Soils Overview

Introduction

A wide variety of soils and landscapes comprise the state of Florida.  These include:

  • The red, loamy soils of the upper Florida Panhandle;
  • the poorly drained, sandy soils of the flatwoods;
  • the peat soils of the northern Everglades; and
  • the shallow, limerock-influenced soils of extreme south Florida

What is Soil??

Soil is the portion of the earth's crust in which plants can grow if water and temperature are adequate, at least the minimum nutrients are available, and toxic substances are in low concentration. All soils develop from weathered rock, volcanic ash deposits, or accumulated plant residues.  The majority of soils are formed from weathered minerals which include:

  • quartz
  • feldspars
  • micas
  • hornblende
  • calcite
  • gypsum

Combinations of minerals into solid masses are called--you guessed it--rocks.

Soils are often deposits of weathered, loosened, or transported particles.  These materials are called parent materials and are deposited by water (alluvium), glaciers (moraines), wind (dunes), or gravity (colluvium).  These deposits (in parentheses above)are called landforms. 

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Soil Biology

When the complex of rock and plant residues described above is occupied and modified by living organisms, the dynamic system that we know as soil develops.

The term soil biota refers to the organisms that spend all or a part of their life cycle in the soil.  They can be divided into soil flora and soil fauna.

Soil Flora

Soil flora refers to a very diverse group of nonanimal organisms that include:

Bacteria

Bacteria are classified (ecologically) as:

  • Autotrophic: satisfy energy needs by utilizing energy released during transformations of inorganic compounds.
  • Heterotrophic: utilize simple sugars and starches, but can also utilize cellulose and other complex substances by means of enzymes.
  • Symbiotic: survive by mutually beneficial relationships with higher plants.

Actinomycetes

Actinomycetes are a group of organisms that are sometimes (incorrectly) grouped with fungi. They have characteristics of both fungi and bacteria, having branching hyphae which are often brightly colored.

Fungi

Fungi make up the majority of the decomposer organisms in many forest soils. Perhaps the most significant group of fungi are those that form symbiotic mycorrhizal associations with tree roots. These mycorrhizae increase the efficiency with which nutrients, which are at very low concentrations in the soil, are uptaken by plants.

Algae

Free-living algae live at the interface of the soil and the atmosphere. Blue-green algae are capable of nitrogen fixation (conversion of atmospheric nitrogen into usable form for plants).

Plant Roots

Roots play an important role in soil development and function. Organic matter is contributed to the lower soil horizons when roots die, promoting the formation of soil structure. The channels left in the soil after roots have decayed improve soil aeration and facilitate the movement of water. Roots also increase the weathering rate of minerals and rock because of organic compounds they secrete or because of the activities of the microorganisms that live in the rhizosphere (the root zone).

Soil Fauna

Soil fauna include all animals that spend at least part of their life in the soil. They are a very diverse group, ranging from moderately large animals that excavate underground burrows, to microscopic mites, nematodes, and protozoans that reside in the films of water coating soil particles.

Soil Invertebrates

The burrowing activities of soil invertebrates influence soil aeration and structure, soil drainage, and soil development.

Mollusks

Mollusks are more abundant in richer soils, where calcium needed for their metabolism is abundant.

Earthworms

These animals are responsible for large-scale soil mixing. This takes surface organic matter deep into the mineral soil, promoting soil structure and bringing minerals from lower horizons to the soil surface.

Millipedes

These animals play an important role in the initial decomposition of organic matter in forest soils. They are most common on moist sites.

Termites

Termites play a major role in many tropical soils as soil mixers and, as earthworms do, aid in the incorporation of organic matter.

Ants

Ants alter the bulk density of soils. In areas of high activity significant quantities of material are brought to the surface from lower horizons. This material accumulates at the surface and after a prolonged period it forms the surface of the mineral layer. As predators they affect the composition of the soil fauna.

Mites

Mites are one of the most numerous groups of animals in the soil, with numbers as high as 10,000 individuals per square meter. They exist mainly in the organic surface layers where they play a major role in decomposition. They also eat bacteria and fungi.

Springtails (Collembola)

These animals are another abundant group in the organic surface layers. They have been reported to reach densities of 50,000 individuals per square meter in a Douglas fir plantation. They feed on living and dead plant material, feces, bacteria, and algae.

Potworms (Enchytraeids)

Potworms are small white worms that can reach densities of 250,000 individuals per square meter. They eat dead organic matter and small feces. They ingest small mineral particles and probably play an important role in mixing organic matter into the mineral soil.

Nematodes

These animals are small roundworms that are best known for their parasitism of plants and are not known to be involved in the decomposition of organic matter.

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The Origin of Florida's Soil Materials

The Florida plateau consists of the present peninsula plus a submerged shelf in the Gulf of Mexico that extends the length of the state.  From about 100 million to 20 million years ago, the Florida peninsula existed in an environment similar to today's Bahaman Banks, where pure limestone and dolomite rocks were deposited.

These rocks contain little or no quartz sand or clay materials, except in the Panhandle where fragments of rocks were brought in by rivers from the north.  These limestones and dolomites make up the Florida artesian aquifer which provides massive amounts of water to wells and springs.

