Copyright: Holm Voigt
Copyright: Holm Voigt

Holm Voigt is Junior Researcher at the Centre for Development Research, Department of Ecology and Natural Resources Management in Bonn, Germany and is currently doing his PhD.

“Hydrological Dimensions of Dryland Afforestation in Central Asia” is your research topic. What exactly is your research all about?

In straightforward words my research is an assessment how much groundwater trees of three different species consume in the irrigated drylands of Uzbekistan within the Aral Sea Basin.

Decades of water withdrawals for irrigated agriculture from the main tributaries Amudarya and Syrdarya slowly cut off their waters from reaching the Aral Sea. As an effect, the formerly 4th largest fresh water lake in the world evaporated with today only around 10% of its former surface area left, which still is decreasing.

A second consequence of this intensification of agricultural irrigation is salt accumulation in the soils of the irrigated lands. Soil salination reduces agricultural crop yields and can lead to abandonment of degraded croplands. Yet, well adapted tree species are able to survive and remain productive on such degraded lands. Their roots reach deeper into the ground than roots of annual crops so that they are able to take up the groundwater which is a less saline environment and thus require little irrigation.
I assess the impact of afforestation efforts on the hydrological cycle at field scale. More specifically I quantify the amount of water which is transported through the tree. I am also determining the driving factors of tree water uptake of three different tree species used for afforestation, namely Elaeagnus angustifolia, Ulmus pumila and Populus euphratica.

My results contribute to further assessments of the impact of afforestation on water resources, especially when tree planting is considered for large areas and increased water consumption might deplete the groundwater table.
It was interesting to find out that Elaeagnus angustifolia which features a high biomass production actually uses relatively little water. Another fascinating outcome and experience was the regeneration capacity of Populus euphratica. This species survived poorly after planting, but those trees which finally grew reproduced vigorously through root sprouts and now dominate the study site. This depicts an important point: research on trees needs time as to uncover and account for long-term processes.
A big part of my work is rather methodological. It was surprising to see that a widely applied method for assessing water fluxes inside tree stems had several theoretical and practical pitfalls that often preclude accurate quantification of tree water use. I therefore applied a different approach based on groundwater measurements and analyses of soil water fluxes to cross-check these findings. This led to more consistent results.


What has changed in Uzbekistan because of the climate change during the last years? Why is adaptation to climate change so important for the future?

Around 60% of the people living in the study area work in the irrigated agricultural sector. They heavily depend on the water supplies from the Amudarya for irrigated crop production as well as for domestic use. During the past decades extremely dry years (low flows in summer, the main cropping and irrigation season) repeatedly threatened the livelihoods of the rural population in the region. Accordingly, a most tangible impact of climate change in the region will be on water resources. Water supplies in summer are expected to decrease. This will put additional pressure on the agricultural livelihoods. Innovative agricultural techniques are urgently needed in order to use resources more efficiently and to limit degradation to a minimum. Alternative landuse strategies might be one tool to adapt to changing conditions. Afforestation as an example requires less irrigation water and additionally gives the opportunity of income diversification by providing timber and non-timber products.

My research is of very practical nature, as it contributes to recommendations on suitable species and scale of afforestation efforts in Uzbekistan. We collaborate very closely with a local NGO which supports local farmers. They promote innovative agricultural practices such as the idea of planting trees on degraded croplands is. However, if afforestation efforts are getting more frequent, it needs to be considered, that this might significantly alter the hydrological cycle. My research findings deliver the basis for the respective assessment.

If validated at other locations, the approach I apply to quantify tree water use by analyzing groundwater and soil water fluxes might furthermore simplify and increase precision of assessments of tree water use.

What is your personal recommendation for living sustainable in daily life?

Within daily local life I think that everybody can contribute to a sustainable living by means of rather simple and small actions. Working in an international institution, I very much appreciate and try to foster (intercultural) exchange with colleagues. I do believe that we have to learn a lot about different cultures when we want to live together in a globalized world.

With respect to the more ecological issues of sustainability, there are plenty of small actions like quick ventilation instead of continuously tilted windows when the heating is on, turning lights off when not needed or not using plastic bags for shopping just to name a few. These can easily be adopted to the personal daily routine. From my personal experience I can tell that often it is rather an issue of will than a lack of knowledge.
One example I am confronted with on a daily basis in Bonn is public mobility: I often wonder how many cars there are on the streets of Bonn, most of them with only one person inside. From my point of view Bonn is a good place for taking the bike, not only for the sake of keeping the ecological footprint at a low level.

Link to Holm Voigt, Centre for Development Research, Bonn

Pictures: By courtesy of Holm Voigt