ESPM 134 Final Studying

Past Management Practices in CA Forests

3 common characteristics:

• 100+ years of fire suppression and exclusion

• grazing

• widespread timber harvesting

Effects of historic management on current forests:

• dense, homogenous, 2nd growth forests

• susceptible to stand-replacing fires and vegetation shifts

• many conifers are not able to produce a soil/aerial seed bank. Live trees are required to regenerate conifer species. During stand-replacing fires, Shifts in vegetation species may occur.

Contemporary Forest characteristics and altered fire regime

• increased tree density → increased competition and higher drought stress and mortality.

• Increased mortality in large trees specifically

• Altered Fire regime: greater potential for stand-replacing fire effects

• Larger patches of stand-replacing effects on forests

Resilient Forests - Historic Sierras

• Historic Sierras had mosaics of vegetation and gaps within the landscape. Fewer trees led to heterogeneity of disturbances that happened.

• more frequent yet smaller fires, leading to landscape-level mosaics of vegetation in plant communities

Benefits of Heterogeneity and incorporation in Forest Management

Benefits:

• Creates variation in plant community types across a landscape, higher biodiversity, habitat types, resilience to disturbance

Incorporation into Forest Management:

• work with natural gradient because of microclimate variation: more dense vegetation on south-facing slopes (wetter and cooler compared to north-facing slopes), aspect and the soil type → use these gradients in mechanical treatments

• use wildfire in areas that already have low to moderate severity fire, incorporate variation into the restoration/planting of species

Fire and Fire Surrogate Study at Blodgett Forest Objectives (NOT DONE)

Study Objectives:

• Mechanical only units: two stage prescriptions → 1.) crown thinned followed by thinning from bellow 2.) mech mastication of understory (appx. 90%),

Mechanical Thinning Only

• Ecological Application: Reduction in fuels, increased heterogeneity in thinning treatments (intentional gaps

• Pros: more control over the outcome, less risk compared to prescribed burning, economic value, immediate growth response

• Cons: It changes the fuel structure but does not get rid of them entirely (you still have to find ways to remove fuels on the surface).

• 3 Constraints:

  • 1.) Operational: Mechanical thinning operations are very limited due to steep slopes and roadless areas

  • 2.) Legal: land restrictions in where you can implement mechanical thinning treatments

  • 3.) Administrative: proximity to sensitive features that limit where you can operate

Fire Only treatment

• Ecological Applications: mineral deposition increases pine tree regeneration and it heats up the soil

• Pros: consumes all fuels and is naturally heterogeneous

• Cons: There are many legal/operational restraints → the proximity to urban areas/houses, proper burning windows, climatic conditions

  • lack in control of burning (risk of fire escaping), fire causes short-term injuries and stress to trees

Fire and mechanical Thinning Treatments:

• Ecological Applications: Mech thinning replicates self-thinning from resource competition, drought, or insect outbreaks. Prescribed burns replicate natural wildfire events

• Pros: Mechanical thinning prepares forest for better burning condiitons and leads to the highest reduction in fuels. It is economically valuable and provides all of the ecological benefits from fire (mineral deposition in soil)

• Cons: Increased risk of high severity from build up of surface fuels and then burning them. There are also two times the amount of constraints in planning these management practices (accessibility issues, getting legal permits for mechanical thinning and burning, proper climatic conditions)

Wildland Fire Use

• Pros: Natural ignition of fire and letting it burn is significantly cheaper since you don’t have to plan for fire lines and a holding crew.

  • higher pyrodiversity: diversity of fire characteristics and behavior (fire frequency, intensity, and type)

  • high legal and operational feasibility

• Cons: only allowed under limited conditions (very remote areas), risks = fire and smoke. There are a lot of costs that go into burning (labor, permitting, insurance)

• Examples: Illilouette Creek Basin, Sugarloaf Creek Basin

How are mechanical treatments ecologically different from fire?

