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.

No description available.

<i>Brunchorstia pinea</i> (Karst.) Hohn [perfect = <i>Ascocalyx abietina</i> (Lagerb.) Morelet] causes shoot dieback in conifers. Damage of Scots pine plantations in Britain was first reported in the late 1970s, previously only Corsican pine was damaged. In both these species initial shoot tissue symptoms of water soaked and necrotic development in the buds and internodes were shown to develop earlier in the winter than they did in Europe and N.America. The milder winter conditons in Britain were thought to be invovled. Internode infections were relatively more frequent compared with bud infections in Scots pine than in Corsican pine. This leads to proportionally more shoot deaths due to internode girdling in Scots pine than in Corsican pine. In both species bud scales, proximal portions of the leaf scales and internode epidermis were proposed as sites of infection. Corsican pine was more susceptible to infection by <i>B.pinea</i> than Scots pine but not to development of necrosis in the tissue. Norway spruce was successfully infected which gives the first record of <i>B.pinea</i> on Norway spruce in Britain. Pyncidial production was greater on diseased Scots pines than Corsican pines and was believed to influence potential epidemic development. Variation in susceptibility within a Scots pine stand was associated with β-phellandrene levels of the cortical monoterpene component. High altitude favoured <i>B.pinea</i> as shoot vigour was low. It was proposed that prolonged periods of high humidity favoured <i>B.pinea</i> survival in shoot tissues as well as dissemination and germination of spores. Winter shading did not influence <i>B.pinea</i> development. Recent attacks of <i>B.pinea</i> in Britain were not due to increased pathogen virulence. Apothecia which are rare in Britain, were found in association with unusual environment conditions. Recent outbreaks of <i>B.pinea</i> were thought to be due to environmental conditions reducing host vigour and favouring <i>B.pinea</i> development.

Within close packed kiln dried Sitka spruce timber a disfiguring sapwood stain, caused by <I>Ophiostoma piceae</I>, frequently developed. Spoilage was investigated through research into nutritional status, moisture content and wettability of Sitka spruce timber, physical conditions within stacks of timber, moisture and nutritional requirements of <I>O. piceae</I> and infection of timber by <I>O. piceae</I>. Recommendations to minimise spoilage of kiln dried timber were made. Carbon and nitrogen compounds abundant in softwood did not result in greater growth than others. Cellulose and lignin were not degraded; <I>O. piceae</I> was unable to grow into wood. Saturated atmospheres of monoterpenes reduced growth rate, pigmentation and coremia formation on agar. Kiln dried batten surfaces contained 18% glucose, 8 times higher than green or air dried timber. However, growth was not nutritionally limited on air dried compared to kiln dried wood. The carbon/nitrogen ratio of kiln dried battens (4500:1) was 3 times higher than green timber and 9 times higher than air dried timber. The minimum relative humidity for growth of <I>O. piceae</I> was 93%, at which the moisture content of Sitka spruce sapwood was 21%. Stain coverage increased from zero at a batten moisture content of 15%, to 10% cover at 25% moisture content. Partially air dried timber developed greater stain coverage than kiln dried timber stored in similar pack types. Stain development was greater in summer than winter, when it was limited by temperature. Maximum mean batten stain cover (32%) developed in close packed wrapped partially air dried timber during warm and wet weather conditions. Kiln dried stickered timber only developed a lower mean batten surface moisture content than close packed timber during the summer. Moisture content of individual rows of battens within packs stored in the sawmill yard developed different moisture contents and stain coverage. Greater staining developed on rows with higher moisture content, which tended to be located toward the upper surfaces of packs exposed to percolating rainwater.

A description of the development and subsequent use of an integrated and semi-stochastic computer simulation model, <I>GHAFORGROM</I> (Ghana Forest Growth and Yield Simulation Program), designed to investigate forest tree dynamics and also predict growth and yield of timber in the tropical forests of Ghana is presented. This simulator considers many aspects of natural forest growth including species-group-specific individual tree diameter growth based on competition, mortality and recruitment. The 687 tree species used in these studies have been aggregated into 13 species groups. The simulator is based on a new individual tree-based distance-dependent diameter increment model. Diameter increment of a tree is predicted by a multiplicative composite function of initial diameter, relative tree dominance index, and (or) categorical site index. The based function of diameter increment on diameter is an extension of a power-exponential growth function. The relative tree dominance index of a subject tree is defined in terms of a new competition index. This index is the sum of the ratios of volume of overtopping competing trees to the volume of the subject tree, where the competitor trees are within a radius of 20 m of the subject tree for large-sized trees and 1.5 m of the subject tree for medium- and small-sized trees. The probability of mortality of a tree is defined in the form of a logistic function based on the explanatory variables of functions of diameter and stand density, including basal area per hectare and volume per hectare for each species group. The total amount of recruitment at 10 cm diameter is predicted as a linear function of stand basal area, stand volume and categorical site variables. It is hoped that the model will provide practical steps to improved natural tropical forest management in Ghana, leading to higher sustainable timber yields.

