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- Avaliação do curso de Engenharia FlorestalPublication . Almeida, C.A.M.; Quinta-Nova, L.C.; Caseiro, Nuno; Rodrigues, A.M.; Delgado, F.M.G.; Frazão, Francisco; Pereira, Fernando Leite; Martins, Manuel; Morais, Maria CristinaO relatório resulta do trabalho de avaliação ao curso de Engenharia Florestal levado a cabo pela equipa de Auto-Avaliação da Escola Superior Agrária de Castelo Branco. Esta equipa, designada pelo conselho científico com a finalidade de proceder a todas as solicitações de avaliação tanto dos cursos como da instituição, é basicamente composta por um coordenador e um elemento de cada unidade departamental. Decorrente do tipo de curso que se está a avaliar juntam-se à equipa os respectivos coordenadores do curso e um relator. Além deste elementos participaram também neste trabalho um representante dos alunos (designado pela associação de estudantes) e dois funcionários representantes do pessoal administrativo e do pessoal não docente. Em termos metodológicos optou-se pelo seguimento do guião proposto pelo CNAVES, tendo-se recolhido informação de diversos modos: pesquisa documental e bases de dados nos serviços administrativos, inquéritos auto administrados a alunos, docentes e funcionários, inquérito postal aos diplomados e entrevistas directas às entidades empregadoras. Uma vez recolhida e tratada a informação procedeu-se à sua análise crítica tendo como referência os trabalhos de avaliação que até então decorreram relativamente à Escola e ao curso de Produção Florestal que antecedeu o actual curso de Engenharia Florestal.
- Radiation balance of an isolated holm oak tree (Quercus rotundifolia Lam.) in a mediterranean savannah-type woodlandPublication . Pereira, Fernando Leite; Valente, Fernanda; David, Jorge SoaresIn closed canopy forests the energy absorbed by the trees can be adequately estimated solely from the vertical radiation fluxes. However, in isolated or widely spaced trees this approach is no longer valid and radiation fluxes in all directions must be accounted for. An adequate estimate of the tree available energy is critical to model and calculate both interception losses and transpiration. Within a study where interception loss in a sparse evergreen oak woodland (montado) of Southern Portugal is evaluated and mod¬elled, the net amount of radiant energy absorbed by an isolated holm oak tree (Q) was measured under different radiation conditions. The measuring and calculating proce¬dure was based on the integration of the flux density of net radiation (Rn) at different points of a cylindrical surface (S) enclosing the tree crown. A set of 4 net radiome¬ters were used: one at a fixed position, on the top of the crown, and the remaining 3 mounted on a standing structure that could be moved around the tree to measure Rn fluxes through the inferior and lateral sides. Measurements of Q were made for 8 dif¬ferent days, during the first 3 months of 2006. Night time measurements of Rn were also done, but with the net radiometers at fixed positions around the tree. The meteoro¬logical conditions during the measurements included clear sky and cloudy days, some of which with light rain. Net radiation at the top of the crown accounted for about 72 % of the total energy absorbed by the tree, and this is reflected by the good linear fit between Q and Rn above the crown. Meteorological conditions seem to have some influence on this relationship, as suggested by the differences on the adjusted linear models when total, clear sky, cloudy or rainy data sets were used. The occurrence of rain tends to cause a slight increase in Q in comparison to dry conditions, for identical levels of Rn. Q also shows a strong linear response to solar radiation (Rs), given the dependence of net radiation upon short wave radiation. The same happens with the component of Q received by the top crown surface. However, energy absorbed lat¬erally is much less dependent on Rs, and the inferior component of Q is completely independent of solar radiation. Under conditions when rainfall interception is most likely to occur, i.e. cloudy/rainy days, the daily time-course of Q follows closely those of Rs and Rn, with a maximum of only 75 W m-2 (expressed per unit of leaf area). Similar maximum daily values were observed in other studies with different species but under similar weather conditions. During the night, net radiation should not have a significant spatial variability and Rn around the canopy should be relatively homo¬geneous. Accordingly, night time estimates of Q were obtained from measurements of Rn at fixed positions, which were considered representative of the Rn fluxes around the tree.
