Post on 30-May-2018
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)
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 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
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?