Hi Erica,
I was not aware of the FS database. Thank you! I like the thoughts on indicator plants.
In my own observations of the region, I have found what I call "soil development" to be one of main determinants of vegetation. This is particularly true of the northern half of the Washington, which has not had much time to develop soil, since the retreat of the ice sheet. To me, a "developed soil" is one in which parent rock has weathered down and accumulated as finer particles, and/or has been colonized by plants for a long time, thus acquiring organic matter, and all of those luscious qualities gardeners look for. But developed soil is rare in the mountainous Inland Northwest- maybe 10% of the landscape. Much of our horticulture comes from agricultural areas, river valleys, and grasslands, and doesn't doesn't translate well onto our rugged, brushy, shallow-soiled landscape.
Your valley shows the full spectrum of soil development, from the bare rock on the ridges then sterile gravels, then colonized gravels, then stony soil, and then the deep dark soil of the creek bottom. The soil is moving. The best stuff all moves down. Bitterbrush (Purshia) is an indicator of undeveloped sterile soils- it can live here because it is a colonist nitrogen fixer. It grows on stony slopes, sand dunes, and in the understory of frequently disturbed pine forests. In soils with more organic matter, sagebrush will replace bitterbrush. Both species are indicators of some of the driest conditions in our region. Bitterbrush, being N fixing, is superior browse for ungulates, and crucial food source for seed eating rodents. It is so attractive to animals, that the Sanpoil Indians avoided it in the Spring, thus avoiding ticks. Both bushes yield a profusion of fibrous bark on favorable sites, once used for clothing.
These shrubs tend to prevail over
native grasses where the summer precipitation is lacking. That is why, as you move east of the Cascades, you encounter less shrub steppe more grasslands. You are moving from a West Coast (Mediterranean) winter precipitation regime, to a Continental summer monsoon regime. Grasses also do better at higher altitudes, which
experience less summer dryness. By the time you get to Eastern Idaho, Central Montana, and Wyoming, you're in bison country. Mismanagement of grazing achieves the same affect as low summer precipitation- it creates shrub lands out of grasslands.
Undeveloped soils can be used to advantage. In some cases, as on talus slopes, moisture availability might be very high, due to reduced evaporation and low plant completion. Riparian colonists, like cottonwood and siberian elm, can grow in bare sand and gravel in otherwise dry sites. Most fruit trees are slope adapted, and do excellently where there is just a little dark soil forming between the stones (as in basalt). Among the reasons for this are: air drainage, temperature moderation, condensation,
freedom from grass competition, freedom from competition from taller riparian and climax trees, and reduced browsers accessibility. Elderberries, particularly in the southwest, will grow here and there on such slopes- not necessarily because there is any ground water there. On stony slopes, plant establishment may be a greater challenge than moisture availability. It is hard for a seed to find foothold in stone.
Of coarse, slope direction matters. In general, east facing slopes are the best for fruit trees. In hot arid locations, north may be best. South is workable if there is moisture. West facing slopes are very harsh.
Basalt seems weather into the most fertile floury soils around. It seems great for everything. But some plants, like apricots, seem to prefer coarser soils from metamorphic rock. And it seems like the more geologicaly "recycled" parent rock is, the less fertile it is. Sandstone and gniess tend to be bad. Some rocks form poor soils simply because of the way they break down physically. Granite that rots into coarse sand will be infertile. Granite that breaks down into a mixture of fine and coarse particles, especially clay, can be fertile. Limestone isn't terribly common in our region. Caliche is or main calcareous rock.Slow breakdown of rock by plants (humic acid) seems to result in fine soil more often than mere physical weathering. Soil deposited by water can vary in texture depending on what part of the former watercourse you're in. My place was under an ancient glacial lake! Soil blown in from grinding glaciers is the awesomest, but don't let it blow away again!
Tall leafy forbes, perenial grasses, and leafy deciduous trees/shrubs, in that order, are the best creators and indicators of developed of soil. Fire is helpful in developing soil where significant organic matter is retained below the soil surface. When shallow rooted vegetation (like doug firs) is burned, the soil may be briefly fertilized, but loose organic matter. The more plant material returning to the soil each year, the more developed it will be. Woody growth, especially in our semi-arid climate, tend to lock up nutrients and stall soil development. Evergreen trees and shrubs, are the poorest nutrient cyclers, and can colonize nutrient poor soils (they are adapted to conserve nutrients). Most native conifers can colonize a fresh road cut, whereas grasses and forbs may take many years. Conifers can take hold at low nutrient conditions and perpetuate them indefinitely. Conifer forests with less forbs, grasses, and deciduous shrubs in their understory are less fertile- this is is either due to soil texture, or some factor preventing understory plants from establishing. In our dry conifer forests, light is not a limiting factor. Water and nitrogen are limiting factors.
Soil
wood is another important vegetation determining factor. Fallen wood stores moisture. Most of a douglas firs' fine
roots grow in soil wood. Soil wood promotes rhizomatous shrubs like snowberry and oregon grape. Soil wood does not promote soil development, because it is slow to release nutrients, and does not shed organic matter deep within the soil. A conifer forest has a very thin layer of organic soil, the deeper soil will be sterile.
