Introduction to axiophytes
The concept of axiophytes was developed here in Shropshire, building on the work of Charles Sinker who, in the 1970s, drew up lists of notable plants for identifying what were called Prime Sites for Nature Conservation (now known as Local Wildlife Sites). The term axiophytes was coined by Alex Lockton in 2005 to formalise the concept as distinct from rarity or threat as a feature with which to classify sites.
>> Origin of the word
Axiophytes are “worthy plants” - the 40% or so of species that arouse interest and praise from botanists when they are seen. They are indicators of habitat that is considered important for conservation, such as ancient woodlands, clear water and species-rich meadows. Lists of axiophytes provide a powerful technique for determining conservation priorities. Sites with many axiophytes are usually of greater importance than those with fewer; and changes in the number of axiophytes in a site over time can be used for monitoring the outcome of management practices.
How the axiophyte list is made
The key thing for the list is that it should be drawn up independently of the evaluation of a site. You can make an argument for the conservation of any site by looking at it in isolation and arguing that this species or that is important. But if you draw up your definitive list first, then you can use it to evaluate all sites in future and there will be no bias in the subsequent assessment. (Of course if the list itself is biased towards, say, calcareous sites, then all the analyses will all be biased, but the aim here is to get a good list in the first place.)
To decide on your axiophytes you need to decide what it is you want to conserve. In Britain this will be clean water habitats, ancient habitats that are either undisturbed or consistently managed over many years, species-rich habitats, etc. Most experienced conservationists are fairly familiar with these concepts, even if they are not formalised, and they are recognised in the existing nature reserves and protected sites. The Ratcliffe Criteria are a good starting point.
>> The Ratcliffe Criteria
Once you have a clear idea of what it is you want to conserve, you can start to draw up a list of species that are strongly indicative of these places. They are not habitat indicator species as such, because those are normally restricted to just one or two habitats. Nor are they necessarily rare or threatened, although any species restricted to ancient and unusual habitats is likely to be uncommon and decreasing (we don’t tend to protect the common and thriving species). You need a very good site-specific database to do this analysis mathematically, but someone with a lot of experience can make a good stab at it anyway. Choose species that are:
- Largely (about 90%) restricted to conservation habitats
- Not too common (recorded in fewer than about 25% of tetrads in the county)
- Generally declining, at least historically (with conservation efforts some might increase, and we wouldn’t want to strike those off)
- Not too rare (it is very hard to tell whether a rarity is really habitat specific or just happens to be in a nice site)
- Reasonably well recorded and straightforward to identify;
- and the list needs to be representative of the range of habitats that you want to conserve.
An exception to the 25% rule can be made for species in conservation habitats that are particularly well represented and widespread in any particular county. It should not be assumed that a very rare species that just happens to be in a good site is an indicator of that habitat - look at its distribution elsewhere for evidence of this.
It has taken us 20 years to come up with our list of axiophytes, and further changes are possible. Small changes to the list make very little difference to most analyses, but obviously we want it to be as accurate as possible. Originally we did not include bryophytes but we found that acid habitats were under-represented in the analyses, so to recognise peat bogs and acidic flushes and woodland we included a few lower plants.
A flaw in the process?
One problem we have not been able to overcome is that axiophyte lists represent species diversity. There are some habitats that are worthy of conservation that have very few species in them. The main example is oligotrophic lakes, which have very few plants but are of particular importance for conservation. This is a limitation that should be borne in mind. But we have never argued that axiophytes are a panacea for all conservation decisions - sites can of course also be protected for other reasons, including water chemistry, rare species protection and animal species.
How to use axiophytes
The simplest thing is simply to count the number of axiophytes in a site. A Wildlife Site should have at least 10 species of axiophyte in Shropshire and a SSSI should have 30 or more (this is based on an analysis of what such sites typically have rather than being a criterion for selection). Using axiophytes requires a thorough survey, of course, because a partial list of little use, but a good idea is to combine a number of lists collected over a 10-year period to get an assessment of the value of a site.
Once you have a list of axiophytes for a site, you can look more closely at the list and see what features they represent. Wetland sites would be expected to have mainly wetland species, but sometimes one might be surprised to find that a dry grassy bank has an exceptional number of them, perhaps, or there might be a strong element of woodland species. As the axiophytes are habitat indicators, it is worth taking notice of them.
Change can be detected by the use of axiophytes, either to give an overall impression of the state of a site (increasing numbers of species is usually a good thing) or to give specific details of the direction of change (a loss of wetland species suggests that it is drying out).
Shropshire Axiophyte List
>> Axiophytes (csv file for spreadsheets)
>> Axiophytes (pdf)
>> Several other counties have their own axiophyte lists, which you can download here (xlsx file).
Examples and studies
>> Some axiophyte research (BSBI Recorder 15 (2011) pp. 9-14)
>> New Flora of Attingham
>> Flora of Haughmond Hill
>> Axiophytes in the Meres & Mosses
>> Shrawardine Pool 2014 (dissertation by Sue Townsend)