Biogeography of salt marsh plant zonation on the Pacific coast of South America

Aim

The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large‐scale variation in salt marsh plant community structure.

Location

A 2,000‐km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper‐arid at low to hyper‐humid at high latitudes.

Methods

Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large‐scale variation in salt marsh plant community structure.

Results

Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper‐arid and semi‐arid climates, but not in arid, humid and hyper‐humid climates. Latitudinal variation in low‐marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances.

Main conclusions

Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change.     

Parallel evolution of leaf pubescence in Encelia in coastal deserts of North and South America

Summary Members of the shrub genus Encelia occur in the arid coastal regions of western North America and South America along gradients of precipitation extending from less than 50 mm annually to somewhat over 350 mm. At moist ends of the gradient species possess glabrate, green leaves. Proceeding to drier regions, the species possess progressively more pubescent, whiter leaves. Leaf absorptance to solar radiation decreases with precipitation in an identical pattern along gradients in both North and South America.     

High-fidelity representation of climate variations by Amburana cearensis tree-ring chronologies across a tropical forest transition in South America

Numerous ring-width chronologies from different species have recently been developed in diverse tropical forests across South America. However, the temporal and spatial climate signals in these tropical chronologies is less well known. In this work, annual growth rings of Amburana cearensis, a widely distributed tropical tree species, were employed to estimate temporal and spatial patterns of climate variability in the transition from the dry Chiquitano (16–17°S) to the humid Guarayos-southern Amazon (14–15°S) forests. Four well-replicated chronologies (16–21 trees, 22–28 radii) of A. cearensis were compared with temperature and precipitation records available in the region. The interannual variations in all four A. cearensis tree-ring chronologies are positively correlated with precipitation and negatively with temperature during the late dry-early wet season, the classic moisture response seen widely in trees from dry tropical and temperate forests worldwide. However, the chronologies from the dry Chiquitano forests of southern Bolivia reflect the regional reduction in precipitation during recent decades, while the chronologies from the tropical lowland moist forests in the north capture the recent increase in precipitation in the southern Amazon basin. These results indicate that A. cearensis tree growth is not only sensitive to the moisture balance of the growing season, it can also record subtle differences in regional precipitation trends across the dry to humid forest transition. Comparisons with previously developed Centrolobium microchaete chronologies in the region reveal a substantial common signal between chronologies in similar environments, suggesting that regional differences in climate are a major drivers of tree growth along the precipitation gradient. The difficulty of finding A. cearensis trees over 150-years old is the main limitation involved in the paleoclimate application of this species. The expansion of monocultures and intensive cattle ranching in the South American tropics are contributing to the loss of these old growth A. cearensis trees and the valuable records of climate variability and climate change that they contain.     

A populational survey of amino acids in Prosopis species from North and South America

Leaf extracts of 540 plants representing 24 species of the genus Prosopis from North and South America were analyzed by 2-D PC and high voltage electrophoresis for their protein and non-protein amino acids. In addition to the presence of the usual protein amino acids, most of the species examined contained high concentrations of the non-protein amino acids, pipecolic acid, 4-hydroxypipecolic acid and proline.     

Recent growth increase in endemic Juglans boliviana from the tropical Andes

The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.     

Climatic signals in growth and its relation to ENSO events of two Prosopis species following a latitudinal gradient in South America

Semiarid environments throughout the world have lost a major part of their woody vegetation and biodiversity due to the effects of wood cutting, cattle grazing and subsistence agriculture. The resulting state is typically used for cattle production, but the productivity of these systems is often very low, and erosion of the unprotected soil is a common problem. Such dry‐land degradation is of great international concern, not only because the resulting state is hardly productive but also because it paves the way to desertification. The natural distribution of the genus Prosopis includes arid and semiarid zones of the Americas, Africa and Asia, but the majority of the Prosopis species are, however, native to the Americas. In order to assess a likely gradient in the response of tree species to precipitation, temperature and their connection to El Niño southern oscillation (ENSO) events, two Prosopis species were chosen along a latitudinal gradient in Latin America, from northern Peru to central Chile: Prosopis pallida from a semi‐arid land in northern and southern Peru and P. chilensis from a semiarid land in central Chile. Growth rings of each species were crossdated at each sampling site using classical dendrochronological techniques. Chronologies were related with instrumental climatic records in each site, as well as with SOI and N34 series. Cross‐correlation, spectral and wavelet analysis techniques were used to assess the relation of growth with precipitation and temperature. Despite the long distance among sites, the two Prosopis species presented similar responses. Thus, the two species' growth is positively correlated to precipitation, while with temperature it is not. In northern Peru, precipitation and growth of P. pallida present a similar cyclic pattern, with a period of around 3 years. On the other hand, P. pallida in southern Peru, and P. chilensis also present this cyclic pattern, but also another one with lower frequency, coinciding with the pattern of precipitation. Both cycles are within the range of the ENSO band.     

