Phenological and growth responses of Papaver radicatum along altitudinal gradients in the Canadian High Arctic

Phenology and growth of Papaver radicatum Rottb. was monitored over four summers (1990–1993) at 12 sites, along a dolomitic and a granitic altitudinal gradient (330 m a.s.l.–770 m a.s.l.) at Sverdrup Pass, central Ellesmere Island, Canada. The gradients provided substantial differences in environmental characteristics. Three of the four seasons (1990, 1991 and 1993) had more than 400 thawing degree-days (TDD) in the valley, while the 1992 season had less than 300. The granitic sites had consistently higher temperatures than the dolomitic sites, despite their northerly aspect. Increasing elevation reduced total degree-day accumulation ( c . 40 degree-days/100 m) and length of potential growing season. The proportion of the population producing flower buds was similar at all sites in any given year, but there were differences among years. Production of flowers and fruits per site, decreased with altitude along the dolomitic gradient in 1991 and 1992. There was no difference in the number of buds or flowers produced per plant with increasing altitude, although larger plants with multiple flowers were found only on low elevation granitic sites. Plants from the dolomitic sites were smaller and flowered, on average, after the site accumulated 150 degree-days, while plants on the granitic sites were larger and bloomed after 200 degree-days. Papaver is able to grow and reproduce over a wide range of environmental conditions and moderate climate warming would likely promote its growth and establishment, unless other factors, especially snow-free periods and water availability, become limiting.     

Some effects of giant Andean stem-rosettes on ground microclimate,and their ecological significance

The effect of giant Andean stem-rosettes (Coespeletia lutescens) on air and soil temperatures was studied in the Páramo de Piedras Blancas (Venezuela) at 4265 and 4385 m altitude during the dry season, which is the coldest season in this tropical mountain area. Maximum air temperatures beneath a plant canopy were only slightly higher than in the open. Minimum temperatures below the stem-rosettes were 4.7° to 7.0°C higher than in the open. This substantially reduced the intensity of nightly freezing. Soil temperature minima at 20 cm depth were 2.4° to 4.2°C higher below plants, but maxima were somewhat lower than in bare soil. These microclimatic alterations are ecologically significant for stemprosette seedlings, which should have a higher probability of survival due to the reduced frequency of frost and needle ice formation below large plants. Warmer soils at night should also result in greater water uptake by seedlings during the early morning hours, thus reducing dry-season mortality.     

Diversity of zonal páramo plant communities in Ecuador

Patterns of vascular plant species diversity in high‐altitude Ecuadorian ecosystems (‘páramos’) are examined. Data from two independent surveys were used: the first from 12 different locations and 192 samples, the other from 18 locations and 243 samples. These surveys included 348 and 284 species, respectively. The data confirmed the occurrence of two main zones in terms of vascular plant species diversity. The grass páramo and superpáramo were distinguished by differences in plant cover, species richness, α‐diversity and β‐diversity. The transition between these two zones begins at around 4000 m. Grass páramo samples comprised more species but the strong dominance of tussock grasses resulted in low equitability compared with the superpáramo, where safe sites for plant survival are limited and the environment does not permit continuous grass cover. Turnover of species across the altitudinal gradient is higher in the grass páramo than in the superpáramo. This is due largely to agricultural fires at lower altitudes, which create a fine‐scale mosaic of burned patches that enhances variability at this scale. Despite the loss of equitability, intermediate levels of fire disturbance appear to promote species richness within the samples. It is suggested that the complex patterns of páramo diversity in the Ecuadorian Andes are largely the outcome of three interrelated factors: altitude, disturbance and the availability of safe sites at the highest altitudes.     

