The natural distribution of Sitka spruce is examined in relation to the species' role in British forestry. Particular attention is therefore given to a description of habitats on the Queen Charlotte Islands, and also on the adjacent mainland of British Columbia where Sitka spruce is sympatric with white spruce (Picea glauca) and hybridisation occurs. Examples of genetic variation are given and it is suggested that a knowledge of the genecologv of the species in its natural habitat would help to elucidate its full ecological and genetic potential in Britain.

The Upper Palaeozoic bedrock, which is of sedimentary and volcanic origin, is briefly described. The origin of the Forth as a series of depressions in the bedrock surface probably owes much to erosion of a pre-existing Tertiary landscape during phases of Quaternary glaciation. The late Quaternary history of the area is described, relating the distribution of the sediments deposited in the Forth to climatic events and changes in relative sea-level. Since the acme of the last main glaciation about 20,000 years ago, late Devensian marine and estuarine sediments have been deposited on the underlying glacial till sheet at altitudes ranging from more than 120 m below O.D. to at least 46 m above O.D. Similarly, raised and buried beaches and their deposits occur at altitudes from 40 m above O.D. down to around 10 m below O.D. in the estuary. During the Flandrian, sea-level has fluctuated, reaching its maximum (about 11 to 15 m above O.D.) about 6500 years ago. The typical deposit of this period is the carse clay which forms a series of extensive, fertile raised mudflats around the estuary. The calcareous marine faunas of the carse clay and older deposits are outlined.

The taxonomic and phylogenetic affinities of Sitka spruce (Picea sitchensis) are reviewed in relation to the more general picture of spruce biogeography and evolution.

The pattern of climatic variation over estuaries and their environs is, to a considerable extent, controlled by aspect, slope and elevation in addition to orientation of the major relief features with respect to the movement of principal weather systems. Data from the few climatological stations within the immediate vicinity of the estuary and Firth of Forth demonstrate the essentially maritime nature of climate, and indicate also that there is a dominantly west–east gradient of change in most climatological variables. Below the high water mark the movement of water in tidal ebb and flow and river inflow modify atmosphere–surface interactions over relatively short spatial and temporal scales. Observations from a fixed instrument tower on Skinflats in the middle estuary and from Inchkeith Lighthouse indicate that tidal water movements exert varying degrees of control over sub-surface heat fluxes, air movement in the atmospheric boundary layer and the inland penetration of coastal weather systems such as the typical east coast haar.

Because of the wide latitudinal range of Sitka spruce, trees of different origin show very large differences in growth rate and adaptability when grown on a variety of sites in Britain. The Forestry Commission has forty-eight seed origin trials, planted between 1929 and 1975, which are now beginning to provide a good overall picture of this variation. On the other hand, differences in morphology and colour are relatively minor, so that it is very difficult to identify the seed origin of a stand of trees on visual grounds alone. Southerly origins (below Latitude 47°N) grow fastest, but they suffer more severe frost damage, particularly in the nursery, and tend to have lower density timber than those from 53°N or above.

The hydrography of the Forth estuary is described, and various modelling studies that have been carried out are briefly summarised. The description of the hydrography includes information on the currents, salinity, temperature, tidal elevations, and turbidity, as well as physical dimensions and freshwater inputs. The vertical salinity structure of the estuary varies from the well-mixed state to the partially-mixed state, depending on the freshwater input and the tidal range (which determines the amount of turbulent kinetic energy available for mixing). The tides in the estuary exhibit double high and low waters because of shallow-water effects, and there are observations of a small tidal bore. The resuspended solids are found to account for a large fraction of the biochemical oxygen demand in the water column. The modelling studies range from an early physical model, to an analytical model of water-quality, to more recent numerical models produced by the Forth River Purification Board and Imperial Chemical Industries, which were developed in order to assess the impact of proposed discharges on water-quality. Finally, currently active projects are described and suggestions for future work given.

