Mapping Your Tree Inventory: Starter Guide for Municipalities

A current tree inventory forms the foundation for professional tree management. Without good insight into your tree population, it's impossible to conduct effective policy, manage risks, or plan budgets. More and more municipalities are discovering that digital tree inventory is not a luxury, but a necessity.

As a municipality, you bear a legal duty of care for your trees. Without registration, you cannot prove you meet this obligation. After incidents, the first question from insurers and judges is: 'What was the last inspection date?' A current tree inventory with inspection history is your most important defense against liability claims.

Climate adaptation requires data. One mature tree has the cooling capacity of ten air conditioners, and the National Tree Standard sets a target of 30% crown coverage per neighborhood. To know if you meet that — and where you need to invest more — you first need to know what you have. Without inventory, climate policy remains guesswork.

Since January 1, 2024, the Environment Act requires every municipality to establish a building contour for tree felling. To effectively enforce this and assess permit applications, you need to know where which trees are located. A digital tree inventory makes these legal tasks manageable and verifiable.

Organizations start from different situations. Some municipalities still work with paper archives — planting records in folders, map material from the nineties. Others have Excel files per district or work with a GIS system where trees appear as points on the map, but without real management workflows.

The differences are large, but every starting point offers connection points. Municipalities with only paper have the most catching up to do, while organizations with GIS data already have a spatial foundation. Excel-based administration is workable for small numbers, but doesn't scale with growth. Professional management systems with full lifecycle management — from planting to felling, with inspection history and reports — are still relatively rare.

The good news: every starting position is a starting position. Existing data, however basic, is more valuable than you think. Even an outdated Excel file contains information you don't need to collect again.

The IMBOR standard (Information Model Public Space Management) defines what data you record per tree at minimum. By following this standard, you ensure comparability with other municipalities and compatibility with national systems.

For each tree, you register a unique tree number as identification, the GPS location with coordinates accurate to at least one meter, and the tree species with scientific name. Additionally, you record the trunk diameter (measured at 1.30 meter height), the height class in meters, a condition assessment of health, and the location type — grass, pavement, or tree pit.

Municipalities wanting more expand this with planting year, crown diameter, future expectation, and safety class according to the A/B/C/D classification. The more you record, the better you can justify management decisions — but start with the basics and build from there.

Er zijn verschillende methoden om een bomenbestand in kaart te brengen. De keuze hangt af van factoren zoals budget, gewenste nauwkeurigheid en de grootte van het areaal.

The costs of a tree inventory vary considerably and depend on multiple factors. The level of detail plays a significant role: a basic registration with just location, species, and dimensions is considerably cheaper than a comprehensive inventory with all IMBOR attributes or a combined safety inspection.

The chosen method also affects costs. Traditional fieldwork with tablet and GPS is labor-intensive, while LiDAR technology can be more cost-effective for larger areas. The size of your tree population naturally plays a role too — economies of scale only emerge with larger numbers. Additionally, the accessibility of your trees is relevant: trees in busy built-up areas take more time to inventory than street trees along clear roads.

Always request multiple quotes from specialized tree consultancies and get well-informed about what is and isn't included in the price. A good inventory is an investment that pays for itself through better management and reduced liability risks.

An Excel file with 50,000 trees becomes unworkable. No version control, no mobile access, no link to inspection history. At some point you need to make the step to a real management system — and the sooner you do that, the less duplicate work you have.

A good system integrates with national standards. The BGT (Large-Scale Topography Base Registration) registers trees as vegetation objects, IMBOR provides standardized attribute definitions enabling comparability, and BOR systems connect tree management with other public space management. By connecting to these standards, you prevent building an isolated island.

A workable system has a mobile app for field registration, with automatic synchronization between office and field. You want to be able to view inspection history per tree, handle reports of damage or complaints, and generate reports for policy and accountability. Without these functionalities, you'll still fall back on Excel and loose notes in practice.

Setting up a tree inventory follows a series of logical phases. Start by inventorying what you already have — collect all existing sources such as Excel files, GIS layers, and paper archives. Then determine your scope: do you include only street trees, or also forest plantings and private trees on municipal land?

Choose your attribute set based on the IMBOR standard and Handboek Bomen, so your data is future-proof. Select an inventory method that fits your budget and area — fieldwork, LiDAR, or a combination. Also decide early whether you execute the work yourself with your own green managers, or outsource to a tree consultancy.

Choose a management system before you start inventorying, not after. Many municipalities make the mistake of first collecting data and only later thinking about where that data goes. Plan quality control with samples of at least 5-10% of registered trees. And set up the management process immediately: plan the update cycle so your data stays current.