Lecture Flashcards
What is the most widespread and destructive defoliator of coniferous forests in western NA?
- Western Spruce Budworm
What does WSB feed on?
- Larvae emerge after overwintering at same time as new spruce buds emerge and feed on them
- Coevolution to emerge at same time as buds develop on trees
What is the tree scale habitat of WSB?
- Bud flush: timing and abundance
- Size of Crown and available foliage (puffy = lots of food)
What is the stand scale factors of WSB?
- Species composition (homogeneous good for connectivity, hetero bad)
- Stand structure (Vertical heterogeneity and multiple age classes good, spin down from top and reach more food sources of lower tree tops)
- Site quality
- Standscale alone cannot fully explain spatiotemporal patterns of insect outbreaks
What could control the expansion of distinct and randomly distributed infestation patches to more continuous landscape level outbreaks?
- Landscape-level factors:
- Composition, configuration of host populations (connectivity, abundance)
- Adult moth dispersal and pred-prey interactions (dense forest decreases bird predators and increases dispersal)
What could control the expansion of distinct and randomly distributed infestation patches to more continuous landscape level outbreaks?
- Regional Factors:
- Physiography
- Climate (moisture deficits, warm dry conditions to disperse and survive, autumn precipitation)
- Drought year before outbreak causes outbreak initiation due to survivability and dispersal as well as increased nutrition in hosts from stress forcing more sugar into needles
What are the most important infestation predictors?
- Proximity to infestations in the previous year
- Landscape-scale host abundance
- Dry autumn conditions
What scale is the most important to manage for WSB outbreaks?
- Landscape because these are the factors that contribute most to the outbreaks
Pattern and fire
Species compostition and structure, including fuel amounts, size classes and arrangement
- Affects how a fire will burn
Low severity fire and where in BC does it occur
- Ecological effects minimal, species are adapted
- Fire consumes surface fuel, not into large tree canopy
- Dry forest that experiences frequent fire (except for the modern suppression)
- Interior BC, Douglas Fir, Ponderosa Pine
Severity
- Ecological effects above and below ground of a disturbance
High severity fire and where in BC does this occur
- Ecological effects profound
- Big highly flammable trees not adapted to fire, tree crowns burn
- Coastal and northern forests
Mixed severity fire and where does it occur
- Some patches of high and of low severity
- Dry and northern forests
- More common/dominant in NA than previously thought
Patch size of low severity fires
- Openings created by fire within which post-fire regeneration occurs
- Low-severity fire regime generally has small patches in larger matrix of homogeneous forest cover
Ponderosa pine forests and fire
- Open forest so fire moves quickly across landscape, consumes fuel on surface, doesn’t burn in one place for long, bark resistant to fire, not very flammable
- Small patches with homogeneous matrix
Patch size of mixed severity fires
- Results in both large and small patches from areas of low, moderate, and high severity fire
Patch size of high severity fires
- Small patches of isolated extreme fire activity or very large patches that an remain treeless for up to a century after the fire
High elevations and fire
- not well adapted to fires
- Regeneration time may be long
Landscape Metrics: Patch Edge
- Calculate edge index by measuring whole perimeter of disturbance (fire), including the undisturbed islands within patch
- Compute ratio between total perimeter and the perimeter of a circle of same size to get edge index
- Can be adapted to measure/compare edges around areas affected by different severities (fire)
High vs. low edge index
- High: very impactful for regeneration
- Low: less edge and less recolonization options and longer regeneration time
Which is easier to define, edges of high or low severity fire patches?
- High severity is more prominent
- Low severity is diffuse and difficult to define
What shape does a patch of wind driven fire take?
- Oblong or oval
Which fire regime has higher edge index value?
- Mixed
- Indicates greater landscape level heterogeneity in pattern
Describe fire characteristics of high vs. low severity or index
- Low severity: small patches, low edge index, highly similar pre-post fire
- High severity: large variable patches, depends on topography, moderate edge, high index, low pre-post fire similarity
- Mixed severity: moderate patch size, high edge, moderate pre-post fire similarity