Topography: It is the description of the physical features of a place.
- describes configuration of the ground, its altitude, slope, aspect, etc.
- affects vegetation through climate, soil formation processes, soil moisture, soil nutrients, etc.
Topographic Factors can be classified into:
- Configuration of land surface
- Aspect and exposure
1. Configuration of the land surface
It influences vegetation through its effect on temperature, wind movement, etc.
- In a hills and valley country, sunlight reaches the valley late in the morning and disappears early in the afternoon.
- The shade of the neighboring hills makes valley colder in winter and that of radiated heat makes the valley hot. So, diurnal and seasonal temperatures of the valley differ from the temperatures on the hills. Pool frost occurring on hills and in valleys affects the vegetation.
- It also affects wind movements. It results in more rain in the east and less in the western Nepal. It has greater influence on humidity and temperature variance eventually affects vegetation of the site.
- It affects vegetation through solar Radiation, temperature and rainfall
- The intensity of radiation goes beyond optimum limit has a dwarfing effect on shoot, the growth of root being favored.
- Temperature as it is higher and lower the optimum level, affects the species composition and the site quality.
- Similarly, rainfall affected by altitude affects the temperature and moisture resulting in the change in the nature of vegetation. It has been estimated that about half the water vapor in the air lies below 2000m while three quarters lies below 4000m and so, high mountain range is a very effective barrier for the monsoons.
- Slope affects run-off and drainage having a profound influence on the moisture regime of the soil. As a general rule, the steeper the slope, the greater the run-off and better the drainage.
- Slope modifies the intensity of insolation, temperature and moisture of the surface soil
- Slope also affects erosion and depth of soil as greater the slope, greater the erosion. The depth of soil in the hills varies with the increasing slope.
- Thus, slope affects vegetation of the site through afffecting the run-off, insolation, temperature, moisture and depth of soil
4. Aspect and Exposure
- Aspect-the direction towards which a slope faces
- Exposure-the relation of a site to weather conditions, especially sun and wind
- Both determine the amount of insolation received by a hill slope. In Nepal, southern slope is warmer than the northern slopes and consequently temperature differs.
- We can see different species on different aspect of a hill.
- Similarly, different aspects receive insolation differently. The eastern slope is exposed to the sun in the earlier part of the day and so dew is seen. In the morning, soil moisture has not melted resulting in seedlings being killed. Whereas, the western aspect has desiccating effect due to noon’s sun.