Laguna Seca Research Articles

Effects of Eight Years of Collecting on the Persistence of Liometopum apiculatum Ant Nests in Rangelands of Charcas, San Luis Potosí, Mexico

In Mexico, the pupae of the reproductive castes of the ant Liometopum apiculatum, escamoles, are highly valued in traditional and gourmet cuisine in the country’s central region. Escamoles are collected during the dry season of the year. The recommended collecting process is to open the ant nest by removing soil until the rearing chamber and the trabeculae with attached escamoles are found. A well-managed ant nest can be collected repeatedly for approximately 12 to 40 years. In Charcas municipality, San Luis Potosí, Mexico, 400 ant nests were located and checked under two land tenure conditions: the Laguna Seca private ranch and the Pocitos communal ejido. The exploitation of escamoles on both tenures was characterized by recording the number of dead and live ant nests. This work evaluated the condition of the ant nests registered in 2012 after eight years. The hypothesis was that ant nests’ survival would be greater in the private than in the communal land. The percentage of living ant nests on the ejido decreased by 35.67%. In contrast, on the ranch, it was 26.88%. The percentage of relocated ant nests was lower on the ejido, 37.43%, compared to the ranch, which was 48.1%. The number of dead ant nests on the ejido increased to 33.51% and on the ranch 15.0%. As predicted by the hypothesis, ant nest survival was higher on the private ranch than on the communal ejido lands because of stronger control of the extraction process.

Laguna Seca sediments reveal environmental and climate change during the latest Pleistocene and Holocene in Sierra Nevada, southern Iberian Peninsula

Sedimentation in most glacial lakes and wetlands in the Sierra Nevada (southern Iberian Peninsula) began after the last deglaciation and since the Younger Dryas (YD)-Early Holocene (EH) transition. Therefore, until now, studies on older sedimentary records were lacking in this alpine area, which limits the paleoenvironmental and paleoclimatic information to the Holocene. In this study, we studied palynomorphs from the alpine record from Laguna Seca (LS), the longest and oldest (∼18,000 cal yr BP = 18 kyr) sedimentary record in the Sierra Nevada to investigate the response of forests and lake environments in the western Mediterranean area to climate changes and human impact during the latest Pleistocene and Holocene. The deepest lake conditions occurred during the last deglaciation, indicated by the occurrence of Pediastrum algae, which showed highest abundances during the Heinrich Stadial 1 (HS1) and Bølling-Allerød (B-A) transition. Xerophyte herbs such as Artemisia, Ephedra, and Amaranthaceae were highest during the late B-A and YD indicating regional aridity. Poaceae (grasses) were maxima in the B-A and EH, probably indicating expansion in the barren areas after deglaciation. Maximum in temperature and humidity during the EH and cooling and aridification in the Middle (MH) and Late Holocene (LH) are indicated by the changes in the abundance of deciduous Quercus and Pinus forest species. Botryococcus algae increased during the Early Holocene, while the rest of the algae almost vanished, which could indicate that the lake became very productive but shallower until 8.2 kyr. The lake level lowered and became seasonal in the Middle-Late Holocene transition, coinciding with the regional climate aridification. Microcharcoal analysis done on the palynological preparations agrees with the vegetation changes, showing maxima in the EH and MH, related with the maximum in regional forest occurrence, and a decrease in the LH when the Mediterranean vegetation, and thus fuel availability, diminished. This record shows evidence of anthropogenic impact in the last centuries by cultivation, reforestation, cattle grazing, enhanced erosion and eutrophication.

