- Slope: is the gradient or steepness of a particular surface of the Earth. The slope affects
the rate of water run-off. A steep slope encourages fast run-off of water and can cause
soil erosion. The soil tends to be shallow and infertile with reduced plant growth.
Plants are small and few animals present. A gentle slope favours slower flow of surface
water, reduces erosion, and increases availability of water to plants. The direction and
steepness of a slope also influences the surface temperature of the soil. - Altitude: is theheightof the land above sea level. At high altitudes the temperature is
lower, the wind speed is greater, and the rainfall less. Environments at higher altitudes
are also more likely to experience snow conditions. Altitude plays a role in vegetation
zones. At high altitudes, less plant and animal species are found Plants growing at
mid-altitudes experience more stunted growth. Plants at sea-level are abundant. - Aspect: refers to the position of an area in relation to the sun or wind or wave action.
It is the direction that the slope faces i.e. North, East, West. In South Africa rain fall is
more common on the south-eastern slopes, therefore these tend to be forested or rich
in vegetation. The slopes facing the other way (north west) tend to be drier.
- Edaphic factors
Edaphic factors are those factors related to the soil. The qualities that may characterise the
soil include drainage, texture, or chemical properties such as pH. Edaphic factors affect the
organisms (bacteria, plant life etc.) that define certain types of ecosystems. There are certain
plant and animal types that are specific to areas of a particular soil type. The particular
factors we will consider include the pH of the soil and soil structure.- pH of soilis a measure of how acid or alkaline soil is and can be measured by the pH
scale. The pH scale ranges from 0 to 14. Neutral solutions have a pH value of 7. Acid
solutions have a pH value of less than 7 and alkaline solutions greater than 7. Litmus
paper or universal indicator can be used to determine whether a solution is acid or
alkaline.
Figure 9.14: pH scale for soil.NOTE:
Did you know that some species of Hydrangea flowers are natural pH indicators? The flowers
of theHydrangea macrophyllaandHydrangea serratacultivars, can changes colour depend-
ing on the relative acidity of the soil in which they are planted. In an acidic soil with a pH
below 6, the flowers will usually be blue. However in an alkaline soil with a pH above 6,
the flowers will be more pink. Moving the plant from one soil to another results in a change
in flower colour if the pH of the soil is different (see Figure 9.16).270 9.5. Ecosystems