Urban trees are critical for mitigating urban heat and delivering ecosystem services, yet their growth is increasingly constrained by drought stress under changing climatic conditions. Engineered substrates incorporating porous, water-retaining recycled aggregates (RA) from construction and demolition waste (C&DW) offer a promising approach to improving substrate performance while promoting resource circularity. However, the long-term effects of RA composition on tree performance remain insufficiently understood. In a four-year field study (2020–2024), we investigated the growth and ecosystem service provision of Tilia cordata planted in substrates amended with 25 %, 50 %, or 75 % (v/v) RA, derived either from brick-rich or cementitious (concrete, mortar, plaster) waste. Compared to the unamended control, substrates with 75 % brick-enriched RA increased stem diameter growth by 13.6 %, and enhanced transpiration cooling and carbon fixation by up to 42 % and 71 %, respectively. Treatment effects were strongly mediated by contrasting edaphic drought conditions during hot summer periods. In contrast, high proportions of cementitious RA induced drought stress and growth reductions. These findings demonstrate that selectively composed RA substrates—particularly those enriched with brick waste—can enhance tree performance under drought. This supports targeted recycling strategies and policy frameworks that prioritize brick-rich C&DW fractions for use in urban greening applications.
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Philipp Stinshoff,
Sebastian Knoll,
Liliane Busse,
Swantje Duthweiler,
Christoph Moning,
Stephan Pauleit,
Brigitte Helmreich
Infiltration swales are considered an essential and multifunctional component of water-sensitive urban design. To maintain their functionality, a robust planting is required. However, species selection poses a major challenge due to the extreme site conditions. To identify stress-resistant species, container experiments with 60 perennial species native to Germany were used to investigate their performance and responses to multiple stressors typical for urban swales receiving traffic area runoff. As plant performance is more severely affected if multiple stressors occur rather than single ones, test plants were exposed to de-icing salts, cyclic flooding, and drought. Species were selected primarily for their drought tolerance, as it was assumed that their adaption to drought might also be advantageous for the other stressors. The resistance to drought was examined in a reference group and was approved for 90 % of the experimental species. With a low mortality rate of < 25 %, 72.2 % of the species confirmed as drought tolerant also proved robust to the multiple stressors of an infiltration swale and are therefore recommended for use. Considering all experimental species, significant effects of the multiple stressors compared to the reference group were only found in mortality and a visual vitality score. Data on growth height, chlorophyll fluorescence, and phenology (e.g., flowering time) did not differ significantly between the groups. However, there were large species-specific variations to be considered and investigated in further research. The study serves as a basis for a resilient greening of urban infiltration swales with native species. It is essential to their implementation, as more research is needed to date.
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Sebastian Knoll,
Simon Mindermann,
Lauren Porter,
Stephan Pauleit,
Swantje Duthweiler,
Johannes Prügl,
Brigitte Helmreich
Construction and demolition waste (CDW) represents one of the most significant waste streams worldwide. Due to a high brick content, CDW amended soil substrates are expected to improve water retention, benefitting urban trees. In this two-year field study evaluating the effects of CDW on the water holding capacities of urban tree substrates, six substrate mixtures are tested. Three test substrates contained a standard CDW mixture with 30 % and three 60 % bricks. Soil water contents were monitored and plant available water contents (PAWC) were analysed. From soil water contents and PAWC, the relative extractable water contents (REW), and subsequently the number of days with REW < 40 % and water stress intensity (WSI) are calculated. The substrates with enhanced brick content showed higher PAWC. However, the effect of brick on PAWC was only significant at a minimum of 30 % bricks in the substrate. Pore size distribution of the brick fraction confirmed the assumed relationship between addition of brick and increased PAWC. Substrates with an enhanced brick content showed reduced numbers of days with REW < 40 % and a reduction in WSI. Our findings demonstrate that CDW has potential to foster water holding capacities of urban tree substrates.
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Other publications
Philipp Stinshoff,
Brigitte Helmreich,
Swantje Duthweiler,
Christoph Moning,
Sebastian Knoll,
Johannes Prügl
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