摘要:

Patterns of seasonal and yearly variation in the abundance of the pine weevil,Hylobius abietis(L.) (Coleoptera: Curculionidae), were determined on clear‐cuttings of various age in southern Sweden. New clear‐cuttings were established during each of five consecutive years, and the numbers of weevils caught in pitfall traps baited with α‐pinene and ethanol were recorded weekly during the season for up to 6 yrs on these areas. In total, 74 281 weevils were trapped. On fresh clear‐cuttings, the catches increased drastically once migrating weevils had arrived in spring. Catches peaked in May and July but were lower in June, when oviposition underground is most intense. The catches declined suddenly in the middle of August, coincident with the weevils becoming post‐reproductive. On older clear‐cuttings, most weevils were caught before migration in spring; thereafter the catches gradually decreased from June to September. Pine weevils were even abundant on 5‐yr‐old clear‐cuttings. Relationships between trap catch and weevil‐induced seedling mortality were examined on fresh clear‐cuttings and on the same areas over the following 3 yrs. A significant relationship between these two variables existed only for the 2‐yr‐old clear‐cuttings. Therefore, trapping data alone appear to be insufficient in forecasting seedling damage.

ISSN:0282-7581    

DOI:10.1080/02827589709355405

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Swedish forestry handbooks recommend that strip cutting should be practiced on forested slopes, and that uncut buffer strips should be left between clear‐cut areas and streams, because uptake by the remaining trees is believed to prevent leaching of N to the streams. We have tested this hypothesis using the assumption that, if it is true, these techniques should lead to increased diameter growth in the trees downslope of the clear‐cut because N is the growth‐limiting nutrient in Swedish mineral soils. Increment cores from trees growing downslope of 8–18‐yr‐old clear‐cuts were studied, therefore, at five sites in northern and one site in central Sweden. Growth was not influenced by the cutting at any site for the first 3 yrs, and it increased at only two of the sites thereafter. The results indicate that stands left downhill of clear‐cuts do not always act as a catch crop for leaching N.

ISSN:0282-7581    

DOI:10.1080/02827589709355406

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The response of young Norway spruce (Picea abies(L.) Karst.) to removal of overstorey birch (Betulaspp.) was investigated in an experiment where suppressed spruce were released before, during or after the growing season. The response was monitored in terms of growth and levels of injuries. Examinations were made at the time of release, performed periodically from 1986 to 1988, and after release every autumn up to 1991. The results indicate that there can be considerable losses due to mechanical damage caused by wind and snow and that the spruce may suffer a temporary growth reduction after release. However, no significant differences in the growth or damage levels were detected between the treatments. Injuries in the absence of mechanical damage were negligible. The stability of the residual stand improved considerably within 1 yr after treatment, and after 3 yrs no further damage occurred. Spruce released in spring increased in stability, expressed as the height‐to‐diameter ratio, faster than spruce released in summer, which in turn increased faster than spruce released in autumn.

ISSN:0282-7581    

DOI:10.1080/02827589709355407

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Site index and productivity of artificially regenerated stands of silver birch (Betula pendulaRoth) and downy birch (Betula pubescensEhrh.) on former farmland in southern and central Sweden were examined. The material comprised sample plots in 27 stands, measured in both 1990 and 1993. Silver birch was the dominating species in most stands, and the average site index (SI) was nearly 28 m. Site quality ranged from 5.3 m3ha−1yr−1(equivalent, from tables, to a SI of 22 m) to 11.4 m3ha−1yr−1(equivalent to an extrapolated SI of 32 m). Soil moisture was the only site factor tested that significantly affected SI for silver birch. Moist sites were found to be inappropriate for this species especially on fine‐textured sediment soils. On moist sites, SI for downy birch was as high as SI for silver birch. Growth of artificially regenerated silver birch on former farmland differed significantly from growth of naturally regenerated birch on forest sites, according to two Swedish growth simulators.

ISSN:0282-7581    

DOI:10.1080/02827589709355408

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effects, in terms of economic value and harvest potential, of adopting restricted timber management practices promoting the preservation of biodiversity are analysed in a 5620 ha boreal forest landscape in southeast Norway. A forest management model based on ecological principles aiming at preservation of biodiversity, e.g. by adopting restricted silvicultural treatments imitating the effects of natural processes, such as forest fires, is applied. The forest area is divided into four separate classes reflecting the probabilities of forest fires, and different treatment options are assigned to each of the classes. These options comprise extended rotation periods and treatments such as clear‐cutting with retention of seed trees and shelterwood cutting. A management problem specified as maximization of net present value subject to a requirement to preserve (medium term) about 10% of the forest area for a period of 70 yrs is solved by means of linear programming. Compared with current timber management practices, the net present value of the restricted management problem is reduced by 14% (15%) for a real rate of discount of 3% (4%) pro anno. The annual harvest flow is reduced by 11–33%. For a management problem comprising even‐flow harvesting constraints in addition to biodiversity constraints, the net present value is reduced by 16% (19%).

