Comparative analysis of policies to deal with wildfire risk
Carreiras, M. ; Ferreira, A.D.J. ; Valente, S. ; Fleskens, L. ; Gonzales-Pelayo, O. ; Rubio, J.L. ; Stoof, C.R. ; Coelho, C.O.A. ; Ferreira, C.S.S. ; Ritsema, C.J. - \ 2014
Land Degradation and Development 25 (2014)1. - ISSN 1085-3278 - p. 92 - 103.
public-participation - forest owners - fire regimes - management - portugal - perspective - examples - impacts - system - region
Fires are the main driver of land degradation in forest areas in Mediterranean sub-humid regions and are likely to increase as a result of climate and other global changes. To prevent deleterious processes induced by fire, several policies and strategies have been implemented at national and regional scales. We perform a comparative study of policies and strategies of Portuguese and Spanish (Comunitat Valenciana) cases in order to assess the differences between them and identify their roles in forest fire prevention and in combating and mitigating impacts. To this end, we analyse the sustainability objectives stated in the legislation of each country to identify the strategies used to deal with forest fires and the extent to which they are integrated to achieve the sustainability objectives they pursue. The comparative analysis includes an assessment of sustainability, evaluated by the explicitness of the objectives, and identification of how the lines of action contribute to reach these objectives. We found different levels of complexity and that the adoption or rejection of some of the techniques is closely related to the tradition and the experience of local communities. This analysis highlights the importance of local characteristics and the stakeholders, involvement in designing effective strategies to reduce fire risk
Dynamic friction coefficient measurement of granular fertiliser particles
Grift, T.E. ; Kweon, G. ; Hofstee, J.W. ; Piron, E. ; Villette, S. - \ 2006
Biosystems Engineering 95 (2006)4. - ISSN 1537-5110 - p. 507 - 515.
spread pattern-analysis - spinning disc spreader - simulation-model - tool spat - examples
Theoretically, in the absence of friction, when a particle is sliding along a straight radial vane, mounted on a flat disc which is spinning at a constant rotational velocity, its radial and tangential velocity are equal at any point along the vane. In reality, there are disturbances causing I difference between the radial and tangential velocities, Such as drop mechanics, mechanical (Coulomb) friction. aerodynamic effects, as well as particle bouncing effects against the vane and other particles. These factors were Jumped together and termed the 'friction coefficient'. The tangential particle velocity at the discharge point was assumed constant, since the particle was assumed in direct contact with the vane until emanation. The radial particle velocity was measured at a distance of 0.4m from the disc edge with an optical sensor developed in earlier research. A theoretical analysis was used to obtain equations that allowed determination of the mechanical friction coefficient of individual particles. based on the measured radial velocity and the assumed constant tangential velocity. For experiments, a commercial single disc spreader fitted with a flat disc and straight radial vanes was used. The results for urea fertiliser showed near-Gaussian distribution of the friction coefficients, with a mean value of 0.36 and a standard deviation of 0.1 among 812 measurements. In addition, an inversely proportional relationship was found between the friction coefficients and the particle diameters.
Epidemic spread of a lesion-forming plant pathogen - analysis of a mechanistic model with infinite age structure
Powell, J.A. ; Slapnicar, I. ; Werf, W. van der - \ 2005
Linear Algebra and Its Applications 398 (2005). - ISSN 0024-3795 - p. 117 - 140.
focus expansion - linear determinacy - invasion speed - dispersal - disease - competition - demography - examples
In many invasive species the number of invading individuals is proportional to the time since the population has established (its `age`), not its density. Examples include plant diseases which spread via lesions, which grow on leaves with time and produce ever-increasing amounts of infective material. In this paper, a Leslie matrix model is developed to represent the age structure and reproductive potential due to lesions, particularly for mycelial colonies associated with fungal plant pathogens. Lesion size (and therefore age) is bounded by leaf size, which can be quite large, leading to large matrices. The production of new mycelial colonies is affected by dispersal of spores from the reproductive age-classes of existing colonies, so that dispersal must be included in the matrix model by convolution operators. The infinite-dimensional version of the model is more tractable than the large, finite models, and is used to determine an upper bound on rates of invasion. The model is applied to model the life history of the oömycete Phytophthora infestans, causal agent of potato late blight disease. It is shown that the infinite-dimensional model closely predicts behavior of finite-dimensional models, cut off at certain age-classes of lesions because of finite leaf size. Surprisingly, the infinite-dimensional model is more tractable than finite-dimensional model versions, yielding robust results for practical situations