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1.
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.  相似文献   

2.
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.  相似文献   

3.
The use of agroforestry systems in which pruning from trees is used to mulch the companion crops is an important area of research in the tropics. However, previous studies mostly evaluated the contribution of mulch to soil improvement and rarely examined the effect of mulch on weeds. Field experiments were conducted during the 1995 and 1996 growing seasons to investigate the effects of mulch from three woody fallow species on weed composition, biomass and maize grain yield. Treatments consisted of mulch from Leucaena leucocephala, Gliricidia sepium, and Senna siamea applied at rates of five and three tons dry matter ha–1 at planting and three weeks after planting (WAP), respectively, an unmulched treatment that received 90 kg N ha–1 of inorganic fertiliser, and an unmulched control plot that received no fertiliser. In both years and sampling dates, plots mulched with G. sepium and S. siamea had significantly lower weed density and biomass than the control plot in each of the sampling times and year of study. There was no significant difference in either weed density or biomass between the plot mulched with L. leucocephala and the unmulched plots. Mulches from G. sepium and S. siamea reduced weed density and weed biomass, while L. leucocephala was less effective in reducing weed biomass and weed density. Weed reduction by the mulches was in the order G. sepium S. siamea > L. leucocephala. Sedges were the dominant species in all the treatments except in G. sepium plots, where Talinum triangulare and other broadleaved species were dominant.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   

4.
The effect of tree species on the characteristics of the herbaceous stratum, during the first five years of a fallow, was evaluated in the North of Cameroon (average annual temperature 28.2 °C, total annual rainfall 1050 mm). Treatments included a natural grazed herbaceous fallow, a natural ungrazed herbaceous fallow and three planted tree fallows (Acacia polyacantha Willd. ssp. campylacantha (Hochst. ex A. Rich.), Senna siamea Lam. and Eucalyptus camaldulensis Dehnh.), which were protected against grazing. Because tree species influenced light interception in different ways, as well as having different root patterns, they had different effects on the herbaceous stratum in terms of species composition and biomass. The grazed herbaceous fallow maintained the greatest species richness. Protection against grazing or the introduction of tree species associated with the absence of grazing induced both a progressive evolution to a particular species composition. The ungrazed herbaceous fallow consisted mainly of Andropogon gayanus Kunth, which provided the greatest biomass (8 t dry matter ha–1 at the end of the fallow period). E. camaldulensis provided little shade and the lowest fine root mass in the top layer allowing the growth of A. gayanus and thus a greater herbaceous biomass (3.5 t DM ha–1) than that found under the other tree species. Under the heavy shade of A. polyacantha, the herbaceous stratum consisted mainly of annual Pennisetum spp. (2.2 t DM ha–1) and showed the greatest N concentration (1.3%), probably due to N2 fixation by the tree species. After the fourth year, despite the relatively open tree canopy, S. siamea, which showed the highest fine root mass, had a strong depressive effect on the herbaceous stratum. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

5.
Traditional agroforestry systems in the communal areas of Zimbabwe are described. There are systems centered on main fields, on home gardens, on homesites and on grazing areas. In the main fields, the major tree-related management practice is the conservation of preferred indigenous fruit trees. Fruit trees are also the focus of forestry activities around the gardens and the homesite; but here it is the planting of exotic species. In a localized area of Zimbabwe Acacia albida is important in fields. There is almost no use of tree fallows in Zimbabwe. Trees in grazing areas have numerous roles, but at present there is little knowledge about traditional management practices in these areas. In the development of agroforestry systems in Zimbabwe it is suggested that those systems designed to improve fodder production will make a significant contribution to farm productivity because of the importance of cattle in the farming system and the present fodder shortage. Interventions involving the planting of fruit trees are likely to be very successful, as there is much interest in such planting. Another area that needs to be developed is that of tree plantings to improve soil fertility.  相似文献   

