Growth and productivity of mixed species in forest stands in nothern Portugal
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2014
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Florestas mistas são sistemas complexos em que árvores de diferentes espécies interagem entre si e com o ambiente que as rodeia. Existem argumentos sólidos a favor da silvicultura de povoamentos mistos e da sua potencial capacidade produtiva comparada com povoamentos puros. Para compreender bem estes sistemas complexos é necessário fazer a previsão das dinâmicas existentes no povoamento em diversos ambientes e/ou formas de gestão. Estudos acerca da produtividade de ecossistemas florestais ajudam a quantificar o carbono sequestrado e, em consequência, fornecem os dados necessários que são usados na gestão das florestas. A produtividade primária líquida (PPL) é uma variável frequentemente usada em estudos de ecologia e, mais recentemente, para analisar o impacto da mudança climática global nas espécies vegetais e nos ecossistemas florestais.
Foram objectivos desta tese de doutoramento analisar se os povoamentos mistos têm maior produtividade e mais benefícios do que os povoamentos puros das espécies componentes e preparar metodologias de trabalho que permitam quantificar produtividade em cenários de mudança climática.
Este estudo foi realizado em duas áreas distintas: a) em 15 povoamentos de pinheirobravo (Pinus pinaster Aiton), 15 povoamentos de carvalho-negral (Quercus pyrenaica Willd.) e 9 povoamentos de mistura destas espécies, não equiénios, distribuídos pelo distrito de Vila Real; b) num ensaio experimental de plantação mista de castanheiro (Castanea sativa Mill.) e pseudotsuga (Pseudotsuga menziesii (Mirb.) Franco) com 21 parcelas com composição pura e mista em blocos casualizados completos, localizado em Bemlhevai, distrito de Bragança.
O estudo em Vila Real quantificou biomassa aérea e PPL aérea de pinheiro-bravo, carvalho-negral e dos povoamentos mistos e avaliou a relação entre a PPL e as características dos povoamentos. Os valores médios de PPL dos povoamentos mistos foram superiores aos povoamentos puros. A biomassa aérea não foi significativamente diferente entre os três tipos
de povoamento mas os valores mais elevados foram encontrados nos povoamentos mistos. Modelos de regressão mostraram uma forte relação entre biomassa aérea e área basal em todos os povoamentos. A eficácia produtiva foi também significativamente maior nos povoamentos mistos. Um modelo ecofisiológico de base processual, Biome-BGC, foi usado na mesma área de estudo, para examinar a importância do local e de factores ecofisiológicos na produtividade dos povoamentos de pinheiro-bravo e carvalho-negral, e analisar o potencial impacto das mudanças climáticas e do aumento de CO2 na atmosfera. O modelo foi parameterizado e preparado para aplicação em povoamentos puros com o fim de analisar resultados e testar metodologias que poderão ser aplicadas futuramente em povoamentos mistos. O modelo forneceu uma boa estimativa de PPL e observou-se uma forte correlação entre os valores medidos e os valores estimados. Previu-se um aumento de PPL com o aumento de CO2, e uma diminuição de PPL num clima mais quente e com menos humidade no solo. Estes resultados confirmam que a precipitação é um parâmetro essencial no crescimento e produtividade na floresta Mediterrânea e demonstraram a capacidade do modelo para simular o comportamento destes ecossistemas, encorajando a continuação da aplicação de simulações com o Biome-BGC em Portugal.
Em Bemlhevai procedeu-se à avaliação das dinâmicas de crescimento e comparou-se biomassa aérea e PPL aérea das duas espécies em parcelas puras e mistas nas proporções 1:1 e 1:3. Observou-se maior altura, diâmetro e biomassa aérea na P. menziesii do que na C. sativa.
