The role of extreme rain events in driving tree growth across a continental‐scale climatic range in Australia

Alison J O'Donnell,Kathryn J Allen,Pauline F Grierson,Michael Renton

doi:10.1111/ecog.05671

Alison J O'Donnell, Kathryn J Allen + Show 2 more

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https://doi.org/10.1111/ecog.05671

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Abstract

Rainfall regimes in many parts of the world have become increasingly dominated by fewer, but more extreme, rainfall events. Understanding how tree growth responds to changes in the frequency and intensity of rain events is critical to predicting how climate change will impact on forests and woodlands in the future. In this study, we used five tree‐ring records of the native Australian conifer Callitris columellaris that span a large (> 20°) latitudinal and climatic gradient from the mesic (tropical) north to the xeric (semi‐arid) south of Australia to investigate how inter‐annual and spatial variation in the delivery of rainfall (the intensity and frequency of rain events) influences tree growth. In semi‐arid biomes (~300–400 mm rainfall annually), tree growth is most strongly related to the amount of rainfall from heavy (> 75th percentile) rain days or the number of extreme (> 90th percentile) rain days, regardless of differences in the seasonal distribution and average intensity of rainfall among sites. Our findings also indicate that there is likely a minimum threshold amount of daily rainfall (~5 mm) that is required to stimulate tree growth in the semi‐arid zone. In contrast, in the tropics (> 800 mm annual rainfall), inter‐annual variation in growth is best explained by total growing season rainfall or the number of rain days > ~5 mm (~50th percentile of rain days) rather than extreme rainfall. Our findings indicate that not all rain events are important for driving tree growth, which has important implications for interpreting climatic signals in tree rings. Our findings also indicate that projected increases in the intensity of extreme rain events are likely to have contrasting impacts on tree growth across biomes, with greater and positive impacts on growth in semi‐arid biomes and potentially negative impacts on growth in tropical biomes of Australia.

Highlights

Extremes of rainfall are potentially more important drivers of plant processes than mean conditions (Knapp et al 2002, 2008, Kulmatiski and Beard 2013, Reyer et al 2013, Zeppel et al 2014)
Despite pervasive observations and projections of increases in the frequency and intensity of extreme rainfall events in many regions of the world (IPCC 2013, Alexander 2015, Monier and Gao 2015, Donat et al 2016, Good et al 2016, Mallakpour and Villarini 2017, Myhre et al 2019), remarkably little is known of how important extreme rain events are for driving plant processes, the growth of woody plants, and how plant growth may respond to changes in the frequency and intensity of extreme rain events
Extreme rain events are important for driving tree growth in semi-arid Australia, where we found that the heaviest 10–25% of rain days explain the most inter-annual variation in growth of Callitris columellaris

Summary

Introduction

Extremes of rainfall are potentially more important drivers of plant processes than mean conditions (Knapp et al 2002, 2008, Kulmatiski and Beard 2013, Reyer et al 2013, Zeppel et al 2014). The importance of extreme rain events for driving ecosystem productivity and woody plant growth likely differs among biomes depending on their typical potential evapotranspiration and rainfall rates (Reynolds et al 2004, Gerten et al 2008, Knapp et al 2008, Kulmatiski and Beard 2013, Guan et al 2014, Zeppel et al 2014, Manea and Leishman 2018). Extreme rain events can infiltrate deeper into the soil profile and result in proportionately smaller evaporative losses than smaller rain events in xeric biomes (Kulmatiski and Beard 2013, TugwellWootton et al 2020) and may be important for driving woody plant growth by increasing water availability in the root zone (Knapp et al 2008, Raz-Yaseef et al 2012, Kulmatiski and Beard 2013). There is very little empirical evidence of the role of extreme rain events in driving the growth of plants, the growth of woody plants in shrub- or tree-dominated ecosystems across both mesic and water-limited biomes (Beier et al 2012; but see Kulmatiski and Beard 2013, Ye et al 2016)

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