From about 25 to 20 million years ago, changes associated with mountain formation throughout the Gulf coast caused streams to bring deposits of sand, clay, marl, phosphatic boulders, and limestone on top of the Florida aquifer.

Due to the dominance of carbonate-rich rocks in Florida's geology, karst topography is widespread.

  • karst topography:  Landscapes that are generally lacking in rivers, marked by sinkholes* and caves; these features are formed because the underlying rock dissolves more easily than most rock.

*Sinkholes are formed by solution of limestone near the surface and consequent collapse of the overlying material into the solution cavities.  If surface runoff carries clay sediments into the depression, a lake or marsh may form. Sinkholes are rare where the sedimentary cover over the limestone is more than about 60 meters thick.

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Physiographic Subdivisions of Florida

The physiography of Florida is the result of erosion, deposits, and solution-related processes that have formed the land over time.  There are ten major physiographic subdivisions in Florida:

  • 1 - Sea Island District
    The sea island district of northeastern Florida ranges from upland terraces to plains and ridges.  Soils are dominantly sandy but significant expanses of clayey deposits exist.  The ecosystems associated with this district include pine flatwoods, dunes, and salt marshes.
  • 2 - Eastern Flatwoods District
    This district is located on the eastern side of the state and is generally low and flat.  It originated as a series of barrier islands and lagoons and is presently consists of broad expanses of flatwoods with prairies, ridges, and a variety of coastal features.  Soils are sandy with significant areas of peat deposits.  The ecosystems associated with this district include pine flatwoods, prairies, cypress ponds, dunes, and mangroves.
  • 3 - Gold Coast - Florida Bay District
    This is a uniformly low-lying district and includes the area of slow south and southwestward drainage from Lake Okeechobee (the Everglades), with coastal ridges, mangrove swamps, and the Florida Keys.  Parent material is largely limestone rock with a sand, marl, and organic material covering.  The ecosystems associated with this district include marshes, dwarf cypress, prairies, rocklands, and mangroves.
  • 4 - Southwestern Flatwoods District
    Located on the southwestern corner of the peninsula, the landscapes of this district include low plateaus and ridges, flatwoods, prairies, rockland/marl plains, and a variety of coastal features.  Soils are sand, clay, limestone, and organic deposits.  The ecosystems associated with this district include pine flatwoods, prairies, cypress ponds, mangroves, and dunes.
  • 5 - Central Lake District
    This district is made up of sandhills and lakes typical of the central Florida ridge.  It is a sandhill karst terrain with many solution basins.  The permeable sands and rapid internal drainage of this region make it the principal recharge area of the Florida aquifer.  Soils are sand, clay, and organic deposits.  The ecosystems associated with this district include sandhills and sand pine scrub.
  • 6 - Ocala Uplift District
    The Ocala uplift district is a very diverse region with a wide range of elevations, landscapes, and soil materials.  It is located in northwestern quarter of the Florida peninsula and extends north-northwest to the eastern side of the Panhandle.  The landscapes include rolling karst plains, stream-sculpturedhills, flats, swamps, and sandhills.  The karst plain in the central part of the district grades to sandy flatwoods toward the west and south. The northern part of the district is upland with moderate to high clay content in the soil.  The northeastern portion is a sandhill terrain and the eastern section is upland with clay deposits.  The ecosystems associated with this district include mixed hardwood forests, pine flatwoods, and sandhills.
  • 7 - Tifton Upland District
    Located in the north central portion of the Florida Panhandle, this upland district's topography is controlled by thick deposits of sediments that have been sculptured by surface drainage.  Soil materials are clay or loam, topped by a varying thickness of sand.  The ecosystems associated with this district include pine and mixed hardwood forests.
  • 8 - Dougherty Karst District
    This district is located in the northwest central portion of the Panhandle and is characterized by limestones close to the surface with predominantly karst landscape development.  Elevations are low relative to the Tifton Upland and Southern Pine Hills Districts to the east and west where thick deposits of younger materials control topography.  Soil materials are clay or loam with a sandy cap exceeding 2 meters in thickness in the southern and eastern parts of the district.  The ecosystems associated with this district include pine and mixed hardwood forests.
  • 9 - Apalachicola Delta District
    Located in the south-central portion of the Panhandle, this district is built with sediments deposited by the Apalachicola River.  Landscapes range from relic deltas, ridges, and lagoons to river terraces, delta plains, and barrier islands.  Karst topography is absent and soil materials are sandy to loamy.  The ecosystems associated with this district include pine flatwoods, mixed hardwood swamps, salt marshes, and dunes.
  • 10 - Southern Pine Hills District
    This district is located in the far western portion of the Panhandle, this district is an area of thick sediments.  The northernmost, highest sections are stream-sculptured from an alluvial plain over a layer of sand, gravel, silt, and clay.  Intermediate elevations consist of ridges formed by coastal sediments, and the coastal strip consists of relic lagoon and barrier island features.  Soil materials are loam and clay to the north with an increasing thickness of sand toward the southern part of the district.  The ecosystems associated with this district include pine and mixed hardwood forests, sandhills, and dunes.