Water relations and gas exchange in Coespeletia moritziana (Sch. Bip) Cuatrec., a giant rosette species of the high tropical Andes

Giant rosettes are ones of the most striking features of the vegetation in the high tropical Andes, with Coespeletia moritziana reaching the highest altitudes up to 4,600 m a.s.l. Different from other giant rosettes, this species grows on rock outcrops with poorly developed soils and where water availability may be limited. Two questions are addressed in this study: How does this species respond in terms of water relations to maintain favorable gas-exchange conditions? Considering that adult plants rely on a water-reserving central pith, how do early stages respond to this environment??s extreme conditions? Water relations and gas-exchange studies were carried out on juveniles, intermediate and adult C. moritziana plants during wet and dry seasons in Páramo de Piedras Blancas at 4,200 m a.s.l. Adult plants maintained higher leaf water potentials (??_L) during the wet season, however, no differences between stages were found for the dry season. Minimum dry season ??_L were never near the turgor loss point in any of the stages. Juveniles show a more strict stomatal control during the dry season to maintain a favorable water status. Net photosynthesis significantly decreased in intermediate and juvenile stages from wet to dry seasons. Our results suggest that C. moritziana resists more extreme conditions compared to other Andean giant rosettes     

Searching for Altitudinal Zonation: Species Distribution and Vegetation Composition in the Superpáramo of Volcán Iliniza, Ecuador

Altitudinal variation of the zonal superpáramo vegetation was studied between 4300 and 4630 m to test a possible occurrence of a fine altitudinal zonation within the superpáramo belt. A rectangular grid of 1 m² sample plots was established; 25 replicate plots separated by a 3 m space were located along a 100 m long transect parallel to the contours, and there were 17 such transects separated by 20 m of altitude. Species were scored using a 7-grade cover scale and basic environmental data were gathered for each sample. Major changes occur over a short altitudinal range, at around 4400 m, which corresponds to a transition between the lower and upper superpáramo. Species richness sharply declines but species turnover (per altitude) increases along the altitudinal gradient. The correlation between richness and bare ground or rock cover is negative, but the correlation to rocks becomes positive above 4500 m. Species from lower altitudes tend to have narrower altitudinal range, although a large number of species appear to be indifferent to altitude. Direct ordination analyses indicate that high-altitude species show stronger correlation to environmental variables, especially rock, than species from lower altitudes. TWINSPAN cluster analysis delimited 15 groups of samples. There is a change in the clustering pattern along the altitudinal gradient from a horizontal (i.e., within altitude) to vertical (i.e., across altitude) arrangement of the cluster groups, although this pattern is partly obscured at the highest altitudes due to a large number of empty samples. MANOVA tests for samples from adjacent altitudinal levels indicate two distinct altitudinal breaks at lower altitudes, corresponding to the Loricaria-belt in lower superpáramo and the transition between lower and upper superpáramo, while no indication of a zonation was found in upper superpáramo.     

Climate sensitivity of purple cone spruce (Picea purpurea) across an altitudinal gradient on the eastern Tibetan Plateau

Picea purpurea (Purple cone spruce) is a dominant and widely distributed tree species in the subalpine area of the Wanglang Nature Reserve. We investigated variations in radial growth and its response to climate in P. purpurea along an altitudinal gradient. In this study, P. purpurea chronologies were developed from three altitudinal sites ranging from 2850 to 3250 m above sea level. Correlation analysis and principal component analysis were used for all the chronologies to detect the growth patterns at different altitudes. Correlation analysis was used to assess the relationships between chronologies and climatic factors. Tree-ring widths among the three elevations were all positively correlated with June maximum temperature in the current year. Radial growth at the higher altitude was more sensitive to temperature than those of the two lower altitudes. Ring-widths at the low and middle sites were mainly negatively affected by temperatures in the previous growing season (June and August). Spruce growth at the upper site was strongly positively affected by temperatures in the previous winter, the current spring and current growing season. Climatological analysis revealed that elevation-dependent and elevation-independent signals were present in this semi-humid subalpine area. Precipitation was not the main factor affecting the tree growth in the growing season throughout the study area. The noteworthy findings were that the lag effects of temperatures to spruce growth was more significant at the low and middle altitude sites, and spruce growth at the high altitude site clearly benefited from the warmer climate before and during the growing season. This study will provide a basis for better predicting forest dynamics and carrying out vegetation restoration in the future.     

