History of the Gatineau Hills Ecosystems Over the Past 1000 Years

History of the Gatineau Hills Ecosystems over the past 1000 years Konrad Gajewski & Karen Neil Laboratoire de climatologie et paléoclimatologie Laboratory for Paleoclimatology & Climatology Département de géographie / Department of Geography Coring lake and bog sediments Université d’Ottawa / University of Ottawa Pollen records extracted from lake sediments We have produced pollen records provide a history of the vegetation surrounding from two lakes in the area: Lab Noir, the lake. Pollen from the various trees, shrubs located near Ripon and Lac Brulé, and herbaceous plants is blown around by the near Notre-Dame-de-la-Salette wind, and therefore provides a regional picture and not far from the Black Mine. of the vegetation changes associated with past Although these are a distance from climate variability and disturbances such as fire Gatineau Park and Ottawa- or windstorms. These records provide a picture Gatineau, the inferences we make of the relative abundance, as some trees from these sites would also apply to produce a lot of pollen relative to their these areas. We are working in Lac abundance on the landscape (for example, Armida, near Wilson’s Corner, pine, oak), and other fewer pollen relative to where we are looking at the longer- their abundance (e.g., maple). However, we can term history of the vegetation. still see how the vegetation changed over the Finally, we sample many lakes in course of years to millennia. Schematic of the process the region to gain an understanding of pollen analysis. of the modern limnology and ecology of lakes in the region. Study sites in the Gatineau Hills Sampling varved sediments using a freezer-corer. Varves in lac Brulé sediments. Each couplet of dark and light layers represents one year of sediment accumulation. The pins delimit ten years. Schematic of how pollen is transported to a lake. Mean July Total annual Ragweed Maple Temperature Precipitation White Pine Hemlock Beech Alder Charcoal 2000 C 1900 The lake sediments also record the history fo the aquatic flora and 1800 B4 fauna. Fossils such as diatoms (aquatic algae), chironomids (non- 1700 biting midges) and cladocera (water fleas), for example, leave B3 1600 fossils in the lake sediments. We can therefore determine how past 1500 B2 climate changes and disturbances affected the aquatic 1400 B1 ecosystems. A preliminary diagram of the diatom succession in lac 1300 Brulé shows some changes assocaited with the transition from the Year AD 1200 Medieval Warm Period to the Little IceAge. 1100 1000 A Planktonic Benthic 900 800 700 600 16 18 19 225 275 325 0100140204002550016320204007140102003604803604806000600 16 18 19 240 290 340 AulocoseiraCyclotella TOTAL bodanicaCyclotella var. intermediamichiganianaCyclotella rossiCyclotella stelligera AsterionellaFragilaria formosa undiff.UndistinguishableAchnanthesAchnanthidium TOTALBrachysiraCymbella TOTAL TOTALEpithemia TOTALNavicula TOTALNitzschia TOTAL TOTAL 3 2 -2 -1 °C mm % x10µ m cm yr 2000 The shorter record of each pair is from Lac Noir and the longer from Lac Brulé. The zones, A-C on the right 1900 1800 correspond to different periods: A is the Medieval Warm Period, B3 & B4 are the Little Ice Age and C is the 1700 European settlement. Zones B2 & B3 are the transition from the Medieval Warm Period to the Little Ice Age. 1600 Notice how the records from the two sites closely resemble each other, except for that of hemlock. We think a 1500 1400 fire may have caused a reduction in hemlock in the region around Lac Brulé, but not around Lac Noir around 1300 Year AD AD1350. Then, around AD1600, a climate deterioration caused the entire area to change slightly in vegetation 1200 composition, as white pine increased and hardwoods such as beech and maple decreased. During the Little 1100 1000 Ice Age, alder and other indicators of disturbance also increased in abundance. Finally in the past 100 years, 900 the agriculture associated with European settlement increased the abundance of weeds such as ragweed. 800 700 Note the increase in charcoal associated with the arrival of European farming and other activities, as well as 10 10 20 30 10 20 20 20 40 60 80 20 20 10 10 10 10 10 10 10 10 indication of a fire around Lac Brulé at the end of ZoneA. Percentage (%) The first columns show the temperature and precipitation reconstructed using these pollen records. References (copies available on request) Acknowledgements Lafontaine-Boyer, K and K Gajewski. 2014. Vegetation dynamics in relation to late-Holocene climate variability and disturbance, Outaouais Québec, Canada. Holocene 24: 1515-1526. Funded by an NSERC DIscovery Grant. We would like to Paquette, N and K Gajewski. 2013. Climatic change causes abrupt changes in forest composition, inferred from a thank Nathalie Paquette, Karelle Lafontaine-Boyer and high-resolution pollen record, Southwestern Quebec, Canada. Quaternary Science Reviews 75: 169-180. Emily Cooper for access to the results of their theses, and Cooper, E. 2015. Cladocera communities of Lac Brulé in response to climatic variability of the past 1200 yearsMSc the various landowners for access to the lakes of the areas. thesis: Ottawa-Carleton Institute of Biology, University of Ottawa..

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