Format: ORAL

Ana P. Portela 1,2,3, Joo Gonalves 1,3,4, Isabelle Durance 5, Cristiana Vieira 6, Joo Honrado 1,2,3

1 CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal 2 Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, 4099-002 Porto, Portugal 3 BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Campus de Vairão, 4485-661 Vairão, Portugal 4 proMetheus—Research Unit in Materials, Energy and Environment for Sustainability, Instituto Politécnico de Viana do Castelo (IPVC), Avenida do Atlântico, No. 644, 4900-348 Viana do Castelo, Portugal 5 Water Research Institute and School of Biosciences, Cardiff University, The Sir Martin Evans Building, Museum Avenue, Cardiff, CF10 3AX, United Kingdom 6 Museu de História Natural e da Ciência da Universidade do Porto (MHNC-UP/UPorto/PRISC), Praça Gomes Teixeira, 4099-002 Porto, Portugal.

Droughts significantly impact forest ecosystems, reducing forest health and productivity. Droughts thus compromise key forest functions such as carbon sequestration and consequently nature-based solutions for climate change mitigation and adaptation. Riparian forests play key roles in the functioning of aquatic and terrestrial ecosystems. However, there is limited understanding of the response of riparian forests to drought. Here we investigate riparian forest drought responses and resilience to an extreme drought event at a regional scale. Specifically, we examined riparian forest drought response strategies and how drought event characteristics, average climate conditions, topography, soil and vegetation structure and functional composition shape the resilience of riparian forests to drought. We used a time series of Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) derived from Sentinel-2 satellite imagery to calculate the resistance to and recovery after an extreme drought (2017-2018) in 49 sites across an Atlantic-Mediterranean climate gradient in North Portugal. We used generalized additive models and multi-model inference to understand which factors explained drought responses. We found a trade-off between drought resistance and recovery, as well as contrasting strategies across the climatic gradient of the study area. Riparian forests in Atlantic areas showed higher resistance, while those under Mediterranean influence showed a higher recovery than the former. Canopy structure and climate context were the most relevant predictors of drought response. However, three years after the extreme drought, median NDVI and NDWI across the study area had not returned to pre-drought levels. Our study shows that riparian forests present trade-offs between drought resistance and recovery and may be susceptible to extended drought legacies associated with extreme and/or recurring droughts, similarly to upland forests. This work highlights an underestimated component of riparian ecosystems vulnerability to climate change and emphasises the need for further understanding on long-term resilience to drought.