Thanks Toby for taking questions!
In your book you use an oak tree to describe the many rolls of a tree. I am interested in that process as it relates to evergreen trees. Could you compare the transpiration of moisture and soil building qualities, etc? I live in Southwest Montana in a monoculture of Douglas Fir and have a hard time picturing this forest as the climax of succession. Could this forest at one time have been filled with many species of trees? Could this forest ever return to that state?
Doug fir is usually more of a mid-succession tree, though they can get very old. But in much of the greater NW (and SW MT is part of that) hemlock, true firs, and sometimes cedars, which are all less shade tolerant, are the late-succession dominants. Probably not "many" species of trees, but 2-4 or so in that area. I'm not a complete expert on MT, though, so a local ecologist would know better.
The thing we've learned about forests is that they are naturally patchy. Part of a forest would be late succession (they don't say climax any more, since that implies an end or target, and the forest is too dynamic and changing for that) but there are always local burns, blowdowns, bugs and blights, etc., to keep things much more mixed than the old view allowed for. And then there were native people setting fires all over the place, but they did that for thousands of years, so that was "natural" by some definitions, too.
around here we have both evergreen and deciduous oaks. they play different roles in the forest ecosystem and the soil food web.
the evergreens shade the soil year around. this is usually where the spots that stay moist longer are, in dense patches of say live oak you wont get much light to the forest floor. this is where grapes are good as they grow into the canopy, or growing things that like the shade when its 110f outside mid summer(blueberries). they drop leaves on a year around basis, little by little so they build the leaf litter slower like the turtle. over time this creates a thick layer of forest duff and humus, with little in the way of annual plants growing naturally.
where as the deciduous oaks let lots of light in during the winter(say a black oak), things can be grown during this time when the winter rains are plentiful. and still in the summer you get the shading effect to help protect tender crops. the leaf litter cycle is different with the deciduous trees. they drop all the leaf litter at once, usually smothering any green grasses or clovers or whatever growing beneath. all winter this composts and gets wormed up. by mid winter its not as thick, things start to grow, popping up in the holes and cracks in the leaf litter perfect little micro climates for seed starting. by spring its nice, lush and productive. so the deciduous tree acts like the rabbit when it comes to leaves, it goes real fast and then takes a break, goes real fast again and takes a break for a season.
i prefer to have a mixed canopy of about 20-25% evergreen and 75-80% deciduous where i live. this gives me good production. also take into account you dont want solid forest cover. little meadows and pasture areas make forest even more productive. i like to shoot for around 50/50 tree/open areas.
this also goes farther than just oaks of course.
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