Effectiveness of water-saving technologies during early stages of restoration of endemic Opuntia cacti in the Galápagos Islands, Ecuador

Abstract

Restoration of keystone species is a primary strategy used to combat biodiversity loss and recover ecological services. This is particularly true for oceanic islands, which despite their small land mass, host a large fraction of the planet’s imperiled species. The endemic Opuntia spp. cacti are one example and a major focus for restoration in the Galápagos archipelago, Ecuador. These cacti are keystone species that support much of the unique vertebrate animal community in arid zones, yet human activities have substantially reduced Opuntia populations. Extreme aridity poses an obstacle for quickly restoring Opuntia populations though water-saving technologies may provide a solution. The aim of this study was to evaluate current restoration efforts and the utility of two water-saving technologies as tools for the early stages of restoring Opuntia populations in the Galápagos archipelago. We planted 1,425 seedlings between 2013 and 2018, of which 66% had survived by the end of 2018. Compared with no-technology controls, seedlings planted with Groasis Waterboxx ® water-saving technology (polypropylene trays with water reservoir and protective refuge for germinants) had a greater rate of survival in their first two-years of growth on one island (Plaza Sur) and greater growth rate on four islands whereas the “Cocoon” water-saving technology (similar technology but made of biodegradable fiber) did not affect growth and actually reduced seedling survival. Survival and growth rate were also influenced by vegetation zone, elevation, and precipitation in ways largely contingent on island. Overall, our findings suggest that water-saving technologies are not always universally applicable but can substantially increase the survival and growth rate of seedlings in certain conditions, providing in some circumstances a useful tool for improving restoration outcomes for rare plants of arid ecosystems.

Full text

Submitted 9 July 2019
Accepted 4 November 2019
Published 3 December 2019
Corresponding author
Patricia Jaramillo,
patricia.jaramillo@fcdarwin.org.ec
Academic editor
Timothy Scheibe
Additional Information and
Declarations can be found on
page 15
DOI 10.7717/peerj.8156
Copyright
2019 Tapia et al.
Distributed under
Creative Commons CC-BY 4.0
OPEN ACCESS
Effectiveness of water-saving technologies
during early stages of restoration of
endemic Opuntia cacti in the Galápagos
Islands, Ecuador
Patricia Isabela Tapia1,2,*, Luka Negoita2,*, James P. Gibbs3and
Patricia Jaramillo2,4
1School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, Tyne and Wear,
United Kingdom
2Charles Darwin Research Station, Charles Darwin Foundation, Santa Cruz, Galápagos, Ecuador
3Department of Environmental and Forest Biology, State University of New York, Syracuse, NY,
United States of America
4Facultad de Ciencias, Universidad de Málaga, Málaga, Spain
*These authors contributed equally to this work.
ABSTRACT
Restoration of keystone species is a primary strategy used to combat biodiversity loss and
recover ecological services. This is particularly true for oceanic islands, which despite
their small land mass, host a large fraction of the planet’s imperiled species. The endemic
Opuntia spp. cacti are one example and a major focus for restoration in the Galápagos
archipelago, Ecuador. These cacti are keystone species that support much of the unique
vertebrate animal community in arid zones, yet human activities have substantially
reduced Opuntia populations. Extreme aridity poses an obstacle for quickly restoring
Opuntia populations though water-saving technologies may provide a solution. The
aim of this study was to evaluate current restoration efforts and the utility of two
water-saving technologies as tools for the early stages of restoring Opuntia populations
in the Galápagos archipelago. We planted 1,425 seedlings between 2013 and 2018, of
which 66% had survived by the end of 2018. Compared with no-technology controls,
seedlings planted with Groasis Waterboxx R
water-saving technology (polypropylene
trays with water reservoir and protective refuge for germinants) had a greater rate of
survival in their first two-years of growth on one island (Plaza Sur) and greater growth
rate on four islands whereas the ‘‘Cocoon’’ water-saving technology (similar technology
but made of biodegradable fiber) did not affect growth and actually reduced seedling
survival. Survival and growth rate were also influenced by vegetation zone, elevation,
and precipitation in ways largely contingent on island. Overall, our findings suggest that
water-saving technologies are not always universally applicable but can substantially
increase the survival and growth rate of seedlings in certain conditions, providing in
some circumstances a useful tool for improving restoration outcomes for rare plants of
arid ecosystems.
Subjects Biodiversity, Conservation Biology, Ecology, Plant Science, Environmental Impacts
Keywords Opuntia echios,Opuntia megasperma, Restoration, Groasis waterboxx, Water-saving
technology, Conservation, Keystone species, Adaptive management, Islands, Galápagos Islands,
Ecuador
How to cite this article Tapia PI, Negoita L, Gibbs JP, Jaramillo P. 2019. Effectiveness of water-saving technologies during early stages of
restoration of endemic Opuntia cacti in the Galápagos Islands, Ecuador. PeerJ 7:e8156 http://doi.org/10.7717/peerj.8156