6.
An on-farm trial was conducted to determine dry matter production of four fodder tree species and their effect on soil water and maize production. The trees were planted in rows intercropped with maize. The four tree species selected were Acacia karroo Hayne (indigenous fodder tree), Leucaena leucocephala (Lam.) De Wit (nitrogen fixing), Morus alba L. (fodder and fruit), and Gleditsia triacanthos L. (fodder and fuel). Volumetric soil water was measured in the upper 0.3 m of soil in each row of the trial using the time domain reflectometry technique. The neutron probe technique was used for monitoring the water content deeper in the soil. Geostatistical methods were used to analyse treatment differences in the upper 0.3 m of soil. The soil water content did not differ significantly between the maize and tree rows indicating that competition for water in the upper horizon was not the reason for lower maize yields. However, at greater soil depths (75–125 cm) trees in the wide spacing used less water than those in the narrow spacing. Light interception was an important factor in reducing maize yields in the row nearest to the trees. High soil water values recorded during summer indicated that in the current cycle of good rainfall the plants in the agroforestry trial were not stressed. Thus the trees do not compete with the crops for soil moisture in good rainfall seasons. However, this study would need further evaluation for the competition for water for the low rainfall years. Since the trees have access to water at greater depths, they are likely to be more productive into the dry season than shallow rooted crops.  相似文献   

7.
Dry, dehiscent fruits ofAcacia tortilis provide important fodder for pastoral livestock in dry seasons on the central Borana Plateau, fruits ofA. nilotica may also be useful during drought. Information was needed on fruit yield to assess what these species could contribute to improved calf feeding systems based on local resources. Fruit production of 10 mature trees per species was measured at five sites for seven months during 1988–9 (n=50 per species). Fruit yields varied according to site, season and species x site (each atP<0.001), but there was no main effect of species (P=0.13). Yields were not correlated with trunk diameter at breast height (DBH) or canopy area within or across species (P>0.05 in all cases). Yields ranged from 0 to 40 kg DM per tree overall, with an average of 5.3 kg DM per tree (or 65 g DM/m2 of canopy area). This average tree had a DBH of 26 cm and a canopy area of 81 m2. Low and highly variable fruit yields appear to constrain enhanced use of these species here. These species warrant further attention in research and development, however, given their strategic value as forage resources in pastoral systems and their ability to persist in variable environments.  相似文献   

8.
To meet their wood, fodder and fruit needs, resource-poor farmers with only small land holdings are forced to mix trees in their food crop plots. An experiment was conducted to study the effect of nine tree species planted at 312.5 trees ha–1 (4×8 m) on the yield of bananas planted at 625 stools ha–1 (4×4 m) and beans (80000 plants ha–1) as well as the wood production of the trees when intercropped. In addition, an economic analysis was done to compare the different tree/banana/bean associations.After three and one-half years, wood volume (in m3 ha–1) ofGrevillea robusta (18.1), was highest and that ofErythrina poeppigiana (2.7),Cedrela odorata (2.4) orMarkhamia lutea (0.8) was the lowest. Volume ofCedrela serrata (13.7) was not significantly different from that ofAlbizia chinensis (12.8) but was significantly higher than that ofLeucaena diversifolia (6.8),Acrocarpus fraxinifolius (6.7) orCalliandra calothyrsus (6.0).None of the tree species had a significant influence on the yields of the bananas and none affected the yield of the bean crops until the seventh cropping season, three years after the trees were planted. In that year, Grevillea reduced bean yield by 29%, Albizia by 34% and Leucaena by 36%. From the economic analyses, all the treatments except Leucaena and Markhamia had positive net benefits relative to the control (banana/bean) but the results were highly variable.C. serrata was found to be the best tree to be intercropped in a banana/bean system.  相似文献   