Influence of geological faults on dissolved arsenic concentrations in an overexploited aquifer with shallow geothermal heat

Hydrochemical and mineralogical analyses were performed to identify the main processes that contribute to the concentration of total inorganic arsenic (iAs) in groundwater within the northern portion of the Laguna Seca aquifer in Guanajuato State, Mexico. The spatial extent of the study area spans across a large graben with pore-waters that contain the highest dissolved arsenic concentrations in the basin. This scale of study was chosen to test the hypothesis that normal faults act as conduits for rising geothermal waters carrying arsenic into the shallow aquifer that has been historically depressurized by irrigation pumping. The arsenic content in outcrops ranged from 3.5 to 19.5 ppm. The major minerals are quartz, plagioclase, micas, and zeolites. Multivariate cluster and Principal Components Analyses on the chemical composition and temperature of 15 wells in the study area suggest that silicate weathering is the dominant water-rock interaction that explains the observed concentrations of major ions and arsenic in groundwater. The sampled irrigation and municipal wells ranged from 190 to 550 m in depth and had temperatures ranging from 28.3 to 45.2 °C. Cluster II had the highest temperature, and greatest mineralization (total dissolved solids), and it was more influenced by regional flow than Cluster I. The concentration of iAs ranged from 16 to 229 μgL−1, all of the samples exceeded the maximum concentration suggested by the World Health Organization (10 μgL−1). Four samples belonging to Cluster II exceeded the maximum concentration set by Mexican regulations (25 μgL−1) by at least five times. The highest concentration of arsenic in surface rock coincides spatially with Cluster II wells. Geothermal heat and long pore-water-residence times enables the dissolution of silicate minerals which increases the pH (from 7.3 to 9.1) and consequently drives desorption of arsenic from mineral surfaces. During the dry season the iAs content increased in all wells from 6 to 138 μgL−1 compared to the wet season. This could be attributed to the increase in pumping that occurs then. The close proximity of Cluster II wells to newly mapped faults within the graben supports the hypothesis that Cluster II wells intercept regional groundwater flow that ascends through those previously unmapped faults.

Post-glacial evolution of alpine environments in the western Mediterranean region: The Laguna Seca record

In an effort to understand how alpine environments from the western Mediterranean region responded to climate variations since the last glacial-interglacial transition, a detailed chronological control and sedimentological analysis, supported by magnetic susceptibility, total organic carbon and C/N data, were carried out on the sedimentary record of Laguna Seca (LS). This is a latitudinal and altitudinally (2259 masl) key alpine wetland site located in the easternmost area of the Sierra Nevada, southern Iberian Peninsula, where sediments accumulated during Heinrich Stadial 1, Bølling-Allerød (B-A) and the Younger Dryas (YD) - previously unrecorded in alpine Sierra Nevada. Climate controlled sedimentation in LS and three coarse-grained and one fine-grained facies association are differentiated, which help us decipher the paleoenvironmental evolution of LS: (1) subaerial cohesionless debris flows during a paraglacial stage; (2) till or nival diamicton during a small glacier/nivation hollow stage; (3) massive mudstone by suspension settling of clays into standing water during a lacustrine stage; and (4) frost-shattering breccia deposited inside the lacustrine stage, probably during the YD, and linked to a periglacial substage. The development of a previously existing small glacial cirque during the Last Glacial Maximum (LGM) in the LS basin at an elevation between 2500 and 2300 m could be supported by the important availability of slope sediments glacially-conditioned such as debris flows, reworked by paraglacial slope processes during the first deglaciation stages, confirming previous studies of landforms in the catchment area and the LGM-Equilibrium Line Altitude estimation above 2400 masl in Sierra Nevada. Mean sediment accumulation rates in the LS sedimentary units (4.21 and 0.28 mm/yr during the paraglacial - small glacier/nivation stage and the lacustrine stage, respectively) confirm that geomorphic activity accelerated just after glaciers retreated due to a slope adjustment and high availability of glacially conditioned sediments. An abrupt change in paleoenvironmental and paleoclimatic conditions occurred in LS at ∼ 15.7 cal kyr BP. This change was probably due to an increase in temperature and precipitation in the western Mediterranean region during the B-A. At LS, this resulted in significant ice-melt, forming a deep-water lake in LS with important organic matter contribution until the end of the Early Holocene (except in the YD when the lake level probably dropped), but elsewhere a general glacier recession in the Sierra Nevada and an expansion of the Mediterranean forest in the southern Iberian Peninsula. Finally, the general long-term aridification that occurred during the Middle Holocene until the present in the western Mediterranean region triggered an important environmental change transforming LS into an ephemeral wetland with an increase in aquatic productivity.