<Emphasis Type="Italic">Hypericum</Emphasis> species in the Páramos of Central and South America: a special focus upon <Emphasis Type="Italic">H. irazuense</Emphasis> Kuntze ex N. Robson

Knowledge about members of the flowering plant family Clusiaceae occurring in the tropical mountain regions of the world is limited, in part due to endemism and restricted distributions. High altitude vegetation habitats (Páramos) in Central and South America are home to numerous native Hypericum species. Information related to the phytochemistry of páramo Hypericum, as well as ecological factors with the potential to influence chemical defenses in these plants, is briefly reviewed. Results of the phytochemical analysis of Hypericum irazuense, a species collected in the páramo of the Cordillera de Talamanca in Costa Rica, are presented. Lastly, guidelines for the viable and sustainable collections of plant material, to facilitate future investigations of these interesting plants, are given.     

Low temperature resistance in saplings and ramets of Polylepis sericea in the Venezuelan Andes

The frequent occurrence of all year-round below zero temperatures in tropical high mountains constitutes a most stressful climatic factor that plants have to confront. Polylepis forests are found well above the continuous forest line and are distributed throughout the Andean range. These trees require particular traits to overcome functional limitations imposed on them at such altitudes. Considering seedling and sapling stages as filter phases in stressful environments, some functional aspects of the regeneration of Polylepis sericea, a species associated to rock outcrops in the Venezuelan Andes, were studied. We characterized microclimatic conditions within a forest, in a forest gap and surrounding open páramo and determined low temperature resistance mechanisms in seedlings, saplings and ramets. Conditions in the forest understory were more stable compared to the forest gaps and open surrounding páramo. Minimum temperatures close to the ground were 3.6 °C lower in the open páramo compared to the forest understory. Maximum temperatures were 9.0 °C higher in the open páramo. Ice nucleation and injury temperatures occurred between ?6 and ?8 °C for both ramets and saplings, an evidence of frost avoidance to low nighttime temperatures. In this particular forest, this resistance ability is determinant in their island-like distribution in very specific less severe temperature habitats.     

Factors Controlling Compositional Changes in a Northern Andean Páramo (La Rusia,Colombia)

In this study, we aimed to assess the processes controlling compositional change in a Northern Andean páramo highly affected by human‐induced disturbances over the last few decades (La Rusia, Colombia). Along the 3000–3800 m asl altitudinal range, we randomly sampled fifty 10 × 10 m plots. Therein, we measured altitude and variables related to soil conditions (i.e., moisture, nutrient contents, bulk density, and texture), occurrence of human‐induced disturbances (i.e., fire, vegetation clearing, potato cultivation, and cattle grazing), and land‐use history. We also recorded richness and abundance of plant species, identifying them as exotic or native. We differentiated four groups of plots according to their species composition. The groups had significant differences in altitude, soil conditions, land‐use history, and particularly, in richness of exotic species and exotic/native cover ratio. They could be ascribed to shrub‐ and grass‐páramo vegetation types based on their relative dominance of woody and herbaceous species; however, these groups were not arranged according to the hypothetical composition of altitudinal belts, but rather formed a mosaic of patches. This mosaic was determined not only by altitude but also by soil conditions and disturbance history of sites. Our results corroborate recent findings which highlight shrub‐ and grass‐páramo vegetation types as patches of contrasting species composition and structure that depend on local environmental variables, as well as human‐induced disturbances as a major determinant of compositional discontinuities in these ‘high mountain’ tropical ecosystems.     

Long‐term limnological changes in the Ecuadorian páramo: Comparing the ecological responses to climate warming of shallow waterbodies versus deep lakes

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Does plant height determine the freezing resistance in the páramo plants?

