Publicação
Assessing the role of macro- and microclimate on Holm oak performance in Mediterranean drylands
| Resumo: | Mediterranean drylands are expected to become drier due to climate change. This may aggravate desertification by increasing dryland susceptibility to land degradation, leading to the loss of biodiversity and ability to provide ecosystem services. In Mediterranean Basin drylands, a large area is occupied by oak woodlands, a semi-natural agro-silvopastoral system called Montado in Portugal. In the drier areas, where Montado seems to act as a buffer against desertification, the dominant tree species is Holm oak (Quercus ilex subsp. rotundifolia), However, in the last decades, a declining trend has been reported for Holm oak woodlands, mostly attributed to unsustainable land management, biotic factors and to an increase in aridity at a regional scale. Also, at a local scale, it has been shown that microclimate conditions driven by topography have a major influence on this species natural regeneration rates. Over the last decades, many (re)afforestation with Holm oak have been implemented to revert Montado’s decline and combat desertification, although not always successful. The aim of this work was to study the effect of macro- and microclimate on Holm oak performance, specifically on acorn germination and first summer seedling survival. Holm oak acorns were collected along a climatic gradient based on long-term precipitation (30 yrs.), resulting in 6 macroclimate provenances. In 2 sites, the driest and the wettest sites of the gradient, areas with contrasting microclimates were selected using Potential Solar Radiation (PSR) as a proxy of microclimate conditions. Holm oak performance was, thus, studied along a macroclimate gradient and in microclimate contrasting conditions. Holm oak acorns from each provenance where characterized biometrically and acorn production evaluated. Germination of acorns and seedling survival were evaluated under greenhouse similar conditions and in the field under contrasting macro- and microclimate conditions. We found that macro- and microclimatic provenance influences acorn size and germination. Drier sites and more exposed areas (higher PSR) had bigger acorns with higher germination. Field conditions did not seem to affect germination but rather the first summer seedling survival. The survival of Holm oak seedlings to the first summer was significantly higher in the wetter site and in less exposed areas than in the drier site and in more exposed areas. This work provides guidelines to increase Holm oak seedling quantity and quality in nurseries to be used in (re)afforestation plans and to improve Holm oak young seedling survival, either by focusing (re)afforestation in microclimatic favorable areas (using remote sensing derived information like PSR), or by providing additional assistance to seedlings growing in drier and/or more exposed areas. In addition, it may also help to better understand Holm oak seedling mortality and/or natural regeneration patterns. Hence, these findings may contribute to improve the success of Holm oak (re)afforestation as a critical restoration tool to combat desertification in Portuguese drylands, and revert Holm oak Montado’s decline, particularly under a climate change scenario |
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| Autores principais: | Serafim, João Afonso Machado Pinto de Aguiar |
| Assunto: | afforestation climate change Quercus ilex seedling survival seed provenance |
| Ano: | 2019 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Mediterranean drylands are expected to become drier due to climate change. This may aggravate desertification by increasing dryland susceptibility to land degradation, leading to the loss of biodiversity and ability to provide ecosystem services. In Mediterranean Basin drylands, a large area is occupied by oak woodlands, a semi-natural agro-silvopastoral system called Montado in Portugal. In the drier areas, where Montado seems to act as a buffer against desertification, the dominant tree species is Holm oak (Quercus ilex subsp. rotundifolia), However, in the last decades, a declining trend has been reported for Holm oak woodlands, mostly attributed to unsustainable land management, biotic factors and to an increase in aridity at a regional scale. Also, at a local scale, it has been shown that microclimate conditions driven by topography have a major influence on this species natural regeneration rates. Over the last decades, many (re)afforestation with Holm oak have been implemented to revert Montado’s decline and combat desertification, although not always successful. The aim of this work was to study the effect of macro- and microclimate on Holm oak performance, specifically on acorn germination and first summer seedling survival. Holm oak acorns were collected along a climatic gradient based on long-term precipitation (30 yrs.), resulting in 6 macroclimate provenances. In 2 sites, the driest and the wettest sites of the gradient, areas with contrasting microclimates were selected using Potential Solar Radiation (PSR) as a proxy of microclimate conditions. Holm oak performance was, thus, studied along a macroclimate gradient and in microclimate contrasting conditions. Holm oak acorns from each provenance where characterized biometrically and acorn production evaluated. Germination of acorns and seedling survival were evaluated under greenhouse similar conditions and in the field under contrasting macro- and microclimate conditions. We found that macro- and microclimatic provenance influences acorn size and germination. Drier sites and more exposed areas (higher PSR) had bigger acorns with higher germination. Field conditions did not seem to affect germination but rather the first summer seedling survival. The survival of Holm oak seedlings to the first summer was significantly higher in the wetter site and in less exposed areas than in the drier site and in more exposed areas. This work provides guidelines to increase Holm oak seedling quantity and quality in nurseries to be used in (re)afforestation plans and to improve Holm oak young seedling survival, either by focusing (re)afforestation in microclimatic favorable areas (using remote sensing derived information like PSR), or by providing additional assistance to seedlings growing in drier and/or more exposed areas. In addition, it may also help to better understand Holm oak seedling mortality and/or natural regeneration patterns. Hence, these findings may contribute to improve the success of Holm oak (re)afforestation as a critical restoration tool to combat desertification in Portuguese drylands, and revert Holm oak Montado’s decline, particularly under a climate change scenario |
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