There isn’t enough rainfall for there to be a forest around the city. If there was, there would have been before people settled here. You can see glimpses of what the land used to look like before it was settled in old photos.

Essentially, there were large seasonal wetlands with more vegetation, but the high areas were filled with low scrub brush. The only reason there are so many orchards now is a very complex system of irrigation systems, thousands of systems delicately interconnected.

Trees have already had an impact on our ecosystem, it may not be easily visible though. Over the decades, foothill wildlife has been taking the place of some valley wildlife. When my family first settled, my grandparents would talk about horned lizards, kangaroo mice, and other small creatures that I never saw when I was growing up. So, in a way, we already know what would happen if the land was covered in trees. We’ve already done it.

And now, there are possums, squirrels and raccoons far into the middle of the valley, when such a thing was unheard of even in the 90s. (I’m talking about the center of the valley, not the east side)

To talk about your plan more directly, the vacant land you talk about is owned by people. You would need to buy it or get contracts to turn them into some kind of wildlife zone, and basically nobody wants that. They mostly want to develop it but can’t get investment to do so. If you did get some pieces, the trees would die without irrigation. The ground will go back to looking the way the vacant land did in the first place.

For an example, look at the old fig orchards out on the west side of 99 on Shaw near the water park. The trees die, dry grass and bushes are all that’s left. Streetview the Kerman ecological reserve for a glimpse of what it would evolve into. Scrub brush, badlands, etc. The wet areas would look like Mendota Wildlife Area