Neotropical ecosystems between treeline and snowline, called páramos, stretch along Andean ranges from Costa Rica to northern Peru. The páramo climate is characterized by regular night frosts occurring throughout the year. Páramo plants use two strategies to deal with freezing temperatures. They either avoid ice formation in the tissues or tolerate extracellular ice formation. We tested the microclimate hypothesis, which suggests that the freezing resistance of the páramo plants is determined by plant height, that is, that taller plants experience a milder microclimate and avoid freezing, whereas smaller plants are exposed to the more extreme thermal conditions near the ground and tolerate them. We measured the temperature at which ice formed inside the plants (the ‘exotherm’), and compared it with the temperature at which 50% damage to the tissue occurred (Lt50); a significant difference between the exotherm and Lt50 would indicate freezing tolerance whereas the absence of a difference would indicate avoidance by supercooling. We analysed the freezing resistance of 38 common Ecuadorian páramo species. We found no correlation between plant height and freezing resistance mechanism or injury temperature and reject the microclimate hypothesis. Tolerant plants reach higher altitudes than avoidant plants, but their altitudinal ranges largely overlap and the Lt50 does not differ between them. These results suggest that there is no qualitative difference between the two strategies to survive the páramo frosts. Shrub leaves were injured at significantly lower temperatures than other life forms, such as herbs, which may reflect leaf anatomical differences among the plants.     

Latitudinal and altitudinal patterns of plant community diversity on mountain summits across the tropical Andes

The high tropical Andes host one of the richest alpine floras of the world, with exceptionally high levels of endemism and turnover rates. Yet, little is known about the patterns and processes that structure altitudinal and latitudinal variation in plant community diversity. Herein we present the first continental‐scale comparative study of plant community diversity on summits of the tropical Andes. Data were obtained from 792 permanent vegetation plots (1 m²) within 50 summits, distributed along a 4200 km transect; summit elevations ranged between 3220 and 5498 m a.s.l. We analyzed the plant community data to assess: 1) differences in species abundance patterns in summits across the region, 2) the role of geographic distance in explaining floristic similarity and 3) the importance of altitudinal and latitudinal environmental gradients in explaining plant community composition and richness. On the basis of species abundance patterns, our summit communities were separated into two major groups: Puna and Páramo. Floristic similarity declined with increasing geographic distance between study‐sites, the correlation being stronger in the more insular Páramo than in the Puna (corresponding to higher species turnover rates within the Páramo). Ordination analysis (CCA) showed that precipitation, maximum temperature and rock cover were the strongest predictors of community similarity across all summits. Generalized linear model (GLM) quasi‐Poisson regression indicated that across all summits species richness increased with maximum air temperature and above‐ground necromass and decreased on summits where scree was the dominant substrate. Our results point to different environmental variables as key factors for explaining vertical and latitudinal species turnover and species richness patterns on high Andean summits, offering a powerful tool to detect contrasting latitudinal and altitudinal effects of climate change across the tropical Andes.     

Nucleotide polymorphisms related to altitude and physiological traits in contrasting provenances of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>)

Variation of sequences of six EST-derived markers was investigated in three Norway spruce (Picea abies [L.] Karst.) provenances originating from different altitudes growing at two contrasting trial plots in Slovakia (Veľky Lom 450 m a.s.l., Mútne-Zákamenné 1,250 m a.s.l.) within a spin-off experiment of the IUFRO 1964/68 Inventory Provenance Experiment with Norway spruce. Single nucleotide polymorphisms (SNP) were identified and differences in allele frequencies at polymorphic sites were tested against altitude or associated with physiological and growth traits (chlorophyll a fluorescence, frost resistance, height, diameter, budburst phenology).     

Brazilian Páramos II. Macro- and mesoclimate of the campos de altitude and affinities with high mountain climates of the tropical Andes and Costa Rica

