Ramiro Pablo López

The role of nurse plants in the establishment of shrub seedlings in the semi-arid subtropical Andes

In the nurse plant syndrome, or nurse association, seedlings (beneficiaries) are associated with adult shrubs/trees (benefactors). This phenomenon has been documented in several regions of the planet. Abiotic stress amelioration (one mechanism of facilitation) is one of the causes of this association. Most of the studies addressing the nurse syndrome have been conducted on spatial scales of a few hectares and have focused on only one or a few species. Moreover, there is an almost complete lack of studies addressing the incidence and characteristics of the nurse phenomenon in the arid Andes of South America. We undertook a first approximation to the study of facilitation in these ecosystems. The study was conducted at local and regional scales and involved the assessment of the spatial distribution of juveniles (seedlings and saplings) of 51 populations of 16 shrub and 12 cactus species in relation to shrub cover at 20 localities of the Prepuna (subtropical Andes of Bolivia and Argentina, 20–26°S). In terms of spatial distribution, the juveniles of most of the populations of shrubs studied were distributed both under the shrubs and in open spaces, thereby showing an apparent indifference to microhabitat. Globose and opuntioid cacti were preferentially distributed below the canopies of shrubs and were usually more associated with the dominant shrub species, which stood out as better potential nurses. The pattern was consistent throughout the region, including the more mesic and arid localities. The fact that Prepuna woody species are capable of establishing in open spaces would confer this region a greater resilience. Our findings further suggest that community dynamics in arid and semi-arid environments are more variable than previously thought.

The importance of shrub cover for four cactus species differing in growth form in an Andean semi-desert

Abstract Question: Factors influencing seedling establishment are known to vary between open sites and those protected by plant cover. In many desert regions, protected microhabitats below shrubs are essential for establishment of many cactus species. Very little is known about these factors for Andean cacti and how the importance of vegetation cover varies with cactus species. Are Andean cacti associated more frequently to vegetation cover than to open ground? Are they associated to certain shrub species? Is the distributional pattern in relation to cover similar for different cactus species? In what microhabitat (below or away from shrubs) are cactus seeds more abundant? These questions are addressed for the case of an Andean semi-desert. Location: Semi-arid tropical Andes, La Paz department, Bolivia. Methods: We examined 132 isolated shrubs ≥ 50 cm along a line across two microhabitats: areas below and away from shrubs/trees. Shrub crown size was measured. The among-shrub samples were taken from open spaces contiguous to each of the sampled shrubs. In both microhabitats, all cactus species were recorded. The cardinal direction of the cacti was also registered. Correlation between canopy diameter and number of beneficiaries was evaluated for Prosopis flexuosa. The cactus seed bank in each microhabitat was also studied. Results and Conclusions: The four cactus species found behaved differently in relation to shrub canopies. These distributional differences could be due to differences in growth form. Columnar cacti apparently need the shade of shrubs. Only the columnar species is able to grow near the base of the tallest nurse species. The opuntioid cacti studied seem more facultative: although apparently preferring shrub under-canopies, they are able to establish in open ground. The globose cactus is the most indifferent to the presence of plant cover. These patterns parallel others found in North America. The capacity of different cacti to appear in open spaces could be related to vegetative propagation, and not necessarily to seedling tolerance of heat. Nomenclature: Anderson (2001) for cacti; Beck & Valenzuela (1991) for the other families.

Gap analysis of two savanna-type ecoregions: a two-scale floristic approach applied to the Llanos de Moxos and Beni Cerrado, Bolivia

