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The perpetuation of the reigning dominants in climax woodland, and the maintenance of species diversity, are discussed by reference to published work: the importance of the regeneration gap is outlined, and seed production and seedling mortality are investigated as being key factors in the establishment of young trees. Beech masting has been studied by an eight-season record of seed production by individual trees in many places, developing a unique series of objective records for England. There appears to be a basic biennial masting pattern, with a requirement for suitable climatic conditions and the proximity of other beech trees for effective cross-pollination. The effects of defoliation upon the growth of young oaks has been investigated by a controlled experiment on 196 saplings in a plot in Wolverhampton. This has contributed data on a larger population for a longer period than has previously been published. The responses of the trees to light defoliation were not marked but, as the level of defoliation increased, greater numbers of growth zones, more leaves and smaller leaves became apparent, together with impaired relative growth rates and abnormal wood structure. Ramets of cloned oak have been established in a unique outdoor plot. Their synchronous phenology permitted further analysis of defoliation responses, including field measurements of photosynthetic rates. Tree shelter tubes were shown to promote earlier second flushes and to lessen fluctuations in temperature and maintain high humidity. Observations have been made in woodlands, especially in the West Midlands where surveys have established that natural regeneration is taking place, at least in the gaps created by fallen trees. The possibility of encouraging natural regeneration of trees and ground flora on land set aside from agriculture is considered. A synthesis is made of the topics investigated, discussing the origin of the intermittent nature of the phenomena of growth spurts and masting.

The common scoter (Melanitta nigra) is a UK priority species that has experienced severe declines in breeding numbers over the last 30 years. The Flow Country in north Scotland is an internationally important wetland, where the decline of iconic species, such as the common scoter, is particularly concerning. This thesis takes a unique approach to investigating the causes of waterbird decline by combining detailed contemporary ecological data with geospatial modelling and palaeolimnological reconstructions. Detailed surveys were undertaken to characterise the current physical, chemical and biological conditions within 18 Flow Country lochs. These data were used for exploratory analyses and as explanatory variables in a general linear model that examined the predictors of common scoter loch value (SLV). Statistically significant predictors of SLV proved to be dissolved organic carbon, water depth and sediment type. The landscape scale features associated with common scoter distribution in the Flow Country were explored using a species distribution modelling (Maxent) approach. Influential landscape features were found to be proportion of surrounding forestry close to a loch, the soil moisture and bedrock geology. Two theories for common scoter decline were developed using these contemporary data sources; (i) the competitive balance between brown trout and common scoter has altered in recent decades, resulting in less food, (ii) the physico-chemistry of lochs has been altered by afforestation adversely affecting physical loch structure and/or invertebrate food supply. Theories for decline were explored using two palaeolimnological approaches. Multi-proxy top-bottom analysis of cores from 18 lochs demonstrated that these are dynamic environments which have undergone substantial change over the last 150-200 years. Multi-proxy analysis of high temporal resolution cores from four lochs indicated that the study sites have gradually become more productive over the last 150 years, with a distinct shift towards more meso-oligotrophic conditions since the 1980s. These data strongly support the theory that forestry has affected the lochs of the Flow Country, probably due to drainage and fertiliser application resulting in the lochs becoming less oligotrophic. The associated shifts in community composition could have resulted in the lochs being less profitable or suitable for common scoter who typically breed at low nutrient, oligotrophic sites.