Influence of el nIño Southern oScIllatIon PerIodS on  
Plant denSIty of hoffmannSeggIa aPhylla (fabaceae), an  
endangered SPecIeS  
InfluencIa de loS PeríodoS de el nIño oScIlacIón del Sur en la denSIdad  
vegetal de hoffmannSeggIa aPhylla (fabaceae), una eSPecIe en PelIgro  
1,3  
Felipe S. Carevic * & Roberto Contreras  
Summary  
Background and aims: Studies on the natural regeneration of plant species under  
hyperaridity conditions have been scarce, mainly because of the low germination  
percentage of the species under these conditions. Presumably, sporadic  
phenomena such as the El Niño Southern Oscillation (ENSO) could have a positive  
effect on the natural germination of these species, although this effect has not yet  
been satisfactorily explored.  
1
. Laboratorio de Ecología Vegetal,  
Facultad de Recursos Naturales  
Renovables, Universidad Arturo  
Prat, Iquique, Chile  
2
y
. Centro Regional de Investigación  
Desarrollo Sustentable de  
M&M: To test the crucial assumption of our statement, a hyperarid region (average  
rainfall below 5 mm/year) was used as a model to determine the effect of ENSO  
years on the natural regeneration rate of adult individuals of the endemic legume  
Hoffmannseggia aphylla (retama) in the Atacama Desert, northern Chile. Thus, the  
vegetation density of an endemic leguminous species in a sector of the Pampa del  
Tamarugal, Tarapacá Region, northern Chile, was analyzed for six years.  
Results: The density of this species increased during ENSO years, mainly due to  
water flows from the highest sectors of the Tamarugal pampas, such as the town of  
Pica, in addition to the increase in humidity and summer rainfall.  
Atacama (CRIDESAT), Universidad  
de Atacama, Copiapó, Chile  
3
. Millennium Nucleus on Applied  
Historical Ecology for Arid Forests  
Aforest). Santiago de Chile  
(
Citar este artículo  
Conclusion: Our results highlight the transcendence of the ENSO in the regeneration  
of leguminous plants.  
CAREVIC, F. S. & R. CONTRERAS.  
023. Influence of “el niño  
2
southern oscillation” periods on  
plant density of Hoffmannseggia  
aphylla (Fabaceae) an endangered  
species. Bol. Soc. Argent. Bot. 58:  
Key wordS  
Atacama desert, ENSO, Fabaceae, Hoffmannseggia, Hyperarid, legume.  
reSumen  
257-265.  
Introducción y objetivos: Los estudios sobre la regeneración natural de especies  
vegetales en condiciones de hiperaridez han sido escasamente estudiados en  
terreno, principalmente por el bajo porcentaje de germinación de las especies  
en estas condiciones. Presumiblemente, fenómenos esporádicos como El Niño  
Oscilación del Sur (ENOS) podrían tener un efecto positivo en la germinación natural  
de estas especies, aunque este efecto aún no ha sido explorado satisfactoriamente.  
M&M: Para testear la suposición crucial de nuestra afirmación, se utilizó una  
región hiperárida (precipitación promedio inferior a 5 mm/año) como modelo para  
determinar el efecto de los años ENOS en la tasa de regeneración natural de  
individuos adultos de la leguminosa endémica Hoffmannseggia aphylla (retama)  
en el desierto de Atacama, norte de Chile. Así, se analizó durante seis años la  
densidad vegetal de esta especie en un sector de la Pampa del Tamarugal, Región  
de Tarapacá, norte de Chile.  
Resultados: La densidad de esta especie se incrementó durante los años ENOS,  
principalmente por los caudales de agua provenientes de los sectores más altos  
de la pampa del tamarugal, como el poblado de Pica, además del aumento de la  
humedad y las precipitaciones estivales.  
Conclusión: Nuestros resultados destacan la trascendencia del ENOS en la  
regeneración de plantas leguminosas.  
PalabraS claveS  
Desierto de Atacama, ENSO, Fabaceae, hiperárido, Hoffmannseggia, leguminosa.  