INTRODUCTION
The restoration of previously abundant keystone species is one way to combat loss of
biodiversity and ecological services (Grime, 1998). This is particularly true on oceanic
islands, which comprise little of the planet’s land mass yet host a disproportionate amount
of its imperiled species (Myers et al., 2000;Campbell & Donlan, 2005). The Galápagos
archipelago is a case in point: its land area is minimal (8,006 km2) yet it hosts a remarkable
array of endemic life forms with as many as 60% of its 168 endemic plant species now
threatened with extinction (Black, 1973;Tye, 2007). Active restoration programs are
underway throughout the archipelago. For example, Project Isabela (1997–2006), was
the world’s largest restoration effort at the time and dedicated to eradicating introduced
mammal herbivores on multiple islands in the archipelago (Cruz et al., 2009;Carrion et al.,
2011).
The Opuntia spp. cacti (prickly pear cactus) are a major focus for restoration in the
Galápagos archipelago, Ecuador, which hosts six endemic species, with 14 total taxa when
including varieties. Human impact in the Galápagos archipelago has steadily increased over
the last 200 years (Jaramillo, 1998), resulting in declines of Opuntia populations on these
islands (Snell, Snell & Stone, 1994). Several factors have been attributed as the primary
threats to Opuntias including herbivory by introduced mammals (Grant & Grant, 1989),
extinction of keystone predators that once regulated numbers of cactivores (Sulloway
& Noonan, 2015), and the increased intensity of El Niño events likely driven by climate
change (Snell, Snell & Stone, 1994;Hicks & Mauchamp, 1996). Opuntia cacti provide many
ecosystem services for other native and endemic species (Grant & Grant, 1981;Hicks &
Mauchamp, 1995;Hicks & Mauchamp, 1996;Gibbs, Marquez & Sterling, 2008). Examples
include Galápagos giant tortoises and land iguanas that depend on Opuntia cacti as a food
source while also contributing to Opuntia regeneration through seed dispersal (Hamann,
1993;Snell, Snell & Stone, 1994;Gibbs, Marquez & Sterling, 2008;Gibbs, Sterling & Zabala,
2010;Jaramillo, Tapia & Gibbs, 2018). Efforts are being made to protect and restore
populations of these imperiled cacti (Hicks & Mauchamp, 1996) but it is not clear which
factors most control Opuntia populations (Sulloway & Noonan, 2015). Opuntia declines
on Plaza Sur Island, for example, are especially pronounced (60% reduction since 1957)
despite the eradication of introduced goats since the populations are likely too low to
successfully regenerate in the presence of native herbivory (Grant & Grant, 1989;Snell,
Snell & Stone, 1994;Sulloway & Noonan, 2015).
Severe aridity poses an obstacle for restoring plant communities over much of Galápagos
due to the inherently slower growth and low germination of plants growing in these
conditions, including xerophytes such as Opuntia cacti (Hicks & Mauchamp, 1996). The
lowland zones of the archipelago, where Opuntias are most common and historically
abundant (e.g., Snell, Snell & Stone, 1994;Hicks & Mauchamp, 1996;Browne et al., 2003),
can receive less than 10 cm rainfall annually (Trueman & D’Ozouville, 2010). Though
these conditions are normal, they increase the time it would take for small populations
of Opuntias to return to historic sizes (Grant & Grant, 1989;Helsen et al., 2009). Rapid
restoration through active planting of these species is critical for reducing the risk of
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 2/19

extinction until their threats are better understood and before other threats such as
invasive plant species make it more difficult or impossible for Opuntias to naturally
regenerate (Mauchamp et al., 1998;Helsen et al., 2009). ‘‘Water-saving’’ technologies
are tools that may help increase survival and growth of planted cactus seedlings while
reducing the need for manual watering and speeding the restoration process (Kulkarni,
2011;Hoff, 2014;Jaramillo et al., 2014;Jaramillo, 2015;Jaramillo et al., 2015;Faruqi et
al., 2018;Jaramillo, Tapia & Gibbs, 2018;Peyrusson, 2018;Peyrusson, 2018). The Groasis
Waterboxx R
(Groasis) and biodegradable Cocoon system are two relatively inexpensive
water-saving technologies that can be easily implemented during the planting process
(Appendix S1). These technologies function by holding water in basins that surround
the young plant and feed water to the soil at a slow but constant rate through capillary
action via a short length of rope that connects the basin to the soil. Aside from the
physical design differences that influence where the plant is relative to soil surface and
biodegradability, the main difference in these technologies is that Groasis actively collects
dew and rainwater, while the Cocoon technology is only filled with water once at the time
of planting (Appendix S1). Although these particular technologies show much promise
through anecdotal evidence and reports, there remains a dearth in formal scientific
studies evaluating their efficacy (but see Liu, Li & Ren, 2014). Therefore, the objective
of the current study was to evaluate current restoration efforts and test the utility of
two water-saving technologies as tools for restoring Opuntia populations in the Galápagos
archipelago. Through this objective we hope to better understand the utility of water-saving
technologies for restoring these and other keystone plant species in arid island ecosystems
throughout the world.
MATERIALS & METHODS
Study area, focal species, and water-saving technologies
The Galápagos archipelago is located in the Pacific Ocean, about 1,000 km west of the coast
of mainland Ecuador (1◦390N, 92◦00W to 1◦260S, 89◦140W, WGS 84, Fig. 1) (Dirección
del Parque Nacional Galápagos, 2014). Our study focused on measuring the utility of
water-saving technologies for enhancing cactus growth and survival of four endemic
Opuntia taxa within the archipelago: Opuntia echios var. echios Howell, Opuntia echios var.
gigantea Howell, Opuntia megasperma var. megasperma Howell, and Opuntia megasperma
var. orientalis Howell (Hicks & Mauchamp, 1996). We evaluated two technologies: Groasis
Waterboxx R
(Groasis), a protective polypropylene box that collects rainwater that it
provides to the plant (Hoff, 2014); and the Cocoon system, a 99% biodegradable box that
contains and provides water to the plant similar to Groasis, but Cocoon is only filled with
water at the time of planting (Land Life Company, 2015;Faruqi et al., 2018;Appendix S1).
These water-saving technologies have been proposed as a tool to assist plant restoration
of Opuntia taxa via ‘‘Galápagos Verde 2050’’ (GV2050), a project started by the Charles
Darwin Foundation in 2013 with the mission of restoring degraded ecosystems and aiding
with sustainable agriculture in the Galápagos archipelago (Jaramillo et al., 2014;Jaramillo
et al., 2015;Jaramillo, Tapia & Gibbs, 2017). GV2050 seeks to restore ecosystems by using
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 3/19

