The centenary pluviometer: A pioneer dendrochronological study in South America

In 1931, Krebs and Fischer, published El pluviómetro secular (The centenary pluviometer) an analysis of tree rings of Prosopis caldenia Burkart (caldén) in the central Argentinean Pampas which, according to the date, may be considered as one of the first dendrochronological studies in South America.     

Growth dynamics and disturbances along the last four centuries in the Prosopis caldenia woodlands of the Argentinean pampas

Semiarid woodlands of the Argentinean pampas are dominated by Prosopis caldenia Burkart (caldén) (Fabaceae). This area has experimented severe changes over the last centuries, and fire events, overexploitation and land use changes have shaped the landscape. A sound knowledge of these disturbances and their effects on woodland dynamics is essential to plan a management and wise use of caldén woodlands. The objective of this study is to analyse the relation between growth dynamics and disturbances of P. caldenia woodlands in the last four centuries in the Argentinean pampas. Fire frequency and growth releases were analysed using dendrochronological techniques in three sampling sites (n = 86). Mean radial growth varied between 1.88 and 2.49 mm year⁻¹, according to the site. One chronology covered the 1738–2011 period, the largest one for the Argentinean pampas. Fire frequency was higher during the aboriginal period (18th–19th centuries) and mid-twentieth century. Growth releases were consistent at all sampling sites and they all had a positive association with sheep introduction after the aboriginal settlement. These results demonstrated that the use of fire by aborigines challenged the widespread concept of an idyllic relation between them and forests. Growth releases were linked to sheep introduction, consistent with records of massive deforestation which took place at the end of the 19th century, resulting in a savannah forest physiognomy. The concept of caldén forests being open to semi-open should be reconsidered in the light of these new insights.     

How aridity variations affect Prosopis caldenia growth in transitional forests in the semiarid Argentinean Pampas

The semiarid Pampas in central Argentina, occupied by caldén’s (Prosopis caldenia Burkart) woodlands (caldenales), had been affected by several wet and dry periods in the last century. Nowadays, the caldenales cover about 17 million hectares of central Argentina and their current state is critical due to massive deforestation rates. Caldén has an important dendrochronological potential since it produces sensitive tree rings linked to climate oscillations, fire events, competence, insect breakout, among others. The standard dendrochronological analysis can be improved with new advances in serial modeling and multivariate ordination techniques for handling problems related to the comparison of dendrochronological samples. We applied a statistical algorithm, BIOdry, which integrates conventional procedures for modeling patterns between annual diameter increments and drought. P. caldenia dendrochronological data were used accounting for multiple sources of variation from the sample design, and comparing patterns from contrasting climatic portions of the study site. The relation between diameter growth dynamics of caldén with temperature and precipitation fluctuations along the second half of the last century was analyzed. Populations at the Northern limit of its natural distribution area were selected. Monthly temperature and precipitation were evaluated in order to identify relative water surplus and deficit periods and an annual aridity index (AAI) was calculated. The objectives of the present work were: to analyze, describe and model response patterns between the P. caldenia diameter growth increment and the AAIs. A common growth response pattern and differences in tree and population level were also analysed. The algorithm BIOdry showed a good behavior, according to the considered statistical parameters (all the fixed effects were statistically significant). Several and common problems associated with the nature of the tree-ring data in modeling (pseudorreplication, autocorrelation, and nested random effects) were efficiently addressed. P. caldenia diameter growth, at tree level significantly responds to different AAI variation intensities along the studied period. A high frequency growth variability at population level was detected when trees establishment happened. These associations ended when trees become older. Low frequency growth variability at population level was significant throughout the analyzed period, presumably linked to age and management history. These results provide news insights in relation to the climate impact on growth dynamics of caldén in the Argentinean pampas and the value of new statistical tools in order to improve dendrochronological studies.     

Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas

Aim The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting. Location Pampas grasslands, Argentina. Methods We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers. Results Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks). Main conclusions The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.     

