Changing fire regimes
Humans have altered fire regimes directly through management and
indirectly by altering the earth’s climate, and such shifts are almost
certainly also changing pyrodiversity. Perhaps the most clear effects of
altered fire regimes on pyrodiversity are seen where fire exclusion and
suppression policies have dramatically reduced burned area and shifted
fire severity patterns in fire-adapted forests (Mallek et al.2013). Conversely, climate change is increasing fire activity by
lengthening fire seasons and increasing water deficits (Flanniganet al. 2009; Abatzoglou & Williams 2016; Westerling 2016;
Hessburg et al. 2019). Given the strong link between climatic
water deficit, fire activity and pyrodiversity, these changes may
increase pyrodiversity in the short term where deficits of fire activity
currently exist but could result in lower levels of pyrodiversity for
areas with high levels of contemporary burn activity (Fig. 4a).
Additionally, in many areas larger fires are increasingly accompanied by
ever larger and simpler shaped patches of high-severity effects (Stevenset al. 2017; Steel et al. 2018), which could result in
lower pyrodiversity at fine scales. Where the frequency of high-severity
fire exceeds the natural range of variation of an ecosystem, higher
rates of type-conversion (e.g. from forests to shrubland) may occur
(Coppoletta et al. 2016; Welch et al. 2016). This may be
particularly problematic in dry areas where a further increase in water
deficit can lead to a consistent loss in productivity (Hessburg et
al. 2019) or when wildfires interact with other climate-exacerbated
disturbances such as periodic drought and beetle infestations (Coopet al. In Press). Ultimately, climate-related shifts in
pyrodiversity are likely to be uneven across the western United States
and globally. How these changes impact biodiversity and ecosystem
process may depend on whether emerging pyrodiversity patterns result in
a dramatic departure from historic fire regimes (Fig. 5).