Abstract
BackgroundRecent projections expect that Vietnam will be affected most severely by climate change with higher temperatures, more precipitation and rising sea levels. Especially increased temperatures will worsen the situations in cities, amplifying the urban heat island effect. Green infrastructures, i.e. urban trees are a common tool to improve the urban micro-climate for humans. Vital and well growing trees provide greatest benefits such as evaporative cooling, shading, air filtering and carbon storage. However, urban tree growth is often negatively affected by urban growing conditions such as high soil sealing with compacted tree pits providing small growing spaces with limited water, nutrient and oxygen supply, further warm temperatures and high pollution emissions. This study analyzed the growth of urban and rural African mahogany (Khaya senegalensis (Desr.) A. Juss.) trees in the city of Hanoi, Vietnam and the effects of the surrounding climate conditions on tree growth.ResultsThe results showed that rural African mahogany trees grew better than trees situated in the city center, which is contrary to other results on tree growth of temperate and subtropical cities worldwide. Moreover tree growth was similar regardless of the time of growth. Other results regarding stem growth of African mahogany located in different areas of Hanoi (east, west, north, city center) revealed a better growth in the northern and western outskirts of the city compared to the growth of trees in the city center.ConclusionAfrican mahogany trees in the urban centers of Hanoi showed a decreased growth compared to rural trees, which was likely induced by a low ground-water level and high pollution rates. In view of climate change and global warming, the decreased tree growth in the city center may also affect tree service provision such as shading and cooling. Those climate mitigation solutions are strongly needed in areas severely affected by climate change and global warming such as Vietnam.
Highlights
Recent projections expect that Vietnam will be affected most severely by climate change with higher temperatures, more precipitation and rising sea levels
The results show how urban trees will be influenced by the urban heat island effect and climate change, helping to find common and practical solutions for mitigation measures to climate change with vital and benefitting green infrastructure
The smallest African mahogany had a dbh of 44.1 cm, while the largest tree had a dbh of 123.1 cm and the average dbh was 73.4 cm with 16.0 cm standard deviation for all trees
Summary
Recent projections expect that Vietnam will be affected most severely by climate change with higher temperatures, more precipitation and rising sea levels. Possible solutions for climate change adaption and mitigation measures are urban green infrastructures, especially urban trees, which are getting increased attention due to their effects of ameliorating their surrounding micro-climate (Dimoudi and Nikolopoulou 2003; Foster et al 2011; Roy et al 2012). Urban trees influence the climate of a city by e.g. evapotranspiration and air cooling (Rahman et al 2017a, 2017b) as long as water availability allows, shading (Akbari et al 2001; Lee et al 2013), air purification (Bell et al 2011), wind buffering (Nowak and Dwyer 2007), carbon storage (Nowak and Crane 2002; Davies et al 2011), reduction of rainwater-runoff (Armson et al 2013), biodiversity preservation (de Groot et al 2002; TEEB 2011) and esthetic features for recreation means (Tyrväinen et al 2005)
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