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Long-term redevelopment of resource islands
in shrublands of the Great Basin, USA
LESLEY R. MORRIS,
1,
THOMAS A. MONACO,
1
ROBERT BLANK,
2
AND ROGER L. SHELEY
3
1
United States Department of Agriculture, Agricultural Research Service, Forage and Range Research Laboratory,
Utah State University, Logan, Utah 84322 USA
2
United States Department of Agriculture, Agricultural Research Service, Great Basin Rangeland Research Unit,
Reno, Nevada 89512 USA
3
United States Department of Agriculture, Agricultural Research Service, Range and Meadow Forage Management Research,
Burns, Oregon 97720 USA
Citation: Morris, L. R., T. A. Monaco, R. Blank, and R. L. Sheley. 2013. Long-term redevelopment of resource islands in
shrublands of the Great Basin, USA. Ecosphere 4(1):12. http://dx.doi.org/10.1890/ES12-00130.1
Abstract. Soil resource availability in semi-arid and arid shrubland ecosystems is highly heterogeneous
and includes patterns of accumulation primarily beneath shrubs as opposed to shrub interspaces. These
resource islands contribute to ecosystem resilience after natural disturbances such as fire, yet very little is
known regarding their redevelopment following soil disturbance and shrub re-colonization. Cultivation
involves the removal of native vegetation and mixing of soils both vertically and horizontally. The old
fields in this study offered a unique look at the long-term redevelopment of resource islands under shrubs
where cultivation was abandoned nearly a century ago. Using adjacent pairs of previously cultivated and
native shrubland from three soil series, we sampled surface soils (0–5 cm) in microsites under shrubs and
in the interspaces between them to examine if the soil fertility in old fields (C, N, P, Ca, Mg, K) had regained
similar microsite patchiness to the native shrubland, if the values of each soil fertility measure in old fields
were different from native shrubland, and if the overall microsite fertility under shrubs in old fields was
different from non-disturbed microsites. We found that while most of the resource island patterning had
redeveloped, the content of each fertility measure had not recovered to pre-disturbance levels. Further, the
recovery was different between the soil series and between sites with different dominant shrub species.
There were also differences between sites within the same soil series, suggesting that historical cultivation
practices may influence resource island recovery in multiple ways. Overall, under-shrub microsite fertility
in previously cultivated areas was distinct from comparable under-shrub microsites in native areas in two
out of the three soil series. These findings suggest that while patterning may redevelop within 90 years, it
may take over a century for resource island fertility to fully re-establish in some formerly cultivated soils.
Key words: Artemisia nova;Artemisia tridentata; coppice dunes; ex-arable fields; islands of fertility; land-use legacies; old
fields; soil heterogeneity.
Received 8 May 2012; revised 26 September 2012; accepted 27 September 2012; final version received 3 January 2013;
published 21 January 2013. Corresponding Editor: D. P. C. Peters.
Copyright: Ó2013 Morris et al. This is an open-access article distributed under the terms of the Creative Commons
Attribution License, which permits restricted use, distribution, and reproduction in any medium, provided the original
author and sources are credited.
E-mail: LesleyRMorris@gmail.com
INTRODUCTION
Resource islands, also known as ‘‘fertile is-
lands’’ or ‘‘coppice dunes,’’ are formed through
hydrological and aeolian processes, which redis-
tribute and deposit sediments, leading to an
accumulation of nutrients under woody species
(Schlesinger et al. 1990, Ravi et al. 2007). Plant-
soil and ecogeomorphic feedbacks also contrib-
ute to the formation and maintenance of resource
vwww.esajournals.org 1January 2013 vVolume 4(1) vArticle 12
islands, which may assist in the perpetuation of
woody vegetation (Charley and West 1975,
Doescher et al. 1984, Schlesinger et al. 1990, Stavi
et al. 2009, D’Odorico et al. 2010, Ravi et al. 2010).
For example, deposition of soil and litter under
shrubs can create more porous conditions that
increase infiltration and water availability for
shrubs (Stavi et al. 2009). Although resource
islands are common in many arid and semi-arid
ecosystems around the world, their role in either
degradation or stability of ecosystems can differ
(Stavi et al. 2009, Sankey et al. 2012). In arid
grassland systems, formation of resource islands
is recognized as a form of degradation resulting
from woody-shrub encroachment into grasslands
where soil nutrients were previously more
homogenous (Schlesinger et al. 1990, Stavi et al.
2009, Ravi et al. 2010). This shift has important
ecological implications for plant community
composition, hydrological and biogeochemical
cycling, and ecosystem response to regional
climate change (Schlesinger et al. 1990, D’Odor-
ico et al. 2010, Ravi et al. 2010). Conversely, in
shrubland ecosystems, resource islands provide
critical heterogeneity for herbaceous species and
resistance to disturbance (e.g., invasive species)
and their loss represents degradation to ecolog-
ical condition (Bechtold and Inouye 2007, Davies
et al. 2007, Hoover and Germino 2012, Preve´y et
al. 2010).