• Mechanical treatments compact the soil while fire treatments heat and deposit minerals

• mechanical treatments change fuel structure, while fire consumes them

• Fire treatments produce minerals in soil that allow pine seedlings to regenerate. Mechanical treatments do not do this

• Fire treatments remove competing shrub species, allowing for new tree seedling regen

What does it mean when a fuel treatment has a life span?

There is a specific amount of time where fuel treatments will work effectively. After this amount of time, they arent able to reduce fire behavior as well.

• Life span = 10 years depending on:

  • type and intensity of treatment

  • site productivity

  • interactions with other disturbances/stressors

Long - term impacts of fire management on Illilouette Creek Basin

Illilouette Creek: Conifer dominated in 1970s after fire suppression → denser and more homogenous trees.

• Post-fire: Fire created a more spatially heterogeneous environment, stopped conifers from drying out and encroaching on meadows

• increased stream flow and decrease in drought-related mortality

Fire Treatment Benefits on Landscape scale Resilience

Benefits of Fire to a landscape:

• reduces tree density → increase in water availability

• less competition increases overall health of trees post fire

• Reduces wildfire risk and increases resilience in the face of disturbance

Long-term Managed Fire Impacts on Landscape scale resilience

• Overall reduction in forest carbon but are more stable

• increased water benefits on reduced forest cover: this leads to more persistent snowpack and increased soil moisture/water storage

• High pyrodiversity: more variation in fire behavior leads to more variation in plant communities across space and time

  • more fire variation leads to increased biodiversity of pollinators and understory plants (higher to replicate with prescribed burning) and overall resilience

What are the future climatic changes in California?

• temperature increase of over 1 celcius

  • increase in the frequency of heatwaves

• A drier overall future (some areas may exhibit slight increases in precipitation)

  • increase in drought risk

• earlier snowmelt (30-80 days earlier) and less snowpack (loss of 75%)

  • mid-elevation will have the most impact

What are the short term impacts of climate change on Fire?

• warmer and drier days → more bad fire days

• longer fire seasons: in the sierras, the fire season traditionally happens in the late summer and fall. Now, as the climate becomes hotter and drier, this season may be extended

• Wet pulses of growth = moments of significant growth → vegetation dries out → high fuel production

• increased drought: drought-stressed trees are more prone to bark beetles, fungal pathogens

• high mortality → high fuels → more potential for increase in fire frequency and severity

What are the long-term effects of Climate change on fire?

Changing vegetation types leads to new fire regimes

• This creates positive feedback loop shifting towards shrub-dominated landscape (when the impact of a change re-enforces that change)

  

What are some Climate Change-related synergies?

drought-stressed trees are more vulnerable to bark beetle outbreaks and fungal pathogens. This increased mortality adds to the over-abundance of forest fuels and increases the risk of severe wildfire

Why do North vs South facing slopes effect vegetation differently? How does slope affect vegetation on N or S slopes?

• South Facing slopes are dried because they are exposed to more sunlight and higher temperatures. This leads to more evaporation and extreme environments for plants

• North Facing slopes are cooler and wetter because they are more shaded.

• Steeper slopes have less soil and less water, so therefore less vegetation

What can we do to create more resilient forests?

• Restore historical forest structure through replicating historical disturbances

• Implement historical disturbance through fuel treatments:

  • mechanical thinning

  • wildfire and prescribed burning

  • mechanical thinning and fire

What are the various fire regimes within CA forests? How do they relate to Climate and Fire?

• In dry forests, fuel-limited systems cause fire

• in cold-wet forests, temperature-limited systems cause fire

How are climate, bark beetles, and fire related?

As climate change increases the fire seasons, it allows bark beetles to complete more generations per year and reproduce at a faster rate.

•  no overwintering freeze and less mortality, plut they have a longer warm period

• The MPB now can have two gens/year and double their pop

What are the landscape level effects of pre-fire mortality?

• Immediate response: Decrease in canopy fuel moisture with high tree mortality

• 10 yrs from now: decrease in canopy fuel load and increase in live surface fuel

How is the vegetation predicted to change under current Climate conditions?

