Encontrados 48 documentos, a visualizar página 1 de 5
Wildfire selectivity for land cover type: does size matter ?
Barros, Ana M.G.; Pereira, J.M.C.Previous research has shown that fires burn certain land cover types disproportionally to their abundance. We used quantile regression to study land cover proneness to fire as a function of fire size, under the hypothesis that they are inversely related, for all land cover types. Using five years of fire perimeters, we estimated conditional quantile functions for lower (avoidance) and upper (preference) quantil...
A test for directional-linear independence, with applications to wildfire orien...
GarcÃa-Portugués, Eduardo; Barros, Ana M.G.; Crujeiras, Rosa M.; González-Manteiga, Wenceslao; Pereira, J.M.C.Original Paper ; A nonparametric test for assessing the independence between a directional random variable (circular or spherical, as particular cases) and a linear one is proposed in this paper. The statistic is based on the squared distance between nonparametric kernel density estimates and its calibration is done by a permutation approach. The size and power characteristics of various variants of the test a...
Spatial characterization of wildfire orientation patterns in California
Barros, Ana M.G.; Pereira, J.M.C.; Moritz, Max A.; Stephens, Scott L.Using 100 years of fire perimeter maps, we investigate the existence of geographical patterns in fire orientation across California. We computed fire perimeter orientation, at the watershed level, using principal component analysis. Circular statistics were used to test for the existence of preferential fire perimeter orientations. Where perimeters displayed preferential orientation, we searched for evidence of...
Soil nitrogen availability in olive orchards after mulching legume cover crop r...
Rodrigues, M.A.; Correia, C.M.; Claro, Ana Marília; Ferreira, I.Q.; Barbosa, José Carlos; Moutinho-Pereira, J.M.; Bacelar, E.A.; Fernandes-Silva, A.A.A natural source of nitrogen (N) is needed to increase soil fertility in traditional olive orchards and to maintain the N nutritional status of olive trees. With this aim, we studied the introduction of legume cover crops in two olive orchards, which were converted into mulches and left on the ground as phytomass after they had been cut. The experiments were carried out in Suçães and Qta do Carrascal, NE Portug...
Sustainable management of olive rainfed orchards by the introduction of legumin...
Correia, C.M.; Brito, Cátia; Fernandes-Silva, A.A.; Bacelar, E.A.; Gonçalves, B.M.; Ferreira, H.; Arrobas, Margarida; Moutinho-Pereira, J.M.The olive sector has a crucial economic, social, cultural and ecological relevance in the Mediterranean region, where tillage and herbicides application are still generalized practices. However, these practices oppose the recommendations of UE Common Agricultural Policy and thus, management methods that decrease requirement for agricultural chemicals are needed to reduce adverse environmental impacts. Moreover,...
Green manure legumes affect seasonal soil and leaf CO2 exchange rates in an oli...
Correia, C.M.; Brito, Cátia; Fernandes-Silva, A.A.; Bacelar, E.A.; Gonçalves, Berta; Ferreira, Helena; Moutinho-Pereira, J.M.; Arrobas, MargaridaManagement methods that decrease requirement for agricultural chemicals are needed to reduce adverse environmental impacts. Moreover, they can play an important role in atmospheric C02 emission and fixation. We propose green manure legumes to reduce erosion, soil compaction and nitrate pollution, to improve biodiversity, soil carbon sink and fertility, to save fossil fuels and to increase yield and the nutritio...
Short and long-term benefits of white lupin as a cover crop on olive physiology
Brito, Cátia; Moutinho-Pereira, J.M.; Bacelar, E.A.; Gonçalves, Berta; Ferreira, Helena; Santos, D.; Rodrigues, M.A.; Correia, C.M.Several positive effects of cover crops in orchards have been documented, including improvement on soil properties, which are reflected on tree physiological performance and yield. The use of legume species, such as white lupin, can provide other gains since they can fix atmospheric N2, reducing the cost with N fertilizers. However, this species need to be sown every year, which is costly and laborious. So, we ...
Oxidative stress and antioxidant responses in olive tree subjected to cover cro...
Correia, C.M.; Brito, Cátia; Santos, D.; Bacelar, E.A.; Gonçalves, Berta; Ferreira, Helena; Moutinho-Pereira, J.M.; Rodrigues, M.A.Since Mediterranean basin is particularly vulnerable to present and future climate variability and climate change, olive tree will experiment some hard changes in its environment. Under adverse conditions, imbalances in metabolic processes may lead to increased accumulation of ROS, forming a potential threat of oxidative damage to cells. We propose green manure legumes to shift tillage, in order to improve soil...
Fire frequency analysis in Portugal (1975-2005), using Landsat-based burnt area...
Oliveira, Sofia L.J.; Pereira, J.M.C.; Carreiras, João M.B.Fire frequency in 21 forest planning regions of Portugal during the period 1975–2005 was estimated from historical burnt area maps generated with semi-automatic classification of Landsat Thematic Mapper (TM) satellite imagery. Fire return interval distributions were modelled with the Weibull function and the estimated parameters were used to calculate regional mean, median and modal fire return intervals, as ...
Identifying geographical patterns of wildfire orientation: a watershed-based an...
Barros, Ana M.G.; Pereira, J.M.C.; Lund, Ulric J.We searched for geographical patterns in the orientation of wildfires, using watersheds as spatial support for the analysis. An 1975–2005 annual fire atlas of mainland Portugal was used to compute the orientation of fire perimeters and watersheds, using principal component analysis. Circular statistics were employed to test for the existence of a preferred, as opposed to random, mean fire orientation in each ...
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