Patterns of post-drought recovery are strongly influenced by drought duration, drought frequency, post-drought wetness and bioclimatic setting

Abstract:

Understanding vegetation recovery after drought extremes is critical for predicting vegetation dynamics under a drier and hotter climate. Australia experienced a drought extreme known as Millennium Drought (MD), and suffered from vegetation decline and mortality across natural ecosystems. Most prior assessments focused on the impact during the drought, with little attention to vegetation recovery post drought and its determinants. This study leveraged remote sensing products of different sources – fraction of absorbed photosynthetic active radiation based on optical data and canopy density derived from microwave data – and random forest algorithms to assess post-drought recovery over Australian natural vegetation during a period centered on the MD. Post-drought vegetation recovery was prevalent across the continent, with more than 60% seeing full recovery within about 6 months. Canopy density from VOD was slower to recover than leaf abundance seen in FPAR. Persistent decline was most strongly controlled by drought return interval, post-drought hydrological condition, and drought length. Stress droughts delayed recovery more than pulse droughts, and led to a higher frequency of persisting decline. Moderately dry to average post-drought conditions resulted in slower and less complete recovery than wet post-drought conditions. Persisting decline was most common in savannas and semi-arid regions, while forests and semi-arid regions had the longest recovery times. In addition to describing these tendencies, the study provides quantitative thresholds of response that can help improve the modeling of ecosystem dynamics in response to climate extremes.