Appendix 11. Vegetation Surveys

From PRAGMO
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to navigation Jump to search

Navigate to: Hydromorphology // Macroinvertebrate // Fisheries // Hydrology // All Appendices

Scientific best practice

In-channel vegetation

  • Assess species as well as morphotypes.
  • Consider vegetation succession when setting expectations and creating a monitoring strategy.
  • Use aerial photography, hydroacoustic methods, remote sensing, and modelling alongside more traditional approaches.
  • Consider geomorphological interactions as well as external factors such as shading and grazing.
  • Use the BACI approach (before-after-control-impact) with both positive and negative controls.

See England et al. (2021) [1]

Riparian vegetation

  • The monitoring strategy should reflect and account for the timesecale of the expected response.
  • Assess ground beetle response to restoration using pit-fall traps and hand searches - Find out more.

See England et al. (2021) [1]

1. Introduction to macrophyte and vegetation surveys

Macrophytes are larger plants living in streams and rivers, including all vascular plants, bryophytes, stoneworts (Characeae) and macro-algal growths, visible by naked eye. Their distribution in a stream is related to the physiological demands of the plant, its ability to tolerate the local environmental conditions (nutrient abundance, substrate, waterflow, and flow regime, temperature, shade…), the dispersal history of the plant, and its interactions with other plant species especially on non-disturbed zones with macrophytes abundance (Methods in stream ecology). Seasonal changes in macrophyte biomass in temperate streams are also associated with a combination of changes in light and temperature between summer and winter (Champion and Tanner2000, Riis et al. 2003). Macrophytes play an important role in stream ecology by providing oxygen, pollutant retention, shelter for macro-invertebrates and fish, support for eggs and periphyton. They also have important influences on stream ecology and morphology by affecting bed substrate composition and modifying local flow conditions. Macrophytes collectively create a diversity of habitat beneficial for the overall stream ecology and catchment biodiversity.

2. Actual method to study macrophytes (See section on LEAFPACS for more details)

The use of macrophytes as indicators of ecological quality in running waters is based on the fact that certain species and species groups are indicators of specific running water types and are adversely affected by anthropogenic impact. Recognising that their role in contributing to stream habitat is important one standardized method (that meets the WFD specification) is now used to monitor macrophytes. This method is called LEAFPACS2, and is derived from LEAFPACS (Willby et al, 2012). It is a methodological approach for determining the ecological status of a river based on the nutrient-tolerant score of each species and their abundance. It also includes other indices for river morphology, flows and community richness.

This method consists of an exhaustive inventory of the macrophytes in a reach, whether 100m or 500m in length, chosen subjectively by the surveyor to get a “representative sample” of the stream macrophyte community. Obviously, survey biases between operator can occur, especially since there is no standardized length for sampling between 100, 500m or by defining a ratio between river width and the length to monitor (LEAFPACS). Moreover, this method is designed to assess the organic pollution of the river but can only provide an approximate measure of factors that reflect habitat type and macrophyte relationships.

This sampling method can also be used to identify changes in channel macrophyte diversity, flow conditions and substrate stability.

In general, macrophyte monitoring using the LEAFPACS methodology is not so well suited to the assessment of restoration schemes in large rivers or deep-water sites.


Application to river restoration

The sampling methodology described above can be applied in a BACI (Before-After-Control-Impact) study to investigate the change in vegetation cover and diversity of macrophytes within a restored reach as part of a program to evaluate river restoration. However, the nutrient status is unlikely to be a reliable indicator because full vegetation recovery will probably take years.

Considering the wide effect of river restoration on adjacent floodplains it is necessary to extend the vegetation monitoring to sections of the floodplain that have the potential to be affected by restoration measures. Not including this step would risk underestimating the effects of restoration work, restrict evaluation and potentially fail to identify all the benefits (or not) occurring outside of the riverbed.

For riparian and floodplain habitats, two simple sampling methods exists to survey vegetation recovery after restoration measures.

Find out more about LEAFPACS2

3. Quadrat method

The quadrat method is widely used and recommended by the National Vegetation Classification Handbook to name vegetation habitat. To accurately record changes over time and make comparison between surveys this method should be applied with fixed quadrats, repeating the quadrat surveys for several years in order to record long term environmental changes. For designing a quadrat study the step can be:

  1. Design the sampling density before restoration work and record quadrat locations using a GPS. Replicate quadrats are located within and outside the area of work, but also within and outside and the overall area affected by be restoration measures (e.g. they can be in the stream for macrophytes or in the adjacent floodplain). The quadrat should be located to represent the diversity of habitat before and after work. For macrophytes, sampling design should include the most of the common features (pools, runs, riffles, steps…).
  2. Once restoration works have been completed and the site has settled down, locate the quadrat at the exact same place using GPS coordinates or any markers that have been installed before restoration.
  3. Conduct repeat surveys of the quadrats for several years and monitor physical parameters (water flow, substrate…) to understand which environmental parameters are having the greatest effects following restoration and driving development of the plant community.

