60 research outputs found
Modelling regeneration in tropical forests
No full textThe mechanisms through which tropical trees, and thereby tropical forest areas, regenerate themselves remain little understood. The area of greatest ignorance in the life cycle of tree species is the early pre-seedling stage and, therefore, a set of experiments to investigate this stage was undertaken. Firstly, a field experiment to measure the secondary dispersal dynamics of three pioneer tree species in the Barro Colorado Island (BCI) forest of Panamá was carried out. Seeds were sown out in the forest and later recovered by excavating the surface soil where they were sown. The results of this project gave an estimate of the displacement and burial percentages to be expected for a small clump of seeds dispersed onto the forest floor. An assessment was made of the relative importance of abiotic and biotic mechanisms of secondary dispersal. Secondly, a modelling and field experiment used a soil water and heat transport model to characterise and predict soil drying in forest gaps. A three scenario modification to the gap-understorey dichotomy was suggested by the field measurements and model results. Thirdly, a modelling project used s simulation of the ground-level radiation regime of a forest, based on data from BCI, to investigate the relationship between high light areas and the areas delimited as gaps according to four different definitions. In addition to proposing a new method of surveying large forest areas for gaps, this project produced a well-validated model of forest structure. Finally, the results and programme produced during these three projects were synthesised into a description of several forest simulation sub-models, and possible directions for further research were outlined that may combine these into a full simulation model for a tropical forest.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Progress towards the CBD protected area management effectiveness targets
No full textThe management effectiveness of protected areas is a critically important consideration for their conservation success. Over 40 different protected area management effectiveness (PAME) data collection tools have been developed to systematically assess protected area management effectiveness. Many of these assessments have recently been collated into the Global IUCN Protected Area Management Effectiveness (PAME) database. We use the PAME database together with and the World Database on Protected Areas (WDPA) to assess current progress towards the Convention on Biological Diversity’s (CBD) 2010 and 2015 targets for PAME, which call for at least 30 per cent and 60 per cent of the total area of protected areas to have been assessed in terms of management effectiveness, respectively. We show that globally 29 per cent of the area protected has been assessed and 23 per cent of countries have reached the 60 per cent target. In addition 46 per cent of countries have reached the 30 per cent target. However, analytical results show that there are biases in the type of protected area assessed; protected areas with larger areas, and protected areas designated as National Parks (IUCN category II) are much more likely to have conducted a PAME assessment. In addition there is a paucity of PAME assessments from Europe and North America, where assessments of protected area management may already be integrated into protected area planning and monitoring systems, creating a challenge for reporting to the CBD. We further discuss the potential and limitations of PAME assessments as tools for tracking and evaluating protected area management, and the need for further assessment tools to address the ‘equity’ elements of Target 11 of the CBD
Calculating downward longwave radiation under clear and cloudy conditions over a tropical lowland forest site: an evaluation of model schemes for hourly data
No full textWhen will rejection of parasite nestlings by hosts of nonevicting avian brood parasites be favored? A misimprinting-equilibrium model
No full textIt has been suggested that discrimination and rejection of the nestlings of avian brood parasites are most likely to evolve when the parasite nestling is raised alongside the host nestlings, for example, many cowbird-host systems. Under these circumstances, the benefits of discrimination are high because the host parents may save most of their brood. However, there is a general absence of nestling rejection behavior among hosts of nonevicting parasites. In a cost-benefit equilibrium model, based on the premise that host species learn to recognize their offspring through imprinting on first breeding, we show that nestling recognition can be adaptive for hosts of cowbirds, but only under strict conditions. Namely, when host nestling survival alongside the parasite is low, rates of parasitism are high and the average clutch size is large. All of these conditions are seldom simultaneously achieved in real systems. Most importantly, the parasite nestling, on average, does not sufficiently depress host nestling survival to outweigh the costs of nestling recognition and rejection errors. Thus, we argue that nestling acceptance behaviors by hosts of nonevicting brood parasites may be explained as an evolutionary equilibrium in which recognition costs act as a stabilizing selection pressure against rejection when most of the host's offspring survive parasitism. Copyright 2003.brood parasitism; cost-benefit equilibrium; cowbirds; nestling rejection; nonevicting parasites; probability tree model
When will rejection of parasite nestlings by hosts of nonevicting avian brood parasites be favored ? A misimprinting-equilibrium model
No full textHow to fit nonlinear plant growth models and calculate growth rates: An update for ecologists
