Leaf size, litter flammability, and restoration fire: Changes in stand composition influence pattern of burning

Over the last century, fire exclusion in the forests of the Sierra
Nevada has allowed surface fuels to accumulate and has led to
increased tree density. Community composition has also been altered as
shade tolerant tree species crowd out shade intolerant species. To
restore forest structure and reduce surface fuels, managers have
increasingly used prescription burning.  Prescribed burns are
constrained by factors that may not simulate natural burning patterns,
and could affect the extent to which this management practice can
return forested ecosystems to naturally functioning systems. For
example, prescribed burns may not mimic natural lightning-ignited
patterns in that they are often designed to produce homogeneous
burning patterns.  Evidence from replicated burns in Sequoia National
Park suggests that burn heterogeneity is a primary influence on
patterns of tree mortality and understory species composition.
Furthermore, current forests differ from historical conditions not
only in total fuel loads, but also in the composition of species that
contribute to the surface fuel bed.  The role that changes in stand
composition may play in influencing burning patterns has been
relatively neglected.  Evidence from both prescribed fire and wild
fire at Sequoia National Park suggests that leaf size, by changing
litter bulk density, significantly influences patterns of burn
heterogeneity and severity.  Shorter-leaved shade tolerant species,
which have increased since fire exclusion, may play a negative
feedback role by reducing fire severity.