Plant of the Week: Where Plants Grow
The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in "Plant of the Week." Please consult your local Extension office for plants suitable for your region.
For the past two decades the hillside trails here on Mt. Sequoia where I live in Fayetteville have been my wintertime haunts as I walk the dogs and get a spot of exercise. From the top where I park to be bottom of the hill is about 600 feet of elevation change and over that range, I see a different array of wildflowers depending on whether I’m near the top or near the bottom of the slope.
The entire hillside is a typical east-facing oak-hickory forest of the Ozark highlands with most of the soils derived from weathered sandstone and shale. Very little, if any limestone, is present in the sections I traverse. The soil is a heavy clay with a liberal scatter of small to larger sandstone rocks. A couple sandstone outcrops appear as I head down. Near the bottom of the slope and on a couple shelves where topsoil washed down from above and has accumulated, there is enough soil for marginal farming activity.
The forest is all second growth, with many of the trees more than 75 years old. At least one old homesite is found on the slope and the remnants of several stone walls where the hard-working farmers and their kids removed the larger rocks from their small fields. I’d guess, based on the age of the trees and my scant understanding of the farm economics of the early 20th century, attempts at farming the hillside probably stopped in the 1920’s or 30’s. Probably they grew a little corn, maybe some tobacco and even some cotton on their small patches.
The hillside became a part of the adjacent church camp and essentially remained undisturbed until current times. Wildflowers hunkered down, dealing with more and more shade each year, periods of heat, drought and winter-wet soils as the great sorting experiment began. The need for more sunlight has become an overriding factor with these wildflowers. Today, gaps in the canopy with better light have better displays of wildflower color than the more shaded sections, even though all of these plants are adapted to lower light conditions.
The top of the hill is steeper and drier than the shelves and base of the hill. Soil water is connected in one continuous column from the top of the hill to the base. This water column has considerable mass and gravity exerts significant downward pressure on the stored water. Working against the force of gravity is the capillary pull of the small pores of the clay soil. Any loosely held water (water held in larger pores) moves down the face of the slope while the clay holds some back for reserve. Because of the nature of water movement in this steep soil profile, the base of the hill is the last to dry out and the first to revive after a dry spell.
This differential in moisture is reflected by the plants I see as I move down-slope in the spring. Most of the wildflowers at the top of the hill will grow just fine in the better soils at the bottom of the hill, but the plants that need better, more moist soil will not migrate up the hill into the drier soils.
Pepperwort, rue anemone, spring beauty, oxalis, and comfrey are well represented in the more difficult soils at the top of the hill. On the shelves of the middle region mayapple and Christmas fern begin appearing along with the wildflowers from higher up the hill. At the bottom of the slope in the best soils with less severe drought, trout lilies, trilliums, bloodroot and fragile fern appear with all the others from above.
The east facing position on the hill makes it a more benign site than were it facing south or west where the summer heat-load would be greater. The north face, where my house sits, is even more benign but only a few fragments of the original flora remain there.
These incremental shifts in vegetation are everywhere you look and are mediated by a range of subtle factors such as soil moisture, soil chemistry, pH and all manner of environmental conditions. The next time you drive down a road or walk down a trail, look at how the plants change around you and try to puzzle out why it is happening.
For more information about horticulture or to see other Plant of the Week columns, visit Extension’s Website, www.uaex.edu, or contact your county extension agent. The Cooperative Extension Service is part of the U of A Division of Agriculture.
Klingaman, a retired extension horticulturist who is now operations director for the Botanical Garden of the Ozarks in Fayetteville, Arkansas, has created is a library of hundreds of plant histories that run in newspapers across the state and have become a favorite of gardeners in Arkansas and beyond. We hope you'll enjoy our extensive archive of his works and return each week to see what's new.