Prescribed fire is an effective restoration measure for increasing boreal fungal diversity

Intensive forestry practices have had a negative impact on boreal forest
biodiversity, subsequently, the need for restoration is pressing.
Polypores (wood-inhabiting fungi) are key decomposers of dead-wood, but
due to the lack of coarse woody debris (CWD) in forest ecosystems, many
species are threatened. Here, we study the long-term effects on polypore
diversity of two restoration treatments; creating CWD by felling whole
trees and prescribed burning. This large-scale experiment is located in
spruce-dominated boreal forests in southern Finland. The experiment has a
factorial design (n=3) including three levels of created CWD (5, 30 and 60
m3 ha-1) crossed with burning or no burning. In 2018, 16 years after the
initiation, we inventoried polypores on ten experimentally cut logs and
ten naturally fallen logs per stand. We found that overall polypore
community composition differed between burned and unburned stands.
However, only red-listed species' abundances and richness were
positively affected by prescribed burning. We found no effects of CWD
levels created mechanically by felling of trees. We show, for the first
time, that prescribed burning is an effective measure for restoring
polypore diversity in late-successional Norway spruce forest. Burning
creates CWD with certain characteristics that differ from what is created
by CWD-restoration by felling trees. Prescribed burning promotes primarily
red-listed species, demonstrating its effectiveness as a restoration
measure to promote diversity of threatened polypore species in boreal
forest. However, as the CWD that the burning creates will decrease over
time, to be functional, prescribed burns need to be applied regularly at
the landscape scale. Large-scale and long-term experimental studies, such
as this one, are invaluable for establishing evidence-based restoration
strategies.