vegetation of a hill gRassland of the Paititi natuRal  
ReseRve (PamPa biome) and eaRly detection of non-  
native sPecies acting as invasive  
vegetación de un Pastizal seRRano de la ReseRva natuRal Paititi (bioma  
PamPa)y detección temPRana de esPecies no nativas actuando como invasoRas  
1
& Viviana M. Comparatore  
María L. Echeverría * , Sara I. Alonso  
Resumen  
Introducciónyobjetivos:Lasespeciesinvasorasrepresentanlamayoramenazapara  
la conservación. Los objetivos de este estudio fueron identificar la flora del pastizal  
serrano de la Reserva Natural Paititi, realizar la detección temprana de especies  
vegetales exóticas que pudieran estar actuando como invasoras y establecer la  
situación actual de aquellas especies nativas consideradas amenazadas.  
1
. Universidad Nacional de Mar del  
Plata, Facultad de Ciencias Agrarias,  
Ruta 226, km 73.5, Balcarce,  
Buenos Aires, Argentina  
2
. Universidad Nacional de Mar del  
M&M: Siguiendo el gradiente altitudinal se seleccionaron 14 sitios donde se registraron  
Plata, Facultad de Ciencias Exactas  
y Naturales, Funes 3250, Mar del  
Plata, Buenos Aires, Argentina.  
Instituto de Investigaciones  
las características ambientales  
y la cobertura-abundancia de las especies  
vasculares. Con los datos recabados se realizó un Análisis de Coordenadas  
Principales (ACooP) que originó unidades de vegetación que fueron descritas  
según características ambientales, especies identificadas y tipo de comunidad  
vegetal. Adicionalmente, se destacaron las especies amenazadas y las exóticas  
más abundantes, en consecuencia consideradas invasoras.  
Marinas  
CONICET  
y Costeras (IIMyC),  
Resultados: La riqueza total fue de 370 especies, correspondiendo el 26,5% a  
exóticas. Se identificaron 30 especies amenazadas. El ACooP reconoció ocho  
unidades de vegetación. Las especies consideradas invasoras fueron Dactylis  
glomerata, Senecio madagascariensis, Holcus lanatus y Racosperma melanoxylon,  
estas dos últimas con los mayores valores de cobertura.  
Conclusiones: Para conservar la biodiversidad y minimizar el proceso de invasión, los  
esfuerzos de manejo deberían enfocarse en monitorear las especies amenazadas y  
controlar el avance de las invasoras. La detección temprana de dichas especies en  
ambientes similares sería fundamental para reducir invasiones vegetales.  
Citar este artículo  
ECHEVERRÍA, M. L., S. I. ALONSO  
V. M. COMPARATORE. 2023.  
&
Vegetation of a hill grassland of  
the Paititi Natural Reserve (Pampa  
biome) and early detection of non-  
native species acting as invasive.  
Bol. Soc. Argent. Bot. 58: 71-90.  
PalabRas clave  
Especies exóticas, pastizales serranos, áreas protegidas, especies amenazadas.  
summaRy  
Background and aims: Invasive species are the greatest threat to conservation. The  
objectives of this study were to identify the flora that thrive in a hill grassland of the  
Paititi Natural Reserve, to perform an early detection of non-native plant species  
that might be acting as invasive, and to establish the current situation of the native  
species considered threatened.  
M&M: Following the altitudinal gradient, 14 sites were selected; the environmental  
characteristics and cover-abundance of the vascular plant species were recorded  
in each site. With the collected data, a Principal Coordinate Analysis (PCooA)  
was performed to group the sites into vegetation units that were later described  
considering environmental characteristics, identified species and plant community  
type. Additionally, the threatened species were specified, as well as the most  
abundant exotic ones, therefore considered invasive.  
Results: Total richness reached 370 species, 26.5% corresponding to non-native  
ones. Thirty threatened species were identified. The PCooA grouped the sites  
into eight vegetation units. The non-native species considered invasive were  
Dactylis glomerata, Senecio madagascariensis, Holcus lanatus and Racosperma  
melanoxylon, these last two reached the highest coverage-abundance values.  
Conclusions: To conserve biodiversity and minimize the invasion process,  
management efforts should be focused on monitoring the threatened species and  
controlling the advance of the non-native species acting as invasive. Early detection  
of those species in similar environments would be fundamental to facilitate rapid  
responses towards reducing invasions.  
Recibido: 13 Ago 2022  
Aceptado: 22 Nov 2022  
Publicado en línea: 17 Feb 2023  
Publicado impreso: 31 Mar 2023  
Editor: Juan Carlos Moreno Saiz  
Key woRds  
ISSN versión impresa 0373-580X  
ISSN versión on-line 1851-2372  
Exotic species, mountain grasslands, protected areas, threatened species.  
71  
Bol. Soc. Argent. Bot. 58 (1) 2023  
intRoduction  
& Cock, 2001; Waterhouse, 2003; Brancatelli et al.,  
020).  
