Disturbance and productivity interactions mediate stability of forest composition and structure

Area of Science:

• Forest Ecology
• Fire Ecology
• Dendrochronology

Background:

• Conifer forests historically shaped by fire are changing due to fire exclusion.
• Ecological responses to fire exclusion vary, even with similar historical fire regimes.
• Understanding drivers of forest composition and structure change is critical for conservation.

Purpose of the Study:

• To investigate how historical disturbance frequency and site productivity influence forest stability after fire exclusion.
• To analyze changes in species composition and structure across a gradient of forest types.
• To differentiate effects of fire exclusion from high-severity fire impacts.

Main Methods:

• Spatially explicit dendrochronological reconstruction of tree population dynamics and fire regimes.
• Analysis of forest composition and structure stability along an ecological gradient (pine, mixed-conifer, spruce-fir).
• Comparison of forest responses under varying site productivity and historical disturbance levels.

Main Results:

• Forest structural density increased across all sites.
• Species composition remained stable in low (pine) and high (spruce-fir) productivity forests.
• Intermediate productivity mixed-conifer forests showed the least stable composition, shifting to fire-sensitive species within 20 years of fire exclusion.
• Fire exclusion can mimic high-severity fire impacts by altering selective pressures from disturbance to productivity.

Conclusions:

• Site productivity is a primary control on forest composition and structure stability, overriding historical fire regimes.
• Fire exclusion drives significant shifts in forest dynamics, particularly in mixed-conifer ecosystems.
• Restoring disturbance-adapted characteristics in intermediate productivity forests is vital for climate change adaptation and resilience.