In semi-arid shrubland ecosystems, sagebrush
taxa (Artemisia)areconsidered‘‘foundational
species’’ that modify ecosystem processes, stabi-
lize plant communities, and whose removal
decreases resistance to invasive species (Preve´y
et al. 2010). Artemisia can influence the micro-
habitat characteristics underneath the shade of
their canopy by lowering temperatures, increas-
ing relative humidity, and increasing soil mois-
ture (Chambers 2001, Davies et al. 2007, Stavi et
al. 2009). In addition, Artemisia species form
microsite zonal differences in horizontal resource
availability (Young and Palmquist 1992, Davies
et al. 2007). In comparison to interspaces, soils
under the canopy of sagebrush tend to have
elevated nutrient pools of carbon and nitrogen
(Burke et al. 1989, Bolton et al. 1993, Bechtold
and Inouye 2007, Davies et al. 2007), potassium
(Doescher et al.1984, Chambers 2001), soil mi-
crobial biomass (Burke et al. 1989, Bolton et al.
1993), and higher rates of nitrogen mineralization
(Bolton et al. 1990). Distribution patterns for
phosphorous, magnesium, and calcium, howev-
er, are less consistent; some report higher
concentrations under shrubs (Doescher et al.
1984, Chambers 2001), while others report no
difference (Charley and West 1975, Doescher et
al. 1984, Burke et al. 1989). The combination of
these under-shrub microsite characteristics has
been found to play an important role in the
spatial distribution and abundance of the under-
story herbaceous vegetation with greater bio-
mass, cover, and density found in the subcanopy
zones of Artemisia species (Davies et al. 2007 ).
Resource islands in Artemisia-dominated
shrublands are also a critical part of herbaceous
vegetation heterogeneity and seedling establish-
ment after disturbances, such as fire (Davies et al.
2009, Boyd and Davies 2010). For example, after
shrublands burn, resource islands contain greater
seedling density, height, and reproduction of
native and introduced perennial grasses than
burned interspaces, suggesting that pre-burn
shrubcovermaybevitaltorecoveryand
restoration seeding following fires (Boyd and
Davies 2010). Rehabilitative grass seeding has
also achieved greater seedling emergence and
establishment in former resource islands than
interspaces after Artemisia and other shrubs were
removed manually with minimal soil disturbance
(Wood et al. 1982). Several studies have exam-
ined the duration of time these islands are
discernible after sagebrush removal and distur-
bance (e.g., fire). One study showed that ‘‘ghost’’
resource islands were still detectable up to 9
years post fire (Halvorson et al. 1997), while
another found that when sagebrush are cut and
removed without additional soil disturbance,
resource islands remain for 6–14 years (Burke et
al. 1989, Bechtold and Inouye 2007).
With under-shrub and interspace differences
playing such a central part in Artemisia ecosystem
functioning, management practices that disturb
the soil (e.g., seeding, chaining, and amend-
ments) and possibly alter this heterogeneity need
to be explored to determine how they affect
ecosystem resilience (Charley and West 1975,
Hoover and Germino 2012, Sankey et al. 2012).
However, little is known about the duration of
time necessary for resource islands to reform
after soils are homogenized by human distur-
bance. The only study that has addressed this
vwww.esajournals.org 2January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
question tested soils under shrubs 8 years after
they were transplanted into a soil uniformly
mixed to 50 cm (McGonigle et al. 2005). It was
estimated to take 32 years for organic carbon to
reach comparable levels to an undisturbed
community, as opposed to phosphorous, which
accumulated more rapidly, taking only 8 years to
reach half the value recorded in the undisturbed
site (McGonigle et al. 2005). To our knowledge,
there are no studies that have addressed the
formation of resource islands on disturbed soil
where Artemisia communities have redeveloped
through secondary succession from local seed
sources over the long term.
Formerly cultivated old fields, where native
Artemisia plant communities have begun to re-
establish, offer a unique setting to examine the
potential redevelopment of resource islands over
the long term. Cultivation homogenizes soil
fertility and structure for maximum crop pro-
duction (Homburg and Sandor 2011). In old
fields, the native shrubland was removed and
soils were broken up and mixed both vertically
and horizontally through plowing and harrow-
ing (Morris and Monaco 2010). Resource islands
and soil heterogeneity are thereby converted into
a more homogenous pattern across the field
(Charley and West 1975, Wood et al. 1982,
Robertson et al. 1993). On a landscape scale,
processes like nitrogen mineralization may be
similar between old fields and noncultivated
land but their distribution is altered because the
spatial aggregation has been removed (Bolton et
al. 1993, Robertson et al. 1993). This effect is
further enhanced with the application of fertiliz-
ers (Standish et al. 2006). Soil homogenization on
old fields due to cultivation can contribute to the
dominance of early successional species, like
exotic annual species (Robertson et al. 1993,
Standish et al. 2006). Therefore, many old fields
become dominated by invasive plants and
annual grasses for decades to over half a century
after abandonment (Daubenmire 1975, Elmore et
al. 2006). However, some old fields have under-
gone autogenic succession and the shrublands
have re-established, in part, since cultivation was
abandoned (Morris et al. 2011).