89°0'W89°30'W90°0'W90°30'W91°0'W91°30'W
0°30'N
0°0'
0°30'S
1°0'S
1°30'S
0 40 8020
km
80°0'W85°0'W90°0'W
0°0'
5°0'S
Ecuador
Galápagos
Archipelago
Santa Cruz
Floreana
Isabela
Baltra
San Cristóbal
Española
Marchena
Santiago
Pinta
Fernandina
±
Islands included in stud y (bold)
Islands
Plaza Sur
0 0.50.25
km
0 1,000500
km
Figure 1 Map of the Galápagos Islands, Ecuador. Islands included in the current study are darkened and
labeled in bold.
Full-size DOI: 10.7717/peerj.8156/fig-1
a data-informed experimental approach for understanding the best conditions, methods,
and tools for successful plantings of native and endemic species (Jaramillo et al., 2015).
Planting and data collection
A total of 1,425 cacti (1,137 Opuntia echios var. echios, 68 Opuntia echios var. gigantea, 24
Opuntia megasperma var. megasperma, and 196 Opuntia megasperma var. orientalis) were
planted on six islands (Baltra, Española, Floreana, Plaza Sur, San Cristóbal, and Santa
Cruz) between 2013 and 2018 (Table 1). Permission to plant Opuntias within protected
sites on these islands was granted by the Dirección del Parque Nacional Galápagos (DPNG)
through permit number PC-11-19 (Table 2). To evaluate the factors most important for
successful Opuntia restoration, data were used only from Opuntias that were grown from
seed and planted using either Groasis, Cocoon, or control (no technology) treatments on
Floreana, Santa Cruz, Baltra, and Plaza Sur islands yielding a sample of 1,029 Opuntia
individuals of three taxa (Table 1).
Planting sites on each island were selected based on locations where historic Opuntia
populations were known to have thrived but are now in decline (Hicks & Mauchamp,
1996;Sulloway et al., 2013;Sulloway & Noonan, 2015;Table 2). For example, since 1957
the Opuntia population on Plaza Sur Island has had an overall mortality of more than
60% and at Cerro Dragon on Santa Cruz Island there has been an overall loss of 78%
(Sulloway & Noonan, 2015). Seedlings were planted from seeds collected in each respective
planting location using standardized seed collection and stratification techniques and
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 4/19

Table 1 Total number of Opuntia spp. individuals planted by island by Galápagos Verde 2050 (2013–2018). Numbers in parentheses ‘()’ are the
number of individuals used in the current study analysis (Figs. 3 &4).
Species Baltra Española Floreana Plaza Sur San
Cristóbal
Santa
Cruz
Opuntia echios var. echios 400 (349) – – 737 (601) – –
Opuntia echios var. gigantea – – – – – 68 (60)
Opuntia megasperma var. megasperma – – 20 (19) – 4 (0) –
Opuntia megasperma var. orientalis – 196 (0) – – – –
Table 2 List of all sites of Galápagos Verde 2050 Opuntia spp. restoration and number of Opuntia spp. individuals planted (2013–2018). Num-
bers in parentheses ‘()’ represent the percent of individuals that have survived through 2018.
Island Site Name # Planted UTM EastaUTM Northa
Antiguo basurero 158 (69%) 804668 9950436
Casa de piedra 125 (74%) 802460 9948203
Jardín ecológico Aeropuerto 1 (100%) 804100 9950795
Baltra (70%)
Parque Eólico 116 (68%) 803992 9950909
Española (79%) Las Tunas 196 (79%) 199759b9849118b
Botadero de basura 3 (33%) 781054 9858587
Cementerio 7 (29%) 780322 9858645
Escuela Amazonas 5 (40%) 779594 9858865
Gobierno Parroquial Floreana 1 (0%) 779530 9859029
Floreana (40%)
Oficina Técnica Parque Nacional Galápagos 4 (75%) 779531 9859244
Centro 254 (62%) 815800 9935365
Los Lobos Este 253 (47%) 815936 9935354
Plaza Sur (61%)
Oeste Cerro Colorado 230 (76%) 815304 9935602
San Cristóbal (100%) CA Jacinto Gordillo 4 (100%) 209711b9900150b
Colegio Nacional Galápagos 2 (50%) 798782 9918296
Espacio Verde ABG 8 (88%) 797864 9918887
Fundación Charles Darwin 51 (67%) 800106 9917856
Santa Cruz (65%)
Oficina Técnica Parque Nacional Galápagos 7 (29%) 799811 9917994
Notes.
aUTM Zone =15M, datum =WGS84
bUTM Zone =16M
grown for one year at the Charles Darwin Research Station, Santa Cruz Island, before
transferring to each site on each island (Jaramillo, Tapia & Gibbs, 2017,Table 2). Each
seedling was randomly assigned a treatment of either control (no technology), Groasis, or
Cocoon, ensuring an adequate sample of replicates within each treatment and site. The
number of controls was maintained at one control for every five technology treatment
replicates. A greater proportion of Groasis replicates were used because the overarching
goal of this work is to successfully restore populations of Opuntias and current anecdotal
evidence and observations suggest this technology provides the greater benefit for achieving
this. The uneven design does not impact our analyses or interpretation of results since
we ensured a relatively adequate number of controls within each island. In total, 823
Groasis, 38 Cocoons, and 168 controls were used in the analysis. Planting locations for
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 5/19

