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1.
Summary Acoustic Emission (AE) was measured in 30 mm-thick backsawn and quartersawn Tasmanian Oak (Eucalyptus regnans F. muell) boards drying at temperatures in the vicinity of 20 °C. By varying the diffusion coefficient used in a non-linear drying simulation program, calculated half-thickness moisture profiles were matched to measured profiles in a sample board. Once the measured and calculated drying behaviour was satisfactorily matched, the AE measured in an endmatched board closely followed the surface instantaneous strain calculated with the program. The AE activity increased once the surface instantaneous strain attained the proportional limit. The AE is not simply related to drying temperature or humidity but rather to a complex interaction between the two parameters.Symbols ca Moisture concentration in air (kg/m3) - cs Moisture concentration at the board surface (kg/m3) - D Diffusion coefficient (m2/hr) - DBT Dry bulb temperature (°C) - ei Instantaneous strain - RH Relative humidity (%) - WBT Wet bulb temperature (°C) - Basic density (kg/m3) The author is pleased to acknowledge the assistance of Emeritus Professor A. R. Oliver, Associate Professor P. E. Doe, University of Tasmania, the Australian Furniture Research and Development Institute and the Tasmanian Timber Promotion Board  相似文献   

2.
The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and 5.0 m s−1. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding air (ψs − ψ∞) is used to determine the convective mass flux at the surface. Also, ψs − ψ∞ is more appropriate than the water vapour pressure difference (pvs − pv∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the constant drying rate period. Received 27 February 1998  相似文献   

3.
Little information is available on soil respiration and microbial biomass in soils under agroforestry systems. We measured soil respiration rate and microbial biomass under two age classes (young and old) of a pecan (Carya illinoinensis) — cotton (Gossypium hirsutum) alley cropping system, two age classes of pecan orchards, and a cotton monoculture on a well-drained, Redbay sandy loam (a fine-loamy, siliceous, thermic Rhodic Paleudult) in southern USA. Soil respiration was quantified monthly during the growing season from May to November 2001 using the soda-lime technique and was corrected based on infrared gas analyzer (IRGA) measurements. The overall soil respiration rates ranged from 177 to 776 mg CO2 m–2 h–1. During the growing season, soil respiration was higher in the old alley cropping system than in the young alley cropping system, the old pecan orchard, the young pecan orchard, and the monoculture. Microbial biomass C was higher in the old alley cropping system (375 mg C kg–1) and in the old pecan orchard (376 mg C kg–1) compared to the young alley cropping system (118 mg C kg–1), young pecan orchard (88 mg C kg–1), and the cotton monoculture (163 mg C kg–1). Soil respiration was correlated positively with soil temperature, microbial biomass, organic matter, and fine root biomass. The effect of alley cropping on soil properties during the brief history of alley cropping was not significant except in the old systems, where there was a trend of increasing soil respiration with short-term alley cropping. Over time, different land use and management practices influenced soil properties such as soil temperature, moisture, microbial biomass, organic matter, and fine root biomass, which in turn affected the magnitude of soil respiration. Our results suggest that trees in agroforestry systems have the potential to enhance soil fertility and sustainability of farmlands by improving soil microbial activity and accreting residual soil carbon.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

4.
Overstory conditions influence understory microclimate and resource availability, leading to gradients in evaporative demand and moisture availability that influence seedling water relations. Partial canopies may either reduce seedling moisture stress by ameliorating environmental conditions, or increase moisture stress by reducing soil moisture availability. This study used stable isotope ratios of oxygen (δ18O) and carbon (δ13C) and mass-based foliar nitrogen concentrations to investigate changes in transpiration (E), stomatal conductance (gs) and intrinsic water use efficiency (iWUE) of pine seedlings across an overstory gradient from open canopy gap environments to closed canopy forest. Foliar δ18O increased sharply from basal areas of 0–10 m2 ha−1 in Pinus banksiana, Pinus resinosa, and Pinus strobus seedlings, followed by a more gradual increase with further increases in basal area. Foliar δ13C followed a similar, but less pronounced pattern in P. banksiana and P. strobus seedlings, and had no apparent relationship with overstory basal area in P. resinosa seedlings. The slope of the δ18O:δ13C relationship was positive for every species. Foliar nitrogen concentrations were not correlated with overstory basal area. These results suggest seedling E declined as overstory basal area increased due to reductions in gs, while iWUE increased slightly from open gaps to partial canopy environments. Open gap environments appear to provide sufficient moisture to sustain high leaf-level gas exchange rates in the species we studied, while relatively small increases in overstory basal area apparently promote rapid declines in gs, leading to greatly reduced seedling water loss and small increases in iWUE.  相似文献   

