If the harvesting rate is above the sustainable rate (ability to regenerating), the amount of next harvest season would be declined. To know the rate of sustainability , first we may need to know the total stock of those specific resources and its regenerating period. So, how we can measure the stock of those natural capital? or on a specific example of a Non-timber forest product?
You need to compare the yield of NTFP and their harvesting. Maybe you need specific inventories (but it is so expensive) or comparing the expected production (for example, data from other forests) with the extraction (market data) if these figures are available. Besides, in some NTFPs, you must estimate the percentage of the production consumed by wildlife and livestock. An example could be wild edible mushrooms.
Thank you very much Prof. Luis. This is really helpful to lead me in further step. We have few inventories data under supported by WWF-Cambodia, but they are not enough to do the best estimation to run any simulation model. I'm considering to apply InVEST model to see available stock first, then probably do inventories in some plot according to Land-Use type with slope or aspects.
Yes, you have to look the inventory data of the specific NTFP, or you can do the inventory yourself.