the mountain pine beetle: ideas on population dynamics & management in lodgepole pine
TRANSCRIPT
The Mountain Pine Beetle: Ideas on Population Dynamics & Management in
lodgepole pine
(1) I’ll review some of the basics of Dendroctonus ponderosae (MPB) as I go along.
(2) I’ll concentrate on MPB host selection behavior and barkbeetle management.
(3) I hope my thoughts will not crash: They’re new.
Whenyou’re lookingunder the barkof a dead pine, the MPBgalleries are sometimesdifficult to describe.
Important Review Topics:
1. MPBs have a sophisticated host selection scheme;
2. Populations disperse out of their host trees in spring and go into a down-
wind-random-dispersal flight;
3. Pioneering females find a weakened pine and expel a population-attracting
pheromone – cis-verbenol.
4. When the MPB attack density of a selected pine reaches a point where the
sexes are 50:50 the tree is no longer attractive. Why? At mating males
expel a masking pheromone – verbenone.
5. The switching mechanism takes over if the MPB population is high.
There are scattered susceptible lodgepolepines across the landscape – focus trees.
So let’s look at an endemic MPB population
The members of a low MPB population have the tough task of being able to find & colonize these scattered, water-stressed focus trees.
What they have is a super host-selection scheme.
Flying MPB Adults
MPB population isin a down-wind randomdispersal flight.
Susceptible pine (focus tree)
Pioneer
cis
-ver
be
no
l MPB populationnow flies up-wind in a concentratedflight.
Dispersal loss dropssignificantly.
Mass Attack
1st 2nd
Flying MPB Population
Susceptible pine (focus tree)
Pioneer
cis
-ver
be
no
l
1st 2nd
Random dispersal
Dispersalmortality is huge
Directedconcentration
Lowmortality
Dispersal flight:• Search the landscape for susceptible hosts – focus trees.• Mixes the gene pool and this is important: a period when the fittest are selected.• Provides a huge source of dispersal-mortality.
Concentration flight:• Provides a beacon to the formerly-dispersing beetles.• Ends a major source of population mortality. Even dumb beetles survive when their sense the aggregant.
Thoughts on Dispersal & Concentration Flights.
When the MPB population is low the host selection flight is desperately important in finding these scattered hosts.
Remember there are few scatteredfocus trees acrossthe landscape.
Few
MPB Latent Population
B.C.Long term drought pattern
200910yr October
Drought Index of NOAA
As a drought continues, more and more trees are stressed and more focus trees are created.
As more weakened trees are attacked, the higher goes the MPB population – exponentially!
“Once the population is high look out for the switching mechanism?”
When MPB population is high example
A focus tree is attracting males and females via the pheromone cis-verbenol produced by attacking females. Host volatiles also play a role in the bouquet of attraction.
But just at matingmales produce theanti-aggregant, verbenone.
Hours/minutes
Acc
um
ula
tive
atta
ck
Focus tree
Hundreds of males & females
attacking the focus tree
When thesexes arepaired
Time 1
Thetree is no longer attractive.
Time 2
Recipienttree
Time 3Neighboring tree is attacked
Spread of an MPB Spot in Lodgepole Pine: theswitching mechanism. The formerly concentrating
MPB, switch to the next largest tree(s)
F
R2
More spread of an MPB-Lpp Spot: the switching mechanism continues and beetles keep on picking-off the biggest recipient tree.
F1
R1
R2
R3
F2
R2
R3
In lodgepole pine, why do the MPBs switch attacks to the largest recipient trees?
The phloem of Lpp isthin! Whereas the phloemof ponderosa pine is thick.
During the first years of the outbreak the MPB population suffers “normal curve” mortality.
All 98.8% 69.9%
Tree DBH
% Mortality% Mortality Good SurvivalGood Survival
Fr
Why? Lodgepole pines have thin bark! The trees with small DBH have the thinnest phloem & highest brood mortality.
“…look at the variance.”
In lodgepole pine the MPBs that were concentrating on a focus tree switch their attacks to the next biggest recipient-tree. Ultimately they do a “diameter-limit cut.”
Switching mechanism (continued)
Meanwhile, the drought continues
(1) More and more focus trees & recipient trees are created: this increase is coupled with --
(2) Continuing use of the switching mechanism in host selection – less selection of the keenest beetles,
(3) Switching behavior signifies more and more brood trees are established & MPB populations go even higher.
The drought continues!
2015
Myriad of focus trees across the watersheds right at the time beetles start to emerge in
spring!
Early spring flight (…for whatever reason some emergefirst.)
Main spring flight
Time (days)
% E
mer
ge
nc
e
Flying Pop.
Freshly attacked trees are common since they were
infested by the small early emergence1.
Barley significant dispersal flight.
Cis
-ve
rbe
no
l
Massive generalspring emergence ispointed in the right directionand any tree is attacked.
1 Remember, lotsof focus trees.
There is synchrony between MPB emergence andattraction to new pheromone source.
There is no synchrony and MPB population dispersesuntil susceptible hosts are found.
Any Lpp
Susceptible Lpp
Concentration Dispersal PopulationLow High
Huge outbreaks have a synchrony between spring emergence and aggregating pheromone
No Dispersal Just Synchrony Between Emergence and Aggregants – Any Pine Is
Attacked
Can you all see that inbreeding is rampant?
So where have we been in this discussion?
