OLGA

Module 1: Sustainable wood use along watercourses

Promote ecosystem services and regional added value of agro-wood structures

 
© Himbeerspecht | Liane Hoder

Smaller watercourses are important landscape elements in urban and rural areas. They provide a range of ecosystem services, such as climate regulation, watercourse and flood protection, recreation or biodiversity conservation. According to the EU Water Framework Directive, however, only 6.7% of surface waters are in good condition. OLGA is therefore researching how the ecological condition of small watercourses can be improved by sustainably planting agrowood structures near the banks.

What ecosystem services do agrowood plantations along watercourses provide, especially in terms of watercourse , climate and flood protection and for the protection of biodiversity?

What economic perspectives and marketing opportunities arise here for farmers and landowners and how can agricultural wood be made better known as an agricultural product and energy resource?

The following activities are being carried out within module 1:

  • Monitoring of the microclimate of woody streams by means of water level and temperature measurements and the investigation of the existing biological macrozoobenthos in the years 2021, 2022 and 2023 
  • Modelling the effects of vegetation on flood retention and aquatic habitats using habitat modelling and the development of flood scenarios
  • Structural analysis of agricultural woods and visualisation using 3D laser scanning
  • Investigation of the plant physiology and rooting of agricultural trees and shrubs in order to gain insights into the development of the microclimate, the water balance and the rooting dynamics of these wood species
  • Implementation of an agro-wood plantation in the Dresden region

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Measurement campaign launched: Investigations in and on agroforestry plantations along watercourses

What are the effects of riparian agroforestry structures on microclimate and biodiversity?

Study areas with agricultural wood plantations in the OLGA project | © TU Dresden/IfW, Manuel Wewer

In addition to naturally grown riparian woody plants, agricultural woody structures can contribute to shading the watercourse and thus cooling it down. The fall of leaves in autumn can also serve as a food source for microorganisms living in the water body. Plants act against erosion and can reduce pollutant inputs from agriculture into the watercourse. Woody agricultural plantations along watercourses can also contribute to flood protection, as the trees have a retention effect due to their flow resistance and thus slow down flood waves.

So what exactly must these agricultural wood structures be like, i.e. which tree species should be used and how should they be planted so that they have a positive effect on the climate in and around the watercourse, on the soil and on biodiversity? The TU Dresden's science partners have launched a comprehensive measurement campaign at three sites in the Dresden region to answer this question.


Climate and woody plant parameters are the focus of the investigations

Agricultural wood plantation with poplars at the Peickwitzer Mühlengraben near Senftenberg | © Biomasse Schraden e. V.

Another agricultural wood structure included in the investigations is located at the Wiesengrundbach in Klingenberg-Colmnitz near the Tharandt Forest. Here, the surveys are in the area of flowing waters, as well as at another site at a renaturalised watercourse section of the Mortelbach near Waldheim (LK Mittelsachsen). The Chair of Hydraulic Engineering collects information on the hydraulics of watercourses, the microclimate of watercourses and the macrozoobenthos (benthic invertebrate fauna) and investigates the correlation between these parameters.

In addition to the woody plant physiological, climatic and hydraulic measurements, the Chair of Biodiversity and Nature Conservation is supplementing the investigations with analyses of the woody plant structure and, the position of the trees and the flowing water in the space using high-resolution, terrestrial 3D laser scanning. Based on the laser scanning data, a digital terrain model of the study areas is created. Furthermore, the soil composition and the vegetation composition in the plantation itself and in the surrounding agricultural areas will be investigated and the diaspora bank analysed on the basis of soil samples.

The TU Dresden's measurement campaign will run this year and next. It is intended to provide information on the multifunctional and biodiverse implementation of an agricultural wood structure.

Criteria defined: Potential areas for agricultural wood plantations in Dresden and the surrounding area

Overview of excluded and potential areas based on arable land, fallow land and grassland | © Herzig/Schwarz ArcGIS Pro (2021)

Staff members of the Chair of Biodiversity and Nature Conservation at the TU Dresden supervised a student project work within the OLGA project as part of the Master's degree course in Spatial Development and Natural Resource Management, which is carried out in cooperation between the TU Dresden and the Leibniz Institute for Ecological Spatial Development. As part of the work, the area potential for planting agricultural trees in Dresden and the surrounding districts was analysed. In addition to the energetic utilisation of the fast-growing wood, the ecological condition of flowing waters is to be improved in accordance with the EU Water Framework Directive. 
A catalogue of criteria regulating requirements, exclusion areas and legal framework conditions for potential areas of agricultural timber planting served as a starting point:

  • Current land use: arable land, grassland, fallow land
  • Distance to water bodies: 60 m surrounding
  • Distance to settlement and traffic areas: 8 m
  • Exclusion: Area natural monuments, core zones of national park and biosphere reserve, legally protected biotopes, floodplains
  • Slope: max. 20 %
  • Area size: 2-20 ha per agroaric wood plantation
Section of a potential area (orange) for agricultural wood structures along the streams Triebisch and Kroatenwasser near Grillenburg in the Tharandt Forest | © Herzig/Schwarz ArcGIS Pro (2021)

Using data sources from the Saxon State Office for Environment, Agriculture and Geology and the Saxon State Office for Geographic Information and Surveying, the potential areas were determined with the help of the geographic information system ArcGIS Pro.  

