Climate change, trees and Victoria Park. | Wat On Earth

Elms in Victoria Park, Kitchener in 1897. The trees in the photograph became waterlogged and died due to the rise in the watertable due to the creation of Victoria Park (Photograph courtesy of Joseph Schneider House, Kitchener.)

In 1968 an elm tree was cut down in Victoria Park because it was infected with Dutch Elm Disease. A slice of this tree was donated to the Biology-Earth Sciences Museum at the University of Waterloo. The elm has been analysed by the counting and measurement of tree-rings, and examination of oxygen and hydrogen isotopes to reveal a variety of information about the local climate dating back to 1736. The information gathered from the elm tree was also compared with a white pine log from a buried corduroy road found near Bleams Road, Kitchener, which lived from about 1650 to 1810 and one of the oldest maple trees in Waterloo County (the Merlau Maple), which lived from about 1610 to 1990. These three trees have provided an opportunity to compare the signature of recent climate changes in different parts of the county. Samples of wood, spanning ten-year intervals, were analysed for the isotopic ratios of oxygen and hydrogen to reconstruct changing temperature and humidity. Tree-ring widths also vary as the tree's growth rate responds to climate conditions.

oxygen isotope estimates of air moisture

Today, the climate of southwestern Ontario is humid with precipitation in all months, resulting in cold snowy winters and warm humid summers. During the end of the nineteenth century the region experienced lower annual temperatures and precipitation amounts. The Victoria Park elm grew in a discharge zone (where the groundwater moves towards the stream). The isotope study noted that the elm gave a predictable response, according to available instrumental and historical climate records. The Merlau Maple, on the other hand, was situated in a groundwater recharge zone (where water percolates into a sand or gravel aquifer), in an upland area surrounded by heavy bush. This setting masked some of the responses to climate noted in the Victoria Park elm, in part because of direct input from snowmelt, which affected the oxygen and hydrogen isotope ratios in the water used by the tree.

The Victoria Park elm was part of the natural forest prior to settlement. The tree-ring width shows marked changes in growth rate that match up with climatic fluctuations. Slower growth occurred during the early 1800s because of competition with other vegetation and waterlogged soil conditions brought about by moist climate. Water stress, this time caused by dry conditions, also led to slow growth during the late 1800s. Lake construction during the summer of 1895 with the establishment of Victoria Park may have had an influence as well; some of the neighbouring trees died at this time. The early 20th century spurt of growth corresponds to the subsequent clearing of competing vegetation and stabilization of the groundwater table. The return to average growth rates in the mid-1900s suggests that closure of the canopy had re-occurred, with renewed competition from neighbouring trees.

The results of studying the trees points out the interesting relationship between climate and the history of local settlement and development. Early rural settlement occurred during climatic conditions favorable to agricultural development. Firm establishment of an agricultural base prior to the climatic deterioration of the late 1800s may have played an important role in supporting industrialization and urbanization that carried on into the late 20th century.

three-ring indexes from Niagara Encarpment compared to Victoria Park elm and Bleams Road white pine

Among other points of interest, the Merlau Maple clearly shows one very poorly developed growth ring corresponding to the year 1816. This ring grew during the bad summer following the eruption of Tambora volcano on Sumbawa Island, east of Java. This year became known as "the year without summer," marked by prolonged cold weather, which significantly shortened the growing season, and long twilights and spectacular sunsets caused by the volcanic dust in the atmosphere. Evidence for this event in the Victoria Park elm is less clear, since growth was already suppressed in the early 1800s by other factors.

Isotope studies were carried out by William Buhay and Thomas Edwards of the Department of Earth Sciences, University of Waterloo. Tree-ring measurements were made by Roger Suffling, School of Urban and Regional Planning, University of Waterloo.