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1.
Artemisia ordosica is an excellent sand-fixing shrub for sand stabilization in northwestern China. Sand dune stabilization, a critically important process, leads changes in abiotic factors, such as soil structure and nutrient contents. However, the effects of factors on an A. ordosica community following sand stabilization remain unclear. In this study, we used canonical correspondence analysis (CCA) to examine the relationships between A. ordosica communities and environmental factors at three habitats: semi-fixed dune (SF), fixed dune with low-coverage biological soil crust (F), and fixed dune with high-coverage biological soil crust (FC) in Mu Us desert. The mean height and coverage of plants increased with sand stabilization, while species diversity and richness increased initially and then reduced significantly. Correlation analysis and CCA revealed that slope, soil organic carbon, and nutrient contents, proportion of fine soil particles, soil moisture, and thickness of biological soil crust were all highly correlated with vegetation characteristics. These environmental factors could explain 40.42 % of the vegetation–environment relationships at the three habitats. The distribution of plant species was positively related to soil moisture in the SF dune. Soil moisture, soil nutrient, and fine-particle contents mainly affected plants distribution in the F dune. In the FC dune, distribution of plant species was positively and negatively correlated with the thickness of biological soil crust and soil moisture at a depth 0–20 cm, respectively. The dominance value of typical steppe species increased significantly following sand-dune stabilization and relations between species and samples in CCA ordination bi-plots showed that perennial grasses could invade the A. ordosica community on FC, indicating A. ordosica communities had a tendency to change into typical steppe vegetation with the further fixation. We conclude that the significant differentiation not only occurred in community characteristics, but also in the relationships between vegetation and environmental factors among the three stages of dune fixation. So, restoration of degraded dune ecosystems should be based on habitat conditions and ecological needs. 相似文献
2.
Microclimate and nutrient dynamics in a silvopastoral system of semiarid northeastern Brazil 总被引：2，自引：0，他引：2
There is little available information on nutrient cycling and the controls of ecosystem processes in land use systems of dry neotropical regions. In this study, we conducted field and glasshouse experiments to investigate the influence of Ziziphus joazeiro and Prosopis juliflora trees on microclimate and nutrient dynamics in pastures ofCenchrus ciliaris in semiarid northeastern Brazil. We found that soil moisture was lower under the crowns of P. juliflora trees during early season in comparison to patches ofC. ciliaris (grass patches), but the presence of Z. joazeiro had no effect on soil moisture. Soil and air temperatures were lower under Z. joazeiro in comparison to grass patches but P. juliflora had little effect on temperature. Losses of P from all litter types were lower under the crowns of Z. joazeiro trees, but losses of biomass and N from litter were not consistently affected by the presence of trees. Soil net N mineralized was greater under both tree species, in comparison to grass patches. However, net soil N mineralized per gram of total soil N was greater under the crowns of the potentially N2 fixing P. juliflora, in comparison to grass patches, while there were no significant differences betweenZ. joazeiro crowns and grass patches. In the glasshouse study, plant biomass and nutrient uptake was greater in soil collected under the crowns of both tree species, in comparison to soil from grass patches. Our results indicate that the preservation of native trees or introduction of exotic tree species in C. ciliaris pastures in semiarid northeastern Brazil significantly affects microclimate and the dynamics of litter and soil nutrients, and may contribute to increases in the cycling rate of nutrients in these systems. Index terms: buffel grass, caatinga, nitrogen mineralization, Prosopis juliflora, Ziziphus joazeiro.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
3.
P. Ahmed 《Agroforestry Systems》1991,14(1):23-37
A system of land use of alkaline wastelands of the Indo-Gangetic plain has been proposed consisting of planting Prosopis juliflora, a multi-purpose tree species, with the objectives of economic return as well as soil amelioration. Tree farming onalkaline wastelands provides not only fuel, fodder, timber and income to the rural population but also shows good effects in improving the soil characteristics. The detailed costs of such an agroforestry system on alkali soils have been worked out and the mean annual production of Prosopis juliflora on soils of different pH have been analysed. In spite of the high cost of establishing a plantation, an economic analysis of the system yields a 9.5% internal rate of return which is reasonably high for degraded lands of strongly alkali soils and also viable within the economic structure of the region. 相似文献
4.