After the analysis had been carried out, 2,480 areas were considered for the establishment of agroforests, which lie within a radius of 40 km around the city limits of Dresden and fall within the specified area size of 2-20 ha per agroforestry plantation. These have a total area size of 8,951 ha, which corresponds to a share of grassland, arable land and fallow land of 7 %. Most of the potential areas are rather small and reach the minimum size of 2 ha. The average size of all potential areas is 3.6 ha, with the largest area being 17.2 ha. Areas larger than 20 ha are also potentially suitable for planting several agroforestry plantations, the size of each not exceeding 20 ha. 

The results of the work provide an initial assessment of possible land uses with agricultural wood in the Dresden region.  The catalogue of criteria will be further specified in the further course of the project in order to finally determine the land potential and feasible areas for implementation.

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HERZIG, Marie, SCHWARZ, Lena (2021)Etablierung von Gehölzen zur Verbesserung des ökologischen Gewässerzustandes - Analyse zum Flächenpotenzial in der Stadt Dresden und umgebenden Landkreisen (GIS-Auswertung). Student work at the TU Dresden, Faculty of Environmental Sciences in the Master's programme in Spatial Development and Natural Resource Management, within the framework of the OLGA project. 

Can agroforestry structures along watercourses reduce flood risk?

Floods are natural events. The starting point is long-lasting, large-scale continuous rainfall or short, heavy rainfall events. When the resulting water masses become too large, rivers and streams overflow their banks and flood the foreland. These floodplains act as natural retention areas that can absorb and hold back large amounts of water. In this case, the vegetation along the watercourses can have a braking effect on the water masses, delay the flood wave and reduce the runoff peaks.

Within the OLGA project, the Institute of Hydraulic Engineering and Technical Hydromechanics at TU Dresden is investigating the extent to which riparian vegetation (including agroforestry structures) can reduce the flood risk in downstream settlement areas. One study area in OLGA is the renaturalised section of the Wiesengrundbach stream in Klingenberg-Colmnitz in the district of Sächsische Schweiz-Osterzgebirge.

The simulation below shows that the agricultural wood plantation established to the left of the road running from the northwest to the south retains the water only minimally and thus does not really serve as a retention area in this case. The reasons for this are the damming of the water to the right of the road, because the Wiesengrundbach crosses underneath it through a pipe, and the deepening of the stream at the level of the plantation.

What's in bloom? Vegetation mapping in and around agroforestry structures

The most common plant species in and around the OLGA agroforestry study areas (from top to bottom): common colewort (Geum urbanum), meadow bluegrass (Poa pratensis) and catchweed (Galium aparine).
Photos from top to bottom: Animaflora PicsStock, skymoon13, Marco Warm - all stock.adobe.com.

In order to evaluate our study areas at the Peickwitz millrace near Senftenberg (Bandenburg) and at the Wiesengrundbach near Dresden (Saxony) from a nature conservation perspective, vegetation surveys were carried out in the herb layer in early summer 2021. We investigate the influence of the agroforestry plantations on plant diversity and use adjacent reference areas (agricultural areas, marginal, flowering and riparian strips of water bodies) as a comparison. As there is forest in the vicinity of the agroforestry plantations, we extended the study design by five circular survey areas along the transect* agroforestry plantation - agroforestry area - forest and additionally five along the transect agroforestry plantation - agroforestry area/ riparian strip - railway line at the Peickwitz millrace. The aim of the transect analysis is to identify possible dispersal routes of plant species and to find out whether the agricultural wood plantations could be part of a biotope network in the respective landscape context. Railway lines are also relevant for the spread of neophytes.
In total, the species composition and cover was recorded on 55 plots, 25 plots are located at the Wiesengrundbach and 30 plots at the Peickwitz millrace.

In the agricultural woodland plantation at the Wiesengrundbach, a total of 22 species were logged, with common colewort (Geum urbanum) and meadow bluegrass (Poa pratensis) being particularly common and having high cover levels. Almost two thirds of the species are found both in the forest and in the open country. 

At the Peickwitz millrace, 19 species could be recorded. Catchweed (Galium aparine) was the most common species with the highest cover percentages. More than half of the species are purely open-land species that occur, for example, in herbaceous vegetation, margins or as field weeds. One third of the species can be found both in the forest and in the open landscape. On the reference areas, the total number of species ranged from 9 (Wiesengrundbach, reference area agricultural area) to 36 species (Peickwitz millrace, field edge).

Further analyses will be carried out in the coming months. We will report on their results in due course.

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*Transect: Along a transect, a marked straight line, data are recorded at fixed intervals. This method is used when you want to establish a spatial relationship to the object of investigation. This method is often used in ecology (botany and zoology), for field investigations (mapping) and in geology and geoecology.
(Source: 
https://www.pflanzenforschung.de/de/pflanzenwissen/lexikon-a-z/transekt-10152, accessed on 30.11.2021)