I am using the Crop Pollination model and I have some difficulties in interpreting my results. As for as I understood, the supply map (see reply) should be more crisp while the abundance (picture below) should be smoother, since it includes foraging activity and flight range. However, in my case the situation is quite the opposite. What could cause this behavior?
Thanks for your help!
Pollinator supply map
Hi @matteoriva ,
Thank you for writing in with your question.
The results from InVEST’s Crop Pollination model match the spatial resolution of the input Land Use/Land Cover (LULC) raster. Therefore, if the resolution of your LULC is relatively coarse, the results will also be relatively coarse (the same resolution). What is the resolution of your LULC map?
Please note the model’s limitations as described in the User Guide, namely, the last two paragraphs of that section. Perhaps more relevant, the Data Needs section explains that the LULC raster, “must be of fine enough resolution to capture the movements of bees on a landscape. If bees fly 800 meters on average and cells are 1000 meters across, the model will not fully capture the movement of bees from their nesting sites to neighboring farms.”
You may need to find a finer resolution LULC map if you want finer-scale spatial results. Some sources of global LULC data are listed here.
I don’t think I made myself clear. I am not referring to the resolution, but merely to the difference between the map of supply and the one of abundance. As I understand, the abundance map should be smoother given the fact that it takes flights range and behavior into account. Whereas the supply map is purely based on the LULC and therefore should be more crisp. Why is this not the case?
Hi @matteoriva , good question.
Reading the User Guide, this is not strictly true. Supply is also a function of the “Floral Resource” of the all the cells within foraging distance of the pollinator, with the influence of the FR decaying with distance.
Hi @dave thanks for your reply. Yes, I oversimplified, but according to the “test data” and also to the YouTube tutorial video, the abundance map should indeed be smoother than the supply map. Again, why is this not the case for me (see maps in the main post)?
I think for both supply and abundance, the “smoothness” is a function of the same parameter: the effective foraging distance of the species. \alpha_s in equations 53 & 55.
It’s very hard to tell just by looking at the map which is “smoother”. A lot is influenced by color scheme, and how colors are mapped to the values. Are you using a discrete scale where there are a limited number of colors and each color is assigned a range of values? Or a continuous scale where the color can change continuously relative to the pixel values?
Others with more experience with this model can correct me, but there’s not anything obviously wrong here to my eye. If I look at the results from the sample data we ship with invest, I also have a hard time saying which map is smoother.