The Dutch standard for visual tree safety inspection based on VTA methodology and CROW guidelines.

Every BVC inspection starts with positive identification of the tree. The Boomnummer (tree number) is the unique administrative identifier that links the field inspection record to the municipal GIS database. In practice, this number is typically pre-loaded from the asset register, and the inspector verifies that the physical tree matches the recorded position. Species identification uses the scientific name (Boomsoort) — for example, Quercus robur for pedunculate oak or Tilia x europaea for common lime — because common names vary regionally across the Netherlands. Correct species identification is critical for the inspection because certain species have characteristic failure modes: willows (Salix) are prone to crown breakage, beeches (Fagus) are susceptible to Meripilus giganteus root decay, and horse chestnuts (Aesculus) frequently develop bark inclusion defects.

The Stamdiameter (stem diameter) is measured at 1.30 meters height — the international standard known as DBH (diameter at breast height). The CROW guideline defines seven diameter classes ranging from 0-10 cm for young plantings to over 100 cm for monumental trees. Diameter directly correlates with the tree's potential hazard radius: a large-diameter tree with a defect can cause far more damage than a small one with the same defect type. The Boomhoogte (tree height) is recorded in seven classes from "tot 6 m" (up to 6 meters) to "24 m en hoger" (24 meters and above) per the SUF-BVC standard. Height determines the fall zone and therefore the target area for risk assessment.

The Verschijningsvorm (growth form) captures the tree's management type, which directly affects the expected crown architecture and associated failure risks. A Knotboom (pollard) is regularly headed back and develops characteristic knuckle joints that require different inspection criteria than a Vrij uitgroeiend (free-growing) tree. Leiboom (espalier) and Vormboom (topiary) trees are architecturally shaped and may have pruning wounds that create entry points for decay fungi. Zuilvorm (columnar) and Kandelaber (candelabra) forms have specific crown dynamics in wind loading. The Plantjaar (planting year) provides age context — a 150-year-old oak in poor condition has different management implications than a 15-year-old tree with the same vitality score.

The BVC data fields are defined in the CROW Richtlijn Boomveiligheidsregistratie and the SUF-BVC data exchange standard.

The VTA (Visual Tree Assessment) method developed by Claus Mattheck is the scientific foundation of the BVC. VTA works on the principle that trees exhibit external symptoms — the "body language of trees" — that indicate internal mechanical defects. The inspector walks around the tree and examines it systematically from crown to roots, looking for visual indicators of structural compromise. Each defect is first assigned a Plaats (location): Kroon (crown), Stam (trunk), Stamvoet (root collar/base), or Maaiveld (root zone/soil level). This four-zone anatomy is fundamental because the failure consequence varies dramatically by location — a cavity in the crown risks branch failure, while the same cavity at the root collar risks total tree instability.

The Type Gebrek (defect type) field captures the specific VTA symptom observed. A Plakoksel (included bark) occurs where two stems or a stem and branch grow together without forming a proper union — the bark is trapped between the two parts, creating a structural weakness that can split under wind or snow load. Dood hout (dead wood) indicates branches that have lost all cambial activity and are susceptible to brittle fracture without warning. Holte / Inrotting (cavity or internal decay) reveals that the tree's wood is being broken down by fungi, reducing the load-bearing cross-section. Scheur (crack) is a separation in the wood grain that can propagate under mechanical stress. Zwam / Vruchtlichaam (fungus or fruiting body) is the most significant indicator of internal decay — the presence of species like Ganoderma, Inonotus, or Meripilus often means extensive wood degradation invisible from the surface.

Mechanische schade (mechanical damage) covers wounds from vehicle impact, mower strikes, construction work, or vandalism that breach the bark barrier and expose sapwood to infection. Wortelschade (root damage) includes severed roots from excavation, soil compaction from heavy machinery, grade changes that smother roots, or root decay. Root damage is particularly insidious because it can compromise the tree's entire anchorage system while remaining invisible at the surface. Each defect also receives a Gevolg (consequence) classification that predicts the failure mode: Takbreuk (branch failure), Stambreuk (trunk failure), or Instabiliteit / Windworp (instability or uprooting). The consequence determines the potential severity of harm — branch failure may injure a pedestrian, while trunk failure or uprooting can be fatal and cause major property damage.

The VTA methodology was developed by Claus Mattheck and forms the foundation of the VTA Mattheck Tree Assessment. Similar defect recording systems are found in the FLL Baumkontrollrichtlinie for the German context.

The Conditie / Vitaliteit (condition or vitality) field is a five-level rating from Goed (Good) to Zeer slecht / Dood (Very Poor or Dead). This is distinct from the safety classification — a tree can be in poor biological condition but still be structurally safe if it has no mechanical defects, and conversely a vital, healthy tree can be a Risicoboom if it has a large cavity at the base. The condition assessment looks at crown density, leaf size and color, shoot extension growth, dieback percentage, and overall vigor. A tree rated Goed (Good) has a full crown with strong growth and less than 10% canopy loss. Voldoende (Sufficient) indicates normal growth with minor dead wood and slight crown transparency — the most common rating for mature urban trees.