Increasing demand for timber, fuelwood and other forest products has outstripped production in many areas of the semi-arid tropics, leading to deforestation and land degradation resulting from erosion and nutrient depletion. Agroforestry offers the potential to provide forest products, improve productivity and reduce soil erosion and environmental degradation. However, as previous reports have shown that competition between trees and crops for water in semi-arid areas adversely affects crop yields, attention has turned towards studies of the existing practice of boundary planting, where low tree planting densities and the associated benefits of land demarcation and soil stabilisation increase the viability of incorporating trees into crop land. The aim is to select and manage tree species in ways that limit their negative effect on crop yields and improve the overall value of the system. The present study was carried out at Machakos (1° 33' S, 37° 14' E, altitude 1660 m) in the Kenyan highlands, where the bi-modal annual rainfall of c. 740 mm is divided approximately equally between two rainy seasons (short rains, October-February, long rains, March July). The experiment was set up in April 1993 to examine the influence of tree/crop interactions on system productivity. Each 18 x 18 m plot, except for the sole crop plots, contained a central row of trees planted at 1 m spacing. Four overstorey agroforestry treatments were examined between March 1996 and March 1998; these included two indigenous species, Croton megalocarpus and Melia volkensii, and two exotic species from Central America, Senna spectabilis and Gliricidia sepium. Beans (Phaseolusulgaris) and maize (Zea mays) were grown during the short and long rains respectively. M. volkensii and S. Spectabilis exhibited similar leafing phenology patterns, losing almost all leaf cover during the long dry season (July-October) and flushing before the ensuing rains. During the short dry season, S. spectabilis lost few leaves, whilst M. volkensii lost some leaves before flushing prior to the onset of the long rains. M. volkensii lost a large proportion of its leaf cover during the 1997/98 short rains due to the unusually high soil moisture content. C. megalocarpus although predominantly evergreen, lost a large proportion of its leaves during dry periods, whereas leaf area increased rapidly under wetter conditions. G. sepium had one annual period of low leaf cover during the long dry season and did not regain full leaf cover until mid-way through the short rains. The three-dimensional model of canopy photosynthesis and transpiration, MAESTRA, was parameterised for C. megalocarpus and M. volkensii using existing models to describe the response of photosynthesis to light and temperature and stomatal responses to light and vapour pressure deficit. The photosynthesis model fitted the experimental data well, but stomatal conductance in C. megalocarpus, although showing responses to light and vapour pressure deficit, was not closely correlated with ambient environmental conditions. M. volkensii had higher leaf area than C. megalocarpus for most of the 18 month simulation period, comprising three rainy and three dry seasons; modelled assimilation for this period was 49 % greater in M. volkensii, while canopy water use efficiency and transpiration were respectively 35 and 11 % higher. These differences accounted for the more rapid growth rate and greater competition with adjacent crops associated with M. w1kenrii relative to C. megalocarpus. Above-ground woody biomass production was greatest in M. volkensii, followed by S. spectabilis, C. megalocarpus and G. sepium; production during the fourth and fifth years after planting ranged between 2.8 and 4.9 t ha-¹ yr¹. Crop production in the agroforestry treatments was always lower than in sole crops due to below-ground competition for water and, in seasons with higher water availability, shading by the trees. Of the agroforestry systems examined, seed production for beans was highest under M. volkensii and G. sepium, followed by C. megalocarpus and S. spectabilis. Grain production in maize was greatest under C. megalocarpus, followed by G. sepium, S. spectabils and M. volkensii. Mean annual aboveground biomass production including maize grain and stover, bean seed, woody biomass and tree leaves in the M. volkensii treatment exceeded that for the sole crop plots, even though rainfall during 1996 and 1997 was only 61 and 95 % of the long term average. Although the biomass production of leaves was not estimated for S. spectabilis and G. sepium, the results obtained suggested that biomass production was greater than that obtained under sole crop cropping. The inverse correlation between tree and crop yield suggests that the value of the tree products must exceed the associated crop losses if benefits are to be obtained from agroforestry. M. volkensii is valued in areas of Kenya where markets for its products exist and therefore shows great promise for extension in semi-arid areas; where necessary, pruning may be used to reduce competition with crops and increase the length of clear bole. C. megalocarpus is widely used as a shade tree in East Africa and seems well suited for this purpose as its impact on adjacent crops was least of all the tree species examined. S. spectabilis, although having straight unbranched stems, exhibited a level of competition with adjacent crops that would necessitate a high value for its timber products to warrant its adoption. The least suitable tree species of those examined was G. sepium, whose poor form and susceptibility to attack by fungal pathogens and insects severely undermined its potential value for use in agroforestry systems.

