Riparian quality: QBR index (qualitat del bosc de ribera or
riparian forest quality)
Points to be taken into consideration prior to the use of the
STEPS TO FOLLOW
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
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
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
Avoid the disturbance caused by the facilities providing access
to the river, which can result in lower values than expected for all the
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
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
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