Soil Resources

Tue, 11/08/2011 - 08:44 -- cadoughe

The mountains of Western North Carolina today are only remnants of those formed long ago. Beginning about 500 million years ago, rifting and continental collision along what is now the east coast of the United States created mountain ranges as high as the Rockies. Beginning 250 million years ago, these mountains eroded to almost nothing and exceptionally warm temperatures led to the evolution and diversification of many new species. From 65 million years ago to present, the older mountain remnants re-formed and eroded to half of their original height forming what we know as the Southern Appalachian Mountains.

Millions of years of geologic processes, weathering and climate variability have resulted in a wide variety of soil types. Over the last two centuries, human-caused soil disturbance has increased considerably. During the early settlement period, subsistence farming on steep slopes, burning, and logging practices led to severe erosion and hydrologic changes across the landscape. Today, another more complex mix of practices threatens the soil resource.

Soil Formation

Soil systems

Soil is a critical support system for trees and other plants, and its variable properties play an integral role in all other biological systems. Soil is formed through processes that take thousands of years to complete.
Several factors have influenced the formation of the region’s soil: topography, geology, climate, vegetation, elevation and time. The parent material is predominantly crystalline rocks with varying degrees of mica content, and metasedimentary rocks. Precipitation levels across the region range widely from 40-80 inches annually. The interaction of these factors has led to unique and highly variable soil patterns and properties across the mountain region.

Soil types are further categorized by permeability, porosity, and texture. Permeability is how quickly water moves through soil and the ability of water to be held for plant use. Permeability is partially affected by porosity, which is the amount of empty space between soil particles. Soil texture (the proportion of sand, silt, and clay) is an important determinant of drainage, water holding capacity, aeration, susceptibility to erosion, organic matter content, and buffering capacity.
Three major soil systems are found in Western North Carolina; their differing properties relate primarily to elevation change. A fourth type, the felsic crystalline system, is found here but to a much lesser extent. This latter system is similar to soils found in the Piedmont region.

Soil Systems

Broad basins, river terraces and flood plain system

This system is characterized by wide valleys and rounded, low hills with few steep slopes. Easy access, a temperate climate, and pleasant landscapes make these areas desirable for development and have historically been the region’s urban, industrial, and agricultural centers. This is the youngest of the three systems.

Although prone to flooding in the river basins, these soils are ideal for agriculture, as higher elevation soils have shifted downward over time, increasing soil productivity. These soil profiles have relatively higher temperatures that enable microbes to break down organic material, thereby increasing nutrient supply and water-holding capacity while improving soil structure and preventing erosion.

Low and intermediate mountain system

Found between 1,400 - 4,600 feet above sea level, these soils are influenced by elevation, aspect, exposure, and forest cover. Typically taking hundreds of thousands of years to form, the predominant features include steep slopes and ridges as well as steep, narrow, wet valleys. These are the most common soils below 3,000 feet and have well developed profiles. They are acidic and highly weathered, and often colored red, orange, and yellow.

High mountain system

High mountain systems are generally found above 4,600 feet and have unique characteristics. Their formation is limited by frigid soil temperatures, resulting in less developed soil profiles with minimal microbial activity. Vegetative cover includes spruce-fir stands as well as heath and grassy balds.

High elevation frigid soils

High elevation frigid soils are unique to the region. They are characterized by organic rich soils and cool, moist microclimates. Low temperatures significantly reduce the rate of decomposition and increase the amount of leaves and decaying vegetation. The difficult terrain and rocky soils limit their use for agriculture. Found at the highest peaks, these soils are forested and provide timber, wildlife habitat, and watershed protection. The forests on these sites contain northern hardwoods and conifers, resembling cool, moist, temperate forests of the northeastern United States.

Southern Appalachian fens and bogs

Fens are high mountain wetlands which differ significantly from most soils found in the region. Fens are the result of groundwater seepage to the surface. High levels of calcium as well as other minerals are found in these soils, making it possible for only select vegetation to thrive.

Mountain bogs are generally wet and soggy. Groundwater seepage, rain and snow are the sources of water that feed the bogs. Their primary location is valleys and gentle slopes. Predominant vegetation includes rhododendron thickets as well as mixed stands of red maple, eastern hemlock, and eastern white pine. Overgrazing has occurred in nearly all of the bogs. In addition, non-native invasive species and flooding by beavers threaten their existence.