Setting a baseline

There’s been persistent media comment this year highlighting the scale of loss of wildlife, especially mammals, birds and insects, together with some hyperbolic headlines1. But where does this sense of drama take us? Most reports headline percentage losses over time. Beyond confirming the broad trend of loss, what do these numbers signify?

Humans have destroyed 83% of wild mammals (Guardian 21 May 2018)

…42% of terrestrial animal and plant species….have declined in population size in the last decade…(UN IPBES May 2018 )

Britain has lost half its wildlife (Guardian 26 March 2018 )

Following decades of decline until the 1990s, Scotland’s stock of natural capital has stabilised and is now at its highest level since 2000 (Scottish Natural Heritage April 2018 )

10 species at risk of extinction amid fears Scotland is missing wildlife targets (Sunday Herald 3 June 2018 )

These diverse headlines serve to confuse and all really are quite arbitrary, illustrative at best. They come from studies comparing population levels over time and so comparisons depend especially on when the original measurements happen to have been initiated. It’s not surprising that these tend to be pretty short-term, because there’s hardly any such measurement recorded earlier than the mid-twentieth century. Most are much more recent.

I’m arguing that we need to set these rather random statistics in a wider context. We should be concerned especially about losses of wildlife that result from human actions (or inaction); human impacts on nature began hundreds, even thousands, of years ago. While these impacts have accelerated in recent decades, we would have to go back a long way to find a clear starting point.

For Scotland, there’s little argument that the most recent ice age effectively wiped the slate clean to around 12,000 years ago. Slowly, the first tundra vegetation was replaced on lower ground mainly by woodland and wetland habitats giving homes to a wide variety of plants and animals. A few small groups of people roamed these landscapes, but their impact to begin with was insignificant. It’s possible that their hunting and fishing reduced the numbers of some large mammals and birds, but direct evidence for this in Scotland is lacking.

The first evidence of substantial landscape change followed the arrival of the first farming families, between 6,000 and 5,000 years ago. The pollen record from sediment cores shows changes in tree cover and increase in open ground from this time. These changes will have had many knock-on effects on animals and plants, favouring those using open ground at the expense especially of woodland species. So part of the loss we are now seeing will be for species which had prospered from earlier human impacts. We lack any measure of the extent or quality of the main habitats that long ago, and so it’s hard to say very much about the associated wildlife population levels. But, if our concern is to put right adverse human impacts on nature in Scotland, then this period (around 6,000 years ago) must represent our effective baseline. We should at least think through how our present-day wildlife might compare.

I’m not trying to make an argument that this ‘status quo ante’ should, or could, ever be restored, but I do argue that such a long term perspective helps us to think through our best response and action to restore loss. There’s a campaign (Nature Needs Half) which helps us to cut through the confusion. Its message is simple and direct; to ensure that nature has enough space to thrive. This then directs us to think about wildlife at a landscape scale, rather than only the remaining intact fragments.

For Scotland, woodlands and wetlands along with their characteristic animals and plants have suffered especially grievously. Setting aside the myth of an ancient Great Wood of Caledon unbroken from coast to coast, the best available evidence suggests these woodlands at their peak can have covered no more than half of Scotland2. But that is a lot more than present-day cover of less than a fifth. And most present-day woodland takes the form of dense plantation rather than the more open native woodlands; a few mainly isolated scraps of these are all that remain.

The extent of wetlands – swampland, marshes and low lying bogs – perhaps once covered around a quarter of Scotland, before being reduced rapidly from the 1700s onwards following drainage for farmland. Beyond well-documented large scale developments such as the Carse of Stirling, thousands of small local schemes dried out wet hollows and straightened waterways. These losses have been rather overlooked3, leaving wetland plants, wildfowl and animals clinging on to fragments of suitable habitat along ditches and remaining wet hollows.

A third large area of Scotland remains too high, or too exposed to Atlantic gales, to sustain woodland. While high mountain plateaux may include our least modified wildlife habitats, much moorland and upland bogs continue to be damaged for example through excessive grazing by sheep & deer. We can be confident there’s more moorland and heath than in prehistoric times, since a large area of this open ground would carry woodland if grazing was reduced, so one can argue that some moorland wildlife abundance has been artificially high4.

The biggest cause of loss of woodland and wetland has been conversion to farmland5, over many centuries. While it’s wrong to dismiss present day intensive farmland as an ecological desert, the wildlife now found there must be able to tolerate open ground and regular disturbance.

Take, as one example, the corncrake. Present-day numbers (and geographical extent) are a fraction of those recorded as recently as the late 1800s; but those corncrakes depended on extensive hay meadows and cereal crops managed without machinery. In the pre-farming landscapes, corncrakes were probably restricted to wet grasslands in the valleys of our main river systems. Now they are restricted to small-scale mixed farming in the Highlands and Islands. Skylark, lapwing and many other valued open ground farmland birds probably benefited in the same way from open fields replacing woodland. The wild plants now found around farmland tend to be pioneer species (often regarded as weeds), contrasting with many woodland plants and insects requiring shade or rotting timber to thrive. In the same way, a wetland bird such as the bittern, requiring extensive reed beds, no longer breeds in Scotland. But these were recorded regularly on the menu for medieval banquets.

Another human impact has been numerous introductions of animals and plants which would not otherwise be seen in Scotland. These bring varied, often negative, consequences. Grey squirrels from North America compete with native red squirrels; burrowing rabbits brought from southern Europe by the Romans undermine flood banks but feed native stoats, foxes and buzzards; Japanese knotweed and giant hogweed from central Asia infest our riverbanks and so on.

Efforts to make sense of all this are no small task. A National Ecosystem Assessment in 2011 informed a 2016 State of Nature report compiling evidence of recent change covering thousands of terrestrial and freshwater species from 1970 to 2013. There has also been an effort to compile a ‘biodiversity intactness index’ which at least seeks to work from a baseline set 500 years ago (although most figures similarly relate to the last 50 years or so). But even 500 years ago Scotland’s native woodlands had largely been cleared. We must not overlook the longer timescales of change.

A recent review in New Scientist6 recognises the complications, despite which we can be sure that wildlife is in serious decline due to human impacts. Losses have been grievous but apocalyptic language is hard to justify; there is so much still of value that can be put right. I believe our actions must be framed by cool appraisal of evidence with our understanding of what has changed and why, fashioning storylines which explain, for different parts of Scotland, what has happened and how things can be better. The headline is that we need more woodland (but not intensive plantation) and especially more wetland wherever opportunities arise.