I have made a case that small forests openings, at the average intensity and size that is occurring here, is having little effect on the overall forest health. I am not talking about areas with dense subdivided lands. We have our share of rural subdivisions where the average parcel size is less than 160 acres, where the population density can greatly effect forest systems like wildlife and erosion. On the balance however, the parcels are 160a or greater over hundreds of thousands of acres.
For the case of these openings used for weed, what sometimes occurs in the vicinity of these openings is probably having a cumulative impact on watershed resources more often than not. The unanswered question in my mind is what extent of grows actually have significant chronic pollution. One in twenty? One in five? Of what I have seen on the ground, Id say at least 10% of grows I come across have a significant chronic sediment source that was caused by or was accelerated by growers. But I dont believe I have seen enough to really know. The majority of the time I am seeing abandoned grows anyways, so by their nature there is a higher probability for problems.
Where the biggest impacts are occurring is where they interact with past land use, primarily logging. Once you get off the beaten path you find yourself in steep terrain with old skid trails everywhere. Growers find these old trails and reopen them for various uses and it is here where things go bad.
Most, if not all, of these legecy trails simply pushed the fill from cutting through the mountain right over the side and into the creeks and draws they passed by. Following the historic logging blitzes of the 50-60s, most of the stream crossings are still gradually bleeding out the deposited dirt. When we encounter these in Timber Harvest Plans today, we pull all the old fill, excavate and restore the correct channel bed, stabilize the banks, and put it to rest.
Unfortunately one out of (a unquantified number) of rural landowners are attempting to re-use these relic roads. In some cases they re-awaken old wounds that have stabilized, often leading to drastic consequences like debris slides that deliver into important streams.
If the growers want to avoid the Simpsons Mobs (aka the public), they will be wise to avoid such issues and actively educate themselves and their peers about preventing sediment pollution. If I were a grower, I would start here: http://www.krisweb.com/biblio/gen_mcrcd_weaveretal_1994_handbook.pdf