The legacy of pine plantations on fire severity

Abstract

In Mediterranean ecosystems, afforestation efforts have created landscapes with high fuel loads and continuity that, in combination with warmer and drier conditions, may intensify fire activity. Yet, the relative contribution of afforestation to current fire severity remains little explored. We hypothesized that, under Mediterranean conditions, pine plantations can generate high-intensity fires that increase fire severity and show limited post-fire recovery compared with other vegetation types. We integrated Sentinel-2 imagery with digital terrain models, vegetation maps, and national forest inventories to assess fire severity (dNBR) and one-year post-fire recovery from three large wildfires in Spain. We then used linear models to investigate the patterns of fire severity and early recovery across vegetation types. Change-point models were applied to pine plantations to evaluate whether reducing tree density beyond a specific point can limit fire severity. Pine plantations exhibited significantly higher severity and lower early recovery than other vegetation types, particularly in areas with high tree densities and abundant shrub cover. Moreover, proximity to pine plantations was associated with increased fire severity in adjacent vegetation, whereas reducing tree density below a threshold of 440 trees/ha mitigated fire severity within plantation stands. Policy implications. Our findings provide quantitative evidence that pine plantations can exacerbate fire severity under contemporary climate conditions, and that, once burned, these areas seldom recover. Effective spatial planning and management of tree plantations is therefore essential in order to promote more sustainable fire regimes in Mediterranean ecosystems. Therefore, carbon mitigation strategies should carefully consider the risk of establishing dense and continuous pine plantations when implementing future afforestation programmes.