Edge effect on bird nest predation in the fragmented caldén (<Emphasis Type="Italic">Prosopis caldenia</Emphasis>) forest of central Argentina: an experimental analysis

Clearing of caldén (Prosopis caldenia) forests for agriculture and cattle raising in east-central La Pampa Province, central Argentina, has created a highly fragmented landscape, a condition that has resulted in adverse effects on birds in other forests, mainly through increased predation rates near forest edges. We evaluated bird nest predation rates using artificial nests, assessing the effects of forest fragment size, distance to the edge and nest height. We measured survival rate of 570 artificial nests located in trees, in bushes and on the ground, at different distances from the edge, in six forest fragments ranging in size from 2.1 to 117.6 ha, during two consecutive breeding seasons. Nest predation rates were significantly related with the number of days of exposition of the nest, nest height and distance to the edge, whereas fragment size and year of the experiment were not associated with predation rates. Ground nests were less likely to be predated than those located in bushes and trees. Predation rates decreased with the distance to the edge, showing a pattern consistent with the existence of an edge effect.     

Botanical origin of honey from south of Calde´n district (Argentina)

We performed palynological analysis of 75 honey samples from the south of Caldén district, which is the part of the phytogeographical province del Espinal. Prosopis caldenia , "caldén" (Fabaceae) is the dominant arboreal species in this region. 79 pollen types that belong to 36 plant families were identified. Honeydew elements are absent or present in negligible amounts. Native flora is intensely utilized. Main nectar sources that characterize monofloral honey samples, are these natives Condalia microphylla (Rhamnaceae), Prosopis sp. and Vicia sp. (Fabaceae), Larrea divaricata (Zygophyllaceae) and Brassicaceae, which are foreign to the area. The pollen from these plants along with the pollen of Trichocline sp. (Asteraceae) and Prosopidastrum globosum (Fabaceae), Schinus fasciculatus (Anacardiaceae), Astereae and Lycium sp.(Solanaceae), characterize honey from Caldén.     

Effect of a postfire environment on the establishment of Prosopis caldenia seedlings in central semiarid Argentina

Abstract The objective of this work was to evaluate postfire environmental effects on the emergence, survival and growth of Prosopis caldenia seedlings in relation to different controlled fire frequencies, seed scarification methods, and planting site. Seedling emergence was significantly higher in experimental units exposed twice and three times to controlled fire than in unburned experimental units. The highest average seedling survival was recorded with triple exposure to controlled fires. Emergence, survival and growth of seedlings from seeds exposed to acid scarification and 600°C for 5 min were higher in the burned experimental units than in the unburned ones. In the former, seedling survival was higher beneath a P. caldenia canopy than in an adjacent open site, though seedling emergence was similar in both planting sites. Our results suggest that postfire conditions characterized by a reduction in the vegetative cover and competition interference and an increase in soil temperatures and nutrients levels (e.g. nitrogen and phosphorus) may facilitate the establishment of P. caldenia seedlings in the Caldenal.     

Rodent seed predation on tree invader species in grassland habitats of the inland Pampa

Woody plant invasion in grassland ecosystems is a worldwide phenomenon, and biotic interactions as competition and predation have been invoked as a possible barrier to woody encroachment in many ecosystems. We evaluated the role of rodents as seed predators in Pampean grasslands, and we assessed the differences in removal by rodents between one native species, Prosopis caldenia (Caldén) and one exotic species, Gleditisia triacanthos (Honey locust). The experiment was conducted at different phases of the rodent population cycle in two grassland communities, a remnant of a native grassland and a post agriculture grassland (old field). The amount of seed loss caused by predation was estimated by a bait-removal experiment in foraging stations. We estimated the frequency of foraging stations with consumption, the overall amount of seed predation and the individual rate of seed predation. The total amount of seed removal and the individual rate of seed removal were higher for P. caldenia than for G. triacanthos, in the native grassland than in the old field, and in autumn when rodent density was maximum. Overall, the role of rodents on woody seed removal varied according to the plant species and depending on the local conditions that vary through time and space.     