5.
In 1987–89 the CATIE-GTZ Agroforestry Project set up experiments with five timber tree species planted in single lines on twelve farm boundaries in cooperation with local farmers. When the trees were five years old, their height, diameter and total stem volume were: Acacia mangium 17 m, 19 cm and 67 m3 km–1, Cordia alliodora 14 m, 20 cm and 46 m3 km–1, Eucalyptus deglupta 22 m, 24 cm and 85 m3 km–1, Tectona grandis 17 m, 20 m and 64 m3 km–1, Terminalia ivorensis 18 m, 23 cm and 104 m3 km–1. Considering these excellent growth rates, planting of Cordia alliodora, Eucalyptus deglupta and Tectona grandis in lines on farm boundaries should be promoted. T. ivorensis and A. mangium are not recommendable for sites with impeded drainage because of mortality caused by root rot, mostly due to Rosellinia sp.  相似文献   

6.
Schinus terebinthifolius Raddi (Anacardiaceae) and Rapanea ferruginea (Ruiz & Pavon) Mez (Myrsinaceae) are two neotropical pioneer trees with wide geographical distribution in South America, highly degree of adaptation to different soil conditions and intense regeneration in areas with anthropic activities. With the aim to recommend the use Schinus and Rapanea in gallery forest restoration programs, we conducted an experiment with the objective to analyze the capacity of these two pioneer trees to tolerate soil flooding, mainly by accessing the effects of flooding on leaf gas exchange, growth and dry matter partitioning. Seedling survival throughout the 56-day flooding period were 100 and 90% for Schinus and Rapanea, respectively. The mean values of stomatal conductance (gs) and net photosynthesis (A) observed in the control seedlings were, respectively, 0.4 mol m–2s–1 and 14 mmolm–2s–1, for Schinus, and 0.5 mol m–2s–1 and 14 mmolm–2s–1, for Rapanea. On day 20 flooding reduced gs and A by 36 and 29% in Schinus, and 81 and 61% in Rapanea. At the end of the experiment, significant decreases were also observed for root and whole plant biomass, in both species. Based on the results, we concluded that seedlings of Schinus and Rapanea can survive and grow throughout a medium period of soil waterlogging, in spite of the alterations observed in their physiological behavior, such as the decreases in stomatal conductance and in whole plant biomass.  相似文献   

7.
A model was developed to estimate the stable timber output from shade stands of Cordia alliodora in coffee farms. The model predicts, for stand densities between 120–290 trees/ ha, timber yields of 9–24 and 6–15 m3/ha/yr of total and commercial overbark volumes, respectively. Current harvest rates in four sample farms are below these figures.The model is used to describe the transient trajectory (in terms of timber output over time) of Cordia alliodora stands with different initial DBH distributions. Practical recommendations are derived as to how farmers should manage their trees to achieve stable timber outputs in the shortest time possible.  相似文献   

8.
A drying experiment with 36 mm thick softwood boards having an average initial moisture content of approximately 1.2 (dry basis) was performed. Drying temperatures of 40, 60 and 80°C were used. Relative humidity and superficial air velocity were maintained at 40% and 3.0 m s?1, respectively. Internal moisture content was monitored along the process in the single direction of the internal flux of water. Loss in mass of the entire timber board was also determined. An effective coefficient of mass transfer was tuned to internal experimental profiles of moisture content by involving the Fick’s second law. An explicit finite difference method for the numerical solution of the mass balance represented by the Fick’s equation was combined with the simplex method of optimization to obtain a mass transport parameter in the magnitude of 1.5–3.5 × 10?9 m2 s?1. A positive and significant effect of temperature on the effective diffusion coefficient, which was well described by an Arrhenius type expression, was deduced from this investigation. Although a negative effect of the average moisture content on the internal resistance to mass transfer was also observed, it was much less evident; mainly above the wood fiber saturation point. A negligible influence of the local moisture content on the investigated transport parameter was noticed when either a linear or a nonlinear model correlating these variables was adopted.  相似文献   

