The Methods: Researchers started with old, grassy fields in Pennsylvania and then created four treatments. The four treatments were "mowed lawn", "bark mulch", "gravel mulch", and "unmowed old field". Reserchers set up the plots one year, and monitored the plots the two following years for a variety of soil characteristics.
The Results: Lawn soils and unmowed soils were relatively similar for most measured characteristics, although mowed lawns had more weeds and less carbon sequestration than unmowed fields. Lawns and unmowed plots were more acidic and dryer than mulched plots, but were cooler and had more soil microorganisms. When comparing the mulches, bark mulch was less basic, wetter, cooler, and more microbially active than gravel mulch. An earlier study by the same authors found that bark mulch plots have the lowest soil nitrogen, while vegetated plots are intermediate, and gravel mulch plots have the highest soil nitrogen.
The conclusions: The "best" ground cover to use is highly context dependent. Each cover type provides unique ecosystem services and disservices. Plants that are limited by water may prefer bark mulch, while plants that are limited by fertility may prefer gravel mulch, and plants that are limited by soil temperature may prefer vegetated ground.
Citation: Byrne, L.B., Bruns, M.A., and Kim, K.C., 2008. Ecosystem Properties of Urban Land Covers at the Aboveground–Belowground Interface. Ecosystems 11: 1065–1077
Available at: JSTOR
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