Our study used old fields where cultivation
was abandoned over 90 years ago to examine the
potential for long-term redevelopment of re-
source islands in the Great Basin region, USA
by comparing soils from under-shrub and inter-
space microsites in old fields and adjacent native
shrublands (Morris et al. 2011). In this region,
farmersofthiseradidnotusesynthetic
fertilizers, although manuring (spreading animal
waste) and plowing under crop residues as a way
of maintaining fertility was common (MacDon-
ald 1909, Widstoe 1911). Therefore, the legacy of
farming could include increased or decreased
nutrient loads (McLauchlan 2006 ). We assume,
given the mixing of soils horizontally and
vertically during cultivation, that the resource
island patterns had been homogenized within
our old fields (Charley and West 1975, Wood et
al. 1982, Bolton et al. 1993, Robertson et al. 1993,
Homburg and Sandor 2011). Therefore, our
study addressed three questions: (1) Have re-
source island patterns re-established in old fields,
i.e., are soil nutrient differences under shrubs and
interspaces similar to those found in native
shrublands? (2) Are the soil fertility measures of
total organic carbon (C), total nitrogen (N),
bicarbonate-extractable phosphorous (P), and
ammonium acetate-extractable potassium (K),
magnesium (Mg), and calcium (Ca) under shrubs
comparable to the values in native shrublands?
(3) Has the overall soil fertility re-established
under the shrubs or is it different from the native
shrubland?
METHODS
Study area
Research was conducted in the northwestern
corner of Utah at the northern edge of the Great
Basin floristic region (Fig. 1). The area is
bordered by the Raft River Mountains to the
north and the Grouse Creek Mountains to the
West. Average annual precipitation is 25 cm, and
annual maximum and minimum temperatures
range from 18 to 338C (Morris et al. 2011).
Average elevation of the study areas is 1,680 m.
European settlement of the Park Valley area
began in the late 1860s and early 1870s. The
introduction of livestock to the area accompanied
the settlers, with the heaviest grazing occurring
prior to the 1930s. In the early 1910s, a land boom
associated with dry-land wheat farming occurred
within the region, but dry farms were abandoned
in just over a decade (Morris and Monaco 2010).
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MORRIS ET AL.
Paired sets
Our experimental design used paired sets of
historically cultivated soils and adjacent noncul-
tivated soils; an approach that enables the closest
possible comparison of soil differences (Hom-
burg and Sandor 2011). We used aerial photo-
graphs from the 1950s, 1970s, 1980s, and 2000s,
verified against original homestead records and
tract books, to locate old fields that were dry
farmed in the early 1910s, and then abandoned
(Morris 2012). For this study, we selected six
paired sets where each was located within 500 m
of each other on the same property, with the
same grazing history, and the same soil series
and slope.
The six paired sets, named after the patentee
on the original homestead, the tract book
applicant or land company ownership, were
located in three different mapped soil series:
Lembos (Swenson), Acana (Alder and Scott), and
Kunzler (Druehl, Pacific Land and Water Com-
pany [PLWC], and Atherley) (NRCS 1993). The
Lembos is a moderately deep, well drained and
permeable soil derived from alluvium of tuffa-
ceous sandstone and limestone (NRCS 2010).
Lembos soil is classified as a coarse-loamy,
mixed, superactive, mesic Xeric Argidurid
(NRCS 2010). The potential plant community
(reference state without pervasive human distur-
bances) at this site is dominated by Wyoming big
sagebrush (Artemisia tridentata Nutt. ssp. wyomin-
gensis Beetle & Young) with bluebunch wheat-
grass (Pseudoroegneria spicata [Pursh] A. Lo¨ve) as
the most common understory perennial grass
(NRCS 1993). There is approximately 20%less
Wyoming big sagebrush cover in historically
cultivated sites in the Lembos soils (Morris et al.
2011). The Acana soil is classified as loamy,
mixed, superactive, mesic, shallow Haploxeralfic
Argidurids (NRCS 2010). Potential vegetation at
the sites in this soil is characterized by black
sagebrush (Artemisia nova A. Nelson) with the
perennial grasses Indian ricegrass (Achnatherum
hymenoides [Roem. & Schult.] Barkworth) and
needle and thread grass (Hesperostipa comata
[Trin. & Rupr.] Barkworth) in the understory
Fig. 1. Map showing the Great Basin Floristic Region in the western USA and the location of the study area in
the northwestern corner of Utah.
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MORRIS ET AL.
(NRCS 1993). There is about 10%less black
sagebrush cover in historically cultivated sites in
the Acana soils (Morris et al. 2011). The Kunzler
soil is classified as a coarse-loamy, mixed, super-
active, mesic Durinodic Xeric Haplocalcid (NRCS
2010). Potential vegetation at the sites in this soil
is dominated by a mix of Wyoming big sage-
brush and black greasewood (Sarcobatus vermic-
ulatus [Hook.] Torr.) (NRCS 1993). There is about
5%less Wyoming big sagebrush cover in
historically cultivated sites in the Kunzler soil
(Morris et al. 2011).
