Habitat Suitability Index

[rethgar]

Here's a question:

Habitat Suitability Index a useful tool or a load of cobblers?

I'll elaborate, I have used HSI a fair bit over the past few years to identify suitable ponds for Triturus cristatus and I have to say the result have been mixed. For those who don't know how it works there are basically a series of categories each given a score resulting in an overall score from 0 to 1.
Criteria are:

Location
Pond area
Pond drying
Water quality
Shade
Fowl
Fish
Ponds
Terrestrial habitat
Macrophytes

All of these are intended to be done by quick visual assessment, barring location and ponds (which is the number within a certain radius). This I think is where it comes unstuck, many of these categories are so horrendously subjective that the results vary from surveyor to surveyor. I have looked at ponds with an excellent score which I would have scored poor. Macrophyte cover for example, we score higher for more plants, but should this include things like bulrush? Some think so others not...

So in addition to the first (and perhaps unhelpfully closed question). Can we make this work better? If so how?

My initial thoughts include the need to be more specific with the macrophyte definition, egg laying and cover plants only. The number of ponds should be those with GCN present only rather than any old pond.

I realise that this is intended only to give an indication of suitability but it is being used more and more to determine survey resourcing and I think that this may be a little dodgy.

Thoughts?

 

[TheMattSign]

I would say it depends on how it's being used how granular you want to get. It sounds like it started out as a "rough" tool and now is being used for more than it was initially intended. I think you have the right idea though on how to make it better though, better descriptions that make the ratings more objective. You could get as granular as you wanted with that. You could go as simple as x, y and z will give you a high rating while j, k and l will give you a low rating the whole way to giving a detailed description to each rating for each category. I don't know much about the species you are targeting and have never used the HSI so I can't really give any more details other than you're on the right track. Sounds like this is a much needed overhaul that would make this tool really useful so good luck!

 

[Kaysie]

I've used HSI for a variety of species (caudates, turkeys, squirrels, etc.), and found it to be kind of hit or miss. I think one thing the HSI fails to take into account, which is especially true for amphibians, is the historic land use. If the land has been disturbed at any time in the past, it has a definite correlation to caudate populations.

 

[rethgar]

Historic and current land use are something I always look at too. Though to be honest the UK is almost 100% disturbed at one time or another through development, agriculture, recreation and general idiocy. I think maybe degree of severance should also be considered.
HSI is quite contentious among ecologists. I think there has been an over reliance on it as a tool at the expense of both experience and common sense.

Something I have noticed is that getting a licence to disturb seems easier and easier. Mainly I think because it isn't policed as severely as bats, say. And while I think bat licensing in this country is somewhat over onerous newt licensing is a joke.

A little off topic there but it irritates me.

 

[caleb]

Macrophyte cover for example, we score higher for more plants, but should this include things like bulrush? Some think so others not...

Duckweed is specifically excluded, isn't it? I guess it is rather subjective with bulrush- you could even argue that a heavy bulrush stand is not actually part of the pond.

The number of ponds should be those with GCN present only rather than any old pond.

I don't think that's really practical, as you'd have to have done a full survey of the area before doing the HSI, which kind of defeats the object.

I think maybe degree of severance should also be considered

This is included in one of the variables- I can't remember if it's the 'ponds' one, or 'terrestrial habitat'. Historic land use might be less useful for GCN than for other species, as the vast majority of GCN ponds are man-made...


It seems odd to me that it uses the geometric mean- I don't think there's any mathematical justification for this (as everyone's comparing the same 10 variables), and it makes it more complicated to calculate (do you carry a scientific calculator in the field?).

You might want to ask the same question on RAUK- I'm sure lots of people there have plenty of experience with it.

 

[rethgar]

Regarding the number of ponds: that's the one that mention severance but curiously not relating to the one you're assessing. Also maybe I should have said ponds with biological records indicating suitability.

As for the calculator, well yes I do usually have one in my bag but usually I just note the scores and then I have a spreadsheet to do the calculations...