Los bosques estacionalmente secos del Perú: un re-análisis de sus patrones de diversidad y relaciones florísticas

Los bosques estacionalmente secos en el Perú constituyen un conjunto de ecosistemas que incluye tres grandes grupos florísticos: bosques costeros, interandinos y orientales. Con la excepción de los bosques estacionalmente secos de las llanuras costeras del norte del país, hasta hace poco la ausencia de datos hacía difícil describir adecuadamente estos grupos en base a su florística. En los últimos 20 años, en estos bosques se han generado diversos estudios florísticos e inventarios botánicos enfocados en plantas leñosas, que han llenado vacíos de conocimiento en áreas críticas. Con estos estudios hemos generado la base de datos DRYFLOR Perú que a la fecha incluye 526 inventarios cuantitativos (listas de especies en áreas discretas incluyendo registros de sus abundancias) y que nos permiten confirmar la distinción florística de los tres grandes grupos. Adicionalmente logramos reconocer claramente dos subgrupos de bosques estacionalmente secos costeros (de llanura y de montaña), dos subgrupos interandinos (valles del Marañón-Mantaro y del Pampas) y tres subgrupos orientales (valles del Huallaga, Tambo y Urubamba). Todos los subgrupos tienen un ensamblaje de especies de plantas leñosas que los distingue y caracteriza en términos de abundancia, frecuencia, riqueza de especies y niveles de endemismo. Si bien ahora podemos describir mejor la heterogeneidad florística de los bosques estacionalmente secos en el Perú, hemos identificado vacíos de conocimiento importantes que requieren de atención prioritaria: i) requerimos de esfuerzos de inventario adicionales en los bosques orientales, ii) necesitamos resolver las afinidades florísticas de los bosques del valle del Apurímac, iii) nuestros datos coinciden en poco más del 75% con las definiciones y distribución de bosques secos del reciente Mapa Nacional de Ecosistemas del Perú, y será necesario revisar el concepto de bosque estacionalmente seco para lograr capturar adecuadamente su distribución en este instrumento de gestión.

Seasonally dry forests in Peru are a combination of ecosystems that include three large floristic groups: coastal, inter-Andean and eastern forests. Except for the seasonally dry forests of the northern coastal plains of the country, until recently it was difficult to explore what occurred floristically within each group due to lack of data. However, in the last 20 years various floristic studies and botanical inventories focused on woody plants have managed to fill knowledge gaps in critical areas. With these studies we have generated the DRYFLOR Peru database that to date includes 526 quantitative inventories (lists of species in discrete areas, including records of their abundances) and that allows us to confirm the floristic distinction of the three large groups. Additionally, we were able to clearly recognize two subgroups of seasonally dry coastal forests (on coastal plains and along the Andean piedmont), two inter-Andean subgroups (within the Marañón-Mantaro and Pampas valleys) and three eastern subgroups (within the Huallaga, Tambo and Urubamba valleys). All subgroups have an assemblage of woody plant species that distinguishes and characterizes them in terms of abundance, frequency, species richness, and levels of endemism. Although we can now better describe the floristic heterogeneity of seasonally dry forests in Peru, we have identified important knowledge gaps that require urgent attention: i) we require additional inventory efforts in the eastern forests, ii) we need to resolve the floristic affinities of the forests of the Apurímac valley, iii) our data agree in little more than 75% with the definitions and distribution of dry forests of the recent National Ecosystem Map of Peru, and it will be necessary to review the concept of seasonally dry forests to adequately capture its distribution in this management tool.

Global patterns of vascular plant alpha diversity.

Global patterns of regional (gamma) plant diversity are relatively well known, but whether these patterns hold for local communities, and the dependence on spatial grain, remain controversial. Using data on 170,272 georeferenced local plant assemblages, we created global maps of alpha diversity (local species richness) for vascular plants at three different spatial grains, for forests and non-forests. We show that alpha diversity is consistently high across grains in some regions (for example, Andean-Amazonian foothills), but regional 'scaling anomalies' (deviations from the positive correlation) exist elsewhere, particularly in Eurasian temperate forests with disproportionally higher fine-grained richness and many African tropical forests with disproportionally higher coarse-grained richness. The influence of different climatic, topographic and biogeographical variables on alpha diversity also varies across grains. Our multi-grain maps return a nuanced understanding of vascular plant biodiversity patterns that complements classic maps of biodiversity hotspots and will improve predictions of global change effects on biodiversity.

Evolutionary diversity in tropical tree communities peaks at intermediate precipitation.