The Pampa biome, an extensive South American  
2
Biological invasions have been recognized  
in many parts of the world as the main agents grassland region located in Uruguay, southern  
of change in natural environments, generating Brazil, and central Argentina (Scottá & da Fonseca,  
harmful effects on ecosystems and biodiversity and 2015) (Fig. 1A), has a high degree of landscape  
imposing an enormous cost on human productive fragmentation. It was formerly characterized by  
activities (Wittenberg & Cock, 2001; Pyšek & grasslands and, to a lesser extent, shrubs (Cabrera,  
Richardson, 2010; van Kleunen et al., 2018). The 1968; Cabrera & Zardini, 1978). However, the  
invasive plants are the non-native plant species advance of the agricultural frontier has generated  
also called introduced, alien, or exotic species– a homogeneous matrix of mainly agricultural lands  
that after their introduction into non-native natural interspersed with areas of natural or semi-natural  
environments, may spread, invading the new vegetation, generally not cultivable (Herrera et  
territory and generating a high impact on the al., 2020). As a result, this region faces a serious  
new ecological niches (Bentivegna & Zalba, and growing challenge associated with an increase  
2
014). Nevertheless, not all non-native species in invasive non-native species (Frangi, 1975;  
become invasive, and the ones that do, are invasive Bilenca & Miñarro 2004; Echeverría et al., 2017;  
only in some places, since the term invasive is Brancatelli & Zalba, 2018).  
associated with specific environmental conditions  
Toward the south of the Pampa biome, the  
(Weber & Gut, 2004; van Kleunen et al., 2018). Tandilia Hill System in Buenos Aires Province  
However, species with a history of invasiveness (Argentina) (Fig. 1A-B) is a discontinuous chain  
tend to repeat this behavior in the places where of low hills (called sierras in Spanish) and rocky  
they are introduced (Baskin, 2002). According outcrops. The Tandilia Hill System is approximately  
to van Kleunen et al. (2018), the definition of an 350 km in length × 60 km in maximum width and  
invasive species implicitly assumes that the non- less than 600 m elevation, extending NW to SE  
native species should be locally abundant (i.e. (Dalla Salda et al., 2006). In these low mountainous  
produces offspring in large numbers). Therefore, by areas, the development of agricultural activities  
increasing their abundance in the near future, non- is difficult, which facilitates the conservation of  
native species can become invasive.  
pristine vegetation remnants known as mountain  
Protected areas are a key component in grasslands (Frangi, 1975; Alonso et al., 2009a;  
responding to degradation and environmental Herrera et al., 2017; Kristensen et al., 2014;  
changes. However, invasive plant species are a Echeverría et al., 2017; Brancatelli et al., 2020).  
serious problem for protected area managers around These areas are considered biodiversity “hotspots”  
the world (Foxcroft et al., 2017; Brancatelli et al., because they harbor numerous native and endemic  
2
020). The management of these areas regarding species, some of which are threatened (Delucchi,  
invasive species involves different strategies: A) 2006; Herrera & Laterra, 2011; Kristensen et al.,  
prevention and exclusion; B) early detection and 2014; Echeverría et al., 2017). Threatened species  
rapid assessment; C) control, containment, and are considered priority species to preserve, and  
eradication (Rejmánek, 2000). Although prevention therefore a fundamental pillar to guide biodiversity  
is the most efficient control strategy, on certain conservation and sustainable development policies  
occasions, invasive species are already established (IUCN, 2022). At the same time, native species  
in the territory (Anderson et al., 2014; Brancatelli are a very important source of ecosystem services  
&
Zalba, 2018). Since the plants are usually (Barral & Maceira, 2012; Herrera et al., 2017). The  
distributed in patches or aggregates according to the Strict Nature Reserve of the Paititi Private Natural  
environmental characteristics, carrying out floristic Reserve (PNR) is the largest nature reserve of the  
surveys in different sites of the area of interest Tandilia Hill System. This reserve is considered  
is essential for the early recognition of current a Valuable Grassland Area (Bilenca & Miñarro,  
or potential invasions and the establishment of 2004) and an Area of Interest for Conservation  
management methodologies aimed at minimizing and Ecotourism (Chebez, 2005). The wide  
the process of invasion in early stages (Wittenberg environmental heterogeneity present in the PNR has  
72  
M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
Fig. 1. A: Map of South America (light gray), with delimitation of the Pampa biome (dark gray), modified from  
Scottá and Da Fonseca (2015), and of Buenos Aires Province (dotted line); B: Buenos Aires Province with  
delimitation of the Tandilia Hill System and Paititi Natural Reserve (PNR); C: Delimitation of the Strict Nature  
Reserve area of the PNR (dotted line). Each marker shows one of the sites (S) selected for the study; D:  
Topographic profile reflecting the altitudinal gradient of the study area and the location of the analyzed sites.  
