Vascular flora of a Yungas forest in Jujuy province , northwestern Argentina

A floristic survey was carried out in Yungas forests of the San José de Chijra river basin (Jujuy, Argentina). This is the first comprehensive study of vascular plants made in the area, a region relatively unknown in terms of vegetation. We present the results of this field survey; 172 species, 127 genera and 51 plant families are documented. Of these, 149 are native and 17 are endemic. Of the latter, three are endemic to Argentina, 11 to northestern Argentina, and three to Jujuy province. Families with the greatest number of species were Asteraceae (50), Solanaceae (13), Fabaceae (12), and Poaceae (8). According to IUCN criteria, two species are classified as threatened. Our data substantially increase our knowledge of the diversity of the regional flora and will provide an important contribution in developing conservation policy.


INTRODUCTION
In South America, mountain cloud forests occur in the Andes from Colombia and Venezuela to Argentina (Brown and Kapelle 2001).These forests are characterized by both their high biodiversity and their beneficial ecosystem services, especially those related to hydraulic regulation processes (Brown and Kapelle 2001;Cuesta et al. 2009).
In southern areas, mountain cloud forests are characterized as "Selva Tucumano-Boliviana" and correspond to the Yungas phytogeographical vegetation classification (Hauman 1931;Cabrera 1976;Cabrera and Willink 1973).The Yungas lies on the eastern side of the Andes from central Bolivia (Tarija and Chuquisaca) as far as the La Rioja region in Argentina, and forms a single biogeographical, ecological, and social unit (Cabrera 1976;Grau and Brown 2000;Navarro and Maldonado 2002).
The Argentine Yungas presents phytogeographical differences across latitude and altitude, respectively, because of strong environmental gradients and noncontinuous distribution along the mountain peaks.Depending on the altitude, we distinguish between transition forest (350-500 m above sea level [a.s.l.]), lower mountain forest (550-1,600 m a.s.l.) and upper mountain forest (1,,500 m a.s.l.) (Cabrera 1976).The Yungas is also divided into three latitudinal sectors: north, center and south (Brown and Ramadori 1989).
The forests of the San José de Chijra river basin in Jujuy province are located in the central sector of the Argentine Yungas and belong to the lower and upper mountain forest phytogeographical districts.The tree composition in this area of the Yungas is well-described (Digilio and Legname 1966;Brown et al. 1985;Brown and Ramadori 1989;Morales et al. 1995;Carranza 2003;Cuyckens 2005;Romeo and Cruz 2005;Romeo et al. 2011), but data on the shrub and herb layer is lacking.
Since 1974, the forests of the San José de Chijra river basin have been under protection, mainly to avoid soil erosion.However, these forests face permanent transformation and habitat loss with the substitution of natural forest with huge cultivations of Pinus spp.and Eucalyptus spp., and transhumance livestock farming (Braun Wilke 2001).
We present a comprehensive list, including conservation status and economic value, of the vascular plant species of the Yungas forests of San José de Chijra river basin in Jujuy.(native, exotic, endemic); and c) the conservation status (IUCN 2012(IUCN , 2014(IUCN , 2015)).
Specimens were identified using determination keys, specialized literature, comparisons with specimens identified by specialists listed in the Herbarium of "Museo de Ciencias Naturales de Salta" (MCNS) collection, and help from expert taxonomists.Because of floral characteristics are indispensable for correct species iden tification, three species not in flower -Chloris sp.(Poaceae), Euphorbia sp.(Euphorbiaceae), and Plantago sp.(Plantaginaceae) -could only be identified to genus.Specimens were deposited in the herbarium of the Cátedra de Botánica Sistemática y Fitogeografía, Facultad de Ciencias Agrarias, Universidad Nacional de Jujuy (Argentina).Nomenclature of the flora agrees with the database of the Missouri Botanical Garden (Tropicos 2015) and the "Catálogo de las Plantas Vasculares del Cono Sur" of the Darwinion Institute (Zuloaga et al. 2016).

RESULTS
We identified 172 plant species belonging to 127 genera and 51 families (Table 1).Of these, 149 are native to the study area, and 17 are endemic (three to Argentina, 11 to northwestern Argentina, and three to Jujuy province).Six are exotic (Zuloaga et al. 2016).

Study site
The San José de Chijra river basin (24°08ʹ S, 065°17ʹ W) is located in province of Jujuy, northwestern Argentina (Figure 1).The river basin comprises an area of Yungas forests belonging to the lower and upper mountain forest phytogeographical districts (Cabrera 1976).This area is characterized by numerous, dendritic streams that during the rainy season flow into the San José de Chijra River, one of the principal permanent tributaries of the Río Grande de Jujuy (Santamans and Franco 2010).The soil belongs to the Palpalá type (Serranías Los Perales -Zapla association) with stream terrace and shore soils of the fluvisoles mólicos type, this last one are characterized by being poorly developed and drained.Towards the interior, soils belong to the "phaeozem háplico" type and are characterized by being well developed and structured, with an organic layer present (Santamans and Franco 2010;Rosas and Chayle 2011).The annual mean temperature is 16°C and the annual mean precipitation is 861 mm.There are notable differences in the amount of precipitation between the rainy (200 mm) and dry seasons (<15 mm) (Buitrago 2000).

Data collection
During 2012 and 2013 we surveyed for plants along 21 transects, each 10 × 100 m.We botanized vascular plants in flowering state.For each plant we recorded: a) the habit (tree, shrub, herb); b) the distribution status

DISCUSSION
Elsewhere in Argentina, in other studies, Asteraceae, Solanaceae, Fabaceae, and Poaceae have also been found to be the richest families, for example, the whole of Argentina (Zuloaga et al. 1999), or the lower and upper mountain Yungas forest of the Serranía de Zapla (Entrocassi 2016), and the hills of Calilegua (Bulacio and Ayarde 2009).In our study, the forest comprises 21.76% (37) of the trees species reported for the entire Argentine Yungas and 22.42% for the central sector (Morales et al. 1995).
In conclusion, our list highlights the high diversity of native, endemic and threatened vascular plant species of the Yungas forests of the San José de Chijra river basin.
Our study shows the presence of a floristic ensemble with high conservation value.

Figures 2 .
Figures 2 .Frequency of plant families collected in the Yungas forests of the San José de Chijra river basin (Jujuy, Argentina).Plants within families are grouped in three vegetation layers (herb, shrub, and tree).
Continued Martín et al. | Vascular flora of a Yungas forest in northwestern Argentina
Continued Martín et al. | Vascular flora of a Yungas forest in northwestern Argentina