Decoding Past Climates
Past Plants and the Climate of Low Hauxley, Amble
by
Dr Martha Gibson, Palynologist

Department of Geography and Environmental Sciences, Northumbria University*

*Now University of West Virginia, Morgantown, West Virginia, USA

Introduction

Plants are excellent indicators of climate; different plants grow under different very particular conditions. Some plants liking it shady and wet (stinging nettles), some liking it dry (pine trees), some liking their soil to be acidic (heather), and so on. Therefore, the remains of plants found can be used to reverse engineer the conditions these plants lived in, such as temperature range, amount of rainfall, soil pH and disturbance levels.

The ability of plants to indicate temperature and rainfall is of particular interest to climate scientists and those who study fossils alike. Ancient plants were just as fussy about where they grew so they can also be used to reconstruct the climate of the past. This allows us to see how climate has changed over time and help us predict how this change might effect where plants are able to grow in the future. This has important ramifications for food security as the land available for growing crops could become limited. For Blyth and its sand dunes climate change will have implications for coastal erosion and flooding as plants are vital for maintaining the stability of the sand dunes and preserving the coastline.

Unfortunately, large plant fossils like branches, fruits and leaves are rare. Instead, scientists turn their attention to a different part of the plant – their pollen grains. Although they are impossible to see without a microscope they are as easy to tell apart as their parent plants. Plants plants produce millions of these grains every year and the sheer quantity of pollen in the fossil record makes them one of the most valuable tools for reconstructing environmental and climate change. By looking at the different kinds of pollen found in the fossil record, palynologists (those who study fossil pollen grains) can build up a picture of what the plants and climate of the past was like, literally from the ground up!

A good example of this is the study done by J B Innes and R M Frank in 1988 on the fossil pollen found in (200 to 5,000 years BC according to Dr Clive Waddington of Archaeological Research Services Ltd in 2011) old peat, remnants of a mummified forest, from Low Hauxley, near Amble.

What can we do with Pollen

This pollen allows us to reconstruct the ancient vegetation that lived along the northeast coast during this time. Changes in the type of pollen found in the layers of peat tell us how the vegetation changed through time.

The pollen tells us that, before the coastline was framed by dunes, a swampy mire bordered the coast behind which an alder forest grew with birch, oak and willows trees too. Living in the shaded and wet habitat underneath the forest canopy was an understory vegetation of honeysuckle, ivy, meadowsweet, buttercups and bullrushes. Over time, a drying out of the mire caused a change in the vegetation, with the alder forest becoming more a birch forest instead. The drying of the mire caused a drop in water level, encouraging acid tolerant plants like Sphagnum moss, sedges and heather to flourish. As the mire dried out further, mixed birch and oak trees were dominant. At the same time, plants indicative of open ground such as plantains, dandelions, docks and sorrels, plume thistles and ferns appear which tell us there were open areas neighbouring the woodland.

Once the dunes became established, we eventually see the end of the local woodland with the only woody plants remaining being heather and hazel. This change coincides with the movement of sand onto the mire, and we see plants appear which thrive in sandy habitats such as pine, maple, roses, ferns appear alongside many open ground herbs such as mugworts, campion, starwort, bellflowers, devil’s-bit, docks and sorrels, dandelion and daisies. The latter are herbaceous plants and suggest there were still some ponds behind the dunes.

Using Fossil Pollen from Lower Huxley

In this study we use the published fossil pollen data to reconstruct the past climate. By combining the climate preferences of all the plants present at any one time we can reconstruct what the overall climate was then and see whether the ancient climate of Low Hauxley was different to the present-day climate of Blyth and the U.K. (ECMWF data; WorldClim 2.1).

Reconstructions show that the average annual temperature across the year at Low Hauxley was 8.6 ˚C, approximately 1 ˚C lower than present-day Blyth (9.5˚C). While winter temperatures at Low Hauxley were 1.5 ˚C, 3 ˚C cooler than present day (4.5 ˚C), summer temperatures were 16.8 ˚C, over 1˚C warmer at present (15.7 ˚C). Average annual rainfall at Low Hauxley (711 mm) was almost identical to present-day (718 mm) and rainfall seasonality (how even rainfall falls across the year) was very similar in the past (18.8) to the present-day national average (20.9).

Interestingly the climate at Low Hauxley remained stable and unchanged throughout the creation of the dunes implying that climate was not responsible for the changes in the vegetation, instead human activities and changes in wind direction and/or sea level are more likely to have caused the drying out of the mire and accompanying changes in vegetation.

Editorial Comment
Looking back 5,000 years ago the climate was a bit different, summers were slightly warmer (by about 1 degree C) and winters colder (by about 4.5 degree C) but rainfall was almost the same. This is in line with global trends which show about ½ degree C as shown in Figure 7. The Hauxley mean annual temperature (MAT) drop over the period studies is about the same (1 degree C) as shown in Figure 5.

Above all, the climate was more or less constant during the period of time studied. However, the pollen shows that the plants that grew in Lower Hauxley were changing. This change in vegetation cannot be attributed to a changing climate. However, it is possible, as mentioned above, that the decline of woodland here might be due to human activity? At around this time people were changing the way they got their food. They were moving on from a hunter gather lifestyle to start to control their environment to make it more suitable for wild animals and to increase their numbers; an early version of animal farming. They then started to clear the forests to grow their own food in small forests in clearing they had made. It might be this trend to deforest the landscape that we are seeing in the pollen from Hauxley.

Looks around you now and you can see how this has ended up. Most of Britain was covered in forest but now most of the trees have been cut down by our distant ancestors to help them grow food and raise animals. Are we seeing the very beginning of agriculture, our ancestors starting to change their environment, in the peats of Lower Hauxley?

Interestingly, one of the last remaining woody plants was Hazel. The nuts from the Hazel tree were known to be a very important food for our ancestors. Perhaps the survival of this plant was not accidental, is it another early example of farming for food?
More by Martha

We reconstructed Britain of millions of years ago to see what climate breakdown will involve (spoiler, lots more floods)

References quoted
Innes, J.B. & Blackford, J.J. (2017). Palynology and the study of the Mesolithic-Neolithic transition in the British Isles. In The archaeological and forensic applications of microfossils: a deeper understanding of human history. Williams, M., Hill, T., Boomer, I. & Wilkinson, I.P. Geological Society. 7: 55-78.

C Waddington (2011) Low Hauxley, Northumberland: a review of archaeological interventions and site condition Archaeological Research Services Ltd Report No. 2010/25 Revised November 2011

Innes J.B. & Frank R.M. (1988). Palynological evidence for late Flandrian coastal change at Druridge Bay, Northumberland. Scottish Geographical Magazine 104: 14-23.