Records and Stratigraphical Ranges of South American Tayassuidae (Mammalia, Artiodactyla)

Tayassuidae represent one of the first mammalian immigrants that entered South America during the “Great American Biotic Interchange.” However, the exact moment of its arrival for the first time in South America is controversial. Three genera are recognized in South America: Platygonus, Catagonus, and Tayassu. This paper aims to: (1) review the paleontological record of the South American Tayassuidae and update it; and (2) discuss its geographical and statigraphical distribution pattern in South America. The genus Platygonus (middle Pliocene to early Pleistocene) is registered in Argentina, Uruguay, Colombia, and Bolivia; Catagonus (late Pliocene? to Recent) in Argentina, Uruguay, Brazil, and Bolivia; and Tayassu (middle Pleistocene to Recent) in Argentina, Uruguay, and Brazil. Platygonus and Catagonus have adaptations to dry and relatively open environments; in contrast, Tayassu is adapted mainly to humid climates and woodland and forest environments. The faunal changes that took place since the middle-late Pliocene could have been strongly influenced by climate. Open and arid environments developed during the glacial cycles, allowing the latitudinal expansion of Platygonus and Catagonus. Considering ecological and anatomical information, it is possible to infer that Platygonus species were replaced by those of Catagonus since the middle Pleistocene, probably due to a reduction of the open environments to which Platygonus species were better adapted. The alternation of these mainly arid or semiarid, cold conditions with warmer and more humid short pulses would have allowed the posterior expansion of Tayassu species. According to phylogenetic analysis and chronological as well as geographical evidence, Platygonus and Catagonus represent two Tayassuidae lineages that originated in North America and then migrated to South America. This migration would have occurred on more than one occasion and with different taxa. Evidence indicates that Tayassu represents a lineage that differentiated in the Southern Hemisphere and then migrated to North America.     

Tree-ring isotopes from Araucaria araucana as useful proxies for climate reconstructions

Tree-ring width (TRW) chronologies have been widely and long-time used to reconstruct past climate variations in the Andes in South America. The use of tree-ring isotopic chronologies is still not widespread in this region although they have proved to be very efficient climate proxies. Araucaria araucana (Molina) K. Koch is a conifer tree species with some multi-century-old individuals that offers an excellent opportunity to measure stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in cellulose from long tree-ring records. Here, we explore whether current or stored carbohydrates are used for A. araucana radial growth and we assess the potential of a tree-ring isotopic record of to study past climate variability. Eleven A. araucana cores from a dry and high-elevation forest at the northern border of Patagonia, Argentina (38°55’S, 70°44’W) were selected for stable isotopes analyses. The strong correlation between the isotopic composition of the first and second parts of the same ring, but also the strong relationships between δ¹³C and δ¹⁸O records with climate parameters of the current growing season such as temperature, show that tree-rings are built mostly with carbohydrates produced during the current growing season with little or no supply from storage or reserves. This finding leads to reconsidering the interpretation of the legacy effect (i.e. ecological memory effects) based on the previously described strong negative correlation between A. araucana TRW chronologies and previous growing season temperature and suggests a dependence of radial tree growth on the level of development of organs. Regarding climate sensitivity, the A. araucana tree-ring δ¹³C chronology is strongly related to current summer temperature (r = 0.82, p < 0.001), vapour pressure deficit (VPD; r = 0.79, p < 0.001), precipitation (r = −0.53, p < 0.001) and SPEI2 (r = −0.73, p < 0.001). These strong relationships support the use of δ¹³C of A. araucana tree-ring cellulose to reconstruct past temperature variations at regional scale in relation with large-atmospheric drivers of climate variability such as the Southern Annular Mode. The A. araucana tree-ring δ¹⁸O chronology is also correlated with temperature (r = 0.42, p < 0.01) and VPD (r = 0.45, p < 0.01) of the winter preceding the growing season. This suggests that trees are using water from precipitation infiltrated in the soil during the previous recharge period (autumn-winter). The weak correlations of δ¹⁸O with current summer atmospheric conditions and the decoupling between δ¹⁸O and δ¹³C, may be due to a high rate of oxygen exchange between sugars and xylem water (P_ex) during cellulose synthesis, which dampens evaporative isotopic fractionation.     