Global patterns of species and evolutionary diversity in plants are primarily determined by a temperature gradient, but precipitation gradients may be more important within the tropics, where plant species richness is positively associated with the amount of rainfall. The impact of precipitation on the distribution of evolutionary diversity, however, is largely unexplored. Here we detail how evolutionary diversity varies along precipitation gradients by bringing together a comprehensive database on the composition of angiosperm tree communities across lowland tropical South America (2,025 inventories from wet to arid biomes), and a new, large-scale phylogenetic hypothesis for the genera that occur in these ecosystems. We find a marked reduction in the evolutionary diversity of communities at low precipitation. However, unlike species richness, evolutionary diversity does not continually increase with rainfall. Rather, our results show that the greatest evolutionary diversity is found in intermediate precipitation regimes, and that there is a decline in evolutionary diversity above 1,490 mm of mean annual rainfall. If conservation is to prioritise evolutionary diversity, areas of intermediate precipitation that are found in the South American 'arc of deforestation', but which have been neglected in the design of protected area networks in the tropics, merit increased conservation attention.

Substrate, moisture, temperature and seed germination of the threatened endemic tree Eriotheca vargasii (Malvaceae) / Sustrato, humedad, temperatura y germinación de semillas del árbol endémico amenazado Eriotheca vargasii (Malvaceae)

Abstract We studied the germination of Eriotheca vargasii (Malvaceae), a poorly known endemic Peruvian Andean tree species characteristic of the dry forests of the Torobamba river valley, Peru. We determined seed characteristics, embryo morphology, viability, and assessed the influence of substrate (natural soil and commercially prepared media), temperature (controlled at 25 ºC and at ambient temperature between 18-22 ºC), and moisture (25 % and 50 % field capacity) on seed germination. Most seeds were ovoid in shape and although they contained well-developed embryos, only 46 % of them were viable. Substrate moisture levels had no influence on germination capacity or rate. In contrast, temperature and substrate type showed strong effects on germination. We observed the highest proportion of germinated seeds in prepared media at both temperatures tested (> 61 %). Furthermore, substrate types also influenced germination rates, with lower values in natural soil. The strongest effect on germination rates was by temperature, enhancing the difference in responses in substrate types (up to 90 % in commercially prepared media at 25 ºC). The low proportion of germinated seeds in soil (< 39 %), together with external local stress factors (e.g. grazing impact by herbivores), may be the critical factors contributing to the nearly total absence of seedlings and saplings of E. vargasiiin the study area despite abundant seed production. In order to ensure a supply of E. vargasii seedlings for reforestation efforts, we recommend producing E. vargasii plants in nurseries and conducting reforestation trials. We suggest that germination of seedlings is done following guidelines from this study. Rev. Biol. Trop. 66(3): 1162-1170. Epub 2018 September 01.

Resumen Estudiamos la germinación de Eriotheca vargasii (Malvaceae), un árbol endémico poco conocido de los andes peruanos y carácterístico de los bosques secos del valle del río Torobamba. Determinamos las características de la semilla, la morfología del embrión y la viabilidad; además evaluamos la influencia del sustrato (suelo y sustrato preparado comercialmente), temperatura (controlada a 25 ºC y sin control entre 18-22 ºC) y humedad (25 % y 50 % de capacidad de campo) sobre la germinación de las semillas. La mayoría de las semillas tuvo forma ovoide y aunque la mayoría contenía embriones bien desarrollados, sólo el 46 % de estas fue viable. Los niveles de humedad del sustrato no tuvieron influencia sobre la capacidad o tasa de germinación, mientras que la temperatura y el tipo de sustrato si tuvieron efectos visibles. Observamos las proporciones más altas de semillas germinadas en los sustratos preparados y en ambas temperaturas (> 61 %). Adicionalmente, el tipo de sustrato también influenció las tasas de germinación, con valores más bajos en el suelo natural. El efecto más fuerte sobre las tasas de germinación se dió por la temperatura, aumentando las diferencias de las respuestas de acuerdo al tipo de sustrato (hasta un 90 % de germinación en sustratos preparados comercialmente y a 25 ºC). La baja proporción de semillas germinadas en el suelo (< 39 %), junto con factores locales de estrés externos (como por ejemplo el impacto por herbivoría), pueden ser elementos clave que están contribuyendo a la casi ausencia total de plántulas de E. vargasii en el área de estudio, a pesar de una producción de semilla abundante. Para asegurar proveer plantones de E. Vargasii para esfuerzos de reforestación, recomendamos producir plantas de esta especie en viveros y realizar experimentos de reforestación. Sugerimos que la germinación de las plántulas se haga siguiendo las recomendaciones de este estudio.

