Tropical Alpine Ecosystem Research Articles

Integrative taxonomy and biogeography of the genus Oxytrechus (Coleoptera: Carabidae: Trechini) in the tropical alpine ecosystem of Ecuadorian Andes, with the description of six new species

Summary This study presents a taxonomic revision of the species of the ground beetle genus Oxytrechus Jeannel, 1927 that inhabit the superpáramo of the Andes of Ecuador, which constitutes the uppermost zone of the tropical alpine ecosystem, above 4200 m. Sixteen species, displayed in three clades, were recorded in this environment, six of which are described as new: Oxytrechus antisanae n. sp. (Mt Antisana), O. giachinoi n. sp. (Mt Illiniza), O. hamatus n. sp. (Mt Atacazo and Pichincha), O. prunai n. sp. (Mt Guamaní), O. reflexus n. sp. (Mt Illiniza and Mt Corazón), and O. robbiolai n. sp. (Mt Pichincha). New distributional data are presented for O. chioriae Quéinnec & Ollivier, 2019, O. lallemandi Jeannel, 1927, O. moreti Mateu, 1988 and O. zoiai Casale & Sciaky, 1985. The first molecular phylogeny of the group, based on fragments of four mitochondrial and two nuclear genes, is given. Dichotomous identification keys are provided to the species groups and the included species. Based on systematic sampling, Oxytrechus exhibits the highest degree of microendemism among páramo ground beetles. No species has been found in more than two sky islands, and half of the species recorded in the superpáramo are single-mountain endemics. As regards their conservation status, eight species (two thirds) can be classified as vulnerable or endangered, due to a mix of low abundance, narrow distribution range, microendemism, limited ecological tolerance, habitat destruction and effects of climate change.

The ghost of past climate acting on present‐day plant diversity: Lessons from a climate‐based delimitation of the tropical alpine ecosystem

AbstractHabitat stability is important for maintaining biodiversity by preventing species extinction, but this stability is being challenged by climate change. The tropical alpine ecosystem is currently one of the ecosystems most threatened by global warming, and the flora close to the permanent snow line is at high risk of extinction. The tropical alpine ecosystem, found in South and Central America, Malesia and Papuasia, Africa, and Hawaii, is of relatively young evolutionary age, and it has been exposed to changing climates since its origin, particularly during the Pleistocene. Estimating habitat loss and gain between the Last Glacial Maximum (LGM) and the present allows us to relate current biodiversity to past changes in climate and habitat stability. In order to do so, (i) we developed a unifying climate‐based delimitation of tropical alpine regions across continents, and (ii) we used this delimitation to assess the degree of habitat stability, that is, the overlap of suitable areas between the LGM and the present, in different tropical alpine regions. Finally, we discuss the link between habitat stability and tropical alpine plant diversity. Our climate‐based delimitation approach can be easily applied to other ecosystems using our developed code, facilitating macro‐comparative studies of habitat dynamics through time.

Habitat preference and vulnerability to drought of three Hypericum species of the páramo

ABSTRACT Background Páramos are tropical alpine ecosystems where climate change is expected to cause yet unknown consequences for plant growth, ecosystem structure, ecosystem function and the provision of ecosystem services. Aim To quantify the relationship between environmental factors (abiotic and biotic) and the spatial distribution of three common Hypericum species in the páramo and their physiological vulnerability to drought. Methods We recorded soil water content, soil temperature, and vegetation cover in 10 plots along a moisture gradient. Additionally, we measured a series of physiological traits associated with the risk of drought-induced mortality. Results We found that H. goyanesii and H. juniperinum mainly grew in areas with high soil water content, and similar high vegetation cover. These two species had wider xylem vessels, showed anisohydric behaviour and were equally vulnerable to cavitation with low safety margins against hydraulic failure. H. mexicanum grew in places with less vegetation cover, lower soil water content, and higher soil temperatures. H. mexicanum showed a different strategy that probably allows it to thrive in these conditions; it maintains high values of water potential at noon and has narrower xylem vessels, making it less vulnerable to cavitation. Conclusion The distribution of the three Hypericum species in the páramo responds essentially to soil water content, in line with the physiological mechanisms of the species to cope with water deficit. Hypericum species from moist habitats could decline if longer drought episodes become more common in the future.