9.
In tropical areas of Mexico, Leucaena leucocephala is widely used in silvopastoral systems. However, little information exists on other native woody species of high forage potential, such as Guazuma ulmifolia. The aim of this study was to evaluate the components of biomass, forage yield and quality, and availability of N in fodder banks of L. leucocephala, G. ulmifolia, and a mixture of both species during dry and rainy seasons, under sub-humid tropical conditions. The experimental unit was a 5 × 10 m plot, containing three rows with 2 m between rows; each row had 20 plant positions with 0.50 m between plants. Within each plant position there was either a single plant, in the case of pure-crop, or two plants, in the case of mixed of both species. A complete randomized block design with three repetitions was used. In both seasons, there were a significantly greater proportion of leaves in the G. ulmifolia fodder banks (71 %) and in mixed fodder banks (69 %) than in L. leucocephala fodder banks (64 %). Consequently, these systems had leaf-to-stem ratios of 2.4, 2.2 and 1.9, respectively. The forage yield of fodder banks was not influenced by season. The mixed fodder bank had greater forage yield (5.1 t DM ha?1) than the L. leucocephala fodder bank (3.4 t DM ha?1) in each season. Additionally, the mixed fodder bank accumulated more forage yield during the experimental period (10.2 t DM ha?1 year?1) than G. ulmifolia (9.0 t DM ha?1 year?1) or L. leucocephala (6.9 t DM ha?1 year?1). The concentrations of CP, C and C:N were not influenced by season. Forage NDF and ADF concentrations were greater in the rainy season (476 g kg?1 DM) compared with the dry season (325 g kg?1 DM). Mixed fodder banks had the greatest N yield (185.9 kg ha?1) and consequently the greatest availability of N (371.8 kg N ha?1 year?1). We conclude that mixed fodder banks of L. leucocephala and G. ulmifolia are a better option for improving productivity and forage quality in comparison with pure fodder banks in Yucatan, Mexico.  相似文献   

10.
An agroforestry and soil conservation needs assessment survey conducted in southern Zambia revealed valuable insight into needs, constraints and development options as perceived by smallholders themselves. Inadequate efforts to conserve soil are due to technical and socio-economic factors, they do not result from a lack of awareness of the widespread erosion threat. Fruit tree planting, windbreak establishment as well as the protection of the natural Faidherbia albida regeneration in cropland are popular agroforestry interventions whose positive effects are widely acknowledged. Forty-two perennial species were found to directly contribute to people's diet. Although local fuelwood and fodder shortages as well as the need for fencing are recognized only few respondents envisage agroforestry solutions such as fuelwood and fodder tree planting or live fencing. Most smallholders are interested in tree planting but have so far only planted few trees. Those planted are usually exotic fruit trees. Drought hardly, termite and browse resistant perennials adapted to smallholder tree planting must be provided by the extension services. The widespread exclusion of women from decision making and the lack of tenure security hampers female participation in agroforestry development and consequently threatens sustainable development altogether.  相似文献   

11.
The cashew-coconut system in the Coast Province of Kenya was appraised to determine the efficacy and adoption potential of a fruitcrop based agroforestry intervention designed to increase the productivity of the system. Fruitcrops on farmers plots ranged between 16–22 species. They featured mainly as understorey trees in cashew-coconut plots and upper storey of foodcrop plots. Fruit tree management was generally poor.Between 67–100% of farmers interviewed were interested in planting more fruit trees on their farms. Envisaged cash generation was a major reason for their interest. Preferred species were generally adapted exotics. Preference was in the order ofMangifera indica, Citrus sinensis, C. reticulata > Cocos nucifera, Anacardium occidentalis, Carica papaya > Passiflora edulis var. flavicarpa,Ananas comosus, Syzygium cumini, Citrus limon, Musa sapientum, Persea americana > Musa paradisiaca, Citrus aurantifolia Annona spp. Locational differences existed in exact order of preference within the groupings. Constraints to fruit production included lack of improved fruit tree seedlings, low proficiency in fruit seedling production, transportation, no capital for initial investment, damage by wild animals, prolonged dry spells, and frequent die back of fruit trees. Based on its high adoption potential, a fruitcrop based agroforestry intervention is recommended for increasing the productivity of the cashew-coconut system of Kenya.Possible agroforestry technologies in which fruitcrops could feature are discussed.  相似文献   