each seedling were determined haphazardly in the field at each site using the basic criteria
that a seedling could be physically planted while not being in direct competition with
other plants (i.e., the substrate was soil rather than rock and free of overarching vegetation
that would shade the seedling). Truly random selection of specific planting locations was
impractical due to the large heterogeneity of exposed bedrock and competing vegetation,
so locations were often chosen opportunistically. Though planting locations were not
random, treatment assignment was random and thus our methodology does not interfere
with our primary goal of evaluating the use of water-saving technologies. Plantings were
conducted according to established methods for installing Groasis, Cocoon, and controls
(Miranda, Riganti & Tarrés, 1987;Hoff, 2014;Land Life Company, 2015). Wire fences were
secured and maintained around each individual planting on Plaza Sur, Baltra, and Española
islands to prevent herbivory from land iguanas or giant tortoises present on those islands
but absent from other islands where Opuntias were planted. Planting site co-variates were
recorded at time of planting: elevation, soil type (rocky-sand, rocky-clay, rich-clay, rich,
sandy, and clay), vegetation zone (arid, littoral, and transitional; Johnson & Raven, 1973),
and treatment (control, Groasis, and Cocoon). Growth (vegetative height) and qualitative
plant state (‘‘good’’, ‘‘regular’’, ‘‘poor’’, and ‘‘dead’’) were noted during each repeated
visit approximately every six weeks following planting. Aside from ‘‘dead’’ which was
non-arbitrary and easy to identify, the other states were based on the subjective relative
appearance of the plant (i.e., degree of desiccation or browning of cladodes). Though these
assignments were not objective, they were not used for our analysis and simply provide a
quick way to gauge the relative state of the plants.
Two-year survival and growth rate of seedlings were used to evaluate restoration success
(Menendez & Jaramillo, 2015). Two-year survival was quantified as whether or not a
seedling survived for at least two years after planting—the period of greatest mortality risk
(we found 79% survival in the first year and 86% survival in the second year, compared
with 99% survival in the third year). For this analysis, only plants that had the potential
to grow and survive for two years were included. However, while the analysis was based
on seedlings planted up until 2019, additional monitoring data from those plants until
September 2019 allowed us to increase the sample of plants for which we could model
two-year survival. Relative growth rate was calculated based on the vegetative height of
each seedling over time. Whereas survival is the primary metric for establishing success
of population restoration, growth rate can indicate the speed of ecosystem recovery due
to the rate of increase in the biomass of a keystone species (Grime, 1998), and may also
indicate the time to reproductive maturity in Opuntias (Racine & Downhower, 1974). An
additional environmental covariate of total precipitation across the six months following
planting was compiled based on available climate data from 2013 to 2019 (Trueman &
D’Ozouville, 2010;Charles Darwin Foundation, 2018).
Data analysis
All statistical analyses were conducted using the R statistical software package v3.3.3 (R
Core Team, 2017). To test the overall effect of water-saving technologies on the restoration
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 6/19

of Opuntia cacti, a model comparison approach was implemented using fixed- and
mixed-effects regression models of the form:
2-year survival logistic fixed-effect model
2YearSurvival =α+β1×treatment +β2×6MonthPrecip+β3×Zone +β4×elevation+
β5×island
Relative growth rate linear mixed-effect model
log(RGR)=α+β1×treatment +β2×6MonthPrecip +β3×SoilType +β4×Zone +
β5×elevation+β6×PlantAge +β6×island +N(0,σ 2
PlantID)
The growth rate model is a general linear mixed-effects regression fit using the ‘lme4’
package (Bates et al., 2015). Relative growth rate (RGR) was calculated as the relative rate
of increase in height over time and was log-transformed to meet assumptions of normality.
Growth rates of zero were excluded from this analysis to maintain normality. Plant age was
included in the model to account for the fact that RGR changes as seedlings get older. Plant
ID is included as a random effect. Random effects account for within-group correlation
that results from non-independent data points (Pinheiro & Bates, 2000). For example,
our growth data are based on repeated measures of each individual plant, which means
that growth measurements are not independent within an individual plant. The random
effect for Plant ID allows us to include all observations in our analysis by accounting for
this non-independence. The two-year survival model tested the overall survival of each
seedling two years after planting and was fit using a generalized linear model function with
a binomial family logit function in the ‘base’ package (R Core Team, 2017). Because only
one data point was available for each plant, the lower sample size required a simpler model
in which soil type was removed in order to allow the model to converge successfully and
no random effects were necessary. These models were then compared to null models using
the likelihood-ratio to test for the effect of treatment on growth rate and survival. Null
models were the same as the models listed above except for the exclusion of technology
treatment. A significant difference between the two models indicates that the variable that
was excluded (i.e., treatment) is a significantly important predictor.
We examined the relative effect of each variable within the growth rate and survival
models to assess the relative importance of technologies as well as other environmental
factors such as soil type and elevation. All continuous variables in our models were
standardized by subtracting the mean and dividing by two times the standard deviation
in order to relativize the effect of each variable coefficient on growth rate and two-year
survival (Gelman, 2008). Confidence intervals (95%) for each coefficient in each full
model were then generated through the ‘‘profile’’ method (Stryhn & Christensen, 2003)
and plotted for visual comparison. P-values were generated for each coefficient in the
logistic regression based on the Wald statistic. For the mixed effect growth rate model,
P-values were generated using the Satterthwaite method in the ‘lmerTest’ package in R
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 7/19