Patterns in climate and seedling establishment at a dry tropical treeline

In some internal valleys of the northern Andes, precipitation at treeline elevation is seasonal, with one or two dry periods that could exert a strong control on tree seedling survival. However, little is known about (1) the severity of the dry periods, due to a lack of climate data, or (2) the effect of drought on tree seedling demographic dynamics and how this is modulated by local plant interactions in these tropical-alpine ecosystems. We studied annual precipitation variation and seedling demography and ecophysiology in relation to microclimate and neighboring plants in a dry treeline ecotone at 3100 m a.s.l in the Venezuelan Andes. We selected seedlings of the dominant tree species Cybianthus marginatus and Clusia multiflora at three sites, each with three adjacent 10 × 10-m plots within the forest, forest border, and páramo. For both species, seedling density was zero in the páramo and did not differ between border and forest. Growth rates were low for both species, but higher for Cybianthus in the border than in the forest. Survival rates were high in both environments. Low assimilation and transpiration rates were found in both species regardless of the environment. The spatial association of seedlings with moisture-regulating elements such as mosses, ferns and basal rosettes may indicate a benefit of better hydric conditions in their neighborhood. Our study shows a strong limitation for tree establishment in the páramo, but high rates of survival at the edge of the forest. This suggests a scenario of slow potential forest expansion at this tropical treeline, tree cover advancing in a closed front by the successive formation of forest-edge vegetation allowing tree seedling establishment outside of the forest.

Microclimatic Warming Leads to a Decrease in Species and Growth Form Diversity: Insights From a Tropical Alpine Grassland

Due to warming, changes in microclimatic temperatures have shifted plant community structure and dynamics in tundra and alpine regions. The directionality and magnitude of these changes are less known for tropical alpine ecosystems. To understand the likely trajectory of these shifts in the Andes, we conducted a warming experiment in the northern Andes—using open-top chambers (OTC). In this study, we ask (1) how do OTCs affect air and soil temperatures in microclimates of tropical alpine regions, year-round and during the dry season? (2) What are the effects of 7 years of warming on (a) the aboveground biomass (AGB) and (b) the plant taxonomic and growth form diversity? We installed five monitoring blocks in 2012 at ca. 4,200 m asl with 20 OTCs and 50 control plots randomly distributed within each block. We measured AGB, plant community diversity, and growth form diversity between 2014 and 2019. After 7 years of warming, we found significant increases in mean monthly (+0.24°C), daily (+0.16°C), and night air temperatures (+0.33°C) inside the OTCs, and the OTCs intensified microclimatic conditions during the dry season. Additionally, OTCs attenuated extreme temperatures—particularly in the soil—and the number of freezing events. AGB significantly increased in OTCs, and by 2019, it was 27% higher in OTCs than in control. These changes were driven mainly by a progressive increment of tussock grasses such as Calamagrostis intermedia, typical of lower elevations. The increase of tussocks led to a significant decrease in species diversity and evenness inside OTCs, but not in species richness after accounting by sampling time. Furthermore, cushions and herbs decreased inside OTCs. Our results show that experimental warming using OTCs in equatorial regions leads to decreased daily thermal amplitude and night temperatures rather than the level of increase in mean temperatures observed in temperate regions. The increase of tussocks and decrease in diversity of species and growth forms due to prolonged modifications in microclimatic temperature might be a step toward shrub-dominated ecosystems. Further research on this topic would help understand shifts in growth form dominance and the direction and rate of change of the system.

Insights into the functional ecology of páramo plants in Colombia

AbstractPáramos are exceptionally species‐rich tropical alpine ecosystems that provide several important ecosystem services, including carbon storage and water provision. The responses of páramo plant species to climatic change are largely unknown, but classifying species by functional type and ecological strategy can help reduce complexity for modeling and conservation efforts. We measured 22 traits in 42 plant species with various growth forms in the Colombian Andes. We classified plant ecological strategies using CSR (C: competitor, S: stress tolerator, and R: ruderal) analysis and identified plant functional types (PFTs) using hierarchical clustering of principal components. Additionally, we calculated the functional originality of each species to identify species with unique trait combinations. We identified a high degree of convergence among traits and strategies, with most species characterized by the S and SC strategies. Considering the full set of traits, only three PFTs were identified: one composed of forbs and shrubs with tender leaves (PFT1), another composed only of species with rosettes form (PFT2), and a third composed of shrubs with tough leaves (PFT3). Values of functional originality were generally low, suggesting high redundancy in plant traits. PFT2 species, mostly rosettes, exhibited the highest functional originality of all the groups. Our results imply the existence of a limited set of ecophysiological strategies in the páramos, likely driven by the extremely stressful conditions in these systems. This functional redundancy may indicate heightened vulnerability to environmental changes; however, the presence of multiple species with shared functional traits could provide some resilience to disturbance.Abstract in Spanish is available with online material.