Recibido: 22 Ago 2022  
Aceptado: 1 Jun 2023  
Publicado impreso: 30 Jun 2023  
Editora: Natalia Aguirre Acosta  
ISSN versión impresa 0373-580X  
ISSN versión on-line 1851-2372  
257  
Bol. Soc. Argent. Bot. 58 (2) 2023  
IntroductIon  
(Ministerio de Medio Ambiente, 2022). The  
main threat to natural H. aphylla populations  
The natural regeneration processes of plant in northern Chile is associated with the current  
species are currently considered one of the main depletion of the water table, which may be a  
problems facing climate change because the real direct cause of the decline in legume populations  
effects of this problem on the reproductive rates of (Chavez et al., 2013). Former studies denoted  
the species are still unknown (Peters et al., 2012). that the water flux into the aquifer of Pampa del  
In this sense, the Atacama Desert is no stranger Tamarugal, is calculated to be between 880 and  
to this type of process, mainly because of four 1000 l/s, while the water outflow is estimated  
determining factors: 1) the effect of the decrease to be as high as 4000 l/s (Dirección General de  
in precipitation recorded at the beginning of Aguas, 2011; Calderón et al., 2015; Viguier et al.,  
this century in northern Chile (Soto & Ulloa, 2019). In this ecosystem, groundwater aquifers  
1
997); 2) the decrease in relative soil humidity are the only source of water, which are fed by the  
in this area (Neilson et al., 2017); 3) the increase rainfall, glaciers and snowmelt from the Andes  
in salinity in high Andean limnetic bodies Mountain range. This shrub has conditions of  
(
Gajardo & Redón, 2019); and 4) the decrease successful natural adaptability in arid soils with  
in the groundwater table (Viguier et al., 2019). high salinity (even with electrical conductivities  
This type of groundwater has been described as of 182 Ds/m) and nitrogen impoverishment in the  
one of the main sources of water supply for the edaphic stratum (León et al., 2017). However,  
maintenance of the vegetation present in this the natural regeneration of plant species in this  
ecosystem, but the effect of precipitation pulses area is almost null due to the almost nonexistent  
or the occurrence of climatic phenomena such precipitation averaging 1 mm/year and the  
as the El Niño Southern Oscillation (ENSO) presence of a saline crust layer on the edaphic  
could have some impact on vegetation density surface (León et al., 2017). In this sense, it fails  
(
Squeo et al., 2006). In the past decade Chile has to form a homogeneous shrub stratum, as the  
experienced a mega drought, where the presence distribution of individuals on the ground is not  
of a strong ENSO during most of 2015 stood out very dense, with individuals that seem to form  
(
Garreaud et al., 2019).  
mosaics following the floods that usually occur  
The natural regeneration of desert leguminous in this ecosystem (Lewis & Sotuyo, 2010).  
species under ENSO conditions has scarcely Once established, adult individuals of Prosopis  
been evaluated under field conditions (Kraus et tamarugo Phil., for example, would depend on  
al., 2007). The occurrence of this phenomenon the flow of water present at the phreatic level,  
is a powerful tool for evaluating this type of which is usually present in the first meters of soil  
ecological condition in plants, as precipitation depth owing to its ascent by capillarity (Calderón  
and humidity tend to increase in arid areas of et al., 2015). Preliminary results have indicated  
northern Chile when ENSO is present (Acosta a favorable increase in the regenerative rates  
et al., 2015). The genus Hoffmannseggia Cav. of the species, although this trend should be  
(
Fabaceae) has a wide distribution, including further explored in detail, considering edaphic  
the arid and semi-arid regions of Argentina, factors and flooding episodes during the summer  
Chile, Peru, and Bolivia in South America, and (Carevic, 2020). Regarding this condition, natural  
Mexico and the southwestern United States seed germination could occasionally occur as a  
in North America (Kraus et al., 2007). In the result of summer precipitation and water flooding  
Atacama Desert, Hoffmannseggia aphylla (Phil.) during ENSO periods and to a lesser extent  
G.P. Lewis & Sotuyo (Spanish “retama”) is during Interdecadal Pacific Oscillation (IPO)  
an endemic phreatophyte shrub legume that periods. However, this effect has not yet been  
fixes atmospheric nitrogen, and its distribution explored in this species.  