The Beni savannas (locally referred to as pampas) is composed of two clearly differentiated ecoregions, the Llanos de Moxos (or Moxos) and the Beni Cerrado. Both tropical savannas are shaped to a greater (Moxos) or lesser (Beni Cerrado) by cycles of drought and flood and the labor of generation of farmers. It contains floristic elements of four biogeographic regions (Amazonian, Chaco, Cerrado and Chiquitana). However, in spite of their biological richness, they are little represented in the National System of Protected Areas (SNAP, in Spanish). By employing an ecoregion and sub-ecoregion approach, we examined the representation of both savanna-type ecoregions in the Departmental System of Protected Areas (SDAP, in Spanish), which includes national, departmental, municipal, and private protected areas. The study also enabled us to compare Bolivia’s newest ecoregion/vegetation zones maps as applied to the both savannas and to produce a sub-ecoregion map for the Beni department (northeastern Bolivia). Our results show that the Llanos de Moxos and the Beni Cerrado are found in protected areas of departmental and municipal level. Although they are still under-represented (mainly the Beni Cerrado), they have nonetheless important extensions inside these protected areas. A better representation of these zones would guarantee improved levels of protection of these unique ecosystems. On the other hand, our study shows the importance of the conservation-representation target relationships (sensu Rodrigues et al. 2004). This is the first time that this approach is used to examine gaps of floristic representativeness of savanna-type ecoregions showing that the traditional 10% minimal conservation target should be used with caution.

Representation of Andean Dry Ecoregions in the Protected Areas of Bolivia: The Situation in Relation to the New Phytogeographical Findings

Bolivia is a megadiverse country. A large part of its biodiversity is due to the fact that in its territory different biogeographical regions meet. As a preliminary means to understand how this biodiversity is being protected, three previous studies undertook an evaluation of how well represented the ecological regions were in the National System of Protected Areas (NSPA). However, the most recent biogeographical findings in Bolivia call for a new analysis of this sort. We try to achieve this, emphasizing the situation in the Andean dry regions, which have been given scarce priority, despite their high biological value. In general, xeric ecoregions are under-represented while humid ones are over-represented. The Prepuna and the central altiplano (which includes the Dry Puna sub-ecoregion) are not represented within the NSPA, nor is the Beni Cerrado sub-ecoregion. The Inter-Andean Dry Valleys cover only ca. 0.5% of the protected area, in spite of their diverse flora and status as one of Bolivia’s most important centers or endemism. Although the diverse Chiquitos Dry Forest is well represented, it is protected mostly as an ‘Integrated Management Natural Area’, and thus lacks full protection. The Semi-Humid Puna and the Flooded Savannas of the Moxos Plains, important subdivisions of two main ecoregions, are markedly under-represented in the NSPA, despite the importance of Moxos plains as a center of endemism for birds. Other ecoregions have a representation in the NSPA which can be considered adequate or even excessive. The over-representation of the humid Yungas mountain forests seems to be justified as this is probably Bolivia’s most important center of diversity and endemism. There is a need for a more proper distribution of some protected areas which consider true limits, size, diversity, endemism and other attributes of the different ecoregions in a more rigorous manner.

Pollination biology of Oreocereus celsianus (Cactaceae), a columnar cactus inhabiting the high subtropical Andes

The geographical dichotomy hypothesis suggests that columnar cacti in the tropics depend primarily on bats for pollination. This dependence may to be less in the outer tropics where many columnar cactus species (or their populations) show a relatively generalized pollination system with both nocturnal (moths and bats) and diurnal pollinators (bees and hummingbirds) (geographical dichotomy hypothesis). This hypothesis has been mostly tested in the northern tropics; nonetheless, our knowledge of columnar cactus species inhabiting the southern tropics is still scarce. The aim of this project was to evaluate the pollination biology of Oreocereus celsianus, a columnar cactus with restricted distribution in the subtropical Andes, to determine if the pollination system of this cactus tends to be more generalized than specialized because of the geographical position where it occurs. Observations of frequency of visit showed that Patagona gigas (Giant Hummingbird) is the main pollinator of the flowers, visiting them when they are opening (afternoon of the first day). Bees, wasps and moths were occasional visitors of the flowers. None of them seem to act as pollinator. Autogamy, geitonogamy and xenogamy treatments produced high fruit set, showing that O. celsianus has an unusual mixed mating system. The results suggest that this Andean columnar cactus is partially specialized on hummingbirds, with most pollination service performed by a single species, and it has the capacity of selfing (‘fail-safe’ pollination system). This mixed mating system (both outcrossing and selfing) may be a response to the unpredictable environment of the Prepuna in the subtropical Andes.

