Cork oak (Quercus suber L.) and holm oak (Quercus rotundifolia Lam.) are key species in Mediterranean oak woodlands and silvopastoral systems in the Iberian Peninsula named montados in Portugal and dehesas in Spain. Montados and dehesas have high ecological and socio-economic value, but these systems, among other challenges, are threatened by high adult oak mortality. Previous research focused on identifying mortality drivers such as pathogens, effects of climatic change, or inadequate management practices, but oak mortality spatial and temporal variability received less attention.

Here we use the national database of cutting requests from the Portuguese Forest Authority (ICNF) as a proxy for cork and holm oak mortality to characterize spatial patterns and identify main regional areas of mortality in Portugal for the between 1997 and 2019. We use a structured data selection protocol for retaining mortality-related records for both oak species. We use Average Nearest Neighbor (ANN), Incremental Spatial Autocorrelation (ISA), and Getis–Ord Gi* hotspot analysis at two complementary scales: local (1 km) and regional (10 km) for oak mortality spatial analysis.

Results show that oak mortality is strongly spatially aggregated and deviates significantly from a random spatial distribution. There are areas consistently concentrating high oak mortality, although spatial patterns vary with scale. Cork oak shows areas concentrating high mortality namely in Ribatejo region with additional mortality concentration in southern and coastal regions in Alentejo. In contrast, holm oak shows more fragmented mortality spatial patterns, with recurrent areas of high mortality in the regions of Alentejo (Évora and Beja districts) and Beira Baixa, (Castelo Branco).

Our results suggest that public administration records on tree mortality may be used to get ecological insights and support spatial monitoring of oak mortality. Additionally, identification of areas concentrating high oak mortality will contribute to prioritize ground truth measurements, and potential conservation and forest management strategies. Finally, identifying areas that consistently concentrate high oak mortality may also contribute to identify and integrate main environmental and management variables driving oak mortality in such regions.