9.
Summary A 2-D mathematical model was developed to simulate moisture movement and heat transfer in width and thickness directions within a softwood board during drying. The model is based on wood physiological features and behaviour observed during drying. In sapwood, liquid water movement is assumed to be a consequence of capillary action between liquid and gas phases inside the cell lumens. However, liquid flow does not occur in wood close to the exposed surfaces because at timber surfaces the wood cells are damaged during the sawing process and consequently the liquid column is broken. In heartwood, liquid flow is negligible since the pits are normally aspirated during the formation of heartwood in the growing tree. Water vapour moves under a partial vapour pressure gradient while bound water diffuses within the wood material due to differences in chemical potential. The model was solved numerically to predict moisture-content profiles. Experiments were undertaken to measure the moisturecontent gradient. Samples were removed from a tunnel dryer at intervals throughout drying, frozen overnight and then cut into slices for moisture-content determination. The experimental results were used to verify the model.This work is supported by the New Zealand Foundation of Research, Science and Technology under contract CO4415  相似文献   

10.
A dramatic decline in forest cover in eastern Africa along with a growing population means that timber and poles for building and fuelwood are in short supply. To overcome this shortage, the region is increasingly turning to eucalyptus. But eucalyptus raises environmental concerns of its own. Fears that it will deplete water supply, affect wildlife and reduce associated crop yields have caused many countries in the region to discourage farmers from planting this exotic. This paper is part of a series of investigations on the growth and water use efficiency of faster growing eucalyptus hybrids, which was introduced from South Africa to Kenya. The hypothesis is that the new hybrids are more efficient in using water and more suitable for the semi-arid tropics than existing eucalyptus and two popular agroforestry species. Gas exchange characteristics of juvenile Eucalyptus grandis (W. Hill ex Maiden), two eucalyptus hybrids (E. grandis × Eucalyptus camaldulensis Dehnh.), Grevillea robusta (A. Cunn) and Cordia africana (Lam) was studied under field and pot conditions using an infrared gas analyzer was used to measure photosynthetic active radiation (PAR), net photosynthetic rate (A), stomatal conductance (g s) and transpiration rate (E) at CO2 concentrations of 360 μmol mol−1 and ambient humidity and temperature. A, E and g s varied between species, being highest in eucalyptus hybrid GC 15 (24.6 μmol m−2 s−1) compared to eucalyptus hybrid GC 584 (21.0 μmol m−2 s−1), E. grandis (19.2 μmol m−2 s−1), C. africana (17.7 μmol m−2 s−1) and G. robusta (11.1 μmol m−2 s−1). C. africana exhibited high E values (7.0 mmol m−2 s−1) at optimal soil moisture contents than G. robusta (3.9 mmol m−2 s−1) and eucalyptus (5.3 mmol m−2 s−1) in field experiment and G. robusta (3.2 mmol m−2 s−1) and eucalyptus (4.2 mmol m−2 s−1) in pot-grown trees. At very low soil moisture content, extremely small g s values were recorded in GC 15 and E. grandis (8 mmol m−2 s−1) and G. robusta (14 mmol m−2 s−1) compared to GC 584 (46.9 mmol m−2 s−1) and C. africana (90.0 mmol m−2 s−1) indicating strong stomatal control by the species. Instantaneous water use efficiency ranged between 3 and 5 μmol mmol−1 and generally decreased with decline in soil moisture in pot-grown trees but increased with declining soil moisture in field-grown trees.  相似文献   

11.
Summary The instantaneous profile method was used to establish the boundary desorption curve of the effective water conductivity function of red pine (Pinus resinosa Ait.) sapwood in the radial and tangential directions from nearly saturated to dry conditions at 18, 56 and 85 °C. The results obtained demonstrate that the effective water conductivity is a function of moisture content, temperature, and direction of flow. The effective water conductivity increases by several orders of magnitude (104–105) as moisture content increases from dry to nearly saturated conditions at a given temperature. The effective water conductivity also increases by a factor varying between 10 and 50 as temperature rises from 18 to 85 °C in the moisture content range considered. The variation of the moisture content–water potential relationship with temperature can explain part of the temperature effect. The effective water conductivity was generally higher in the radial direction than in the tangential direction in a ratio varying from about 1/1 to 3/1 depending on moisture content and temperature. Finally, the flux–gradient relationships obtained at given moisture contents were found to be linear, confirming the validity of using a moisture flux equation considering the water potential gradient as the driving force for the experimental conditions considered in the present work. The knowledge of the effective water conductivity function and of the moisture content–water potential relationship allows the utilization of a two-dimensional model of moisture movement in wood during drying using the gradient in water potential as the driving force for drying at temperatures up to 85 °C. Received 27 February 1998  相似文献   