(Kuznetsova, Brockhoff & Christensen, 2017). P-values generated from mixed-effect models
are not always accurate, but we include these values for the sake of highlighting the degree
to which variables differ in their relative importance. Furthermore, all significance values
generated in this way were consistent with confidence interval results. Coefficients for
logistic models were back-transformed to odds ratio by exponentiating and subtracting
one. In this way the coefficient values can be interpreted as the proportional effect of each
variable on increasing (or decreasing if negative) the probability of two-year survival. Each
model was fit using data from all four islands included in the analysis (Baltra, Floreana,
Santa Cruz, and Plaza Sur), but due to high control treatment mortality on Plaza Sur, the
models were also tested using data that excluded Plaza Sur as well as using data exclusively
from Plaza Sur. Continuous variables were standardized within each of these three analyses.
When testing with data exclusively from Plaza Sur, ‘‘island’’ was removed from the models
and treatment type consisted of only Groasis and controls because no Cocoons were used
on Plaza Sur. Finally, the current state of all planted individuals included in the analysis
(up through 2018) was plotted as stacked bar plots to visualize rates of survival between
islands and treatments.
RESULTS
General outcomes
Of the 1,425 Opuntia spp. individuals planted between 2013 and 2018, (most plantings
were made in 2015 and 2016, Fig. 2), 943 Opuntias remained alive by the end of 2018
(66% overall survival, Fig. 2). Of those individuals planted at least three years prior to
2019, Opuntia mortality three years after planting fell to 1% and overall survival leveled
at 67%. On Plaza Sur, 737 Opuntia individuals were planted between 2015 and 2018 with
452 survivors by the end of 2018 (an increase of 106% from the last recorded population
estimates of 426 in 2014 (Jaramillo, Tapia & Gibbs, 2017)). Survival of seedling plantings
on Plaza Sur was 26.8% (n=82) for controls and 62.2% (n=519) for Groasis (Fig. 3A).
Survival of seedling plantings on Floreana was 66.7% (n=3) for controls and 31.2%
(n=16) for Groasis (Fig. 3B). Survival of seedling plantings on Baltra was 79.7% (n=74)
for controls, 45% (n=20) for Cocoon, and 65.5% (n=255) for Groasis (Fig. 3C). Survival
of seedlings planted on Santa Cruz was 77.8% (n=9) for controls, 27.8% (n=18) for
Cocoon, and 72.7% (n=33) for Groasis (Fig. 3D).
Outcomes across all islands
Treatment type (Groasis, Cocoon, or Control) was associated with growth rate (χ2(2)
=54.54, P<0.001) and two-year survival rate of Opuntia seedlings (χ2(2) =41.53,
P<0.001). In the two-year survival logistic regression, elevation (1.88, P=0.001) and
littoral zone (13.72, P<0.001) had odds ratios with confidence intervals that did not
overlap zero (Fig. 4A). Groasis technology had a positive odds ratio of 1.28 (P<0.001),
while Cocoon had a negative odds ratio of −0.89 (P<0.001) (Fig. 4A). In the growth
rate regression, littoral zone (0.48, P<0.001), plant age (−0.51, P<0.001), rocky-sand
soil (−0.3, P=0.026), and six-month precipitation (0.23, P=0.033) all had effect sizes
with confidence intervals that did not overlap zero (Fig. 4B). Groasis technology had a
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 8/19

Figure 2 Total Opuntia spp. restoration from 2013 to 2018 across Baltra, Española, Floreana, Plaza
Sur, San Cristóbal, and Santa Cruz islands. Values above bars indicate total surviving individuals by the
end of each year (y-axis values). Values at the bottom indicate the total number of individuals planted
each year.
Full-size DOI: 10.7717/peerj.8156/fig-2
positive effect size with a coefficient of 0.52 (P<0.001), while Cocoon had an insignificant
coefficient (P=0.179) (Fig. 4B).
Outcomes on plaza sur island only
On Plaza Sur Island, treatment type (Groasis or Control) was associated with growth rate
of Opuntia species (χ2(1) =18.92, P=0.001) and two-year survival rate of Opuntia
seedlings (χ2(1) =23.44, P<0.001). In the two-year survival logistic regression, littoral
zone (379.63, P<0.001), elevation (1.54, P<0.001), and six-month precipitation (−0.67,
P<0.001) had odds ratios with confidence intervals that did not overlap zero (Fig. 4C).
Groasis technology had a positive odds ratio of 3.7 (P<0.001) (Fig. 4C). In the growth
rate regression, littoral zone (0.49, P<0.001), plant age (−0.26, P<0.001), six-month
precipitation (−0.23, P=0.001), and elevation (0.17, P=0.012) all had effect sizes with
confidence intervals that did not overlap zero (Fig. 4D). Groasis technology had a positive
effect size with a coefficient of 0.46 (P<0.001) (Fig. 4D).
Outcomes on all islands excluding Plaza Sur
Treatment type (Groasis, Cocoon, or Control) was associated with growth rate of Opuntia
species (χ2(2) =17.8, P<0.001), but not with two-year survival rate of Opuntia seedlings
(χ2(2) =1.85, P=0.397). In the two-year survival logistic regression, transition zone
(-0.99, P<0.001) and littoral zone (−0.77, P=0.013) had negative odds ratios with
confidence intervals that did not overlap zero (Fig. 4E). Both Groasis and Cocoon
technologies had insignificant negative odds ratios of (P=0.236) and (P=0.305)
respectively (Fig. 4E). In the growth rate regression, plant age (−0.83, P<0.001), six-
month precipitation (0.52, P<0.001), and rocky-clay soil (−0.23, P=0.032) had effect
sizes with confidence intervals that did not overlap zero (Fig. 4F). Groasis technology had
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 9/19