Plant diversity patterns in neotropical dry forests and their conservation implications.

Seasonally dry tropical forests are distributed across Latin America and the Caribbean and are highly threatened, with less than 10% of their original extent remaining in many countries. Using 835 inventories covering 4660 species of woody plants, we show marked floristic turnover among inventories and regions, which may be higher than in other neotropical biomes, such as savanna. Such high floristic turnover indicates that numerous conservation areas across many countries will be needed to protect the full diversity of tropical dry forests. Our results provide a scientific framework within which national decision-makers can contextualize the floristic significance of their dry forest at a regional and continental scale.

Large-scale patterns of turnover and Basal area change in Andean forests.

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.

Forgotten forests--issues and prospects in biome mapping using Seasonally Dry Tropical Forests as a case study.

BACKGROUND: South America is one of the most species diverse continents in the world. Within South America diversity is not distributed evenly at both local and continental scales and this has led to the recognition of various areas with unique species assemblages. Several schemes currently exist which divide the continental-level diversity into large species assemblages referred to as biomes. Here we review five currently available biome maps for South America, including the WWF Ecoregions, the Americas basemap, the Land Cover Map of South America, Morrone's Biogeographic regions of Latin America, and the Ecological Systems Map. The comparison is performed through a case study on the Seasonally Dry Tropical Forest (SDTF) biome using herbarium data of habitat specialist species. RESULTS: Current biome maps of South America perform poorly in depicting SDTF distribution. The poor performance of the maps can be attributed to two main factors: (1) poor spatial resolution, and (2) poor biome delimitation. Poor spatial resolution strongly limits the use of some of the maps in GIS applications, especially for areas with heterogeneous landscape such as the Andes. Whilst the Land Cover Map did not suffer from poor spatial resolution, it showed poor delimitation of biomes. The results highlight that delimiting structurally heterogeneous vegetation is difficult based on remote sensed data alone. A new refined working map of South American SDTF biome is proposed, derived using the Biome Distribution Modelling (BDM) approach where georeferenced herbarium data is used in conjunction with bioclimatic data. CONCLUSIONS: Georeferenced specimen data play potentially an important role in biome mapping. Our study shows that herbarium data could be used as a way of ground-truthing biome maps in silico. The results also illustrate that herbarium data can be used to model vegetation maps through predictive modelling. The BDM approach is a promising new method in biome mapping, and could be particularly useful for mapping poorly known, fragmented, or degraded vegetation. We wish to highlight that biome delimitation is not an exact science, and that transparency is needed on how biomes are used as study units in macroevolutionary and ecological research.

Mapas y clasificación de vegetación en ecosistemas estacionales: un análisis cuantitativo de los bosques secos de Piura / Vegetation maps and classification in seasonal ecosystems: a quantitative analysis of the Piura dry forests

Estudiamos datos de inventarios florísticos de 65 parcelas de 0,1 hectáreas de la vegetación estacional de las llanuras costeras de Piura usando métodos multivariados y análisis de composición florística. Identificamos seis grupos de vegetación, de los cuales cinco coinciden con tipos de vegetación descritos hace casi 100 años por Augusto Weberbauer. Por el contrario, de las ocho categorías de bosque seco definidas recientemente por el Proyecto Algarrobo para el área de estudio, ninguna pudo ser reconocida adecuadamente mediante métodos numéricos. Concluimos que los mapas y datos generados por Weberbauer resultan ser más exactos y revelan mejor las relaciones florísticas de la vegetación estacionalmente seca de Piura. Por lo tanto, sugerimos el uso más frecuente de las descripciones propuestas por Weberbauer para la región, paralelamente a los del Proyecto Algarrobo.

We studied data from 65 0.1-hectare floristic inventories from the seasonal lowland vegetation in coastal Piura by using multivariate methods and analyses of floristic composition. We identified six vegetation groups, five of which greatly coincide with vegetation types already described 100 years ago by August Weberbauer. In contrast, we were not able to accurately identify any of the eight dry forest categories recently defined by the Proyecto Algarrobo for the study area using numerical methods. We conclude that the maps and data generated by Weberbauer are more accurate and better reveal the floristic relationships of the seasonally dry vegetation in Piura. Therefore, we suggest a more widespread use of the descriptions made by Weberbauer in the region, parallel to those of the Proyecto Algarrobo.