Hi Richard, this is a really complicated but very important question! I think you need to break it down a little in order to identify why you are wanting/needing to measure the change in connectivity, why at a national scale and how you define habitats. Each of these issues can have a multitude of defensible answers and as a consequence there is no single simple indicator that will suit everybody. I agree with your pragmatic approach of looking for something that we can measure but I believe that you are already seeking to measure the desired outcomes of Aichi rather than its outputs.

Acting as devil’s advocate, at one extreme, if our objective is to simply assess if the Aichi targets have been met, repeated habitat mapping followed by GIS and geostatistical analysis of adjacency and structure would suffice. Important questions even for this solution are the scale/detail at which you map and how to define habitats (remembering the agreement talks of natural habitats which I don’t view as a binomial characteristic). The resolution of mapping (I’m assuming that national is simply for presentation) and categorisation will influence measures of fragmentation and adjacency and the potential impact is well known through issues such as the Modifiable Areal Unit Problem (MAUP). The aim of the CBD is global, if this is divided between nations, even with the strictest protocols, it will give inconsistent results.

At the other extreme, species distributions may give a better representation of biodiversity, but they don’t necessarily match habitats and the selection of appropriate indicators may not be consistent over time due to extraneous events; supposing you had selected ash trees in Britain! Again there are issues surrounding resolution and frequency of mapping.

Sorry if this is all sounding very negative, I’m sure we share the same overall aims, but I feel we need a holistic, global environmental monitoring approach combined with a better understanding of how the environment works. I don’t think we can do this as a census coverage at an appropriate scale and we are still at the early stages of developing a sampling approach (we have a functioning system for UK, and moving towards that Europe, but the world is a big place).

Time is the elephant hiding in the room, how frequently do we need to (can we?) sample/measure, how do we recognise a true signal from the noise. I know from Countryside Survey that problems are magnified as soon as you start to monitor rather than survey and it is hard to identify how ‘fit for purpose’ information is. And finally, when will we appreciate and learn how to estimate the consequences of ecological relaxation time? We move towards SMART objectives (specific, measurable, achievable, realistic and timely), expecting the world to respond quickly it doesn’t very often!

PS Sorry if this is an incomprehensible ramble that doesn’t answer your question....

David,

Thank you very much for giving the matter so much thought. I was very interested to read your views on scale and resolution in relation to habitat mapping. Your thoughts about species selection and extraneous events, recognising a true signal from the noise, and relaxation times all seem very relevant to my question. I look forward to receiving responses from others that build upon, add to or counter these points.

Best wishes

Richard