Important Facts About Forest Health Aerial Overview Surveys

Overview Surveys...

record only red trees representing recent damage that is visible from the air (it does not include older grey attacks, current or green attacks)
rely heavily on the skill of the person mapping to determine the tree species, damaging agent, location and severity of observed disturbances and so is subject to variation due to the mappers abilities. Personal preference of surveyors is most evident in their habit of either "lumping" damage into large polygons or "splitting" the same disturbances into many smaller polygons or spots.
are recognized as being far less accurate in both positioning and severity rating than detailed operational surveys conducted at lower elevations and slower air speeds (usually from helicopters)
tend to over-estimate the numbers of trees killed particularly as the scale decreases (mapping at 1:250,000 is less accurate than 1:100,000)
by compromising accuracy (vs. detailed operational surveys), the overview has the advantage of being the fastest, most efficient method of annually surveying the entire province using the same method. It is also usually compiled well before the detailed aerial survey data thus the summary maps and tabulated data are made available much sooner, usually by early November, and provides vital information for strategic decisions by the Ministry of Forests

Assumptions

Areas and volumes presented in the tables represent the gross forested land base (no net downs by operability, riparian areas, etc.) unless otherwise specified.
Very few air calls are verified from the ground and rely on the accuracy of local knowledge and historic pest activity
Assume that data is collected in the same manner province-wide. For the last 10 years, damage caused by major bark beetle species in some of the regions has been recorded using operational survey methods while other regions have been surveyed using the FIDS overview method. The data summaries combined the detailed aerial survey information with overview survey data. An assessment of infestation growth can only be made in areas where surveys were conducted using the same methodology from year-to-year.
Spot data area conversions: FIDS created a standard that small spots (2-10 trees) cover an area of .25 ha of severely (30+%) infested forest; larger spots (11-50 trees) represent .5 ha. There is some debate on whether this rating should be changed to light (1-10%) to moderate (11-29%) severity as it better reflects reality. However, the default severity for all spots of a severe (30+%) rating appears reasonable when the conversion from trees/ha to % attacked is done. Specifically, small and large spots (average mature stocking of 250 sph) covers the entire range of severity classes (small spots = 2-10 trees/.25 ha = 3% to 48% of trees attacked = light to severe; large spots = 11-50 trees/.5 ha = 25% to 40% = moderate to severe). If you assume that the average spot infestation contains 10 to 25 trees, the severe intensity rating appears to be adequate.
The volume calculated from combining several severe spots should be equivalent to enclosing all of these spots in one light polygon (this is likely a weak assumption).
The entire forested area of the province is flown annually, however, weather, funding, availability of surveyors and aircraft may not permit this to happen in all areas. The 2000 survey has been the most comprehensive survey of the province since the function was transferred from the CFS in 1995. Areas not flown (not due to weather) were known to have had minimal forest health activity (i.e., Sunshine Coast, Campbell R., South Island Forest Districts) as observed by MOF and Licensee staff. These areas have a low frequency of disturbance but are surveyed more formally if unusual disturbances are noted.

Last updated on November 2, 2005
The contact for this web page is: tim.ebata@gov.bc.ca


	• Top • Copyright • Disclaimer • Privacy	• Feedback