- Transpiração em povoamentos adultos de eucalipto e de pinheiro bravoPublication . Pereira, Fernando Leite; David, Jorge Soares; Madeira, Manuel ValerianoFoi realizado um estudo com o objectivo de quantificar os consumos de água por transpirarão em dois povoamentos adultos de eucalipto (Eucalyptus globulus Labbill) e de pinheiro bravo (Pinus pinaster Aiton), respectivamente. A estimativa destes consumos foi feita recorrendo a dois métodos distintos: o balanço de água no solo e o modelo de Penman-Monteith (aplicado numa versão unilaminar). Os resultados obtidos indicam que, em qualquer dos povoamentos, a transpiração está sobretudo dependente da disponibilidade de água no solo, tendo-se verificado que a transpiração acumulada ao longo dos anos de 1992 e 93 é muito próxima do valor da precipitação efectiva no mesmo período. A realização de medições de condutância estomática revelou que ambas as espécies apresentam padrões de variação horária e sazonal, que traduzem a capacidade destas espécies em controlarem eficazmente as perdas de água por transpiração, quer quando aumenta a secura do ar, quer quando se reduz a humidade no solo. A comparação directa das estimativas da transpiração fornecidas pelos dois métodos utilizados revelou algumas diferenças que, no entanto, parecem aceitáveis tendo em conta que estes métodos são concebidos para aplicações em escalas temporais distintas.
- Modelling interception loss from evergreen oak Mediterranean savannas: Application of a tree-based modelling approachPublication . Pereira, Fernando Leite; Gash, John H.C.; David, Jorge Soares; David, Teresa S.; Monteiro, Paulo R.; Valente, FernandaIn a previous study, it was shown that an isolated, fully saturated tree-crown behaves like a wet bulb, allowing evaporation of intercepted rainfall to be estimated by a simple diffusion equation for water vapour. This observation was taken as the basis for a new approach in modelling interception loss fromsavanna-type woodland, whereby the ecosystem evaporation is derived by scaling up the evaporation from individual trees, rather than by considering a homogeneous forest cover. Interception loss from isolated trees was estimated by combining the aforementioned equation for water vapour flux with Gash’s analytical model. A new methodology, which avoids the subjectivity inherent in the Leyton method, was used for estimating the crown storage capacity. Modelling performance was evaluated against data from two Mediterranean savanna-type oak woodlands (montados) in southern Portugal. Interception loss estimates were in good agreement with observations in both sites. The proposed modelling approach is physically based, requires only a limited amount of data and should be suitable for the modelling of interception loss in isolated trees and savannatype ecosystems.
- A tree-based approach for modelling interception loss from evergreen oak mediterranean savannasPublication . Pereira, Fernando Leite; Gash, John H.C.; David, Jorge Soares; David, Teresa S.; Monteiro, Paulo R.; Valente, FernandaEvaporation of rainfall intercepted by tree canopies is usually an important part of the overall water balance of forested catchments and there have been many studies dedicated to measuring and modelling rainfall interception loss. These studies have mainly been conducted in dense forests; there have been few studies on the very sparse forests which are common in dry and semi-arid areas. Water resources are scarce in these areas making sparse forests particularly important. Methods for modelling interception loss are thus required to support sustainable water management in those areas. In very sparse forests, trees occur as widely spaced individuals rather than as a continuous forest canopy. We therefore suggest that interception loss for this vegetation type can be more adequately modelled if the overall forest evaporation is derived by scaling up the evaporation from individual trees. The evaporation rate for a single tree can be estimated using a simple Dalton-type diffusion equation for water vapour as long as its surface temperature is known. From theory, this temperature is shown to be dependent upon the available energy and windspeed. However, the surface temperature of a fully saturated tree crown, under rainy conditions, should approach the wet bulb temperature as the radiative energy input to the tree reduces to zero. This was experimentally confirmed from measurements of the radiation balance and surface temperature of an isolated tree crown. Thus, evaporation of intercepted rainfall can be estimated using an equation which only requires knowledge of the air dry and wet bulb temperatures and of the bulk tree-crown aerodynamic conductance. This was taken as the basis of a new approach for modelling interception loss from savanna-type woodland, i.e. by combining the Dalton-type equation with the Gash’s analytical model to estimate interception loss from isolated trees. This modelling approach was tested using data from two Mediterranean savanna-type oak woodlands in southern Portugal. For both sites, simulated interception loss agreed well with the observations indicating the adequacy of this new methodology for modelling interception loss by isolated trees in savanna-type ecosystems. Furthermore, the proposed approach is physically based and requires only a limited amount of data. Interception loss for the entire forest can be estimated by scaling up the evaporation from individual trees accounting for the number of trees per unit area.
