Tree species from two contrasting habitats for use in harsh urban environments respond differently to extreme drought
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The role of trees in city cooling has warranted much attention based on concerns over climate change and urban expansion. Simultaneously, there is an interest in introducing species from dry habitats to cope with the increasing risks of drought under climate change. The general understanding is that the evolutionary adaptation to respective resource supplies in species’ habitats affects their environmental tolerance. The physical performances of six frequently planted species, originating from two contrasting habitats, were tested in a drought experiment. We (1) investigated if species from drier habitats are more drought tolerant than species that have evolved in Central European woodlands under a temperate climate regime and (2) discussed the effect of tolerance on the cooling potential of these trees. Native species from mesic habitats maintained only 48% of their controls sap flux and of these species, Tilia cordata had the worst performance with premature leaf senescence. Species from drier habitats had less reduction in sap flux (60%) but lower stem growth, possibly favouring (fine) root development into deeper soil layers, as observed when comparing linden species. Higher stem water exploitation and stronger regulation of water use at high evaporative demand were further reaction patterns that likely helped species from dry habitats maintain good physiological functions. Therefore, even under sustained drought, we expect them to have a higher cooling capacity. As a conclusion, they should be favoured for planting in extreme urban environments. Systematic screening and testing of promising species from target habitats is recommended to diversify the choice of species.
KeywordsClimate change Cooling effects Drought tolerance Sap flux density Resistance Urban trees
We thank the heads and staff members of the municipal nursery of Munich-Laim for their support and encouragement to conduct our field study there. The authors would also like to express their gratitude to Felix Seebauer and Jonas Schweiger for their assistance in field data collection. This work was supported by the Bavarian State Ministry of Education, Cultural Affairs, Science and Arts, Munich, Germany [VIII.2-F1116.WE].
Compliance with ethical standards
The experiments comply with the current laws of Germany.
Conflict of interest
The authors declare that they have no conflict of interest.
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