Abstract
Drought and warming increasingly are causing widespread tree die-offs and extreme wildfires. Forest managers are struggling to improve anticipatory forest management practices given more frequent, extensive, and severe wildfire and tree die-off events triggered by “hotter drought”—drought under warmer than historical conditions. Of even greater concern is the increasing probability of multi-year droughts, or “megadroughts”—persistent droughts that span years to decades, and that under a still-warming climate, will also be hotter than historical norms. Megadroughts under warmer temperatures are disconcerting because of their potential to trigger more severe forest die-off, fire cycles, pathogens, and insect outbreaks. In this Perspective, we identify potential anticipatory and/or concurrent options for non-timber forest management actions under megadrought, which by necessity are focused more at finer spatial scales such as the stand level using higher-intensity management. These management actions build on silvicultural practices focused on growth and yield (but not harvest). Current management options that can be focused at finer scales include key silvicultural practices: selective thinning; use of carefully selected forward-thinking seed mixes; site contouring; vegetation and pest management; soil erosion control; and fire management. For the extreme challenges posed by megadroughts, management will necessarily focus even more on finer-scale, higher-intensity actions for priority locations such as fostering stand refugia; assisted stand recovery via soil amendments; enhanced root development; deep soil water retention; and shallow water impoundments. Drought-induced forest die-off from megadrought likely will lead to fundamental changes in the structure, function, and composition of forest stands and the ecosystem services they provide.
Highlights
Widespread tree die-offs and extreme wildfires are increasingly being triggered by drought and warming across the globe (IPCCa, 2014; Hartmann et al, 2018; Brando et al, 2019a)
Ecological cascades triggered by extreme hotter drought and multi-year to multi-decadal megadrought in the Western U.S could progress through alternate states from climate-disturbed forest, to woodland, shrubland, invasive grassland, and even extremely degraded ecosystems (Allen et al, 2007; Romme et al, 2009; Cobb et al, 2017)
Preservation of existing forest might be feasible at finer scales of stands using higher intensity and potentially novel management. In this Perspective, we focus on forest management options under megadrought, which are largely constrained to finerscale, higher-intensity practices
Summary
Widespread tree die-offs and extreme wildfires are increasingly being triggered by drought and warming across the globe (IPCCa, 2014; Hartmann et al, 2018; Brando et al, 2019a). Being considered is the option to let forests progress through change and try to somewhat modify that change rather than prevent it (Millar and Stephenson, 2015) This might be relevant for regional-scale megadroughts— multi-year to multi-decadal droughts with levels of aridity that are as dry as the extreme droughts of the twentieth century— which have been documented in long-term tree-ring data and precipitation records throughout many regions worldwide (Ault et al, 2016; Ault and St. George, 2018). We (1) introduce a scenario framework to discuss potential ecological trajectories and management options; (2) briefly recap traditional forest management options and emerging concepts for dealing with hotter drought events; (3) highlight finer-scale, higher-intensity stand management options that might be used in an attempt to buffer forests from megadrought (extending initial general concepts noted by Millar and Stephenson, 2015); and (4) propose that novel challenges associated with mitigating megadrought impacts need to be considered, evaluated, and researched more extensively to enhance our forest treatment toolbox for more effective forest management under emerging global change stresses
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