The influence of the de Vries (∼ 200-year) solar cycle on climate variations: Results from the Central Asian Mountains and their global link

Long-term climatic changes related to solar forcing were examined using millennium-scale palaeoclimatic reconstructions from the Central Asian mountain region, i.e. summer temperature records for the Tien Shan mountains and precipitation records for the Tibetan Plateau. The reconstructions were based on juniper tree-ring width records, i.e. Juniperus turkestanica for the Tien Shan and Sabina przewalskii for the Tibetan Plateau. The data were processed using spectral and wavelet analysis and filtered in the frequency range related to major solar activity periodicities. The results obtained for various tree-ring chronologies indicate palaeoclimatic oscillations in the range of the de Vries (～ 210-year) solar cycles through the last millennium.The quasi-200-year variations revealed in the palaeoclimatic reconstructions correlate well (R² = 0.58–0.94) with solar activity variations (Δ¹⁴C variations). The quasi-200-year climatic variations have also been detected in climate-linked processes in Asia, Europe, North and South America, Australia, and the Arctic and Antarctica. The results obtained point to a pronounced influence of solar activity on global climatic processes.Analysis has shown that climate response to the long-term global solar forcing has a regional character. An appreciable delay in the climate response to the solar signal can occur (up to 150 years). In addition, the sign of the climate response can differ from the solar signal sign. The climate response to long-term solar activity variations (from 10s to 1000s years) manifests itself in different climatic parameters, such as temperature, precipitation and atmospheric and oceanic circulation. The climate response to the de Vries cycle has been found to occur not only during the last millennia but also in earlier epochs, up to hundreds of millions years ago.     

Dendroclimatological assessment of Polylepis rodolfo-vasquezii: A novel Polylepis species in the Peru highlands

In spite of enormous diversity in tree species, dendrochronological records in the tropical Andes are very scarce. Therefore, it is necessary to increase the search for new tree species with high dendrochronological characteristics in the tropical Andes, including the humid Puna of Peru. We present the first tree-ring chronology from Polylepis rodolfo-vasquezii, a recently described tree species in the Central Andes of Peru between 4000 and 4400 m elevation. Fifty trees were sampled in the district of Comas, Peru. After establishing the anatomical characteristics that delimit the annual growth rings, we developed a ring-width chronology by applying conventional dendrochronological techniques. The chronology covers the period 1869–2015 (157 years) and is well replicated from 1920 to present (> 20 samples). The statistics used to evaluate the quality of the chronology indicate that the P. rodolfo-vasquezii has similar values of MS, RBAR and EPS to those shown by other Polylepis spp chronologies. To determine the main climatic factors controlling the growth of P. rodolfo-vasquezii, we compared our chronology with local and regional temperature and precipitation records. Growth season temperature (November to May) seems to be the main climatic factor modulating inter-annual variations in the growth of this species. The sensitivity to inter-annual temperature variations highlights the potential of P. rodolfo-vasquezii to provide climatically sensitive dendrochronological records in the Central Andes. To our knowledge, this is the first tree-ring record in South America displaying significant relationships with temperature over the tropical Atlantic Ocean.     