led to the development of a great diversity of native  
Considering the value of the PNR as a refuge for  
fauna (Cicchino & Farina, 2007; Isacch et al., 2016; the flora and fauna of the grasslands and hill areas  
Arcusa, 2016; Ferreti et al., 2019; O’Connor et al., of the southeastern extreme of the Tandilia Hill  
2
020). Regarding the plant species, Echeverría et System and the possible threat posed by invasive  
al. (2017) carried out a floristic survey in the PNR plants to biological diversity, it is important to  
and identified 360 species, more than 25% being know the distribution and representativeness of  
non-native species. These authors alerted that some the plant species that can be found in the reserve.  
of those species may become invasive and thus Therefore, the objectives of this work were: 1)  
contribute to the deterioration of the natural areas to identify all the vascular plants (native and  
of the reserve.  
non-native ones) that thrive in sites with different  
73  
Bol. Soc. Argent. Bot. 58 (1) 2023  
environmental characteristics in the PNR; 2) to between 32 °C and below 0 °C, with a mean annual  
quantify their abundance in order to carry out the temperature of 14 °C. Rainfall is usually distributed  
early detection of non-native species that might throughout the year with an average of 850 mm per  
be acting as invasive ones; 3) to establish the year (Falasca et al., 2000; INTA, 2022).  
current situation of those native species that were  
considered threatened in Buenos Aires Province.  
Sampling and data collection  
Following the altitudinal gradient, 14 sites were  
selected. These sites varied in the physiognomy of  
the vegetation (grasses, shrubs, or trees), dominant  
species, and predominant substrate (soil, rock, or  
water). The sites were georeferenced using a global  
mateRials and methods  
Study area  
The study was conducted in the hill grassland positioning system (GPS) and digitized on an  
ecosystem of the PNR located in the southeastern aerial image of the study area (Fig. 1C-D). A plot  
Tandilia Hill System, in the southeast flank of was delimited at each site based on the concept of  
2
Sierra de Difuntos (37° 54′ S - 57° 49′ W; geodetic minimum area, with plot size ranging from 4 m to  
2
datum WGS84), belonging to the orographic group 200 m (Matteucci & Colma, 2002; Escaray, 2007).  
of Sierras de Mar del Plata (Guazzelli, 1999), The soil type was identified. Additionally, electrical  
in General Pueyrredon district, Buenos Aires conductivity, pH, organic matter content, and  
Province, Argentina (Fig. 1B). The main vegetation available phosphorus were determined in ten soil  
landscape is a large open area covered with grasses subsamples of the first 10 cm of the profile by the  
(
grasslands), although there are also oreophilic Soil Analysis Laboratory of Balcarce Agricultural  
steppes, scrublands, and hydrophilic communities Experimental Station belonging to the Instituto  
Cabrera, 1968; Cabrera & Zardini, 1978). In Nacional de Tecnología Agropecuaria.  
particular, in the mountainous areas, different The floristic composition and the specific cover-  
(
types of grassland and other plant communities can abundance in each plot were determined from  
thrive, such as the shrubs and scrubs that are typical september 2018 to december 2019. To estimate  
of mountain and rocky soils (Frangi, 1975).  
species coverage, the Braun-Blanquet cover-  
The PNR is divided into two areas: one dedicated abundance scale modified by Westhoff and Maarel  
to educational, recreational, and livestock activities, (1978) was used.  
and the other one categorized as a Strict Nature  
The taxa surveyed were determined at the  
Reserve so it remains as an area with minimal specific level based on the following flora book  
anthropic interference. The study was carried out collections: Flora of the Province of Buenos Aires  
in the Strict Nature Reserve, where there is a hill (Cabrera 1963, 1965a, 1965b, 1967, 1968 and  
area called Sierra Chica and a stream surrounding 1970) and Flora Argentina (Zuloaga et al., 2012a,  
the base of the west slope of that hill, forming a b; Zuloaga et al., 2014a, b). For each species,  
small pond before continuing its N-E path (Fig. botanical family, origin (non-native, native, or  
1
C). Sierra Chica is oriented N-S, with a maximum cosmopolitan), and threatened situation in Buenos  
elevation of 156 m.a.s.l. in the rocky area at the Aires Province (Delucchi, 2006) were determined.  
top, and a minimum of 86 m.a.s.l. in the pond. The  
hill blocks are mainly composed of a crystalline Analysis of data  
basement on which Eopaleozoic sediments were  
Total richness (number of species), as well as  
deposited. This sediment accumulation gave rise to richness per site, representativeness of botanical  
the development of Mollisol soils of variable depth, families, and distribution of species by category  
loamy texture, high content of organic matter, and of origin were determined. Correlations between  
slightly acidic pH (Osterrieth & Cabria, 1995; Dalla site altitude and percentage of species according to  
Salda et al., 2006; Álvarez et al., 2012). The climate origin (native versus non-native + cosmopolitan)  
of the region is humid-subhumid, mesothermal, were calculated using the Pearson correlation (r)  
with low water deficiency, noticeable seasonal test (α = 0.1%) through the “cor.test” function of  
variation in temperature, and a short cold period. It the “corrplot” package of RStudio software Version  
is also characterized by maritime temperate ranging 1.2.5033 (R Core Team, 2014).  