Homeostatic Response to Three Years of Experimental Warming Suggests High Intrinsic Natural Resistance in the Páramos to Warming in the Short Term

Páramos, tropical alpine ecosystems, host one of the world’s most diverse alpine floras, account for the largest water reservoirs in the Andes, and some of the largest soil carbon pools worldwide. It is of global importance to understand the future of this extremely carbon-rich ecosystem in a warmer world and its role on global climate feedbacks. This study presents the result of the first in situ warming experiment in two Colombian páramos using Open-Top Chambers. We evaluated the response to warming of several ecosystem carbon balance-related processes, including decomposition, soil respiration, photosynthesis, plant productivity, and vegetation structure after 3 years of warming. We found that OTCs are an efficient warming method in the páramo, increasing mean air temperature by 1.7°C and mean daytime temperature by 3.4°C. The maximum air temperature differences between OTC and control was 23.1°C. Soil temperature increased only by 0.1°C. After 3 years of warming using 20 OTC (10 per páramo) in a randomized block design, we found no evidence that warming increased CO2 emissions from soil respiration, nor did it increase decomposition rate, photosynthesis or productivity in the two páramos studied. However, total C and N in the soil and vegetation structure are slowly changing as result of warming and changes are site dependent. In Sumapaz, shrubs, and graminoids cover increased in response to warming while in Matarredonda we observed an increase in lichen cover. Whether this change in vegetation might influence the carbon sequestration potential of the páramo needs to be further evaluated. Our results suggest that páramos ecosystems can resist an increase in temperature with no significant alteration of ecosystem carbon balance related processes in the short term. However, the long-term effect of warming could depend on the vegetation changes and how these changes alter the microbial soil composition and soil processes. The differential response among páramos suggest that the response to warming could be highly dependent on the initial conditions and therefore we urgently need more warming experiments in páramos to understand how specific site characteristics will affect their response to warming and their role in global climate feedbacks.

The role of dispersal for shaping phylogeographical structure of flightless beetles from the Andes.

BackgroundPáramo is a tropical alpine ecosystem present in the northern Andes. Its patchy distribution imposes limits and barriers to specialist inhabitants. We aim to assess the effects of this habitat distribution on divergence across two independently flightless ground beetle lineages, in the genera Dyscolus and Dercylus.MethodsOne nuclear and one mitochondrial gene from 110 individuals from 10 sites across the two lineages were sequenced and analyzed using a combination of phylogenetics, population genetic analyses, and niche modeling methods.ResultsThe two lineages show different degrees of population subdivision. Low levels of gene flow were found in Dyscolus alpinus, where one dominant haplotype is found in four out of the six populations analyzed for both molecular markers. However, complete population isolation was revealed in species of the genus Dercylus, where high levels of differentiation exist at species and population level for both genes. Maximum entropy models of species in the Dercylus lineage show overlapping distributions. Still, species distributions appear to be restricted to small areas across the Andes.ConclusionEven though both beetle lineages are flightless, the dispersal ability of each beetle lineage appears to influence the genetic diversity across fragmented páramo populations, where Dyscolus alpinus appears to be a better disperser than species in the genus Dercylus.

Insight into the stable isotopic composition of glacial lakes in a tropical alpine ecosystem: Chirripó, Costa Rica

AbstractTropical high‐elevation lakes are considered sentinels of global climate change. This work characterizes the hydrological conditions of tropical alpine glacial lakes located in the highlands of Chirripó, Costa Rica, using a unique data set of water stable isotopes (δ2H and δ18O) in precipitation, stream water, and lake water between September 2015 and July 2017. A combined dataset of bathymetric, hydrometric, and isotope data collected between July 2016 and July 2017 on Lake Ditkevi was used to calculate the annual water balance of the lake. Evaporation to inflow ratios from three lake systems was estimated using a linear resistance model, the experimentally estimated local evaporation line of Chirripó, and the first glacial lake water evaporation lines in the region. The temporal isotopic variations (δ18O, d‐excess, and lc‐excess) confirm variations in the dry and wet season evaporative conditions for the glacial lakes and consistently average annual low evaporation to inflow (E/I) ratios in the range of 2.0 ± 0.8% and 18.1 ± 12.2%. Lake Ditkevi's water balance indicates annual steady‐state conditions, with an estimated evaporation loss of 650 mm/year (10.0 ± 5.0% of inflow), a high‐water contribution to the catchment (90% of inflow), a residence time of 0.53 ± 0.27 years, and a catchment scale (0.289 km2) water yield or depth equivalent run‐off of 278 mm/yr. These results provide novel information about water balance and evaporation losses in tropical alpine glacial lakes, which can serve as baseline information for future isotope‐based hydro‐climate research in high‐elevation regions in the tropics and elsewhere.

