Project Report
Project Lead/Researchers:
William “Billy” Beck, associate professor, Natural Resource Ecology and Management/forestry specialist, Iowa State University Extension and Outreach forestry specialist
Katherine Kral-O’Brien, Assistant professor, Natural Resource Ecology and Management
A recent Leopold Center for Sustainable Agriculture (LCSA) award seeks to quantify ecosystem goods and services of saturated riparian forest buffers (SRFB) – a novel edge-of-field conservation practice with a significant perennial woody vegetation component (i.e., trees!). The award builds upon a previous LCSA effort that established a 3.5-acre research, teaching, and extension SRFB in central Iowa in 2021.
The practice has potential to provide farmers with a multitude of tangible benefits in addition to water quality enhancement (e.g., fuelwood, wildlife habitat), with cost-share available through the Natural Resources Conservation Service (NRCS) code CP-22S. The practice has seen low adoption rates, however, which may be partially driven by a lack of knowledge among farmers regarding the planting and maintenance of trees, and concerns over establishing woody vegetation adjacent to crop fields and tile lines (Iowa Learning Farms Farmer Leadership Circle, 2021). To highlight tangible on-farm benefits of the practice, researchers are quantifying nitrate removal (primary focus of the practice) along with a range of “compound benefits” such as tree growth (i.e., wood production) and pollinator use. To address concerns over trees adjacent to tile lines, annual “scoping” of tiles is being undertaken to quantify woody root intrusion – which will be correlated with water table depth fluctuations and tree species treatments (Photo 1).
Nitrate Removal
Over the 4-year life of the SRFB, bi-weekly groundwater nitrate sampling indicates a mean nitrate concentration reduction of 66% from incoming tile water to the edge of the 50’ buffer. Individual tree species treatment blocks show an interesting preliminary trend in performance, with swamp white oak reducing nitrate concentration by 84%, hickory/pecan by 72%, and sycamore by 42%.
Pollinator Use
Annual pollinator presence surveys were initiated in 2024, which found a range of honeybee, hoverfly, and butterfly species present – notably black swallowtail, pearl crescent, and monarch. Plant-pollinator interactions are expected to increase as the native tree, shrub, and forb components mature.
Root Intrusion
The lateral tile was first “scoped” in fall 2024, to assess presence of in-tile roots associated with tree species treatments (Photo 1). In-tile rooting was rare overall, regardless of tree species treatment. When roots were encountered, the vast majority appeared to be associated with non-woody vegetation (Photo 2). Roots of woody vegetation were rare, and no observable differences in root prevalence were detected between tree species treatments – which was surprising given the rapid growth of sycamore (mean height of 8.8’) versus swamp white oak and hickory/pecan (3.7’ and 2.2’, respectively) (Photo 3).
Learn More about Trees and Tiles
Numerous extension events have centered on the SRFB site to date. To take a deeper dive, check out the related 2022 Iowa Learning Farms (ILF) virtual field day.