By David Okul
veg monitoring
Reasons for sampling vegetation
In general, sampling is done because it is expensive if not impossible, to assess every plant in a given area. Specifically, sampling vegetation has various reasons including:
- Assessing the effects of vegetation to management
- Estimating the carrying capacity for a given area
- Determining the habitats for various species
- Long term monitoring of vegetation trends
Before starting a vegetation monitoring exercise, it is vital to understand the purpose of sampling. You see, different objectives may require different sampling methods.
Aspects/Attributes of vegetation that can be sampled
Species composition
Species composition (or botanical composition) refers to the contribution of a species to the total vegetation composition. It is usually expressed as a percentage. It is a common attribute in vegetation monitoring as it can be useful indicator of ecological and management processes.
Frequency
It is one of the easiest and fastest attributes for vegetation monitoring. It refers to the number of times a species is present in a given sampling unit. In other words, Frequency seeks to determine the ‘commonness’ of a species. It describes the distribution of plants Frequency attribute may be useful in providing early warning of undesirable change in indicator species. However, the attribute is dependent on quadrat size that it is not ideal to calculate composition from frequency data.
Cover
Generally, ground cover refers to percentage of ground covered by vegetation. Cover can be used to describe vegetation, canopy, foliar, base and ground cover.
Density
In earlier publications, density was synonymous to cover. However, it is used to determine the number of individuals per unit area.
Absolute density
All species
Relative density
Specific species and often expressed as percentage
Production
Arguably, production is the best attribute to describe the roles of a plant species in an ecosystem. The terms associated with biomass are usually related to production.
The attribute of production could also answers the question of ‘how much’. It involves the measurement of size, bulk and weight.
Weight/biomass is the best indicator of dominance. However, obtaining estimates could be time consuming.
Other measures of dominance include
- Basal cover
- Canopy cover
- Ground cover
David Okul is an environmental management professional with over 10 years experience on donor projects, conservation, forestry, ecotourism, and community-based natural resources management. When not working on active environmental management projects, I spend my time writing for Silvica on a variety of topics. The views on this blog post are personal.
