共查询到20条相似文献,搜索用时 0 毫秒
1.
Seedlings sourced through tree nurseries are expected to form an important component of future tree cover on farms. As such, the genetic composition of nursery seedlings is expected to impact on the productivity and sustainability of agroforestry ecosystems. By surveying current practices of nursery managers in five areas from Kenya, Tanzania and Uganda, we quantified parameters associated with the collection, production and distribution of tree germplasm in East Africa. Considerable variation for seed-propagated nursery species was observed in the number of maternal parents (mother trees) sampled to establish nursery lots, the quantity of seedlings raised in nursery lots and the projected number of clients for nursery lots. Current seed collection practice was the most obvious limiting bottleneck in delivering high levels of genetic diversity to farmers. In the 143 cases analysed, seed to establish nursery lots was collected from a mean of only 6.4 maternal parents. In 22% of cases, ursery lots were established from a single maternal parent. On average, each maternal parent produced sufficient progeny to provide all the seedlings received by an individual nursery client. Consequently, the potential impact on farm and landscape genetic diversity of possible non-randomisation of progeny within nurseries is serious. In two instances, pair-wise analysis of transformed data suggested significant differences between geographic areas in the projected number of clients for nursery lots. We discuss improved nursery practices likely to promote genetic diversity, in particular increased maternal parent sampling and germplasm exchange. 相似文献
2.
Dry matter production and nutrient cycling in agroforestry systems of cardamom grown underAlnus and natural forest 总被引:4,自引:0,他引:4
A study on dry matter production and nutrient cycling in agroforestry systems of cardamom grown under N2-fixingAlnus and mixed tree species (non-N2-fixing) was carried out in the Sikkim Himalaya. The stand total biomass, and tiller number, basal area and biomass of cardamom crop was much higher under the influence ofAlnus. Annual net primary productivity ofAlnus trees was slightly higher than mixed tree species in spite of lower stand density ofAlnus. The agronomic yield of cardamom increased by 2.2 times under the canopy ofAlnus. Litter production and its disappearance rates were also higher in theAlnus-cardamom stand. Nitrogen and phosphorus concentrations of different components ofAlnus were higher than those of mixed tree species, whereas their back translocation from leaf before abscission was lower inAlnus. The cardamom based agroforestry system under the influence ofAlnus was more productive with faster rates of nutrient cycling. The poor nutrient conservation and low nutrient use efficiency ofAlnus, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faster cycling of nutrients. 相似文献
3.
Three production systems (robusta coffee, cattle pastures and swidden agriculture), all associated with trees, have provided a strategy for regional development in the Ecuadorian Amazon. Feedback from more than 250 on-farm demonstrations, project evaluations and visitors have all contributed to strengthening the ability of the Ecuadorean Ministry of Agriculture's Forestry Directorate to provide colonists and indigenous groups with management guidelines for low-input sustainable agroforestry production. The existing market for 20 fastgrowing native tree species presents an opportunity for the diversification of farm income (currently dependent on robusta coffee) and for the development of a forest industrial base.The collective area of land owned and operated by these small holders constitutes a national resource and a Collective Forest Estate that can be individually managed. Commercial timber production in these extensive secondary forests can help alleviate conversion of primary forest without taking agricultural land out of production. 相似文献
4.
Wild service tree [Sorbus torminalis (L.) Crantz] is a forest tree widespread in Europe, characterized by a scattered distribution. Its hermaphroditic flowers
are pollinated by insects, and outcrossing is the prominent mating system, also due to the presence of gametophytic self-incompatibility.
Genetic diversity and differentiation of 22 populations from northwestern Italy were investigated by means of variation scored
at 53 polymorphic RAPD (Random Amplified Polymorphic DNA) loci. Populations differed in genetic variation, with Shannon diversity
index ranging from 0.166 to 0.469. According to Analysis of Molecular Variance (AMOVA), most of the genetic variation was
found within populations (61.78%) with a significant proportion of variance attributable to genetic differences between regions
(23.60%) and between populations (14.62%). Evidence for isolation by distance was found in the set of populations sampled.