- Evapotranspiration from a Mediterranean evergreen oak savannah: The role of trees and pasturePublication . Paço, Teresa A.; David, Teresa S.; Henriques, Manuel O.; Pereira, João S.; Valente, Fernanda; Banza, João; Pereira, Fernando Leite; Pinto, Clara; David, Jorge SoaresMediterranean evergreen oak woodlands of southern Portugal (montados) are savannah-type ecosystems with a widely sparse tree cover, over extensive grassland. Therefore, ecosystem water fluxes derive from two quite differentiated sources: the trees and the pasture. Partitioning of fluxes according to these dif- ferent sources is necessary to quantify overall ecosystem water losses as well as to improve knowledge on its functional behaviour. In southern Iberia, these woodlands are subjected to recurrent droughts. Therefore, reaction/resilience to water stress becomes an essential feature of vegetation on these ecosys- tems. Long-term tree transpiration was recorded for 6 years from a sample of holm oak (Quercus ilex ssp. rotundifolia) trees, using the Granier sap flow method. Ecosystem transpiration was measured by the eddy covariance technique for an 11-month period (February to December 2005), partly coincident with a drought year. Pasture transpiration was estimated as the difference between ecosystem (eddy covari- ance) and tree (sap flow) transpiration. Pasture transpiration stopped during the summer, when the sur- face soil dried up. In the other seasons, pasture transpiration showed a strong dependence on rainfall occurrence and on top soil water. Conversely, trees were able to maintain transpiration throughout the summer due to the deep root access to groundwater. Q. ilex trees showed a high resilience to both sea- sonal and annual drought. Tree transpiration represented more than half of ecosystem transpiration, in spite of the low tree density (30 trees ha1) and crown cover fraction (21%). Tree evapotranspiration was dominated by transpiration (76%), and interception loss represented only 24% of overall tree evaporation.
- Modelling rainfall interception by an olive-grove/pasture system with a sparse tree canopyPublication . Valente, Fernanda; Gash, John H.C.; Nóbrega, Cristina; David, Jorge Soares; Pereira, Fernando LeiteThe rainfall intercepted by an isolated olive tree was measured in a traditional olive-grove/ pasture system with a sparse canopy cover. Results from a two-year period of observations are presented. The data are then used to test models of the interception process in this type of agricultural system. Modelling was performed at the single tree level using the sparse-forest version of the Gash analytical model combined with two other methodologies: the wet bulb approach, to estimate the evaporation rate from the wet canopies of individual olive trees, and a newly developed procedure to estimate the canopy structure parameters. Good model performance was achieved at the storm level with model simulations within 1.5% of the observed value, clearly within the expected error of interception loss measurements.