Observou-se maior produção relativa total nas misturas do que nas parcelas puras. C. sativa e P. menziesii mostraram complementaridade no uso dos recursos. No início do estudo as parcelas puras tinham uma biomassa aérea por hectare semelhante às misturas mas, mais tarde, as parcelas mistas obtiveram maior produção. O aumento de produção ao longo do tempo nas misturas parece ser resultado da estratificação do coberto e melhor aproveitamento dos recursos do local. A PPL das misturas foi também maior do que nas parcelas puras. Uma comparação das propriedades do solo e da análise química da folhagem foi também efectuada nas parcelas puras de C. sativa e P. menziesii e na proporção 1:1 para avaliar e perceber se as
misturas tinham vantagens em relação às parcelas puras. A análise das propriedades do solo mostrou diferenças significativas no pH, P e em acidez de troca do solo entre os tratamentos, mas não nas restantes análises de solo realizadas. Resultados da análise da concentração de N, P, Ca e K nas folhas mostrou valores mais altos nas misturas.
Esta tese fornece uma compreensão abrangente das dinâmicas de crescimento de povoamentos mistos no norte de Portugal e mostra que estes podem ser opções de silvicultura atractivas.
Mixed-species forests are complex systems in which individual trees of different species interact with each other and with the environment. There are sound ecological and cultural arguments supporting the interest in mixed-species stands silviculture and its potential increase in productivity vs. single-species. Understanding such complex systems is necessary in order to predict stand dynamics under different environments and/or management regimes. Studies about the productivity of forest ecosystems help to quantify sequestered carbon and provide therefore the data that is used in forest management. Net primary production (NPP) is a key variable in a wide range of ecological studies and is used mainly on ecosystems to evaluate productivity, global carbon balance and more recently to analyse the global climate change impact on species and ecosystems. The main objectives of this study were to analyse if mixed-species can provide greater yields and more benefits than monocultures of the component species and also to prepare work on future methodologies which will allow quantifying productivity in scenarios of climate change. The work was conducted in two study areas: a) uneven-aged forests across the Vila Real district in 15 stands of pine (Pinus pinaster Aiton), 15 stands of oak (Quercus pyrenaica Willd.) and 9 stands of mixed pine-oak, naturally regenerated; b) an experimental block design of twenty-one permanent research plots with pure and sweet-chestnut (Castanea sativa Mill.) and douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) located in Bemlhevai, Bragança. The study in the Vila Real district quantified the aboveground biomass and aboveground NPP (ANPP) of pine, oak and mixed pine-oak forests and evaluated the relationships between ANPP and the stand characteristics. Mixed stands had a significantly higher mean ANPP than pine or oak. Aboveground biomass was not significantly diferente among the three stand types but the higher values were in the mixed stands. Regression models showed a strong relationship between aboveground biomass and basal area in all stands. The production efficiency was significantly higher in mixed stands. An ecosystem process model, Biome-BGC, was also used in the same study area to examine the importance of site and ecophysiological factors on the productivity of the pine and oak forests and to analyse the potential impact of climate change and CO2 increase. The model was parameterized and prepared for pure stands to analyze results and test methodologies that can be extended later to mixed stands. The model provided good estimates of NPP. There was a strong correlation between simulated and measured NPP values in pine and oak stands. The NPP of these forests is predicted to increase with higher CO2 and to decrease in a climate with higher temperature and lower soil moisture. These results confirm that precipitation is a very important climate variable to growth and productivity in Mediterranean forest ecosystems. The results demonstrated the ability of Biome-BGC to simulate forest ecosystems behaviour and encourage the future application of model simulations in Portugal. Growth dynamics were assessed in Bemlhevai and compared the aboveground biomass and NPP of the two species in pure and mixed treatments in proportions 1:1 and 1:3. P. menziesii exhibited greater height, diameter and aboveground biomass than C. sativa. Total relative yield indicated higher productivity in mixtures than in pure treatments. C. sativa and P. menziesii showed complementarity in the use of resources. Early in the development the pure treatments had similar aboveground biomass per hectare as the mixtures, but later on mixtures had more yield than the pure treatments. Mixture yield increase through time appears to be a result of canopy stratification and better use of site resources. ANPP was also higher in mixtures than in pure treatments. A comparison of soil properties (texture and chemical analysis) and a foliage chemical analysis was also carried out in treatments of puré C. sativa, pure P. menziesii and in the 1:1 proportion to evaluate and understand if mixtures had advantages over pure treatments. The soil properties analysis showed significant differences in pH, P and in soil exchangeable acidity among the treatments, but no diferences in the other soil characteristics. Foliar analysis results for N, P, Ca and K concentrations were higher in the mixtures. This thesis provides a comprehensive understanding of growth dynamics of mixed forests in northern Portugal and shows that mixed-species stands can be attractive silviculture options.