Giant stem rosettes have strong facilitation effects on alpine plant communities in the tropical Andes

ABSTRACTBackground: Giant rosettes constitute one of the most distinctive growth-forms in tropical alpine ecosystems. However, their interactions with other plant species remain unexplored in high Andean páramos.Aims: Quantify the effect of a dominant rosette (Coespeletia timotensis) on soil and microclimatic conditions and relate the impacts to plant community structure.Methods: We analysed topsoil temperatures, soil organic matter (SOM) and plant species cover in areas adjacent to C. timotensis and paired areas outside, at three sites (4250–4360 m a.s.l.) in La Culata National Park, Venezuela. Species richness, total vegetation cover and percent cover of each species near and away from the rosettes were compared.Results: Topsoil temperature amplitudes were lower and SOM greater near C. timotensis stems, compared to areas away from them. C. timotensis had a consistent positive effect on species richness, vegetation cover and the cover of many abundant species (including cushions and herbs).Conclusions: The facilitation effects of C. timotensis on abiotic conditions and community structure indicate they play a key role as nurse plants, pointing to giant rosettes as foundation species for the maintenance of plant diversity in the alpine tropics.

Interplay of seasonal sunlight, air and leaf temperature in two alpine páramo species, Colombian Andes

In models of photosynthetic gas exchange, leaf temperature (Tleaf) is often calculated using a combination of derivations of the energy balance equation and measurements of air temperature (Tair). Yet, there are frequently large differences between Tleaf and Tair under natural field conditions, and an energy balance is complicated in complex canopies, especially in tropical ecosystems. In the present study, we aimed to quantify the variation in Tleaf relative to Tair under naturally varying PPFD values in two representative species (Espeletia grandiflora and Chusquea tessellata) of a tropical alpine ecosystem (páramo, Colombian Andes) during both wet and dry seasons. The results of a Structural Equation Model showed that Tleaf was strongly correlated with changes in Tair during both seasons, but large differences (up to 14 °C) occurred between Tair and Tleaf, during the dry season when PPFD varied the most, especially in C. tessellata. Thus, using Tair to proximate Tleaf under variable conditions of incident sunlight could generate substantial errors in estimates of temperature-sensitive physiological processes. These results should be valuable for evaluating the accuracy of carbon and water exchange models within current and future scenarios of climate change in tropical páramos, as well as other ecosystems.

Are the radiations of temperate lineages in tropical alpine ecosystems pre‐adapted?

AbstractAimTropical mountains around the world harbour an extraordinarily rich pool of plant species and are hotspots of biodiversity. Climatically, they can be zoned into montane climates at mid‐altitudes and tropical alpine climates above the tree line. Around half of the tropical alpine species belong to plant lineages with a temperate ancestry, although these regions are often geographically distant. We test the hypothesis that these temperate lineages are pre‐adapted to the tropical alpine climate.LocationNew World, with a focus on tropical alpine Andes.Time periodMiocene to present.Major taxa studiedFlowering plants.MethodsWe build multidimensional environmental models representing the full space of New World climates. We quantify the environmental similarity between the tropical alpine ecosystem and those of potential source areas, while correcting for regional differences by kernel density smoothers. Based on spatial observations of the genus Hypericum (St John's Wort), we quantify niche overlap and test for niche conservatism following intercontinental dispersal using density‐weighted nonparametric tests. A dated species tree, biogeographical estimation, multi‐optima Ornstein–Uhlenbeck models and model selection approaches are used to test for niche shifts during establishment in the tropical alpine Andes.ResultsThe tropical alpine ecosystem is isolated by its climate from adjacent regions and is climatically similar to temperate lowland biomes of both hemispheres. Niche conservatism is evident in the study group, except in the tropical alpine lineage that is characterized by niche expansion and shifts in temperature optima.Main conclusionsOur results reject the pre‐adaptation hypothesis and instead suggest pronounced niche evolution during colonization of tropical alpine ecosystems. Establishment involved substantial niche shifts, mainly in temperature‐related variables, and resulted in a tremendous proliferation of species in the newly invaded tropical alpine ecosystem.