以青海共和盆地沙丘上12年生的中间锦鸡儿人工林为研究对象,并以流动沙丘为对照,探讨在沙丘上建立中间锦鸡儿人工林后,沙丘部位对土壤养分含量以及植物群落的影响。在中间锦鸡儿人工林内沙丘的迎风坡中部、坡顶、背风坡中部和流动沙丘采集土壤样品,深度为0 5,5 10,10 20和20 50 cm。结果表明:与流动沙丘相比,沙丘3个部位中间锦鸡儿人工林0 20 cm的有机质、0 50 cm的全氮和全磷含量得到显著提高。迎风坡中间锦鸡儿人工林0 5 cm深度的土壤有机质和全氮、0 20 cm深度的全磷含量显著高于坡顶和背风坡。在沙丘上建立中间锦鸡儿人工林后,草本植物种类、数量和植被盖度增加,迎风坡草本植物盖度明显高于坡顶和背风坡。 相似文献
5.
To evaluate laboratory germination media, seed germi- nation rates and methodology for both Jatropha curcas and Pongamia pinnata were counted in different germination medium, such as river sand, quartz sand and vermiculite. The seeds of both species were sown at 2-cm depth of river sand, quartz sand and vermiculite. We evaluated methodologies of seeds of J. curcas and P. pinnata by ISTA （Interna- tional Seed Testing Association）. The results showed that river sand is the best medium for tree seeds planted at 2-cm depth of River sand. Vermiculite was second best. On paper media, there were many abnor- mal seedlings and this media were unsuitable for germination of the larger seeds. 相似文献
6.
Conserving forest biodiversity has become a significant global concern. A change in forest composition, compared to pre-industrial values, is an important biodiversity issue. In this regard, there is a significant decrease in Picea glauca densities at the landscape level in boreal mixedwoods of northeastern Canada, compared to pre-industrial abundance. Enrichment planting is considered a promising silvicultural approach for improving P. glauca stocking and re-establishing its natural co-dominance with Abies balsamea. However, optimal enrichment scenarios must be identified, notably regarding site preparation treatments that can enhance planted seedling survival and growth while protecting Abies advance regeneration. We established a field trial in Quebec (Canada), laid out as a complete block split-plot design. Picea glauca and P. mariana seedlings (main plot) were planted according to 3 “microsite” treatments (subplot): (1) planting in the humus layer; (2) planting in the mineral soil, with minimal humus disturbance; and (3) planting in a microsite mechanically-prepared using modified brushsaws. After 3 growing seasons, P. mariana seedlings were taller than P. glauca seedlings, but had smaller ground-level diameters. Seedlings planted in the mineral soil had overcome the initial height difference they had with seedlings planted in the humus and mechanically-prepared microsites, with no interaction with species. Ground-level diameter was similar for seedlings planted in the humus and mechanically-prepared microsites, but smaller for seedlings planted in the mineral soil. Water potentials, available light, and foliar nutrient concentrations were not influenced by treatments or species; survival was >90 %. Our results indicate that P. glauca can be established through enrichment planting in boreal mixedwoods. Localized site preparation is not required to limit initial plantation stress in this ecosystem. 相似文献
7.
A. Khamzina J. P. A. Lamers M. Worbes E. Botman P. L. G. Vlek 《Agroforestry Systems》2006,66(2):129-141
Land degradation is a serious hindrance to agricultural development in Uzbekistan, a country striving to rebuild its agricultural
sector for self-sustained production. The potential of multipurpose trees for upgrading degraded land is enormous. However,
knowledge is lacking about the establishment and growth characteristics of different species, the energy content of firewood
and the nutritive value of fodder. This study presents such data for 10 selected local multipurpose species grown on gleyic
solonchak soil. Elaeagnus angustifolia L. and Tamarix androssowii showed superior biomass growth, respectively producing up to 11.0 and 10.4 t ha−1 of utilizable aboveground dry matter (DM). E. angustifolia showed high potential for rapid establishment evidenced by root elongation of over 100 m tree−1 at the age of 3 years. T. androssowii, Prunus armeniaca L. and Populus nigra var. pyramidalis Spach exhibited the greatest fuelwood characteristics, showing calorific values in the range of 14.4 – 16.2 MJ DM kg−1. E. angustifolia and Morus alba L. demonstrated superior fodder potential given by the crude protein content of 216 and 117 g DM kg−1. Recommendations on species selection are proposed based on various species characteristics. In assessing the potential of
trees for afforestation of degraded land a reliable economic analysis of these aspects must be taken into account. When considering
all characteristics concurrently, a mixture of species instead of monocrop cultivation seems to provide the best solution
for improving degraded land. 相似文献
8.
