The Science of The Walks
Scientific surveys have been carried out, producing large volumes of data and analysis. This page has been written by a trained statistician and researcher to help you get started.
The headlines are:
Soil Surveys
The Borough Council of King's Lynn and West Norfolk claims: "It is the soil conditions along both sides of this walkway which are significantly responsible for the trees' weak growth rates and shortened life-spans." (From August 2004 project update; claim also seen in letters to our MP and a Norfolk Citizen newspaper advert. Emphasis added.)
The most recent soil survey actually says: "there does not appear to be a single soil-based factor to which the reduced tree growth/health may be confidently attributed. There are likely to be a number of chemical and physical factors that may have contributed to create sufficient plant stress to cause the trees to achieve sub-optimum growth. In our opinion for the areas encountered these would include: thin topsoil depth (Seven Sisters Walk and Terrace Walk in particular); Alkaline soil reaction (site subsoils); Waterlogged subsoil (St James Walk only)." (From stage two bid, appendix A4, section 6.1. Again, emphasis added.)
The previous soil survey (A3) says almost exactly the same. The only differences are that "soil-based" is omitted and they found thin topsoil on Broad Walk and some compacted ash fill subsoil.
The tree survey is similar: "soils may be a particular factor in tree decline in some parts of the site" (from A2 section 3.4)
Why does the council claim repeatedly that poor soil is "significantly responsible" when their soil survey only says "may have contributed"? Please ask the council to issue a correction to its newspaper adverts and letters. (Maybe in the style of the Family Fortunes TV show: we said ... but our survey said ...)
In any case, even if the soil is poor, that does not prove it is the cause of any tree problems. It's just another possibility. Is tree performance correlated with soil conditions, or amount of maintenance? We don't know about the soil (too few samples), but there's been little decline in 1998-2004, the best maintenance period for some time.
Basically, the claim the council are making repeatedly is almost completely unproven.
Survey scope
Reading the actual soil survey reports, the consultants state several times things like:
"the purpose of this investigation was to assess the quality and suitability of the soils at The Walks in order to determine any soil-based reasons for the reduced growth potential of the established trees and to identify considerations for replanting." (From A3 section 6.0)
In other words, this survey was looking for what soil problems are causing tree problems and possible problems with replanting. They were not asked whether there are significant soil problems: it's already assumed that there are. Like the rest of the tree plan, it starts with broken assumptions.
Another interesting part of the survey is how the sample locations were selected:
"...pits were located where possible in accordance with the Scott Wilson drawing number D103966/SW/LA01." (From A3 section 2.1)
So, the soil consultants are only testing the places that they are told. To their credit, the next paragraph notes:
"There are likely to be variations in soil conditions across any site, that may not be picked up by the trial pitting/soil examination exercise."
So, why wasn't some form of random sampling used? When a WAG member asked by telephone, they were told that the soil survey was carried out to "underpin" the arboricultural advice. At first glance, that doesn't answer the question: but maybe it does?
Advice against machine use
The soil survey recommendations discourage the use of heavy plant machinery as this will compact the soil (A3 section 7.1). This is also mentioned in the current replacement proposal (A1 page 5). Given heavy machines won't be used, it seems practical to undertake individual tree replacement and soil treatment, rather than large trench excavation.
Advice against nursery trees
Because it is planned to replace entire walks within two years, the proposal is to use nursery-grown semi-mature trees, rather than grow new trees in the Walks and transplant them. This is a problem. From the stage two bid:
"Specimen trees are typically grown in nursery under ideal soil conditions, and as a consequence tend to loose their ability to adapt to adverse soil conditions, including soil alkalinity. Therefore, even when planting trees considered to be tolerant of lime soil, we normally recommend planting semi-mature specimens into soils with a pH value of between 6.0 and 7.8." (A4 section 6.1)
The Walks has alkaline lime soils. The current topsoil has pH value between 7.7 and 8.3, only just including the limit of the recommended range. The subsoil has pH value between 8.1 and 8.4, which is totally outside the range. Also, "it would not be practical to acidify the site's subsoils" (A4 section 6).
The soil consultants make some recommendations, but planting semi-mature trees into unsuitable soil still has risks. With so many trees being replaced, we will see new trees die if the average failure rate is above 0.5% over the 15 year project. What is the forecast mortality rate? Could we reduce it by growing replacement trees in an arboretum in the Walks?