12.
The objective of this study was to compare the effects of woodlots of five tree species, continuous maize (Zea mays L.) and natural fallow on soil water and nitrogen dynamics in western Tanzania. The tree species evaluated were Acacia crassicarpa (A. Cunn. ex Benth.), Acacia julifera (Berth.), Acacia leptocarpa (A. Cunn. ex Benth), Leucaena pallida (Britton and Rose), and Senna siamea (Lamarck) Irwin & Barneby). The field experiment was established in November 1996 in a completely randomized block design replicated three times. Maize was intercropped between the trees during the first three years after planting and thereafter the trees were allowed to grow as pure woodlots for another two years. Transpiration by the trees was monitored when they were 3 years old using sap flow gauges. Soil water content was measured using the neutron probe approach between November 1999 and March 2001. Soil inorganic N profiles were measured when the trees were four years old in all treatments. The results indicated that the trees transpired more water than natural fallow vegetation during the dry season. The difference was apparent at a depth of 35 cm soil, but was more pronounced in deeper horizons. The water content in the entire soil profile under woodlots and natural fallow during the dry period was 0.01 to 0.06 cm3 cm−3 lower than in the annual cropped plots. This pattern was reversed after rainfall, when woodlots of A. crassicarpa, A. leptocarpa, A. julifera, S. siamea and L. pallida contained greater quantity of stored water than natural fallow or continuous maize by as much as 0.00 to 0.02, 0.01 to 0.04, 0.01 to 0.04, 0.01 to 0.03 and 0.00 to 0.02 cm3 cm−3, respectively. Natural fallow plots contained the lowest quantity of stored water within the entire profile during this period. Transpiration was greatest in A. crassicarpa and lowest in L. pallida. All tree species examined were `scavengers' of N and retrieved inorganic N from soil horizons up to 2-m depth and increased its concentration close to their trunks. This study has provided evidence in semi-arid environments that woodlots can effectively retrieve subsoil N and store more soil water after rains than natural fallow and bare soil. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

13.
Alley cropping was introduced in the humid forest zone of Cameroon to increase soil fertility in 1987, but until 1992 the adoption rate had remained low. To better understand the reasons behind this, three types of on farm trials were established from fully researcher controlled to fully farmer controlled. During the evaluation of the technology with farmers a number of modifications were registered (1) Pruning height and frequency: Because of the difficulties to consistently cut back at 30 cm, farmers decided to slash at ground level as they normally do while slashing the natural fallow vegetation. This equally allowed for more flexibility in time of pruning. (2) Cropping intensity and pattern: Initially, alleys were cropped each year. This however had several shortcomings. Having observed the positive impact of incidental fallow period in a farmer's field, it was decided to introduce a fallow phase of at least one year. During the fallow period the plot can be used for fodder production, bee farming and production of stakes. (3) Residue management: Fire went incidentally in a farmer's tree plot after slashing, and the trees were not affected. This gave farmers an alternative way to manage the residue, by controlling the fire, before bringing in other crops such as groundnut and cassava. (4) Agroforestry species: Because Leucaena leucocephala, in spite of it soil fertility restoration potential, rapidly became a noxious weed, farmers have asked for a less invasive species. Calliandra calothyrsus was introduced for this purpose and became a good bee forage. With these modifications, the original alley cropping system has evolved into a rotational tree fallow with higher adoption potential. From about 15 farmers who were testing the technology in 1992, the number increased to 52 in 1996, 120 in 1997 and 236 in 1998. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
A study was conducted to identify and explore indigenous knowledge relating to fodder trees and silvopastoral management systems of small-scale farmers in seasonally dry areas of Jamaica. The objectives of the study were to: 1) explore farmers indigenous knowledge relating to fodder trees and silvopastoral management systems in a subtropical dry climate; 2) examine pastoral land-use systems and technologies in current use; and 3) seek to integrate this information into silvopastoral tree fodder systems. Data were gathered via observation and semistructured interviewing. A snowball sampling strategy was used to purposively select all small-scale farmers who had cattle in the Green Park valley for interview.Of forty farmers interviewed, 37 males (92.5%) and 3 females (7.5%) were primary caretakers of cattle. Twenty-seven of 40 farmers (68%) raised cattle to generate income. During extended droughts farmers are forced to look for alternatives to desiccated, overgrazed pasture grasses, including: 1) local travel to harvest sugar cane tops and to cut Guinea grass (Panicum maximum); 2) purchase of bag feed; and 3) harvest and use of tree fodder. Preferred fodder trees were identified as Bacedar (Guazama ulmifolia), Guango (Albizia saman), Breadnut (Brosimum alicastrum) and Quickstick (Gliricidia sepium).Recommended silvopastoral management systems include fodder hedgerows, three strata forage systems, and living fences. In addition, production of indigenous fodder tree species, introducing improved tree fodder species, and planting improved pasture grasses concurrent with cash trees is suggested.  相似文献   