Field sampling
Soil sampling was conducted in May through
early July of 2009 with paired sets sampled
within one day of each other. We collected soil
samples in the paired sets using predetermined
GPS coordinates to establish 3 linear routes (200 –
300 m) across each condition (cultivated and
native), which ensured sampling was carried out
over a similar area in an old field and the
adjacent native area within the same mapped soil
series (Fig. 2). Sampling began at least 50 m
within the boundary of an old field or away from
roads to avoid edge effects. Since microsite
differences in C, N, P, and K are often highest
in surface soils (0–5cm) (Burke et al. 1989, Bolton
et al. 1993, McGonigle et al. 2005, Bechtold and
Inouye 2007), we collected soils from 0–5 cm
depth midway between the shrub stem and
canopy edge under randomly selected shrubs (4
per linear route; n ¼12) and in the interspaces
midway between shrubs (4 per linear route; n ¼
12). Bulk density was obtained at random
locations in the interspaces (n ¼6) using an
adapted excavation method (Johansen 2011).
Laboratory analysis
The soils were sieved (2 mm) and subsamples
were then used to determine total organic C, total
N, bicarbonate phosphorus, and soil cations in
the lab. For C and N, soils were mechanically
ground, calcium carbonates were removed with
HCl, and then analyzed using a LECO TruSpec
with a certified soil standard (0.13%N; 1.30%C)
for calibration. Bicarbonate-extractable P was
determined using a method adapted from Olsen
and Sommers (1982), with quantification by flow
injection using vanomolybdenate chemistry. Ex-
traction by pH 7.0 ammonium acetate was used
to gauge potentially available soil cations (Ca,
Mg, K) with quantitation by atomic absorption/
emission spectroscopy (Thomas 1982). Soil bulk
Fig. 2. Aerial photo from one of the six paired sets (Druehl) showing approximate locations of 200 meter linear
routes used to sample similar sized areas inside the historically cultivated old field (on the left) and adjacent
native sites within the same soil series (photo from Google Earth, 2006).
vwww.esajournals.org 5January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
density was used to convert C and N concentra-
tions to a per area basis.
Statistical analysis
To examine if resource island patterns and soil
fertility measures were comparable to native
shrublands, we used nested Analysis of Variance
(ANOVA) with microsite (under a shrub or in the
interspace) nested within condition (cultivated or
native) (Burke et al. 1995) for each paired set.
Differences between mean soil fertility measures
were evaluated with a posteriori Tukey HSD
tests. Data were transformed to improve normal-
ity using the Box-Cox transformation function;
however, all tables present the untransformed
means. Three suspected outliers were identified
and the data were checked for normality using
Shapiro-Wilk W tests. Statistical results were
comparable when the outliers were included or
removed; yet they were dropped from analysis to
meet the normality assumptions of ANOVA. Re-
establishment of overall soil fertility under the
shrubs in old fields was examined using discrim-
inant analysis (DA) with all six soil-fertility
measures from only the under-shrub microsite.
The soil fertility measures were standardized to
the maximum value of each variable at each site.
Outliers were removed, and the standardized
data were checked for normality using Shapiro-
Wilk W tests prior to employing DA. Significance
of the discriminant model was evaluated with the
Wilks-Lamda test. All analyses were performed
with JMP 8.0 (SAS Corp.).
RESULTS
Condition (cultivated vs. native) had a signif-
icant effect on P at the Swenson site, and for Mg
in the Alder, Druehl, and PLWC sites (Table 1).
The majority of fertility measures had regained
similar under-shrub to interspace resource pat-
terns when compared to the native condition in
all soils series with two exceptions (Tables 2 and
3). First, K did not show a similar under-shrub to
interspace pattern in the cultivated condition as
was found in native soils at the Swenson site
(Table 3). Values of K were higher under shrubs
in the native condition, and values were the same
across microsites in the cultivation condition,
suggesting that soil K remained homogenized
between the two microsites. Second, in the
Kunzler soil, Ca in the cultivated condition had
not regained an under-shrub to interspace
patterning similar to the paired native condition.
Table 1. Results of nested ANOVA testing the effects of condition (cultivated or native) and microsite (under
shrub or interspace) nested within condition on phosphorous (P), total organic carbon (C ), total nitrogen (N),
calcium (Ca), magnesium (Mg), and potassium (K) at six sites in three soil types (Lembos, Acana, Kunzler).
Degrees of freedom (df ) are indicated for each F-test; * indicates significant effect at P,0.05, ** indicates
significant effect at P,0.01.