The effect of habitat fragmentation on genetic variation was also evaluated. The efficacy of RAPD markers in analysing genetic
variation, and the contribution of the results in terms of the preservation of biodiversity are discussed. 相似文献
5.
The potential contribution of agroforestry systems to the management and genetic resources conservation in iroko (Milicia excelsa), an important and valuable timber tree species in sub-Saharan Africa, is addressed in this paper. The structure and dynamics
of traditional agroforestry systems and the ecological structure of Milicia excelsa populations in farmlands were studied through a survey carried out in 100 farmlands covering the natural range of iroko in
Benin. Forty-five species belonging to 24 plant families were recorded in traditional agroforestry systems. Average tree density
varied from 1 to 7 stems ha−1 with diversity index ranging from 2.6 to 2.9. Milicia excelsa occurred sparsely in agroforestry systems in all regions, with density ranging from 1 to 4 stems ha−1; stand basal area varying from 33.10−4 to 129.10−4 m2 ha−1, and negligible seedling regeneration. However, male and female trees were apparently evenly distributed on farmlands in
all regions (F/M > 0). Iroko trees produced viable seeds with moderate germination rate and early growth (germination rate
22% and height 7.29 cm after 3 months). Suggestions are made regarding optimal densities for iroko conservation in farmlands,
according to farmers’ socioeconomic conditions in different regions, in order to improve traditional agroforestry systems
and their use as biological corridors in conservation of Milicia excelsa genetic resources. 相似文献
6.
The temporary association of annual crops in juvenile tree plantations (Taungya system) can reduce or offset the initial costs of reforestation and hence provide incentives for tree planting on private farms. A replicated systematic spacing design, derived from a Nelder-fan design, was used to study the effects of tree-crop distance on growth and development of the timber species salmwood (Cordia alliodora) or eucalyptus (Eucalyptus deglupta), associated with maize (Zea mays) or cassava (Manihot esculenta), during the first year after transplanting the trees on two sites on alluvial soils in the humid lowlands of Costa Rica. Association with maize did not affect mean tree growth. However, mean eucalyptus and salmwood heights of 7–8 m and 3–4 m, respectively, after one year in pure plantation or associated with maize, were only 4.7 m and 1.4 m, respectively, when associated with cassava. Wider tree – crop spacings were more important for initial salmwood growth than for eucalyptus. It was concluded that the shoot growth characteristics (continuous or episodical growth) of the timber species is a very important consideration when selecting associated agricultural crop species and tree-crop distances. 相似文献
7.
A study on dry matter production and nutrient cycling in agroforestry systems of mandarin grown in association with N2-fixing Albizia and mixed tree species (non-N2-fixing) was carried out in the Sikkim Himalaya. A site with Albizia was referred asAlbizia-mandarin stand and the other site with mixed tree species as mandarin stand. The stand total biomass, net primary productivity and mandarin fruit production was higher under the influence of Albizia. Agronomic yield of crops remained nearly the same in both the stands. Nitrogen and phosphorus concentrations of different components of Albizia were higher than those of mixed tree species, whereas their back translocation from leaf to branch before abscission was lower inAlbizia. The mandarin-based agroforestry is a highly nutrient-exhaustive system evaluated in terms of nutrient exit through the removal of agronomic yield. This system, under the influence of Albizia, was more productive with faster rates of nutrient cycling. Nutrient use efficiency increased under the influence of Albizia, in contrary to the hypothesis that efficiency should decrease with increasing rate of uptake. The poor nutrient conservation of Albizia, and malleability of nutrient cycling under its influence make it an excellent association which promotes higher availability and faster cycling of nutrients.Albizia should be utilised more extensively in the management of mandarin-based agroforestry systems. 相似文献
8.