12.
Predictive models were developed for Cordia alliodora branch and Theobroma cacao branch or leaf biomass,based on branch basal areas (r2 0.79) but the model of C. alliodora leaf biomass, although significant, was of very low accuracy (r2 = 0.09) due to annual leaf fall. At age 10 years, shade tree stem biomass accounted for 80% of the total above-ground biomass of either tree. However, between the ages of 6 and 10 years, the biomass increment of T. cacao branches (3–4t.ha–1.a–1) was similar to that of the shade tree stems. During the same period, the net primary productivity was 35 and 28 t.ha–1.a–1, for the Erythrina poepigiana and and C. alliodora systems, respectively.Cocoa production under either of the shade trees C. alliodora or E. poeppigiana was 1000 kg.ha–1.a–1 (oven-dry; ages 6–10 yr). During the same period, C. alliodora timber production was 9 m3.ha–1.a–1 whilst the leguminous shade tree E. poeppigiana does not produce timber. Litterfall over the same 5 years, including crop and/or shade tree pruning residues, averages 11 and 23 t.ha–1.a–1, respectively. The main difference was due to E. poeppigiana pruning residues (10t.ha–1.a–1).Soil organic material reserves (0–45 cm) increased over 10 years from 198 to 240 t.ha–1 in the E. poeppigiana plots and from 168–184 t.ha–1 in the C. alliodora plots. These values, together with the productivity indices presented, provide evidence that the systems are sustainable.For economic reasons, the use of C. alliodora is recommended under the experimental conditions. however, on less fertile soils without fertilization, the greater biomass and hence nutrient return to the soil surface under E. poeppigiana, might make this the preferable shade tree.  相似文献   

13.
Ericsson  Staffan  Östlund  Lars  Axelsson  Anna-Lena 《New Forests》2000,19(3):227-240
Detailed spatial changes in foreststructure in a central Swedish landscape were examinedusing geographic information system techniques. First,the influence of grazing and burning on forest densityand structure in the 19th century landscape wereanalyzed. Then, the development of the landscapeduring the 20th century, together with the impactof modern forest management methods on foreststructure, were analyzed using historical sources. In1907, over 20% of the 2200 hectare study site wassparsely-wooded (12 m3 ha–1) with old trees.These areas have been reforested with single-storiedmiddle-aged and old pine stands (66 m3 ha–1in 1989) during the 20th century. Firesuppression and changes in land use from subsistence-to-industrialforestry, facilitated Norway spruceregeneration as undergrowth in open Scots pine standsafter logging. This natural regeneration has, to alarge extent, been cut down and replaced by pineafforestation. During the second half of the 20thcentury, the standing timber volume has steadilyincreased, while the mean age of the forest hasdecreased. Today's young dense forests will result inhigher timber values in the coming decades, but theforest has lost a range of ecological niches.  相似文献   

14.
An oxygen electrode was used to estimate the respiration rate of basal 1 cm sections of Prosopis juliflora cuttings. The respiration rate per unit dry mass decreased linearly with increasing diameter at a rate of 0.42 nmol02g–1s–1mm–1 between the range of 1–3 mm diameter. However, as a result of increased mass, total respiration for the whole 1 cm section of tissue increased linearly with increasing diameter. The average respiration rate of the basal 1 cm of stem tissue, measured 14 days after insertion in the propagator, was almost double that of the 1 cm section of tissue above it (1.01 nmol02g–1s–1 compared to 0.57 nmol02g–1s–1). The value of this technique as an aid to our understanding of the development of adventitious roots is discussed.  相似文献   

