Friday, June 19, 2009

Reforestation in a dry environment

My East Coast colleagues don't have to worry much about reforestation; leave the land alone and it will reforest itself naturally. You might want to select what is allowed to come up, and perhaps plant species that you prefer, but even then it's usually "plant and forget".


Out here in the West, it's much more difficult. In the first place, you seldom get natural reforestation, at least not at anything approaching an acceptable time. The rough rule of thumb in the West is that it takes about a thousand years for a devastated patch of land to return to its aboriginal state. Of course, that time period depends crucially on the amount of rain. In the rainy Pacific Northwest, regeneration can complete in about a hundred years; in the Nevada desert, it can take millennia. In my environment, we get about 22 inches of rain per year, which is pretty good by West Coast standards but still well below the 50 inches that is common on the East Coast and the 42 inches that is typical for Eugene, Oregon, just 200 miles north of us.

When an area of forest is cleared, the recovery is carried out in a sequence. First come the manzanita, a scrub brush that burns hot in fires. A few oaks, madrones, douglas first, and ponderosa pines will eventually sprout in the soil and grow slowly (because they're underneath the faster-growing manzanita). After several decades some of these will start overtopping the manzanita, enabling them to grow somewhat faster. They'll also spread more seeds and acorns, restarting the process. However, the manzanita has deep roots and is long-lived, so once it has been established, it can take centuries for it to die out so that the forest reaches its climax stage.

The best way to accelerate this process is to plant seedlings and clear the immediate area. Usually, however, we don't bother clearing -- we just plant the seedlings in areas that have sunlight. There are enough openings to make this a viable strategy.

Before you can plant seedlings, you have to obtain them, and that's a problem. We used to have a state nursery in Oregon that sold seedlings of all kinds. The Ponderosa Pines that we use ran about $0.70 apiece in quantities of one hundred. But the commercial nurseries complained bitterly about the competition from the government, so the state government closed the state nursery. When I asked around at the local nurseries, the price of Ponderosa Pines was around $4.00 apiece. There's definitely something fishy here. Moreover, I couldn't get Ponderosa Pines suited to my altitude.

So I took a different tack this last planting season (December-January). I harvested some of the numerous seedlings that volunteer all over my land and replanted them in new locations. To do this, I just dug around the seedling with a shovel and then lifted a shovel-sized hunk of soil containing the seedling and its roots. Then I carried the seedling to its new already-dug hole and planted it there. This might seem like a simple enough task, but it's a lot rougher when you're carrying a ten pound hunk of soil 600 feet to its new home -- and doing it over and over with dozens of seedlings. But I was determined, and I got a bit more than 40 seedlings planted this last January.

Now, however, comes the real test: keeping them alive through the summer. There's no rain at all from June through November, and this is the period when trees die. Seedlings are especially vulnerable because their roots have not set properly; it takes a full year for the roots to re-establish themselves after replanting.

If you want to water trees, you just use a hose, right? Well, yes, but it's a bit different. It's about 800 feet from the closest water tap to the furthest seedling. That's a long, long way. We have enough hose to handle the problem -- over the years we have acquired lots of hose. The problem is that the furthest seedling is a good deal higher than the tap, and between the pressure loss and the resistance of 800 feet of hose, I get very little flow: perhaps 1 gallon every five minutes. With 40 seedlings to water, you can see the problem.

Fortunately, a solution was at hand: crank up the well pump that feeds the tap. I went to work and cranked it up to about 40 psi (standard household water pressure is about 30 to 25 psi -- but we're on a well and we keep the pressure down around 25 psi to save electricity. With a cranked-up pump, I could get about a gallon a minute.

There are still problems: if I water in the afternoon, the water in the hose is scalding hot (from all that inadvertent solar water heating) and would surely kill the seedlings, so I must either throw away all the water in the hose (perhaps 10 gallons, which takes a while) in order to reach the cooler water, or water at other times of the day.

And then there's hose management. When you're maneuvering hundreds of feet of hose, you spend a lot of effort just moving it around. I use a system in which the hoses are laid out along the general line of trees, but disconnected. I connect each hose in turn as I work my way further out. On the next watering run, I disconnect hoses as I move closer to the tap.

One other trick: I plant my seedlings in deep holes; the seedling ends up about eight inches below the ground surface. Why? Three reasons: first, it provides a small amount of shade for the seedling part of the day, which reduces its water requirements. Second, it gives the seedling access to deeper soil, which holds water longer. And third, the pit holds two or three gallons of water that will soak straight down.

If I do everything right, I might get 90% survival rate. If I underestimate the water needs of the seedlings, that might easily go down to 50% survival rate. And if I don't water at all, the survival rate will be less than 10%. If I get the seedlings through this summer, then I can leave them to nature and they'll sit quiescent for two or three years, getting their root systems big enough to handle growth. Sometime around the fourth or fifth year after planting, they'll start growing vigorously.

That's what it takes to reforest land in southern Oregon. It's a lot of work, and I can only handle maybe a hundred trees per year -- and that's only if I devote a lot of time to the task. And my land could probably hold another thousand trees easily.

1 comment:

Sue said...

Chris, this was really interesting. I had no idea how complex the problem was in the west. In this eastern Kentucky (and through much of the eastern part of the U.S.) reforestation is merely a matter of getting out of the way of the trees. All we have to do is stop mowing an area and it will begin reforesting immediately, unless the surface has been severely damage (as by strip-mining) and then heavily compacted. Thanks for such detailed insight into the difficulties involved in reforestation out west.