Reciprocal interactions between a facilitator, natives, and exotics in tropical alpine plant communities

Facilitation by nurse plants has received considerable attention, but the feedback effects of beneficiaries on the benefactor fitness remain comparatively unexplored. In particular, to our knowledge there have been no studies of feedback effects of exotic species on nurse plants. Furthermore, there have been few studies of how exotic plants interact with native beneficiaries, potentially generating indirect effects on the nurse. Here, through spatial association analyses, we estimate the reciprocal interactions between the cushion nurse-plant Arenaria musciformis, native beneficiaries, and the dominant exotic Rumex acetosella (a fast growing heliophile species) in a tropical alpine ecosystem of the Venezuelan Andes, locally known as páramos. We recorded the density of natives and the exotic within Arenaria cushions and in paired open areas at three sites and calculated Relative Interaction Indices (RII) to explore the effects of the cushion. Then, we analyzed the feedback effects of Rumex and the natives on the density of flowers produced by Arenaria. Finally, we analyzed how Rumex abundance is related to the abundance of native species inside and outside cushions. RIIs indicated a facilitative effect of cushions on the abundance of native plants, but no effect on Rumex. We found a negative relationship between the density of natives and cushion flower density, but no such relationship for Rumex. However, at high densities, Rumex was negatively correlated with the abundance of the natives both inside and outside of cushions. Our results suggest the possibility of complex reciprocal interactions between nurses, natives and exotics, and that native and exotic plants can differ in their feedback effects on nurse cushions. Native plants appeared to be facilitated by cushions and then develop a parasitic relationship with their nurses. In contrast, the exotic Rumex had a neutral interaction with the nurse, but competitive effects on the native beneficiary community, which could indirectly modulate the feedback effects of natives on the nurse. These results highlight the importance of analyzing direct and indirect reciprocal interactions and the impacts of exotic invaders for understanding alpine community assembly.

Migration corridors for alpine plants among the ‘sky islands’ of eastern Africa: do they, or did they exist?

The tropical alpine ecosystem in eastern Africa is highly fragmented among biological ‘sky islands’, where populations of frost-tolerant organisms are isolated from each other by a ‘sea’ of tropical lowlands. One-third of the species in the afroalpine flora are exclusively alpine, but the other species can to varying degrees extend into grasslands and open forests of lower vegetation belts. A long-debated question is whether colonization of the alpine zone of these mountains and subsequent intermountain gene flow entirely depend on long-distance dispersal across unsuitable habitats, or whether suitable habitats shifted far enough downslope under past colder climates to form bridges enabling gradual migration. Here we address this question using a classification tree model. We mapped the extent of the current alpine habitat and projected it to the last glacial maximum (LGM) climate to assess whether gradual migration was possible for exclusively alpine taxa during this glacial period, and thus potentially also during earlier Pleistocene glaciations. Next, we modelled landcover under current and LGM climates to assess whether grassland and open forests could have served as migration corridors for alpine taxa that today extend into lower vegetation belts. We estimated that the LGM treeline was about 1000 m lower and the alpine habitat was about eight times larger than that today. At the LGM, we found that most of the currently fragmented alpine habitat of the Ethiopian highlands was interconnected except across the Great Rift Valley, whereas the solitary mountains of East/Central Africa remained isolated for exclusively alpine species. However, for drought-tolerant alpine species that today extend below the treeline, gradual migration through habitat corridors may have been possible among mountains during the dry glacial periods, and possibly also under the current climate before agriculture transformed the low-lying landscapes.