74  
M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
To associate the sites and generate vegetation  
The vascular species richness in the plots varied  
units with similar characteristics considering their from 6 to 161 species. In the highest sites such  
environmental attributes and the species at each as the hillside and summit areas, the percentage  
site, the qualitative and quantitative variables were of native plants was over 70%, except for site ten  
jointly analyzed by a Principal Coordinate Analysis (S10) (Fig. 2). This trend was confirmed by the  
(PCooA) using Gower similarity coefficient (Gower, correlation between altitude and percentage of  
1
971; Cuadras, 2014). The analysis was carried out native species, which was significant and positive  
in the RStudio software Version 1.2.5033 (R Core (r = 0.67; p-value = 0.00829); consequently, it was  
Team, 2014) using the “cluster” package (Maechler also significant, but negative, between altitude and  
et al., 2016).  
percentage of non-native + cosmopolitan species.  
The vegetation units were described considering  
the environmental characteristics, the identified Relationship between sites  
flora and the type of plant community according  
The first three coordinates of the PCooA  
to Frangi (1975). Additionally, the threatened contribute explaining 45.82, 15.57, and 10.02%  
species were specified, as well as the most abundant of the total variability, respectively. The projection  
non-native ones (≥ 5% cover-abundance values), of the study sites in the three-dimensional space  
therefore considered invasive.  
showed the formation of eight clusters, which  
represent the vegetation units (Fig. 3).  
Results  
Characteristics of the vegetation units  
The soils of the units were dark to very dark  
In the study area, the total richness reached brown and slightly acid (pH= 5.3–5.8); the  
370 vascular species, 72.5% being native, 26.5% superficial horizons had high root density, low  
non-native and 1% cosmopolitan (Appendix S1); electrical conductivity (0.3–0.8 mmhos), low to  
ten taxa, Acmella decumbens (Sm.) R.K. Jansen, moderate phosphorus content (3.4–7.6 ppm), and a  
Aira caryophyllea L., Anthoxanthum odoratum L., high percentage of organic matter (6.3–11.4%). The  
Eryngium ebracteatum Lam., Galium richardianum greatest abiotic differences were established in the  
(
(
GilliesexHook.&Arn.)Hicken,Nassellatrichotoma type and depth of the soil, the slope (Table 1), the  
Nees) Hack, Parodia submammulosa (Lem) R. degree of solar exposure, and the relief position. For  
Kriesli, Plantago lanceolata L., Tripogonella spicata information on the species of each vegetation unit,  
Nees) P.M. Peterson & Romasch., and Wigginsia consult the Appendix S1.  
tephracantha (Link & Otto) D.M. Porter, had not Base Grassland: This unit corresponds to an  
(
been previously detected by Echeverría et al. (2017) area located at the base of the hill (Fig. 4A; Table  
at the study area. The surveyed species belong to 1). The species richness reached 114 vascular  
6
9 families, the most representative ones being plants, 42% being non-native ones. The area was  
Poaceae (78), Asteraceae (72), Fabaceae (21), physiognomically dominated by taxa of the Poaceae  
Cyperaceae (13), Apiaceae (12), Solanaceae (11), family, of the genera Aristida L., Nassella E.  
and Brassicaceae (10) (Appendix S1). Some taxa Desv., Jarava Ruiz. & Pav., and Piptochaetium J.  
were found only in one site and with very low cover Presl. Floristically, the Base Grassland resembles  
values, such as Pterocaulon cordobense Kuntze, the typical “Flechillar” grassland community of  
Hypericum connatum Lam., and Lemna gibba L., the Tandil hills dominated by grasses of stabbing  
while others were found in most of the sites and in caryopses, which look like small arrows (Flechillar  
some of them with more than 50% coverage, such as derives from the Spanish word ‘flecha’, which means  
Racosperma melanoxylon (R. Br.) Mart. The greatest arrow in English). Six of the species mentioned as  
habitat variation was presented by four species, threatened in Buenos Aires Province were found,  
which were found in nine of the fourteen sites, two although only two (Acanthostyles buniifolius (Hook.  
non-native species, Cirsium vulgare (Savi) Ten, and & Arn.) R. M. King & H. Rob. and Senecio selloi  
Senecio madagascariensis Poir., and two native (Spreng.) DC.) had cover-abundance levels greater  
ones, Cypella herbertii (Lindl.) Herb. and Vicia nana than 5% (Table 2). Among the non-native species,  
Vogel.  
Holcus lanatus L. (Fig. 5A) had the highest level of  
75  
Bol. Soc. Argent. Bot. 58 (1) 2023  
Fig. 2. Vascular species richness in 14 sites of the Strict Nature Reserve area of the Paititi Natural Reserve  
(Buenos Aires, Argentina) according to their origin category (native, non-native, cosmopolitan).  
Fig. 3. Principal Coordinates Analysis using combined data of presence/absence of vascular species and  
environmental characteristics of 14 sites (S) in the Strict Nature Reserve area of the Paititi Natural Reserve  
(Buenos Aires, Argentina). The clusters (vegetation units) are indicated by dashed lines on the three first  
principal coordinates.  
