Quantifying hedgelaying success: before and after density analysis

A laid hedge looks completely different from an unlaid one to anyone who knows what to look for. To anyone who doesn’t - the auditor reviewing your management report two years later, the contractor checking they were paid fairly for last season’s work, the landowner asking whether the £15/metre bill was worth it - “it looks thicker” is the most articulate description available. A measured porosity figure before and after, in the same season twelve months apart, turns that subjective impression into a hard, comparable, audit-friendly data point.

This guide covers how to set up the comparison, what numbers to expect, and how to use the result for management reporting.

Setting up the before capture

The most useful before-laying capture is in the summer prior to laying, with the hedge in full leaf, photographed under the overcast-or-front-lit conditions described in the capture guide. Walk the full length, capture a frame every 5–10 metres, upload as a single batch tagged with the hedge ID. The resulting porosity average is your baseline.

Bare-branch winter captures aren’t useless but don’t compare cleanly to leafless post-laying captures because the post-laying hedge is structurally different even before bud break. Summer-to-summer is the cleanest time series.

The post-laying captures

Three captures matter:

• Year 0, immediately post-lay (winter): the hedge is at its densest. Expect 5–20% porosity. The pleached stems form a near-solid wall. This is the “done” photograph for contractor sign-off.
• Year 1, first summer regrowth: new shoots have broken bud and the hedge is filling. 15–30% typically. This shows the lay is taking, not failing.
• Year 3, settled into mature management: 20–40% as the structure normalises and the hedge begins behaving as a managed-but-mature hedge again. This is the long-term figure that demonstrates the lay had a lasting effect.

Reading the numbers

A typical declining hedge that needed laying might measure 50–70% porosity before. After a competent lay, the year-0 figure should be 5–20% - a 30–50 percentage point reduction. By year 3 it should settle in the 20–40% band, well below the pre-lay baseline.

Smaller pre/post drops (10–15 points) suggest the lay wasn’t intensive enough to address the underlying gappiness. The hedge will recover quickly toward its declining state. This is useful information for the contractor: it isn’t a failure, but it tells the landowner this hedge needs another intervention sooner than the typical 15–20 year cycle.

Very large drops (over 60 points) aren’t necessarily better. They can indicate the lay sacrificed key structural stems and the hedge will be slow to break out of the dense stockproof phase. The optimum is intensive enough to reset the structure but not so aggressive that mid-canopy regrowth is suppressed for years.

Contractor reporting

Most hedgelaying invoices are paid per metre with a quality sign-off. Replace “satisfactory” with a porosity figure paired with the year-0 photograph and you have an objective record both parties can refer to next time. For multi-hedge contracts with several teams, the same approach lets the landowner compare quality across teams without it becoming an opinion contest.

Grant and management reports

SFI HRW2 pays for active management. A before/after porosity record is documentation that the management actually happened and produced a measurable change. Pair with photographs, dated invoices, and the hedge ID and you have evidence that holds up to audit.

For longer agreements, the multi-year time series (before, year 0, year 1, year 3) is the kind of data point that supports payment claims through the second and third payment cycles without requiring the management activity to be repeated each year.

Coppicing and gap-up planting

The same approach works for coppicing, with one wrinkle: immediately after coppicing the hedge measures near-100% porosity (almost no structure remains). The meaningful figure is at year 2–3 when regrowth has filled in. So a coppicing time series looks like: before (50–70%), year 0 (90–100%, almost no data), year 2 (40–60%, early regrowth), year 5 (20–40%, mature stage).

Gap-up planting is more linear: each filled gap is a localised porosity change visible in the spatial heatmap. The batch average moves slowly but specific zones drop sharply.

Frequently asked questions