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Efeitos da gestão na diversidade taxonómica e funcional das comunidades de plantas e do banco de sementes dos olivais do Baixo Alentejo
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Resumo(s)
Os olivais tradicionais são um sistema agrícola extensivo com grande diversidade de plantas,
incluindo espécies ameaçadas, mantidas pelas práticas tradicionais de gestão. Estes sistemas encontramse em declínio devido à expansão da agricultura intensiva e, em menor grau, ao abandono.
Neste estudo foram avaliados os efeitos de três modelos de gestão de olivais no Baixo Alentejo
- tradicional (sequeiro, com lavra), abandono (sem gestão) e intensiva (com regadio) - na diversidade
taxonómica e funcional das comunidades de plantas e banco de sementes. Foi ainda avaliado o potencial
do banco de semente para recuperar as comunidades. A gestão tradicional foi usada como referência.
A gestão intensiva provocou uma redução da riqueza específica e da redundância funcional das
comunidades de plantas e do banco de semente, favorecendo a ocorrência de espécies mais ruderais,
com maior altura máxima e floração mais prolongada, incluindo espécies alóctones. O banco de
sementes apresentou elevada dissimilaridade com o banco de sementes dos olivais tradicionais. Os
resultados indicam um depauperamento do banco de sementes num período muito curto, particularmente
das espécies ameaçadas, e alterações profundas na sua composição que irão perdurar mesmo após
eventual conversão.
O abandono dos olivais não afetou a riqueza específica, no entanto conduziu a um aumento da
divergência funcional e favoreceu a ocorrência de espécies com maior peso da semente e floração mais
tardia. Além disso, observou-se a colonização por espécies perenes, algumas ameaçadas, mas,
simultaneamente, uma redução da abundância de algumas espécies arvenses ameaçadas. Contudo, estas
últimas estão presentes no banco de sementes, podendo regenerar se o solo for mobilizado novamente.
Neste estudo evidenciou-se a importância da gestão tradicional para a conservação das
comunidades de plantas arvenses associadas aos olivais de sequeiro, incluindo várias espécies
ameaçadas. A maior redundância funcional nestes olivais sugere alguma resiliência a alterações
ambientais que, contudo, não permite superar os efeitos da gestão intensiva. Deste estudo resultaram
informações relevantes para a conservação destas comunidades de plantas e um catálogo fotográfico de
plântulas de 217 espécies inventariadas.
Traditional olive groves are rainfed extensive agroecosystems that support a species-rich plant community and are the main habitat for several threatened arable species. These unique plant communities, shaped by centuries-old cultivation practices, are currently declining mainly due to the expansion of intensive agriculture and, to a lesser extent, abandonment. This study assessed the effects of three olive grove management practices in Baixo Alentejo, Portugal - traditional (rain-fed, ploughed), abandoned (no management) and intensive (irrigated) - on the taxonomic and functional diversity of aboveground flora and seed bank. The potential for community recovery from seed banks was also assessed. Traditional olive groves were taken as a reference. Intensive management decreased species richness and functional redundancy of aboveground flora and seed bank, favouring ruderal plant species (including exotic species) with longer flowering duration and higher plant height. Dissimilarity between seed banks of intensive and traditional olive groves was the highest. The results indicate an impoverishment of the seed bank over a short period, especially in threatened species, and changes in composition that will last after an eventual conversion. Olive grove abandonment did not affect species richness but increased functional divergence and favoured species traits with higher seed weight and late flowering onset. Abandonment also allowed for colonization by perennials, including threatened species, but simultaneously reduced the abundance of some threatened arable species. However, the latter were present in the seed bank and can regenerate if ploughing practices are restored. The importance of traditional management for the conservation of arable plant communities and several threatened species was highlighted. The highest functional redundancy indicates resilience to disturbances and environmental changes which, however, is not able to overcome the effects of agriculture intensification. This work also provided relevant knowledge for the conservation of arable plant communities occurring in traditional olive groves and a seedling photographic catalogue of the 217 plant species recorded in the study region.
Traditional olive groves are rainfed extensive agroecosystems that support a species-rich plant community and are the main habitat for several threatened arable species. These unique plant communities, shaped by centuries-old cultivation practices, are currently declining mainly due to the expansion of intensive agriculture and, to a lesser extent, abandonment. This study assessed the effects of three olive grove management practices in Baixo Alentejo, Portugal - traditional (rain-fed, ploughed), abandoned (no management) and intensive (irrigated) - on the taxonomic and functional diversity of aboveground flora and seed bank. The potential for community recovery from seed banks was also assessed. Traditional olive groves were taken as a reference. Intensive management decreased species richness and functional redundancy of aboveground flora and seed bank, favouring ruderal plant species (including exotic species) with longer flowering duration and higher plant height. Dissimilarity between seed banks of intensive and traditional olive groves was the highest. The results indicate an impoverishment of the seed bank over a short period, especially in threatened species, and changes in composition that will last after an eventual conversion. Olive grove abandonment did not affect species richness but increased functional divergence and favoured species traits with higher seed weight and late flowering onset. Abandonment also allowed for colonization by perennials, including threatened species, but simultaneously reduced the abundance of some threatened arable species. However, the latter were present in the seed bank and can regenerate if ploughing practices are restored. The importance of traditional management for the conservation of arable plant communities and several threatened species was highlighted. The highest functional redundancy indicates resilience to disturbances and environmental changes which, however, is not able to overcome the effects of agriculture intensification. This work also provided relevant knowledge for the conservation of arable plant communities occurring in traditional olive groves and a seedling photographic catalogue of the 217 plant species recorded in the study region.
Descrição
Tese de Mestrado, Ecologia e Gestão Ambiental, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Plantas arvenses Agroecossistemas Agricultura intensiva Abandono agrícola conservação Teses de mestrado - 2023