Onvoldoende (Insufficient) signals stagnating growth with clear crown transparency or progressive dieback — this tree requires attention and may have a reduced life expectancy. Slecht (Poor) indicates severe decline with more than 30-50% dieback and limited remaining useful life. Zeer slecht / Dood (Very Poor or Dead) means the tree shows no or almost no life functions. The Toekomstverwachting (life expectancy) field provides a forward-looking estimate: more than 15 years, 5-15 years, 1-5 years, or less than 1 year (removal recommended). This estimate is critical for the financial valuation of the tree — Dutch municipalities use the "W-cijfer" (valuation number) system where life expectancy directly affects the calculated monetary value of the tree, which in turn influences legal liability calculations when damage occurs.

The BVK system classifies every inspected tree into exactly one of three categories. Boom zonder gebreken (Tree without defects) means the inspector found no foreseeable safety risks during the visual assessment. The tree is cleared until the next regular inspection cycle, which is typically every three years. This does not mean the tree is perfect — it may have minor biological issues or aesthetic imperfections — but no mechanical defects were observed that could lead to branch failure, trunk failure, or uprooting. This is the most common classification for healthy urban tree populations, typically representing 60-75% of trees in a well-maintained municipality.

Attentieboom (Attention Tree) indicates that defects are present but do not pose an acute or unacceptable risk at the time of inspection. However, the defects require increased monitoring because they may worsen over time. The key management consequence is that the inspection frequency increases from the standard three-year cycle to an annual cycle. Examples include a minor bark inclusion at a branch junction that is currently stable, early-stage fungal colonization that has not yet significantly reduced the wood cross-section, or a small cavity that needs monitoring for expansion. The Attentieboom classification is the critical "watchlist" tier — these trees are safe today but could become Risicobomen if their defects progress.

Risicoboom (Risk Tree) means defects pose an unacceptable risk that must be addressed through active measures. The inspector must prescribe a specific Maatregel (measure) and assign an Urgentie (urgency) timeline. A Risicoboom classification triggers a legal obligation for the tree owner — under the Duty of Care (Zorgplicht), failing to act on a known Risicoboom finding can establish liability if the tree subsequently causes injury or damage. This is the classification that carries the greatest legal weight in Dutch tort law, as documented in case law from the Hoge Raad (Dutch Supreme Court). For practitioners, the transition from Attentieboom to Risicoboom is the most consequential judgment call in the entire BVC process.

For a quantitative approach to tree risk assessment as an alternative to the categorical BVC classification, see the QTRA Tree Risk Assessment. All tree inspection standards are listed in the standards directory.

The Maatregel (measure) field offers seven standardized options drawn from the SUF-BVC data exchange format. Geen maatregel (no measure) applies to trees classified as Boom zonder gebreken. Hercontrole (re-inspection) schedules an additional visual check before the next regular cycle — useful when conditions are borderline or when seasonal factors (leaf-on versus leaf-off) may reveal different symptoms. Nader onderzoek (further investigation) triggers a follow-up assessment using specialized diagnostic tools such as a pulling test (trekproef), sonic tomography, or resistance drilling (Resistograph) — techniques that go beyond the visual scope of a standard BVC to quantify internal decay or root stability. This is a common prescription when the inspector detects fungal fruiting bodies at the base but cannot determine the extent of internal decay from external symptoms alone.

Veiligheidssnoei (safety pruning) is the most common physical intervention — it includes removing dead wood, reducing overextended branches, eliminating included bark junctions, and thinning the crown to reduce wind sail area. Boom verwijderen (tree removal) is prescribed when no other measure can restore the tree to an acceptable safety level, typically when there is extensive basal decay, severe root damage, or complete structural failure is imminent. Verankering aanbrengen (install cabling or bracing) involves installing dynamic or static cable systems to prevent co-dominant stems from splitting or to support structurally compromised branches. Verankering controleren (check existing cabling) is prescribed when a tree already has an installed cable system that requires periodic inspection to verify the anchors and cables remain functional.

The Urgentie (urgency) field defines the deadline for completing the prescribed measure. Acuut (acute or immediate) means the same day or within 24 hours — this is reserved for situations where failure is imminent, such as a leaning tree with exposed roots after a storm. Binnen 1 maand (within 1 month) is high priority, typically for large dead wood over busy footpaths or roads. Binnen 3 maanden and Binnen 6 maanden represent medium and low priority respectively. Binnen 12 maanden (within 12 months) places the measure on the regular maintenance schedule. The Frequentie (next inspection frequency) field is set independently: Attentiebomen receive a 1-year cycle, standard trees receive a 3-year cycle, and in some cases a 5-year cycle may be applied to low-risk tree populations in remote locations.

Inspectors are certified by Groenkeur as Boom Veiligheid Controleur and must follow the CROW guidelines.