Leaf Size and Leaf Area Index in <Emphasis Type="Italic">Fagus sylvatica</Emphasis> Forests: Competing Effects of Precipitation,Temperature, and Nitrogen Availability

Plants across diverse biomes tend to produce smaller leaves and a reduced total leaf area when exposed to drought. For mature trees of a single species, however, the leaf area–water supply relationship is not well understood. We tested the paradigm of leaf area reduction upon drought by a transect study with 14 mature Fagus sylvatica forests along a steep precipitation gradient (970–520 mm y⁻¹) by applying two independent methods of leaf size determination. Contrary to expectation, average leaf size in dry stands (520–550 mm y⁻¹) was about 40% larger and SLA was higher than in moist stands (910–970 mm y⁻¹). As a result of increased leaf sizes, leaf area index significantly increased from the high- to the low-precipitation stands. Multiple regression analyses suggested that average leaf size was primarily controlled by temperature, whereas the influence of soil moisture and soil C/N ratio was low. Summer rainfall of the preceding year was the most significant predictor of total leaf number. We assume that leaf expansion of beech was independent of water supply, because it takes place in May with ample soil water reserves along the entire transect. In contrast, bud formation, which determines total leaf number, occurs in mid-summer, when droughts are severest. We conclude that leaf expansion and stand leaf area of beech along this precipitation gradient are not a simple function of water availability, but are controlled by several abiotic factors including spring temperature and possibly also nitrogen supply, which both tend to increase toward drier sites, thus overlaying any negative effect of water shortage on leaf development.     

The Role of Surface and Subsurface Processes in Keeping Pace with Sea Level Rise in Intertidal Wetlands of Moreton Bay,Queensland, Australia

Increases in the elevation of the soil surfaces of mangroves and salt marshes are key to the maintenance of these habitats with accelerating sea level rise. Understanding the processes that give rise to increases in soil surface elevation provides science for management of landscapes for sustainable coastal wetlands. Here, we tested whether the soil surface elevation of mangroves and salt marshes in Moreton Bay is keeping up with local rates of sea level rise (2.358 mm y⁻¹) and whether accretion on the soil surface was the most important process for keeping up with sea level rise. We found variability in surface elevation gains, with sandy areas in the eastern bay having the highest surface elevation gains in both mangrove and salt marsh (5.9 and 1.9 mm y⁻¹) whereas in the muddier western bay rates of surface elevation gain were lower (1.4 and −0.3 mm y⁻¹ in mangrove and salt marsh, respectively). Both sides of the bay had similar rates of surface accretion (~7–9 mm y⁻¹ in the mangrove and 1–3 mm y⁻¹ in the salt marsh), but mangrove soils in the western bay were subsiding at a rate of approximately 8 mm y⁻¹, possibly due to compaction of organic sediments. Over the study surface elevation increments were sensitive to position in the intertidal zone (higher when lower in the intertidal) and also to variation in mean sea level (higher at high sea level). Although surface accretion was the most important process for keeping up with sea level rise in the eastern bay, subsidence largely negated gains made through surface accretion in the western bay indicating a high vulnerability to sea level rise in these forests.     

A lonely dot on the map: Exploring the climate signal in tree-ring density and stable isotopes of clanwilliam cedar,South Africa

Clanwilliam cedar (Widdringtonia cedarbergensis; WICE), a long-lived conifer with distinct tree rings in Cape Province, South Africa, has potential to provide a unique high-resolution climate proxy for southern Africa. However, the climate signal in WICE tree-ring width (TRW) is weak and the dendroclimatic potential of other WICE tree-ring parameters therefore needs to be explored. Here, we investigate the climatic signal in various tree-ring parameters, including TRW, Minimum Density (MND), Maximum Latewood Density (MXD), Maximum Latewood Blue Intensity (MXBI), and stable carbon and oxygen isotopes (δ¹⁸O and δ¹³C) measured in WICE samples collected in 1978. MND was negatively influenced by early spring (October-November) precipitation whereas TRW was positively influenced by spring November-December precipitation. MXD was negatively influenced by autumn (April-May) temperature whereas MXBI was not influenced by temperature. Both MXD and MXBI were negatively influenced by January-March and January-May precipitation respectively. We did not find a significant climate signal in either of the stable isotope time series, which were measured on a limited number of samples. WICE can live to be at least 356 years old and the current TRW chronology extends back to 1564 CE. The development of full-length chronologies of alternative tree-ring parameters, particularly MND, would allow for an annually resolved, multi-century spring precipitation reconstruction for this region in southern Africa, where vulnerability to future climate change is high.     