Effects of wildland fire on the tropical alpine moorlands of Mount Kenya

Tropical alpine ecosystems serve vital roles in the areas of hydrology, biodiversity and carbon storage, due to their unique set of climatic and topographic conditions. These ecosystems are particularly vulnerable to climate change and anthropogenic influence as they exist in a fragile balance. Mount Kenya is an example of such a tropical alpine environment, and in 2012 a large fire burned through the upper southwestern slopes of the mountain. The fire burned at the transition zone between the moorland and the forest at an elevation of 3300–4000m, and covered almost 100km2. The impacts of this fire on soil properties are investigated three years after the fire. The severity from the time of the fire was determined using a satellite derived index known as dNBR (difference Normalized Burn Ratio). This was used to stratify the fire scar into 3 classes: low, moderate, and high severity areas. Soil samples were collected from the top 10cm layer (O-horizon) in each of these 3 severity classes and from unburnt areas outside the fire scar, and analyzed in the laboratory for physical and chemical properties. The results mostly showed no difference in soil properties between the three severity classes and unburnt areas. Only cation exchange capacity (CEC) and bulk density were found to be significantly different between the severity classes (p<0.001 and p=0.003 respectively), with high severity areas having lower bulk density and higher CEC as compared to unburnt areas. When other explanatory variables were taken into consideration, only CEC remained significantly different according to severity rating. CEC increased from 40.13cmolckg−1 outside the fire to 65.91cmolckg−1 in the high severity areas. The increase in CEC can be explained either by an increase in organic matter, as partially burnt material gradually incorporated into the soil, or by a change in the quality of the organic matter. Thus the impact of fire on soil properties in the tropical alpine moorland of Mount Kenya appears to be small, at least after 3years.

Nitrogen turnover and greenhouse gas emissions in a tropical alpine ecosystem, Mt. Kilimanjaro, Tanzania

Tropical alpine ecosystems are identified as the most vulnerable to global environmental change, yet despite their sensitivity they are among the least studied ecosystems in the world. Despite its important role in constraining potential changes to the carbon balance, soil nitrogen (N) turnover and plant availability in high latitude and high altitude ecosystems is still poorly understood. Here we present a first time study on a tropical alpine Helichrysum ecosystem at Mt. Kilimanjaro, Tanzania, which lies at an altitude of 3880 m. Vegetation composition is characterized and major gross N turnover rates are investigated using the 15N pool dilution method for three different vegetation cover types. In addition greenhouse gas exchange (CO2, N2O and CH4) was manually measured using static chambers. Gross N turnover rates and soil CO2 and N2O emissions were generally lower than values reported for temperate ecosystems, but similar to tundra ecosystems. Gross N mineralization, NH4 + immobilization rates, and CO2 emissions were significantly higher on densely vegetated plots than on sparsely vegetated plots. Relative soil N retention was high and increased with vegetation cover, which suggests high competition for available soil N between microbes and plants. Due to high percolation rates, irrigation/rainfall has no impact on N turnover rates and greenhouse gas (GHG) emissions. While soil N2O fluxes were below the detection limit at all plots, soil respiration rates and CH4 uptake rates were higher at the more densely vegetated plots. Only soil respiration rates followed the pronounced diurnal course of air and soil temperature. Overall, our data show a tight N cycle dominated by closely coupled ammonification-NH4 +-immobilization, which is little prone to N losses. Warming could enhance vegetation cover and thus N turnover; however, only narrower C:N ratios due to atmospheric nitrogen deposition may open the N cycle of Helichrysum ecosystems.

Mexican alpine plants in the face of global warming: potential extinction within a specialized assemblage of narrow endemics

Alpine ecosystems occur under extreme climatic conditions and, as a result, house a unique and vulnerable biota. They are very scarce at tropical latitudes; in Mexico occur mainly along the Trans-Mexican Volcanic Belt, where species richness is not high but narrow endemics stand out. We investigate the effects of climate change under hypothesized contrasting climate warming scenarios using ecological niche modeling of five microendemic alpine species. Occurrence data was obtained mainly from field trips, but herbaria were also examined. A total of 21 climatic and topographic variables, as well as individual selections of 12–16 variables were employed to construct models with Maxent and GARP. Depending on the number of occurrences, current models were validated with Partial-ROC or Jackknife procedures; and projections to 2050 and 2070 were made using two Representative Concentration Pathways and two Global Circulation Models. All species’ models showed a clear pattern of contraction under the explored scenarios; over 58 % of contemporary climatic distribution disappeared, suggesting that analyzed species face imminent extinction due to climatic habitat loss. The models are useful in representing the endemic component of Mexican alpine grassland by reciprocal correspondence in geographic distribution, and we consider it as a highly endangered ecosystem due to climate change, which is probably applicable to other tropical alpine ecosystems. The Pico de Orizaba volcano seems the best option to preserve due to its extension and elevation. However, further studies at finer scales are needed to improve in situ preservation and conservation strategies that include translocation, assisted migration and seed banking.

