摘要:

Dormant one‐year‐old seedlings ofAcer platanoidesL. were subjected to a range of cold storage temperatures for 6, 9 and 12 weeks followed by forcing at 20°C. For all storage temperatures there was a marked effect of exposure time on post‐chilling heat requirement for bud burst. The effect of temperature, however was less pronounced than the general assumption, in particular the chilling efficiency of 0°C was higher than reported by others. It is suggested that the optimum chilling temperature, i.e. the temperature that most efficiently reduces the need for heat units for bud burst, rises during the chilling process. This supports the hypothesis of a dynamic temperature response during dormancy release. A uniform bud burst could be obtained by exposing the plants to 0–8°C for 9–12 weeks. Terminal buds of insufficiently chilled trees frequently had bud burst later than the laterals, suggesting a higher demand for chill units and/or heat units for bud burst.

ISSN:0282-7581    

DOI:10.1080/02827589809382955

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Monte Carlo computer simulations were carried out in order to compare unrestricted phenotypic and restricted combined‐index selection, applied over one generation of single‐pair mating, for a wide range of family sizes and heritabilities, and for two sizes of breeding populations. The simulations demonstrate that when restrictions are imposed to control reduction of diversity to equivalent population size (status number), there are situations where phenotypic selection will achieve greater gain than that achievable by combined‐index selection. On average, unrestricted phenotypic selection was found to be similar to or better than restricted combined‐index selection at the same status number for heritabilities higher than 0.2. For lower heritabilities, phenotypic selection was less efficient. Selection in larger families resulted in greater gain, but at the expense of genetic diversity. Unrestricted phenotypic selection often proved to be a more efficient method, preserving more genetic diversity per unit gain. Restricting the number of selections per family is an efficient method to balance gain and diversity after combined‐index selection. The size of the breeding population appeared to have a minor effect on gain, but can affect the rate at which overall genetic diversity is eroded.

ISSN:0282-7581    

DOI:10.1080/02827589809382956

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of early selection of clones in the nursery on field performance after 6 yrs in the field were studied in a material comprising 794 cutting propagated clones ofPicea abies(L.) Karst. A 20% selection for height in the nursery gave gains of approximately 3% in height after 6 yrs. Attempts to improve the early selection procedure were made. Stratification of the nursery beds in two blocks according to location had almost no effect on the gain, arid selection within growth rhythm classes was less effective. Correlations between other characters measured in the nursery and field characters were generally low. The positive, though moderate, relationships between nursery height and height after 6 yrs in the field are encouraging for further research to improve selection efficiency.

ISSN:0282-7581    

DOI:10.1080/02827589809382957

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Single‐tree functions to predict the diameter of the thickest living branch and the branchiness (the proportion of the cross‐section area of branches to the stem‐surface area) based on the relative tree height for the live crowns of standing trees are presented. The study also considers the diameter of the thickest dead branch, the cross‐section area of branches, and the stem‐surface area using data from temporary sampling plots in southern Sweden. The diameter of the thickest living branch correlated closely with the stem diameter near this branch. The diameter of the thickest living branch decreased from crown base and upwards. The diameter of the thickest dead branch increased to a relative tree height of about 50%, and then decreased beyond. For a biological diameter of the thickest living branch modeling approach, the residuals indicated no major trend and the root mean square error (RMSE) value was rather low. The branchiness was predicted by variables describing the size of branches, the number of branches per whorl, the distance between whorls and by the stem‐surface area. In the for timber marketable part of the stem, the branchiness increased with increasing relative tree height.

ISSN:0282-7581    

DOI:10.1080/02827589809382958

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a distance‐dependent yield model for a mixed stand of Scots pine (Pinus sylvestrisL.) and Norway spruce (Picea abies(L.) Karst.) that accounts for the possible mixture effects separately for each tree and can be numerically optimized. The model consists of distance‐dependent single‐tree growth models, distance‐independent height models, distance‐dependent mortality models, and a distance‐dependent thinning algorithm. The thinning algorithm is controlled by the stand basal areas that trigger thinnings, and the relative removals from different tree species and diameter classes. The role of the thinning algorithm is to specify the trees to be harvested; this information is not contained in the decision variables. The algorithm removes trees starting with those individuals that face the most competition. The usage of the yield model together with a nonlinear optimization algorithm was illustrated by an example; the optimal thinning regime was determined for a mixed stand in which the age of pine and spruce was the same. Maximization of soil expectation value called for late and heavy first thinning and shorter rotation than applied in normally practiced forestry. In the one‐thinning regime, spruces were harvested from above and pines from all size classes. When two thinnings were applied, small and large pines are removed in both thinnings, whereas spruces are thinned from below in the first thinning and from above in the second thinning.

