RT Journal Article SR Electronic T1 Designing Urban Pavement Sub-Bases to Support Trees JF Arboriculture & Urban Forestry (AUF) JO JOA FD International Society of Arboriculture SP 121 OP 126 DO 10.48044/jauf.1998.015 VO 24 IS 3 A1 Palle Kristoffersen YR 1998 UL http://auf.isa-arbor.com/content/24/3/121.abstract AB In Denmark, poor growth conditions for urban trees have been perceived as a problem since the 1980s. Restricted planting-pit sizes are mainly responsible for this problem. In 1996, a survey found that the average size of municipal planting pits had increased from 0.1 m3 (3.5 ft3) in the late 1960s, to 3.4 m3 (120 ft3) in 1996. To increase the volume of the planting pit, several materials have been introduced to mix with soil to allow root growth under pavements. Three methods are available for installing these materials under pavements. During the last 5 years, more than 800 trees have been planted on more than 30 sites using these materials and installation methods. Every method has advantages and disadvantages. No serious difficulties due to load-bearing capacity or frost heaves have been recorded.