Mountain Pine Beetle Outbreaks
Population Characteristics Host Selection Behavior Stand/Host Conditions
(1) Initial Phase
NormalDispersal flightsAggregant productionConcentration flightsBrood establishment
70-90 yrs old lodgepole – scattered drought stressed trees (focus trees)Stagnant growth (intra specific competition high) Fire exclusion for many yrsNo silvicultural treatmentsDrought conditions continue
(2) Tree to tree spread
NormalDispersal flightsAggregant productionConcentration flightsBrood establishmentSwitching behavior wide-spread
70-90 yr old trees in drought stressFocus trees wide-spreadNo fires and stand thinningsDrought continuesMassive stand mortality
(3) Population eruption
No dispersal flightsAggregants in synchrony with emergence commonAny tree attackedPopulation inbreeding occurs leading to population decline
All 70-90 yr old trees in drought stressFocus trees ubiquitousStand replacement fires possibleLandscape-wide pine mortalityPine regeneration begins across landscape after outbreak and fires
“…ok, from the top.”
(1) The Initial Phase of a MPB Outbreak
Host Selection
- Normal - Dispersal flights - Aggregants produced - Concentration flights - Broods established
Stand/Host Conditions
- 70-90 yr old Lpp, scattered drought stressed focus trees- Stagnant growth (intra specific competition high)- Fire exclusion for many yrs- No silvicultural treatments- Drought continues
Initial Phase
As a forest manager, now is the time to thin these stands!! Why? (1) to prevent the switching mechanism (2) to increase stand vigor and, ultimately, reduce numbers of focus trees and (3) to strategically use synthetic semiochemicals (attractants and repellants)
Distance between focus tree and recipient tree neededto prevent the switching mechanism.
(2) Rapid Tree to Tree Spread
Host Selection
- Normal - Dispersal flights - Aggregants produced - Concentration flights - Broods established - Switching behavior wide spread!
Stand/Host Conditions
- 70-90 yr old Lpp, scattered drought stressed focus trees- Stagnant growth (intra specific competition high)- Fire exclusion for many yrs- No silvicultural treatments- Drought continues- Massive stand mortality begins!- Massive MPB population explosion begins!
Rapid Spread Phase
What can you do?
(1) Worry about stand replacement fires,(2) Salvage for income and fire prevention,(3) Thin drastically those stands as yet un-infested(4) Forget the use of synthetic attractants or
repellents – big waste of money.
Synchrony of emergence & attraction begins – Wham!!
(3) MPB population eruption
Host Selection
- No dispersal flights
- Aggregants in synch withwith beetle emergence
- Any tree attacked
- Population inbreedingoccurs leading to populationdecline.
Stand/Host Conditions
- 70-90 yr old Lpp, focus trees ubiquitous
- Stand replacement fires common
- Drought probably continues
- Landscape mortality
- Pine regeneration begins across landscape after outbreaks and fires.
Eruption Phase
What can you do?
(1) Pray for good mkt. in forest products.
(2) Salvage
Don’t concern yourself aboutLpp – it’ll take off on its own.
Don’t worry about theMPB population, it’llcrash on it’s own.
1. Inbreeding2. Dumb beetles - few fat bodies
- poor responders- infertile
Why?
We’ve actually studied barkbeetles to prove that within any population there are dumb beetles.
Dumb Beetles for
Attractive bait (log with beetles imbedded)
Fan
Jar
One of a group of 3 olfactometers – used to collectattracted beetles: studies on Ips paraconfusus
05 25 45 etc.
Concentric release pts. of 05m – 2k m
…and we collectedbeetles from within anoutbreak and froman endemic area.
20
05
15
10
25
30
005 25 45 100 500 1K 2K
%R
eco
very
Distance to Olfactometer (m)
Beetles from endemic area
Beetles from outbreak area
Test to see if beetles from an endemic area werebetter responders to attractants.
Freshlyemerged
Caughtresponding
Emergence cage
Logs infested with beetles about to emerge.
Responding beetles
Emerging beetles
No. of re-runs
% R
eco
very
Responding beetles
Emerging beetles
No. of re-reruns
A test to shows that beetles who responded previouslywere better suited to find attractants
Highest Qual. Food
Lower Qual. Food
Low Qual. Food(Dry and fermenting)
Days
84 1612 20
% O
f L
og
s In
fest
ed
Lpp logs attacked by Ips spp. and quickly caged.
Release and response of barkbeetles that fed on high-qual. food.
Release and response of barkbeetles that fed on low-qual. food.
Release and response of barkbeetles that fed on awful-qual. food.
A test showing how food quality affects theability of barkbeetles to respond to attractants.
Some Conclusions on MPB PopulationDynamics
• When populations are latent, there is strong selection for the keenest beetles – strong flyers and response to host and pheromone plumes over long distances is the selection mechanism.
•There is a huge dispersal loss and only keenest survive.
• Population as well as individuals are tied in to the condition of the hosts – focus trees are stressed trees and many focus trees spells the beginning of population increase.
• Countless focus trees across the landscape ultimately eliminates the flight dispersal and selection of keen beetles as well as there is an increase in inbreeding -- all important causes of population collapse.
• Massive reduction in the quality of the MPB population and lack of host material is the end of the outbreak.
Outbreak collapse is due to lack of synchrony between spring emergence & response to volatile cues. Which, in turn, is due to lack of nearby susceptible host material.
Any Lpp
Susceptible Lpp
Concentration Dispersal PopulationLow High
• No hosts nearby• Pop. poor quality• Residual MPB pop. is seed corn for next latent pop.
Initial Phase of MPB build up
1. Thinning is mandatory before manyfocus trees are created. 2. Use of synthetic attractants andrepellents should be studied.
- confusion technique- push-pull studies- trapping
3. Bring back fire into the ecosystem.
As Forest Managers, What Do We Do?
Silvicultural studies in the South clearly show there is no control during the eruptive phase of a SPB outbreak.
Makes sense
Thinning southern pines
Thinning lodgepole pine
Bring fire back into the silviculturalequation
Well, I see it’s timeto quit.