Teak (Tectona grandis L.f.) is considered to be an extraordinarily durable building timber with a worldwide reputation. Its widespread use has
entailed the over-exploitation of natural forests and a large reduction in natural diversity. Fifteen microsatellite markers
were used to study the genetic variability and structure of 166 teak trees distributed over the whole natural area of teak.
Analysis showed that in the teak natural area there were four main centers of genetic variability. Two clusters were in India
and could be considered as main centers of genetic diversity in teak. The third cluster mainly consisting of populations in
Thailand and Laos was genetically very distinct from the Indian populations but presented only half as much allelic variability.
A fourth cluster from Central Laos showed even less genetic variability. The use of SSR markers for conservation of teak forest
diversity is discussed. 相似文献
9.
By using random amplified polymorphic DNA (RAPD) technique, this paper studied the genetic diversity and genetic differentiation
of Lithocarpus harlandii populations in three forest communities (coniferous forest, coniferous and broad-leaved mixed forest, and evergreen broad-leaved
forest) with different succession stages in Tiantai Mountain in Zhejiang Province. The results showed that a total of 173
repetitive loci were produced in 60 individuals of L. harlandii by 12 random primers, among which, 152 loci were polymorphic, and the total percentage of polymorphic loci was 87.86%. The
average percentage of polymorphic loci of the populations was 65.32%, and their total genetic diversity estimated by Shannon
information index was 0.4529, with an average of 0.3458, while that judged from Nei’s index was 0.3004, with an average of
0.2320. The percentage of polymorphic loci, Shannon information index, and Nei’s index of the populations were in the sequence
of coniferous forest community > coniferous and broad-leaved mixed forest community > evergreen broad-leaved forest community.
Analysis of molecular variance (AMOVA) showed that 72.85% of genetic variance was found within the populations, and 27.15%
of genetic variance resided among the populations. The coefficient of gene diferentiation was 0.2277, and the gene flow was
1.6949. The genetic structure of L. harlandii was influenced not only by the biological characteristics of this species, but also by the microenvironment of different
communities. The mean of genetic identity among three populations of L. harlandii was 0.8662, and the mean of their genetic distance was 0.1442. The genetic similarity between coniferous and broad-leaved
mixed forest community and evergreen broad-leaved forest community was the highest, while that between evergreen broad-leaved
forest community and coniferous forest community was the lowest. The unweighted pair group method with arithmeticmean (UPGMA)
cluster analysis based on Nei’s genetic distance showed that conierous and broad-leaved mixed forest community first gathered
with evergreen broad-leaved forest community, and then with coniferous forest community.
__________
Translated from Chinese Journal of Ecology, 2007, 26(4): 509–514 [译自: 生态学杂志] 相似文献
10.
11.
The conversion of anthropogenic into more natural, self-regenerating forests is one of the major objectives of forestry throughout
Europe. In this study, we present investigations on permanent plots with different silvicultural treatment in NE German pine
stands. Management of old-growth pine stands on acidic and nutrient-poor sandy sites differs in fencing, thinning, and planting
of certain tree species. The investigations were carried out on the community, population, and individual level of the pine
forest ecosystems. Thus, vegetation changes, size and height of tree populations, and height increment of tree individuals
were observed over a time span of 6 years. Special attention was paid to short-lived tree species such as, e.g., Frangula alnus and Sorbus aucuparia, as well as to Fagus sylvatica as one of the most typical forest tree species of Central Europe. Vegetation changes are interpreted as a consequence of
natural regeneration of formerly degraded forest sites, involving an increase in nutrient availability. High browsing pressure
can be considered as a key factor for the inhibition of tree seedlings and growth of saplings. Some Sorbus aucuparia individuals, however, succeeded in growing out of the browsing height also in unfenced stands. Few found specimens of Fagus sylvatica proved that this species is able to establish spontaneously on these relatively dry, acidic sites under continental climate
influence. Such natural regeneration processes, also including spontaneous rejuvenation of trees, can be integrated into silviculture
as passive forest conversion management. An active management like thinning of stands, planting of trees, and fencing can
accelerate forest conversion with regard to height growth and species number of trees. 相似文献
12.