Species tree phylogeny,character evolution,and biogeography of the Patagonian genus <Emphasis Type="Italic">Anarthrophyllum</Emphasis> Benth. (Fabaceae)

Geologic events promoting the aridization of southern South America contributed to lineage divergences and species differentiation through geographic (allopatric divergence) and biotic and abiotic factors (ecological divergence). For the genus Anarthrophyllum, which is distributed in arid and semi-arid regions of Patagonia, we assessed how these factors affected species diversification and reconstructed its possible biogeographic history in South American arid environments. Sequences were obtained from two molecular markers: the ITS nuclear region and the trnS-trnG plastid region. Using Parsimony, Maximum likelihood and Bayesian inference individual gene trees were reconstructed, and a species tree was obtained using multi-species coalescent analysis. Divergence times among species were estimated using secondary calibrations. Flexible Bayesian models and stochastic character mapping were used to elucidate ancestral geographic distributions and the evolution of the floral and vegetative phenotypes in the genus. Gene trees and species tree analyses strongly support Anarthrophyllum as monophyletic; all analyses consistently retrieved three well-supported main clades: High Andean Clade, Patagonian Clade 1, and Patagonian Clade 2. Main diversification events occurred concomitant with the Andean uplift and steppe aridization; the Andean mountain range possibly acted as a species barrier for the High Andean Clade. Vegetative traits showed adaptations to harsh climates in some clades, while pollinator-related floral features were associated with independent diversification in bee- and bird-pollinated clades within both Patagonian Clades. In conclusion, evolutionary and biogeographic history of Anarthrophyllum resulted from the action of ecological, historical, and geographic factors that acted either alternatively or simultaneously.     

Potential of Schinopsis lorentzii for dendrochronological studies in subtropical dry Chaco forests of South America

The lack of knowledge about species with well-delimited annual rings has hampered the development of dendrochronological records in the subtropical Chaco region of South America. In this contribution, we present the first tree-ring chronology of Schinopsis lorentzii (Anacardiaceae), a dominant species in the semi-arid Chaco. Cross sections were collected near Las Lajitas, Salta, Argentina, and processed following the methods commonly used in dendrochronology. Annual growth variations between radii from a single individual and between radii from different trees were highly correlated. To determine the climatic parameters that control radial growth, we compared annual tree-ring variations against regional temperature and precipitation records. Correlation functions indicate that tree growth is highly influenced by spring–summer rainfall variations, which represent more than 80% of the total annual precipitation. The chronology, which covers the interval from 1829 to 2004, provides a context for the unprecedented increase in precipitation since the mid-1970s in the region. The climatic-sensitivity of S. lorentzii provides a unique opportunity to reconstruct precipitation variations during past centuries in the extensive semiarid regions of subtropical South America.     

Evolutionary importance of the relationship between cytogeography and climate: New insights on creosote bushes from North and South America

Relationships between genome size and environmental variables suggest that DNA content might be adaptive and of evolutionary importance in plants. The genus Larrea provides an interesting system to test this hypothesis, since it shows both intra- and interspecific variation in genome size. Larrea has an amphitropical distribution in North and South American deserts, where it is most speciose. Larrea tridentata in North America shows a gradient of increasing autopolyploidy; while three of the four studied South American species are diploids, Larrea divaricata, Larrea nitida, Larrea ameghinoi, and the fourth is an allopolyploid, Larrea cuneifolia. We downloaded available focal species’ georeferenced records from seven data reservoirs. We used these records to extract biologically relevant environmental variables from WorldClim at 30 arc seconds scale, to have a broad characterization of the variable climatic conditions of both regions, and a climatic envelope for each species. We estimated relative DNA content index and relative monoploid genome values, by flow cytometry, of four most abundant Larrea species throughout their respective ranges. Then we winnow the bioclimatic dataset down to uncorrelated variables and sampled locales, to analyse the degree of association between both intra- and interspecific relative DNA content and climatic variables that are functionally relevant in arid environments using Pearson correlations, general linear and mixed effects models. Within the genus Larrea, relative DNA content increases with rising temperature and decreases with rising precipitation. At the intraspecific level, all four species show relative DNA content variation across climatic conditions. Larrea is a genus that shows genome size variation correlated with climate. Our results are also consistent with the hypothesis that extreme environmental pressures may have facilitated repeated whole genome duplication events in North America, while in South America, reticulate evolution, as allopolyploidization, and speciation might have been climate-dependent since the Oligocene.     