Decrease in Doug Fir and grasslands

increase in chaparral, desert scrub, some mixed conifer, ponderosa pine

What are Climate Adaptive Strategies that we can take in the face of Climate Change?

RAD → Resist, Accept, Direct

• R → Resistance: maintain the current conditions to prevent them from getting worse, protect valuable species

• R → Resilience:  prescribed burns and thinning to allow forests to be wetter and regenerative after fire

• R → Response: Facilitate the conditions required to transition forests from their current → plant something different after fire that will tolerate future conditions

What are the three factors that make up a fire regime

1.) Climate

2.) Vegetation

3.) Ignitions

What are the determinants of population Change?

What are the determinants of environmental favorability regarding population change? which factors are constant and which change year to year?

• Abiotic Factors (impact birth rate, death rate, immigration and emigration rates: geography, landscape, soil, climate

  • geographic and landscape factors = constant

• Biotic Factors: Food quality and natural enemies

  • natural enemies, food availability change year to year

• Disturbance Factors: Humans and weather (change year to year)

what is a degree day? How is it calculated? link this to changes in the climate we have been seeing. 

• Degree Day: measure of heat accumulation to predict/monitor insect development stages (eggs hatching, adult emergence from pupa)

  • T determines how many generations can be completed per year

• Calculated by:

  

• Degree days are important because they allow us to predict population outbreaks and understand population cycles for management practices.

• Linked to Climate: Warmer temperatures facilitate the transition from endemic species to outbreak by allowing greater proportional survival. As climate change causes average temperatures to increase, we can expect more proportional survival of insect populations, which could perpetuate more outbreaks

Mountain Pine Beetle Impacts and Temperature

• Warm winter temp -→ greater proportional survival: transition from endemic to outbreak

• temp = good indicator of population cycle (beetle development rate and timing)

• MPG egg stage is very vulnerable to temperature. The timing of adult emergence and oviposition determine whether eggs are exposed to extreme temperatures

What is a cold-adapted species?

• Insects that depend on low temperatures to trigger development

• A longer warm season or early spring can cause phenological mismatch and cause issues with development

• Example: Winter moths (Operopthera brumata) are synchronized to oak bud emergence. The warm temperatures cause winter moth to hatch before oak bud emergence → missed feeding window

What are the biotic factors of pest population management/suppression

Top down: Natural enemies, parasitism, and disease

• Spruce Budworm are suppressed by parasitoid wasp

• In warm winters (Abiotic factor) the spruce budworm can

Bottom up: Host plant quality and availability

• Plant Stress drought causes plants to reallocate N to increase it in the sap which decreases tree defenses, making stressed plants yummy for bark beetles and sap feeders

• Plant vigor Strategies: healthy trees (vigorous plants) allow eggs to be laid selectively (gall formers, leaf miners, shoot feeders)

Lateral Factors: insects at the same trophic level change bottom up factors for other insect species

• Ex: Winter Moth and Green Oak Tortrix: Winter moth develops earlier → induces tree defense chemicals and increase the tannins in the tree → reduces GOT success (they emerge later)

• Pine Sawfly and Pine Butterfly (scotch pine): PSF feeds on needles → the tree sends more N and terpenes to PS which improves quality for PB larvae

How does density dependence affect pest populations?

• Density Dependent factors: affect populations based on size or density

  • Negative density dependence: leads to state of equilibrium

    • Density increases → death rates increase but birth remains the same, leads to oscillating around carrying capacity

    • If population starts low and birth rate is high then birth will decrease as death increases and again reach equilibrium

  • Positive density dependence leads to a state of instability

    • Density increases as births increase and if death remains constant then will get to a point where parasitoids can’t keep up 

      

  • T = critical threshold density

  • If they are above the threshold, we would expect their population to continue in growth until something happens

  • If they start below the threshold, then they would decrease to extinction until something happens

Define endemic vs incipient vs irruptive phases of beetle attacks; which ones are associated with positive vs negative density dependence