Pacific shoot‐gall disease control in annual bluegrass putting greens using a new formulation of abamectin

AbstractThe Pacific shoot‐gall nematode (Anguina pacificae Cid del Prado Vera & Maggenti, 1984) is a devastating pest on annual bluegrass (Poa annua L.) putting greens in coastal Northern California, USA. Frequently used plant protection compounds such as fenamiphos and azadirachtin are either no longer registered or very expensive and have often resulted in nematode suppression at best. A new formulation of abamectin (Divanem®; Syngenta, Greensboro, NC) was tested at two rates (0.15 and 0.30 kg a.i. ha−1) and two application frequencies (2X vs. 4X) in comparison to fluopyram (Indemnify®; Bayer CropScience, St. Louis, MO) applied at the rate of 0.5 kg a.i. ha−1 on three California golf courses: Pasatiempo, Santa Cruz; Laguna Seca, Monterey; and Del Monte, Monterey. Fluopyram showed the best efficacy regarding recovery from and protection against the Pacific shoot‐gall disease. Generally, only two applications were required for season‐long protection. Four applications of the new formulation of abamectin at the high rate were often necessary to achieve efficacy similar to fluopyram. Overall, abamectin represents another new plant protection tool that offers a treatment alternative for the management of this pathogen. Neither product had much effect on populations of soil‐dwelling A. pacificae, spiral (Helicotylenchus spp.), ring (Criconemoides spp.), and root‐knot (Meloidogyne spp.) nematodes.

On the Job

Brandy Falconer is the Communications Manager at the WeatherTech Raceway at Laguna Seca in Monterey, California. The raceway is a paved road racing track used for both auto racing and motorcycle ra...

NECESSITY OF INTERVENTION POLICIES FOR TAILINGS IDENTIFIED IN THE ANTOFAGASTA REGION, CHILE

The aim of this work was to establish the intervention requirements of 30 tailings deposits located in the region of Antofagasta, Chile, identified in the National Tailings Survey carried out by the National Service of Geology and Mining of the Chilean government in 2017. For the evaluation, the data of 49 geochemical characterizations of the samples registered as of October 2017 were considered. The methodology used for evaluation was based on the Dutch Soil Regulation Circular, from which two ways of assessment were developed. The first approach uses a simple graphic method that depends only on the concentration of the elements in the solid phase of tailings and the percentage of clay in the soil. The second approach considers that the information related to the clay percentage is not available, therefore, this work defines the concepts of threshold factor and adjusted threshold factor. Using the proposed method, this work presents the analysis carried out on the elements of environmental significance related to mining activity in Chile: Cu, Cr, Ni, Zn, Pb, As, Cd and Hg. The methodology allows delimiting areas of foreseeable risks for people and/or environment, resulting in three criteria for each element: 1) requires intervention, 2) requires conditional intervention, 3) does not require intervention. These results are summarized by means of a final score that determines the level of priority assigned to each sample. The analysis of results indicates that Hg intervention is not required, there being only one case requiring conditional intervention. Regarding Cu and Zn, 100 % of the measurements indicated at least the requirement of a conditional intervention. Within the region, the commune of Sierra Gorda contains 67 % of the tailings whose intervention must be prioritized according to the score obtained (greater than four out of a possible maximum of eight). On the other hand, the two tailings of greater tonnage (the sites of Talabre and Laguna Seca) do not present a requirement for priority intervention at the moment.