In order to understand the relationship between population succession and its genetic behavior, random amplified polymorphic
DNA (RAPD) technique was used to analyze the genetic diversity of Quercu glandulifera var. brevipetiolata populations in three forest communities with different succession stages (coniferous forest, coniferous and broad-leaved
mixed forest, evergreen broad-leaved forest). The results showed that 145 repetitive loci were produced in 60 individuals
of Q. glandulifera using 11 primers, among which 120 loci were polymorphic, and the total percentage of polymorphic loci was 82.76% with an
average of 64.14%. Estimated by the Shannon information index, the total genetic diversity of the three populations was 0.4747,
with an average of 0.3642, while it was 0.3234, with an average of 0.2484, judged from the Nei index. Judged from percentage
of polymorphic loci, Shannon inform at ion index and Nei index, the genetic diversity followed a decreasing order: coniferous
forest > broad-leaved mixed forest > evergreen broad-leaved forest. Analysis of molecular variance (AMOVA) showed that 69.73%
of the genetic variance existed within populations and 30.27% of the genetic variance existed among populations. The coefficient
of gene differentiation (GST) was 0.2319 and the gene flow (N
m) was 1.6539. The mean of genetic identity among populations of Q. glandulifera was 0.8501 and the mean of genetic distance was 0.1626. The genetic identity between the Q. glandulifera population in the coniferous forest and that in the coniferous and broadleaved mixed forest was the highest. UPGMA cluster
analysis based on Nei’s genetic distance showed that the population in the coniferous forest gathered with that in the coniferous
and broad-leaved mixed forest firstly, then with that in the evergreen broad-leaved forest. The genetic structure of Q. glandulifera was not only characteristic of the biological characteristics of this species, but was also influenced by the microenvironment
in different communities.
__________
Translated from Journal of Northwest Forestry University, 2008, 23(1): 18–22 [译自: 西北林学院学报] 相似文献
13.
Arazá (Eugenia stipitata), a fruit shrub originating from Western Amazonia, was evaluated growing in association with timber shade trees (Acacia mangium or Cordia alliodora) or with plantain (Musa sp.) as a potential commercial species for the tropical moist lowlands of Talamanca, Costa Rica. Height and crown width of
the four-year-old shrubs varied between 2.7–2.8 m and 2.9–3.1 m, respectively. Flowering was positively correlated with initial
fruit formation 1 month later and initial fruit formation with fully developed fruits a subsequent month after that. Three
to four-year-old plants produced 20.0, 20.0, and 24.5 t ha−1 yr−1 (fresh fruits) in associations with A. mangium, C. alliodora and plantain, respectively, with higher production in rainy months. Fruit production in later years under C. alliodora (six to eight-year-old shrubs) was 26.5 t ha−1 yr−1. Where markets exist for E. stipitata fruit, the association can be recommended for tropical humid lowlands of Central America. 相似文献
14.
Evaluation of native tree species for the rehabilitation of deforested areas in a Mexican cloud forest 总被引:3,自引:0,他引:3
Four native tree species (Liquidambar styraciflua, Juglans pyriformis, Podocarpus matudae, and Carpinus caroliniana) were evaluated for their suitability in rehabilitating degraded areas of Mexican cloud forest. Plant survival and growth in height and diameter were determined in three mixed-experimental plantations with different land use histories; their performance was compared with two on-farm plantations started by landowners for forest restoration. Nearby forest fragments were controls for soil compaction. An experimental plantation with remnant trees had the highest plant survival (82%), height, basal diameter and relative growth rate. The plantation with the steepest slope had high plant survival (63%) and growth. The plantation characterized by dominance of grasses and compacted soils had the lowest survival (22%) and growth. On-farm plantations had good establishment of planted trees (5–10 species planted), and facilitated the recruitment of 9–11 woody species. Carpinus and Liquidambar appear to be suitable species for reforestation in all these areas. Podocarpus grew relatively slowly, although it performed well in two experimental sites. Juglans had high survival (76%) under the stressful conditions of the most adverse site, and therefore may be useful for rehabilitation of degraded sites. Differences among species and sites strongly suggest that species success depends on plantation site quality. 相似文献
15.