Aim This paper presents a basic analysis of the macro- and mesoclimate of the Brazilian campos de altitude, a series of cool–humid, mountaintop grasslands in southeastern Brazil, and compares results with data from other tropical as well as temperate alpine sites. Location Beginning at altitudes of 1800–2000 m, the campos de altitude are found atop the highest summits of the main ranges of the southeastern Brazilian Highlands, between the states of Santa Catarina and Minas Gerais/Espírito Santo. Methods Macro- and mesoclimatic parameters for the campos de altitude are derived from both original data and previously reported results. Parameters include approximate radiation budgets, temperature lapse rates, seasonal and diurnal patterns in temperature, occurrence of frost, elevational gradients in precipitation, and interannual and seasonal patterns in precipitation. Using multivariate techniques and simple numerical contrasts, the climate of the campos de altitude is compared to climates of other tropical as well as temperate alpine sites. Results With respect to patterns of seasonality and the marked influence of polar frontal activity, the macroclimate of the campos de altitude is typically tropical-marginal. However, in reference to actual temperature and precipitation values, the length and profundity of the dry season, average humidities and cloudiness, the climate of the campus de altitude more closely corresponds to that of more inner-tropical systems. These commonalities are best developed with respect to páramo climates of the northern Andes and, especially, Costa Rica. Main conclusions Their very different latitudinal and geographic positions notwith- standing, the campos de altitude and high mountain formations of the N. Andean and Central American Cordillera show clear macroclimatic congruities. In these congruities reside both the environmental basis for strong Andean–southeast Brazilian biogeographic connections, and the context within which evolutionary and ecological parallelisms have developed in the biota of these two widely separate neotropical mountain systems.     

Freezing tolerance in grasses along an altitudinal gradient in the Venezuelan Andes

The tropical high Andes experience greater daily temperature oscillations compared to seasonal ones as well as a high frequency of night frost occurrence year round. Survival of organisms, under such environmental conditions, has been determined by selective forces which have evolved into adaptations including avoidance or tolerance to freezing. These adaptations have been studied in different species of trees, shrubs and perennial herbs in páramo ecosystems, while they have not been considered in grasses, an important family of the páramo. In order to understand survival of Poaceae, resistance mechanisms were determined. The study was performed along an altitudinal gradient (2,500–4,200 m a.s.l.) in the páramo. Supercooling capacity and frost injury temperature were determined in nine species in order to establish cold resistance mechanisms. Grasses registered a very low supercooling capacity along the altitudinal gradient, with ice formation between −6 and −3°C. On the other hand, frost injury temperature oscillated between −18 and −7°C. Our results suggest that grasses exhibit freezing tolerance as their main cold resistance mechanism. Since grasses grow at ground level, where greatest heat loss takes place, tolerance may be related to this life form as reported for other small life forms.     

A tool to assess the ecological condition of tropical high Andean streams in Ecuador and Peru: The IMEERA index

The main objective of this study was to develop a highland Andean streams ecological assessment tool for managers to determine the biological quality in this broad area of South America. Sampling was conducted during the dry season at 123 sites in eight watersheds of high Andean streams from south of Peru to North of Ecuador. The sites were at elevations above 2000 m a.s.l., and ranged in anthropogenic disturbance from none or little (reference) to highly disturbed. Using the physicochemical, hydromorphological and aquatic macroinvertebrate assemblage attributes of the reference sites, two different elevation bioregions were identified (from 2000 to 3500 m a.s.l. and those sites at altitudes higher than 3500 m a.s.l.). Differences between these two bioregions were related to the change in altitude of the most relevant environmental factors, i.e., temperature, oxygen content of the water and the extent of forested vegetation in the basin and in the riparian zone. These features were paramount to having different macroinvertebrate assemblages as demonstrated by an MDS analysis of our data. Two versions of the multi-metric index IMEERA were developed (the acronym comes from the Spanish name ‘Índice Multimétrico del Estado Ecológico para Ríos Altoandinos’) that corresponded to the two bioregions. In the lower altitude bioregion (Bosque river type, IMEERA-B index), the pressure gradient was driven by the organic pollution and the hydromorphological degradation. While in the higher elevation bioregion (Páramo and Puna river types; IMEERA-P river type), the gradient was driven by the organic pollution and the habitat heterogeneity. The IMEERA B index includes six macroinvertebrate metrics using its richness, habit characteristics and tolerance/intolerance to disturbances (EPT taxa, % clingers, % climbers, intolerant taxa, ABI and % tolerant taxa). The IMEERA P index was calculated using four metrics corresponding to macroinvertebrate richness and its tolerance/intolerance to disturbances (total taxa, intolerant taxa, ABI and % tolerant taxa). The index was validated with a set of independent data from the headwaters of Guayllabamba River in Ecuador.     