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Management Considerations

Soil is the least renewable physical component of the forest ecosystem. Once lost it is probably the most difficult resource to replace.  Much of the very fertile soil on moderate topography in climates suitable for high-production forestry have been claimed by agriculture.  Our need for food has traditionally outweighed our need for forest products. Thus foresters and private nonindustrial forest (PNIF) landowners are frequently left with less productive soils.

Due to this limitation, foresters generally have fewer options for manipulating soil physical and chemical properties than does the farmer.  Foresters can fertilize some types of sites and use fire or mechanical site preparation to improve the fertility of the land after harvesting, but trees generally must be grown with the soil resource we have inherited or purchased.

For more information, visit our Fertilization page or read the SREF publication, Soil pH and Tree Species Suitability.

Harvesting activities have the potential to adversely effect the soil:

Soil Disturbance

Disturbances to the soil from harvesting can vary from a slight disturbance to the forest floor to complete loss of the upper soil horizons. The degree of ground disturbance is determined by the type of harvesting equipment used and the time of year harvesting takes place.

Level of Soil Disturbance Associated with Different Types of Harvesting Equipment

The least soil disturbance occurs with skyline yarding, a harvesting method in which logs are moved from the stump to the landing (where logs are loaded onto trucks) suspended in the air by a taut cable.

High lead yarding, the most common harvesting method on the west coast, disturbs the soil significantly more than skyline yarding. In this method the logs are dragged to a central landing by a slack cable, and there is considerable soil disturbance on the yarding roads.

The highest degree of disturbance is associated with tractor or skidder yarding. This method involves a wheeled or tracked vehicle dragging the log from the harvesting site to the landing by a cable.

Time of Year to Harvest

In more northern climes, disturbances to the soil can be minimized by harvesting during the winter months when snow acts as a protective layer over the soil. In Florida this is not an option.

Disturbance to the soil can be minimized by scheduling harvesting activities during the dry season when the soil is less likely to by moved or altered by heavy equipment.

Effects on Soil Stability

On steep slopes, the stability of the soil may be significantly reduced to the point where mass soil movement occurs (slides, slumps, and debris avalanches). The topography of Florida rarely lends itself to these types of effects, but there are some areas, particularly on the Panhandle, where consideration to mass soil movement is appropriate.

Alteration in Soil Temperature

Changes in soil temperature occur as a result of clearcutting. The extent of these changes depends on the degree of mineral soil exposure and the reduction in the depth of the surface organic matter accumulation.

Roots are largely confined to the surface organic layers. Where these layers contain nutrient-poor material, the plants will experience inadequate nutrition and grow very slowly. The restriction of roots to the surface of the forest floor, which may dry out during the dry period, make seedlings susceptible to drought injury or death.

Exposure of mineral soil reduces temperature extremes at the soil surface which can be beneficial to plants, but in environments with hot summers, soil temperatures may increase to levels that are lethal for many plants.

Alteration of Soil Physical Properties

Use of heavy machinery can alter:

  • soil structure
  • porosity and density
  • pore size distribution
  • aeration
  • water retention
  • infiltration capacity
  • and hydraulic conductivity

The degree of alteration depends on:

  • the weight of equipment and logs being yarded
  • the number of times heavy equipment and logs pass over the soil
  • and soil water content

Some findings: In one study on the impacts of forest operations on soil physical properties, soil density increased exponentially with increasing number of passes of a tractor. One pass of a tractor on wet soil resulted in as much compaction as four trips on a dry soil!

This illustrates the need to schedule harvesting activities during the dry season.

Loss of the forest floor from harvest operations exposes the mineral soil to compaction and to the impacts of rain. Both of these can lead to loss of surface soil structure and puddle formation. A structureless surface layer with a thickness of only a few millimeters can be enough to alter the infiltration rate significantly and result in surface runoff and erosion.

Take-Home Message

It is important to remember that in most cases the productive potential of the site is vested in a relatively thin surface layer of soil. Erosion of only a few centimeters of this surface layer may be accompanied by significant reductions in plant growth.

The choice of harvesting method and type of equipment should be influenced by soil fertility, stability, compactability, and erodability. Postharvesting site treatments, choice of species to plant, and regeneration method should also be influenced by the soil properties of the site.

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References

  • Fisher, R.F., A.S. Jenson, D.M. Post, D.L. Rockwood, W.H. Smith, and E.T. Sullivan.  Forest Management for Small Ownerships. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville. 33 pp.
  • Kimmons, J.P. 1987. Forest Ecology. Macmillan Publishing Company, N.Y. 531 pp. 
  • Miller, R.W. and R.L. Donahue. 1990. Soils: An Introduction to Soils and Plant Growth.  Prentice Hall, Inc., Englewood Cliffs, N.J. 768 pp.
  • Myers, R.L. and J.J. Ewel (editors). 1990. Ecosystems of Florida. University of Central Florida Press, Orlando, Florida. 765 pp.
  • Pritchett, W.L. and J.W. Gooding. 1975. Fertilizer Recommendations for Pines in the Southeastern Coastal Plain of the United States. Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida, Gainesville.

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