Traditions of Early Human Groups in Baja California and Possible Routes for the Peopling of the Peninsula

Ideas concerning the initial peopling of the Baja California Peninsula have dramatically changed in recent decades. In the late 19th and early 20th centuries, the native inhabitants of the southern part of the Baja California Peninsula were believed by some to have come from Melanesia, based on the perceived similarity in skull morphology. Since the middle of the 20th century, most researchers propose that initial populations entered from the north by land, bringing with them 2 distinct cultural traditions. The first wave was thought to have been an incursion of Paleoindians with Clovis-type fluted points. The second wave refers to groups who occupied ancient lake shores, such as Laguna Seca Chapala, and who were considered as belonging to the Western Pluvial Lakes (WPL) tradition. Eventually people moved down to the southern tip of the peninsula, pushed by subsequent groups. The entry of human groups from the Mexican mainland across the islands in the central Gulf of California has also been suggested; early entries by other groups have been proposed as well. A migration from Australia to the Cape Region across the southern Pacific has also been argued. This paper summarizes recent archaeological evidence from radiocarbon dates, geomorphological settings, subsistence strategies, and material types and technologies indicating that Paleocoastal migrants may have reached the Cape Region during the Terminal Pleistocene. However, some of the early lithic artifacts and technologies in the Cape Region show similarities to the WPL tradition, such as leaf-shaped points, an eccentric crescent, and end and side scrapers. This evidence suggests that perhaps a Paleocoastal group and a WPL group reached the southern part of the peninsula at around the same time and that they had some kind of interrelation that is reflected in their lifestyles and materials, which were principally adapted to coastal life.

Partos y precipitación anual previa en tres ranchos ganaderos del Altiplano Potosino-Zacatecano

Functional relations between calving percentage (y) and total previous year’s rainfall (TPYR, x) were estimated using data from three private cattle ranches in the Potosino-Zacatecano highlands. TPYR data were obtained from the two official weather stations nearest to each ranch and with the same climate type. Using these relations, the calving percentage that occurred in 2015 (a year not included in the estimation of these relations) was predicted and statistically collated for the Laguna Seca (LS), San Jose (SJ) and El Porvenir (EP) ranches. Estimated correlations between calving percentage and rainfall were positive and significant for each ranch. Simple linear regression models were: y=26.2800 + 0.0629 (x) for LS; y=30.2438 + 0.0973 (x) for SJ; and y=23.6172 + 0.0808 (x) for EP. The variation in the calving percentage explained by TPYR was 59.2 % for LS, 62.0 % for SJ and 84.9 % for EP. Calving percentages recorded during 2015 for EP and LS (72.2 and 64.0 %, respectively) were greater than the 95 % confidence intervals, due to various recent improvements in herd reproduction; on the other hand, the calving percentage recorded during 2015 for SJ did fall within this range.

Historia ambiental de la Laguna Seca, Tartagal Salta, Noroeste Argentino

Fil: Fierro, Pamela Tatiana. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Universidad Nacional de Jujuy. Facultad de Ingenieria; Argentina

Chert quarries and workshops in the Humid Pampa sub-region: New contributions on exploitation techniques and circulation through study of chaînes opératoires

The study of technological organization associated with hunter-gatherers groups has been one of the topics of greatest interest in the archaeological research of the Pampean region. In this sense, the aims of this paper were to interpret the role of the Cerro Largo Formation chert in the technological practices of human groups and to discuss how this rock was used and transported in the center of the Humid Pampa sub-region during the Late Holocene. We will present the techno-morphological analysis on chert artifacts recovered from Boca de la Sierra workshop in order to identify how this stone was used at the beginning of its exploitation. Then, we will compare and discuss diverse chaînes opérotoires on chert found in archaeological sites located at different distances from the sources. In Boca de la Sierra workshop, we recorded three initial forms of exploitation of the nodules. The Cerro Largo Formation chert had been transported from this workshop to other sites in the form of different kinds of partially and/or totally decorticated cores, nodules, large flakes, and possibly tools. In those sites located at a short distance from the quarry workshops (Empalme Querandíes 1 and Laguna La Barrancosa 2) we observed complete chaînes opérotoires organized through débitage, with low production of standardized blank and a high frequency of external flakes used as blank for the manufacture of different kinds of tools. In those sites located at a long distance from the quarry workshops (Laguna La Larga and Laguna Seca 2), we recorded chaînes opérotoires developed almost entirely. Even though some expedient tools are recorded, the greatest maximization in the use of Cerro Largo Formation chert is remarkable. The high proportion of standardized, small and shaped tools, the identification of exhausted cores, the use of a bipolar technique, and the presence of resharpening flake edges show a curated technological strategy. Finally, the presence of complete chaînes opérotoires close to the hills allow us to infer direct access to the outcrops and an easy acquisition of chert; whereas the features observed in the other sites indicate that the chert acquisition was done by specific trips or by social exchange and interaction networks with other groups.