Find out more about the Quadrat method

4. Belt transect method

The belt-transect method is a combination of quadrat and transect sampling. The belt-transect can be applied when the objective is to assess the effect of an environmental gradient on the vegetation. For example, by repeating several quadrats following the transect line, along habitat components and their gradient (water depth, substrate differences, groundwater level, soil differences…). By restoring a river section, we modify the environmental controls, consequently leading to changes in the vegetation that highlight the benefits (or not) of restoration work. The following steps can be used to monitor the effects of river restoration using the belt-transect method:

  • Design the sampling strategy before the restoration work to locate transects which should be recorded by GPS. Replicate transects are located within and outside the area of work, but also within and outside and the overall area affected by restoration measures (this can be in the stream for macrophytes or in the adjacent floodplain). The transects should be located to represent the diversity of habitat and environmental gradient before and after work. For macrophytes sampling design should include the most of the common features (pools, runs, riffles, steps…).
  • Complete restoration work and habitat alteration
  • Locate the transect along the exact same line using the GPS coordinates or any landmark that has been identified and recorded at the start.

Monitor the transects over several years (three to five) and for macrophytes monitor the physical parameters (water flow, alkalinity, substrate, shading, nutrient concentrations…) in addition, to understand which environmental parameters determine species establishment and affect development of the plant community. The belt-transect, compared to other transect methods, can give an estimate of the cover and abundance of species. Moreover, the quadrat size can be adapted to the habitat sampled (marshland, banks, macrophytes in the river).

5. Remote sensing

Useful for monitoring river channels in general and therefore can be helpful to assess linear changes in channel habitat and fluvial features, in riparian structure, floodplain vegetation and habitats. Although not a method to apply if species identification is the main purpose of the survey, it can be a good method to assess vegetation cover, and to some extent structural composition and complexity. Therefore, remote sensing can be a valuable addition to monitoring restored river sections and floodplains. It can be part of a programme to monitor a variety habitats and geomorphological processes, and not specifically conducted for vegetation monitoring Future development will enable the assessment of plant health, water temperature and turbidity.

6. Method comparison and suitability for monitoring restoration zones

Table A11.1 : Comparison of methods
Method Good ecological state Time Reflect changes of river restoration Accuracy in plant community's identification and structure Applicable to floodplain and associated habitat Objectivity
LEAFPACS Yes ++ ++ (if adapted) ++ No No
Permanent quadrats No +++ +++ +++ Yes Yes (but subjectively located regarding to the future restoration work)
Transects No +++ +++ +++ Yes Yes (but subjectively located regarding to the future restoration work)
Remote sensing No +++ ++ (on associated river habitat) + Yes Yes

For all these studies a BACI method should be employed. Two types of controls should be used for the monitoring:

  1. Controls inside and outside of the area of restoration work and the area of influence of the restoration measures (floodplains and downstream, for example) are critical for interpreting ecological changes and describing the effects due to restoration, by highlighting the impacts of the environmental factors that have been modified.
  2. The use of a pristine river state as an example of the habitat and environmental conditions river restoration is aiming to achieve for a particular river section. The river has to be of the same morphology, but some parameters are likely to differ and a good comparison between two rivers is potentially difficult. For example, the lack of macrophytes is not always an effect of anthropogenic impact but a characteristic feature due to shading or some other factor. In geological formations like the flysch, or in the central part of deeper rivers macrophytes may be absent due to the habitat limitations imposed by geology and substrate, water depth, current flow velocity, turbidity, etc..

7. References

Hauer, F. R., & Lamberti, G. (Eds.). (2011)
Methods in stream ecology. Academic Press.
Fluvial Remote Sensing for Science and Management (2012)
Patrice E. Carbonneau, Hervé Piégay. Copyright © 2012 John Wiley & Sons, Ltd. DOI:10.1002/9781119940791.
JNCC, (2003)
Monitoring Floating Water-plantain, Luronium natans. Conserving Natura 2000 Rivers Monitoring Series No. 10, English Nature, Peterborough.
Life in UK Rivers (2003)
Monitoring Ranunculion fluitantis and Callitricho-Batrachion Vegetation Communities. Conserving Natura 2000 Rivers Monitoring Series No. 11, English Nature, Peterborough.
Lovett, S., and Price, P. (1999)
Riparian Land Management Technical Guidelines, Volume 1: Principles of Sound Management.