Abbots Park, St. Albans

Remedial soil de-compaction and improvement

Abbots Park, in St. Albans, Hertfordshire, is a residential estate comprising blocks of flats, maisonettes and town houses set within approximately 7 acres of grounds. There are many trees on the site, over 100 of which are protected by Tree Preservation Orders (TPOs).

Thinktrees Ltd (formerly P.F.Melarange Arboricultural Consultancy Ltd) were instructed by the Abbots Park Residents Association to carry out a combination of vertical mulching and radial trenching within the root zone of a declining oak tree located within one of the communal gardens. The oak had been showing signs of early decline, including a sparse crown and reduced extension growth (annual lengthening of the twigs), which is likely to be attributed to historic soil compaction and root damage caused during the construction of the adjacent buildings.

Our objective was to improve the condition of the soil around the tree to be more conducive to root growth. In order to achieve this, 10 radial trenches were excavated using a SoilPick (a tool which uses compressed air, in the same way as an AirSpade, to displace soil from around the roots and break up compacted areas). Each trench was approximately 2.4m long, 30cm wide and 30cm deep. These were backfilled with leaf mould and compost, then the lawn surface was reinstated.

Radial trench excavated using an airspade.

Arborist using a Soilpick to carry out root collar excavation

Arborist using a soilpick to excavate a radial trench.

Decayed root colonised by honey fungus Armellaria sp.

While excavating the trenches, we found a number of decayed roots of a large diameter, indicating that there had been significant retrenchment of the root system. In some cases, smaller fibrous roots were growing in the shallower soil directly above the decayed roots. The soil improvement that we have carried out should allow the root system to re-establish itself, and the tree to recover.