A closed tree canopy, will help preserve it's own moist enviroment, but reduce drying winds, higher organic content in the soil (generally but not always), soil that is not compacted so it absorbs whatever rain there is more effectively, continuous natural mulching from leaf litter, and I'm sure other facts.

Contrast to a yard environment (which is really a grassland Savannah environment in most cases). Trees are exposed to hotter ground temps resulting in increased drying, some level of compaction, competition from grasses, exposure to drying winds, exposure to direct sun (trunk branches and all), at most a small mulched area, etc.

So in short, your on the right track. A yard is a much tougher environment in many cases.

Arktrees

That makes sense. Trees in groups make their own shelter belt, in essence.

They also probably have more going on underground than the trees in your yard: a more extensive network of roots with mycorrhizal relationships that help channel more nutrients and water to them than they would have on their own. Add to that the many other beneficial creatures that live there and years worth of fallen leaves to retain moisture.

Here is a link that might be useful: mycorrhizal overview

In many cases, the single most important difference may be poor root system development/adaptation due to problems associated with the way the trees were grown before being planted and the way they were ultimately planted/transplanted.

Mycorrhiza association is another biggie, and may especially be important (more so, in other words) with some species. Multiple factors, from soil profile disruption to topsoil removal and from the flora profile of the site to how the area is maintained, can all play an important role with this factor.

And the third key thing that came to mind after reading the OP, was the environment (moisture, winds, light exposure, etc) fostered by the forest canopy compared to that of a yard.

some of the ecosystem restoration and remediation projects in the US and elsewhere involve semi-natural and even formal row planting of trees.

I'd say there's both scientific and observational evidence out there that trees and other plants, when dense enough, benefit the water system significantly

a good example is how the state of MD requires any new construction to build in stormwater systems / habitat offsets that appear to include ponds, appropriate native tree planting and other native shrubs and grasses.

I lived up there quite a while, and the difference between there and the free-for-all, socialized cost private development in Alabama is simply amazing. Even a quick t-storm here fills the streams with red clay silt from construction sites and overwhelms water systems. (It does not help that they let farms pull drainage ditches from their field into the county storm water evacuation system that we paid for, sad to see it happen, especially when the extra water caves in the side of the road)

Hogmanay,

How does that relate to the topic of this thread? Am I missing your point?

While mowing today I was thinking my yard is not even a good grassland. The sun gets to beat right down on that soil through only a few inches of grass. Even along the highway they have more.

It relates to trees and ground water / surface water and "management" of same.

It shows deliberate projects use dense planting to preserve or restore areas in comparison to singular or sparse yard- like planting or in comparison to areas with no formal program for such....

Hogmanay, I still have no idea how that relates to this topic. Does anyone else?

Sort of, but here's another off-topic subject - Some farm fields in West-central Indiana have had new tile work this spring - The newest systems allow the tiles to be closed to conserve moisture during drought! Most fields around here (including ours) have open tile systems, which allow for better field drainage. However, tiling can work against you in a drought, so if you can close off the tiles, there's that much extra water!

Back to forests, the woods around here still look okay. I've got a few shrubs I planted in the woods that don't look too well, but they ARE still alive (there's always next year...)! I think the shade and the wind reduction is the most important thing for reducing moisture loss. Our ground could easily absorb 2 inches of rain right now without it running off - Some fields have cracks so big that you can reach your arm into them! This is the worst dry spell we've had since 1908 or something - We're dryer than the dust bowl years!

It's a little funny to look out at and see my backyard consists of 95% of crunchy brown grass, and yet my trees are lush green and the grass directly around the fences of the trees are a nice dark green.

We're due to get a little rain tonight; emphasis on "little". The weatherman already warned ahead of time to not get excited, because the rain would not be nearly enough to help the vegetation around here. In other news, the grape vines are thriving...

Tornado, the difference of which you speak is the subject of books. Permaculture vs. industrial landscaping.

hogmany, too broad of a brush to paint our whole state, IMO, at least from the view down here. Just be glad there IS construction near you. Nothing much going on around here... for decades. I used to live up north, too, and am so glad to be away from contrived neighborhoods of pointlessly curved streets and cookie-cutter housing with identically landscaped lawns (that some hired hands installed) that nobody ever ventures into, all consisting of the same plants in the same "foundation planting" with the lawn-tanker-truck making its' rounds, and those little signs in every yard reminding everyone to stay off of the toxic "barefoot lawn."

The taproots being undisturbed on the trees alone probably helps tremendously. Anyone who has dug up even a red oak out of the woods, can attest they have long taproots on even small trees. The rest was already mentioned, forest settings conserve moisture and slow erosion etc. My take on Hogmany is that the excess water goes to areas where they drain to other areas or watersheds, to low areas that hold the extra water in ponds or other bodies of water. That's what I've observed happen in my area. I guess they aren't handling the runoff the same where he is now vs MD. It seems like there are always floods in Mississippi, Alabama, Louisiana and other Southern gulf states, I always figured because there are many bodies of water all around. Is there a better way for the water to be stored/diverted as Hogmany thinks?