Open Space Institute has granted resources to map resource and habitat heterogeneity for an area I am somewhat familiar with. The lands include unmanaged forests, a variety of wetlands, streams, swales and vernally wet areas, upland shrub and managed forest as well as some obvious signs of glacial activity. I would like to find out what would be the best method for collecting ground-truth data about these areas of land.
Dear Mila,
I think that it is very important to know;
What kind of data do you want as ground truth? Qualitative or quantitative ones?
Which features of landscape are more important to the habitat description that you are interested? Vegetation cover, soil variation, relief, humidity, temperature?
These things are important to decide about the stratification of your samples.
Another basic thing is the variability and the minimum area of each sample (or subsamples?)
What is the desirable error to your analyses?
The total size of the study area (and each thematic strata) are important too.
So, I think that there isn't a specific answer for your question but all these additional questions will be helpful to define your methodology.
Haron
Depending on the size of your area and the type of ground truth information you desire, as Haron also suggested, you should create transects through the area at certain spatial intervals and annotate your ground truth along the transect. An easy with to do this is with a differential GPS that you can load a data dictionary library of your desired information and easily select it while walking the transect. Of course heavy canopy cover can make this hard so you can look into getting a backpack mounted GPS with a stronger signal. Take a look at trimble's GPS units. I use the GeoXT in low cover areas. If your area is very large you may be able to find airborne imagery of the area at local county offices. They usually share for research purposes at no cost.
My cruise grids seem to work well to collect this information, and the latest method used is % cover of herbaceous, shrub, and mid-story, canopy cover and dominant tree crown cover. Noting occurrences in the grid and in the grid area of conspicuous habitat features helps too: snags, nests of any type, shelter sites such as dens and ledges, river and stream banks, etc. is so far the best way I've found to establish their presence in inventory sample data.
At this point I have to say I am unconvinced that inventory is useful at a distance of more than 300 feet. Even a large area of forests covered in the dominant specie or other land cover types will show notable heterogeneity even within that scale.
Somehow the federal inventories seem to interpret information from much further spacing for habitat and for forest characteristics (including size class and timber volume). Hundreds and hundreds of feet apart, even thousands, or one inventory point per forest. Having worked on two of these inventories, I can conclude that it just doesn't tell a forester enough about a place to assist in actual decisions. All it does is help us describe a place in a vague way, maybe note a few special characteristics, perhaps better than planning purely by stand type.
Luckily I have also cruised forests with more traditional methods, and I have to say I would not feel confident about a plan lacking that.
Its beyond me as to why cruise inventory is not required for a federally granted (or grantable) management plan.
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