November 2024: What Role Does the Seed Bank Play in Riparian Restoration?

Riparian areas are those found along bodies of water and are composed of cottonwoods, willows, dogwoods and other water-loving grasses, wildflowers, trees and shrubs. These ecosystems are some of the most commonly degraded environments, especially in the intermountain West where mining and dams have altered the landscape. Due to their proximity to streams and rivers, riparian ecosystems experience variable water flows, logjams, flooding and other disturbances. A review of various scientific studies concluded that ecosystems that are adapted to frequent disturbances tend to have a robust and diverse seed bank, a naturally occurring reservoir of local seed that has been stored in the soil.

This study in Sweden aimed to investigate the role riparian seed banks have in restoration success. It has been shown that seed dispersal is a prominent limiting factor in the success of restoring biodiversity in riparian systems. While studies have shown that water-transported seed is important in restoration, the researchers wanted to assess if dispersal is limited by the structural complexity and water flow in streams and rivers. They also wanted to understand how viable the riparian seed bank is as a source for vegetative recovery as it is not impacted by the physical structure of the system. 

The researchers measured multiple variables including seed dispersal at different flows, complexity of the landscape and how it affects seed dispersal, and most importantly, the composition of the seed bank and how it compared to species composition of restored areas. 

The researchers found conclusive evidence that seed is dispersed more evenly across the landscape during low water flow, and water bodies with more complexity (pools, boulders,  logjams) disperse more seed. These findings are supported by similar studies. They also found a poor seedbank and a low similarity with the surrounding riparian vegetation. 

The researchers concluded that the often hands-off approach to revegetating restored riparian systems may limit success due to the weak seed bank and importance of stream structural complexity in seed dispersal. Instead, they suggest that focusing on active dispersal of seed may be more critical in riparian restoration in high elevation landscapes.