is limited to the northern part of this desert,  
Previous studies carried out in arid ecosystems  
specifically the Pampa del Tamarugal in northern have reported a positive effect of precipitation  
Chile (Lewis & Sotuyo, 2010). Recently, this during ENSO events on the density of plant  
species has been considered as “endangered” species growing at low altitudes above sea  
258  
F. S. Carevic & R. Contreras, Densidad de Hoffmannseggia aphylla en el norte de Chile  
level; although the same precipitation was not spring (September). For this objective, 38 linear  
significant for the increase in primary productivity transects of 95 m were georeferenced within the  
of species established at high altitudes (2,500 m grid, with points every 5 m. Flower sprouting  
above sea level) (Squeo et al., 1999). However, was assessed semi-annually during the period  
the influence of seasonal environmental of 2012-2016 by tagging the flowers which  
parameters and their effects on plant density emerged using a thread of a particular color,  
and reproduction parameters in legume species with a distinctive color used for period so that at  
growing under hyperarid conditions are poorly harvest, flower production as well as pods could  
understood, considering that climate may play an be attributed to the respective period of sprouting  
important role in monitoring and predicting plant (Leport et al., 2006). For this purpose, we selected  
viability and reproduction. We hypothesized that 12 adult individuals of H. aphylla. This tagging  
the increased surface water flow resulting from was also used to record the total number of flowers  
precipitation during ENSO years would have an produced per plant (total number of tags per  
incremental effect on the germination rate and plant), and the number of pods per plant (number  
flower parameters (number of flowers, number of of tags with a date of flower sprouting), and the  
pods per plant and percentage of flower abortion) proportion of aborted flowers. For environmental  
of H. aphylla seeds in northern Chile. Thus, our characterization, two meteorological stations were  
objective was to evaluate the long-term impact of established near the study area to record daily  
environmental variables during ENSO events in environmental conditions (ambient temperature,  
northern Chile on the reproductive and ecological precipitation, wind speed, and solar radiation),  
parameters of H. aphylla, an endangered endemic both located on slopes, to determine the effect of  
species of the Atacama Desert.  
flooding on the study area. The first was located  
in Canchones (UTM: 7739099, 443867; 1005 m  
a.s.l.), located 1.5 km from the study area. Another  
meteorological station was in the town of Pica  
materIalS and methodS  
(
UTM: 7734562, 465733; 1345 m a.s.l.), 15 km  
Study area  
from the study area. Similarly, five digital soil  
The study was carried out within the natural humidity probes (ECHO) were established at 0.6  
habitat of H. aphylla in Pampa del Tamarugal, m depth distributed in the study area to record  
northern Chile. The climate of this area is the seasonal evolution of this parameter. Each  
hyperarid. The site was dominated by P. tamarugo, humidity sensor was separated by approximately  
H. aphylla, and Atriplex atacamensis Phil. 70 m from each other.  
The latter two species are small shrubs that are  
sparsely distributed on the grid. The study area Statistical analysis  
is characterized by extreme hyperarid conditions,  
To evaluate interannual differences in H.  
with annual precipitation not exceeding 0.6 mm/ aphylla density and flower parameters (number of  
year, which occurs mainly during the summer flowers, number of pods per plant and percentage  
season (Carevic et al., 2021). However, there of flower abortion), we used a linear general  
are years with rainfall pulses that exceed 7 mm/ model by means of repeated measures. The flower  
year, especially in sectors with an altitude above parameters data were log-transformed ln (x+1)  
sea level higher than that present in Canchones to increase linearity and reduce the correlation  
(
Arenas 2019; Lanino & Poblete, 2022).  
between the mean and variance. Relationships  
between meteorological and edaphic data  
(temperature, precipitation, solar radiation,  
Experimental design  
During the period 2012-2018, an experimental wind speed, and soil humidity) and H. aphylla  
grid of 3.1 ha was established in the Canchones density and flower production were evaluated  
sector in the Pampa del Tamarugal, northern using multiple matrix correlations (r). Data was  
Chile to evaluate H. aphylla density using the analyzed by using SPSS Statistics for Windows,  
transect line method (Cox, 1981). Sampling was Version 23.0 (IBM SPSS Statistics for Windows,  
carried out during the fall (May) of each year and Version 23.0. Armonk, NY: IBM Corp).  
