European aspen (Populus tremula L.): a review with particular reference to Scotland II. Values, silviculture and utilization

Interest in European aspen (Populus tremula L.) has increasedin recent years as a result of efforts to restore and extendnative woodland, and to diversify the range of species usedin forestry plantations. Aspen is a straightforward tree tomanage; it is of considerable ecological value and capable ofproducing utilizable timber. Planting of aspen in native woodlandis currently limited by a shortage of plants of Scottish origin.Propagation from seed, whilst possible, has not been practised,and recent efforts to produce stock have concentrated on vegetativemeans. The use of aspen as a component of plantation forestrycould be increased on appropriate sites; it is an excellentamenity species and its timber is currently acceptable as chipwoodand could complement the production of poplar timber in thelowlands. However, on the basis of limited data, growth ratesand stem form of aspen in Scotland appear to be rather poorerthan on the European continent where aspen is a significanttimber producing species. More would also need to be known aboutits susceptibility to disease before its timber production potentialcould be evaluated properly.     

European aspen (Populus tremula L.): a review with particular reference to Scotland I. Distribution, ecology and genetic variation

European aspen (Populus tremula L.) has attracted relativelylittle research attention in Britain. Interest in the specieshas increased in recent years because of efforts to restoreand extend native woodland, of which aspen is an infrequentbut important component species. This paper draws together informationfrom British, European and Russian literature on the ecologyand genetics of aspen. The species is distributed throughoutBritain in many different types of woodland. It is particularlycommon in the Scottish Highlands and Islands where it occurson a diverse range of sites from sea cliffs to near the treeline.It is associated with a distinct insect fauna, several speciesof which are considered endangered. Information is lacking onseveral fundamental aspects of the ecology and genetics of aspenin Scotland including seed production, growth rates, geneticvariation and its conservation value and status in native forestecosystems. Some useful information on these topics is presentedfrom studies of aspen elsewhere in Northern Europe, particularlyNorway.     

Productivity of Sitka Spruce in Northern Britain 2. Prediction from Site Factors

Productivity and site data from 187 temporary sample plots wereanalysed by multiple regression analysis to derive models inwhich site variables accounted for 78–86 per cent of thevariation in Sitka spruce productivity (General Yield Class,GYC). Climatic variables (accumulated temperature and windiness)extrapolated from meteorological data and tatter flag resultsaccounted for up to 78 per cent of the variation, the contributionof edaphic factors being small. The best regression models wereassociated with confidence limits of about ± 2.5 m³ ha^–1y^–1 and the mean error for predicting GYC for a forestblock (acquisition) was calculated to be ±1 m³ ha^–1y^–1 These figures were confirmed by the results of a validationsurvey and the application to field prediction of productivityis described.     

Stability of Coniferous Tree Stems in Relation to Damage by Snow

In this work both conical and paraboloidal conifer stems aretaken to bend along curves calculated to produce uniform strainin the outer wood. Such curvature has been observed in windtunnel tests. From these curves for various displacements theresistive bending moment produced by the elasticity of the stemmay be calculated. The maximum value of this is related to thebreaking stress of the timber. The bending moments applied bythe weights of stem, crown and snowload are calculated by obtainingthe appropriate lever arms from the stem bending curves. Appliedand resistive bending moments are compared for 20m-high treesof various types. Densely grown trees of low taper are leaststable. Open grown trees with conical stems and high taper aremost stable. The effects on tree stability of wind, a leaningstem, an asymmetrical crown and basal bowing are also investigated.     

A Comparison Between European Continental and British Provenances of Some British Native Trees: Growth, Survival and Stem Form

Data describing the growth, survival and stem form of: a) Europeancontinental, and b) British provenances of trees native to Britainwere collated from Forestry Commission records. The growth ratesof European continental provenances of Scots pine (Pinus sylvestris),silver birch (Betulo pendula), sessile oak (Quercus petraea)and common alder (Alnus glutinosa) were inferior to those ofBritish provenances in 90 per cent of cases. European provenancesof these species also showed inferior survival. The growth ratesof continental provenances of beech (Fagus sylvatica) were superiorto British provenances in about 50 per cent of cases, provenancesfrom northern France, Belgium and Holland being the fastestgrowing. Relationships between the relative height growth offoreign provenances and latitude were demonstrated for Scotspine, silver birch and beech (relative height growth = the heightgrowth of a foreign provenance expressed relative to that ofBritish provenances at the same site). The continental provenancesthat grew best originated at 0–4° south of the latitudesof the planting sites. Relative height growth decreased bothnorth and south of these latitudes. In the case of oak, relativeheight growth did not vary widely between origins. The survivalof continental provenances of Scots pine was particularly pooron exposed upland sites. The stem form of British provenancesof Scots pine was intermediate between Fennoscandian provenancesand provenances from the rest of Europe. In oak and beech therewas generally little difference in stem form between Britishand continental provenances, but the best continental provenances(Belgian beech; French oak) were most reliable. The growth andsurvival of native trees is interpreted in the light of thepost-glacial history of these species. The implications regardingthe continued use of seed of native hardwoods imported fromcontinental Europe are discussed.     

The influence of some forest operations on the sustainable management of forest soils-- a review

This review paper describes the nature and scale of changesto forest soils brought about by forestry operations. A relativelynon-technical approach is adopted with the aim of stimulatingdebate within as wide an audience as possible. The paper doesnot aim to be exhaustive but rather a position statement. Areaswhere further study is required are highlighted. The concept of sustainability is explored in relation to forestsoils, and the condition highlighted is that impacts of forestmanagement operations should not, in the long term, exceed thecapacity of soil to recover by natural processes (e.g. erosionlosses should not exceed soil formation rates, nutrient removalsshould not exceed nutrient inputs etc.). Soil erosion, nutrientremoval, compaction, and changes in organic matter content andsoil water status are identified as the most important processesinvolved in the impacts of management. The impacts of some of the more intensive forest managementregimes on soil compaction, nutrient removal and erosion ratesappear to be of similar magnitude to the recovery capacity ofsoils. Where the most intensive forms of forest operation areused on susceptible sites some degree of long-term soil degradationappears to be likely, and it can be regarded as valid to describesuch management practices as unsustainable. However, the scaleof occurrence of such management is probably relatively modest,and decreasing. On less susceptible sites, and where less intensiveforms of management are employed, impacts on soils are low enoughfor management to be regarded as sustainable, and are oftenless than under pre-existing land uses. Compaction caused byheavy harvesting and extraction machinery, nutrient depletionresulting from whole tree harvesting on infertile sites whererotations are short, and erosion following cultivation and harvestingon erodible soils are the greatest causes of concern. Compliancewith recent Forestry Commission guidelines should lead to lowerimpacts than those recorded during recent decades. However,rotation-length audits of the impacts of different forest managementregimes on a range of site types are needed before definitivestatements about the sustainability of management operationscan be made.     

Influence of Site Factors on the Response of Sitka Spruce to Fertilizer at Planting in Upland Britain

Data from Forestry Commission fertilizer experiments were analysedto determine the influence of site factors on the growth responseof Sitka spruce (Picea sitchensis (Bong.) Carr.) following applicationsof phosphate and potassium at time of planting. Multiple regressionanalysis revealed that growth response was influenced by soiltype and was related to the foliar nutrient levels of untreatedcontrols. Growth response to application of phosphate was alsoinfluenced by lithology. No relationships were found betweengrowth response and elevation or annual rainfall. Received 29 January 1990.