Limits to tree species invasion in pampean grassland and forest plant communities

Factors limiting tree invasion in the Inland Pampas of Argentina were studied by monitoring the establishment of four alien tree species in remnant grassland and cultivated forest stands. We tested whether disturbances facilitated tree seedling recruitment and survival once seeds of invaders were made available by hand sowing. Seed addition to grassland failed to produce seedlings of two study species, Ligustrum lucidum and Ulmus pumila, but did result in abundant recruitment of Gleditsia triacanthos and Prosopis caldenia. While emergence was sparse in intact grassland, seedling densities were significantly increased by canopy and soil disturbances. Longer-term surveys showed that only Gleditsia became successfully established in disturbed grassland. These results support the hypothesis that interference from herbaceous vegetation may play a significant role in slowing down tree invasion, whereas disturbances create microsites that can be exploited by invasive woody plants. Seed sowing in a Ligustrum forest promoted the emergence of all four study species in understorey and treefall gap conditions. Litter removal had species-specific effects on emergence and early seedling growth, but had little impact on survivorship. Seedlings emerging under the closed forest canopy died within a few months. In the treefall gap, recruits of Gleditsia and Prosopis survived the first year, but did not survive in the longer term after natural gap closure. The forest community thus appeared less susceptible to colonization by alien trees than the grassland. We conclude that tree invasion in this system is strongly limited by the availability of recruitment microsites and biotic interactions, as well as by dispersal from existing propagule sources.     

Tree-ring analysis of white cedar (Thuja occidentalis L.) archaeological and historical wood in Québec City (Québec,Canada)

In Québec City, a segment of an old wooden palisade built for protection was found buried in situ. The palisade was excavated by the Laval University archaeology field school in 2004–2005, and 29 posts were recovered and sampled. The palisade enclosed the Intendant's Palace compound, which was the residence of the governor of New France at the end of the 17th century. Tree-ring analysis was performed on wood excavated from the Intendant's Palace archaeological site (PDI) and additional wood from two historical military buildings, the Artillery Park (ART) (early 18th century) and the Québec Citadel (CIT) (17th–19th centuries). Wood identification revealed that white cedar (Thuja occidentalis L.) was used for wood construction at the three sites. Many trees used for the construction of the PDI palisade were felled after the 1690 growing season, likely in September/October 1690. Posts probably came from trees growing close to the site on the banks of the Saint-Charles River. A white cedar ring-width chronology from the Rimouski area, approximately 300 km northeast of Québec City, along the St. Lawrence River, was used for cross-dating. Archaeological and historical wood samples from two of the three sites (PDI and ART) were first assembled in a 235-year tree-ring chronology, called the Québec chronology, extending from 1489 to 1723. The two master chronologies (Québec and Rimouski) were merged into a single 513-year tree-ring chronology (1489–2001), called the Saint-Laurent chronology.     

Ancient mtDNA Analysis of Early 16th Century Caribbean Cattle Provides Insight into Founding Populations of New World Creole Cattle Breeds

The Columbian Exchange resulted in a widespread movement of humans, plants and animals between the Old and New Worlds. The late 15^th to early 16^th century transfer of cattle from the Iberian Peninsula and Canary Islands to the Caribbean laid the foundation for the development of American creole cattle (Bos taurus) breeds. Genetic analyses of modern cattle from the Americas reveal a mixed ancestry of European, African and Indian origins. Recent debate in the genetic literature centers on the ‘African’ haplogroup T1 and its subhaplogroups, alternatively tying their origins to the initial Spanish herds, and/or from subsequent movements of taurine cattle through the African slave trade. We examine this problem through ancient DNA analysis of early 16^th century cattle bone from Sevilla la Nueva, the first Spanish colony in Jamaica. In spite of poor DNA preservation, both T3 and T1 haplogroups were identified in the cattle remains, confirming the presence of T1 in the earliest Spanish herds. The absence, however, of “African-derived American” haplotypes (AA/T1c1a1) in the Sevilla la Nueva sample, leaves open the origins of this sub-haplogroup in contemporary Caribbean cattle.     