Shrubs as foundation species in a high tropical alpine ecosystem: a multi-scale analysis of plant spatial interactions

Background: Studies on plant–plant interactions in alpine ecosystems show a strong bias for temperate vs. tropical latitudes and pay limited attention to the implications of biophysical heterogeneity beyond the local plant scale.Aims: To evaluate the effects of a dominant shrub (Hypericum laricifolium) on community organisation, integrating multiple scales of analysis, in a high Andean páramo in Venezuela.Methods: We compared plant cover, species richness and Shannon diversity between plots placed under the shrub and outside (plant scale); quantified the spatial relations of Hypericum with its conspecifics, heterospecifics and rocks at different radial distances, using covariance functions (patch scale); analysed the effects of Hypericum shrubs on total species richness in the community (site scale); and evaluated the consistency of our results among four sites within the same region (between-site scale).Results: Average species richness, Shannon diversity, and the abundance of common forbs and conspecific shrubs were consistently higher inside the Hypericum shrub, while the exotic Rumex acetosella was more abundant in open areas. However, the aggregated spatial distribution of conspecifics and other species extended beyond the local plant scale and there were no clear effects of Hypericum shrubs on community-level species richness.Conclusions: Shrubs can function as foundation species in tropical alpine environments, modifying local community structure and alpha diversity, but not necessarily the species richness of the overall community. Our results stress the need of analysing multiple spatial scales to interpret the role of plant–plant interactions (facilitation/competition) in heterogeneous alpine ecosystems.

Plant–plant interactions in tropical alpine environments

Plant–plant interactions are increasingly recognized as a key driver of community organization and ecosystem processes in alpine environments. However, patterns and mechanisms of plant–plant interactions remain largely uncharacterized in tropical alpine ecosystems (TAE) which represent as much as 10% of the total surface area of alpine ecosystems worldwide. In this paper, we review (1) the ecological and environmental features that are specific to TAE in comparison with other alpine ecosystems, (2) the existing literature on plant–plant interactions in TAE, and (3) whether patterns and mechanisms of plant–plant interactions established in extratropical alpine zones can be extended to TAE. TAE are located predominantly in South America, East Africa, and South-East Asia where they show a unique combination of environmental characteristics, such as absence of persisting snow cover, high frequency of diurnal freeze–thaw cycles and needle-ice activity, and a decrease in precipitation with increasing altitude. These environmental characteristics result in the presence of giant growth forms with a great architectural diversity. These biotic and abiotic characteristics influence the outcome of plant–plant interactions by imposing other types of environmental constraints than those found in extratropical alpine environments, and by potentially generating distinctive patterns of niche differentiation/complementarity between species and populations. To generalize the conceptual framework of plant–plant interactions in alpine environments, we advocate that TAE should be investigated more thoroughly by applying designs, methods and hypotheses that are used currently in temperate areas and by conducting studies along large latitudinal gradients that include tropical regions.

Flowering phenology of tropical-alpine dwarf trees on Mount Kinabalu, Borneo

The flowering phenology of five alpine dwarf-tree species was observed in the summit region (3900–3950 m elevation) of Mt. Kinabalu on Borneo Island from March 1998 to November 2001. For each target species, 20–50 individual plants were numbered in two observation plots and the number of inflorescences was monitored at 2–3-mo intervals. The flowering patterns varied among species. Rhododendron buxifolium bloomed extensively every March–May at the main plot but the flowering pattern at the subplot was less predictable. Mass flowering occurred in March 1998 when drought stress was very severe due to an El Niño event. Rhododendron ericoides showed continuous flowering throughout the year and high synchrony between the plots. Extensive flowering of Leptospermum recurvum occurred synchronously within and between plots in the early half of 1999, then flowering activity decreased greatly. Photinia davidiana showed an annual flowering cycle but the timing of the peak flowering differed between the plots. Vaccinium stapfianum showed synchronous flowering between the plots and the flowering peak appeared at longer than 1-y intervals. Plant size was positively correlated with mean flower production in all species, and with the flowering frequency of R. ericoides, R. buxifolium, and V. stapfianum at one of the plots at least. Two fleshy-fruited species, P. davidiana and V. stapfianum, had high selfing ability for fruit production and showed relatively low flowering synchrony among individuals in comparison with the other species. These results indicate that the trigger for initiation of flowering may differ among sympatric species in a tropical-alpine ecosystem at least in normal years.