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  1. Abstract Aim

    We examined tree beta diversity in four biogeographical regions with contrasting environmental conditions, latitude, and diversity. We tested: (a) the influence of the species pool on beta diversity; (b) the relative contribution of niche‐based and dispersal‐based assembly to beta diversity; and (c) differences in the importance of these two assembly mechanisms in regions with differing productivity and species richness.

    Location

    Lowland and montane tropical forests in the Madidi region (Bolivia), lowland temperate forests in the Ozarks (USA), and montane temperate forests in the Cantabrian Mountains (Spain).

    Methods

    We surveyed woody plants with a diameter ≥2.5 cm following a standardized protocol in 236 0.1‐ha forest plots in four different biogeographical regions. We estimated the species pool at each region and used it to recreate null communities determined entirely by the species pool. Observed patterns of beta diversity smaller or greater than the null‐expected patterns of beta diversity implies the presence of local assembly mechanisms beyond the influence of the species pool. We used variation‐partitioning analyses to compare the contribution of niche‐based and dispersal‐based assembly to patterns of observed beta diversity and their deviations from null models among the four regions.

    Results

    (a) Differences in species pools alone did not explain observed differences in beta diversity among biogeographic regions. (b) In 3/4 regions, the environment explained more of the variation in beta diversity than spatial variables. (c) Spatial variables explained more of the beta diversity in more diverse and more productive regions with more rare species (tropical and lower‐elevation regions) compared to less diverse and less productive regions (temperate and higher‐elevation regions). (d) Greater alpha or gamma diversity did not result in higher beta diversity or stronger correlations with the environment.

    Conclusion

    Overall, the observed differences in beta diversity are better explained by differences in community assembly mechanism than by biogeographical processes that shaped the species pool.

     
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  2. Abstract Aim

    Ecological niches shape species commonness and rarity, yet, the relative importance of different niche mechanisms within and across ecosystems remains unresolved. We tested the influence of niche breadth (range of environmental conditions where species occur) and niche position (marginality of a species’ environmental distribution relative to the mean environmental conditions of a region) on tree‐species abundance and occupancy across three biogeographic regions.

    Location

    Argentinian Andes; Bolivian Amazon; Missouri Ozarks.

    Time period

    2002–2010.

    Major taxa studied

    Trees.

    Methods

    We calculated abiotic‐niche breadths and abiotic‐niche positions using 16 climate, soil and topographic variables. For each region, we used model selection to test the relative influence of niche breadth and niche position on local abundance and occupancy in regional‐scale networks of 0.1‐ha forest plots. To account for species–environment associations caused by other mechanisms (e.g., dispersal), we used null models that randomized associations between species occurrences and environmental variables.

    Results

    We found strong support for the niche‐position hypothesis. In all regions, species with higher local abundance and occupancy occurred in non‐marginal environments. Observed relationships between occupancy and niche position also differed from random species–environment associations in all regions. Surprisingly, we found little support for the niche‐breadth hypothesis. Observed relationships between both local abundance and niche breadth, and occupancy and niche breadth, did not differ from random species–environment associations.

    Main conclusion

    Niche position was more important than niche breadth in shaping species commonness and rarity across temperate, sub‐tropical and tropical forests. In all forests, tree species with widespread geographic distributions were associated with environmental conditions commonly found throughout the region, suggesting that niche position has similar effects on species occupancy across contrasting biogeographic regions. Our findings imply that conservation efforts aimed at protecting populations of common and rare tree species should prioritize conservation of both common and rare habitats.

     
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  3. Summary

    Recent studies have demonstrated that ecological processes that shape community structure and dynamics change along environmental gradients. However, much less is known about how the emergence of the gradients themselves shape the evolution of species that underlie community assembly. In this study, we address how the creation of novel environments leads to community assembly via two nonmutually exclusive processes: immigration and ecological sorting of pre‐adapted clades (ISPC), and recent adaptive diversification (RAD). We study these processes in the context of the elevational gradient created by the uplift of the Central Andes.

