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

Abstract

Understanding vegetation recovery after drought is critical for projecting vegetation dynamics in future climates. From 1997 to 2009, Australia experienced a long‐lasting drought known as the Millennium Drought (MD), which led to widespread reductions in vegetation productivity. However, vegetation recovery post‐drought and its determinants remain unclear. This study leverages remote sensing products from different sources—fraction of absorbed photosynthetically active radiation (FPAR), based on optical data, and canopy density, derived from microwave data—and random forest algorithms to assess drought recovery over Australian natural vegetation during a 20‐year period centered on the MD. Post‐drought recovery was prevalent across the continent, with 6 out of 10 drought events seeing full recovery within about 6 months. Canopy density was slower to recover than leaf area seen in FPAR. The probability of full recovery was most strongly controlled by drought return interval, post‐drought hydrological condition, and drought length. Full recovery was seldom observed when drought events occurred at intervals of 3 months or less, and moderately dry (standardized water balance anomaly [SWBA] within [−1, −0.76]) post‐drought conditions resulted in less complete recovery than wet (SWBA > 0.3) post‐drought conditions. Press droughts, which are long term but not extreme, delayed recovery more than pulse droughts (short term but extreme) and led to a higher frequency of persistent decline. Following press droughts, the frequency of persistent decline differed little among biome types but peaked in semi‐arid regions across aridity levels. Forests and savanna required the longest recovery times for press drought, while grasslands were the slowest to recover for pulse drought. This study provides quantitative thresholds that could be used to improve the modeling of ecosystem dynamics post‐drought.

Drought legacies and ecosystem responses to subsequent drought

“…Furthermore, resilience to a subsequent drought is probably decreased by drought frequency, that is the number of consecutive drought events. Several studies in fact support the notion that a higher drought frequency decreases both resistance (Bose et al, 2020; Xu et al, 2021) and recovery (Gao et al, 2018; Peltier & Ogle, 2019; Szejner et al, 2020; Jiao et al, 2021; Serra‐Maluquer et al, 2021). However, the opposite, that is a higher drought frequency leading to a higher resilience, has also been shown (Yao et al, 2022; see also the above section on adaptations shaping the resilience to a subsequent drought event).…”

“…Lindberg and Bengtsson (2006), Coyle et al (2017); 8. Saatchi et al (2013), Kannenberg, Novick, et al (2019), Jiao et al (2021), Senf et al (2021); 9. Griffin‐Nolan et al (2018), Sala et al (2012), Petrie et al (2018), DeVries et al (2016), Yang et al (2018), DeVries et al (2019), Wigneron et al (2020); 10.…”

Revisiting the cumulative effects of drought on global gross primary productivity based on new long‐term series data (1982–2018)

“…Previous studies have reported that long‐term drought leads to a prolonged recovery period of vegetation, in which the rate of increase of GPP is significantly smaller than the recovery after short‐term drought (Hoover & Rogers, 2016; Li et al, 2019). Furthermore, long‐term drought could result in an incomplete GPP recovery, i.e., GPP could not restore to pre‐drought levels (Jiao et al, 2021). All those above negative effects result in a larger CV in GPP under longer CED.…”

Warmer and drier conditions have increased the potential for large and severe fire seasons across south‐eastern Australia

“…Increased exposure of forests to high‐severity fire will undoubtably increase CO 2 emissions (Bowman et al., 2021) and reduce stored carbon across vast areas of south‐eastern Australia (Fairman et al., 2022). The impacts of these shifts in fire regimes will be compounded further by drought, which will likely decrease ecosystem resistance and impair ecosystem recovery (Enright et al., 2015; Jiao et al., 2021; Nolan et al., 2021). Targeted management of ecosystems aimed at increasing resistance and resilience will be required to mitigate the elevated risk of high‐severity fires over the region (Bowman, Kolden, et al., 2020).…”