Mummified fossil of Keteleeria from the Late Pleistocene of Maoming Basin,South China,and its phytogeographical and paleoecological implications

Keteleeria is a small genus of Pinaceae now mainly restricted to eastern Asia. Although this genus has been documented with a wide distribution in the geologic record of Europe, North America, and Asia, its history in low‐latitude areas (including South China) has remained obscure. In this paper, a fossil wood of Keteleeria sp. is described from the Late Pleistocene (29–27 ka BP) of the Maoming Basin, South China. This wood is the most ancient megafossil evidence of Keteleeria within the modern distribution area of this genus. The fossil records of Keteleeria suggests that this thermophyllous genus migrated into South China by the Middle Pleistocene escaping from glacial cooling and became widespread over this region in the Late Pleistocene beginning from the interglacial stage preceding the Last Glacial Maximum. The analysis of growth rings in the fossil wood and its comparison with those of modern Keteleeria davidiana (Bertrand) Beissner indicates that in the Late Pleistocene of Maoming Basin (29–27 ka BP) there was a humid climate with less pronounced seasonality of precipitation than that seen in the subtropical monsoonal climate of modern northeastern Vietnam. Apparently, the Maoming Basin was influenced by interglacial regime with summer–monsoon circulation. The previously proposed method to distinguish between evergreen and deciduous conifers based on growth ring anatomy, is not reliable because of the wide variance and ambiguity in its results.     

Afforestation of Tropical Pasture Only Marginally Affects Ecosystem-Scale Evapotranspiration

Evapotranspiration (ET) from tropical ecosystems is a major constituent of the global land–atmosphere water flux and strongly influences the global hydrological cycle. Most previous studies of ecosystem ET have been conducted predominantly in tropical forests, and only few observations cover other tropical land-use types such as pastures, croplands, savannas or plantations. The objectives of our study were: (1) to estimate daily, monthly, and annual ET budgets in a tropical pasture and an adjacent afforestation site, (2) to assess diurnal and seasonal patterns of ET, (3) to investigate environmental controls of ET, and (4) to evaluate the soil infiltration potential. We performed eddy covariance measurements of ecosystem ET in Sardinilla (Panama) from 2007 to 2009. Daily ET (2.6 ± 1.0 mm day⁻¹) was significantly lower in the pasture compared to the afforestation site (3.0 ± 0.9 mm day⁻¹). The highest ET was observed during the wet–dry transition period in both ecosystems. However, differences in daily ET between sites were relatively small, particularly during the wet season. Radiation was the main environmental control of ET at both sites, however, we observed considerable seasonal variation in the strength of this control, which was stronger during the wet compared to the dry season. In 2008, total annual ET was only slightly higher for the afforestation (1114 mm y⁻¹) than the pasture site (1034 mm y⁻¹). Our results suggest that afforestation of pasture only marginally increases ecosystem-scale ET 6–8 years after establishment. Differences in soil infiltration potentials between our sites seem to explain this pattern.     

Argentinean native wood species: Physical and mechanical characterization of some Prosopis species and Acacia aroma (Leguminosae; Mimosoideae)

One of the problems in marketing the wood of Prosopis and Acacia is the lack of standardization of its qualities. The aim of this paper was to obtain a preliminary detection of some properties of the wood of four species of the genus Prosopis and one species from Acacia grown in Argentina. To accomplish this objective, the content of extractives and some physical and mechanical characteristics were analyzed.The density ρ₁₂ of all the species indicates that these woods range from heavy to very heavy (?0.69 g/cm³). The total volumetric shrinkage values are low, less than 10%, for all species. The parallel compression strength and the shear strength for all the species indicate a very resistant wood (?46.93 MPa and ?18.35 MPa, respectively). Brinell hardness was higher than 5 kg/mm² in all cases. The species with less content of extractives is P. ruscifolia (approximately 9% of anhydrous mass) whereas A. aroma was the one with the greatest content (approximately 25% of anhydrous mass in the heartwood).