| Added on 30/12/2011 | Article |
Tree Protection Boxes
Case Study
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A method statement addressing the issue of tree protection was requested by the local authority. My role was to carry out a site survey and produce both a survey report and method statement.
The site consisted of a disused block of flats (picture 1) and car parking areas. These were to be demolished and replaced with new luxury flats. The site didn't actually contain any trees which were to be retained (it only contained a few declining Cherry trees and regenerating Sycamore). But a line of council owned mature Pine trees were located by the roadside just outside the boundary to this site, and these were identified during the survey as requiring special protection.
The first issue was the two Pine trees standing on either side of the access driveway (see picture 3). These were considered to be very vulnerable to collision damage from the large stream of expected construction traffic (cranes, lorries etc).
Secondly, the linear group of Pines located on the grass verge (picture 2) were thought to be at risk from contractor parking. Space for such parking would be difficult especially when construction of the site advances to the point where on-site parking is not possible. As you can see from the above pictures, access onto the grass verge could be straightforward resulting in soil compaction and possibly physical tree damage.
Protection for the two isolated trees consisted of a wooden box constructed around each tree stem. A very basic drawing, which defined the main dimensions and minimum material specification, was produced on CAD and included with the method statement.
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This specification also called for further protection around the bottom of each box by way of water filled 'bollards' but the builders included a robust wooden bumper rail into the design to act as an alternative.
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The line of trees were enclosed within a fence and water filled bollard perimeter, which would prevent car parking and material storage in this area.
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The method statement included drawings and plans detailing the position of the fencing and a time table defining the time when they need to be erected.
Design
When designing tree protection boxes it is important to ensure that they are not fixed directly to the tree stem with any kind of solid brace. If they are, then any collision movement would be transmitted directly to the tree which we are trying to avoid. They need to be self supporting and if possible anchored into the ground. On hard surfaces where anchorage is not possible, they need to be heavy with extra weight placed at the bottom edge (this could consist of railway sleepers or water filled bollards). There must be space between the tree trunk and box edges to allow for some movement of the box without pressuring the tree. It is then hoped that if a vehicle contacts the box it will resist the collision and only move if this becomes excessive.
The following pictures were snapped a few years ago. The box protecting the tree is too small to offer proper protection against collision. There is insufficient room for movement and one side of the box is pressed against the tree trunk. However, it does serve to prevent bark abrasions and does catch the attention of drivers which is important. A box around the tree does make a point of saying that the tree is important.
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