Effect df P C N Ca Mg K
Lembos
Swenson site
Condition 1, 2 98.87** 0.02 0.02 0.24 0.09 3.83
Microsite [condition] 2, 44 0.90 64.36** 38.53** 0.33 9.32** 64.83**
Acana
Alder site
Condition 1, 2 0.02 0.08 0.09 0.58 68.33** 0.09
Microsite [condition] 2, 44 47.99** 31.13** 19.25** 1.33 0.04 23.39**
Scott site
Condition 1, 2 0.03 1.80 0.26 0.11 0.90 0.02
Microsite [condition] 2, 44 17.19** 3.08* 3.98* 2.29 4.97 5.50**
Kunzler
Druehl site
Condition 1, 2 0.19 0.49 0.01 0.54 41.95* 2.65
Microsite [condition] 2, 42 33.04** 3.78* 1.64 6.12** 0.23 4.31*
PLWC site
Condition 1, 2 1.12 1.07 1.95 12.99 234.98** 0.05
Microsite [condition] 2, 43 25.10** 43.52** 23.40** 5.38** 0.32 15.50**
Atherley site
Condition 1, 2 0.14 0.59 1.66 0.88 0.01 0.60
Microsite [condition] 2, 42 11.35** 21.91** 8.49** 7.88** 0.85 15.53**
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MORRIS ET AL.
Table 2. Mean (se) soil fertility of phosphorous (P), total organic carbon (C), and total nitrogen (N) for condition
(cultivated or native) and microsites (under shrub or interspace) at the six sites in three soil series (Lembos,
Acana, Kunzler). Significant differences among means within a site and soil fertility measure are indicated with
contrasting letters (a posteriori Tukey tests a¼0.05). Recovery of resource island patterning is demonstrated
when the relation between the under shrub and interspace microsites is the same between conditions.
Significant differences in means under shrubs are emphasized in bold.
Condition
P (mmol/kg) C (g/m
2
) N (g/m
2
)
Under Interspace Under Interspace Under Interspace
Lembos
Swenson
Cultivated 0.48 (0.05)
a
0.55 (0.05)
a
1229 (107)
a
517 (28)
b
124 (7)
a
69 (4)
b
Native 1.28 (0.15)
b
1.35 (0.11)
b
1292 (107)
a
564 (35)
b
125 (7)
a
77 (4)
b
Acana
Alder
Cultivated 0.95 (0.07)
a
0.48 (0.02)
b
1605 (121)
a
902 (82)
b
137 (6)
a
109 (6)
b
Native 1.00 (0.07 )
a
0.51 (0.02)
b
2001 (165)
a
934 (67)
b
177 (13)
a
105 (4)
b
Scott
Cultivated 1.12 (0.07)
a
0.60 (0.03)
b
1376 (132)
a
976 (50)
a,b
117 (7)
a
100 (4)
a
Native 0.96 (0.06 )
a
0.70 (0.12)
b
1009 (85)
a,b
960 (117)
b
122 (12)
a
91 (6)
a
Kunzler
Druehl
Cultivated 1.60 (0.19)
a
0.58 (0.04)
c
687 (71)
a,b
491 (56)
b
73 (3)
a
64 (5)
a
Native 0.84 (0.06)
b
0.61 (0.04)
c
807 (119)
a
631 (98)
a,b
73 (5)
a
66 (5)
a
PLWC
Cultivated 1.51 (0.13)
a
0.82 (0.11)
b
1853 (152)
a
854 (67)
b
158 (9)
a
104 (6)
b
Native 0.92 (0.05)
b
0.47 (0.03)
c
1011 (53)
b
547 (47)
c
104 (5)
b
69 (4)
c
Atherley
Cultivated 0.99 (0.09)
a
0.65 (0.03)
b,c
766 (55)
b
512 (47)
c
76 (4)
b
60 (4)
c
Native 0.88 (0.06)
a,b
0.60 (0.06)
c
1140 (104)
a
600 (41)
b,c
103 (9)
a
73 (3)
b,c
Table 3. Mean (se) soil fertility of calcium (Ca), magnesium (Mg), and potassium (K) for condition (cultivated or
native) and microsites (under shrub or interspace) at the six sites in three soil series (Lembos, Acana, Kunzler).
Significant differences among means within a site and soil fertility measure are indicated with contrasting
letters (a posteriori Tukey tests a¼0.05). Recovery of resource island patterning is demonstrated when the
relation between the under shrub and interspace microsites is the same between conditions. Significant
differences in means under shrubs are emphasized in bold.