Mixed-species forests are complex systems in which individual trees of different species interact with each other and with the environment. There are sound ecological and cultural arguments supporting the interest in mixed-species stands silviculture and its potential increase in productivity vs. single-species. Understanding such complex systems is necessary in order to predict stand dynamics under different environments and/or management regimes. Studies about the productivity of forest ecosystems help to quantify sequestered carbon and provide therefore the data that is used in forest management. Net primary production (NPP) is a key variable in a wide range of ecological studies and is used mainly on ecosystems to evaluate productivity, global carbon balance and more recently to analyse the global climate change impact on species and ecosystems. The main objectives of this study were to analyse if mixed-species can provide greater yields and more benefits than monocultures of the component species and also to prepare work on future methodologies which will allow quantifying productivity in scenarios of climate change. The work was conducted in two study areas: a) uneven-aged forests across the Vila Real district in 15 stands of pine (Pinus pinaster Aiton), 15 stands of oak (Quercus pyrenaica Willd.) and 9 stands of mixed pine-oak, naturally regenerated; b) an experimental block design of twenty-one permanent research plots with pure and sweet-chestnut (Castanea sativa Mill.) and douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) located in Bemlhevai, Bragança. The study in the Vila Real district quantified the aboveground biomass and aboveground NPP (ANPP) of pine, oak and mixed pine-oak forests and evaluated the relationships between ANPP and the stand characteristics. Mixed stands had a significantly higher mean ANPP than pine or oak. Aboveground biomass was not significantly diferente among the three stand types but the higher values were in the mixed stands. Regression models showed a strong relationship between aboveground biomass and basal area in all stands. The production efficiency was significantly higher in mixed stands. An ecosystem process model, Biome-BGC, was also used in the same study area to examine the importance of site and ecophysiological factors on the productivity of the pine and oak forests and to analyse the potential impact of climate change and CO2 increase. The model was parameterized and prepared for pure stands to analyze results and test methodologies that can be extended later to mixed stands. The model provided good estimates of NPP. There was a strong correlation between simulated and measured NPP values in pine and oak stands. The NPP of these forests is predicted to increase with higher CO2 and to decrease in a climate with higher temperature and lower soil moisture. These results confirm that precipitation is a very important climate variable to growth and productivity in Mediterranean forest ecosystems. The results demonstrated the ability of Biome-BGC to simulate forest ecosystems behaviour and encourage the future application of model simulations in Portugal. Growth dynamics were assessed in Bemlhevai and compared the aboveground biomass and NPP of the two species in pure and mixed treatments in proportions 1:1 and 1:3. P. menziesii exhibited greater height, diameter and aboveground biomass than C. sativa. Total relative yield indicated higher productivity in mixtures than in pure treatments. C. sativa and P. menziesii showed complementarity in the use of resources. Early in the development the pure treatments had similar aboveground biomass per hectare as the mixtures, but later on mixtures had more yield than the pure treatments. Mixture yield increase through time appears to be a result of canopy stratification and better use of site resources. ANPP was also higher in mixtures than in pure treatments. A comparison of soil properties (texture and chemical analysis) and a foliage chemical analysis was also carried out in treatments of puré C. sativa, pure P. menziesii and in the 1:1 proportion to evaluate and understand if mixtures had advantages over pure treatments. The soil properties analysis showed significant differences in pH, P and in soil exchangeable acidity among the treatments, but no diferences in the other soil characteristics. Foliar analysis results for N, P, Ca and K concentrations were higher in the mixtures. This thesis provides a comprehensive understanding of growth dynamics of mixed forests in northern Portugal and shows that mixed-species stands can be attractive silviculture options.
Descrição
Tese de Doutoramento em Ciências Agronómicas e Florestais
Palavras-chave
Crescimento , Quercus pyrenaica , Pinus pinaster , Castanea sativa , Pseudotsuga menziesii , Povoamentos mistos , Produtividade primária líquida , Modelo Biome- BGC