Ants can be the heroes of forest regeneration

A forest isn’t just a bunch of trees. Among the branches, roots, and soils are a network of mutualistic interactions. Organisms provide services for others and take payment for their work. But how well do these interactions recover from human-caused disturbances? A new study by Carmela Buono and colleagues has looked at the resilience of animal-mediated seed dispersal in some North American forests that have regenerated from agricultural clearing.

More than 95% of New York state forests — including the Binghamton University Nature Preserve — are secondary forests, which sprung up on land once cleared for agriculture. While parts of these regenerated forests, such as the overstory, have recovered well, they are missing other aspects of biodiversity — particularly when it comes to understory plants such as native wildflowers.

One reason the plants might be missing is that their seed carriers are missing. Many plant species rely on a mutual relationship with ants to disperse their seeds. In fact, northeastern North America is one of the major hotspots of ant-plant mutualism. However, it also happens in parts of Europe, Australia, South Africa and northeastern Asia, Buono said in a press release.

“These plants evolved with seeds that have an appendage rich in fats attached to them, and that’s very attractive to woodland ants,” she said. “Ants need fats just as much as protein and sugar, and it’s hard to find foods rich in fats in the forest.”

The study focused on ants in the genus Aphaenogaster, the Woodland Ant. Aphaenogaster is a keystone seed disperser for over one-third of the understorey herbaceous community. Woodland ants take the seeds with fatty rewards back to their nests, protecting them from consumption by rodents and other organisms. Once the fatty appendages are consumed, the ants — in a kind of insect housekeeping — remove the seeds from the nest, dispersing them far from the original plant. It’s a mutually beneficial arrangement.

The ecologists found seed dispersal was lower and more variable in secondary forests than in remnant forests. The most significant influence in seed removal was the abundance of mutualists. The big problem appears to be competition with invasive slugs, which are found mainly in the regenerated woodlands and also have a taste for fatty seed appendages. Slugs often prefer forest edges, and secondary forests may be located closer to habitats that slugs prefer, such as open meadows or active farms, Buono said.

The findings suggest that functional resilience to disturbance is variable and that understanding the effect of disturbances on mutualistic interactions is critical to understanding the capacity for diversity resiliency. This work provides important insights into the dynamics of mutualistic interactions and how the resilience of critical ecosystem functions can be affected.

Buono and colleagues conclude that their work has implications for conservation and restoration. In their article, they write:

“First, we emphasize the importance of preserving remaining remnant forest ecosystems to provide critical source populations of plants and ants for recovery. Second, given that not all secondary forests are resilient to historical forest disturbance suggests that forest patches with intact seed dispersal interactions might be prioritized for potential locations of active restoration of understory plants, or there may need to be efforts to augment or enhance this interaction in some forests. While the presence of seed dispersal function and mutualistic ants does not directly determine plant community resilience, their documented importance on understory plant populations and communities means that maintenance of this function will be essential to conserving and facilitating the recovery of understory plant communities.”

READ THE ARTICLE

Buono, C.M., Lofaso, J., Smisko, W., Gerth, C., Santare, J. and Prior, K.M. (2023) “Historical forest disturbance results in variation in functional resilience of seed dispersal mutualisms,” Ecology, p. e3978. Available at: https://doi.org/10.1002/ecy.3978.