An estimation of the floristic richness of Bolivia’s Andean dry valleys

We estimate plant species richness of Bolivian Andean dry valleys applying the species/genus ratio of Compositae to all reported genera for those regions. The results suggest the existence of around 1500 species in the Bolivian dry valleys (12.6% more than the species recorded). A brief biogeographical analysis of our results suggests that the use of species/genus ratio of Compositae to estimate the size of the flora in Bolivian Andean dry valleys should be considered with caution, since the central Andes are geologically very young, and explosive speciation processes have taken place only in some taxa (mainly in Bromeliaceae and Cactaceae). We offer some evidence pointing to the possibility that the Andean dry valleys may possess many more species than suggested by the Compositae species/genus ratio. We discuss the implications of our estimation for conservation of the Andean dry valleys, which only represent 0.7% of the protected area of Bolivia.

Challenges and opportunities for the Bolivian Biodiversity Observation Network

Pragmatic methods to assess the status of biodiversity at multiple scales are required to support conservation decision-making. At the intersection of several major biogeographic zones, Bolivia has extraordinary potential to develop a monitoring strategy aligned with the objectives of the Group on Earth Observations Biodiversity Observation Network (GEO BON). Bolivia, a GEO Observer since 2005, is already working on the adequacy of national earth observations towards the objectives of the Global Earth Observation System of Systems (GEOSS). However, biodiversity is still an underrepresented component in this initiative. The integration of biodiversity into Bolivia’s GEO framework would confirm the need for a country level biodiversity monitoring strategy, fundamental to assess the progress towards the 2020 Aichi targets. Here we analyse and discuss two aspects of the process of developing such a strategy: (1) identification of taxonomic, temporal and spatial coverage of biodiversity data to detect both availability and gaps; and (2) evaluation of issues related to the acquisition, integration and analyses of multi-scale and multi-temporal biodiversity datasets. Our efforts resulted in the most comprehensive biodiversity database for the country of Bolivia, containing 648,534 records for 27,534 species referenced in time and space that account for 92.5% of the species previously reported for the country. We capitalise this information into recommendations for the implementation of the Bolivian Biodiversity Observation Network that will help ensure that biodiversity is sustained as the country continues on its path of development.

ÁREAS DE ENDEMISMO EN EL SUR DE LOS ANDES CENTRALES

This paper analyzes the distribution of vascular plants species endemic to the southern central Andes (south-western Bolivia and north-western Argentina). All 540 species endemic to the study regions (approx. 720600 km2) have been included in the analysis. The main part of the endemic species is found in semiarid habitats between 1500-3500 m asl pointing to the topographically complex plateau, slope, and valley system of the southern central Andes as the main locations for its endemic flora. The distribution of the endemic species within arid sites is in contrast with that of vascular plant diversity in general, as the most diverse habitat of the region is the moist subtropical Tucumano-Bolivian Yungas forest of the eastern Andes slope. A total of 17 well defined and partly overlapping distribution patterns were indentified. The broadest distribution pattern defines a general area of endemism for the southern central Andes. This area extends through nearly the entire region and is defined by species that are widespread within the region in desert to sub-humid environments of the high Andes, slopes, or valleys. Nearly all other areas of endemism are nested within this broad distribution pattern as successively north-south overlapping areas along the slopes and valleys of the Andes and the Pampeanas Range. Despite the distributional bias of endemism towards the arid sites almost half of the endemic species are restricted to a few high endemic areas that lie in juxtaposition to the main rainfall zones. These areas contain the widest habitat ranges in terms of altitude and rainfall within the region with the endemic species being equally variable in altitude and moisture requirements. Previous defined phytogeographic units were not recognized among the distribution patterns. However, the northern part of the Prepuna can be defined as two partly overlapping distribution patterns.