Bogs and climate

The foundation of all the research we do is the link between bogs and climate. This page provides a brief introduction to the subject, but for a bit more detail why not check out this blog post.

There are many different types of peatland.  The most basic division is between bogs and fens.  Bogs are nutrient poor, have low pH, are generally dominated by mosses. Fens on the other hand are more nutrient rich, have neutral pH, tend to be dominated by grasses or rushes.

As you may have guessed, we are more interested in bogs – the website’s not called ‘Fenology’ after all!  In fact we are most interested in a particular type of bog called an ‘ombrotrophic’ bog.  Ombrotrophic (meaning ‘rain-fed’) bogs get all their moisture from precipitation (rain, snow etc.).  This means that any change in the hydrology of the bog is directly related to climate – mainly to precipitation but also to temperature because that affects how much of this water evaporates. Fens on the other hand, receive water from groundwater flow, as well as from precipitation and so climate is often not the main factor in their evolution.

On the surface of an ombrotrophic bog there tend to be three main features: pools (essentially very large puddles), lawns (large flat areas of moss) and hummocks (high lumps of moss and other plants that form small hillocks). The growth and distribution of plants and animals (e.g. testate amoeba) between these different landforms is predominantly related to hydrology (i.e. how deep the water table is).  Let’s take plants as an example.

At any given point in time at the edge of a large pool, where the water-table is at or very near the surface, certain species will thrive, others will just about be able to survive and others still will not be able to grow at all.  The same is true on a high hummock where the water table might be 50 cm below the surface – a different group of species to the pool edge will thrive, some others will just about be able to make it and those that thrived at the pool edge will not be able to survive – it is simply too dry for them.

The important point is that the hydrology of an ombrotrophic bog will change over time.  A pool may dry up and turn into a lawn meaning that those species that lived on the edge of it will disappear, the ones just about surviving will begin to thrive and maybe some species that like dry hummocks will begin to creep in.  Eventually the lawn may become even drier and a hummock will form – then the species will change again.  Remember that any change in hydrology, causing a change in species distribution, is related to climate (ok, there are some technicalities that mean it’s rather more complicated than that, but the general point remains).

Over long periods of time – thousands of years – ombrotrophic bogs, which are acidic and largely oxygen free environments, except very near the surface, will accumulate peat because dead plant remains do not decay fully and are gradually overgrown by new plant communities.  As the bog grows upwards, a record of all the changes in plant communities we have just described will be preserved.

What that means is that we can now stand on the bog surface and take a core back down through all the accumulated layers and analyse what’s been happening over time.  Sometimes these cores can be over 10 metres deep and hard work to retrieve, but the reward is always worth the effort.  Peat bogs began growing at the end of the last ice age, as the glaciers and ice sheets melted away, so we can potentially study climate change over the past 10,000 years or more!