Ants play a significant role in forest regeneration, according to a recent study by Binghamton University, State University of New York. Take a walk through an old-growth forest in early spring and you’ll be dazzled by wildflowers whose jewel-like tones shine from the forest floor.
But in newer forests, spring ephemerals such as trillium, wild ginger, violets and bloodroot are fewer. The reason may be some less flamboyant inhabitants of the forest: Aphaenogaster sp. or forest ant.
“A lot of people haven’t heard of them, but they’re the powerhouse of moving seeds and they’re called ‘keystone dispersers,'” explained Carmela Buono, a doctoral student in biological sciences at Binghamton University.
More than 95% of New York State’s forests—including the Binghamton University Nature Preserve—are secondary forests that have grown on land that has been cleared for agriculture. While parts of these restored forests, such as overgrowth, have recovered well, other aspects of biodiversity are lacking – particularly in understory plants such as native wildflowers.
Many plant species rely on a mutualistic relationship with ants to disperse their seeds. In fact, northeastern North America is one of the main hotbeds of the ant-plant mutualism, although it also occurs in parts of Europe, Australia, South Africa and Northeast Asia, Buono said.
“These plants have evolved with seeds that have a fat-rich appendage, and that’s very attractive to forest ants,” she said. “Ants need fat as well as protein and sugar, and it’s hard to find fat-rich foods in the forest.”
Glossy black and medium-sized forest ants are a native species that live in logs, forest leaves and under rocks. Forest ants carry seeds with fatty rewards back to their nests, protecting them from being eaten by rodents and other organisms. Once the fat appendages are consumed, the ants—in a kind of insect scavenging—remove the seeds from the nest and scatter them far from the original plant. It’s a win-win arrangement.
“There are so many interesting, complex parts to this interaction depending on the types of seeds the ants prefer, so you can get this beautiful mixing of flower species in forests,” Buono said.
How are old growth forests different?
Old-growth forests are a rare treasure that plays an important role in maintaining species diversity, Buono pointed out. Pockets of ancient forest cover in the Northeast remain in some areas, often on land deemed unsuitable for agriculture.
It differs from secondary forests literally from the ground. Land previously cleared for agriculture is flat, while old-growth forests have a “pit and mound” topography. “It’s uneven, because of years and years of trees falling,” Buono explained.
Pits are left from the roots of uprooted trees pulled from the ground, while mounds are created from excavated root and soil. The species within the two forest types are also different, with rapid colonizers moving into younger forests. An established forest often contains a greater number of shade-tolerant plants in the understory.
There are slightly fewer forest ants in secondary forests, possibly due to their displacement during years of agricultural use. Differences in forest canopies and the amount of light reaching the forest floor could also play a role, but that remains to be explored, Buono said.
The real problem seems to be competition with invasive slugs, which are mostly found in regenerated forests and also have a taste for fat seed appendages. Slugs often prefer forest edges, and secondary forests can be located closer to habitats that slugs prefer, such as open grasslands or active farms, Buono said.
To restore newer forests to a healthier state, we need to look beyond the trees to the diversity of insects, which scientists say play a vital role in the forest ecosystem. “Ants are beneficial. They’re not as charismatic as butterflies or bees that help pollinate flowers, but they’re just as important,” Buono said.