9.
Early establishment of seedlings in reclaimed oil sand areas is often limited by low nutrient and water availability due to factors such as strong understory vegetation competition. Management practices such as nursery fertilization and field weed control could help early establishment of planted seedlings and reclamation success. We investigated the effect of nursery nutrient loading and field weed control on the growth, nitrogen (N) retranslocation within seedling components, and plant N uptake from the soil for white spruce (Picea glauca [Moench] Voss) seedlings planted on a highly competitive reclaimed oil sands site for two years. Exponential fertilization during nursery production increased the root biomass but not the nutrient reserve in the seedling. In the field experiment, on average across the treatments, 78 and 49% of the total N demand of new tissue growth in the first and second year were met by N retranslocation, respectively. Though exponential fertilization did not affect N retranslocation, it increased the percent height and root collar diameter growth. Weed control increased not only the growth of seedlings by increasing soil N availability, but also N retranslocation within the seedlings in the second year after outplanting. We conclude that vegetation management by weed control is feasible in improving the early growth of white spruce seedlings planted on reclaimed soils and facilitate tree establishment in the oil sands region. Optimization of the nursery exponential N fertilization regime for white spruce may further help with early revegetation of reclaimed oil sands sites. 相似文献
10.
The influence of woody and herbaceous plant competition, either alone or in combination, on microclimate and growth of planted eastern white pine (Pinus strobus L.) seedlings was examined over four consecutive growing seasons in a central Ontario clearcut. Treatments that manipulated the comparative abundance of these two plant functional groups significantly affected light availability, soil moisture, and air and soil temperature regimes. These microclimate alterations, coupled with the relative competitiveness of herbaceous and woody vegetation, corresponded to temporal changes in vegetation cover and dominance. The more rapid colonization and growth of the herbaceous plant community, dominated by bracken fern (Pteridium aquilinum) and ericaceous shrubs (Kalmia sp., Vaccinium sp.), resulted in this form of vegetation being a comparatively important early competitor for soil moisture. As the woody plant community, dominated by naturally regenerated trembling aspen (Populus tremuloides Michx.), grew in height and leaf area, it became a comparatively strong competitor for both light and soil moisture. For all vegetation treatments combined, white pine seedling growth responses were strongly correlated with total cover of competing vegetation and its relative influence on above- and belowground microclimatic variables. Higher total cover of competing vegetation was generally associated with lower light and soil moisture availability and cooler soil temperatures. Multiple regression analyses indicated that pine seedling relative height growth increased with soil moisture content and growing season soil heat sum, while seedling relative diameter and relative volume growth increased with light availability. 相似文献
11.
In the Sahel of Africa, where 90 % of the population depends on natural resources for their livelihood, a large part of the soils are structurally unstable,prone to crusting and hard setting, and have low water holding capacity, which hamper vegetation establishment.The effect of soil restoration techniques on survival and growth of seedlings of Acacia nilotica, Acacia tortilis and Jatropha curcas was tested in completely barren, degraded land in a Sahelian ecosystem in Burkina Faso. A total of522 seedlings(174 plants of each plant species) were planted in a randomized complete block design with three replicates combining three soil preparation techniques:half-moon, za¨? and standard plantation. Survival and growth rates evaluated over 20 months were significantly higher using the half-moon technique compared with the other two techniques. Survival rates of plant species planted using half-moon technique were 62.5, 28.57 and10.71 % for A. nilotica, A. tortilis and J. curcas respectively, but in za¨? and standard planting, seedling survival was zero. The low survival rate of J. curcas using the half-moon technique may indicate that J. curcas is unsuitable for barren and degraded land, whereas A. nilotica and A. tortilis appear to be promising tree species for rehabilitation of degraded land. 相似文献
12.
Paulo Henrique Muller da Silva Fabio PoggianiEdson Seizo Mori 《Forest Ecology and Management》2011,261(11):2075-2080
Some Eucalyptus species are widely used as a plantation crop in tropical and subtropical regions. One reason for this is the diversity of end uses, but the main reason is the high level of wood production obtained from commercial plantings. With the advancement of biotechnology it will be possible to expand the geographical area in which eucalypts can be used as commercial plantation crops, especially in regions with current climatic restrictions. Despite the popularity of eucalypts and their increasing range, questions still exist, in both traditional planting areas and in the new regions: Can eucalypts invade areas of native vegetation, causing damage to natural ecosystems biodiversity?The objective of this study it was to assess whether eucalypts can invade native vegetation fragments in proximity to commercial stands, and what factors promote this invasive growth. Thus, three experiments were established in forest fragments located in three different regions of Brazil. Each experiment was composed of 40 plots (1 m2 each one), 20 plots located at the border between the forest fragment and eucalypts plantation, and 20 plots in the interior of the forest fragments. In each experimental site, the plots were paired by two soil exposure conditions, 10 plots in natural conditions and 10 plots with soil exposure (no plant and no litter). During the rainy season, 2 g of eucalypts seeds were sown in each plot, including Eucalyptus grandis or a hybrid of E. urophylla × E. grandis, the most common commercial eucalypt species planted in the three region. At 15, 30, 45, 90, 180, 270 and 360 days after sowing, we assessed the number of seedlings of eucalypts and the number of seedlings of native species resulting from natural regeneration. Fifteen days after sowing, the greatest number of eucalypts seedlings (37 m−2) was observed in the plots with lower luminosity and exposed soil. Also, for native species, it was observed that exposed soil improved natural germination reaching the highest number of 163 seedlings per square meter. Site and soil exposure were the factors that have the greatest influence on seed germination of both eucalypt and native species. However, 270 days after sowing, eucalypt seedlings were not observed at any of the three experimental sites. The result shows the inability of eucalypts to adapt to condition outside of their natural range. However, native species demonstrated their strong capacity for natural regeneration in forest fragments under the same conditions where eucalypts were seeded. 相似文献
13.
Floristic composition and soil characteristics of tropical freshwater forested wetlands of Veracruz on the coastal plain of the Gulf of Mexico 总被引：1，自引：0，他引：1
We studied the influence of geomorphological setting and soil properties on the vegetation structure, composition and diversity of five forested coastal wetlands in Veracruz on the Gulf of Mexico. These swamps are located on floodplains and in dune depressions. We recorded 109 woody and herbaceous species. The most frequent species were the trees Pachira aquatica, Annona glabra, Diospyros digyna and Ficus insipida subsp. insipida, the lianas Dalbergia brownei and Hippocratea celastroides and the hemi-epiphyte Syngonium podophyllum. The Shannon-H diversity index varied from 2.659 to 3.373, density from 1750 to 2289 stems ha−1 and basal area from 32.7 to 76.42 m2 ha−1. The classification analysis defined two groups: one corresponded to forested wetlands along the floodplain (Apompal, Cienaga, Chica) and the other included Mancha and Salado, in dune depressions. PCA ordination of soil parameters during the rainy season explained 67.0% and during the dry season 69.1% of the total variance. In the rainy season Mancha and Salado samples remain close together because they have lower Mg, Na, K, % Total C and % Total N values. Apompal and Chica samples remain close to each other because of their high levels of % Total C, % Total N, Mg, Na and high soil water content. Cienaga samples are separated from the others because of high values of P, Ca and Eh as well as high water levels. In general, soil parameter ordination during the dry season showed that redox potential, P, water level and water content decreased in the forested wetlands and Na values increased in Chica. The soil textures identified were clay, sandy clay loam, sandy loam and clay loam; clay texture dominated alluvial processes in the floodplain (e.g., Cienaga). The forested wetlands in the floodplains had similar vegetation and the same happened in the dune depressions but soil characteristics were more variable in both cases. Plant diversity in floodplains tends to be relatively high, and the presence of adjacent tropical forests probably increases its richness, except in cases in which there are stressing factors, such as salinity. The forested wetlands studied showed dominant floristic elements, which extend north into Florida such as A. glabra and Ficus aurea. Other dominant elements such as P. aquatica are also found in Central and South America. The forested wetlands studied are subjected to continuous deforestation to transform the land into farming or ranching activities, this being a common practice throughout the distribution range of these forests. 相似文献
14.
Herbivory may be an important factor affecting seedling survival of exotic species invading new habitats. We evaluated the effect of vertebrate herbivory on the seedling survival of two widely planted and invasive tree species (Pinus radiata and Eucalyptus globulus), in a Mediterranean-type ecosystem of central Chile. An important role of herbivory on seedling survival of these two species in their introduced ranges has previously been documented. However, this has mainly been evaluated in forest plantations where habitat and vegetation conditions differ from wild habitats in which invasion occurs. We planted seedlings with and without protection against vertebrate herbivores in different aspects (a mesic south-facing slope and a xeric north-facing slope) and vegetation cover (open sites and sites with patchy tree cover). We found that regardless of aspect or vegetation cover, herbivory, in this case mainly caused by exotic vertebrates, significantly and negatively affected seedling survival of both species. However, while the effect of herbivory on P. radiata was significant in every vegetation and habitat condition, for E. globulus, the effect of herbivory was significant only for open sites in the mesic habitat. These results suggest that, as observed in forestry plantations, vertebrate herbivory may constrain seedling establishment of these two exotic trees and potentially impede the invasion. However, the importance of herbivory in controlling exotic species may vary depending on the vegetation and habitat conditions in some species such as E. globulus. 相似文献
15.
Severe dieback symptoms were observed in a 490‐ha moist ash (Fraxinus angustifolia) lowland forest stand, comprising trees over 100 years old and in 100 ha of newly planted F. angustifolia near Sinop, in Turkey. Five of the 10 soil samples collected around stem bases of the diseased trees were baited using ash leaves and yielded a Phytophthora sp. This heterothallic species produced non‐caducous, non‐papillate sporangia in non‐sterile soil extract, and fluffy, even growth on corn meal and potato dextrose agars, and suppressed, even growth on grated carrot agar. Isolates were identified as Phytophthora taxon salixsoil based on internal transcribed spacer DNA sequences. This species has been recently redesignated as P. lacustris. Three isolates were found to be pathogenic when inoculated on the stem bases of three‐year‐old F. angustifolia saplings. 相似文献
16.
Chuck Rhoades David Loftis Jeffrey Lewis Stacy Clark U.S.D.A. Forest Service 《Forest Ecology and Management》2009,258(7):1211-1218
After more than 50 years of research and selective breeding, blight-resistant American chestnut (Castanea dentata) trees will soon be available for planting into the species’ pre-blight range. Increased understanding of the regeneration requirements of pure American chestnut (C. dentata [Marsh.] Borkh.) will increase the success of future efforts to establish blight-resistant chestnut. We quantified survival and initial growth of bare-root American chestnut seedlings at five locations in eastern Kentucky, USA. We used a split-plot design to compare seedlings planted within adjacent mesic and xeric sites treated with either a two-age shelterwood overstory treatment or a midstory removal treatment. The silvicultural treatments and topographic settings allowed us to evaluate chestnut seedling performance under four light and site productivity combinations. Seedling survival was 57% and seedling height averaged 94 cm following two growing seasons. Seedling survival was negatively related to sand and coarse fragment content, but was unrelated to silviculture treatment or topographic position. Chestnut seedlings grew best in shelterwood overstory treatments areas on mesic sites. Seedlings growing in shelterwood overstory treatment areas added 3- and 3.5-times more height and stem increment compared to seedlings planted after midstory removal. Seedling leaf mass and foliar nitrogen (N) content were also greatest in shelterwood plantings on mesic sites. The high-light environment created by shelterwood overstory removal resulted in better initial seedling growth, but the moderate-light of the midstory removal treatment may ultimately provide chestnut seedlings a greater advantage over competing vegetation. 相似文献
17.
Integration and role of planted trees in a bush-fallow cultivation system in central Zambia 总被引：1，自引：0，他引：1
E. N. Chidumayo 《Agroforestry Systems》1988,7(1):63-76
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. 相似文献
18.
[目的]明确高寒沙区不同植被类型对土壤性质改良效果的差异,探讨各植被区沙地土壤恢复过程的异质性和人工林木的可开发利用潜力。[方法]以沙珠玉治沙试验林场内不同生长年限的人工植被为研究对象,分析高寒沙区6种植被类型区(乌柳、青杨、赖草、柠条、沙棘、柽柳)以及3个对照区(农田、流动沙丘、丘间沙地)土壤的机械组成、p H值、有机质及全N、全P、全K等理化性质指标。[结果](1)植被恢复生长51年后,从黏粒和粉砂粒增加的比例角度分析,土壤质地改良顺序为沙棘(206.3%)柠条(108.5%)青杨(70.5%)乌柳(56.8%)赖草(54.1%)柽柳(42.3%);从全N、全P和全K增加的比例角度分析,土壤养分改良顺序为青杨(198.2%)柠条(166.7%)沙棘(155.3%)乌柳(82.6%)赖草(75.4%)柽柳(53.9%),土壤全P含量偏低,平均0.42 g·kg-1;(2)植被恢复生长51年后,柠条、沙棘、青杨、赖草、乌柳和柽柳林下0 30 cm土壤有机质含量依次为20.19、18.25、30.81、23.57、22.13和10.62 g·kg-1,比流动沙丘或丘间沙地相应的提高了766.7%、702.4%、689.8%、517.4%、491.5%和343.9%。[结论]随着植被恢复年限的增加,土壤质地和养分状况得到显著改善,但土壤p H值的变异系数较小;各样地土层间有机质含量差距不断扩大,表聚性越来越明显,并且随深度增加各土层恢复效果存在滞后性。柠条和沙棘适宜在共和盆地推广种植,建议实施适当地抚育管理措施,以促进高寒沙区林场实现可持续经营发展。 相似文献
19.
Unsuccessful colonization by indigenous tree species into established plantations has retarded the succession of artificial plantations to more natural, secondary forests in South China. To understand how to improve colonization by seedlings of indigenous species, we determined how performance of indigenous seedlings is affected by seedling species (the shade-intolerant Castanopsis chinensis, the moderately shade-intolerant Michelia chapensis, and the shade-tolerant Psychotria rubra), the site into which the seedlings were transplanted (a mixed-legume plantation, a eucalyptus plantation, a mixed-native plantation, a mixed-conifer plantation, and a shrubland), and site preparation (removal or retention of understory vegetation and litter). Seedling survival and growth were generally increased by removal of understory vegetation and litter. C. chinensis and M. chapensis grew better in the mixed-legume and mixed-conifer plantations, while P. rubra grew better in mixed-native and mixed-conifer plantations. Responses of the transplanted seedlings to environmental factors were species specific. The effects of light on seedling survival and growth were correlated with the shade tolerance of the species. Soil moisture was important; it was positively correlated with survival but negatively correlated with growth of C. chinensis seedlings. Growth of C. chinensis and M. chapensis was positively correlated with soil potassium, while growth of P. rubra was positively correlated with soil organic matter but negatively correlated with soil hydrolyzed nitrogen. These findings suggest that we should select suitable native species under the different plantations before improvement of plantations. Light and soil moisture are most important environmental factors for the selection of species specific. Site preparation and fertilizer are needed during the improvement of those plantations. 相似文献
20.
In Canada's eastern boreal forest, the stagnant growth of black spruce (Picea mariana (Mill.) BSP) seedlings is often observed in the presence of ericaceous shrubs such as Kalmia angustifolia L. Many mechanisms, including allelopathic interference, reduced soil N mineralization, soil enzymes inhibition, and direct resource competition have been proposed to explain poor spruce growth in the presence of Kalmia. However, the relative importance of direct competition versus indirect interference remains unclear. Our objective was thus to adequately isolate the “Kalmia effect” from other growth-limiting factors and to determine if removal of Kalmia also resulted in fundamental changes in the biochemical properties of the forest floor. By sampling plots established in 2000, we evaluated how Kalmia eradication and spot fertilization influenced soil nutrient availability, N mineralization rates, microbial basal respiration and biomass, as well as planted black spruce seedling growth, dimensions, and foliar nutrient concentrations 6 years later. We measured higher extractable-P, mineralizable-N, seedling dimensions and growth rates, as well as lower extractable-K, total-K, basal respiration and microbial biomass, in plots without Kalmia than in those where Kalmia had been maintained from 2000 to 2006. Our results thus confirmed that Kalmia eradication over 6 years not only improved the growth and nutrition of black spruce seedlings, but also resulted in fundamental changes in the biochemical properties of the forest floor. We demonstrated that along with direct competition for resources, Kalmia interferes indirectly with black spruce by modifying nutrient cycling and energy fluxes in soil. Higher indices of available C in plots with Kalmia corroborates that Kalmia tannins or rhizodeposition may reduce N mineralization by stimulating microbial immobilization, a relation that however needs to be confirmed with longer term laboratory incubations. Our results indicated that although it had a positive influence on seedling growth, the fertilization effect was confined to the first few years following treatment application, and failed to influence soil processes as did Kalmia eradication. Further monitoring will indicate if the increased litterfall in fertilized plots will eventually initiate a second wave of fertilizer-induced changes to soil processes, as observed in other ecosystems. 相似文献