A Striking Profile Surveying soils Knowledge in Restoration Science
C.C. Rhoades*, S.P. Miller, M.A. Callaham, Jr., L. Heneghan
USFS Rocky Mountain Research Station; Fort Collins, CO; crhoades@fs.fed.us
Soils knowledge occupies a central role in restoration science. If restoration
represents an “acid test” for ecology, what is the pH (and relevance) of soils knowledge
to restoration pursuits?
To address this question, we characterized how soils
information appears in peer-reviewed restoration literature. Our survey was based on
manipulative experiments and case studies published in the journal Restoration Ecology.
First, a broad overview found that specific soils terminology appeared in the titles of a
third of all empirical restoration studies published in the journal. Then, to categorize
how soils knowledge benefits restoration, we sorted information by restoration 1)
objectives, 2) site conditions, 3) soil treatments and 4) soil responses. Our review
evaluated articles from one-quarter (one issue per volume; n ~ 150 articles) of studies
published since the inception of Restoration Ecology in 1993.
Restoration Objectives
Frequency
0.8
Soil-related objectives most often targeted the
influence of soil manipulations on revegetation.
Assessing site degradation and tracking recovery
of nutrient capital or biogeochemical processes
following restoration activities were also common.
Concerns regarding the challenge of achieving
nutrient conditions that favor native species but
preclude dominance by weedy or non-native invasive
species motivated many studies.
This goal
characterized restoration initiating both from
infertile (e.g., mine spoils) and nutrient enriched
land (e.g., former agricultural fields).
(Soil Terminology in titles)
0.6
0.4
0.2
0.0
1993 1995 1997 1999 2001 2003 2005
16
12
10
8
6
4
Occurrences
10
8
6
4
2
0
Restoration science frequently assesses soil amendments aimed at enhancing establishment
success and plant growth. Inorganic fertilizer was the most prevalent soil treatment both at
the field and individual plant scales; mulch and compost types were also used to increase soil
fertility. Mycorrhizal inoculation of seedlings via spore or topsoil additions was the secondmost popular soil amendment. Salvage, storage and application of topsoil to field studies were
typical for revegetating mine lands, road corridors and burned areas. Soil stripping and sod
cutting were practiced to treat nutrient-enriched agricultural soils and eutrophied wetlands.
Carbon addition, either as sawdust and sucrose, was employed to reduce plant available soil
nitrogen and favor native species. Prescribed burning, herbicide application and grazing were
practices that were frequently conducted prior to establishing experimental trials, but were
rarely assessed experimentally; these practices are known to alter soil processes and may
influence study results.
Soil Responses
Edaphic Responses
10
Total soil nitrogen and organic matter stocks, followed by indices of plant nutrient availability
were measured most frequently in Restoration Ecology articles. A wide variety of Invertebrate
soil fauna were utilized as bioindicators to assess recovery of aboveground structure and
habitat. In contrast, edaphic change associated with faunal activity was scarce. Response of
soil chemistry, water relations, microbial activity and fungal symbionts were equally-well
represented.
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Invertebrate
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3.0
Occurrences
12
Soil Treatments
15
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Restoration Science relies on a broad variety of soils knowledge. Most reported soil attributes
responded to ecosystem changes that occurred within a few years of initiating restoration
treatments;
a limited number of studies documented pedogenic development (i.e. horizon
formation) in response to SOM and nutrient accumulation, chemical leaching and hydrologic
fluctuations that occurred over decades.
The resolution of soil classification included in many studies (i.e., USDA Soil Taxonomy soil series)
may overlook important fine-scale spatial variability. Greater detail regarding soil heterogeneity,
such as that occurring along topographic gradients and across habitat boundaries, can assist in
the design of restored ecosystems that closely mimic the belowground function and structure
of reference areas.
1.0
po
Digging Deeper …
Research conclusions often invoked unmeasured soil responses to restoration treatments,
climate fluctuation, historic disturbance (e.g.,herbivory, tillage) or species effects (e.g., shrub, Nfixer encroachment) to explain findings that could not be attributed to experimental treatments.
Explicit consideration of previous land-use and the consequences of herbicides, fire and grazing
on soil processes should lead to more effective restoration efforts.
2.5
th
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14
Soil-Related
Objectives
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Occurrences
A variety of edaphic information was commonly
included as part of pre-restoration site assessment.
Candidate and reference site comparisons were a
typical index of soil degradation used both to
identify obstacles to restoration and to define
baseline conditions for monitoring project
success. The most frequent form of soil
degradation was nutrient enrichment of former
agricultural soils and other sites affected by
nutrient loads in atmospheric deposition, runoff or
groundwater.
Soil Treatments
14
Site Conditions
18
Occurrences
Title Search
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Restoration Science currently presents soil knowledge in a piecemeal fashion, fragmented along
disciplinary lines (e.g. nutrient, biotic, hydrologic). Researchers aiming to promote the relevance
of soil science to ecosystem Restoration must highlight cases where integrated assessment of
below-ground processes (e.g. Spatially or disciplinarily) yielded practical knowledge that
resulted in successful restoration manipulations or monitoring.