Latest developments of dendro-archaeology in the French Alps: Assessing changes in mountain forests exploitation over the last millennium

Dendrochronological studies are carried out on rural buildings in the French Alps for twenty years. In this contribution, we examine an extensive dataset of larch timbers (n = 1294) that were dendrochronologicaly dated at 139 buildings. This material yielded felling dates spanning the 11th century to the 20th century and contributed to improve our knowledge of human occupation and exploitation of mountain forests during the second millennium CE. From the 11th to the 14th century, rural populations increasingly exploited older forests. The crises of the 14th century led to a significant decrease in construction and by extension in tree cutting. The beginning of the 15th century marks a resumption of construction and felling which is continuous until the beginning of the 20th century. There is a relationship between the age of harvested trees, the number of dates and population fluctuations, which corroborates findings at the European scale. Regional trade probably influenced the stem diameters used in constructions in the immediate vicinity of the forests. Logging regulations can be perceived through variations in the age of harvested trees. The 14th century gap in felling dates would also mark a transition period in the exploitation of mountain forests and by extension a transformation of the economy.     

Pampas fox (Lycalopex gymnocercus) of the Argentine Pampas as intermediate host for Neospora caninum

The Pampas fox (Lycalopex gymnocercus) is the most abundant wild canid from South America. This wild canid inhabits grasslands, open woodlands, and areas highly modified by extensive ranching and agricultural activities. We aimed to evaluate Neospora caninum infection in tissues from the Pampas fox from Argentina. A total of 41 free-living Pampas foxes were sampled in rural areas located in the Humid Pampas region, Argentina. Brain tissue and different muscles were assessed by histologic and molecular methods. No N. caninum cysts were observed in brain and muscle tissue samples analyzed by histology and immunohistochemistry. Molecular N. caninum identification from brain tissue was based on amplification by PCR of Nc-5 gene and ITS1 rRNA fragments and subsequent sequencing. The presence of N. caninum DNA was 74% (23/31) for the Nc-5 gene and was confirmed by a second ITS1 PCR in 55% (17/31) of the brain tested. Thirteen ITS1 consensus sequences were obtained, and all have a 99.58–100% similarity with N. caninum reference sequences. Only 4% (1/23) of muscles samples analyzed were positive for the Nc-5 gene of N. caninum. This study demonstrated a high prevalence of N. caninum DNA in brain from free-ranging Pampas fox of the Pampa Argentine, thus confirming that this wild canid is a wide distributed intermediate host.     

Genotyping Yersinia pestis in Historical Plague: Evidence for Long-Term Persistence of Y. pestis in Europe from the 14th to the 17th Century

Ancient DNA (aDNA) recovered from plague victims of the second plague pandemic (14^th to 17^th century), excavated from two different burial sites in Germany, and spanning a time period of more than 300 years, was characterized using single nucleotide polymorphism (SNP) analysis. Of 30 tested skeletons 8 were positive for Yersinia pestis-specific nucleic acid, as determined by qPCR targeting the pla gene. In one individual (MP-19-II), the pla copy number in DNA extracted from tooth pulp was as high as 700 gene copies/μl, indicating severe generalized infection. All positive individuals were identical in all 16 SNP positions, separating phylogenetic branches within nodes N07_N10 (14 SNPs), N07_N08 (SNP s19) and N06_N07 (s545), and were highly similar to previously investigated plague victims from other European countries. Thus, beside the assumed continuous reintroduction of Y. pestis from central Asia in multiple waves during the second pandemic, long-term persistence of Y. pestis in Europe in a yet unknown reservoir host has also to be considered.     

Community Impacts of Prosopis juliflora Invasion: Biogeographic and Congeneric Comparisons

We coordinated biogeographical comparisons of the impacts of an exotic invasive tree in its native and non-native ranges with a congeneric comparison in the non-native range. Prosopis juliflora is taxonomically complicated and with P. pallida forms the P. juliflora complex. Thus we sampled P. juliflora in its native Venezuela, and also located two field sites in Peru, the native range of Prosopis pallida. Canopies of Prosopis juliflora, a native of the New World but an invader in many other regions, had facilitative effects on the diversity of other species in its native Venezuela, and P. pallida had both negative and positive effects depending on the year, (overall neutral effects) in its native Peru. However, in India and Hawaii, USA, where P. juliflora is an aggressive invader, canopy effects were consistently and strongly negative on species richness. Prosopis cineraria, a native to India, had much weaker effects on species richness in India than P. juliflora. We carried out multiple congeneric comparisons between P. juliflora and P. cineraria, and found that soil from the rhizosphere of P. juliflora had higher extractable phosphorus, soluble salts and total phenolics than P. cineraria rhizosphere soils. Experimentally applied P. juliflora litter caused far greater mortality of native Indian species than litter from P. cineraria. Prosopis juliflora leaf leachate had neutral to negative effects on root growth of three common crop species of north-west India whereas P. cineraria leaf leachate had positive effects. Prosopis juliflora leaf leachate also had higher concentrations of total phenolics and L-tryptophan than P. cineraria, suggesting a potential allelopathic mechanism for the congeneric differences. Our results also suggest the possibility of regional evolutionary trajectories among competitors and that recent mixing of species from different trajectories has the potential to disrupt evolved interactions among native species.     

