Steeplands

• Definition
• Further description
• General environment
• Global extent and location
• Land use
• Main production constraints
• Summary
  

Definition

In the context of agricultural problem soils, steeplands are areas where a high slope inclination dominates the problems related to agricultural land use.  Steeplands are characterized by slope inclinations of more than 12 %.  Moreover, soils of steeplands are often very shallow because of active erosion processes.  In the World Reference Base (WRB) soil classification system steeplands may occur in the following Reference Soil Groups:  Andosols, Arenosols, Calcisols, Leptosols, Regosols and Cambisols. Steeplands' soils are usually extremely variable, due to site specific differences in geology, geomorphology, vegetation and rainfall.  However, much of the steeply sloping lands in the mountainous parts of the world carry Leptosols.

Further description

The soils on slopes are often young because of natural and accelerated erosion processes which either cause that the topmost layers are continually being lost, or that they are continually being overlain by the deposition of materials moving down slope. Mass movements such as landslides and mud flows are specific to steeplands. They may be triggered by seismic activity or by exceptionally prolonged and heavy rainstorms, and may be caused by the undercutting of riverbanks, or by excavations into hillsides for quarrying or road construction. Mass movements are also common in areas where there have been geologically-recent changes in the hydrological base level.
The physical, chemical and biological characteristics of steeplands' soils are strongly conditioned by the nature of the parent material. Calcareous parent materials are richer than the non-calcareous ones.  However, the types of soil parent material in steeplands are very varying and because of geological folding and faulting in hilly and mountainous areas, rapid changes in the parent material may occur over short distances.
Furthermore, soils of steeplands are strongly influenced by a number of specific factors such as slope aspect and climate – elevation interactions.

General environment

Steeplands occur in many different land types. They are the result of continuing slow geological processes of uplift and formation of new land masses, their wearing down by wind and water erosion, the removal of eroded materials by wind, water, gravity, and in a few places, by glaciers.
Where the geomorphology of an area is not affected by volcanic eruptions or tectonic movements, processes of rock weathering, geological erosion and sediment transport may slowly expose harder rocks that give rise to steep slopes as a result of their greater resistance to weathering compared to surrounding rocks. For example, where sedimentary rocks or very fluid volcanic lavas have been laid down in layered horizons of contrasting hardness, and which are now either level-bedded or tilted, short sections of steep slopes may occur below the hard rock bands where the intervening softer materials have been worn away.

Global extent and location

Steeplands occur in all parts of the world from the tropics to the cold polar tundra and from coastal areas to the tops of the highest mountains.  Leptosols are the most important soils of mountain regions.  Leptosols are (together with Cryosols) the most widespread Reference Soil Group covering globally an area of approximately 1655 million ha (see table).  Their greatest extent is found in the mountainous areas of Asia and South America, the Saharan and Arabian deserts, the Ungava peninsula of northern Canada and the Alaskan mountains (see figure).

Land use

Steeplands are often under natural vegetation, restricted to forestry use only or used for extensive grazing. For arable cropping steeplands have severe physical limitations with a high risk for occurrence of erosion processes.  However, in steeplands, there exists a vast range of varying land use combinations due to the differing agroecological conditions and socio-economic circumstances over relatively short distances.  In smaller isolated steepland areas, the type of land use may be more closely related to the land use practised in the surrounding flatter lands, e.g. the same type of arable agriculture, or it may differ from and complement the land use practised in the flatter lands, e.g. livestock grazing on steeplands to complement arable agriculture in the adjacent flatlands.  If steeplands are utilized in a slash and burn system they degrade after a few years with severe soil erosion symptoms.  Steeplands can be stabilized by terracing and conservation-effective agricultural practices.

Main production constraints

Main production constraints of steeplands are soil degradation and continuing soil loss due to active soil erosion processes.  The main factor limiting production on steeplands is the effective rooting depth of soil.  Therefore it is common to the steeplands' soils that they have a rather limited water holding capacity, a limited volume of soil root anchorage, are well drained and lack high level of soluble salts.  Biological soil activity may be temporarily inactivated through drought.
The fertility of soils in steeplands may be very variable, depending on the parent material (which influences soil texture and clay mineral type), type of vegetation, land use and climate which will affect the organic matter content and nutrient dynamics.
Furthermore, production constraints depend mainly on the (micro-)climatical factors  which can vary even over short distances.  These factor comprise slope inclination, slope aspect, elevation, mean temperature, length of growing period, rainfall reliability and rainfall intensity.

Summary

Steeplands usually dispose of young or weekly developed soils due to active soil erosion processes as well as slow soil formation on resistant parent materials of old geological systems.  Therefore soils of steeplands are often very shallow with few signs of alteration processes and horizon differentiation.  This causes a limited rooting depth of the soil and limitations in the waterholding capacity.  Many steeplands are best left under forest cover or used for extensive grazing.  For sustainable arable crop production on suitable steeplands soil conservation measures and conservation-effective agricultural practices have to be applied.