Altered fire regimes cause long‐term lichen diversity losses

Abstract

Many global ecosystems have undergone shifts in fire regimes in recent decades, such as changes in fire size, frequency, and/or severity. Recent research shows that increases in fire size, frequency, and severity can lead to long-persisting deforestation, but the consequences of shifting fire regimes for biodiversity of other vegetative organisms (such as understory plants, fungi, and lichens) remain poorly understood. Understanding lichen responses to wildfire is particularly important because lichens play crucial roles in nutrient cycling and supporting wildlife in many ecosystems. Lichen responses to fire have been little studied, and most previous research has been limited to small geographic areas (e.g. studies of a single fire), making it difficult to establish generalizable patterns. To investigate long-term effects of fire severity on lichen communities, we sampled epiphytic lichen communities in 104 study plots across California's greater Sierra Nevada region in areas that burned in five wildfires, ranging from 4 to 16 years prior to sampling. The conifer forest ecosystems we studied have undergone a notable increase in fire severity in recent decades, and we sample across the full gradient of fire severity to infer how shifting fire regimes may influence landscape-level biodiversity. We find that low-severity fire has little to no effect on lichen communities. Areas that burned at moderate and high severities, however, have significantly and progressively lower lichen richness and abundance. Importantly, we observe very little postfire lichen recolonization on burned substrates even more than 15 years after fire. Our multivariate model suggests that the hotter, drier microclimates that occur after fire removes forest canopies may prevent lichen reestablishment, meaning that lichens are not likely to recolonize until mature trees regenerate. These findings suggest that altered fire regimes may cause broad and long-persisting landscape-scale biodiversity losses that could ultimately impact multiple trophic levels.

The species diversity × fire severity relationship is hump‐shaped in semiarid yellow pine and mixed conifer forests

“…, Miller et al. ). It is also worth noting that understory plant diversity loss as a result of persistent montane chaparral and other characteristics associated with high severity could have other important implications that manifest in ecosystem services as reduced nutrient availability and disrupted soil hydrology (e.g., higher erosion rates and sediment input into reservoirs) as well as food and forage provisioning (Wells et al.…”

Are plant community responses to wildfire contingent upon historical disturbance regimes?

“…(2015) reported that species with traits resulting in lower environmental stress tolerance (e.g., low specific leaf area) were more likely to disappear after high‐severity fire in FRG I forests, highlighting that high‐severity fire might produce warmer, drier environmental conditions that might be intolerable to plants adapted primarily to low‐severity fire and the relatively mesic conditions provided by forest canopies. Recent research has indicated that altered environmental conditions after high‐severity fire in FRG I/III forests may also cause diversity losses in lichens, another taxonomic group sensitive to large‐scale loss of tree cover (Miller, Root, & Safford, 2018).…”

Fire severity and changing composition of forest understory plant communities

“…The strong and persistent thermophilization observed in stands that experienced moderate‐ and especially high‐severity fire suggests that canopy removal by fire contributed to the strong differences in post‐fire communities among severity classes. Recent research also suggests that altered microclimates caused by high‐severity fire in dry forests may lead to long‐term diversity losses of lichens, another taxonomic group that is characteristic of cooler, more mesic environments (Miller, Root, & Safford, ).…”