    We develop a novel approach and method based on the decomposition of species turnover into within‐ and among‐clade components, where clades correspond to lineages that originated before mountain uplift. Effects of ISPC and RAD can be inferred from how components of turnover change with elevation. We test our approach using data from over 500 Andean forest plots.

    We found that species turnover between communities at different elevations is dominated by the replacement of clades that originated before the uplift of the Central Andes.

    Our results suggest that immigration and sorting of clades pre‐adapted to montane habitats is the primary mechanism shaping tree communities across elevations.

     
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  4. Abstract We introduce the FunAndes database, a compilation of functional trait data for the Andean flora spanning six countries. FunAndes contains data on 24 traits across 2,694 taxa, for a total of 105,466 entries. The database features plant-morphological attributes including growth form, and leaf, stem, and wood traits measured at the species or individual level, together with geographic metadata (i.e., coordinates and elevation). FunAndes follows the field names, trait descriptions and units of measurement of the TRY database. It is currently available in open access in the FIGSHARE data repository, and will be part of TRY’s next release. Open access trait data from Andean plants will contribute to ecological research in the region, the most species rich terrestrial biodiversity hotspot. 
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  5. Bolivian Begonia are among the most poorly studied of American begonias. We provide here a checklist and key to the Bolivian Begonia flora, which currently includes ten sections, 43 species, three subspecies and three varieties. We also fully discuss the nomenclature and typification of all Bolivian Begonia species and designate 16 lectotypes. We describe and provide an illustration of one new species and provide emended descriptions for eight species. We have assessed six species for extinction risk under IUCN Red List criteria and provide four new synonyms. We compare our checklist with previous treatments of Bolivian Begonia and discuss all changes in detail.Las begonias de Bolivia se encuentran entre las begonias americanas menos estudiadas. Proporcionamos una lista de verificación y una clave para la flora de begonias de Bolivia, que actualmente incluye diez secciones, 43 especies, tres subespecies y tres variedades. También proporcionamos una discusión completa de la nomenclatura y tipificación de todas las especies bolivianas de Begonia y designamos 16 lectotipos.  Describimos e ilustramos una nueva especie y adicionamos descripciones corregidas para ocho especies. Evaluamos seis especies en riesgo de extinción según los criterios de la lista roja de la UICN y proponemos cuatro nuevos sinónimos. Comparamos nuestra lista de verificación con tratamientos anteriores sobre las begonias bolivianas y discutimos todos los cambios en detalle. 
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  6. null (Ed.)
    Abstract It is largely unknown how South America’s Andean forests affect the global carbon cycle, and thus regulate climate change. Here, we measure aboveground carbon dynamics over the past two decades in 119 monitoring plots spanning a range of >3000 m elevation across the subtropical and tropical Andes. Our results show that Andean forests act as strong sinks for aboveground carbon (0.67 ± 0.08 Mg C ha −1 y −1 ) and have a high potential to serve as future carbon refuges. Aboveground carbon dynamics of Andean forests are driven by abiotic and biotic factors, such as climate and size-dependent mortality of trees. The increasing aboveground carbon stocks offset the estimated C emissions due to deforestation between 2003 and 2014, resulting in a net total uptake of 0.027 Pg C y −1 . Reducing deforestation will increase Andean aboveground carbon stocks, facilitate upward species migrations, and allow for recovery of biomass losses due to climate change. 
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  8. null (Ed.)
    Weinmannia epicae is described and illustrated. It grows in Andean high-montane forests of the Yungas region in the department of La Paz, northwestern Bolivia, between 2900 and 3300 m. It differs from other morphologically similar species as W. cundinamarcensis, W. haenkeana and W. pubescens by having the maximum number of leaflets pairs usually between 10 to 14, medial leaflets of 1.3 to 2.3 cm, with more or less rough surface and undersurfaces with hirsute to hirsute-villous indument, and mature capsules villous-pubescent of 5-7 × 1.8-2.7 mm, conspicuously pedicellated. The differences with morphological similar species are pointed out, and information on their geographical distribution, ecology, phenology and the assessment of conservation status according to IUCN criteria are provided. 
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  9. null (Ed.)