15.
Shortened fallows have resulted in declining upland rice yields in slash-and-burn upland rice systems in northern Laos. We studied the benefit of planted legume fallows for rice productivity, weeds, and soil nitrogen and phosphorus availability. Four systems were evaluated over a 5-year period: 1-year fallow with native species, 1-year Cajanus cajan fallow, 1-year Leucaena leucocephala fallow, and continuous annual rice cropping. Rice was grown either once each year as continuous annual cropping or in alternate years of 2001, 2003, and 2005. C. cajan and L. leucocephala were sown with rice during the 2001 growing season. In subsequent years, L. leucocephala regenerated from root stock and did not have to be resown, whereas C. cajan was resown in 2003. Establishment of either C. cajan or L. leucocephala had no significant effect on rice yield in 2001, and rice yields ranged from 2.0 to 2.3 t/ha. Rice yields declined rapidly in succeeding years, and rice yields in the four systems ranged from 0.7 to 1.1 t/ha in 2003 and from 0.3 to 0.5 t/ha in 2005. Although two planted fallow systems increased nitrogen input because of greater biomass accumulation in 2003 and 2005 and soil phosphorus availability was higher following L. leucocephala fallow in 2005, there were no significant differences in rice yields among the four systems in either year. Weed biomass during the rice growing season increased each year in all systems and increased more rapidly for continuous annual rice cropping, in which the dominant weed species was Ageratum conyzoides L. Among the other three systems, there were no significant differences in the weed biomass in 2003 and 2005. We conclude that C. cajan and L. leucocephala as 1-year fallows do not offset the negative effects of increased cropping intensity on rice yield in this region.  相似文献   

16.
孟加拉东南部土壤中的砷含量很高,不仅威胁人的健康,而且对土壤也有破坏作用。云南石梓(Gmelina arborea)在孟加拉是个快速生长的树种,也是含砷土壤中的潜力树种。研究评价了含砷试验土中丛枝菌根真菌对云南石梓(Gmelina arborea)生长的影响。播种前,四种不同浓度的砷(10mg·kg-1、25mg·kg-1、50mg·kg-1和100mg·kg-1)被加入到试验土中。记录生长参数,如,植物的根、苗鲜重、干重、冠幅径、根长和苗高、根瘤菌和孢子菌群落。菌根植株较非菌根植株生长好。与其它含砷量高的土壤中植株的生长情况相比,在含砷量为10-mg·kg-1的土壤中,菌根植株和菌根生长效果最佳,菌根植株生物量最高。随着砷浓度的增加,种苗生长,根瘤菌和孢子菌群落均明显降低p0.05)。与非菌根植株比较,菌根植株高生长增加了40%,生物量增加了2.4倍。研究表明,根瘤菌接种可以减少有害土壤中的云南石梓(Gmelina arborea)的初生长的影响。  相似文献   

17.
A major production constraint in arid and semiarid areas of Ethiopia is a lack of water for crop growth. Run off water can be harvested by channeling it into micro- catchments (MC) where it slowly infiltrates into the soil. The increased moisture provides more plant growth in these dry lands. An experiment using MC was conducted in eastern Ethiopia to study the growth of four multipurpose tree species intercropped with grass. Trees and grass were grown in 25 m2 and 100 m2 MC. Plant height, root collar diameter, and mortality rate of trees were determined 12 months after planting. Dry matter yield of grasses and trees were measured and nutrient analysis of plant tissues was determined. In a separate experiment the biomass of trees was determined after 2.5 years of continuous growth without grass competition. Soil moisture, organic matter, texture and bulk density of the soils were also determined. Mean tree height was 10% greater in the 100 m2 than in the 25 m2 MC. Root collar diameter and survival rate showed similar increase with 13% and 7.8% respectively. Acacia saligna and Leucaena leucocephala showed better growth in both plot sizes than the indigenous Acacia seyal and Acacia tortilis. The dry matter yield of grass (Panicum maximum) was over 12 tons/ha and 8 tons/ha in the 100 m2 and 25 m2 plots respectively. Soil moisture content was greater in MC than in control plots with no water harvesting structures with 31% and 24% during the wet and dry seasons respectively. The use of water harvesting can improve fodder production and carrying capacity of the dry lands of Ethiopia.  相似文献   

