Keith Rennolls

The effect of spatial scale on interactions between two weevils and their parasitoid

1. The effect of spatial scale on the interactions between three hymenopteran parasitoids and their weevil hosts was investigated. The parasitoid Mesopolobus incultus (Walker) parasitised Gymnetron pascuorum Gyll.; the parasitoids Entodon sparetus (Walker) and Bracon sp. parasitised Mecinus pyraster Herbst. Both of these weevils develop inside the seedhead of Plantago lanceolata L. but occupy different niches. Seedheads were sampled annually from 162 plants at each of two experimental sites consisting of a series of habitat patches of two distinct sizes. Data were analysed from three site‐years.

Forest height growth modelling

Abstract There are many functional forms which may be used to model height against age, and a variety of methods by which the model parameters may be estimated. There are four main questions that the forest height modeller needs to decide upon. 1. (1) Should each height-age trajectory be modelled separately? 2. (2) What error structure model should be adopted? 3. (3) How should the mortality process be treated? 4. (4) Should measurement errors be taken into account? Possible answers to these questions are considered in the context of the much used Chapman-Richards family of growth models. The appropriate method of estimation follows from the choices that the modeller makes in relation to these questions. Most published work on height growth modelling are regression based, but do not explicitly model error structures and use the corresponding fitting criterion. In contrast, there is the approach which takes growth trajectories as realisations of a stochastic process, with the error structure to be used in the fitting process arising naturally out of the stochastic formulation. Two (essentially equivalent) approaches to stochastic growth curve modelling are reviewed; a diffusion model formulation, and a stochastic differential equation formulation, in which the expected growth curve is the integrated form of the Chapman-Richards growth model. A simpler formulation is used to obtain a descriptive representation of a complete set of height growth trajectories obtained from Sitka spruce sample plots. The simple model adopted ‘overcomes’ the complications of correlated errors that traditionally arise in the analysis of longitudinal data but avoids the sophisticated model specification of the stochastic models.

The effect of spatial scale on interactions between two weevils and their food plant

The effect of spatial scale on the interactions between the weevils Gymnetron pascuorum Gyll. and Mecinus pyraster Herbst and their host plant, ribwort plantain Plantago lanceolata L., was studied. Both weevils developed in plantain seedheads but occupied different niches within the seedhead. Seedheads were sampled annually from 162 plants at each of two experimental sites consisting of a series of habitat patches of two distinct sizes. Data were analysed from three site-years. Our results suggest that the density of available seedheads varied among years and this had a direct effect on abundance. M. pyraster, which develops in the stem within the seedhead, was more sensitive to changes in seedhead density than was G. pascuorum, which develops within the seeds themselves. The presence of a hedgerow along one side of the experimental site affected the pattern of colonisation of newly-created habitat patches by G. pascuorum but not by M. pyraster. Changes in spatial scale did not affect the variability of seedhead and insect densities. G. pascuorum had an aggregated distribution at all the spatial scales considered, but the distribution of M. pyraster was very scale dependent. The distributions of the two weevil species were positively associated amongst infested plants but not amongst infested seedheads. Behavioural and ecological factors that could explain the results of the data analyses are discussed.

Use of Genetic Algorithms for Optimal Topology Determination in Back Propagation Neural Networks

A genetic algorithm is applied to evolve neural network topologies suitable for given problem domains. Certain concepts, from the fields of statistics and genetics, are considered with a view to possible future improvements to the genetic algorithm.

Pipe-model theory of stem-profile development

Abstract The relationship between stem diameter (or sapwood areas), and leaf area has been used in the literature to obtain canopy-driven models of stem form and to estimate canopy sizes from stem measurements. This paper considers pipe models of trees in which a pipe is a vascular (fluid-conducting) tube connecting leaves to roots. A general treatment of such models is considered, and some single descriptive ratio and regression-type relations between conducting cross-sectional area and canopy leaf area are derived. The morphological form of pipes and the relationship between cohorts of pipes and annual rings are discussed. The empirical evidence concerning the functional form of some parameters in the general vascular pipe model is reviewed, with the conclusion that the evidence is not entirely consistent. Finally, a simple heuristic canopy-driven stem-form model is developed which allows non-identity of pipe cohorts and annual rings. Some simple results from a computer implementation of this model are displayed.