The páramo vegetation of Ramal de Guaramacal, Trujillo State, Venezuela. 2. Azonal vegetation

The azonal paramo vegetation present at the top of Ramal de Guaramacal in the Venezuelan Andes was studied by means of observations, plant collections and surveys consisting of a total of 71 small plots of between 0.25 to 6 m2. Azonal vegetation is represented in the study area by habitats experiencing water stress (peat bogs and aquatic vegetation). The azonal vegetation present in two peat bogs areas of Paramo El Pumar (Laguna El Pumar y Laguna Seca), and in a small valley where water collects in Paramo de Guaramacal, near the 'Las Antenas' area between ∼2900 and ∼3000 m were analyzed. A total of 53 morphospecies, belonging to 30 species of vascular plants, 20 species of cryptogams and 3 undetermined species of algae have been documented for the azonal vegetation. The interpretation of a TWINSPAN clustering, based on affinities of floristic composition and species cover, allowed the recognition of six azonal vegetation communities grouped into three alliances and one order. The new alliance Sphagno recurvi-Paepalanthion pilosi groups the new bunchgrass paramo association Paepalantho pilosi-Agrostietum basalis and the both new Sphagnum bog associations: Sphagno recurvi-Caricetum bonplandii and Sphagno sparsi-Caricetum bonplandii. The new alliance Carici bonplandii-Chusqueion angustifolia contains a bamboo paramo ('chuscal') association Carici bonplandii-Chusqueetum angustifoliae growing close to the lake shores, in periodically flooded areas, and characterized almost exclusively by Chusquea angustifolia. The alliance Districho submersi-Isoetion Cleef 1981 is represented by the submerged aquatic community of Sphagnum cuspidatum and the Isoetetum karstenii Cleef 1981.

Geoarchaeology and geochronology of pluvial Lake Chapala, Baja California, Mexico

AbstractStratigraphic exposures in natural profiles, archaeological excavation units, backhoe trenches, and an uncased water well from the Laguna Seca Chapala basin in the Central Desert of Baja California (29°N, 115°W) record lake level and climate changes and provide a context for prehistoric occupation predating 9070 yr B.P. and extending through the Holocene. Lithofacies analysis points to the presence of a large (ca. 66 km2) lake prior to 9070 yr B.P., which desiccated by 7.45 ka yr B.P., promoting rapid dune growth. New dating and redefinition of stratigraphic units in the basin refutes earlier models of lacustrine history and prehistoric occupation including a proposed series of Pleistocene lake levels with associated cultural occupations. The geologic record from the Laguna Seca Chapala basin compares well with other paleoenvironmental records in southwestern North America, supporting interpretations of wet and cool conditions in Baja California during the late Pleistocene and early Holocene. © 2003 Wiley Periodicals, Inc.