Ca (mmol/kg) Mg (mmol/kg) K (mmol/kg)
Condition Under Interspace Under Interspace Under Interspace
Lembos
Swenson
Cultivated 81 (12)
a
88 (12)
a
17 (1)
a
12 (1)
b
16 (1)
c
15 (1)
c
Native 78 (9)
a
91 (11)
a
18 (1)
a
13 (1)
b
36 (2)
a
30 (2)
b
Acana
Alder
Cultivated 98 (8)
a
109 (14)
a
13 (1)
a
13 (1)
a
27 (2)
a
17 (2)
b
Native 80 (6)
a
105 (11)
a
15 (1)
b
15 (1)
b
32 (2)
a
18 (1)
b
Scott
Cultivated 134 (14 )
a
158 (12)
a
14 (1)
a
13 (1)
a
28 (1)
a
24 (1)
b
Native 139 (9)
a
165 (9)
a
16 (1)
a
14 (1)
a
29 (2)
a
23 (1)
b
Kunzler
Druehl
Cultivated 88 (5)
b
103 (3)
a
13 (1)
a
12 (1)
a
33 (3)
a
25 (2)
a,b
Native 98 (2)
a,b
107 (2)
a
10 (1)
b
11 (1)
b
26 (2)
a,b
19 (1)
b
PLWC
Cultivated 94 (2)
a
98 (2)
a
13 (1)
a
12 (1)
a
26 (1)
a
19 (1)
b
Native 57 (4)
c
72 (4)
b
19 (1)
b
19 (1)
b
26 (1)
a
20 (1)
b
Atherley
Cultivated 118 (9)
b
131 (12)
b
13 (1)
a
12 (1)
a
23 (1)
a,b
17 (1)
c
Native 122 (6)
b
176 (6)
a
13 (1)
a
12 (1)
a
31 (2)
a
19 (1)
b,c
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MORRIS ET AL.
At the Druehl site, Ca was lower under shrubs
than interspaces in the cultivated condition while
there was no difference between microsites in the
native condition. In the PLWC and Atherley sites,
Ca content was homogenous across microsites in
the cultivated condition while their paired native
conditions had lower Ca under shrubs than in
the interspaces.
Individual soil-fertility measures in the under-
shrub microsites were generally not different
between cultivated and native conditions, and
when they were, results were variable (Tables 2
and 3). For example, K was significantly lower
under shrubs in cultivated microsites than native
microsites in the Lembos soil, but not at any
other site. There were no significant differences
in any of the mean fertility measures under
shrubs in the Acana soil series. In the Kunzler
soil, there was significantly more P under shrubs
in the cultivated condition at the Druehl and
PLWC sites. Similarly, at the PLWC site, values
were significantly greater for C, N and Ca in
cultivated microsites than native ones, both
under shrubs and in the interspaces. In contrast
to the patterns at Druehl and PLWC, cultivated
microsites at Atherley had significantly lower C
and N than native under-shrub microsites.
Overall soil fertility measures underneath
shrubs between cultivated and native soils were
clearly distinct with 95%confidence at all six sites
(Fig. 3). Microsites under shrubs in the cultivated
condition were significantly different from the
native condition at Swenson, PLWC, and Ather-
ley sites (Table 4). However, the discriminant
function for Alder, Scott, and Druehl sites did not
generate a significant model (Wilks-Lambda test)
because more than half of the variation could not
be explained by the different conditions. The
contribution of individual soil measures to the
overall variation in microsites between cultivated
and native soils was fairly consistent with
ANOVA results. At the Swenson site, the scoring
coefficient for K was the highest, which likely
influenced the separation between under-shrub
microsites, and is consistent with the significant
differences in mean K at this site. At the PLWC
site, there were several significant mean differ-
ences in soil fertility values, and the scoring
coefficients were more equally distributed. At the
Atherley site, Mg had the highest scoring
coefficient, even though Mg was not significant
when analyzed independently with ANOVA.
However, the role of C and K were also highly
influential in the separation between cultivated
and native microsites.
DISCUSSION
With a few exceptions, our study shows that
much of the patchy patterning of elevated soil
fertility under shrubs compared to shrub inter-
spaces has re-established in the 90 years since
cultivation was abandoned. However, the con-
tent of each of these soil fertility measures has not
consistently re-established under shrubs, and the
under-shrub microsites are often different in
cultivated fields than their counterparts in native
shrublands. This study also indicates that re-
source island recovery can be different across
sites that vary in soil series and dominant shrub
species, a finding consistent with reports that
shrub species can have an important influence on
the total pools of C and N under their canopies,
even after cultivation (Jiang et al. 2011). In the
Acana soil, where A. nova was the dominant
shrub species (Alder and Scott sites), there were
no differences in patterning or content in either of
the old fields compared to native shrublands. In
the Lembos and the Kunzler soils, where A.
tridentata was the dominant shrub, differences in
fertility patterning, individual fertility values,
and under-shrub microsite soil fertility persisted.
Shrub island re-establishment within the old
fields in the Acana soils was also consistent with
Morris et al. (2011), who observed vegetation
recovery was highest on the Acana sites. There-
fore, our results are in line with the expectation
that resource island recovery will accompany
recovery of functional native plant communities
at disturbed sites (Preve´y et al. 2010), and the
suggestion that shrubs may not only influence
soil processes, but also soil recovery after
disturbance (Yelenik and Levine 2010).
The resource island patterns at our sites appear
to have mostly re-established, with two excep-
tions. At the Swenson site in the Lembos soil, the
distribution of K was homogenous between
under-shrub and interspace microsites while the
rest of the sites had regained the resource island
pattern typical of soil K in these systems
(Doescher et al. 1984, Chambers 2001). Calcium
also remained homogenous between the micro-
vwww.esajournals.org 8January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
sites in the PLWC and Atherley sites in the Acana
soils and, conversely, became patchy within the
Druehl site. Even though this suggests that the
resource island have not re-established in these
sites, Ca does not consistently develop a resource
island effect across Artemisia shrublands (Charley
and West 1975, Doescher et al. 1984, Burke et al.
