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 (<i>Quercus suber</i> 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.

生态系统恢复力时间的估算结果会因关注的生态组分、功能类型及测量方法的不同而存在差异。本研究针对野火发生8年后的典型西地中海森林类型——栓皮栎（Quercus suber L.）林分，采用三类独立指标估算其恢复力。每类指标分别对应生态系统的一项功能或特征：①归一化植被指数（Normalized Difference Vegetation Index, NDVI），一种基于遥感技术的光合活性替代指标；②植被剖面，基于地表不同高度植被盖度估算得到的指标；③鸟类群落组成（avifauna composition），动物生物多样性的组成组分。野火发生约9年后，NDVI已恢复至接近火前水平的数值。恢复至与火前相似的植被垂直剖面则需要更长时间，初步估算至少需十余年。而火前鸟类群落的恢复则可能需要更长时间，这无法通过本研究为期8年的监测周期完成估算。在本次对比的三类指标中，基于鸟类群落的指标似乎是估算生态系统长期完全恢复所需时间的最具区分度的指标。