Seed release in serotinous lodgepole pine forests after mountain pine beetle outbreak

Area of Science:

• Forest Ecology
• Entomology
• Botany

Background:

• Serotinous lodgepole pine (Pinus contorta var. latifolia) in the Rocky Mountains rely on fire for cone opening and natural regeneration.
• Mountain pine beetle (MPB) outbreaks cause widespread tree mortality, raising concerns about reduced regeneration due to altered cone serotiny.
• MPB-killed trees may lose their canopy-stored seed banks before fire can trigger cone opening.

Purpose of the Study:

• To determine the extent of serotiny loss in lodgepole pine stands following MPB mortality.
• To quantify seed release from canopy cones via breakage and in situ opening, and seed loss to predation.
• To assess the formation of a forest-floor seed bank from buried cones.

Main Methods:

• Studied 20 stands in British Columbia, Canada, categorized by years since MPB mortality (0, 3, 6, 9 years).
• Monitored cone fall, canopy cone opening, seed release, rodent predation, and cone burial over two growing seasons.
• Quantified seed bank loss from MPB-killed trees compared to live control stands.

Main Results:

• MPB-killed stands experienced significantly more cone fall (3.5x) via branch breakage compared to live stands.
• After 6 years, MPB-killed stands released 45% of their canopy seed bank through opening, breakage, and predation.
• A modest forest-floor seed bank (6% of original canopy bank) formed from buried cones, potentially viable after future disturbances.

Conclusions:

• MPB mortality leads to substantial loss of serotinous seed banks, impacting natural regeneration potential.
• Disturbances creating seedbeds are crucial shortly after tree mortality to capitalize on remaining seed banks.
• Sustained seed rain post-outbreak may benefit ground-foraging vertebrates, and buried cones offer future regeneration potential.