Dendroclimatology on the Herstmonceux Estate

Dendroclimatology is the study of tree rings and tree growth and can be used to study the present climate and to reconstruct climates from the past. The rings on a tree are more telling about the climate and how the environment looked hundreds of years ago than just the age of a tree. The size, colour, and density of the rings (see Fig. 1) can tell us a lot about the amount of rainfall in a season, as well as the growth of the tree. Oxygen isotopes within tree rings also record changes in the isotopic ratios of summer rainfall allowing accurate dating to a master chronology that has been established for the period 1200–2000 ce.[1]

Figure 1. Section of a tree core showing annual growth rings (vertical lines above) that was sampled from an ancient oak tree (Quercus robur) along the 1066 pathway on the Herstmonceux Castle Estate.

Twenty tree cores were taken by Dr Simon Coppard from four locations on the estate, at Bader Hill (Castle Gate), from Plantation Woodland, along the 1066 pathway and from the Parkland Pale. These cores have been sent to Prof. Neil Loader at Swansea University for oxygen isotope analysis.

Dendrometers accurately measure tree growth by recording expansion of the tree’s stem and can also measure the expansion and shrinkage of the bark depending on water availability.

On the Herstmonceux estate, four dendrometers were set up on oak trees around the property in March 2021 (Fig. 2). These reflect slightly different habitats on the estate. These sensors measure and record the growth of the tree around the trunk as well as the environmental temperature every four hours. The initial data collected from these sensors were from March 2021 to February 2022 and will continue to record data for the foreseeable future.

The ancient woodland on the estate is a prominent source of biodiversity and by observing the health of the trees, oak trees in this case, the biodiversity can be sustained and even expanded upon in the future. In the South of the U.K., oak trees are being affected by both climate change and diseases such as Acute Oak Decline and Chronic Oak Dieback. Monitoring the health of the oak trees, looking for sign of disease and assessing how they respond to climate change, with hotter, drier summers and wetter, windier winters makes it even more important to study and protect the trees on the estate.

This dendroclimatology study is taking place as part of the Environments of Change project, using different disciplines of research and innovation to look at the historical relationship between humans, nature, and culture, with the aim to educate the public on historical and current environmental aspects of life in East Sussex. Collecting data from the ancient woodlands on the Herstmonceux estate incorporates the two values of the Environments of Change: historical and current environmental information, and the use of different kinds of technology through the use of sensors.

For this study, the data used was collected from March 2021 to February 2022. This was done by directly downloading the data from the dendrometers.

Fig. 3. Downloading tree growth and temperature data.

Sensor 2 (Ancient Woodland) revealed little change in tree diameter from March 2021 to June 2021. The temperature over those months was still relatively low and not ideal for tree growth with the temperature often being below 15℃. from July 2021 to early September 2021, the graph shows a rapid increase in growth. The temperature averaged around 18℃ for that time period, which would help accelerate the growth of the tree. No decrease in tree girth was recorded in the Summer months indicating that water availability was not limiting. The graph plateaus from mid-September 2021 to March 2022 as the temperature starts to regularly dip below 15℃ towards 5℃ to 0℃.

Fig. 3: Graph showing changes in tree girth recorded by sensor 2.
Fig. 4: Graph showing the temperature of the environment recorded by sensor 2.

Sensor 3 (Parkland): There was a steady increase in growth from July 2021 to October 2021 (Fig. 5). During those months the temperature averaged closer to just under 20℃ (Fig. 6). In June and early July a decrease in tree girth was recorded, indicating bark shrinkage most likely as a result of limited water availability in the Parkland and a lack of rainfall. There was a plateau in growth from mid-October to March 2022, where the temperature moved towards 0℃.

Fig. 5: Graph showing changes in tree girth recorded by sensor 3.
Fig. 6: Graph showing the temperature of the environment recorded by sensor 3.

Sensor 4 (Plantation Woodland). Overall, the data showed a general upward trend in tree growth (Fig. 7) as the average temperatures increased leading to the inference that trees spend most of their time growing over the summer months when the weather is much warmer as compared to the winter months.

Fig. 7: Graph showing changes in tree girth recorded by sensor 4.
Fig. 8: Graph showing the temperature of the environment recorded by sensor 4.

Between April 2021 and May 2021 an odd ‘jump’ in the data was recorded which, after examining the sensor, was explained by the sensor having been nibbled on by either deer or squirrels (see Fig. 9). This disturbance caused the dendrometer to jump increasing the measurement. The ruler on the bottom of the dendrometer had been chewed. A similar ‘jump’ in data was seen again in mid-July and early August. With this disruption in data, the general trend can still be seen with the most amount of growth between late April and early August. This follows the same trend as the other sensors due to the temperature ranges being the same as all the sensors were in a close radius on the BISC campus. Adjustments will be made to the data to account for these ‘unforeseen’ disturbances.

Sensor 1 (Lower Ancient Woodland) has an issue with low battery power making it impossible to download the data. A highly specific replacement battery is currently being sent from the Czech Republic, so we anticipate being able to download the data in the next few weeks.

            This project will continue to monitor the health of oak trees on the Herstmonceux Estate and how they cope with increases in stress due to an ever-changing climate and the increased threat of disease. The growing season and dormant periods will be monitored to determine whether any shifts are recorded and whether they vary between different microhabitats on the estate.

Alex Roger, 1st Year Science Student, Queens University (Canada).

[1] Oxygen comes in a variety of non-radioactive isotopes, heavy and light. The more common light isotope oxygen-16 (16O) has 8 protons and 8 neutrons, while heavy oxygen-18, with 8 protons and 10 neutrons. The ratio (relative amount) of these two types of oxygen in water changes with the climate so varies year to year in summer precipitation and thus the growing season which is recorded in the growth rings. We then compare these ratios to a master chronology covering the period 1200–2000 ce.

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