A Cautionary Tale of Birds and Their Trees
By Michelle Werts
Which came first the bird or the tree?
Well, I can’t really answer that question exactly without getting into a lot of complicated — and potentially controversial — details, but I can tell you that the two are intimately connected in ecosystems around the world.
A study published on Friday in Science reveals that large-billed bird populations, specifically the colorful toucan, have severely declined in Brazil’s tropical forests due to deforestation. Something else has disappeared at the same time: large seeds from the forest’s dominant palm tree, the jucara (Euterpe edulis). In their new study, researchers from Brazil’s Sao Paulo State University posit that the two are intrinsically connected, and the result will be a significant evolutionary change for the jucara in the next 100 years — an extremely fast timetable for an evolutionary change. And it all comes back to biology and reproduction.
In order to reproduce, Brazil’s palm trees rely on the rainforest’s bird species to crack and eat their seeds, eventually defecating them in suitable growing locations, where the seeds can take root and sprout new jucara. The jucara, though, produce a range of seed sizes with the largest getting up to 14 mm in size — too large for tropical thrushes, but no problem for the big-billed toucan. Without the massive beaks eating the massive seeds, though, the researchers have observed that the number of small-seed-producing jucara are on the rise, while the big-seed-producing ones aren’t regenerating. While a few millimeters in seed size doesn’t seem like it would matter much, it could mean life or death for the trees in periods of drought, as the smaller seeds hold less water and are more likely to whither during extended dry periods. Hence, the scientists’ prediction of an evolutionary change for the jucara with its big-seeded trees disappearing at minimum, while its small-seed-bearing brethren are potentially not far behind because of their weaker seeds.
The scientists caution that this is a tale that might end up repeating itself around the world thanks to migrations related to climate change. In fact, there are concerns that something similar will happen in the West to another bird and tree pairing.
In the forests of the Rocky Mountains, Clark’s nutcrackers and whitebark pines are estimated to have lived side by side for more than 1.8 million years. The whitebark pine produces large, calorie-rich seeds that the nutcracker feasts upon. As discussed in our web-exclusive feature “Importance of Whitebark Pines and Clark’s Nutcrackers in Western Ecosystems,” in a single year, a single Clark’s nutcracker can squirrel away 98,000 seeds to secret caches, many of them underground and many of them never to be recovered by the bird, which means new whitebark pines. Together, the nutcracker and the pine create an endless reproduction cycle — one that’s being threatened.
Whitebark pine is on the defensive, fighting a battle — and often losing — against white pine blister rust, mountain pine beetles and climate change. As a result, there are anecdotal reports of fewer Clark’s nutcrackers in Montana and Washington. With only two species — Clark’s nutcracker and red squirrels — known to eat and store whitebark pine seeds in a way that allows them to germinate, if the nutcracker goes, things don’t look good for the pine.
More bad news is that the nutcracker isn’t the only species to rely on whitebark pine seeds for sustenance, as more than 110 species have the seed in their diet, including the federally listed threatened grizzly bear. Then, there is the whitebark pine’s role as a keystone and foundation species, due to its role in controlling snowpacks and providing shelter for other species of plants and trees. Yeah, it’s scary, which is why our Endangered Western Forests initiative is working with the best scientists to develop management plans to help the pine and all the critters who love it, as we want to see Clark’s nutcrackers and whitebark pines grace the Rockies for generations to come.