Root Protection Area (RPA)

RPAs on the map are indicated by red lines. Around trees that have no barriers to root growth, the RPA is a simple circle.

The BS5837 calculates the radius of the RPA according to the diameter of the trunk of the tree. The diameter of the RPA increases with the diameter of the trunk. If the tree is "multi-stemmed" this radius is adjusted slightly. 

A barriers file indicates walls, drains, roads, etc which restrict the growth of tree roots. Since total area of the RPA must remain the same, the arc must be extended to compensate for areas where root growth is impeded. The barriers appear as heavy black lines.

In this example, the RPAs of two trees overlap. The BS5837 does not make it clear whether such overlaps are permitted. That is why this program allows you to decide whether or not to accept overlapping RPAs. If you choose to un-tick the "Allow overlaps" tick box, the program will redraw the RPAs extending each tree's area to compensate for the lost area of overlap. (Note that when "Allow overlaps" is un-ticked then only a maximum of 25 trees can be processed at one)

In the case of trees hemmed in by barriers, or when overlaps are not accepted, the required RPAs may not be achievable. In this example, the maximum possible RPAs for trees 12 and 21 appear as thicker red lines. Thick red lines indicate that the RPA does not meet the BS5837 criterion.

Note: These RPA boundary lines can be exported as vector files to standard GIS and CAD programs where they can be edited manually. The polygons produced by this program can be regarded as a first step.