Riparian vegetation is the term used to describe plants living or located on the bank of a natural course of water, such as a river or stream. This bank area, known as the riparian zone, provides an interactive link between the surrounding land and the aquatic system.
Why measure riparian vegetation?
Because an interactive connection exists between the surrounding land and the aquatic system, the types of plants that grow in a riparian zone are known to have a major influence on the ecosystem of the waterway.
Examples of this include:
- Overhanging and semi-aquatic vegetation offer cover protection for fish and invertebrates. Additionally this vegetation provides a food source for aquatic animals, both from the plant material itself, and from insects that may fall off foliage into the water.
- Vegetation growing on the verge of the river offers spawning sites for smaller fish, such as inanga (whitebait).
- Riparian plants act as habitat, cover and a food source for the adult terrestrial stage of aquatic insects.
- Trees that shade a stream help to keep water temperatures lower.
- Roots of trees and other vegetation assist in consolidating and stabilising stream banks.
- Exposed roots and woody debris in the water provide shelter for fish, and additional habitat for invertebrates.
Given that riparian vegetation has considerable impact on waterway ecosystems, it is important to monitor the changes that occur over time.
How is riparian vegetation measured?
Riparian vegetation is determined visually by inspecting and recording percentages of types of plants within a given area.
- Determine the upper bank and lower bank areas using the following diagram to assist in deciding their location. The crossover point between upper and lower banks is located where a significant change in predominant bank angles occurs. This point may not always be as obvious as shown below but by ignoring small differences and concentrating on the predominant angles the crossover point should become obvious.
- Determine the boundary of the upper bank area that extends 5 metres back from the cross over point.
- Using the following ranking categories;
2 equalling 10 to 50% cover, and
3 equalling over 50% cover
The chart shown below provides a description of the various Categories of Vegetation that are likely to be encountered.
- Repeat this process to assess and record the riparian vegetation present in the lower bank area.
As the purpose of collecting data is to observe changes in riparian vegetation, it is important to ensure that the exact same site is used on each occasion monitoring takes place. This can be done by either using a GPS unit to ensure accuracy of location or by comparing photographs of landmarks taken on earlier monitoring visits.
Riparian vegetation categories and their definitions:
| Vegetation Category | Further description |
|---|---|
| impervious | roads and tarsealed/concreted paths, buildings |
| unvegetated | earth, rocks, gravel. |
| lawn | manicured lawn of grass & herb mix, mown very regularly |
| grass & herb mix |
unmanaged, short and long |
| low ground cover | herbaceous (and other) low growing plants, general small garden-variety, and vines/ivy (e.g. aluminium plant, nasturtium) - excludes ‘grass & herb mix’. |
| ferns | ground ferns, both native and exotic |
| rush/sedge/tussock | both native and exotic |
| coarser veg - native | flax, raupo, toe toe |
| coarser veg - exotic | general larger garden-variety plants (e.g. gunnera, pampas, lily, irises, bear's breaches, arum lily, fox glove, bamboo, etc) |
| shrubs - native | hebes, coprosmas, shrub daises, native brooms, divaricating shrubs |
| shrubs - exotic | rhododendron, camelias, hydrangeas, roses, gorse, broom, etc. |
| native trees | incl. cabbage trees, tree ferns, native vonifers (kahikatea, matai, totara) and trees (kowhai, wine berry, ribbonwood, tree fuchsia) |
| exotic deciduous | willow, poplar, elm, walnut, maple, chestnut |
| exotic evergreen | pine, macrocarpa, eucalyptus, acacia |