Evaporation is critical to pH. In an arid area, the pH will be low, and bulrushes will grow in ponds. In very humid areas, where there is little evaporation, sedges may dominate ponds. Cattails have a wide tolerance. pH and evaporation determine stream-side vegetation as well. Places where water is drawn out of the soil by evaporation are the most fertile areas (look for butterfies). Here you will find
nettles, and other tall leafy forbes. Even though sagebrush is an evergreen, and a poor nutrient cycler, sagebrush soils will be fertile because of the minerals drawn up by evaporation. Large Brassica weeds like tumble mustard indicate a fertile basic soil. In many sagebrush soils, there will be a layer of chalky white caliche stone several feet below the surface. Caliche forms at the level where the evaporation and leaching have equalized. In wetter places, we can assume that leaching takes lost minerals to an indefinite depth.Too much evaporation leads to surface mineral deposits, or salt flats, and greasewood shrubs.
Some practices and vegetation types cause acidity by limiting either evaporation or transpiration. This can be seen when bracken ferns take over a pasture or woodlot. In forested place, If grazing devegetates an area, the soil will leach out and become acid. On the flipside, if herbivory is insufficient, shallow rooted woody plants may dominate, the ground will be shaded, and acid conditions will prevail. Bunch grasses are excellent at regulating pH, because they are deep rooted, transpire water efficiently, and let the soil breathe between bunches.
"Savanah trees" are those that can tolerate grass competition. Savanah trees are more compatible with soil fertility than forest trees. Savanah trees include: legume trees, ponderosa and pinyon pines, oaks, and walnut family members. These trees tend to have
deep roots.They tend to be fire adapted.
Forest trees like Douglas Firs, Larches, Red Cedars, and Grand Firs, tend to be less compatible with other plants. The tend to be shade tolerant and have shallow roots. I believe than any alleopathic effects of these plants are insignificant compared to their effects on pH and nutrient cycling. Paul Wheaton seems to be very anti native conifer. This is not a very sophisticated position. At low densities, the intermittent shade and sheltering provide by conifers, even the more "alleopathic" species, is of great benefit. A ponderosa pine never hurt nobody.
You ever think: those wetter places where deciduous forest grow- don't they also get less sunlight because of all the rain clouds? And maybe the reason we don't grow deciduous forests here is as much because of too much sun as not
enough rain? I think a little shade is good for most wild plants here. The damn domesticates are sun hogs though.
The conifers arrange themselves along a moisture gradient, which mostly corresponds to an altitude gradient.
Some plants, like high altitude aspens, may indicate areas of snow accumulation and conservation, more than ground water. North facing cliffs achieve this in arid areas.
Pocket gophers are another overlooked limiting factor. Open areas with high gopher depredation will be dominated by rhizomatous shrubs and unpalatable annual weeds. And don't underestimate herbivory from deer. Deer can totally curb succession away from soil development by causing unpalatable evergreen dominance.
Soil depth is another great determinant. It takes at least four feet of topsoil to grow wheat, and perhaps more for
perennial grasses. Deep, well developed soil has high water storage capacity, but it can only be used by deep rooted plants. Some plants prefer not to grow in deep soils. Gopher vulnerability and grass competition are factors. Only a few fruit trees excel in deep bottom-land soil, and they tend to be the cold tolerant ones. Pears and hawthorns love it. Many of the best edible native plants, like biscuitroot and bitteroot, grow only on the droughty frost-heaved, stony soils of ridge tops.
Camas prefers vernal pools, mucky black soil, and freedom from grass competition. In well drained soils, this condition is only achieved in lenses of soil held by bedrock. If I had to plant camas on Erica's sight, I might burn part of the apsen grove, or make a stone-lined vernal pool in a draw, filled with black mucky soil. Like the soil that forms under sphagnum moss growing on a rock.
But if you really want feral root veggies, I'd sow those dry slopes to salsify, the the valley bottom to yampah and wild carrot, and feral parsnips in those prime evaporating wet spots. Burdock in the shady places around riparian trees. Bull thistles in the slash piles and compacted soils. Evening primrose on the sandy soils. All of these are bienial, vs. perenial. Camas takes a while to develop.
I wouldn't take willow type as a temperature indicator. The whole poplar family is very cold hardy.Willows grow in the Arctic circle.The shrubbier willows are probably more dispersive and browse/beaver resistant.
There don't seem to be many good native indicators of temperature or frost. We don't have many frost sensitive plants in the first place. The dominant plant communities haven't changed much since the ice retreated. There where historic cold spells that froze the major rivers and caused the service berries not to fruit. The native plants seem to simply adjust their timing as they go upslope. The only warm areas in the region are the river valleys, so I'm not sure if the plants that grow only there are just adapted to riverine dispersal (smooth sumac, hackberry, poison ivy, white alder). The best temperature indicators may be exotic plants, like evergreen blackberries. Don't get me wrong, a spruce obviously can hack the cold better than a ponderosa, but that's not going to give you any sharp boundaries about what you can plant.
I think people too often blame temperature or precipitation when they kill plants by planting them where they don't want to grow. An
apple tree doesn't want to grow in a
lawn on a valley bottom. It wants to grow on slope or a in minor draw. People try to plant things on sites where they would face great competition of succession were allowed to proceed. Most of our edible plants naturally grow on sites too dry and marginal for climax forest trees.
From an ecological perspective, the best use of deep soiled areas is grass and grazers. The best use of riparian areas is wetland, fish, and beavers. The best place for orchards are the draws and foothills.
Don't forget to look at the length of first year wood, and whorl spacing on conifers, when making site comparisons. Conifers don't care much for fertility, so greater whorl spacing is a good sign of greater summer precip. Mature conifers which retain their lower branches indicate marginal moisture.Poor recruitment of conifers means marginal moisture. Poor recruitment of deciduous shrubs could just mean deer.
Okay, enough for now. Maybe I need specific questions about how particular plants fit into this framework of determinants.
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