259  
Bol. Soc. Argent. Bot. 58 (2) 2023  
Fig. 1. Precipitation, temperature and humity in the study area. A: Annual precipitation detected in Pica  
(black columns) and Canchones (white columns) (left, above). B: Mean annual summer temperatures (black  
line) and mean humidity (white bars) in Canchones.  
reSultS  
The environmental humidity and temperatures  
detected during summer had different fluctuations,  
During the present study, the presence of two with the highest environmental humidity values  
flooding events during the summers of 2015 and recorded in 2015 and the highest summer  
2
016 was observed, reflected in the increase in soil temperature averages in 2017. Likewise, the density  
humidity during those periods and the presence of determined during 2015 and 2016 was strongly  
summer rainfall that exceeded 4 mm/year in Pica correlated with the environmental humidity detected  
(
Figs. 1; 2).  
during summer 2015 in Canchones (December  
st st  
The most important variation associated with 21 to March 21 ); r=0.56, p<0.01, and with the  
H. aphylla density parameters was related to an annual precipitation recorded in Pica the same  
increase in the number of individuals per area after year (r=0.51, p=0.02). Furthermore, we observed  
the 2015 event (Table 1), when new individuals a significant relationship between soil humidity  
of low size were recorded, typical of regeneration and plant density during the same period (r=0.39,  
phenomena, which subsequently decreased (2017 p=0.03). Regarding flower parameters, we did not  
and 2018).  
find significant differences between numbers of  
260  
F. S. Carevic & R. Contreras, Densidad de Hoffmannseggia aphylla en el norte de Chile  
Fig. 2. Seasonal evolution of average soil humidity by season of the year.  
flower sprouts at population level. Furthermore,  
flower parameters did not show any relationship  
with climatic parameters (Table 2).  
Table 1. Area density of H. aphylla individuals  
during the study. Differences between years are  
denoted by different letters.  
Plant density H. aphylla  
dIScuSSIon  
2
Year  
p value  
Individuals/m  
0.001  
F value  
24.55  
29.09  
30.87  
41.76  
41.08  
21.22  
21.97  
Our findings constitute the first large-scale study  
of the natural regeneration processes generated  
under hyperarid conditions in the Atacama Desert.  
Thus, precipitation generated during ENSO  
events seems to be an essential factor for the  
germination of H. aphylla in northern Chile,  
consistent with previous studies indicating that  
the increase in sporadic water pulses present  
during this phenomenon plays an essential role  
in the regeneration of arid zone plant species  
ab  
2012  
2013  
2014  
2015  
2016  
2017  
2018  
0.12  
b
b
a
a
0.21  
0.22  
0.04  
0.04  
0.001  
0.001  
0.001  
(Gutiérrez et al., 2000; Squeo et al., 2006; León  
0.001  
et al., 2011). In the present study, rainfall recorded  
in Pica, that is, in a sector with a higher altitude  
above sea level, had the greatest relationship with  
the increase in vegetation density of this legume  
(Fig. 3). This record is not surprising, as, in “wet”  
periods, precipitation tends to carry water to lower  
ab  
ab  
0.08  
0.09  
0.001  
0.001  
261  
Bol. Soc. Argent. Bot. 58 (2) 2023  
Table 2. Summarized data on flower sprout at intrapopulation level.  
Periods measured  
April November March November  
Parameter  
December August  
May  
2012  
2013  
2014  
2014  
2015  
2015  
2016  
Number of flowers (mean±SE)  
12±2  
13±4  
10±3  
11±2  
13±2  
13±3  
10±2  
Number of pods per  
plant (mean±SE)  
0
0
0
0
3±2  
3±2  
4±2  
3±3  
2±2  
Percentage of flower abortion (%)  
76.9  
76.9  
69.2  
76.9  
84.6  
areas such as Canchones, where this water forms 50% seem to break the physiological dormancy of  
real lagoons that tend to dry up or infiltrate as the this species. Previous investigations, carried out at  
summer progresses (Houston, 2001). However, the the laboratory level, agree that water availability,  
increase in water availability must necessarily be temperature and increased environmental humidity  
accompanied by an increase in humidity during the are limiting factors for breaking dormancy in  
summer in the same study site for this germination species of this genus (Alves et al., 2018; Moreno  
phenomenon to take place, in which values above et al., 2018).  