76  
M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
Table 1. Slope, soil type and soil depth of the vegetation units of the Strict Nature Reserve area of the  
Paititi Natural Reserve (Buenos Aires, Argentina).  
Slope  
%)  
Soil Depth  
(cm)  
Vegetation Unit  
Base Grassland (S1)  
Soil Type  
(
7 – 9  
< 2  
Typic Argiudoll  
Typic Argiacuoll  
> 100  
> 100  
Pond (S2)  
Mixed Grove (S3)  
< 2  
< 2  
Typic Argiudoll  
Aquic Argiudolls  
Typic Argiudoll  
Hapludoll lytic  
Hapludoll lytic  
Typic Argiudoll  
> 100  
50 – 100  
10 – 80  
1 – 40  
1 – 20  
> 100  
Humid Mountain Grassland (S4, S13)  
Dry Mountain Grassland (S5, S8, S14)  
Rocky Place (S6, S7, S11)  
Spring (S9, S12)  
2 – 45  
2 – 45  
< 2  
Acacia Groove (S10)  
3
cover-abundance (15-25%), followed by Dactylis rock blocks at the top of the hill (Fig. 4D; Table  
glomerata L. (Fig. 5B) (5-15%). 1). In this unit, 81 species were identified being  
Pond: This unit is located in the lowest part of 34.5% non-native and 1.2% cosmopolitan. The  
the study area, surrounding a shallow pond (Fig. flora corresponds to the grassland community  
4
3
B; Table 1). Thirty-five species were found being named “Pajonal (tall grasses) of tussock paspalum”,  
1.4% non-native and 5.7% cosmopolitan. This unit as it is mainly composed of herbaceous plants  
has some floating and marsh plants that are typical but physiognomically dominated by Paspalum  
of the wetlands and watercourses of Buenos Aires quadrifarium Lam (“tussock paspalum”). In fact,  
Province (Appendix S1). In this vegetation unit, this species showed high cover-abundance levels  
one native species was categorized as threatened (50-75%). Three threatened species were found  
(
(
Cypella herbertii ssp. wolffhuegeli (Lindl.) Herb. in this vegetation unit, all with very low cover-  
Hauman) Ravenna) and with very low cover- abundance levels (Table 2). Additionally, Holcus  
abundance level (Table 2). The non-native species lanatus was the non-native species with the highest  
with the highest cover-abundance level was Senecio level of cover-abundance (5-15%).  
madagascariensis Poir (5-15%) (Fig. 5C).  
Dry Mountain Grassland: This unit is found on  
Mixed Grove: This unit corresponds to an very steep slopes and at the top of the hill (Fig. 4E;  
implanted grove following the eastern course of the Table 1). The total richness reached 156 species:  
stream. It is located at the base of the hill (Fig. 4C; 25% non-native and 0.6% cosmopolitan. The  
Table 1). The total richness resulted in 50 vascular vegetation was mainly represented by “flechillas”  
species, and 36% of the species were non-native and dicot species, with less than 20% of tree and  
ones. The vegetation consisted mainly of perennial shrub species. The floristic composition is similar  
species dominated by phanerophytes (34%), Celtis to that found on shrubland, with physiognomic  
tala Gillies ex Planch being the most abundant dominance of Acanthostyles buniifolium, Baccharis  
species. The trees were accompanied by shorter coridifolia DC., B. dracunculifolia ssp. tandilensis  
herbaceous plants adapted to the canopy shade. (Speg.) Giuliano and Colletia paradoxa, and  
Four threatened species were found in this unit, in a lower stratum, the flora varied according  
whose coverage was very low, except for Colletia to the position on the ground. The non-native  
paradoxa (Spreng.) Escal. with 5% (Table 2). No species with the highest level of cover-abundance  
exotic species exceeded 5% cover.  
were Racosperma melanoxylon (5-15%), Dactylis  
Humid Mountain Grassland: This type of glomerata (5-15%), and Holcus lanatus (15-25%)  
grassland occurs in two sectors of the study area: (Fig. 5). Besides, 19 threatened species were found,  
one at the base, near temporary water courses, and three of which had coverage greater than 15%  
another in depressions or meadows between the (Table 2).  
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M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
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Bol. Soc. Argent. Bot. 58 (1) 2023  
Fig. 4. Images of the sites that are part of the vegetation units obtained from the PCooA. A: Base Grassland;  
B: Pond; C: Mixed Grove; D: Humid Mountain Grassland; E: Dry Mountain Grassland; F: Rocky Place; G:  
Spring; H: Acacia Grove.  
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M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
Fig. 5. Most abundant non-native species found in different areas of the Strict Nature Reserve area of the  
Paititi Natural Reserve (Buenos Aires, Argentina). A: Holcus lanatus; B: Dactylis glomerata; C: Senecio  
madagascariensis; D: seedling of Racosperma melanoxylon; E: adult of R. melanoxylon.  