ISSN:0282-7581    

DOI:10.1080/02827589709355409

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Forest biomass databases which go beyond stem volume are needed for carbon balance calculations and also for forest monitoring, forest damage inventories and the solution of other related problems. In this article, it is shown how recursive multiple regression analysis can combine forest inventory data with biomass harvest data. The stand‐level conversion factor derived forPinus sylvestrisL. branch biomass for the “Severka”; Forest Farm shows a reasonable goodness of fit, with a coefficient of determination ofR2=0.87. Statistically significant coefficients were achieved by including stand density and the quadratic mean diameter in the regression. Equations developed for Switzerland, using Burger'sPicea abies(L.) Karst. branch and needle conversion factors for individual trees, showR2=0.87 andR2= 0.91, achieved by takinghdom.50, elevation, diameter at breast height and age into account.

ISSN:0282-7581    

DOI:10.1080/02827589709355410

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The empirical validity of a simple present value model describing forest land prices according to economic fundamentals is examined. The implications of the model are derived and tested by use of time series econometric methods on Danish rent and price data in the period 1911–92. A necessary condition of the model is rejected by the data, probably due to an under parameterization of the model. An extension of the model, including the omitted variable, is suggested and discussed theoretically.

ISSN:0282-7581    

DOI:10.1080/02827589709355411

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Browsing by large herbivores on planted and naturally regenerated conifer seedlings(Picea abiesandPinus sylvestris)was recorded in 104 clear‐cuts in east‐central Sweden during 1990 and in 47 clear‐cuts in 1991. The number of seedlings browsed and the browsing patterns were analysed in relation to seedling type. Browsing frequencies were also compared between forest stands with different site productivities and subjected to different management practices. The variation in the number of seedlings browsed in 1990 was explained mainly by seedling category. Among both planted and naturally regenerated seedlings, pine was browsed more than spruce. Two‐year‐old containerized seedlings of spruce was browsed more than 4‐yr‐old bare‐rooted spruce. In 1991, browsing was more equal among species and seedling types. Number of seedlings with their leader browsed and the amount of biomass left after browsing differed significantly between seedling types. Seedlings that had been browsed in 1990 experienced significantly higher browsing frequencies in 1991 when compared with unbrowsed seedlings. The effects of stand characteristics were not found to be significant.

ISSN:0282-7581    

DOI:10.1080/02827589709355412

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The primary objectives of this study were to describe and compare the competitive strategies of softwood sawmills in five major softwood producing regions of the world, and to discuss the limitations of the well‐known Porter model. Data was collected via personal interviews from 102 companies in Finland; coastal and inland western USA; coastal and inland British Columbia, Canada. Results suggest that “pure”; focus and differentiation strategies are the competitive strategies most commonly followed by sawmills in Finland and inland British Columbia. In the coastal and inland western USA regions “pure”; differentiation and “pure”; cost leadership strategies are dominant in these two geographical regions, respectively. In coastal British Columbia a “pure”; cost leadership strategy and the combination of all strategy types were the two strategies most frequently followed. The competitive strategy followed was found to be related to company size. Large companies more often applied cost leadership strategies and differentiation and focus strategies were typical of small and medium‐sized companies. In general, sawmills in all five regions had difficulties identifying exclusively with one strategy type.

ISSN:0282-7581    

DOI:10.1080/02827589709355413

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In the Nordic countries, the non‐industrial private forest (NIPF) owners play an important role in the roundwood market, and are essential to the successful implementation of environmental policies. We know little about the owners as managers, however; about their goals, procedures for identifying cutting opportunities, or the selection of buyers and price options. To study these issues, I have used a qualitative method, based on personal interviews with 35 owners. The results show that an overriding objective, influencing the cutting patterns of the owners, is to preserve and develop the property. A variety of formal and informal economic, production and environmental, and intangible goals are influenced by this overriding objective. In addition to relying on their own observations of price changes and the recommendations of the forest management plan, owners identify cutting opportunities through neighbours, friends, timber buyers, or extension rangers. Usually the owner uses the same selling form from one time to the next. Dissatisfaction with the result of the last cutting, however, may trigger a search for new options.

ISSN:0282-7581    

DOI:10.1080/02827589709355414

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor