Long-Term Climate Sensitivity of Grazer Performance: A Cross-Site Study

Joseph M Craine

doi:10.1371/journal.pone.0067065

Abstract

Climate change will affect grasslands in a number of ways, but the consequences of a warmer, drier world for grazers is uncertain. Predicting future grazer performance is complex since climate change affects both the quantity and quality of forage through a combination of processes that occur over a range of time scales. To better predict the consequences of climate change for grazer performance, a dataset was compiled of over a quarter million bison weights distributed across 22 US herds that span a large range of climates. Patterns of bison body mass among sites, age classes, and sexes were analyzed with respect to differences in geographic patterns of climate and interannual variation in climate. While short-term effects of climate variability are likely to depend on the magnitude and timing of precipitation during the year, grazers will be negatively affected by sustained hotter, drier conditions most likely associated with reductions in forage quality. Short-term, little effect of high temperatures on bison performance is observed, which suggests that the long-term effects of higher temperatures are likely to accrue over time as nitrogen availability in grasslands is reduced and forage quality declines. If relationships observed for bison are general for cattle, the economic consequences of higher temperatures due to decreased weight gain in US cattle could be on the order of US$1B per 1°C increase in temperature. Long-term monitoring of forage quality as well as native and domesticated grazer performance is recommended to better understand climate change effects on grazers.

Highlights

Over the coming century, mean annual temperatures are predicted to increase globally by 2–7uC while regions such as the North American Great Plains may experience increased or decreased precipitation [1,2]
The strong geographic patterns of bison mass parallel the changes in grass nutritional quality that occur across North American grasslands that are grazed by cattle [4,32]
There is the potential that the relationships between climate and bison mass are not caused by climate and instead are influenced by factors that happen to be correlated with climate

Summary

Introduction

Mean annual temperatures are predicted to increase globally by 2–7uC while regions such as the North American Great Plains may experience increased or decreased precipitation [1,2]. Climate change is likely to affect the growth and reproduction of domestic grazers like cattle as well as native grazers such as bison in North America due in part to the effects of climate on forage quantity and quality [3,4]. Because of their pivotal role in grassland function [5,6,7,8], changes in the performance and ecology of grazers would likely have substantial effects on the functioning of grasslands, and have the potential to incur substantial economic costs. The fundamental differences in grazed and ungrazed grasslands weaken predictions regarding the consequences of climate change for grazers from experiments without them

Methods

Results

Conclusion