The potential allelopathic effect ofCupressus lusitanica, Eucalyptus globulus, E. camaldulensis andE. saligna on seed germination, radicle and seedling growth was investigated with four crops:Cicer arietinum (chickpea),Zea mays (maize),Pisum sativum (pea) andEragrostis tef (teff). Aqueous leaf extracts of all the tree species significantly reduced both germination and radicle growth of the majority of the crops mostly starting from concentrations of 1% or 2.5%. The shoot and root dry weight increase of the crops was significantly reduced after 10 weeks treatment with leaf extracts. Among the four crops, chickpea and teff were most susceptible with respect to germination, and teff with respect to growth. From the overall data the leaf extracts of the four tree species can be arranged according to increasing allelopathic potential:C. lusitanica, E. globulus, E. saligna andE. camaldulensis. It is suggested that the planting ofE. camaldulensis andE. saligna in integrated land use systems should be minimized, whereas the use ofC. lusitanica andE. globulus seems less environmentally damaging in this respect. 相似文献
16.
Analyses of the genetic diversity of matsutake isolates collected from different ecological environments in Asia 总被引:1,自引:0,他引:1
Dapeng Bao Ayumi Koike Fangjie Yao Katsuji Yamanaka Tadanori Aimi Yutaka Kitamoto 《Journal of Wood Science》2007,53(4):344-350
Matsutake mushrooms are able to grow in two kinds of ecological environments: coniferous forests and broadleaf forests. Japanese
matsutake is a form of the matsutake mushroom that mainly appears in coniferous forests in the mid-latitude regions of Asia.
In contrast, matsutake from Yunnan and Sichuan Provinces of China grows in broadleaf forests in low-latitude regions. The
taxonomic relationship and the genetic distance between these two types of matsutake remain unclear. Here, we compared the
random amplification of polymorphic DNA (RAPD) data and the sequences of the internal transcribed spacer (ITS) region and
of variable domains V4, V6, and V9 of mitochondrial small subunit ribosomal DNA (mt SSU rDNA) to determine the genetic differences
of Tricholoma matsutake strains collected from different ecological and geographic environments in Asia. We found few differences in the sequences
of the variable domains, implying that all matsutake strains are the same biological species regardless of their host specificity
and geographical differences. This conclusion is also supported by the sequences of the ITS region. On the other hand, RAPD
analysis revealed that the matsutake mushrooms collected from different ecological environments have genetic differences and
represent distinct varieties. 相似文献
17.
The impact of selective logging on genetic diversity of two tropical tree species with contrasting breeding systems was examined using direct comparison and simulation methods. Shorea leprosula is a diploid and predominantly outcrossed species, whereas Shorea ovalis ssp. sericea is an autotetraploid species with apomictic mode of reproduction. Direct comparison of adjacent natural and logged-over stands showed reduction of genetic diversity of S. leprosula, but not of S. ovalis ssp. sericea. These results clearly demonstrated that a single logging event would cause the genetic erosion of S. leprosula. However, the apomictic mechanisms and the effects of tetrasomic inheritance of S. ovalis ssp. sericea might be a way of maintaining the level of genetic diversity. These results clearly implied that outcrossing species might be more susceptible to the negative impact of logging on genetic diversity than apomictic species. Simulation studies were conducted using three approaches: (1) simulated-removal of individuals based on diameter size classes; (2) simulated-removal of individuals at random; and (3) simulated-removal of individuals in clump. The simulation study based on the first approach showed that the loss of genetic diversity was higher for the Malayan Uniform System (MUS) compared with the Selective Management System (SMS). This might suggest that SMS is more orientated towards the conservation of genetic diversity. In addition, the simulation study showed that to conserve 100% of the total number of alleles, the tolerable cutting limits of S. leprosula in the 50-ha plot of Pasoh FR should be >85 cm diameter at breast height (dbh). Comparison of simulation studies based on the second and third approaches showed that the loss of genetic diversity was more rigorous if logging activities were anticipated through extraction of trees in clump rather than to extract trees at random. Implications of the studies for conserving and managing the tropical forests are discussed. 相似文献
18.