No description available.

No description available.

Artificial inoculations in the Cupressaceae proved that <I>Seiridium cardinale</I> was more virulent than <I>S.cupressi</I> and <I>S.unicorne. Cupressus macrocarpa</I> was found to be highly susceptible to <I>Seiridium</I> canker, <I>C.sempervirens</I> very susceptible, while <I>C.torulosa</I> and <I>C.arizonica</I> were moderately susceptible. <I>Chamaecyparis lawsoniana</I> was highly resistant to <I>S.cardinale</I>, but very susceptible to <I>S.unicorne</I> and moderately susceptible to <I>S.cupressi</I>. Intraspecific variation in susceptibility to <I>S.cardinale</I> was found in <I>C.sempervirens. S.cupressi</I> was more pathogenic than <I>S.unicorne</I> on <I>C.macrocarpa, C.arizonica</I> and <I>C.torulosa</I>, whereas it was less pathogenic on <I>C.sempervirens</I>. Mature bark proved to be more resistant to <I>Seiridium</I> canker than young bark. Low variability in pathogenicity of <I>S.cardinale</I> was found, with only one isolate out of eight proving to be a weaker pathogen. Histological examination of bark of cypress seedlings following infection with <I>S.cardinale</I> revealed the formation of strong necrophylactic periderm as an important resistance mechanism against <I>Seiridium</I> attack, and was particularly marked in <I>C.lawsoniana</I>. Strong necrophylactic periderms were detected in resistant and tolerant clones of <I>C.sempervirens</I>, whereas weak or a series of easily re-invaded ones were found in susceptible clones. Variations in pathogenicity of <I>Seiridium</I> in <I>in vitro</I> inoculations of micropropagated cypress shoots paralleled results found in the glasshouse. Wounding of micropropagated shoots significantly increased the size of lesions caused by all three <I>Seiridium</I> spp. In axenic conditions, hyphae of <I>Seiridium</I> spp. penetrated host tissues through stomatal apertures or directly through the cuticle. Under these conditions, infected tissues of <I>C.lawsoniana</I> formed ligno-suberized barriers as a result of fungal invasion, whereas those of <I>C.sempervirens</I> did not.

This work traces the Maltese Islands' forest history. In prehistoric time the flora changed accordingly to climatic oscillations. The first people of Malta were Neolithic. Their forest clearance and the drying up of the climate led to population collapse. After a period of time, the forest may have recovered allowing colonisation by a Bronze Age people. The Classical Era where Malta's vegetation was changed and arable agriculture prevailed following this. Olive industry finds dating from the Roman period reveal that olive cultivation was widespread. The Arab period saw the depopulation of the Islands allowing forest recovery to take place. The medieval period saw large areas turned to pasture. Grazing reduced the forest to much garrigue-steppe. Later land enclosure for arable agriculture prepared the way for Malta's traditional landscape with cotton cultivation becoming predominant. During the Knights of St. John period (1530-1798), Buskett and other gardens were established. Documentation reveals the survival of holm oak remnants at Buskett and Wied Hazrum. Drawings of the time depict trees near buildings. There also exists a mid-17^th century description of Gozo's vegetation and a tree name list from the 18^thcentury. In the mid-18^th century a project for the widespread cultivation of white mulberries was made. In 1798 the French occupation began, although soon the Maltese rebelled. The revolt lasted two years, during which many gardens were devastated. Reconstruction took up most of the 19^th century. Agricultural expansion left little space for trees in the landscape, creating a treelessness paradigm in the people's culture, although 20^th century tree planting is changing this thus Malta is becoming greener.