No full text1.Plant growth is a fundamental ecological process, integrating across scales from physiology to community dynamics and ecosystem properties. Recent improvements in plant growth modelling have allowed deeper understanding and more accurate predictions for a wide range of ecological issues, including competition among plants, plant-herbivore interactions and ecosystem functioning.2.One challenge in modelling plant growth is that, for a variety of reasons, relative growth rate (RGR) almost universally decreases with increasing size, although traditional calculations assume that RGR is constant. Nonlinear growth models are flexible enough to account for varying growth rates. 3.We demonstrate a variety of nonlinear models that are appropriate for modelling plant growth and, for each, show how to calculate function-derived growth rates, which allow unbiased comparisons among species at a common time or size. We show how to propagate uncertainty in estimated parameters to express uncertainty in growth rates. Fitting nonlinear models can be challenging, so we present extensive worked examples and practical recommendations, all implemented in R.4.The use of nonlinear models coupled with function-derived growth rates can facilitate the testing of novel hypotheses in population and community ecology. For example, the use of such techniques has allowed better understanding of the components of RGR, the costs of rapid growth and the linkage between host and parasite growth rates. We hope this contribution will demystify nonlinear modelling and persuade more ecologists to use these techniques
A review of methods to derive a Global Outlook product for the Hydrological Status and Outlook System (HydroSOS)
No full textReport for World Meteorological Organization
Forest community response to invasive pathogens: the case of ash dieback in a British woodland
No full textLarge-scale mortality events in forests are increasing in frequency and intensity and can lead to both intermediate- and long-term changes in these systems. Specialist pests and pathogens are unique disturbances, as they commonly target individual species that are relatively prevalent in the community. Understanding the consequences of pathogen-caused mortality requires using sometimes limited available data to create statistical models that can forecast future community states. In the last two decades, ash dieback disease has swept through Europe causing widespread mortality of Fraxinus excelsior L. (European ash) across much of its distribution. In the UK, F. excelsior is an abundant and ecologically important species. Using demographic data from an 18 ha plot in Wytham Woods, Oxfordshire, we built models that forecast the response of this forest plot to the loss of F. excelsior. We combine integral projection models and individual-based models to link models of growth, survival and fecundity to population dynamics. We demonstrate likely responses in Wytham by comparing projections under different levels of F. excelsior mortality. To extrapolate results to other systems, we test hypotheses regarding the role of abundance, spatial structure and demographic differences between species in determining community response to disease disturbance. We show that the outcome of succession is determined largely by the differing demographic strategies and starting abundances of competing species. Spatial associations between species were shown to have little effect on community dynamics at the spatial scale of this plot. Synthesis. Host-specific pests and pathogens are an increasingly important type of disturbance. We have developed a framework that makes use of forest inventory data to forecast changes in the population dynamics of remaining species and the consequences for community structure. We use our framework to predict how a typical British woodland will respond to ash dieback disease and show how vital rates, spatial structure and abundance impact the community response to the loss of a key species. Host-specific pests and pathogens are an increasingly important type of disturbance. We have developed a framework that makes use of forest inventory data to forecast changes in the population dynamics of remaining species and the consequences for community structure. We use our framework to predict how a typical British woodland will respond to ash dieback disease and show how vital rates, spatial structure and abundance impact the community response to the loss of a key species
A global-scale evaluation of extreme event uncertainty in the eartH2Observe project
No full textKnowledge of how uncertainty propagates through a hydrological land surface modelling sequence is of crucial importance in the identification and characterisation of system weaknesses in the prediction of droughts and floods at global scale. We evaluated the performance of five state-of-the-art global hydrological and land surface models in the context of modelling extreme conditions (drought and flood). Uncertainty was apportioned between the model used (model skill) and also the satellite-based precipitation products used to drive the simulations (forcing data variability) for extreme values of precipitation, surface runoff and evaporation. We found in general that model simulations acted to augment uncertainty rather than reduce it. In percentage terms, the increase in uncertainty was most often less than the magnitude of the input data uncertainty, but of comparable magnitude in many environments. Uncertainty in predictions of evapotranspiration lows (drought) in dry environments was especially high, indicating that these circumstances are a weak point in current modelling system approaches. We also found that high data and model uncertainty points for both ET lows and runoff lows were disproportionately concentrated in the equatorial and southern tropics. Our results are important for highlighting the relative robustness of satellite products in the context of land surface simulations of extreme events and identifying areas where improvements may be made in the consistency of simulation models
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