Life after Beetle: Stand Dynamics Post-Outbreak(s)

Cooperative Extension SpecialistJodi Axelson, Ph.D.

Types of Disturbance

Key attributes of disturbances include: • Type • Severity • Spatial and temporal characteristicsstand level vs landscape level short-time frame vs long-time frame + return interval & historical range of variability

• Disturbance interactions

Historical Bark Beetle Outbreaks

“After ruining a billion and a half feet of the choicest lumber in the Black Hills and ravaging thousands of acres of the finest pine trees in the West, the little bark beetle has robbed Uncle Sam's forestry division of $10,000,000 in the last ten years…” (Deadwood newspaper ~1890s)

Drought + Bark Beetles

Interaction = Drought → Western Pine Beetle Outbreak

Era of Mega-Disturbance? • Mega-disturbances – defined as capable of

driving abrupt tree mortality of a spatial extent, severity, and frequency greater than that recorded in recent human history

• Hotter droughts are emerging as novel drivers of forest mega-disturbance:Interacting with other stressors such as

outbreaks of insects and pathogensCatalyzing major changes in fire regimes

Millar, C. and N. Stephenson. 2015. Temperate Forest Health in an Era of Emerging Megadisturbance. Science 349:823–826.

Disturbance Interactions

Millar, C. and N. Stephenson. 2015. Temperate Forest Health in an Era of Emerging Megadisturbance. Science 349:823–826.

Hicke, J, A. Meddens, C. Kolden. 2016. Recent Tree Morality in the Western United States by Bark Beetles and Forest Fires. Forest Science, 62: 141-153

Mortality in the West

Hicke, J, A. Meddens, C. Kolden. 2016. Recent Tree Morality in the Western United States by Bark Beetles and Forest Fires. Forest Science, 62: 141-153

Mortality in the West

Bark Beetle Outbreaks

Not all trees are killed in a bark beetle outbreak –why?• Host specific• Size specific• Natural thinning

agentIps attack MPB attack

http://bofdata.fire.ca.gov/board_business/binder_materials/2016/aug_2016/full/full_13.0_presentation-_63_million_dead_trees_and_counting_dr._c.j._fettig.pdf

• Western pine beetle (WPB) - ponderosa pine & coulter pine

• Mountain pine beetle (MPB) - many pine species including sugar pine Size specific: prefer larger trees – trees less than

6" in diameter rarely attacked

• CA fivespined Ips - most common on ponderosa, lodgepole, sugar, and Jeffrey pines Size specific: attack tops of larger trees or attack

smaller trees less than 10” diameter

Bark Beetle Outbreaks

In the central BC on the Chilcotin plateau long-term plots illustrated a shift in the size structure of stands but not species

Post-MPB in Central BC

Overstory shifted to uneven-aged lodgepolepine forest

Understory returned to lodgeople pine and increased in aspen

Post-MPB in Central BC

Axelson J., R. Alfaro, B. Hawkes. 2010. Changes in stand structure in uneven-aged lodgepole pine stands impacted by mountain pine beetle epidemics and fires in central British Columbia. The Forestry Chronicle 86: 87-99.

Post-MPB in Central BC

Post-MPB in Central BC

Post-MPB in Southern BCIn the southern BC forest plots illustrated a shift in the size structure of stands + shift in regenerating species

Even-agedstand withclosed canopy

Heavy pinegrass andmoss coveringforest floor

Axelson J., R. Alfaro, B. Hawkes. 2009. Influence of fire and mountain pine beetle on the dynamics of lodgepole pine stands in British Columbia, Canada. Forest Ecology and Management 257: 1874-1882.

Post-MPB in Southern BC

Post-MPB in Southern BC

Central – South ComparisonStand Type Mean Tree

density (sph)

Mean DBH(cm)

Mean Height

(m)

Mean Percent Species

Dominant Canopy

Even-age 2525 12.54 13.64 97% Lodgepole pine 3% Douglas-Fir

Uneven-age 1180 12.98 11.00 97% Lodgepole pine 3% Trembling Aspen

Sub-Canopy

Even-age 1508 4.55 6.54 87% Lodgepole pine

2% Douglas-Fir 1% Spruce

Uneven-age 2063 3.07 3.73 76% Lodgepole pine 24% Trembling aspen

Post-MPB in Southern AlbertaIn the Rocky Mountains of Alberta long-term plots illustrated a shift in size and species Overstory shifted from lodgepole pine to canopy of

mixed species Understory dominated by shade tolerant species with

no pine regeneration

Saplings Regeneration

Poplar Subalpine fir

Lodgepole pine Interior spruce

Post-MPB in Southern Alberta

29% Overstory Mortality Axelson et al. in preparation

Saplings Regeneration

Overstory

Poplar Subalpine fir

Lodgepole pine

Interior spruce

Post-MPB in Southern Alberta

93% Overstory Mortality

Waterton Lakes National Park 30 years after mountain pine beetle outbreak demonstrates resilience: • Changes in both stand composition and structure – greater

heterogeneity• Higher components of non-pine species - subalpine fir,

white spruce, balsam poplar• Greater variety of stand structures due to canopy mortality,

tree fall, and regeneration• Reduced probability of severe mountain pine beetle

outbreaks spreading across the landscape in the future due to species shifts

Post-MPB in Southern Alberta

Post-Disturbance Northern Rockies

Stevens-Rumann, C., P. Morgan, and C. Hoffman. 2015. Bark beetles and wildfires: How does forest recovery change with repeated disturbances in mixed conifer forests ? Ecosphere 6:1–17