0.0
0.2
0.4
0.6
0.8
1.0
Proportion
A
control groasis
N = 82 N = 519
73.2% dead
26.8% alive
37.8% dead
62.2% alive
0.0
0.2
0.4
0.6
0.8
1.0
B
control groasis
N = 3 N = 16
33.3% dead
66.7% alive
68.8% dead
31.2% alive
dead
bad
normal
good
0.0
0.2
0.4
0.6
0.8
1.0
Proportion
C
control cocoon groasis
N = 74 N = 20 N = 255
20.3% dead
79.7% alive
55% dead
45% alive
34.5% dead
65.5% alive
0.0
0.2
0.4
0.6
0.8
1.0
D
control cocoon groasis
N = 9 N = 18 N = 33
22.2% dead
77.8% alive
72.2% dead
27.8% alive
27.3% dead
72.7% alive
dead
bad
normal
good
Figure 3 State of each planted Opuntia individual by the end of 2018 within each island. (A) Plaza Sur;
(B) Floreana; (C) Baltra; (D) Santa Cruz. ‘‘N’’ indicates the total number of individuals within each treat-
ment on each island. Plant state categories (‘‘good’’, ‘‘regular’’, ‘‘poor’’, and ‘‘dead’’) refer to the subjective
observation of the physical state of the plant. ‘‘Good’’ plants are fully green with no signs of desiccation
or browning in the cladodes, while ‘‘poor’’ plants appear desiccated and browning, and likely to die soon.
The figure is based on the last noted observation of each plant at the end of 2018 and based on only those
data used in the analysis.
Full-size DOI: 10.7717/peerj.8156/fig-3
a positive effect size with a coefficient of 0.4 (P<0.001), while cocoon had an insignificant
coefficient (P=0.261) (Fig. 4F).
DISCUSSION
Water-saving technologies enhanced survival and growth of Opuntia plantings, but benefits
of these technologies were highly contingent upon planting environment. For example,
Groasis technology was effective at increasing growth rate across islands overall, but was
only effective at aiding survival on Plaza Sur Island where Groasis increased the probability
of two-year survival of seedlings more than three-fold (370%) (Fig. 4). Cocoon technology,
however, provided no improvement in growth rate and actually reduced probability of
two-year survival of seedlings by 89% overall (Fig. 4). Although still in its early stages
with all planted Opuntias yet to reach maturity, our restoration efforts have increased the
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 10/19

-2 024
Cocoon***
Groasis***
6-month Precip
Littoral Zone***
Transitional Zone
Elevation**
-0.89
1.28
-0.41
13.72
-0.82
1.88
Odds Ratio
A
C.I. = 7.57 – 25.69
-1.5 -1.0 -0.5 0.0 0.5 1.0
Cocoon
Groasis***
6-month Precip*
Sandy Soil
Rich Soil
RichClay Soil
RockyClay Soil
RockySand Soil*
Littoral Zone***
Transitional Zone
Elevation
Plant Age***
-0.29
0.52
0.23
-0.11
0.05
-0.02
-0.2
-0.3
0.48
0.23
-0.03
-0.51 B
-2 02468
Groasis***
6-month Precip***
Littoral Zone***
Elevation***
3.7
-0.67
379.63
1.54
Odds Ratio
C
C.I. = 80.07 – 6803.78
-1.0 -0.5 0.0 0.5 1.0
Groasis***
6-month Precip**
RockySand Soil
Littoral Zone***
Elevation*
Plant Age***
0.46
-0.23
-0.11
0.49
0.17
-0.26
D
-2 -1 0123
Cocoon
Groasis
6-month Precip
Littoral Zone*
Transitional Zone***
Elevation
-0.45
-0.36
0.73
-0.77
-0.99
-0.17
Odds Ratio
E
-2 -1 012
Cocoon
Groasis***
6-month Precip***
Sandy Soil
Rich Soil
RichClay Soil
RockyClay Soil*
RockySand Soil
Littoral Zone
Transitional Zone
Elevation
Plant Age***
-0.25
0.4
0.52
-0.16
0.11
-0.14
-0.23
-0.04
0.17
-0.05
-0.21
-0.83 F
Figure 4 Plots of the relative effect of variable parameters on two-year survival and growth rate of
planted Opuntia individuals. (A) all islands two-year survival; (B) all islands growth rate; (C) Plaza Sur
island two-year survival; (D) Plaza Sur island growth rate; (E) all islands excluding Plaza Sur two-year sur-
vival; and (F) all islands excluding Plaza Sur growth rate. Each point represents coefficient estimate +/-
95% confidence intervals. P-values are generated based on the Satterthwaite method for growth rate mod-
els and the Wald statistic for survival models (* P<0.05, ** P<0.01, *** P<0.001). Values for two-year
survival models are converted to odds ratio by exponentiating coefficients and subtracting one. Analyses
are based on data from Baltra, Floreana, Plaza Sur, and Santa Cruz islands. Littoral zone values in (A) and
(C) fall outside the scale of those boxes, so confidence intervals are presented as text.
Full-size DOI: 10.7717/peerj.8156/fig-4
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 11/19

