Assessing the postfire resilience of a Mediterranean forest from satellite and ground data (NDVI, vegetation profile, avifauna)

Estimating the resilience time of an ecosystem may lead to different values depending on the compartment or function of interest and the measurement method. We sought to estimate the resilience of a cork oak (Quercus suber L.) stand – a typical west Mediterranean forest type – 8 years after a wildfire, using three independent indicators. Each represents a function or a characteristic of the ecosystem: (i) the Normalized Difference Vegetation Index (NDVI), a remote sensing-based proxy of photosynthetic activity, (ii) the vegetation profile, based on an estimation of the vegetation cover at different heights above ground, and (iii) the avifauna composition, a component of animal biodiversity. The NDVI seems to have recovered a value close to its pre-fire value about 9 years after the fire. Recovering a vertical vegetation profile similar to that before the fire requires a longer time, tentatively estimated to not less than a dozen years. Recovery of the pre-fire avifauna is likely to require an even longer time, which could not be estimated from our 8-year monitoring period. The indicator based on avifauna appears to be the most discriminating indicator, among the three compared here, for estimating the time required for full recovery of the ecosystem over the long term.

生态系统恢复力时长的估算结果会因所关注的生态组分、功能类型以及测量方法的不同而存在差异。本研究以西地中海典型森林类型——栓皮栎（Quercus suber L.）林为研究对象，在野火发生8年后采用三类独立指标对其生态系统恢复力进行估算。每类指标分别对应生态系统的一项功能或特征：(1) 归一化差分植被指数（Normalized Difference Vegetation Index, NDVI）——一种基于遥感技术的光合活动替代指标；(2) 植被垂直结构——基于地表不同高度植被覆盖度的估算结果；(3) 鸟类群落组成——动物生物多样性的组成部分之一。研究结果显示，归一化差分植被指数在野火发生约9年后已恢复至火灾前水平附近。而恢复至与火灾前相似的植被垂直结构则需要更长时间，初步估算至少需十余年。恢复至火灾前的鸟类群落组成则可能需要更久的时间，这一时长无法通过本研究为期8年的监测周期进行估算。在本次对比的三类指标中，基于鸟类群落的指标是估算生态系统长期全面恢复所需时长的最具区分度的指标。