Charles has a deep love for ecology. He enjoys reading about anything related to ecology during his spare time.
Most plant species require a variety of conditions to ensure optimal growth and production. The levels of these conditions are also very critical in determining if a plant is going to be healthy or not. For example, let's compare two very simple plants, the Rice plant and the Aloe Vera plant. These two plants require moisture to survive and grow healthy. However, the level of moisture that each requires is totally different. The Rice plant normally requires a high level of moisture whereas the Aloe Vera plant doesn't really need much moisture. We can therefore make an accurate guess that if we find Rice plants growing healthily on a site, the soil on that site is likely to be wet. So you see that it is possible to make inferences about the ecological conditions pertaining at a site from the plants available on the site.
Plants rely on various environmental factors in different proportions. Some of the common environmental factors that have a huge influence on the survival and optimal growth of plants are Light, Temperature, Continentality, Moisture, Soil PH, Nitrogen, and Salinity. The Ellenberg's indicator values are based on a simple ordinal classification of plants according to the position of their realized ecological niche along an environmental gradient. They were the first model of bioindication proposed and applied to the flora of Germany, and they have a long tradition in interpretation and understanding of plant communities and their evolution. To be able to understand and use these values, we first need to gain an understanding of some key terms.
A niche is a role an organism plays in its community. It is very important to note that habitat of an organism is not the same as its niche. A habitat is simply part of an organism's niche. There are two types of niches which are the fundamental niche and the realized niche. Fundamental niche refers to where a species can live negating the effects of competition, predation, resource location and other factors. The realized niche is where the species tend to live because the factors mentioned above have forced it to retreat from parts of its fundamental niche.
Abiotic factors and Environmental gradient
Abiotic factors are chemicals in the environment or physical forces in the environment. They have a huge influence on living organisms and affect how the ecosystem works. Examples of abiotic factors are wind, soil, nitrogen, water and sunlight. An environmental gradient, on the other hand, is a gradual change in abiotic factors through space (or time). This gradual change can often be represented numerically.
Ellenberg's indicator values are simple indicator values from 1-9, sometimes also from 0 or to 12, for various abiotic factors. Indicator values do not give information about the physiological requirements of a species but they give information regarding the ecological performance of species under competition (potential versus existing real situation). That is they give information about the performance of a plant in its realized niche. They can be used to estimate (abiotic) conditions/key parameters at a site.They can also be used to monitor changes of key parameters over time. The table below gives an illustration of some indicator values for various environmental factors.
|Environmental Factor||Symbol||Indicator value, in the sense of "the species prefer..."|
1=deep shade, 5=semi-shade, 9=full light
1=alpine-subnival, 5=submontane-temperate, 9=Mediterranean
1=euoceanic, 5=intermediate, 9=eucontinental
1=strong soil dryness, 5=moist, 9=wet, 10=aquatic, 12=underwater
Reaction of soil value (PH)
1=extremely acidic, 5=mildly acidic, 9=alkaline
1=least, 5=average, 9=excessive supply
0=no, 1=weak, 5=average, 9=extreme salinity
- The indicator values simply refer to what conditions the plant prefers.
- For a light value of 1, it means the plant prefers to grow in a deep shade. An example of a plant that prefers deep shade is Asplenium scolopendrium (Hart's Tongue Fern). A light value of 9 means the plant prefers to grow in full light. Aster tripolium is an example of such a plant.
- A temperature value of 1 is an indicator of an alpine-subnival climate. An example of a plant that prefers to grow in such temperatures is Chorispora bungeana. A temperature value of 9 is an indicator of a Mediterranean climate. An example of a plant that prefers such temperatures is rosemary.
- Continentality has to do with the climate. A continentality value of 1 refers to an oceanic climate. An example of such a climate is the climate of Western Europe. A continentality value of 9 refers to a continental climate. An example of such a climate is the climate of Eastern Europe.
- A moisture value of 1 is an indicator of extremely dry soils. Plants that normally prefer these soils are drought-tolerant plants and a typical example is Corynephorus canescens. A moisture value of 9 is an indicator of wet soils. An example of a plant that prefers wet soils is Viola palustris.
- A PH value of 1 is an indicator of soils with extreme acidity. An example of a plant that prefers such soils is Bog rosemary (Andromeda polifolia). A PH value of 9 is an indicator of alkaline soils. An example of a plant that prefers such soils is Primula farinose.
- A nitrogen value of 1 is an indicator of extremely infertile soils. An example of a plant that prefers to grow in such soils is Clinopodium acinos. A nitrogen value of 9 is an indicator of extremely rich soil situations such as cattle resting places or near polluted rivers. A typical example of a plant that prefers to grow in such soils is Urtica dioca or stinging nettle.
- A salinity value of 1 is an indicator of soils with low salt content. Plants that prefer these soils are slightly salt-tolerant species, rare to sprout up on saline soils but capable of persisting in the presence of salts. An example of such a plant is Sedum Anglicum. A salinity value of 9 is an indicator of soils with an extremely high salt content. An example of a plant that prefers extremely saline conditions is Agave Americana.
Examples Of How To Make Use Of Ellenberg's Indicator Values For Environmental Monitoring.
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The European Beech (Fagus Sylvatica)
Ellenberg's indicator values for Fagus sylvatica
Here, we are given the Ellenberg's indicators values for Fagus Sylvatica in a realized ecological niche. How can we use these values to estimate the abiotic conditions at the site?
- First and foremost, since we have Fagus Sylvatica growing on our site and we know that its L value is 3, we can predict with a reasonable degree of accuracy that our site is likely to exist in a slightly shaded area.
- We know that its T value is 5. We can therefore predict that the climate of the region is highly likely to be submontane-temperate since Fagus Sylvatica prefers to grow in such temperatures.
- K is 2 and hence we know the climate on our site is also likely to be oceanic. This is because Fagus Sylvatica prefers to grow on sites that have similar climates to that of Western Europe.
- F is 5 which means the soil on the site is likely to be moist. We can give an accurate prediction of this without necessarily feeling the soil.
- R and N are X, where X stands for indifference. This means that Fagus Sylvatica is indifferent to the PH and nitrogen content of a soil. There is no way of predicting the nitrogen and PH of the soil using our indicator values and we might have to run some other tests to determine these values.
- The value of S is 0 which means the soil on the site is likely to have very little salt content.
Andromeda polifolia (Bog rosemary)
Example N indicator value
The N value of Andromeda polifolia is 1 which means it is likely to be found on infertile soils. These types of soils are mostly sandy, well-drained soils.
Urtica dioica (stinging nettle)
Example N indicator value
The N value of stinging nettle is 9 which means it is likely to be found on sites which are close to farms and human settlement and indicates a high presence of nitrogen and other nutrients in the soil.
Although Ellenberg's indicator values can be very powerful in estimating abiotic conditions (for example, if Rhododendron ponticum is found growing in a soil, then that soil is certainly acid. Also, if Scabiosa columbaria is found growing in a soil, then that soil is certainly basic), knowledge of species is needed. Determination down to species level is required to make use of Ellenberg's indicator values.
© 2016 Charles Nuamah