Rocky Place: This unit is located in elevated areas mainly of herbaceous species, and to a lesser extent,  
corresponding to the slopes and top of the hill, with sparse trees and shrubs (38 species). Twenty-five  
abundant rocky outcrops, and stony surfaces (Fig. threatened species were found, most of which had  
4F; Table 1). It is the richest vegetation unit since a low coverage (Table 2). The non-native species  
total of 239 species were identified: 17% non-native with the highest level of cover-abundance was  
and 0,8% cosmopolitan. The vegetation consisted Racosperma melanoxylon (5-15%).  
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Bol. Soc. Argent. Bot. 58 (1) 2023  
Spring: This unit is situated in areas of high to species not previously found in the reserve, possibly  
intermediate position in the hill, rocky outcrops of due to their low frequency. Therefore, the richness  
low blocks, which have flat to concave shape and are amounted to 370 vascular species. This increase  
almost continuous. After the rains, this unit presents did not affect the predominance of the Poaceae  
temporary springs and small holes with little or no and Asteraceae families, which continued to be  
drainage (Fig. 4G; Table 1). The vegetation reached the best represented, and neither did it change the  
20 herbaceous species: 30% non-native species. Most proportion of geographic origin of the species since  
of the floristic components are typically found on the native plants far exceeded the set of non-native and  
water courses of the region, while some are common cosmopolitan species by bringing together 72.5%  
species of the rocky areas. Two threatened native of the species.  
species were found (Juncus pallescens Lam. and  
The vegetation units varied mainly due to their  
Zephyranthes bifida (Herb.) Nic. García & Meerow), position in the relief, the slope, the type and depth  
both with very low coverage (Table 2). No exotic of the soil, and the established plant community.  
species exceeded 5% cover.  
This coincides with several authors who noted  
Acacia Grove: This unit occupies areas on the that the floristic composition and distribution of  
slope of the mountain (Fig. 4H; Table 1). Fifty taxa vascular species in hills and mountain areas are  
were identified in this unit, 42% non-native, and 4% associated with the environmental heterogeneity  
cosmopolitan species. The dominant physiognomic determined mainly by topographic variants, even in  
species was the non-native species Racosperma short distances (Frangi & Bottino, 1995; Guerrero  
melanoxylon, which was accompanied in the lower Campo et al., 1999; Cantero et al., 2014). Among  
stratum by sparse herbaceous species. In fact, the the vegetation units considered in the study area,  
cover-abundance level of R. melanoxylon ranged the flora varied in richness, proportion of species  
between 50 and 70%. Four threatened species with according to their status, and cover-abundance of  
very low coverage were found in this unit (Table 2).  
each species. Some vegetation units were similar  
to the plant communities described by Frangi  
(1975) for the Tandil hills of the Albion Group.  
Threatened species  
In the study area, 30 of the native species In some cases, the resemblance was high, as the  
considered threatened in Buenos Aires Province dominant and main companion species coincided.  
(
Delucchi, 2006) were identified (Table 2). In others, due to the absence of some species or  
Regarding their category of threat, 14 are listed as the replacement of some physiognomic dominants,  
Vulnerable” and four as “Critically Endangered”. the flora seemed to be a variant of the community  
Some of the threatened species were found in two described as “typical”. For example, Nassella  
or more vegetation units, but ten of them were only poeppigiana (Trin. & Rupr.) Barkworth and  
found in a single vegetation unit, in some cases in the Koeleria permollis Nees, dominant species in the  
Dry Mountain Grassland and in others in the Rocky Tandil Flechillar according to Frangi (1975), were  
Place, but always with very low cover-abundance not found in the in Base grassland vegetation unit. A  
levels. In contrast, Acanthostyles buniifolius, similar case was detected in the Rocky place where  
Baccharis dracunculifolia ssp. tandilensis, Colletia the floristic composition of the vegetation unit  
paradoxa, and Senecio selloi exhibited cover- coincides mostly with the community described  
abundance levels ranging from 15 to 25%, and were by Frangi (1975) for Tandil hills named “Roquedal  
found in at least three vegetation units.  
típico” (Typical rocky community), except for  
several species of physiognomic relevance that  
were not found in study area, such as Andropogon  
ternatus (Spreng.) Nees, Arjona tuberosa Cav.  
and Hatschbachiella tweediana (Hook. & Arn.)  
R.M. King & H. Rob., among others. Although  
discussion  
Flora  
In a previous survey of the vascular plants of the the detected absent species should be the object  
Strict Nature Reserve area of the PNR, Echeverría of detailed studies, this situation could be due to  
el at. (2017) identified 360 taxa at the species level. the location of the PNR, exceeding the distribution  
The present study allowed the detection of ten limit of these species. This hypothesis would apply  
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M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
to Hatschbachiella tweediana, a species for which Threatened species  
there are no records in the southern portion of the  
Thirty vascular species listed as threatened  
Tandilia Hill System (Alonso et al., 2009a; Alonso in the Buenos Aires Province (Delucchi, 2006)  
et al., 2009b; Flora Argentina, 2022; Flora del Cono were found. This result coincides with that found  
Sur, 2022; GBIF, 2022; iNaturalist, 2022). In turn, by Echeverría et al. (2017) for the same area of  
some of the absent species, such as Andropogon the PNR, which indicates that no species have  
ternatus and Arjona tuberosa, have been collected disappeared over the last years when the reserve has  
in other hills in General Pueyrredon district, and been closed to the public. These species are mostly  
in Balcarce, a neighboring district (Alonso et al., endemic to the mountain grasslands (Echeverría  
2
009a; Alonso et al., 2009). In these cases, the et al., 2017), so they only thrive in mountain  
action of anthropic alterations (e.g. indiscriminate environments with little intervention, such as  
grazing, urbanization, fire) could have affected the the Strict Nature Reserve area of the PNR. This  
presence of these plants in the study area.  