<Emphasis Type="Italic">Espeletia</Emphasis> giant rosette plants are reliable biological indicators of time since fire in Andean grasslands

Páramo grasslands in the tropical Andes are fire-prone ecosystems and an understanding of their fire ecology is fundamental to biodiversity conservation and ecosystem management. Fire registers are normally impractical in these remote, cloud-covered landscapes, but Espeletia giant rosette plants have been proposed as biological indicators of time since fire in páramos. Espeletia giant stem rosettes tolerate fire well, protecting apical buds in at the heart of their leaf rosettes, and for some species, germination is known to be enhanced by fire. As the plant grows, its dead leaves remain attached to the stem, but fire removes these and resets the “leaf clock”. This study uses a unique register of fires in one Ecuadorian páramo to assess the robustness of this biological indicator. Dead leaf cover on Espeletia pycnophylla giant rosette plants was measured in fifteen different sites with known fire dates from 2000 to 2014. The growth rates of plants at four different elevations were measured over a 2-year period and used to estimate time since fire based on dead leaf cover in the known sites. Estimates were accurate to ± 2 year. Thus, where fire records are missing, relatively easy measurements of growth rates and dead leaf cover of Espeletia giant rosette plants can provide reliable estimates across a wide range of times since fire. This approach has value for direct investigations into fire ecology but also for studies in which controlling for fire dynamics is necessary to reveal underlying patterns. Therefore, this approach also offers a means to obtain better information on other landscape-scale processes such as the impact of climate change on biodiversity or the provision of ecosystem services.     

Tropical and Temperate: Evolutionary History of Páramo Flora

Biogeography of the tropical alpine flora of South and Central America, the páramo flora, has been studied by dividing genera into tropical, temperate, and cosmopolitan chorological flora elements. Published molecular phylogenies of páramo genera are reviewed to summarize knowledge about evolutionary history of the páramo flora and to assess congruence between chorological and phylogenetic approaches. Molecular phylogenies suggest that both the tropical and temperate regions have been important source areas for evolution of the páramo flora. Conclusions derived from chorological patterns regarding origin of genera in páramo are mostly supported by phylogenetic data. Nevertheless, in Chuquiraga, Halenia, Huperzia, and Perezia the chorological scenario is rejected, and in Chusquea-Neurolepis, Elaphoglossum, Gunnera, Halenia, Jamesonia-Eriosorus, and Lasiocephalus independent colonization events from one or several source areas are suggested. Tropical and temperate genera contributed equally to modern species richness of the páramo flora. Among temperate genera, the northern hemisphere genera gave rise to more species in páramo than did genera from the southern hemisphere. So far, no unequivocal evidence has been provided for migration of páramo genera to the temperate zones.     

Phenolics and condensed tannins of high altitude Pteridium arachnoideum in relation to sunlight exposure,elevation, and rain regime

Non-adapted plants growing in high altitude such as bracken fern Pteridium arachnoideum are exposed to environmental extremes that may induce a chemical adaptive response. Here we show that there is a non-uniform distribution of low (LMP) and high molecular weight (HMP) phenolics in the frond parts of P. arachnoideum growing at high elevation. LMP–HMP levels were measured in sun-exposed (E) and self shaded (SS) pinnae between 2100 and 3190 m in the tropical Andes, during dry and rainy seasons. While there was no difference in E vs. SS contents of LMP at 2100 m, E accumulated greater LMP–HMP concentrations relative to SS as altitude increased. This difference was increased during the dry season. Linear correlations between the position of each pinnae relative to the ground level and LMP–HMP occurred along a 2570–3190 m transect. Water restriction in the dry season also caused increase of LMP and HMP. We conclude that excess UV-B radiation and water availability are important modelers of the non-adapted plant acclimation response to stress in tropical high mountain habitats.