Disturbance Regimes

Question 1

What ecosystems does the “Disturbance Regimes in British Columbia” paper refer to

Answer 1

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Question 2

List some common forms of natural disturbance in Coastal BC

Answer 2

Fire
Stand level blowdown
Windthrow of individual trees
Pathogens
Insects
Mass Movements (Landslide/Avalanche/Flooding)

Question 3

In closed canopy forests, there are 4 typical stages of stand development that follow a severe stand initiating disturbance. List and briefly describe them.

Answer 3

1. Stand Initiation - Site colonization and establishment lead to a forest canopy dominated by an even aged cohort of trees in competition for space and resources.
2. Stem exclusion - Space and resources become limiting factors and canopy closes. Competition is intense and the shrub and herb strata are limited due to low light.
3. Understory Re-initiation - Mortality of some over-story trees leads to canopy openings that allow regeneration of the herb strata.
4. OG stage - accumulation of CWD, horizontal and vertical diversification of canopy, increased biomass/diversity of understory.

Question 4

What feature distinguishes the old growth stage on the west coast wet forests?

Answer 4

Fine scale disturbance resultant from the mortality of small groups of trees creating canopy gaps.

Question 5

According to the BC Biodiversity Guidebook, the main disturbance regime in coastal BC is Stand Initiating Fire at mean return intervals of 250 - 350 years. Explain why this seems inaccurate.

Answer 5

If that were the case, then up to 43% of unmanaged forest in coastal BC would be in the stem exclusion/understory re-initiation phases of stand development. In reality up to 97% of unmanaged forests are in the old growth phase, indicating that the mean return intervals of stand initiating disturbance are much closer to 1000 years.

Question 6

Do stand initiating fires homogenize forests? Where are they more likely to occur?

Answer 6

Historical evidence of tree age structure shows that stand initiating fires in coastal BC are typically small and patchy, likely to occur on steep areas and even more likely on south facing slopes. This leaves behind structural elements of the original forest and creates patterns of multi-aged forest at the landscape level.

Question 7

What is the conclusion of the paper, “Disturbance Regimes in Coastal BC”

Answer 7

Daniels and Gray reject that the dominant disturbance type in coastal BC has been stand initiating fires every 250-350 years. They propose that fine scale gap dynamics is the dominant process explaining the structure and dynamics of BCs wet coastal temperate rain forest.