Potential contributions of statistics and modelling to sustainable forest management: review and synthesis.

University of Greenwich, UK. k.rennolls@gre.ac.uk Technical University of Lisbon, Portugal. magatome@isa.utl.pt USDA Forest Service, St. Paul, USA. rmcroberts@fs.fed.us Southern Cross University, Australia. JVanclay@scu.edu.au University of British Columbia, Vancouver, Canada. Valerie.LeMay@ubc.ca National Taiwan University, Taipei, Taiwan. btguan@ntu.edu.tw University of Illinois, Urbana, USA. gertner@uiuc.edu

Models and tools for an integrated European environmental management and decision support system, (IEEMDSS)

This work proceeds from the assumption that a European environmental information and communication system (EEICS) is already established. In the context of primary users (land-use planners, conservationists, and environmental researchers) we ask what use may be made of the EEICS for building models and tools which is of use in building decision support systems for the land-use planner. The complex task facing the next generation of environmental and forest modellers is described, and a range of relevant modelling approaches are reviewed. These include visualization and GIS; statistical tabulation and database SQL, MDA and OLAP methods. The major problem of noncomparability of the definitions and measures of forest area and timber volume is introduced and the possibility of a model-based solution is considered. The possibility of using an ambitious and challenging biogeochemical modelling approach to understanding and managing European forests sustainably is discussed. It is emphasised that all modern methodological disciplines must be brought to bear, and a heuristic hybrid modelling approach should be used so as to ensure that the benefits of practical empirical modelling approaches are utilised in addition to the scientifically well-founded and holistic ecosystem and environmental modelling. The data and information system required is likely to end up as a grid-based-framework because of the heavy use of computationally intensive model-based facilities.

Requirements and design of an integrated European environmental information communication system, (IEEICS)

The needs for various forms of information systems relating to the European environment and ecosystem are reviewed, and limitations indicated. Existing information systems are reviewed and compared in terms of aims and functionalities. We consider TWO technical challenges involved in attempting to develop an IEEICS. First, there is the challenge of developing an Internet-based communication system which allows fluent access to information stored in a range of distributed databases. Some of the currently available solutions are considered, i.e. Web service federations. The second main challenge arises from the fact that there is general intra-national heterogeneity in the definitions adopted, and the measurement systems used throughout the nations of Europe. Integrated strategies are needed.

A new local estimator of regional species diversity, in terms of ‘shadow species’, with a case study from Sumatra

In a local biodiversity inventory the locally rare species are of particular importance. The main problem of sample-based inventories is that many species are so rare that they will not be observed. The observed frequencies of species in the sample provide an estimate of the species proportion in the population. This may be used to estimate the number of species which exist in the population, but which were not observed in the sample (shadow species). This non-parametric approach provides an unbiased estimate of the relative frequency distribution of the species in the population, which differs very significantly from the sample distribution, particularly for the rare species. The approach leads to a new and ecologically meaningful estimator of the Renyi–Hill generalized species diversity measure, which includes species abundance, the Shannon–Weaver and Simpsons diversity measures, amongst others. The use of the estimator is illustrated on data from a biodiversity inventory of trees on a 3-ha forest sample plot in Sumatra.

On the persistence of computer dreams - an application framework for robust adaptive deployment

The anticipated rewards of adaptive approaches will only be fully realised when autonomic algorithms can take configuration and deployment decisions that match and exceed those of human engineers. Such decisions are typically characterised as being based on a foundation of experience and knowledge. In humans, these underpinnings are themselves founded on the ashes of failure, the exuberance of courage and (sometimes) the outrageousness of fortune. We describe an application framework that will allow the incorporation of similarly risky, error prone and downright dangerous software artifacts into live systems - without undermining the certainty of correctness at application level. We achieve this by introducing the notion of application dreaming.