Small-scale genetic diversity in oneseed hawthorn (<Emphasis Type="Italic">Crataegus monogyna</Emphasis> Jacq.) 总被引:1,自引:1,他引:0
We have examined the pattern of random amplified polymorphic DNA (RAPD) variation among six populations of Crataegus monogyna from northern Italy, extending over an area of about 20,000 km2. The aim was to evaluate local differentiation in relation to geographical distance. Of the 73 loci analysed, 65 were polymorphic,
and there were no bands at complete fixation at the population level. The mean genetic diversity was 0.291, with the values
for individual populations ranging between 0.252 and 0.333. According to the analysis of molecular variance most of the genetic
variation was found within populations (about 80%), with a significant proportion being attributable to genetic differences
between populations. No evidence for isolation by distance was found in the set of populations sampled. The efficacy of RAPD
markers in analysing genetic variation, and the contribution of the results in terms of the preservation of biodiversity and
defining the most appropriate strategies for collecting forest reproductive material, are discussed. 相似文献
19.
Adoption potential of selected organic resources for improving soil fertility in the central highlands of Kenya 总被引:1,自引:0,他引:1
Jayne Mugwe Monicah Mucheru-Muna Daniel Mugendi James Kung’u Andre Bationo Franklin Mairura 《Agroforestry Systems》2009,76(2):467-485
Soil fertility decline is the major cause of declining crop yields in the central highlands of Kenya and elsewhere within
the African continent. This paper reports a study conducted to assess adoption potential of two leguminous trees, two herbaceous
legumes, cattle manure, and Tithonia diversifolia either solely applied or combined with inorganic fertilizer, for replenishing soil fertility in the central highlands of
Kenya. The study examined biophysical performance, profitability, feasibility and acceptability, and farmers experiences in
managing and testing the inputs. The study was based on a series of studies incorporating both sociological and experimental
approaches for two and a half years. Results of on farm trials showed that manure + fertilizer and tithonia + fertilizer treatments
increased yields by more than 100% above the control. These treatments were the most profitable having highest net benefits
and benefit cost ratios. They were also the most commonly preferred by farmers who used them on larger plots compared to the
other inputs. In conclusion, cattle manure and tithonia were found to be the organic materials with the highest adoption potential
for soil fertility improvement in this area. Calliandra calothyrsus and Leucaena trichandra, on the other hand, have potential for use as animal fodder. The herbaceous legumes had the least adoption potential due
to poor performance recorded on the farms that possibly led to low preference by the farmers. However, issues of sustainable
seed production could have played a role. This study recommends some policy issues for enhancing adoption and research issues
focusing on exploring strategies for increasing biomass production and use efficiency on farms.
Andre Bationo was formerly working for Tropical Soil Biology and Fertility Institute of CIAT (TSBF-CIAT) as the African network
Coordinator. 相似文献
20.
A population of Norway spruce (Picea abies (L.) Karst.) from southern Poland, named Kolonowskie 0293, exhibited a very high breeding value among 1100 European populations tested in the IUFRO 1964/1968 provenance experiment. However, the original mother stand of that population no longer exists. Owing to international cooperative efforts, a reconstituted clonal seed orchard of that population was successfully established to protect the gene pool of the Kolonowskie 0293 population. 相似文献