Yellowstone, established in 1872 as the world’s first national park, has struggled for over a century with the question ‘What is natural’? Without a management philosophy or debate to guide early actions, all of the large carnivores, except for bears, were eliminated through broad-scale predator control. Subsequently, elk numbers burgeoned, and by the early 1930s artificial control of elk was initiated lasting until 1968. Through this time and before, the impact of elk was debated. Despite this, it was widely agreed that elk were suppressing deciduous woody plant regeneration, and possibly impacting grassland dynamics and changing ecosystem processes and food web structure. This debate led to policy changes that culminated in wolf reintroduction in the mid-1990s. Around that time, willow, then aspen began to grow taller, sparking a debate as to why after decades of suppression. Most research suggested wolf recovery was the cause, yet data for a mechanism were sparse, and distinguishing between behavioral changes in elk foraging and just fewer elk confounded conclusions. Some, primarily Park Service researchers, disagreed; woody vegetation response was not due to wolf-elk relationships but changes in climate. Further, wolves were not the only carnivore that recovered, cougars reestablished naturally and grizzly bear numbers increased.
Results/Conclusions
Post-reintroduction wolf populations increased rapidly reaching some of the highest annual densities in North America. Simultaneously, cougars recovered through immigration and grizzly bear numbers increased (black bear numbers were unknown) and both populations probably reached saturation. Taken together, northern Yellowstone’s restored large carnivore community was the richest in park history and one of the richest in North America. This recovery was fueled by a large elk population, but with restored carnivores they declined, the cause of which is still debated. Besides native carnivores, human take of female elk outside Yellowstone remained high, and primarily took prime-aged females with high reproductive value. Only offtake of humans and wolves is known, leaving cougars and bears some unknown portion and unclear collective impact. Further, drought and and vegetation may have played a role. Since about 2008, carnivore and elk populations have stabilized - a seeming equilibrium - with the cessation of winter die-offs, a characteristic of every winter pre-carnivore recovery. An interesting question is how long will this apparent stability last? Less elk browsing has been a factor in woody vegetation recovery, and led to, for the few taxa studied (beavers and songbirds), increased diversity, population size, and positive feedbacks.