ISSN:0282-7581    

DOI:10.1080/02827589809382959

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of red (R), far‐red (FR) and R + FR light on Norway spruce seed dormancy were studied at five different moisture contents (MC) between 5 and 20%. The degree of dormancy was studied by germinating seeds over a wide range of temperatures in the dark. The non‐irradiated control seeds were shallowly dormant, only a proportion of them germinated and within a limited temperature range. Red light progressively stimulated germination between 5 and 17% MC, but this effect was reversed if a FR treatment followed, although all germination could not be inhibited by one FR pulse. Far‐red light had a slightly stimulating effect at 19% MC. To generate seeds able to germinate over a wide range of temperatures in darkness, an artificial light pretreatment should be given to seeds at MC above 17% in order to receive maximum response.

ISSN:0282-7581    

DOI:10.1080/02827589809382960

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Seedlings of deciduous and coniferous species are easy prey for generalist mammalian herbivores such as meadow voles (Microtus pennsylvanicusOrd.). Among several protection measures available to reduce girdling on seedlings, the use of alternative food is thought to be one promising way of “hiding” valuable seedling species from herbivory. We tested the hypothesis that bark‐use of red oak seedlings (Quercus rubraL.) would be lower when alternative food in terms of less valuable commercial coniferous seedlings was available to voles. Four groups of ten voles each were tested to estimate bark‐use indices on red oak seedlings matched with white pine (Pinus strobusL.), Norway pine (Pinus resinosaAit.) or white spruce (Picea glauca(Moench) Voss), three coniferous species which are occasionally girdled by voles. Laboratory tests lasted 25 days under standardized rearing conditions of temperature (18–20°C), relative humidity (40–60%) and luminosity (16 hL: 8 hD) with winterized seedlings. Red oak seedlings lost between 56% and 76% of the bark on their trunk diameter, depending on their association with specific coniferous seedlings. Use of bark was significantly higher when red oak was matched with white pine, and lower when red oak alone was offered to voles. Coniferous seedlings did not lose more than 7% of their bark from trunk diameter when matched with red oak. Conifers cannot be used as alternative food resources to protect red oak seedlings against vole damage.

ISSN:0282-7581    

DOI:10.1080/02827589809382961

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Analysis of consumer demand for packaging suggests that: plastic packaging is a luxury good, while paper packaging is a normal good, paper packaging demand increases with the price of plastic packaging, and that demand for paper packaging is most sensitive to its own price, and to the income of consumers. In a complementary analysis of input demand in the converting paper industry it was found that the demand for each paper grade is price inelastic, capital and other materials are substitutes for paper, while labor is a complement, technical change rapidly decreases the use of unbleached kraft packaging and industrial converting, and increases the use of other grades. The demand for each paper grade, derived from the consumer demand and the factor demand functions, showed that, from 1983 to 1991, the demand for paper in packaging was influenced mainly by consumer income, and by the price of paper packaging, and less so by the price of paper itself, or by the price of plastic packaging.

ISSN:0282-7581    

DOI:10.1080/02827589809382962

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Data from the Swedish Forest Owner Register of 1993 and Statistics Sweden's special studies in connection with the 1976 and 1992 Census of Agriculture have been used to describe Swedish non‐industrial private forest (NIPF) ownership structure in terms of gender. On a national level, results show that more than one‐third of all owners are women, and that there are clear regional differences. The last years have seen an increase in female share of NIPF ownership. Compared with males, females combine forestry and farming less often. Female‐owned estates are smaller, and more often partner owned. Finally female owners are somewhat younger. Data from the National Board of Forestry's interview inquiry 1994 indicate that there is less forestry activity on holdings with female respondents than male respondents.

ISSN:0282-7581    

DOI:10.1080/02827589809382963

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An application of a forward reaching algorithm of dynamic programming is presented for cross‐cutting trees. Sensitivity analysis was applied for evaluating the effects of various log length and dimension constraints on the produced yield and the relationships between the timber volumes obtained and the dendrometric properties of the data were analysed. The data used consisted of 3283 Scots pine (Pinus sylvestrisL.) stems collected from 52 forest stands located in seven regions in Finland. The timber grades used were branchless logs, logs with living branches, logs with dead branches, pulpwood and waste. It was shown that the volumes of different grades vary considerably when different dimensional criteria are applied and that log length constraints seem to affect the yield more than the limit for the minimum top diameter. By reducing the minimum log length from 37 dm to 22 dm the volume of the branchless log grade was tripled in some stands. The volume gain obtained by loosening the dimension constraints was generally largest in stands of poor quality. The average height of the lower part of the dead crown was found to be the best indicator for the amount of the branchless timber obtained in a stand. In general, the timber volumes obtained varied a lot between the stands of a region as well as within a stand. Especially between‐tree variation within a stand makes the estimation of the timber volume unreliable without some measurement data.

ISSN:0282-7581    

DOI:10.1080/02827589809382964

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor