|عنوان فارسی مقاله:||پیش بینی شاخص مکانی کشتزار های صنوبر داگلاس از متغیرهای محیطی در منطقه مرکزی مسیف فرانسه|
|عنوان انگلیسی مقاله:||Predicting site index of Douglas-Fir plantations from ecological variables in the Massif Central area of France|
|رشته های مرتبط:||محیط زیست و منابع طبیعی|
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Douglas-Fir is the main species used in France for reforesting mid-elevation regions, mostly on former heathlands and coppices. In order to clarify its auto-ecological limits, and to provide forest managers with relevant information for planting, we studied its productivity in a wide range of site conditions. Based on data from 202 Douglas-Fir pure stands at mid-elevation regions, site productivity was assessed using variance analysis with site types, site groups, and multiple regression analysis with ecological variables. Site index, determined from stem analysis data, was used as a species speci®c measure of site quality. Results show that Douglas-Fir site index is correlated to soil nutrient status, and secondarily to soil moisture regime. Mean stand productivity was generally high, but considerable variation in site index was determined within a study area that was classi®ed by forest managers as uniform. Correlation between site classi®cation and site index was con®rmed, because it was based on synoptic factors that are simple and robust indicators of site productivity. Other methods to assess site quality, such as multiple regression on ecological variables and multivariate site groups, appear to be less explicative and robust for predicting site index. The results allow forest managers to predict the site index at parcel scale. Further investigation should be carried out in order to explain the major causes of the unexplained variance of site index by ecological variables, especially genetic variation, and effect of age. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Pseudotsuga menziesii 3 Mirb ) Franco; Site productivity; Site classi®cation; Site index.
Douglas-Fir ®r [3 Pseudotsuga menziesii )3 Mirb ) Franco] has been the main species used in France for reforesting since the 1970s. French plantations consti- tute the widest use of this species 33,30,000 ha 1 ) outside its natural origin area in North America. It iswidelyusedinFranceinmid-elevationregions,such as the Massif Central, which represents about 70% of the total surface of plantations. It has been frequently used to reforest former heathlands and coppices, and its use was encouraged by national grants as in other European countries 3Tyler et al., 1995; Corona et al., 1998). Douglas-Fir is reputed to be a potentially high yielding species 3Tyler et al., 1995), and to be adapted to nutrient-depleted sites with a low water-holding capacity 3De Â court and Nys, 1976). Consequently, is has been introduced on a largerange of site conditions with an objective of increased timber production. However, French foresters recently observed increas- ingproblemsofpests,diseases,andfailuresinuplands 3DSF, 1996). Even if this species is spared serious damage, these problems give rise to questioning Douglas-Fir adaptation and productivity according to site conditions. In spite of the great importance of this coniferous species in the French Massif Central, regional studies on its productivity and auto-ecology are few 3De Champs, 1997). The main work on this topic was madebyDe Â courtandNys31976)inthewesternpartof the Massif in order to establish height-age curves. A bibliographic survey 3Forestry Abstracts 1939±1995, in Marque Â s et al., 1997) stressed that most of the 245 international studies on Douglas-Fir concern silvicul- ture, pests and diseases, genetics, nurseries, and wood quality.Onlyafewstudieswerededicatedtosite-yield relationships and auto-ecology. They mainly relate to the North American origin area 3Green et al., 1989; Klinka and Carter, 1990; Monserud et al., 1990; Monserud and Rehfeldt, 1990), and secondarily to Scotland 3Tyler et al., 1995), and Italy 3Corona et al., 1998). The current survey was integrated in recent efforts in France that focused on linking site index to site classi®cations, and site quality for the major refores- tation species 3Becker et al., 1980; Buffet and Girault, 1989). Methods used for assessing site quality and productivity are various 3Hills, 1952; Jones, 1969; Pritchett and Fisher, 1987). The ®rst one consists of correlating site index with site types according to a local or a regional site classi®cation system 3 synoptic approach). The second one is based on multiple regression analysis between site index and major ecological variables 3 analytic approach). More precisely, this last method uses routinely mea- sured site variables, which are indirect indicators of theecologicalenvironmentofsites3WangandKlinka, 1996), instead of the real causativefactors that control tree growth. Both methods may be useful for predict- ing forest yield. Thus, it is interesting to compare the statistical effectiveness, and the practical implica- tions, of different methods for assessing sites and site quality. Consequently, on the basis of 202 pure and mature Douglas-Fir stands in a mid-elevation region of the French Massif Central, we proposed: 3i) to explain the variation sinsiteindexa mongsit es,toclarifytheauto- ecological limits of these species in Limousin, and consequently,top rovi deforest managers with relevant information for using this species; and 3ii) to validate, and to stress the advantages and limits of using site classi®cationtopredictsiteindex,bycomparisonwith other ecological approaches.