Biodiversity - and how we measure, monitor and restore it - has become a mainstream topic in the past five years. It's now widely accepted that the global climate and biodiversity crises are inseparable, and we can't tackle one without addressing the other. This has been an exciting period for biodiversity scientists, with increased funding opportunities from the public and private sectors (dampened somewhat by recent politics) and even multi-million pound competitions to develop scaleable biodiversity measurement technologies. Yet, despite the mainstream enthusiasm, the word "biodiversity" has become divisive. There is no universally accepted definition of biodiversity or how to measure it, and even recent peer reviewed papers will use the term loosely to describe individual species, taxonomic groups or broader ecological communities. It's not surprising many are confused.
In my own efforts to measure biodiversity, I always come back to asking myself: what would the perfect measure of biodiversity look like? If we start there, we can more easily understand why such a huge number of summarised metrics and definitions exist and further understand how to choose the right approach for our needs. So, what would perfect biodiversity measurement look like? In a perfect world, we would know at any given time where every single living organism was on Earth. From every bacterium in the human gut, to the jellyfish in the sea, birds' eggs hatching in the forest and lichen growing on a rocky outcrop. We would also be able to track the individually unique genetic code for each organism and its clones, and understand its life stage, behaviour and response to stimuli in the environment. With that perfect information streaming in real-time to our imaginary supercomputer, we could track populations of every species on earth, monitor extinctions and invasions, watch evolution happen before our eyes and understand the complex relationships that make up the web of life. Since we're a very long way from achieving this perfection, biodiversity scientists make compromises, usually quite big ones, and we shouldn’t be shy about it.
When setting out to measure biodiversity the first question to answer is the "why?". For biodiversity restoration projects we want to know if we have succeeded to restore a habitat, species or ecosystem. One challenge is that it can take decades or even centuries for restoration to succeed because of ecological time lags. For example, woodland species can be slow to naturally re-colonise a new planted woodland. This is something I explored during my PhD, and although the long-term outcomes of woodland planting were difficult to predict, land-managers can look for indicators – like the arrival of woodland generalists - that suggest restoration is going in the right direction (Watts et al. 2020). Once we know the “why”, we can get to the “how”. There is an almost infinite number of ways we can measure and monitor biodiversity change. In reality, the decision about what to measure and how we do it is based on (1) our own personal or compliance objectives, which might be to monitor a mammal community in response to land-use change or improve soil fertility to improve crop yeilds, (2) what is feasible in terms of methods, technology, and statistical power to detect change, and (3) what is the budget? In reality of course the budget often comes first in, which further limits what is feasible. Once we’ve resolved these three questions we can design a biomonitoring plan which, for me, is the most important step. We can monitor fish using traps, termites captured in test-tubes, mammals using automated camera traps or a combination of all summarised by an index, but once we’ve decided, the key to success in long-term biomonitoring is to stick to the plan. Even if imperfect, repeating the exact same methods year after year can, over time, deliver results that detect change. Some of the most successful long-term biodiversity monitoring projects are based on what would now be considered out-dated or imperfect methods, but the commitment to sticking to the plan over decades has delivered hugely exciting insights into biodiversity dynamics.
