Implications of Precipitation, Warming, and Clipping for Grazing Resources in Canadian Prairies

Published in Agron. J. 106:33–42 (2014) doi:10.2134/agronj2013.0085 Copyright © 2014 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. The magnitude of climate change has been variable depending on location, with accelerated warming at high latitudes (Trenberth et al, 2007), including the Canadian prairies. Average temperatures in this region have increased 1.5°C in the last century, the largest temperature change across Canada (Zhang et al., 2000). Further increases up to 4.5°C are forecast for the Canadian prairies in the next 50 yr (Nyirfa and Harron, 2002). Precipitation trends with climate change are more diffi cult to assess (Christensen et al., 2007). Although precipitation is predicted to increase at high latitudes (Dore, 2005), observed increases have been lower in the prairies than in other parts of Canada (Zhang et al., 2000), and increased variability in precipitation has also been predicted, leading to drier periods (Sushama et al., 2010). Cattle grazing is a major economic activity on an estimated 13 million ha in the Canadian prairies (Vaisey and Strankman, 1999). Warming and altered precipitation have the potential to impact rangeland productivity (Izaurralde et al., 2011), with socioeconomic repercussions (Finger et al., 2010). Although several studies have evaluated the impact of warming on plant production, the results have been varied (Grime et al., 2000; Klein et al., 2007; Wu et al., 2011). Morgan et al. (2008) predicted that forage production in the Great Plains will increase with warming, and three meta-analyses of warming have concluded that plant growth will increase in grasslands (Rustad et al., 2001; Lin et al., 2010; Wu et al., 2011). Th ere is also evidence that productivity at northern latitudes is increasing due to climate change, although this trend is inconsistent across North America (Zhou et al., 2001). Warming can have negative eff ects on biomass, however, if plants are optimally adapted to their current (i.e., lower) temperature (King et al., 1995; Bertrand et al., 2008). Th e response of plant biomass to warming has also been shown to depend on other environmental variables, such as precipitation availability (Hoeppner and Dukes, 2012). Temperature aff ects plant biomass via both direct and indirect mechanisms, which can contribute to varied eff ects of warming on productivity (Shaver et al., 2000). For example, warming may decrease soil moisture (Kardol et al., 2010), in turn limiting plant biomass. Th e relationship between peak biomass and precipitation is generally positive (Sims and Singh, 1978; Wu et al., 2011), and on a continental scale, precipitation is considered the most important driver of grassland distribution and productivity (Milchunas et al., 1994; Knapp and Smith, 2001; Huston and Wolverton, 2009); however, some studies have found no relationship (Frank, 2007) or even a negative relationship (Gilgen and Buchmann, 2009) between biomass ABSTRACT