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Expert evidence rules for tree reports: what US federal and English court rules say

What Federal Rules of Evidence 702, Federal Rule of Civil Procedure 26 and the English Civil Procedure Rules Part 35 say about expert witnesses and their written reports.

Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.

This page reports what the official source says. It is not legal advice: ask the office named here. The three rule sets below govern expert witnesses in court cases. None of them is written for tree reports, and the pages say nothing about arborists. For the work itself, see the guide on the consulting arborist role.

United States: Federal Rule of Evidence 702

Cornell Law School's Legal Information Institute prints Rule 702. It says a witness qualified as an expert by "knowledge, skill, experience, training, or education" may give an opinion if the party offering the witness shows the court that it is more likely than not that four things are true: the expert's specialized knowledge will help the trier of fact understand the evidence or decide a fact in issue; the testimony rests on sufficient facts or data; the testimony is the product of reliable principles and methods; and the opinion reflects a reliable application of those principles and methods to the facts of the case. The committee note on the 2023 amendment says the rule's reliability requirements are for the court to decide under that more-likely-than-not standard, and that each opinion must stay within what a reliable application of the expert's basis and method can support.

United States: Federal Rule of Civil Procedure 26(a)(2)

Rule 26(a)(2) covers disclosure of expert witnesses. It says a party must disclose the identity of any witness it may use at trial to present expert evidence. A witness retained or specially employed to give expert testimony must supply a written report prepared and signed by the witness. The rule lists six contents:

  • Opinions. A complete statement of all opinions the witness will express and the basis and reasons for them.
  • Facts or data. The facts or data the witness considered in forming them.
  • Exhibits. Any exhibits that will be used to summarize or support the opinions.
  • Qualifications. The witness's qualifications, including a list of all publications authored in the previous 10 years.
  • Other cases. A list of all other cases in which, during the previous 4 years, the witness testified as an expert at trial or by deposition.
  • Pay. A statement of the compensation to be paid for the study and testimony in the case.

Unless the court or the parties set another date, the rule puts disclosure at least 90 days before the trial date, or within 30 days after the other party's disclosure when the evidence only rebuts it.

England and Wales: Civil Procedure Rules Part 35

The Ministry of Justice publishes Part 35. Rule 35.1 says expert evidence "shall be restricted to that which is reasonably required to resolve the proceedings." Rule 35.3 says an expert's duty to help the court on matters within their expertise overrides any obligation to the person who instructs or pays them. Rule 35.4 says no party may call an expert or put in an expert's report without the court's permission. Rule 35.6 lets a party put written questions to an expert about the report: once only, within 28 days of service of the report, and for clarification only unless the court gives permission or the other party agrees. Rule 35.10 says a report must comply with Practice Direction 35 and end with a statement that the expert understands and has complied with their duty to the court.

Practice Direction 35 says a report should be addressed to the court and not to the party who gave instructions. It says the report must give the expert's qualifications, list the material relied on, set out the substance of all material facts and instructions, say which facts are within the expert's own knowledge, summarise any range of opinion and summarise the conclusions. It also prints a statement of truth that includes the words that the opinions are the expert's "true and complete professional opinions" and a warning about contempt of court for false statements. Paragraph 2 of the Practice Direction describes the expert's duty as giving objective, unbiased opinions on matters within their expertise and considering all material facts, including those that might detract from the opinion.

Contains public sector information licensed under the Open Government Licence v3.0.

Sources