15.
Both model and field estimations were made of the damage inflicted to coffee plants due to the harvest of timber shade trees (Cordia alliodora) in coffee plantations. Economic analyses were made for different coffee planting densities, yields, and both coffee and timber prices.Damage due to tree felling and log skidding should not be a major limitation to the use of timber shade trees in coffee plantations. The timber price that would balance all discounted losses and benefits to zero, for scenarios with and without trees ranged between 8–20 US $/m3 (current overbark log volume at the saw mill yard is US$ 66/m3). There will be lower margins for coffee damage in high yielding plantations, specially in years of good coffee prices. Nevertheless, the use of timber shade trees is recommended even in these scenarios.  相似文献   

16.
Summary The purpose of this study was to examine the influence of the moisture level on the cell-wall material in wood using pulsed proton nuclear magnetic resonance. The wood species used were western hemlock (Tsuga heterophylla (Raf.) Sarg.) and sitka spruce (Picea sitchensis (Bong.) Carr.), distinguishing between heartwood and sapwood regions. The moisture contents of the specimens were below the fibre saturation point and they were conditioned to equilibrium moisture contents based on initial desorption, adsorption and secondary desorption processes. From the FID experiments, the NMR-based moisture contents and the solid-wood lineshape second moments were determined. Average relative proton-spin densities, which were needed to calculate the NMR-based moisture contents, were determined from known moisture contents and they were: hemlock sapwood: 0.616; hemlock heartwood: 0.537; spruce sapwood: 0.679; and, spruce heartwood: 0.446. The average RSD value, considering both heartwood and sapwood, for western hemlock species was 0.577 and for sitka spruce was 0.563; these are close to published RSD values for other species. The condition as to how the equilibrium moisture content was attained did not influence the second moment for hemlock; however, for spruce sapwood, the second moments were sorption dependent. The hemlock M2 decreased from about 5.1 × 109 s-2 at low MNMR to 4.5 × 109 s-2 (heartwood) and 4.3 × 109 s-2 (sapwood) at higher mnmr. The adsorption and secondary desorption M2 for the spruce sapwood region decreased from about 5.0 × 109 s-2 at low mnmr to about 4.1 × 109 s-2 near the MF, whereas M2 for the spruce heartwood decreased from about 4.3 × 109 s-2 at low MNMR to about 3.5 × 109 s-2 near MF. Extractives may have a key role in obtaining the RSD and second moments.This project was financially supported by the Science Council of British Columbia, MacMillan Bloedel Research. The Natural Sciences and Engineering Research Council of Canada is acknowledged for their support of the NMR spectrometer measurements  相似文献   

17.
Diurnal gas exchange characteristics were measured simultaneously in two mangrove species, Avicennia marina and Bruguiera gymnorrhiza, over 7 d in summer (February–March), to compare their productivity. The study was undertaken in the Beachwood Mangroves Nature Reserve, Durban, South Africa, using fully expanded leaves of young and mature trees at the top of the canopy. Gas exchange was strongly influenced by photosynthetic photon flux density (PPFD), leaf temperature and the accompanying leaf to air vapour pressure deficit ( w). Carbon dioxide exchange was saturated at a PPFD of about 600 mol m-2s-1 in B. gymnorrhiza compared to 800 mol m-2s-1 in A. marina. Maximal CO2 exchange occurred between 12h00 and 14h00 and was consistently greater in A. marina (8.8 mol m-2s-1) than in B. gymnorrhiza (5.3 mu;mol m-2s-1). Mean internal CO2 concentrations ( ci) were 260 l l-1 in A. marina and 252 l l-1 in B. gymnorrhiza. Photorespiratory activity was 32% in A. marina and 30% in B. gymnorrhiza. Mean water use efficiency (WUE) was 8.0 mol mmol-1 in A. marina and 10.6 mol mmol-1 in B. gymnorrhiza. Diurnal leaf water potentials ranged from –0.8 to –3.5 MPa and were generally lower in A. marina.  相似文献   

