New method for rehabilitating damaged soil can help restore urban forests

Urban development often results in stripped and compacted soils that cannot sustainably support trees and landscapes and provide little in terms of environmental benefits. Soil Profile Rebuilding (SPR) is a cost-effective technique that can help rehabilitate these soils to provide documented increases in tree growth and ecosystem services such as carbon sequestration and stormwater management.

The effects of Soil Profile Rebuilding have been carefully evaluated during more than seven years of field research. The process was developed by a Virginia Tech research group led by Dr. Susan Day. Many people contributed to the creation of this specification and the evolution of the research including: Yujuan Chen, W. Lee Daniels, Roger Harris, Rachel Layman, Bill Mauzy, David, Mitchell, Kevin McGuire, Kaj Rolf, Brian Strahm, Abbey Wick, and P. Eric Wiseman.

Where can soil profile rebuilding be used?
This technique is intended to address soil compaction in a sustainable fashion, especially the subsurface compaction common to developed areas. It can be used where there are existing soils that have been compacted by construction, pavement, traffic, or similar activities. It is not appropriate to use within the root zone of established trees and it is not appropriate for remediating engineered soils such as structural soils. It can be used in tight spaces such as street medians or wide-open expanses such as large landscapes that may be planted with combinations of trees, shrubs, perennial beds, or turf. It is also appropriate for gardens and other uses in modified form (i.e., without the tree or shrub planting).

What benefits can soil profile rebuilding deliver?
The effects of soil profile rebuilding have been rigorously studied in fully randomized studies and are documented in numerous peer-reviewed journal articles. Response to any soil management is dependent upon context, so response will vary according to the environment, but can include:

  • Increased tree growth
  • Increased percolation of stormwater through the soil profile
  • Increased carbon storage in stable forms

What typically happens on an urban development site where the soil is NOT rehabilitated?

Typically – and this happens even when you have the best of intentions and high-quality soils – the topsoil gets scraped off, the land is graded and the slopes get altered to direct water away from any buildings. Often new topsoil will be brought in (although not always). If limestone gravel has been used in construction and mixed into the soil, this can also affect pH levels. This all results in very difficult conditions for plant material to grow.

Can SPR be used anywhere?

It can be done on most sites, although some are more suitable than others. If you have just a tiny planting pit, for example, this isn’t the ideal application. And of course, you can’t use it around existing trees.

We saw it done in Arlington, Virginia on a site where the soil was worse than that of our control plots. In Arlington they wanted to use it because they were digging up parts of the street and turning it into planting areas – so they knew the soil they were working in would be very compacted. This was a way for them to achieve a good planting condition much more cheaply, and not worry about sustainability issues that may result from hauling off the soil and bringing in new soil. The tree response was really strong.

Image from video by Vincent Verweij, Arlington County Forester.

See Soil Profile Rebuilding website, video, and specification download links.

See interview by Leda Marritz with Dr. Susan Day on Sustainable Cities Collective.

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