New Karyotypes and Some Considerations about the Chromosomal Diversification of Ctenomys minutus (Rodentia: Ctenomyidae) on the Coastal Plain of the Brazilian State of Rio Grande do Sul

The dominant mammals occupying the subterranean niche in South America are rodents of the genus Ctenomys, which form a large group of 56 species with chromosome numbers ranging from 2n= 10 to 70. In southern Brazil, Ctenomys minutus is the species with the widest geographic distribution, inhabiting sandy fields and dunes extending from Jaguaruna beach in the state of Santa Catarina to the town of São José do Norte in the state of Rio Grande do Sul. Eleven karyotypes (2n= 42; 2n= 46a; 2n= 46b; 2n= 47a; 2n= 47b; 2n= 48a; 2n= 48b; 2n= 49a; 2n= 49b; 2n= 50a and 2n= 50b) were described for this species and zones of hybridization are also known. A sample of 51 C. minutus specimens was collected from five sampling sites about 20 km apart along the coastal plain of Rio Grande do Sul between the municipalities of Tavares (31°23′S 51°09′W) and São José do Norte (31°52′S 51°54′W). We were able to extend the known geographic distribution of C. minutus by 90 km, from Tavares southwards to São José do Norte. During our study we found five karyotypes (2n= 46b, 47b, 48b, 49b and 50b), four of which (2n= 47b, 48b, 49b and 50b) have not previously been described for this species.     

Peripheral vision: science and creole patriotism in eighteenth-century Spanish America

This article examines the study of natural history on the imperial periphery in late colonial Spanish America. It considers the problems that afflicted peripheral naturalists—lack of books, instruments, scholarly companionship, and skilled technicians. It discusses how these deprivations impacted upon their self-confidence and credibility as men of science and it examines the strategies adopted by peripheral naturalists to boost their scientific credibility. The article argues that Spanish American savants, deprived of the most up-to-date books and sophisticated instruments, emphasised instead their sustained experience of local nature and their familiarity with indigenous knowledge. It details how some creole naturalists, such as the Mexican José Antonio Alzate, questioned the applicability of European classificatory systems to American fauna and flora, and it analyses the complex relationship between natural science and creole patriotism.     

Impact of Prosopis invasion on a keystone tree species in the Kalahari Desert

Several Prosopis species were introduced into South Africa in the last century. Since then two species, Prosopis glandulosa var. torreyana and Prosopis velutina have invaded large parts of arid southern Africa. Here, we examine the extent to which increased mortality of Acacia erioloba, a keystone species in the Kalahari Desert, can be attributed to competition for water with Prosopis. We do this for A. erioloba and Prosopis sp. at invaded, as well as cleared sites through a determination of species abundance, canopy vitality, plant water stress and plant water source. Our stable isotope results show that in the riparian zone both A. erioloba and Prosopis are using the same water source. Our results also show that there is a 50 % increase in canopy dieback of A. erioloba in the invaded river plots relative to the cleared river plots. This dieback cannot be related to changes in rainfall and temperature as there were no adverse fluctuations (drought) in the weather in the 10 years preceding our study. We speculate that because A. erioloba is more water stressed in the invaded river plot this increase in mortality and dieback is related to plant moisture stress that is not related to climate but to competition for water with Prosopis. Our study gives strong support for the eradication of Prosopis from rivers in arid parts of Southern Africa.