Riparian Forest Quality: QBR index (qualitat del bosc de ribera)
Points to be taken into consideration prior to the use of the index
1 Selection of the observation area
The entire potential area of development of the riparian habitat should be considered in order to calculate the QBR index. The main channel and the riparian areas should be differentiated (see the drawing on the field data sheet).
Channel: area flooded at least every two years. It is the channel zone up to the bankfull stage.
Riparian area: from the bankfull stage until the area flooded at least once every 100 years. Includes fluvial terraces.
2 Each part is analysed independently
The QBR is a summation index of four parts. Each part is calculated independently and the individual score of each part cannot be either negative or higher than 25.
3 Calculating each part
Each part has 4 main options. Only one of these can be selected, starting with the highest score.
The initial score obtained can be modified according to the positive or negative scoring of the conditions indicated below each part. All conditions can be considered (one condition cannot exclude another even when they are of different sign).
Select only one of the four main conditions.
If the final score is higher than 25 this maximum value should be retained. Negative scores are not possible and in this case a null result will be recorded.
Both river banks should be considered as a unit for any condition.
4 Final score
The final score is the addition of the four parts, and therefore will vary between 0 and 100.
Bridges and roads crossing the river and used to gain access to the sampling point should not be considered to calculate the QBR index. If possible the QBR should be analysed upstream or downstream of these facilities. Other bridges or roads (e.g. those parallel to the river) will always be considered.
Avoid the disturbance caused by the facilities providing access to the river, which can result in lower values than expected for all the reaches.
Several measures made at the same sampling point are more informative of the riparian status. An evaluation every 100 metres is recommended for detailed studies.
1 Total riparian cover
The % cover of all kinds of plants except annuals is measured. Both river banks are considered.
The connectivity between the riparian area and the terrestrial forest ecosystem is a very important attribute, and should be considered carefully.
The vegetation structure is not considered here (see the following part), only the total cover. The role of vegetation as a key element of the riparian ecosystem is emphasized here.
Unasphalted roads or paths less than 4 metres wide are not regarded as elements that threaten connectivity.
2 Cover structure
The score depends on the % forest cover; if trees are absent, shrubs and other low lying vegetation are considered. Both banks should be taken into account.
Linear arrangements (mostly plantations) or disconnected patches may cause the initial value to drop, while helophytes in the channel or the presence of shrubs below the forest cover increase the score.
The main objective of this part is to measure the complexity of the system, which can favour the biodiversity of the riparian habitat both in animals and in plants.
3 Cover quality
The geomorphological type of the stream section should first be established. This is done using the field data sheet.
The number of species of native riparian trees should be counted and the initial score will depend on this number and the geomorphological type (1 to 3).
A tunnel arrangement of trees increases the score, depending on its cover percentage and the gallery-type structure of the vegetation. A gallery is defined in this case as a succession of different species from the bankfull stage to the upper riparian area.
A list of the species considered as allochthonous in the study area is provided on the QBR sheet. These species are penalized in the index.
To establish the geomorphological type we should use the field data sheet. Using the drawing provided, we will mark the score of the left and right banks according to their shape and slope. The final geomorphological score is the sum of both banks modified negatively by the presence of geomorphological structures that appear in low gradient streams, such as islands, or positively by the presence of hard substrates in which the vegetation cannot root. The final score is used to establish the geomorphological type (from 1 to 3) that should he used in the cover quality evaluation.
4 Naturalness of the river channel
Morphological changes occurring in the alluvial terraces, including channel reduction due to agricultural activities, lower the score. The elimination of meanders and river linearization is also considered.
Concrete structures along the length of the riparian habitat have a strong negative effect on the score, while a more moderate penalty is imposed if small concrete structures (such as weirs or walls) are present.
Bridges and small rights of way or paths used to gain access to the river are not considered.
Source: Diputació de Barcelona 2000 (Copyright)
Developed by the Department of Ecology, University of
Barcelona, with the collaboration of the Department of Environment of the