Indicator plants are therefore valuable for rapid decision-making and offer a simple alternative to complex and long-term hydrological measurements and soil physical analyses in agriculture, nature conservation, water management, and landscape planning. They react to changes in soil water balance significantly earlier than soil type and soil moisture characteristics.
The presence or absence, increase or decrease, disappearance or reappearance of indicator plants in a habitat can be recognized even without specialized botanical knowledge.
Indicator plants can be used to quickly and comprehensively identify locations and habitats with a significant influence of groundwater, perched water, slope water or floodwater.
The creeping buttercup (Ranunculus repens), when found in large numbers, indicates compacted, intermittently moist (waterlogged) soil. It is an indicator of soil compaction and fluctuating moisture levels. The occurrence of individual plant species in the landscape depends crucially on the location (climate, soil, other plants, animals, humans). Some species have a low ecological amplitude with respect to individual site factors (e.g., soil moisture, soil pH) and are extremely sensitive to changes in these factors. These species (specialists) can therefore usually only colonize a specific habitat (e.g., calcareous spring meadows). In contrast to generalists, they are highly specialized in their site requirements and can therefore be used as bioindicators (indicator plants).
Giant horsetail (Equisetum telmateia) prefers to grow on carbonate-rich soils in calcareous spring areas. Its presence indicates calcareous spring water. Giant horsetail is an indicator of wet conditions and carbonate soils.
Indicator plants are bioindicators; the ecological condition of a habitat (e.g., the degree of eutrophication of a surface water body) is quickly and comprehensively assessed:
- Assessment of specific site characteristics in a habitat (e.g. frequency and duration of flooding),
- Identification of small-scale site differences within a habitat,
- Detect early changes in location,
- Derivation of the urgency and necessity of measures (e.g., cultural engineering measures such as drainage),
- Quick and easy monitoring of the success of implemented measures.
The common cuckoo flower(Cardamine pratensis) blooms in spring and, when found in large numbers, indicates sites with alternating wet and dry conditions.
Conclusions about the site conditions can be drawn if a particular indicator species (e.g., bistort) is strongly present or if several or many species have the same indicator value (e.g., moisture indicators).
The abundance of bistort (Persicaria bistorta) indicates a damp location and a cool climate. It is an indicator of cool and damp conditions.
There are indicator plants for various site characteristics (e.g. nutrient balance, soil water balance, heat balance, soil pH value, bulk density in the soil).
However, the presence of a single indicator species with a small number of individuals (e.g., a single plant of ragged robin) does not provide a reliable indication of the location.
The slender sedge (Carex acuta) forms species-poor, dominant stands and characterizes moderately wet, periodically flooded sites. It is an indicator of wet and flooded conditions.
The slender sedge (Carex acuta) forms species-poor, dominant stands and characterizes moderately wet, periodically flooded sites. It is an indicator of wet and flooded conditions.
Summary of indicator plants
Moisture indicators: Cabbage thistle (Cirsium oleraceum), Woolly thistle (Cirsium heterophyllum), Marsh thistle (Cirsium palustre), Bistort (Persicaria bistorta), Meadowsweet (Filipendula ulmaria), Woodland forget-me-not (Myosotis nemorosa), Common comfrey (Symphytum officinale), Soft spike-rush (Juncus effusus), Grey spike-rush (Juncus inflexus)
Indicators of wet conditions: Common reed (Phragmites australis), Reed canary grass (Phalaris arundinacea), Slender sedge (Carex acuta), Common rush (Scirpus sylvaticus), Marsh marigold (Caltha palustris), Water ragwort (Senecio aquaticus), Crown lettuce (Willemetia stipitata), Purple loosestrife (Lythrum salicaria), Water avens (Geum rivale), Marsh horsetail (Equisetum palustre)
Flood indicators: Bent foxtail (Alopecurus geniculatus), creeping bentgrass (Agrostis stolonifera), couch grass (Elymus repens), folded sweetgrass (Glyceria notata)
Indicators of alternating wet and dry conditions: Tufted hair-grass (Deschampsia cespitosa), Tall fescue (Festuca arundinacea), Hare's sedge (Carex leporina), Blue sedge (Carex flacca), Common cuckoo flower (Cardamine pratensis), Autumn crocus (Colchicum autumnale), Lady's bedstraw (Galium verum), Hedge woundwort (Betonica officinalis)