population of Opuntia spp. in the Galápagos archipelago by 943 individuals (66% survival
of 1,425 plantings), more than doubling the population of Opuntia cacti on Plaza Sur
Island, from 426 to 878 in just four years (Jaramillo, Tapia & Gibbs, 2017).
These results emphasize the species- and site-specific contingencies of applying water-
saving technologies for plant restorations. For example, Cocoon technology did not provide
any advantage when planting Opuntias in the Galápagos archipelago. This is despite the fact
that in other systems and with other species Cocoon has been shown to increase survival
rates in planted trees from 0–20% to 75–95% (Faruqi et al., 2018). One possible explanation
is that Opuntia cacti have a short initial rooting depth compared to other species (Snyman,
2005), and this may reduce access to the water available from the Cocoon (Land Life
Company, 2015;Appendix 1). Acacia macracantha, for example, has much deeper roots
and has had much greater success when planted with Cocoon technology in the Galápagos
(GV2050, unpublished data).
Although Groasis technology helped increase growth rate of Opuntias overall, it had a
clear, positive effect on the survival of Opuntias only on Plaza Sur Island. A likely factor
contributing to this is that compared to other islands, the majority of Opuntias were planted
on Plaza Sur preceding the greatest period of drought in the Galápagos over the last five years
(Appendix 2;Charles Darwin Foundation, 2018). Despite fairly regular seasonal patterns of
water availability in the Galápagos (Snell & Rea, 1999;Restrepo et al., 2012), there remains
much variability, especially caused by El Niño events (Trueman & D’Ozouville, 2010). In
this way Groasis may have the greatest advantage when ensuring water availability for
Opuntias during periods of especially severe drought, and in particular for seedlings which
rely on periods of greater moisture to germinate and survive (Hicks & Mauchamp, 1996).
Opuntia cacti are typically more resistant to desiccation and water stress compared to
other species that do not have physiological adaptations for surviving low-water desert
conditions (Racine & Downhower, 1974;Dubrovsky, North & Nobel, 1998), and this may
explain why Groasis was only effective for Opuntia cacti under extreme drought. These
findings support the idea that water availability for Opuntias plays less of a role in survival
than previously assumed (Racine & Downhower, 1974;Coronel, 2002;Jaramillo, Tapia &
Gibbs, 2018). These findings do not negate the value of the Cocoon or Groasis technology
for restoration overall, but rather presents the important observation that water-saving
technologies such as Cocoon and Groasis should be considered on a case-by-case basis
and tested with each species and in different environmental conditions before making
expansive planting efforts. Groasis technology may provide a form of insurance for the
unpredictability of extreme drought events and the benefits of using Groasis technology
may in some cases outweigh the costs in the long run (e.g., ∼22 USD per Groasis unit plus
overhead and installation time (Groasis R
, 2019)).
Site co-variates also affected Opuntia survival and growth. In particular, vegetation zone,
elevation, and precipitation were important predictors of Opuntia survival and growth but
as with water-saving technologies, these effects were highly contingent on island. Opuntias
had a greater survival and growth rate in the littoral vegetation zone on Plaza Sur but had
greater survival in the arid vegetation zone on other islands. This effect may be due to an
interaction between environmental and biotic factors unique to Plaza Sur or other islands.
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 12/19

For example, Plaza Sur has especially high land iguana densities speculated to be due to
the loss of its main predator from the island, the Galápagos hawk (Sulloway & Noonan,
2015). This high herbivore density may help keep invasive plant species in check on Plaza
Sur—species that may otherwise shade out Opuntia seedlings on other islands (Schofield,
1973;Hicks & Mauchamp, 1996;Hicks & Mauchamp, 2000).
Surprisingly, the level of precipitation six-months after planting did not increase
seedling survival, and actually decreased survival of seedlings planted on Plaza Sur. This
finding contradicts conclusions from previous work by Coronel (2002) who found that
precipitation during the six months following planting increased Opuntia survival. Coronel
(2002), however, found that the positive effect of rainfall following planting was mostly
evident in Opuntias grown from vegetative cladodes rather than seeds as in the current
analysis. Furthermore, most seedlings were planted on Plaza Sur at the start of a long period
of drought so there was not as much variation in precipitation on Plaza Sur seedlings to
fully test its effects. Elevation was only a significant predictor of survival and growth rate
on Plaza Sur (Fig. 4). This may be in part because although littoral zone on Plaza Sur has
a positive impact on survival and growth, seedlings that are too low in elevation are more
exposed to ocean salt spray which can increase seedling mortality (Boyce, 1954). Soil type
had only marginally significant effects on growth rate (Fig. 4), suggesting that, at least for
Opuntias, substrate is of less importance for growth rate than factors such as vegetation
zone or elevation. The effect of soil type on survival could not be tested with the current
data due to limitations in sample size.
The observational aspects of our study have some inherent limits. Although it seems
likely that extreme drought was the primary driver of control treatment seedling mortality
on Plaza Sur, other effects cannot be ruled out. Plaza Sur is a small island (the smallest
island by far of the four in this analysis: only 13 ha, with the next larger being Baltra at
2100 ha), which could increase the exposure of seedlings to salt spray, exposure to sea
lion activity, as well as a suite of other effects associated with small islands (Lomolino &
Weiser, 2001). It may also be that the high concentration of land iguanas and sea lions (P
Jaramillo, pers. obs., 2018) has impacted the edaphic environment of the island through
their excrement as can be common on seabird islands (Rajakaruna et al., 2009). Thus, the
small area and low variation in elevation, precipitation, and vegetation zones associated
with Plaza Sur plantings suggests that any significant effect of these factors within Plaza
Sur be taken cautiously when generalizing to Opuntia restoration beyond this island. The
experimental treatments of the study involving water-saving technologies, however, do
suggest that extreme drought is the most probable hypothesis for the high control mortality
on Plaza Sur. Another important caveat is that taxon effects are confounded with island
effects. With one exception, each island had a particular species or variety of Opuntia
(Table 1). It is possible that some of the island-based differences are actually due to slightly
different environmental requirements of the Opuntia taxa used in this study.
In conclusion, this study underlines the importance of considering the specific
circumstances and methodologies that affect successful restoration. Water-saving
technologies such as the Groasis Waterboxx R
and Cocoon are promising systems for
restoring species in arid environments but should not be assumed to function equally well
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 13/19

