Canopy gap patterns in Mediterranean forests: a spatio-temporal characterization using airborne LiDAR data

Abstract

Abstract Context In the last century European forests are experiencing tree damage and mortality rise and it is expected to continue due to increased disturbances under global change. Disturbances generally creates canopy gaps, which leads to secondary succession, compositional changes and landscape mosaic transformations. Forest gap characterization has traditionally been performed in light-limited tropical and boreal forests, but no studies have been found on water-limited Mediterranean forests. Characterising canopy gaps and their dynamics in Mediterranean forests will help to better understand their dynamics across landscapes under ongoing global change. Objectives We aimed to characterize canopy gaps and quantify their dynamics identifying hotspots of openings and closings in Mediterranean forests. Methods We used low density multitemporal airborne LiDAR data between 2010 and 2016, over a large region (Madrid, Spain, 1732.7 km2) with forests ranging from monospecific conifer and broadleaved to mixed forests, to delineate canopy gaps. The characterization was made through its Gap Size Frequency Distribution (GSFD) by forest type and year. We analysed canopy gap dynamics and identified statistically significant hotspots of gap openings and closings in each forest type. Results There were major differences between conifers and broadleaved forest in terms of gap characteristics and GSFD. In general, we found a great dynamism in Mediterranean forests with high rates of forest openings and closings, but a net closing trend. A high spatial heterogeneity was observed finding hotspots of gap openings and closings across the entire study area. Conclusions We characterised for the first-time large-scale structure and dynamics of canopy gaps in Mediterranean forests. Our results represents the characterisation of the GSFD of Mediterranean forests and could be considered a benchmark for future studies. The provision of up-to-date periodic maps of hotspots of gap opening, closing and net change help to understand landscape mosaic changes as well as to prioritise forest management and restoration strategies.