The Firth of Forth, in terms of physical oceanography, is part of the North Sea. The general circulation pattern in the firth must be regarded as largely speculative. There have been insufficient measurements of insufficient quality, and what evidence exists leads to the view that what circulation there is, is sluggish and varies from season to season and from year to year.

A description is given of the three principal mechanisms that contribute to circulation. Tides, due initially to astronomical forces, manifest themselves in the Firth of Forth through the rise and fall of the adjacent open sea. This rise and fall, periodic in mid ocean, is no longer strictly so in the firth and neither are the tidal currents. The wind-driven currents in the sea are influenced by the earth's rotation. In the Firth of Forth, some of this influence is retained. Naturally, wind-driven currents are larger near the surface. Finally, when water of different densities meets, overturning causes convection currents. All of these effects are present to some extent in the Firth of Forth. In addition, specific account has to be taken of complicated coastal and bottom topography and river outflow. Some attempt to bring together these effects and available measurements is made in this paper. Lastly, several theoretical models are proposed which account for the magnitudes and directions of the observed steady circulation. Mathematical details are given in appendices.

Sitka spruce is a monoecious, wind-pollinated, cross-fertilising species showing wide genetic variation which suggests heterozygosity for many alleles and natural selection against self-fertilisation. Phenotypic selection for the important trait of vigour is ineffective, so testing progenies of selected individuals and clonal testing is an essential and time-consuming part of any improvement programme. Old trees can be vegetatively propagated by grafting and very young trees by rooted cuttings.

The British tree improvement programme is based, in the short term, on the use of seed collected from superior plantation trees of desirable origins; in the mid term on seed derived from clonal orchards based on mixtures of clones previously tested for superiority in family tests; and in the longer term on highly superior seed or clones derived from a system of recurrent mating with family selection. Three populations are being developed. There is a small interspecific hybridisation programme.

Picea sitchensis has a haploid complement of twelve metacentric or submetacentric chromosomes which are similar to each other in size. Prominent secondary constrictions, which are probably the sites of nucleolus organisers, occur on five chromosomes (N.O.R.s). The DNA content of the haploid, unreplicated chromosome set is 9 × 109 nucleotide pairs and, in spite of earlier claims, probably does not vary significantly between different populations. B-chromosomes occur extensively in the southern half of the species range. They have little effect on growth rate but delay the time of ♂ and ♀ flowering. Meiosis starts and ends in spring, taking about twenty-two days to complete. The B-chromosomes do not pair at meiosis and appear to be distributed at random. There is marked accumulation of B-chromosomes when transmitted through the ♀ parent, possibly due to preferential segregation during meiosis. A balance between gain by accumulation and loss due to delay of flowering may account for the natural distribution of the B-chromosome.

The waters and coastal margins of the estuary and Firth of Forth are important and very valuable biological and recreational resources. They also receive, directly or indirectly, the aqueous domestic and industrial wastes of a quarter of the population of Scotland. It is one task of the Forth River Purification Board to minimise and eventually eliminate any conflict between the effects of these discharges and the various legitimate uses of the waters. Some of the main causes of environmental stress are briefly outlined and the basic strategy by which the problems will be overcome is described.

The natural background concentrations of radioactivity in the waters of the Forth are shown to be only marginally increased by anthropogenic inputs. The nature of the background levels and anthropogenic influences is briefly described.

Young Sitka spruce trees grow slowly, compared with poplar for instance, because of lower photosynthetic rates and slower rates of leaf area production. On the other hand, the canopies of Sitka spruce stands have structural and photosynthetic properties which make them very productive. Both the slow growth of young trees, and the high productivities of closed stands, can be attributed to the needle habit.