Tree Surveys
Compared to the soil claims, the tree survey has been more accurately reported. The council states "they are rapidly falling apart and will continue to do so ... On the Broad Walk Extension it is estimated that 44% of trees would be lost over the next 15 years." (from August 2004 project update and repeats).
While truthful, this is misleading. It seems to assume most trees in condition B/C (meaning "OK but maintenance required") and worse will just be left to die. Even if they continue with the 1998-2004 level of maintenance, it seems unlikely so many will die because the "survey did not show any dramatic decline in the overall condition of the tree cover on the site from that in 1998/9." (A2 section 4) The tree consultant was not asked to estimate likely tree lifespans.
Map showing tree health (531k)
Using a map of the site, it is possible to create graphics showing the state of the Walks trees. The graphic here shows a couple of sections of Broad Walk (top) and Extension Walk (bottom), colouring each tree green (healthy), yellow (OK), orange (OK but failing) or red (failing). (The base drawing is copyright Casella Stanger, the raw condition data is copyright OCA and both are reproduced here for the purpose of reporting current events.)
You can see quite clearly that the red trees are clustered, even on Broad Walk. Replacing sections seems a viable alternative for Broad Walk. Why has the Council not published this sort of graphics?
Using a tree risk assessment and management system (TRAMS) similar to the consultant's recommendations may significantly extend the lives of the current trees, although it won't repair past underfunding. Already, with increased attention since 1998, "the north walk that contains mostly London Plane and Lime, shows improvement in the twig density of the London Plane." (Stage two bid appendix A2 section 3.1) Why don't we try to save the current Walks trees? It looks like it's not too late yet: plan to fill the gaps and replace the "fell now" ones (4 in Broad Walk, 2 in Extension Walk, 1 in St John's Walk, 1 on Tennyson Avenue).
Survey Incomplete?
"The survey was undertaken in late February 2004 and was conducted from ground level. ... the 1998 survey was also carried out in the dormant season ... There is a need to undertake further survey inspections in the late summer / autumn" (A2 sections 1.2, 3.1 and 4.1)
Despite the above clear recommendations in early 2004, we have yet to hear about the further surveys or see a schedule including them, nearly a year later. (15 January 2005)
Will the needed further surveys be carried out? They seem essential for proper tree care.
New Factors
There have been recent developments which the bid may not have taken into account.
Sudden Oak Death
Earlier this year, Forest Research issued a warning (near end of page) naming both beech and horse chestnut as vulnerable to Sudden Oak Death (Phytophthora ramorum). See also the entry for European beech and the DEFRA P. ramorum page. The transmission of Sudden Oak Death to beech is still not really understood.
The stage two plan is to plant cut-leaved beech (Fagus sylvatica "Aspleniifolia") on the near-empty Red Mount Walk, where the elms stood until Dutch Elm Disease in the 1970s. Will we lose Red Mount Walk to disease a second time? Is there a safer alternative?
Horse Chestnut Problems
Horse chestnut can suffer from bleeding canker and leaf miner Cameraria ohridella. Both are on the increase according to publications from Forest Research (near end of page). Lime can also suffer from bleeding canker, although no increase is reported.
Only two cankerous trees were found in the survey. Should we minimise introduction of new trees?
Environmental Concerns
The Walks plans look like they will contribute to climate change globally and locally, and harm local wildlife.
Climate change
This is a factor in two main ways. Firstly, felling and disposing of trees releases some trapped carbon back into the atmosphere, helping to accelerate climate change. The soil cultivation work and drainage improvement work will both release trapped carbon too.
In the simple words of this National Trust Information note: "Clear felling converts a carbon sink into a carbon source." (section 3)
Read more about carbon and trees at globalissues or the WWF panda. The Walks may not be a forest, but it is unnecessary tree clearance which will contribute.
Secondly, more directly affecting Lynn itself, the young replacement trees will absorb and delay less rainwater than the mature trees. Increased run-off from the very bare avenues and their newly-laid paths may overwhelm the planned drainage improvements, cause localised flooding and silt waterways. All of the Walks is a flood risk area on the Environment Agency flood map.
Also, the increased run-off will wash more nutrients out of the soil, possibly restricting tree growth and accelerating eutrophication of nearby waterways. There doesn't seem to be any mention of this problem in the bid.
Read more about trees and flooding from the Forestry Commission sustainable forestry factsheets.
Wildlife
This has been moved to the nature campaign page.