When preparing planning applications, one of the most common points of confusion is how to define whether a tree is “impacted” by a development. The challenge is that different Local Planning Authorities (LPAs) set different requirements for what area needs to be surveyed and recorded. Understanding these differences is essential for producing a valid submission.
The most common approach: the Tree Horizon Line. Many LPAs adopt what is often called the Tree Horizon Line method. This has two parts:
All trees within the red line boundary of the development site.
All trees within 15 metres of the boundary.
This approach is intended to capture not just trees physically on-site, but also those nearby whose roots, canopies, or ecological value could be affected.
The second common approach: Red Line only. Other LPAs take a different view and require only trees within the red line boundary itself. This keeps the survey scope limited to what falls inside the development boundary, excluding off-site trees unless they directly intrude into the site.
A number of LPAs apply variations to the two models above. For example: Red line + 15m expansion (defined as all trees within the site boundary and a surrounding buffer zone) and Parcel expansion (recording of trees within a defined parcel or area extended by 15m, regardless of the exact red line).
Some LPAs have additional or alternative rules that go beyond these broad categories. These may reflect local priorities, ecological considerations, or conservation designations. Where that’s the case, the requirement is normally spelled out in the authority’s validation checklist or planning guidance.
The bottom line is that there is no single national definition of what counts as an “impacted tree.” Each LPA sets its own rules, and applicants need to follow the right approach for their area. Getting this wrong risks delays, invalid applications, or the need for costly resubmissions.
At Joe’s Blooms, we’ve built our tree tool to adapt to the LPA’s stated requirement—whether that’s the horizon line, red line, parcel expansion, or another local variant. This ensures that applications are validated smoothly and that tree-related information is consistent with what the LPA expects.