Experiments have shown that Sitka spruce on poor soils requires relatively frequent applications of fertiliser, phosphorus being most commonly required, other deficiencies in decreasing frequency being potassium, nitrogen and, very rarely, copper. Recent evidence suggests that growth responses to fertilisers are commonest while stands are young and the green canopy is being established. Spruce has a heavy crown and in consequence nutrient demands are high prior to canopy closure. Thereafter, the annual production of foliage by spruce is no greater than that of other species of comparable growth rate and by this stage the establishment of cycles within the tree and through the litter layer enable efficient re-use of nutrients and hence the demands placed upon the soil fall dramatically.

The major sources of domestic and industrial wastes being discharged into the estuary and firth are described and quantified. The effects of these inputs on the quality of the receiving waters, in terms of their dissolved oxygen and micronutrient levels, are discussed.

In the estuary, nitrate is shown to behave in an essentially conservative manner in the winter months; the ammonia distribution exhibits summer maxima as a direct result of the effluent waste inputs; the orthophosphate distribution is characterised by considerable losses in the upper reaches. The data on lateral distributions of micronutrients show marked gradients.

In the firth the significant improvements in waters off the Edinburgh coastline are described. The influence of the existing major discharges on water quality is shown occasionally to extend to the eastern limit of the firth for ammonia and orthophosphate.

The long history of discharge of industrial and domestic waste to the Forth makes the area of particular interest to environmental scientists. The area has been studied both in its own right for the monitoring and control of contamination by trace metals and organohalogen compounds, and in the study of processes which influence the dispersion and effects of these substances. This paper discusses the inputs of contaminants to the area, their occurrence in the water, sediments and biota, and places the Forth in context with other coastal areas of Scotland. The paucity of information concerning organohalogen compounds is contrasted with the extensive work carried out on trace metals.

The general adaptations of the species are described in relation to the environment of its natural distribution and are shown to be well suited to its use as an exotic in forestry. What is known of natural stand dynamics has little relevance to the cultivation of the species in pure plantations but the interaction with climate and soils is important in determining the limits to its growth and in prediction of productivity. Atmospheric humidity, windiness and accumulated temperature appear to be the most influential climatic variables and, given adequate soil conditions, can be used to give good estimates of potential production. Sitka spruce flowers freely and regenerates readily, demonstrating its ability to survive unaided in British conditions.

Sitka spruce is the most important species grown in Scottish forests thanks to its high yield potential, site tolerance and wood properties. It is easily raised from seed or cuttings, and can be readily established and tended under a wide range of site conditions using uncomplicated silvicultural techniques. Spaced furrow ploughing and site drainage are normally required for afforestation; and cultivation may also be desirable prior to restocking. Planting at 2500 trees/ha is done in late winter and spring. Weed control may be necessary, particularly to prevent Calluna-induced growth check. On poor sites, repeated fertiliser application prior to canopy closure can be essential to ensure satisfactory growth, and use of nursing mixtures may be worthwhile. Wherever possible, pole stage crops are thinned regularly to enhance stem quality and diameter growth, but on high windthrow hazard sites the onset of windthrow can be delayed by leaving crops unthinned. After an economic rotation of forty-five to sixty years, crops are clear felled and replanted. During establishment, deer control measures are often required to prevent browsing damage. Damage by insects and fungi is seldom serious, provided that bark-feeding insects are controlled by insecticide at time of replanting, and development of fungal butt rot is minimised by urea treatment of fresh stumps.

Since 1924 the Forth has received effluent from Scotland's major petrochemical industry and refinery in addition to hydrocarbon inputs from many other sources. The firth shows no major effects of this, but the history of inputs, together with the estuary's physical characteristics, have created a large residue of hydrocarbon contaminants especially in its sediments. This paper gives the degree and gradients of contamination in several components and describes the effect of hydrocarbon contaminants on the ecosystem structure.

The major inputs have produced localised lethal effects, in that productive estuarine intertidal habitat has been lost or its functioning altered. The changes are primarily due to organic enrichment with only very near-field toxic effects. Some of the effects result from historical contamination, but existing discharges continue to have a deleterious effect. New petrochemical discharges in both firth and estuary appear to have a minimal impact, although the historical contamination makes it difficult to assess their effects.