Seeing the wood for the trees: New study shows sheep in tree-ring records

July 26, 2011

Nibbling by herbivores can have a greater impact on the width of tree rings than climate, new research has found. The study, published this week in the British Ecological Society's journal Functional Ecology, could help increase the accuracy of the tree ring record as a way of estimating past climatic conditions.

Many factors in addition to climate are known to affect the tree ring record, including attack from parasites and herbivores, but determining how important these other factors have been in the past is difficult.

Working high in the mountains of southern Norway, midway between Oslo and Bergen, a team from Norway and Scotland fenced off a large area of mountainside and divided it into different sections into each of which a set density of domestic sheep was released every summer.

After nine summers, cross sections of 206 birch trees were taken and tree ring widths were measured. Comparing these with local temperature and the numbers of sheep at the location where the tree was growing allowed the team to disentangle the relationship between temperature and browsing by sheep and the width of tree rings.

According to lead author Dr James Speed of the NTNU Museum of Natural History and Archaeology: "We found tree ring widths were more affected by sheep than the ambient temperature at the site, although temperatures were still visible in the tree ring records. This shows that the density of herbivores affects the tree ring record, at least in places with slow-growing trees."

The impact of large herbivores on tree rings has, until now, been largely unknown, so these findings could help increase the accuracy of the tree ring record as a way of estimating past climatic conditions, says Dr Speed: "Our study highlights that other factors interact with climate to affect tree rings, and that to increase the accuracy of the tree ring record to estimate past climatic conditions, you need to take into account the history of wild and domestic herbivores. The good news is that past densities of herbivores can be estimated from historic records, and from the fossilised remains of spores from fungi that live on dung."

"This study does not mean that using tree rings to infer past climate is flawed as we can still see the effect of temperatures on the rings, and in lowland regions tree rings are less likely to have been affected by herbivores because they can grow out of reach faster," he explains.

Tree rings give us a window into the past, and have been widely used as climate recorders since the early 1900s. The growth rings are visible in tree trunk cross sections, and are formed in seasonal environments as the wood is laid down faster in summer than winter. In years with better growing conditions (in cool locations this usually means warmer) tree rings are wider, and because trees can be very long-lived and wood is easily preserved, for example in bogs and lakes, this allows very long time-series to be established, and climatic conditions to be estimated from the ring widths.
-end-
The study was funded by the Norwegian Research Council and the Norwegian Directorate for Nature Management.

James D. M. Speed, Gunnar Austrheim, Alison J. Hester and Atle Mysterud (2011), 'Browsing interacts with climate to determine tree ring increment', doi: 10.1111/j.1365-2435.2011.01877.x, is published in Functional Ecology on 27 July 2011.

Wiley

Related Climate Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Climate Insights 2020: Climate opinions unchanged by pandemic, but increasingly entrenched
A new survey provides a snapshot of American opinion on climate change as the nation's public health, economy, and social identity are put to the test.

Climate action goes digital
More transparent and accessible to everyone: information and communication technologies bring opportunities for transforming traditional climate diplomacy.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

How aerosols affect our climate
Greenhouse gases may get more attention, but aerosols -- from car exhaust to volcanic eruptions -- also have a major impact on the Earth's climate.

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

How trees could save the climate
Around 0.9 billion hectares of land worldwide would be suitable for reforestation, which could ultimately capture two thirds of human-made carbon emissions.

Climate undermined by lobbying
For all the evidence that the benefits of reducing greenhouse gases outweigh the costs of regulation, disturbingly few domestic climate change policies have been enacted around the world so far.

Climate education for kids increases climate concerns for parents
A new study from North Carolina State University finds that educating children about climate change increases their parents' concerns about climate change.

Read More: Climate News and Climate Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.