1989, Chambers 2001). Since these were the only
differences in soil fertility patterning detected, we
suggest that the resource island patterns have
Fig. 3. Scatter plots for the scores of the first two canonical discriminant functions indicating the separation
between under-shrub soil fertility in the cultivated condition (circles) and under-shrub fertility in the native
condition (triangles) at all six sites. The ellipses indicate the 95%confidence region of the group mean.
vwww.esajournals.org 9January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
mostly re-established within the 90 years since
cultivation ceased. The patterning of higher C
and N under shrubs in our study is consistent
with what has been reported for resource islands
in other studies (Burke et al. 1989, Bolton et al.
1993, Chambers 2001, Bechtold and Inouye 2007,
Davies et al. 2007). McGonigle et al. (2005)
suggested that the patterning of C under shrubs
can form ‘‘rather swiftly’’ within 8 years when
shrubs are transplanted. Young and Palmquist
(1992) reported that nitrate levels under the
canopies of A. nova did not show significant
differences from the interspaces until the shrubs
were within a 30–50 year old mature age class.
The design of our study does not allow us to
estimate when shrub island patterns reformed,
however, it would be expected to take longer
when shrubs reestablish from seed than from
transplants.
Decreased soil fertility within soil surface
layers (0–5 cm) in previously cultivated areas is
expected because of soil mixing and nutrient loss
through crop consumption and/or wind and
water erosion (McLauchlan 2006). Both C and
N are often depleted in formerly cultivated soils
(Burke et al. 1995, McLauchlan 2006 ). Further-
more, K and bicarbonate-extractable P are typi-
cally more concentrated at the soil surface within
shrub communities (Doescher et al. 1984, West et
al. 1984), and their content could be diluted
through soil mixing. There were no instances in
our study in which the overall mean values for C
or N were different between cultivated and
native conditions, yet there were significant
differences between microsites for these soil
measures, which is also consistent with other
studies (Bolton et al. 1993, Robertson et al. 1993).
Cultivation mediated losses in soil fertility within
microsites were apparent in the lower C and N at
the Atherley site and lower K at the Swenson site.
These findings are in contrast to those of
McGonigle et al. (2005), who estimated that
values of C could reform under shrubs in
disturbed soils within 32 years. At the Atherley
site, C had not reached comparable values to the
under-shrub microsites in the native shrubland,
even after 90 years. In the latter case, this was the
only site where soil K under sagebrush has not
recovered and is still lower than the mean values
under shrubs and in the interspaces of the
adjacent native shrubland. Potassium is the most
mobile cation from decomposing sagebrush litter
(e.g., K .Mg .P¼Ca) and is expected to
accumulate more quickly in soils under sage-
brush due to its solubility (Mack 1977). Both
sagebrush and litter cover were significantly
lower in the old field compared to the native-
shrubland site (Morris et al. 2011), suggesting
that the lack of sagebrush litter may have
inhibited the recovery of K in soils.
Differences in historical cultivation practices
and equipment can generate different land-use
legacies, even across the same soil type (Coffin et
al. 1996, Buisson and Dutoit 2004). The elevated
levels of P, C, N, and Ca in both under-shrub and
interspace microsites in the PLWC old field may
reflect differences in historic management at this
site compared to others in the same soil series.
Although dry farmers in this region during the
early 20th century did not utilize inorganic
fertilizers, they may have manured and plowed
under crop residues as a way of maintaining
Table 4. Results of multivariate discriminant analysis. Values are scoring coefficients for canonical function 1 for
each soil measure, Wilks-Lambda test statistic, degrees of freedom (df ), P-value, and the number and
associated percentage of misclassified sample units in either the cultivated or native conditions.
Measure or statistic
Lembos Acana Kunzler
Swenson Alder Scott Druehl PLWC Atherley
P 2.79 4.73 2.99 6.45 2.16 2.52
C 3.39 2.70 4.89 1.21 1.03 7.35
N6.68 7.78 1.93 0.44 4.26 1.96
Ca 4.80 5.76 0.83 5.38 5.15 1.07
Mg 4.88 2.81 5.19 5.85 6.36 10.81
K 10.07 3.03 2.08 5.02 0.81 8.25
Wilks-Lambda 0.13 0.54 0.66 0.51 0.13 0.27
df 6, 17 6, 17 6, 16 6, 13 6, 17 6, 15
P,0.0001 0.08 0.30 0.13 ,0.0001 0.0014
Misclassified 1 (4%) 4 (16%) 6 (26%) 3 (15%)0 1(4%)
vwww.esajournals.org 10 January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
fertility on dry farms (MacDonald 1909, Widstoe
1911). The use of manure as a fertilizer has been
found to excessively enrich some soil stocks of P,
C, N, K, and Ca in top soils for up to 2,000 years
(Compton and Boone 2000, Edmeades 2003,
Dambrine et al. 2007). It is possible that
manuring practices in this field were sufficient
enough to alter the soil fertility over the long-
term at this site, especially given the potential for
naturally high levels of calcium carbonates and
Ca enrichment associated with soil mixing
during cultivation to ‘‘sequester’’ or stabilize soil
organic matter (Muneer and Oades 1989, Dam-
brine et al. 2007).
