Empirical Verification
the establishment problem
20–50%
FAILURE RATES DOCUMENTED FOR NEWLY PLANTED URBAN TREES
2014-2022
Independent UK inventories from 2014–2022 document 20–50% failure rates for newly planted urban trees. The default is not working.
What this is
The Urban-Tree Soil-Function Clause Library is a ten-clause, AMA Anläggning-aligned specification and procurement framework. It makes growing-medium performance measurable across the full lifecycle of an urban tree pit — from subgrade acceptance to the end of the 36-month guarantee period.
It replaces supplier claims with evidence. It replaces one-off biological readings with a functional envelope. It replaces tree replacement with soil remediation where the deficit is remediable.
It is written in the language your tender documents already use.
the compaction threshold
the data
A rootable profile requires bulk density below 1.5 g/cm³ to 0.5 m, and below 1.7 g/cm³ to 1 m. Standard road-base compaction closes that door. Bulk density above which root growth is severely restricted (UK Forest Research; Cornell structural-soil trials, Grabosky & Bassuk 1996)
Why it exists
Because the current specification chain has a hole in it.
Designers specify a substrate by name or code. Procurement accepts what is delivered against a paper trail. Inspection signs off installation. The guarantee runs. When the tree fails inside the guarantee period, the contractor replaces the tree. The substrate — the actual reason the tree failed — is never reassessed. The replacement goes into the same soil. The cycle repeats.
This is not incompetence. It is a specification system built to verify delivery of a named product rather than function of an installed root zone. Soil is treated as a consumable. It is not. It is infrastructure. It carries trees for eighty years or it doesn’t.
The Clause Library closes the hole by shifting acceptance from “did the supplier deliver the named soil code” to “does the installed root zone reach agreed functional indicators.”
Empirical Verification
the Swedish evidence
Only 42%
OF 6,936 STREET TREES IN KRISTIANSTAD RATED IN GOOD VITALITY
of 6,936
The 2016 Kristianstad inventory of 6,936 street trees found only 42% in good condition. The remaining trees are stranded in soil that cannot carry them.
Why it exists
The ten clauses
The library follows the actual sequence of an urban tree installation, from ground up.
Subgrade acceptance — What the hole is sitting on before anything else happens. Drainage, compaction state, and contamination status of the receiving ground, before a single cubic metre of substrate is ordered.
Site protection — Protection of adjacent soil volume, root zones, and stockpiles from compaction, contamination, and construction traffic during the works. The cheapest clause to write and the one most commonly missing.
Organic-matter source and maturity — What the organic fraction is, where it came from, and whether it is stable. Immature material continues to decompose in the pit and takes nitrogen, oxygen, and structure with it.
Structural stability — Load-bearing behaviour of the growing medium under the traffic and hardscape it will actually see. Not laboratory bulk density. The state the substrate holds once compacted in place.
Biological and chemical delivery baselines — A functional envelope at delivery: respiration and β-glucosidase alongside soluble nutrients, EC, pH, and CEC. One biological reading is not proof of function. A pattern across indicators is.
Contaminants and chain of custody — Batch traceability from source through blending through delivery. Retained samples. Signed records. The audit trail that makes downstream decisions defensible.
Delivery acceptance — What counts as accepting a load on site. Sampling regimes defined separately for homogeneous mixes and skeletal planting systems, because they fail in different ways.
Installation quality — How the substrate is placed. Compaction limits, layering, moisture state at installation. The clause that catches the field problem the laboratory certificate cannot see.
Twelve-month verification — First-year check on function, not survival. A tree can be alive at twelve months and already committed to failure. Verification catches the trajectory before the guarantee window closes on the wrong evidence.
Thirty-six-month performance and remediation — End-of-guarantee performance against agreed thresholds. Where a tree fails and the soil deficit is remediable, the clause triggers a Soil Function Ladder reassessment and cause-specific remediation. Replacing the tree alone does not discharge the soil-function obligation.
Ten clauses. One auditable trajectory. Evidence at every handover.
Empirical Verification
+35% Larger stems
Larger stem circumference after three years with biologically and physically upgraded planting beds
How it is taught
The library is delivered as a 90-minute workshop that reflect the specification chain.
For designers and specifiers:
Clauses 1, 3, and 8. Drafted live from the room’s own project material. Focus on design and specification levers — what can be written into a document, what can be defended in a design review, what stops the guarantee-period conversation before it starts.
For procurement and inspection:
Clauses 7, 9, and 10. Drafted live from the room’s own tender templates. Focus on acceptance, verification, and enforcement — what an inspector can sign, what a procurement officer can defend, what the 36-month clause actually triggers.
The same ten clauses. Two sides of the same specification chain. When both sides run the same audit, the hole closes.
Both workshops use a neutral audit format. Participants bring a live project, a substrate data sheet, and a bagged soil sample. They leave with three drafted clauses in their own document language, a one-page rung diagnosis for the sample they brought, and a defined next step.
No product is named during the audit. The library is method, not marketing.
The full ten-clause library is available as a PDF for named recipients. It is prepared for review and internal drafting use — enter your details and it is sent to your inbox.
Who it is for
Municipalities operating under AMA Anläggning. Landscape architecture practices working on public realm and hard-surface planting. Consulting arborists advising on tree strategy. Regional networks and procurement organisations working across multiple kommuner. Nurseries and substrate producers who want to be specified on function rather than price.
If your organisation writes, signs, inspects, or is asked to defend the language in a growing-medium specification, this is written for you.
A 90-minute workshop, on-site at your kommun or practice, using your live project material. Delivered in English. Booking currently open for the autumn 2026 and spring 2027 procurement cycles.