correlated with tree size. Of all the trees with bark damage, 22% of the P. pinaster and 14% of the P. radiata had more than half of the stem circumference stripped. A number of these will probably suffer both stem distortion and growth retardation, and some may die.Methods of reducing the incidence of bark damage are discussed.     

Growth and yield of maize and timber trees in smallholder agroforestry systems in Claveria,northern Mindanao,Philippines

On-farm experiments were conducted in the Philippines to study over a 4-year period the growth of two timber trees, gmelina (Gmelina arborea R. Br.) and bagras (Eucalyptus deglupta Blume), and their impact on the grain yield of intercropped maize. The experiment consisted of maize monocropping plots (control) and maize intercropped between trees planted in block (2 × 2.5 m), and hedgerow arrangement (1 × 10 m). Three maize crops were planted in the block plots before canopy closure, and seven maize crops were planted in the hedgerow and monocropping plots. Maize grain yield in the hedgerow and in the block arrangement with gmelina were respectively 37% (16.58 tons ha⁻¹) and 68% (8.3 tons ha⁻¹) lower than in monocropping (26.21 tons ha⁻¹). In the plots with bagras, maize grain yield in hedgerow and in block arrangement were respectively 19% (24.8 tons ha⁻¹) and 66% (10.4 tons ha⁻¹) lower than in monocropping (30.6 tons ha⁻¹). For both tree species, the diameter at breast height (dbh) was greater in hedgerow than in block arrangement, with the difference being more pronounced with age. It was estimated that gmelina planted in hedgerows would produce 6–8 m³ ha⁻¹ of merchantable volume more than if planted in block. The study verifies the hypothesis that intercropping between widely-spaced trees rows (planted at 10 m or more) is more profitable and feasible to smallholders than either maize monocropping or woodlots, and concludes with recommendations on how to further improve the productivity of tree-intercropping systems.     

Water Use of Tree Lines: Importance of Leaf Area and Micrometeorology in Sub-Humid Kenya

In this research the relative importance of leaf area and microclimatic factors in determining water use of tree lines was examined in sub-humid Western Kenya. Measurements of tree water-use by a heat-balance technique, leaf area, bulk air saturation deficit, daily radiation, and soil water content were done in an experiment with tree lines within crop fields. The tree species were Eucalyptus grandis W. Hill ex Maiden, Grevillea robusta A. Cunn. and Cedrella serrata Royle, grown to produce poles on a phosphorus-fixing Oxisol/Ferralsol with (+P) or without (−P) phosphorus application. Doubling the leaf area of Cedrella and Grevillea doubled water use in a leaf area (LA) range of 1–11 m² per tree. The response of Eucalyptus water use (W) to increases in leaf area was slightly less marked, with W = LAⁿ, n<1. Transpiration rate per unit leaf area (Tr) was the other important determinant of water use, being affected by both tree species and phosphorus fertilization. A doubling of the saturation deficit (SD) halved the water use of all trees except for Cedrella +P, in which water use increased. A direct effect of soil water content on water use was only found in Grevillea -P, with a small increase (60%) as available water increased from 1.4 to 8.9% above wilting point (32%). This low direct response to soil water content is probably due to the extensive tree-root systems and the deep clayey soils supplying sufficient water to meet the evaporative demand. Indirect responses to soil water content via decreases in leaf area occurred in the dry season. The results showed that water use of tree lines was more determined by leaf area and transpiration rate per unit leaf area than by micro meteorological factors. The linear response of tree water use to leaf area, over a wide range leaf areas, is a specific characteristic of tree line configurations and distinguished them from forest stands. In tree lines light interception and canopy conductance increase with leaf area much more than a similar leaf area increase would have caused in a closed forest canopy.     

Perspectives on hedgerow intercropping

Hedgrow intercropping (alley cropping) is a relatively new technology involving growing agricultural crops between rows of planted tree species. Leucaena is the most widely studied tree species for the practice and research has indicated that it can yield over 200 kg ha^–1 year^–1 of nitrogen for application in the alleys where crops are planted. More herbage (and nitrogen) are obtained from narrow alleys, and crops utilise the nitrogen better if the prunings are incorporated into the soil before planting. Low pruning heights may prevent shading of the crops.Most of the agronomic aspects of the practice have been investigated in humid lowlands with high rainfall. There is a need to focus research on testing the practice under varied agro-ecological conditions, and using several suitable multipurpose trees species at a wide range of alley width and plant population. Investigations should include more than one crop in the alleys, and at different spatial arrangements. Management schedules, like time and frequency of pruning the trees and method of applying the prunings under different ecological conditions need more research attention. Studies on competition also need to be undertaken in order to suggest improvements to the practice.This paper attempts to put together and discuss some of the recent advances on these and other management aspects concerning hedgerow intercropping, and areas that need further research endeavour are exposed.     

<Emphasis Type="Italic">Pinus radiata</Emphasis> and sheep production in silvopastoral systems at Carngham,Victoria, Australia

This long term experiment provides production data for evaluation of combined forestry and livestock systems. Five systems were established in Pinus radiata planted in 1981 (620 mm average annual rainfall). Sheep were introduced in 1984 and trees were pruned in several lifts. Adjusted tree stockings were (1) 60 widely spaced trees ha⁻¹, (2) 200 widely spaced trees ha⁻¹, (3) 200 trees ha⁻¹ in five-row belts, (4) 1,090 trees ha⁻¹ (unpruned) and 815 trees ha⁻¹, and (5) no trees (open pasture). Tree growth, wool production, liveweight gain and pasture production were measured. At year 25, tree diameter under bark at 1.3 m (DBHUB) in Systems 1, 2, 3 and 4 (unpruned) was 46.0, 39.2, 33.5 and 24.1 cm, while volume of bark-free 6-m butt-logs was 49, 117, 86 and 233 m³ ha⁻¹. Inner rows of System 3 belts contained smaller trees than outer rows. Pruned System 4 trees had slightly greater diameter than unpruned trees. Pasture production declined with tree stocking and time, due to shading and competition. Wool production (WP ha⁻¹) and liveweight gain (LWG ha⁻¹) declined linearly from year 9 to 17 with increasing disparity among systems. In 1998 (year 17) WP ha⁻¹ in Systems 1, 2 and 3 was 64, 16 and 43% of that in open pasture. Further analysis is needed to evaluate the financial costs and returns of various systems under particular rotation lengths and market prices.