What characteristics of urban soils are driving factors for flora and soil fauna abundance, diversity, and community composition?
Soils are a complex, dynamic resource consisting of minerals, organisms, plant roots, and pores. They can retain water in their pores for plants to use and they are a big part of the nutrient cycle, acting as a warehouse holding nutrients for plants to use. The properties of soil allow them to act as filters removing contaminants through chemical, biological, and physical processes. Soils are critical to human life. Unfortunately, urban soils are intensely modified and influenced by anthropogenic activity rendering them less effective at their “job”. By 2050, the world population will surpass 9 billion people. Over half of these people will be living in urban areas. How the continued pressure of anthropogenic stress is affecting soil properties and how these properties are affecting biological diversity are key questions to understand if we are to provide sustainable greenspace in an urban environment.
How was this research conducted?
Soil core samples were collected from vacant lots in Cleveland during the summers of 2014 and 2015. In those same lots, flora was characterized by identifying all the plants growing within the sampling area; plants dominant in the landscape were also recorded. Soil cores were brought to the lab to collect and identify organisms from each. Soil was then sieved to collect small, debris free, particle sizes. This soil was sent for nutrient and metal concentration analysis.
Results to date:
- Variation in community composition (flora and fauna combined) was observed among neighborhoods in 2014 but not 2015. In 2015 planting treatments were installed in half the lots and this disturbance may have affected sampling that year resulting in no variance observed.
- RDA ordination for fauna did not clearly cluster sites by neighborhood suggesting these sites are more homogenous than previously thought. RDA ordination for flora showed loose clustering of sites for 2014 but not 2015. The treatment installation may have affected this result.
- Soil nutrients did not impact fauna structure. Metal burdens did influence soil fauna but correlations could only be made to three taxa: Acari, Collembola, and Formicidae. Interestingly, fauna had more correlations to metals than to heavy metals.
- Floral community variance had inconsistent patterns being influenced by both nutrients and metals in 2014 but only metals in 2015. Flora had more correlations to heavy metals than metals. We are still working on understanding the importance of the relationships identified.
- Very little variance could be explained by either soil nutrients or metal burdens. Landscape analysis and modeling with additional environmental variables (precipitation and temperature) will be performed to try to explain more of the variance in community composition.
- We have shown that although community composition did vary among neighborhoods, the differences were inconsistent and did not fully agree with our hypothesis. It is possible that even with further analyses no strong dissimilarity will be found among the neighborhoods and that Cleveland falls under the urban homogenization hypothesis umbrella with all neighborhoods being more similar in physical structure and biodiversity than dissimilar.
What impact can this research have?
We are working to determine if ecosystem services provided by soil fauna are limited by heavy metal contamination. If so, this would have serious implications for urban farmers and gardeners. Ecosystem services provided by soil fauna include soil aeration, water infiltration, and nutrient cycling. Results will be shared with Extension and others consulting with urban growers who may be able to recommend of action for soil remediation to support the soil biological community.
This project was lead by Nicole Hoekstra. Nicole is a Research Assistant II in the Ag-Urban Landscape Ecology Lab at the Ohio State University. After getting out of the Navy, Nicole studied Molecular Ecology at Winthrop University.
“Each soil has had its own history. Like a river, a mountain, a forest, or any natural thing, its present condition is due to the influence of many things and events of the past.”
– Charles Kellogg, The Soils That Support Us, 1956
This material is based upon work supported by the National Science Foundation under Grant No. 1253197.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.