18.
Seedlings of invasive species often exhibit superior physiological traits that facilitate their spread at early stages of invasion, although it is unclear whether these traits persist at the post-establishment stage. To determine whether mature exotic Acacia spp. possess superior traits over mature native plants, we compared foliar gas exchange and chlorophyll a fluorescence of Acacia auriculiformis and Acacia mangium coexisting with tropical heath forest tree species Buchanania arborescens and Dillenia suffruticosa in Brunei Darussalam. The CO2 assimilation rates of Acacia spp. were significantly higher than those of heath species at current prevailing conditions of ~400 ppm ambient CO2, 1,500 µmol m?2 s?1 photosynthetically active radiation and 30°C leaf temperature. The photosystem II of Acacia spp. exhibited significantly higher maximum quantum yield of primary photochemistry at comparable temperatures, and was more sensitive to an elevated temperature (42°C for 1 h). Better photosynthetic performance of Acacia spp., due to larger stomatal openings, better light harvesting efficiency, and greater plasticity in photosystem II, may enable adult Acacia trees to sustain a competitive growth advantage and suppress native tropical heath forest species. The competitive advantage maintained by Acacia spp. in post-establishment stage likely facilitates the establishment of monospecific Acacia stands in invaded heath forests.  相似文献   

19.
Latin American pastures usually include trees that may be important in sustaining productivity and conserving resources and biodiversity. A participatory survey of trees in seasonally dry pastures of 54 farms in the Caribbean region of Colombia, followed by cluster and correlation analyses, revealed a multistrata configuration. Trees of large stature (e.g., Tabebuia rosea, Albizia caribaea and Sterculia apelata) provided shade and produced timber. The most important fodder trees were those of medium stature (Albizia saman, Guazuma ulmifolia, and Cassia grandis) that produced fruits or pods, while other species were managed as shrubs producing green leaf fodder (e.g., Crescentia cujete and Gliricidia sepium, which was also ubiquitous as living fence posts). Trees were present on between 26 and 69% of the pastures on each farm, at densities varying from less than 3 to more than 50 trees ha−1. There were more trees in drier areas, of lower fertility, with extensive grazing, where milk as well as meat was produced. Most farmers planted timber trees, encouraged regeneration of fodder trees, and knew about fodder species preferences of cattle and the effects of trees on pasture and animal productivity. Their knowledge of tree phenology was less certain and varied even amongst farmers in similar locations. There is scope to develop silvopastoral systems with woody species familiar to farmers, but it is critical to determine how important different vegetation strata are for sustainability of cattle production. An experiment has been established to achieve this, with treatments based on an analysis of how trees are presently used on farms in the region. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

20.
The growing condition of afforestation trees and damage to lower-story trees caused by felling and hauling of upper-story trees in a multi-storied forest in Peninsular Malaysia was surveyed. Seventy months have passed since the planting ofAcacia mangium upperstory trees, which have grown 233 m3/ha in volume. The growth ofShorea leprosula thirty-five months after planting of lower-story trees have reached 5.54 m in height. However, as the ratio of height to basal diameter exceeds 100:1, trees are tapering to a considerable degree. A backhoe was installed in order to fell the upper-story trees. From the results of logging, the damage ratio estimation of the lower-story trees was simulated by using the Monte Carlo method. The damage ratio differed considerably depending on planting patterns, height of upper-story trees and felling skills. The results of this survey proved that the felling and hauling of upper-story trees would be technically feasible in the future, except when one row upper-story trees and one row lower-story trees method were employed.  相似文献   

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