situation reveals the important role of this reserve  
The vegetation units located in high ground in the conservation of mountain grassland flora in  
positions had the highest total richness and native general, and of threatened species in particular,  
flora and the dominance of perennial species, in as well as warns about the vulnerability of poorly  
particular geophytes, in agreement with Cantero et represented taxa and the need to consider them in  
al. (2017) for rocky mountain areas of the Sierra future management plans.  
de Los Cóndores in Córdoba Province (Argentina).  
According to the data collected in the present  
The sites located in high and intermediate positions study, the species Acanthostyles buniifolius,  
of the relief tend to present shallow soils, high Baccharis dracunculifolia ssp. tandilensis, Colletia  
exposure to solar radiation, and a large proportion paradoxa, and Senecio selloii, which have been  
of rocky outcrops and stony surfaces. Therefore, cited as threatened in Buenos Aires Province  
these sites are subjected to greater arid conditions (Delucchi, 2006), were recorded with high levels  
than those located on lower parts of the slopes or of cover-abundance and in several sites. This  
in sectors totally or partially shaded by tree canopy information is encouraging as it indicates that these  
(
Mazzola et al., 2008; Aguirre Mendoza, 2013; entities are currently out of danger in the Strict  
Kristensen & Frangi, 2015). Exotic species are not Nature Reserve area of the PNR. In particular,  
adapted to these environmental conditions, hence for Baccharis dracunculifolia ssp. tandilensis  
their lower number or representability in those sites. and Senecio selloi, changes in habitat preference  
In the rocky areas and elevated slopes of the have been reported in the area: B. dracunculifolia  
study area, the development of phanerophytes is extending from the hills to the plains near the  
restricted, mainly because of the shallow soils, Atlantic Ocean coast (Scaramuzzino et al., 2015;  
and hence greater richness of this kind of species Manfreda et al., 2020) and S. selloi to grasslands  
is found at the base and on the slopes of the hill. dedicated to livestock grazing (Fernández, 2011).  
In addition, in the sites located at lower ground Therefore, new surveys in the province could  
positions, a greater number of non-native species yield information that accounts for the current  
were registered, mostly therophytes. The greater distribution of native species in ecosystems close  
abundance of annual cycle species is related to to the studied one and thus clarifying the threatened  
the greater anthropization that characterizes the status of the species and eventually incorporating  
surrounding rural landscape (Vervoorst, 1967; new taxa into the plant red list.  
Zalba & Villamil, 2002; Cantero et al., 2017).  
The rural fields close to the PNR would act Invasive species  
as plant reproduction reservoirs, and the wind,  
Currently, the most important problems in  
waterways, birds, mammals, invertebrates, and the PNR associated with invasions involve the  
humans as vectors for their dispersal, introduction, non-native species Dactylis glomerata, Senecio  
and spread of plant species in a certain area. This madagascariensis, Holcus lanatus and Racosperma  
situation would promote the colonization and melanoxylon (Fig. 5). These exotic taxa had the  
proliferation of non-native species toward the hill greater cover-abundance values and the ability to  
grasslands of the PNR, thus affecting the ecosystem. thrive in different environmental conditions, since  
83  
Bol. Soc. Argent. Bot. 58 (1) 2023  
they were registered in various vegetation units. All (González et al., 1995; Hussain et al., 2011). The  
of them have already been cited as invasive species seeds have the ability to remain viable in the seed  
in different locations of Argentina and vary in bank for many years and their germination is  
life forms, morphological attributes, reproduction stimulated by occasional fires that scarify the seeds  
strategies and invasion capacity (Ahumada et al., (Arán et al., 2017). It also has gemiferous roots  
2
016). Management efforts on the PNR should be and high seed production (Ahumada et al., 2016;  
focus on monitoring the threatened species and Arán et al., 2017). R. melanoxylon has shown to be  
controlling the non-native with the highest value highly invasive in other mountain grasslands of the  
of cover-abundance in each vegetation unit. The Tandilia Hill System where it occurs in the wild and  
characteristics of each species should be considered it seems to be advancing on adjacent sectors of the  
in planning the management of the invaded hills (Ahumada et al., 2016; Gandini et al., 2019;  
vegetation units, since the integrated control of an De Rito et al., 2020).  