Mid- to Late-Wisconsin Pollen Record of San Felipe Basin, Baja California

A lacustrine sequence from Laguna Seca San Felipe, Baja California, in the southwestern Sonoran Desert, provides the first record of mid- to late-Wisconsin vegetation in one of the driest regions of North America. Pollen analysis was performed in the intermediate part of the sequence from ca. 44,000 to ca. 13,000 14C yr B.P. according to six 14C radiocarbon dates. Sedimentation of eolian sands prior to 44,000 14C yr B.P. indicates dry conditions. High pollen concentration of montane and chaparral species in the pollen assemblages contrast with the modern desert vegetation. Sixty-four pollen types were identified. The source of mid- to late-Wisconsin sedimentation must have been the plant communities in the surrounding highlands of the basin. Mid-Wisconsin pollen assemblages dominated by pines, junipers, and Artemisia reflect humid conditions in the area. By late Wisconsin time, a significant increment in junipers indicates a lowering in the altitudinal ranges of woodlands/chaparral. Pollen from wind-pollinated species is abundant while desert plants, specifically animal or insect pollinated species, are poorly represented. The San Felipe record does not identify the Last Glacial Maximum as the time of greatest effective moisture, as suggested by pluvial lake levels and other paleoclimatic evidence in the soutwestern United States.

Mercury in Morelet's Crocodile Eggs from Northern Belize

Recent studies have examined mercury accumulation in crocodilians. However, though most researchers have focused on tissue concentrations, few have examined mercury levels in crocodilian eggs. In July 1995, we analyzed mercury in 31 nonviable Morelet's crocodile ( Crocodylus moreletii) eggs collected from eight nests across three localities in northern Belize. All eggs were found to contain mercury. Based on an individual egg basis, mean concentration of mercury for all three localities was among the lowest reported for any crocodilian species. When localities were examined separately, mean concentrations for Laguna Seca and Gold Button Lagoon were comparable to those observed in other studies, and the mean for Sapote Lagoon was the lowest ever reported. Based on mean nest concentrations, mercury in eggs from Laguna Seca was approximately two- and tenfold higher than for Gold Button Lagoon and Sapote Lagoon, respectively. Variability in mercury concentrations among localities is likely the result of site-specific differences in mercury input, bioavailabilty, and bioaccumulation. Mercury concentrations were relatively uniform in eggs from the same nest and among nests from the same localities. The presence of mercury in Morelet's crocodile eggs suggests exposure in adult females, developing embryos, and neonates. However, crocodiles in these areas show no overt signs of mercury toxicity, and no indication of population decline is evident. A paucity of data on the effects of mercury on crocodilians precludes meaningful speculation as to the biological significance of tissue and egg concentrations. Controlled laboratory studies and long-term population monitoring are needed to address these questions.

Soil-landscape evolution on a Mediterranean high mountain

During the Quaternary, Sierra Nevada (southern Spain) was affected by several glacial–periglacial episodes, decreasing progressively in intensity with time. These cold episodes alternated with the ones characterized by landscape stability and soil formation. Twelve soils that were formed on pre-glacial surfaces and glacial deposits of various ages were studied in four sectors: Laguna Seca, Lanjarón Valley, Mulhacén Valley, and Corral del Veleta. The soil parent material in all of these sectors was mica schist. Organic matter content, cation exchange capacity (CEC), exchangeable bases, saturation degree, and pH, were found to be not correlated with the age of the surface. The macromorphological differentiation of the soils, their clay and Fe d contents, and especially, the clay and iron oxide accumulation indices, increased with the relative age of the surface. In contrast, the Fe o content and the Fe o:Fe d ratio diminished with the age of the surface. During the last few pedogenic episodes, soils were formed by strong leaching and acidification, but with very little chemical weathering. All of these features suggest that climatic shifts during the pedogenic episodes towards conditions less favourable to soil development, in addition to vegetation changes and disturbances on the soil surfaces, which started by periglacial processes, account for the soil evolution of the Sierra Nevada better than time as the only variable factor. The soils did not develop monotonically with time and the sequence of surfaces cannot be regarded in a strict sense as a chronosequence. The soils developed over a series of stepped pedogenic episodes; in each episode, especially in the oldest, the properties of the soils related to weathering could have approached or reached a steady state. Nevertheless, when these properties are plotted against time, a continued increase in soil development results.

Holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in Chilean Altiplano Lakes

Sediment cores from three shallow (<10 m), saline lakes along a transect of the northern Chilean Altiplano (18°S–27°S) document changes in moisture balance for the mid- to late Holocene. Stable isotopic compositions of ostracods and authigenic carbonate were measured to test whether high altitude (>4000 m a.s.l.) paleoclimatic profiles show coherency within tropical–subtropical circulation patterns. Climatic signals however are partially masked by local environmental systems. Results suggest similar arid mid-Holocene to less arid late Holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance. Isotopic signatures for each lake group in discrete δ 18O vs. δ 13C populations. High isotopic variability results from episodic flooding and brine evolution in the shallow lakes. Laguna Seca (18°11′S, 69°14′W, 4500 m a.s.l.) is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites. High δ 13C values are the result of continuous evasion of CO 2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake. A 3‰ decrease in δ 18O about −4.7 m suggests an abrupt shift to wetter conditions at the transition from mid- to late Holocene. Lagunas Miscanti (23°44′S, 67°46′W, 4140 m a.s.l.) and del Negro Francisco (27°28′S, 69°14′W, 4125 m a.s.l.) each contain only one ostracod species, Limnocythere sappaensis, attesting to higher salinities, although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at Laguna del Negro Francisco. Sediment cores from each lake document more arid conditions in the lower sections, with a sharp shift to wetter conditions in the upper sections. Highly variable isotope values at the transition from mid- to late Holocene suggest rapid, short-term climate shifts during this transition. This overall trend can be correlated from Laguna Seca, Laguna Miscanti and Laguna del Negro Francisco to Lago Titicaca implying climatic coherency along the Altiplano. Isotopic profiles show second order fluctuations and drought events that suggest short-term variability along the transect. In order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses. In the north, convective tropical precipitation dominates Laguna Seca, as for lakes in the Titicaca region. Effective moisture for Lagunas del Negro Francisco and Miscanti follows a south to north gradient generated by cold air masses from `cut offs' of Pacific Westerlies colliding with moist tropical air masses. Coherent shifts in the past therefore imply changes in available tropical air-mass moisture.

Postclassic Maya Communities at Progresso Lagoon and Laguna Seca, Northern Belize

Recent investigations of Post classic Period (A.c. 1050–1528) Maya communities along the Freshwater Creek drainage in northern Belize reveal important trends in the development organization, and economic activities of a political center and three smaller settlements. The Freshwater Creek drainage is likely to have formed an avenue of communication and transport that facilitated the economic integration of these settlements along this waterway. Research at these sites suggests that from A.C. 1050 to 1528, the NE Belize region was home to a number of small settlements and political centers that were actively engaged in local commodity production for local and more distant exchange with maritime traders operating along the Caribbean coast. Evidence of Colonial period Maya occupations along the shores of Freshwater Creek lagoons is also observed, suggesting that Postclassic sites continued to be occupied into the 17th century in this area. Preliminary analysis suggests that Colonial period local economy at these sites was substantially affected by Spanish efforts to subdue and control this region.

Postclassic Maya Communities at Progresso Lagoon and Laguna Seca, Northern Belize

Postclassic Maya Communities at Progresso Lagoon and Laguna Seca, Northern Belize

Three-year survival and growth of provenances of Pinus greggii in the tropics and subtropics

Eleven provenance/progeny tests of Pinus greggii Engelm. were assessed for survival and height at 3 years of age in Brazil, Colombia and South Africa. Trees of P. greggii from sources in northern Mexico (≈ 25°N latitude) were less than half as tall as trees from provenances in central Mexico (≈ 21°N latitude) when established in warm climates of Brazil and Colombia, (4.2 m vs. 1.6 m, respectively). The differences in height growth diminished between southern and northern sources in more temperate climates in South Africa (2.9 m vs. 2.1 m, respectively). External morphological differences in foliage were also pronounced between trees of the two regions when grown as an exotic. Trees from northern sources had shorter, stiffer, needles of darker green color than those from southern provenances. The most promising of the southern provenances across all sites were El Madroño (Queretaro) and Laguna Seca (Hidalgo). La Tapona (Nuevo Leon) and Los Lirios (Coahuila) performed well among the northern sources. Pinus greggii should be tested where low rainfall and cold are considered limiting factors for good growth of P. patula.