18.
Green leaf biomass of Tithonia diversifolia is high in nutrients and recognised as a potential source of nutrients for crops. We conducted a field survey in western Kenya to determine the variation in leaf nutrient concentrations in tithonia grown in naturalised hedges and agricultural fields, and to examine whether leaf nutrient concentrations were related to soil nutrient status. Leaf P and K concentrations were higher in naturalised hedges (3.2 g P kg–1 and 35 g K kg–1) than in unfertilised fields (2.2 g P kg–1 and 23 g K kg–1). The critical level of 2.5 g P kg–1 for net P mineralisation was exceeded by > 90% of the leaves from hedges, but by only 14% from unfertilised fields. Leaf P and K concentration increased linearly with increasing natural logarithm of anion resin extractable soil P and exchangeable soil K, respectively. However, at the same levels of soil available P and K, field-grown tithonia consistently produced lower leaf P and K concentrations than that grown in hedges. This study indicates that biomass from tithonia planted on nutrient-depleted soils would be a less effective source of P and K, via biomass transfer, than tithonia from naturalised hedges.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

19.
To investigate the effect of tree species on soil N dynamics in temperate forest ecosystems, total N (Nt), microbial N (Nmic), net N mineralization, net nitrification, and other soil chemical properties were comparatively examined in beech (64–68 years old) and Norway spruce (53–55 years old) on sites 1 and 2, and beech and Scots pine (45 years old) on site 3. The initial soil conditions of the two corresponding stands at each site were similar; soil types were dystric Planosol (site 1), stagnic Gleysols (site 2), and Podzols (site 3). In organic layers (LOf1, Of2, Oh), Nmic and Nmic/Nt, averaged over three sampling times (Aug., Nov., Apr.), were higher under the beech stands than under the corresponding coniferous ones. However, the Nmic in the organic layers under beech had a greater temporal variation. Incubation (10 weeks, 22 °C, samples from November) results showed that the net N mineralization rates in organic layers were relatively high with values of 8.1 to 24.8 mg N kg–1 d–1. Between the two corresponding stands, the differences in net N mineralization rates in most of the organic layers were very small. In contrast, initial net nitrification rates (0.2–17.1 mg N kg–1 day–1) were considerably lower in most of the organic layers under the conifer than under the beech. In the mineral soil (0–10 cm), Nmic values ranged from 4.1–72.7 mg kg–1, following a clear sequence: August>November>April. Nmic values under the beech stands were significantly higher than those under the corresponding coniferous stands for samples from August and April, but not from November. The net N mineralization rates were very low in all the mineral soils studied (0.05–0.33 mg N kg–1 day–1), and no significant difference appeared between the two contrasting tree species.  相似文献   

20.
Seasonal fodder production responses of five shrubs (Centrosema arenarium, Desmodium strigillosum, Desmodium velutinum, Phyllodium pulchellum, and Tadehagi triquetrum)and five trees (Albizia gummifera, Berlinia grandiflora, Albizia niopoides, Bauhinia monandra, and Inga edulis) to pruning heights ranging from 15 to 75 cm were evaluated during the main-wet, minor-wet, and dry seasons of 1993 and 1994 in the forest-savanna transition zone of West Africa. Fodder from the main-wet season was analysed for nitrogen (N) and phosphorus (P), and dry matter degradation characteristics after 6, 12, 24, 48, 72 and 96 h of incubation in rumen-fistulated N'Dama steers. In the minor-wet season, fodder production of all species increased in response to increasing pruning height with the exception of P. pulchellum and A. gummifera. Highest fodder production was attained at a pruning height of 45 cm for the Desmodium species, 50 cm for P. pulchellum, and 75 cm for the rest of the species. Concentrations of N and P varied significantly among the species; for N the ranges were 28.7–38.8 g kg–1 (shrubs) and 25.3–44.5 g kg–1 (trees), while for P the ranges were 3.26–7.04 g mg–1 (shrubs) and 3.58–6.76 g mg–1 (trees). Dry matter degradation characteristics differed significantly among shrubs and trees; ranges for shrubs were: soluble fraction (a), 128–185; degradable fraction (b), 664–703; potential degradability (PD), 793–857, as g kg–1; rate of degradation (c), 0.0241–0.0308 as % h–1 while for trees ranges were: (a), 139–160; (b), 651–826; (PD), 824–970, as g kg–1; (c), 0.0143–0.0227 as % h–1. Based on fodder production and quality, C. arenarium, D. strigillosum, D. velutinum, B. monandra, I. edulis, and A. niopoides were the most promising species for the development of animal agroforestry technologies in the west African forest-savanna transition zone and similar environments in the tropics.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

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