Fig. 3. Schematic illustration of comparative situation ENSO observed in the study area. A: In 2012.  
Normal periods of rainfall in Pica (1) and environmental humidity in Canchones (2) do not generate an  
incremental variation in the density of H. aphylla population (3). B: In 2015. Increasing rainfall at Pica (4) and  
environmental humidity in Canchones (5), the plant density of H. aphylla increasing notably (6).  
262  
F. S. Carevic & R. Contreras, Densidad de Hoffmannseggia aphylla en el norte de Chile  
There has been some controversy regarding the humidity. It should be noted the positive effect  
effects of environmental variables on germination. that the flooding registered as a result of the  
Formerly, some authors have claimed that precipitation in the Pica sector, contributed to a  
temperature and sunlight are the limiting factors greater extent to the increase in the density of  
for germination processes in plants in the arid H. aphylla plants, which has an explanation due  
zones of Asia (El-Keblawy & Al-Rawai, 2005). to the higher altitude above the ground sea level  
Such studies on the regeneration of native species that Pica presents in relation to the study area  
have been limited to a few years of evaluation and (300 m higher), since when precipitation falls on  
are usually restricted to semiarid ecosystems with that area, the effect of gravity probably allows  
the highest availability of precipitation. In our the displacement of these masses of water to  
study, we found no direct evidence of the effect the flatter areas of the Tamarugal pampa, where  
of sunlight and temperature on H. aphylla density, it was carried out the study. Our research was  
presumably because these parameters remained developed over a long period of time, with the aim  
homogeneous during much of the summer, the of evaluating the effect of climatic phenomena on  
time when increased density was detected (Arenas, the population of an endangered plant species. It  
2
019). Nevertheless, this natural regeneration is essential that monitoring is embedded in a long  
decreased during 2017 and 2018, probably because management program by the accountable agency  
of predation by goat cattle, which is usually or research institutions that is working towards  
abundant in this area and is associated with the the recovery and monitoring of a given threatened  
consumption of native legumes (Carevic et al., species or threatened ecosystem. We highlight  
2
015; Contreras et al., 2020). At reproduction that these benefits of monitoring will be far more  
level, we did not find any relationship between likely to be achieved if the monitoring program is  
climatic traits and flower production. The highest well designed with clearly articulated objectives,  
values of flower abortion and the reduced number with due attention to long term biological traits  
of flowers per plant are not surprising, because and its dynamics based on future climatic effects.  
it has a slow growth with few production of  
leaves and flowers, consistent with the hyperarid  
habitat of Atacama Desert (Lewis & Sotuyo, author contrIbutIonS  
2
010). In conclusion, the presence of ENSO has  
a transcendental influence on the regeneration of  
FC did all experimental work and prepared first  
leguminous plants, especially due to the increase draft of the paper; RC participated on field sampling  
in precipitation in Pica (which only falls within and prepared final version of the paper.  
a few hours) and, to a lesser extent, Canchones,  
which cause water flooding to lower sectors of the  
Tamarugal pampas, a fact that was detected by an acKnowledgementS  
increase in soil humidity. In addition, this effect  
must be combined because it must be accompanied  
Special thanks to Vicerrectoria Investigación,  
by an increase in the average environmental Innovación y Postgrado of Universidad Arturo  
humidity during the summer (January-March).  
Prat, ANID NCS2022_024 Millennium Nucleus  
on Applied Historical Ecology for Arid Forests  
(Aforest) and Junta Vecinal Challajure. To Cynthia  
concluSIonS  
Chávez, Paula Rojas for their support in scientific  
graphic design and Luis Ulloa for their collaboration  
We demonstrate at the field study level, the in field support.  
positive influence of the ENSO phenomenon on  
the natural regeneration rate of H. aphylla in the  
Atacama Desert. The presence of this climatic SuPPlementary data  
phenomenon generates water floodings that allow  
the germination of seeds, although this aspect must  
Supplementary data to this article can be found  
be accompanied by an increase in environmental at: https://github.com/carevicunap/haphylla.  
263  
Bol. Soc. Argent. Bot. 58 (2) 2023  
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