Post-Disturbance Northern Rockies

Stevens-Rumann, C., P. Morgan, and C. Hoffman. 2015. Bark beetles and wildfires: How does forest recovery change with repeated disturbances in mixed conifer forests ? Ecosphere 6:1–17

Post-MPB Central Rockies

Diskin, M., M. Rocca, K. Nelson, C. Aoki, and W. Romme. 2011. Forest developmental trajectories in mountain pine beetle disturbed forests of Rocky Mountain National Park, Colorado. Canadian Journal of Forest Research 41:782–792.

Post-MPB Central Rockies

Diskin, M., M. Rocca, K. Nelson, C. Aoki, and W. Romme. 2011. Forest developmental trajectories in mountain pine beetle disturbed forests of Rocky Mountain National Park, Colorado. Canadian Journal of Forest Research 41:782–792.

Percentage of landscape dominated by each species prior to and during outbreak and hypothetical extreme (all lodgeople >10 cm DBH dead)

California Outbreak

• In the early 2000s, the mountain ranges in southern part of state started to experience elevated levels of tree mortality associated with drought (i.e., precipitation was the lowest in recorded history during 2001-02) and elevated populations of bark beetles and woodborers

• Walker et al. (2006) reported ~12.7% of conifers (3.5 million trees) died between 2001 - 2004. Mortality was widespread and concentrated in several tree species, most notably ponderosa and Coulter pines

Chris Fettig personal communication

• WPB activity peaked in 2002-03, reported to be the most common mortality agent associated with dead and dying pines throughout the region (USDA Forest Service 2002)

• In some areas, mortality was >80% • Ponderosa and Coulter pines >43.2 cm DBH

experienced 73.5% and 78% mortality, respectively

• Despite continuing drought and an availability of suitable hosts, WPB populations rapidly declined in 2004 (Hayes et al. 2009)

California Outbreak

Chris Fettig personal communication

Recruitment Studies in CaliforniaStanislaus Experimental Forest, 5700-5900 ft• Pine seedling density - sugar, ponderosa, and

Jeffrey pine - declined significantly through time:– Pre-logging: 310 tress/acre (766 trees/ha)– Post-logging: 148 trees/acre (368 trees/ha) – 2008 re-measurement: 27.5 trees/acre (68 trees/ha)

• Seedling abundance change from pre-logging (1929) to 2008:– Biggest increase = incense cedar 33.7% to 56.8% – Biggest decrease = sugar pine 12.4% to 3.0%

Knapp, E., C. Skinner, M. North, and B. Estes. 2013. Long-term overstory and understory change following logging and fire exclusion in a Sierra Nevada mixed-conifer forest. Forest Ecology and Management 310:903–914.

Recruitment Studies in CaliforniaTeakettle Exp. Forest, Sierra National Forest, 6200-8500 ft

Seed Rain

Incense cedar

Sugar pine

White fir

Jeffery pine

Zald, H. S. J., A. N. Gray, M. North, and R. A. Kern. 2008. Initial tree regeneration responses to fire and thinning treatments in a Sierra Nevada mixed-conifer forest, USA. Forest Ecology and Management 256:168–179.

Recruitment Studies in California

Levine, C. R., F. Krivak-Tetley, N. S. van Doorn, J.-A. S. Ansley, and J. J. Battles. 2016. Long-term demographic trends in a fire-suppressed mixed-conifer forest. Canadian Journal of Forest Research46:745–752.

Plumas National Forest, 3800-4000 ft

Historical data and reconstruction studies in the Sierra indicate mixed-conifer forests were highly clusteredwith gaps

Near Ackerson Meadow, ToulumneCounty (1941) Old growth stand of

ponderosa pineUC Library, Digital Collections

Historical Perspective

Near Jenkins Hill, Tuolumne County (1941) Ponderosa pine, sugar pine, black oak typeUC Library, Digital Collections

Final Thoughts• Even in the absence of drought tree mortality is

likely to continue - legacy effects of drought and continued bark beetle pressure

• Unknowns - Loss of ponderosa pine at lower elevations? Conversion to other forest types or shrubs? Will pine species across affected areas regenerate? Lag between tree mortality and tree fall down - how

long for the canopy to open up? Fuels – will accumulation change fire behavior and or

impede regeneration?