invader implies, among other requirements, having  
complete knowledge of the bioecology of the invaders in the study area, mechanical controls in  
species (Bentivegna & Zalba, 2014). H. lanatus, D. glomerata and S. madagascariensis  
In relation to the management of the identified  
Senecio madagascariensis is an herbaceous have not been successful while the use of herbicides  
perennial species known as “fireweed”. It belongs has allowed effective chemical controls (Villalba  
to the Asteraceae family and is native to South & Fernández, 2005; Ahumada et al., 2016). In  
Africa and Madagascar. It is a toxic species, the particular case of R. melanoxylon, Arán et al.  
recognized as invasive in different parts of the (2017) proposed controlling this species by cutting  
world (Dematteis et al., 2020). S. madagascariensis down the plants, both adults and juveniles, as well  
has been reported in the Argentinean Pampas as a as uprooting all the roots to prevent new shoots  
weed in extensive farmlands in the past (Verona from emerging. They also recommend minimal  
et al., 1982), while it is currently a problem in soil disturbance to prevent mechanical scarification  
cattle fields and a growing concern in farms under of the seeds in the seed bank. They also suggest  
no-tillage systems and in ruderal areas (Ahumada favoring the colonization of the land with one  
et al., 2016; Dematteis et al., 2020; Diez de or several fast-growing native species to prevent  
Ulzurrun personal communication, 2022). It is a R. melanoxylon seedlings from prospering. On  
species with a high production of seeds per plant the other hand, in a study performed by Campos  
and easy to disperse thanks to a hairy pappus, et al. (2002), the combined felling of trees and  
characteristics that determine their invasive nature. herbicide application was effective at controlling R.  
Dactylis glomerata (“orchard grass”) and H. melanoxylon. Therefore, a similar strategy could be  
lanatus (“Yorkshire fog” or “velvet grass”) are suitable to control the proliferation of this species in  
perennial microthermal species that belong to the the PNR and in other mountain grasslands. Beyond  
Poaceae family. These species are native to Europe this, it is important to consider that the control  
and were brought into Argentina as forage. They strategy must be adjusted to each situation, and may  
escaped from cultivation and have become weed vary depending on the location of the plant invasion  
species that are considered invasive in different on the ground (top, slope, base of the hill).  
parts of the American continent due to their prolific  
It is important to mention that in the study area  
seed production and their ability to reproduce from some non-native species were found that have a  
tillers (Bastow et al., 2008; Ahumada et al., 2016). history of invasion in mountain grasslands of the  
Racosperma melanoxylon (Acacia melanoxylon Pampa biome but with low representativeness  
R. Br.; “Australian blackwood”) is an arboreal in the PNR. Such is the case of Eucalyptus  
species native to Australia that belongs to the camaldulensis Dehnh., Gleditsia triacanthos L.,  
Fabaceae family. In the southeast of Buenos Aires, Ligustrum lucidum W. T. Aiton, Rubus ulmifolius  
it was introduced for its cultivation as ornamental Schott, Pinus radiata D. Don and Prunus mahaleb  
and forestry (Martínez Crovetto, 1947; Carranza, L., among others (Ghersa et al., 2002; Zalba &  
2
007). This evergreen tree causes shade on the Villamil, 2002; Hoyos et al., 2010; Mazzolari  
lower stratum and has allelopathic compounds et al., 2011; Ferreras et al., 2014; Mazzolari  
that affect the growth and survival of other plants & Comparatore, 2014; Ahumada et al., 2016).  
84  
M. L. Echeverría et al. - Vegetación y detección de especies invasoras en un pastizal serrano  
Therefore, periodic monitoring of the evolution  
Finally, we suggest promoting environmental  
of these species’ expansion and rapid actions for education and citizen participation activities  
their control could prevent future problems of plant aimed at valuing and caring for the hill natural  
invasions and facilitate the protection of hill and environments of the Pampa biome and raising  
mountain grassland biodiversity.  
awareness about their importance within the  
Prevention and early detection are the most framework of biodiversity conservation policies.  
efficient methods for dealing with invasive species.  
When the invasion process advances, the possibility  
of carrying out successful control measures acKnowledgements  
decreases, management costs and impacts generated  
by an invasion process increase, and sometimes the  
problem becomes irreversible (Anderson et al., Zugasti, owner of the Paititi Natural Reserve,  
014; Brancatelli & Zalba, 2018). Therefore, to who gave permission to carry out this research  
We would like to thank Esteban González  
2
avoid increasing invasions and the appearance of and provided logistical support. This work was  
a new invasion focus, vegetation units should be financially supported by Universidad Nacional de  
monitored by sporadic surveys. Thus, when an Mar del Plata (Argentina) [research projects AGR  
invasive species is detected, rapid action can be 557/18 and AGR 616/20] and The Neotropical  
taken to restore the affected site or to minimize the Grassland Conservancy.  
invasion process in the early stages, thus preserving  
the biodiversity.  
bibliogRaPhy  
conclusions  
AGUIRRE MENDOZA, Z., N. L. ABAD, B. PALACIOS  
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