Walt, after reading your announcement posted yesterday, I wanted to clarify the precise conservation issue and nomenclature with you a bit.
First, I think you are right on about the impact of Over-Load on the "forest". The trail is extremely narrow (1.5" is generous in most cases), it has no impact on forest canopy or understory structure and especially with the way it enters and leaves the "Pleasure Valley Woods" has very little impact as a corridor for entry.
Furthermore, the traffic on the trail is extremely light... do you have any numbers for that? I would guess it would be no more than 2000-4000 trail users per year. Arguing this could be a double-edged sword however. On the one hand it shows the low-impact of the trail, on the other, it suggests it isn't used much an is, as such expendable. I would say its 'solitude' is precisely what makes it so valuable, and such a draw to the outdoors people looking to get away from humanity for a little while. I don't know about you, but I really get the feeling like I'm out in the middle of nowhere in the woods when I'm on that trail, and its a good feeling.
OK, a quick primer on edge effects: larger "core habitats" are more valuable for animals with more specialized habitat needs, such as the songbirds discussed in the rapid ecological assessment. Larger core habitats means better quality habitat with better resources for the birds, more room for more mating pairs and therefore greater reproductive success.
Edges are bad for these core-loving critters. It goes both ways, for example: many prairie songbirds won't breed successfully in any less than 100 acres of grassland. So for prairie birds, the presence of trees causes habitat fragmentation. For these forest birds, they need large chunks of interior forest. Trails, roads and such can bisect these forests, causing habitat fragmentation to the point that interfere with reproductive success in a number of ways.
The primary concern here, I believe, is brood parasitism by cowbirds. It is not predatory birds, so be clear on that. Cowbirds are birds of fields, edges and disturbed areas (originally they were prairie/savanna birds that followed bison and elk around). As an adaptation to their mobile lifestyle, they do not raise their own young. They find the nest of another songbird, lay their own eggs in the nest and then kick out a few of the songbirds eggs. As a result, the (in this case forest) birds are duped into raising the cowbirds offspring for them. Since they are busy raising the cowbirds young instead of their own, the "nesting success" is reduced, they may not be able to raise enough of their own offspring to effectively maintain their population.
In an idealized situation, the forest songbirds' population should be slowly growing over time. The surplus songbirds can then disperse to new forest tracks to colonize them. These are called "source" populations that are healthy and growing.
There is actually a threshold where, the impacts of edge effects, in many cases largely including (but not limited to) cowbird nest parasitism, actually cause the songbird population to be a "sink". Though the songbirds are present in the forest, they are not reproducing fast enough to maintain a population level. Instead, songbirds from other locations are migrating to the area to pick up the slack. In this way, cowbird predation and other subtitle impacts of poor habitat quality, that might not even be apparent to the birds themselves, can reduce songbird populations on a regional level. This effect is known as an "ecological trap"
A google search of any of the key terms I marked bold in this post will provide you with some reading material if you'd like to know more.
But the gist of it is, as you rightly stated, that Overload is a very small, low-traffic trail that I don't think could possibly have any impact on inducing edge effects or fragmenting the Pleasure Valley Woodland.
