Some people have come up with ways to measure the value of a standing tree. Not surprisingly, there is some controversy and a lot of disagreement about the values going in. Most of what I have seen so far seems to overvalue individual trees and undervalue whole ecosystems. It is sort of a tree rights movement and it seems to me that much of this valuation is designed to be used as a club to pummel developers. This is unfortunate, because there is a real need to develop markets for environmental services, as I have written on several occasions. But everything must be viewed from the system point of view. When you get down to the level of individual tree, you are just being silly.
I got a link to a system called I-Tree. It purports to help value trees in urban settings. I haven’t really done much with it, but I admit that I am a little suspicious of an overarching measurement system. We always have to be careful not to outsource our brains and judgment either to consultants or to systems. As long as these are only tools, it is good.
The I-Tree had a study of the forest in Milwaukee that surprised me so much that I doubt its validity, although I question my own observations too. According to the report, nearly a quarter of Milwaukee’s tree cover is European buckthorn. This is a kind of bush. It is an invasive species, but I just cannot believe it is that common. The parks I know well are covered in oaks and maples. Buckthorns, not so much and even then they are growing in the understory. I suppose there are lots of them because they are small. Supposedly, they make up only 5.5% of the leaf area. But still, that seems out of whack.
I am looking at the places I know well in Milwaukee on Google Earth. Most of the forested and park area is dominated by basswoods and maples, with a lot of oaks and beech trees near the lake. There are also a fair sprinkling of cottonwoods on some of the slopes. Anyway, the report paints a picture of my native city that I don’t recognize. It could be that I just don’t see the vast world of European buckthorn dominating the landscape like dark matter in the universe. I read once that more than half of all the species in the world are a type of beetle. Sometimes things can be strange and not obvious; or it could be that the information fed into the I-Tree tool was faulty. Mistakes in input produce mistakes in output. The problem with a tool like this is that you cannot know for sure w/o taking it apart and the ostensible precision of the graphs and numbers gives you a false sense of certainty.
According to the report, Milwaukee is dominated by buckthorn, box elder and green ash, which together make up around half of all the trees.Green ash is planted by homeowners and the city as street trees, but buckthorn and box elder just grow by themselves.Box elders grow down along the railroad tracks and anyplace you disturb the natural cover, but they are early steps in succession.They don’t live long and are replaced by other treesas the site matures.They are also weedy, weak, short lived and generally undesirable trees.You don’t have to do anything to encourage them.In fact, it is almost impossible to get rid of them if you want to. How depressing is that if they are the forests of Milwaukee?
But I don’t think they are, no matter what the report says.