in all environments and with all species. Even within one system, as in the current study,
the benefits of Groasis vary tremendously and likely depend on the precipitation available
following plantings. It is possible that species already adapted for low water conditions, such
as cacti, have a much higher threshold of drought at which Groasis or other water-saving
technologies provide a benefit. Future evaluations of these technologies should monitor
precipitation to test whether there is a threshold level of drought where these technologies
become more effective. In some cases and for some species there may be no threshold
for effective use as with the Cocoon technology for Opuntias. Preliminary plantings
coupled with extensive environmental and experimental data collection is essential before
large-scale planting efforts are initiated with water-saving technologies. Our work restoring
reproductive Opuntia populations is still in its early stages, but water-saving technologies
may have a profound influence on how quickly we reach sustainable levels of reproductive
Opuntia populations on these islands. Field observations and unpublished data suggest that
Opuntias reach reproductive maturity at between 20 and 40 years of age, largely dependent
on the island and particular taxon (W Tapia, J Gibbs, & F Sulloway, 2019, unpublished
data). A conservative estimate based on current planting survivorship is that at least 60% of
planted individuals (855) will reach reproductive maturity (this is based on our three-year
survival rate of 67%, at which point yearly mortality fell to 1%).
Through our experimental evaluation of restoration methodologies, the Galápagos
Verde 2050 project of the Charles Darwin Foundation presents a model for data-informed
adaptive management and conservation. We hope this model may inspire other restoration
efforts to adopt similar data-informed approaches. Continued monitoring and accounting
for context-specific contingencies in restoration work is essential (Cabin, 2007) and future
restoration efforts should continually adapt management protocols based on current results
(Parma & NCEAS Working Group on Population Management, 1998).
ACKNOWLEDGEMENTS
This is the work of the entire Galápagos Verde 2050 project team of the Charles Darwin
Foundation, particularly María Guerrero, Esme Plunkett, and Paúl Mayorga. Assistance
and advice was also provided by: Jorge Carrión, Christian Sevilla, Danny Rueda, Jeffreys
Málaga, Milton Chugcho, Rafael Chango, Jibson Valle, Francisco Calva, Edie Rosero and
Francisco Moreno from DPNG. Novarino Castillo provided valuable field assistance.
Institutional support was provided by DPNG (Dirección del Parque Nacional Galápagos),
ECOGAL (Aeropuerto Ecológico de Baltra), FAE (Fuerza Aérea Ecuatoriana), ABG
(Agencia de Regulación y Control de la Bioseguridad y Cuarentena para Galápagos), GAD
(Gobiernos Autónomos Descentralizados from Floreana and Santa Cruz). Washington
Tapia, Felipe Cruz †, María del Mar Trigo, and Frank Sulloway provided critical advice
and encouragement. We also thank Washington Tapia and Frank Sulloway for their
observations and data used to estimate age of maturity for Opuntias. Steve Rushton
provided valuable comments on an earlier version of the manuscript. Finally, we thank
our editor Timothy Scheibe and three reviewers: Neftali Ochoa-Alejo, Matthew Madsen,
and F.B. Vincent Florens for their invaluable comments that improved this manuscript.
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 14/19

This publication is contribution number 2289 of the Charles Darwin Foundation for the
Galapagos Islands.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
Funding was provided by the COmON Foundation, The Leona M and Harry B. Helmsley
Charitable Trust, and the BESS Forest Club. There was no additional external funding
received for this study. The funders had no role in study design, data collection and
analysis, decision to publish, or preparation of the manuscript.
Grant Disclosures
The following grant information was disclosed by the authors:
COmON Foundation, The Leona M and Harry B. Helmsley Charitable Trust.
BESS Forest Club.
Competing Interests
The authors declare there are no competing interests.
Author Contributions
•Patricia Isabela Tapia analyzed the data, authored or reviewed drafts of the paper,
approved the final draft.
•Luka Negoita analyzed the data, prepared figures and/or tables, authored or reviewed
drafts of the paper, approved the final draft.
•James P Gibbs conceived and designed the experiments, authored or reviewed drafts of
the paper, approved the final draft.
•Patricia Jaramillo conceived and designed the experiments, performed the experiments,
contributed reagents/materials/analysis tools, authored or reviewed drafts of the paper,
approved the final draft.
Field Study Permissions
The following information was supplied relating to field study approvals (i.e., approving
body and any reference numbers):
Fieldwork and Opuntia plantings were approved by Dirección del Parque Nacional
Galápagos (DPNG) under permit number PC-11-19.
Data Availability
The following information was supplied regarding data availability:
The raw data is available as a Supplemental File.
Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.8156#supplemental-information.
Tapia et al. (2019), PeerJ, DOI 10.7717/peerj.8156 15/19

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