Large grazing animals always did and still do play an important role in the ecology of grasslands.
Native grasses and forbs on grasslands and rangelands across the globe evolved in the presence of large herds of wild ungulates like pronghorn, elk, deer and bison.
Animal impact, such as hoof action, from large grazers helps to increase water and nutrient cycling. In turn, that has significant effects on forage production, species composition of plant communities and forage quality
To put it simply, grass needs grazing animals; grazing animals need grass.
In today's world, the wild ungulates of the past have largely been replaced with cattle. While these domesticated bovines may differ slightly from their wild counterparts, they are still very much an important component of grassland ecosystems, both ecologically and economically.
Because of this importance it is vital we consider how environmental factors such as climate change could affect this symbiotic relationship. A recent study out of Kansas State University conducted by Joseph M. Craine and published in PLOS ONE seeks to understand the effects climate change could cause in grassland ecosystems by examining the long-term climate sensitivity of grazer performance. PLOS ONE is an open-access peer-reviewed scientific journal published by the Public Library of Science.
To do this, a dataset of over 290,000 body masses of bison distributed across 22 herds in the US was compiled. Herds were located across a bioclimatic range of approximately 11°C mean annual temperature and 600 mm of mean annual precipitation.
Craine specifically chose bison because of the restricted genetic differentiation of the herds in hopes of limiting confoundedness between bison genetics and the climate gradients. His study examined patterns of bison body mass among sites, age classes and sexes with respect to differences in geographic patterns of climate and inter-annual variation in climate.
Results indicated that while short-term effects of climate variability are dependent on precipitation, grazers will be negatively affected by sustained hotter, drier conditions. This would mainly be caused by predicted reductions in nitrogen availability in grasslands and decreased forage quality.
Geographic patterns of bison mass suggested that increases in mean MAT could lead to a decrease in body mass of grazing animals. In the dataset analyzed, for every 1 degree C increase MAT, bison mass declined by approximately 13 kg for males and 8.6 kg for females. In addition to temperature having influence on lower bison weights, bison in arid regions tended to be lighter in body mass than those in wetter areas.
These findings suggest climate change has the potential to cause nutritional stress on bison and ultimately reduce their body size over time. This reduction in weight gains would also lead to reductions in economic returns as well.
If the reductions in weight gains in bison transfer to cattle, the economic impact of warming alone could be large. Given the fact there are more than 100 million cattle in North America, the ecological and economic effects of climate change for cattle would be many times that of bison, whose population is far less at only about 500,000 head. Costs to US cattle producers of 1 degree C warming could be in the $1 billion range, either through direct losses in weight gain or the need to supplement to compensate for reduced forage quality.
So what does all this mean for those in the cattle business?
It's hard to say at this point. This is only one study. Hopefully similar studies will be conducted directly with cattle. The important thing is someone is considering the "what ifs."
Factors such as cattle breed, genetic selection, cow size and feed efficiency were not even considered. Neither were specifics on forage species or nutritive value discussed in detail.
With more than 587 million acres of permanent grassland, pasture and rangeland in use for livestock grazing across the US, it seems important we understand the potential detriment of climate change. It appears to me it is vital to the future of our industry.