- Reabilitação do coberto lenhoso ribeirinho nas margens da Lagoa dos Linhos, Mata Nacional do UrsoPublication . Fabião, André; Carneiro, M.; Fabião, António; Pereira, Fernando Leite; Cancela, J.H.; Pimentel, F.To test the viability of riparian cover restoration using common methods of forestation, afield trial consisting on installation of riparian species was performed at Lagoa dos Linhos (Urso National Forest). The species utilized were: Quercus faginea, Q. robur, Salix atrocinerea, Crataegus monoggyna, Populus nigra, Tamarix africana, Acer campestre and A. monspessulanum. Quercus faginea and A. campestre were planted (pure and mixed compositions) and directly sown (pure composition), whereas the remaining species were all planted with mixed composition.Survival and growth were monitored during 34 months, allowing the conclusion that the installation method (sowing or plantation) influenced the survival of A. campestre, which did not succeed in the sown area.
- Modelling rainfall interception by forests: a new method for estimating the canopy storage capacityPublication . Pereira, Fernando Leite; Valente, Fernanda; Nóbrega, CristinaEvaporation of rainfall intercepted by forests is usually an important part of a catchment water balance. Recognizing the importance of interception loss, several models of the process have been developed. A key parameter of these models is the canopy storage capacity (S), commonly estimated by the so-called Leyton method. However, this method is somewhat subjective in the selection of the storms used to derive S, which is particularly critical when throughfall is highly variable in space. To overcome these problems, a new method for estimating S was proposed in 2009 by Pereira et al. (Agricultural and Forest Meteorology, 149: 680-688), which uses information from a larger number of storms, is less sensitive to throughfall spatial variability and is consistent with the formulation of the two most widely used rainfall interception models, Gash analytical model and Rutter model. However, this method has a drawback: it does not account for stemflow (Sf ). To allow a wider use of this methodology, we propose now a revised version which makes the estimation of S independent of the importance of stemflow. For the application of this new version we only need to establish a linear regression of throughfall vs. gross rainfall using data from all storms large enough to saturate the canopy. Two of the parameters used by the Gash and the Rutter models, pd (the drainage partitioning coefficient) and S, are then derived from the regression coefficients: pd is firstly estimated allowing then the derivation of S but, if Sf is not considered, S can be estimated making pd=0. This new method was tested using data from a eucalyptus plantation, a maritime pine forest and a traditional olive grove, all located in Central Portugal. For both the eucalyptus and the pine forests pd and S estimated by this new approach were comparable to the values derived in previous studies using the standard procedures. In the case of the traditional olive grove, the estimates obtained by this methodology for pd and S allowed interception loss to be modelled with a normalized averaged error less than 4%. Globally, these results confirm that the method is more robust and certainly less subjective, providing adequate estimates for pd and S which, in turn, are crucial for a good performance of the interception models.
- Evaporation of intercepted rainfall from isolated evergreen oak trees: Do the crowns behave as wet bulbs?Publication . Pereira, Fernando Leite; Gash, John H.C.; David, Jorge Soares; Valente, FernandaA new approach is suggested for estimating evaporation of intercepted rainfall from single trees in sparse forests. It is shown that, theoretically, the surface temperature of a wet tree crown will depend on the available energy and windspeed. But for a fully saturated canopy under rainy conditions, surface temperature will approach the wet bulb temperature when available energy tends to zero. This was confirmed experimentally from measurements of the radiation balance, aerodynamic conductance for water vapour and surface temperature on an isolated tree crown. Net radiation over a virtual cylindrical surface, enclosing the tree crown, was monitored by a set of radiometers positioned around that surface. Aerodynamic conductance for the tree crown was derived by scaling up measurements of leaf boundary layer conductance using the heated leaf replica method. Thermocouples were used to measure the average leaf surface temperature. Results showed that a fully wet single tree crown behaves like a wet bulb, allowing evaporation of intercepted rainfall to be estimated by a simple diffusion equation for water vapour, which is not restricted by the assumptions of one-dimensional transfer models usually used at the stand scale. Using this approach, mean evaporation rate from wet, saturated tree crowns was 0.27 or 0.30mm h 1, when surface temperature was taken equal to the air wet bulb temperature or estimated accounting for the available energy, respectively.