Our findings are also an important indicator of
the duration of time it takes for soils to recover
from cultivation disturbances in the Great Basin.
There was ;30%less C and N in the old field at
the Atherley site, which was cultivated for
approximately 10 years with about 90 years of
recovery time. Other studies have shown similar
deficiencies after 50 years of cultivation and 53
years of recovery time (Burke et al. 1995). The
Swenson field was only cultivated about three
times by several unsuccessful applicants attempt-
ing to gain the homestead patent for this land.
Although the C and N levels were not different,
this field had less P and K than the native
condition. Fertility of the under-shrub microsites
in the cultivated condition was also categorically
different from the native shrubland condition in
discriminate analysis at Atherley and Swenson.
This suggests that the recovery of soil fertility,
and resource islands, in these soil series of the
Great Basin could take much longer than in the
short-grass prairie (Burke et al. 1995), and oak-
hickory forests in the USA (Robertson et al. 1993).
This kind of long-term legacy has not been
documented in the Great Basin prior to our
study. Since millions of hectares of sagebrush
were once cultivated and then abandoned fol-
lowing the dry farming boom in the early 1900s,
this long-term legacy from cultivation has im-
portant implications for conservation on lands
undergoing secondary succession, future man-
agement and restoration planning, and our
understanding of soil carbon and nutrient cycling
across the region (Morris et al. 2011).
Results from our study indicate that while
patterning of resource islands has mostly begun
to re-establish, soil fertility may not recover
under shrubs after a soil disturbance like
cultivation for nearly 100 years in the Great
Basin. Unfortunately, we cannot determine which
processes present the threshold for recovery of
these values. Other studies examining the recov-
ery of nutrient cycling processes under Artemisia
that have re-established in invasive exotic annual
grasslands have shown that elevated levels of N
will recover along with Artemisia, but they do not
provide any estimates of the age or the amount of
time this process will take (Yelenik and Levine
2010). However, these authors suggested that
decomposition of seeds may increase N under
the Artemisia because of their low C:N ratios
(Yelenik and Levine 2010). This interpretation
suggests that some level of maturity, size, and
reproductive output of Artemisia could be used to
estimate the timeframe for these processes to
recover. One study looking at A. nova demon-
strated that nitrate levels under shrubs increase
with increasing age (Young and Palmquist 1992).
Given these uncertainties, future research should
include determining the threshold values of soil
fertility in resource islands that are capable of
enhancing native recovery and the age structure
at which this occurs. Also, it would be useful to
examine soil fertility measures over the length of
a growing season since our data represent a one-
time sample. Moreover, future research could
improve upon our results using geostatistical
methods, because resource islands are not sym-
metrical and can be heterogeneous even under an
individual shrub (Halvorson et al. 1994).
Research into the re-establishment of resource
islands in sagebrush ecosystems is vital for this
habitat type which is now considered one of the
most imperiled in North America (Noss and
Peters 1995). Once stretching across 63 million ha
in western North America, this ecosystem was
severely altered through historical human activ-
ities (West and Young 2000, Davies et al. 2011).
Understanding the timeframe under which the
patterns and nutrient content of these resource
islands recover can provide more information
about the timeframe under which the function of
these ecosystems can be expected to recover and
how restoration efforts can be directed. Resource
island establishment plays a critical role in plant
community assembly, diversity, resistance to
invasive plants, and resilience following addi-
tional disturbances (Chambers et al. 2007, Davies
vwww.esajournals.org 11 January 2013 vVolume 4(1) vArticle 12
MORRIS ET AL.
et al. 2009, Hoover and Germino 2012). The
timing of resource island re-establishment also
has far reaching implications across North
America and into other arid and semi-arid
ecosystems such as the Mojave Desert (Titus et
al. 2002), the steppes of northern China (Jiang et
al. 2011), or the degraded Mediterranean ecosys-
tems in Spain (Ferrol et al. 2004) where an under-
shrub to interspace patterning represent the
underlying palette upon which diversity and
ecosystem functioning is drawn.
ACKNOWLEDGMENTS
This research was funded by the US Dept of
Agriculture, Agricultural Research Service Area-wide
Ecologically Based Invasive Plant Management
(EBIPM) project. Special thanks to Justin Williams
and Rob Watson for their hard work in the field. We
are extremely grateful for the many hours of labora-
tory analysis conducted by Tye Morgan, Kelli Belmont,
Anna Allen-Pittson and Sabrina McCue. We also thank
Kirk Davies, Lora Perkins, and two anonymous
reviewers for comments on an early manuscript.
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