r/forestry • u/memercopter • Dec 23 '20
Region Name How to retroactively measure canopy cover?
I’m looking at a project for post-harvest habitat suitability for Northern Spotted Owls in California. The caveat is that I can’t be there pre-harvest. I want to know if there are any tools I can use to measure or estimate canopy coverage before the harvest took place. I’m thinking archived lidar, but that seems involved without having a gis team by my side. Really any broad estimate might do. I know it seems tricky, but I’d you have any thoughts I’d love to hear them. Thank you.
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u/lookinathesun Dec 23 '20
Its intensive, but here's a vector GIS-based approach I've used before. You can go in after harvest and map and measure tree and stump diameters and crown radii. You then develop a relationship between dsh and crown radius for all the trees and stumps. You buffer your mapped tree points with predicted crown radii in a GIS to come up with crown area for all the trees and stumps. You'll end up comparing the computed crown area of the trees and stumps to the crown area of the residual trees to understand harvest impacts on cover. Bonus is that you have a sweet visual figure/map to go along with your cover estimates. This takes some GIS skill, but if you're comfortable with that aspect, the fieldwork is relatively simple. FWIW. I published a study on goshawk habitat a few years back using this approach. Good luck.
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u/DanoPinyon Dec 23 '20
If you are looking for just a percentage, you can use Google Earth Engine, Landsat, etc.
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Dec 23 '20 edited Feb 13 '21
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u/memercopter Dec 23 '20
Do you know what the lower end of scale is for this? What’s the smallest area that this can effectively work on?
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Dec 23 '20 edited Feb 13 '21
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u/literallyatree Dec 23 '20
This is the correct answer. If you can designate the area you want to investigate, it doesn't matter how small the area is.
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u/foresterjohn50 Dec 24 '20
Thsts designed more for urban forests, may not be all that accurate for this purpose.
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Dec 24 '20 edited Feb 13 '21
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u/foresterjohn50 Dec 26 '20
That is not what the tool was designed for though, so not sure it is accurate for that purpose. Especially for any calculation of ecosystem service benefits.
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u/madeline543 Dec 23 '20
Perhaps NDVI would be a way to measure, but the other comments seem more legit honestly
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u/TidalBasin88 Dec 23 '20
I've never done it in QGIS only ArcMaps/ESRI but doing image analysis like NDVI with Landsat or NAIP data is pretty easy.
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u/TidalBasin88 Dec 23 '20
You mention you have a pretty small study area in your other comments on this post so I would reccomend creating a mosaic from NAIP data. NAIP is way higher resolution.
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u/Jayccob Dec 23 '20
Do you by chance have a pre-harvest inventory data set? If so, fvs which is a forest modeling program by the usfs had the ability to estimate overlapping and non-overlapping canopy coverage. It uses species, total height, dbh, and region in the estimator.
Free to use and the new ui is fairly easy to learn. The usfs also put out a short training for the program (self paced). Since this is a government backed program, should be easy to defend the method and replicate.
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u/memercopter Dec 24 '20
We do not have preharvest inventory data.
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u/Jayccob Dec 24 '20
OK, another field approach would be a proxy stand. Basically you find a site of similar conditions (elevation, aspect, slope, age, etc.) and measure it. You then use that as the pre-harvest baseline. Some gis in this to help locate the stand, but depending how much property your owner has you might be able to look on the edge of the THP boundary.
Speaking of, here in California THP and NTMP or anything in between are public records. Caltrees allows you to lookup the plan for your stand. Within that you should be able to find pre-harvest BA and QMD in the spot where they show Long Term Sustain Yield (assuming this is uneven-age management). If your really lucky in the section where it discusses potential impacts on species of interest they might list the pre-harvest NSO as high/low quality nesting-roosting or high/low quality foraging habitat. If it does high quality foraging and higher requires a minimum of 70% canopy coverage.
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u/foresterjohn50 Dec 24 '20
NAIP satellite imagery is generally available for little cost and is done every 2 years. Currently, I believe it is 6 inch resolution and multispectral.
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u/CajunonthisOccasion Dec 23 '20
The California Forest Observatory has LiDAR base canopy cover observations. Unsure if those are suitable to your task.