El continente africano está encarando uno de los periodos más secos de las últimas 3 décadas y además continua sufriendo una fuerte deforestación. Los bosques y sabanas africanas han sido objeto de especial atención dado que tanto el cambio climático como las presiones en los usos del suelo han tenido grandes impactos en las reservas de carbono de su vegetación leñosa, con consecuencias inmediatas para el balance global de carbono.

En un nuevo estudio publicado en la revista Nature Ecology and Evolution los científicos han usado nuevos datos del espesor óptico de la vegetación obtenidos vía satélite y basados en microondas pasivas de baja frecuencia (L-VOD en su acrónimo en inglés) para cuantificar cambios en el contenido de carbono de las partes leñosas no enterradas de la vegetación del África sub-Sahariana, entre 2010 y 2016.

“Estudios recientes han mostrado que se ha subestimado fuertemente el número de árboles presentes en zonas áridas. Se ha omitido, así, la reserva de carbono que estos árboles suponen en las evaluaciones globales. El conocimiento de la cantidad, distribución y rotación de carbono en la vegetación africana es clave para comprender los efectos de la presión humana y del cambio climático, pero las carencias en los satélites radar y ópticos y la falta de inventarios de campo sistemáticos han generado una gran incertidumbre en la documentación de las reservas de carbono, y de sus cambios a largo plazo en el continente africano”, ha comentado el Dr. Martin Brandt de la Universidad de Copenhagen.

En este estudio, los autores aplican por primera vez la L:VOD para cuantificar las dinámicas inter-anuales de las reservas de carbono por encima del suelo para el periodo 2010-2016. “Presentamos un análisis temporal de patrones de ganancia y pérdida de carbono en diferentes zonas húmedas del África sub-sahariana en respuesta a la sequía sufrida los últimos años”, ha comentado el Dr. Martin Brandt de la Universidad de Copenhagen.

Se observó un cambio neto general en las reservas de carbono en zonas áridas de -0.07 PG C y -1 asociado a un aumento de la sequía, y un cambio neto de -0.03 Pg C y-1 en áreas húmedas. Estas tendencias reflejan una alta variabilidad inter-anual entre años muy húmedos (2011 y 2013; cambios netos de +0.33 y +1.13 Pg C) y un año muy seco (2015; cambio neto de -1.1 Pg C), asociados, respectivamente, a ganancias y pérdidas de carbono.

“En el presente estudio demostramos, primero, la aplicabilidad de L-VOD para monitorear las pérdidas de carbono debidas a variaciones climáticas, y, segundo, la importancia de las reservas de carbono altamente dinámicas y vulnerables de las sabanas de zonas áridas para el balance global de carbono, a pesar de presentar relativamente bajas reservas de carbono por unidad de área”, ha comentado el Prof. Josep Peñuelas del CREAF-CSIC Barcelona.

Para los autores, este estudio destaca la importancia del monitoreo temporal tanto de la deforestación tropical como de las reservas de carbono en la vegetación leñosa de los ecosistemas de sabana para la evaluación de las reservas globales de carbono.

 

Referencia: Brandt, M., Wigneron, J., Chave, J., Tagesson, T., Penuelas, J., Ciais, P., Rasmussen, K., Tian, F., Mbow, C., Al-Yaari, A., Rodriguez-Fernandez, N., Schurgers, G., Zhang, W., Chang, J., Kerr, Y., Verger, A., Tucker, C., Mialon, A., Vang Rasmussen, L., Fan, L., Fensholt, R. 2018. Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands. Nature Ecology & Evolution, doi: 10.1038/s41559-018-0530-6.

 

The African continent is facing one of the driest periods in the past three decades and continuing deforestation. The forests and savannahs of Africa have attracted particular attention because both climate change and land-use pressure have large impacts on the carbon stocks of woody vegetation, with immediate consequences for the global carbon balance.

In a new study in the journal Nature Ecology and Evolution scientists used a new satellite data set based on vegetation optical depth derived from low frequency passive microwaves (L-VOD) to quantify annual aboveground woody carbon changes in sub-Saharan Africa between 2010 and 2016.

“Recent work showed that the number of trees in global drylands has been greatly underestimated: a carbon stock neglected in global assessments. Knowledge of the amount, distribution, and turnover of carbon in African vegetation is crucial for understanding the effects of human pressure and climate change, but the shortcomings of optical and radar satellite products and the lack of systematic field inventories have led to considerable uncertainty in documenting patterns of carbon stocks, and their long-term change over the African continent”, said Dr. Martin Brandt from University of Copenhagen.

In this study, authors apply for the first time L-VOD to quantify the inter-annual dynamics of aboveground carbon stocks for the period 2010-2016. “Based on calibrated relationships between L-VOD and an existing benchmark map we present and analyse temporal patterns of gains and losses in different humidity zones of sub-Saharan Africa in response to recent dry years”, said Dr. Martin Brandt from University of Copenhagen.

The overall net change in carbon stocks in drylands was -0.07 Pg C y-1 associated with drying trends, and a net change of -0.03 Pg C y-1 was observed in humid areas. These trends reflect a high inter-annual variability with very wet years (2011 and 2013; net changes +0.33 and +1.13 Pg C) and a very dry year (2015; net change -1.1 Pg C) associated with carbon gains and losses respectively.

“In this study we demonstrate, first, the applicability of L-VOD to monitor the dynamics of carbon loss and gain due to climate variations, and second, the importance of the highly dynamic and vulnerable carbon pool of dryland savannahs for the global carbon balance, despite the relatively low carbon stock per unit area”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

For the authors this study thereby highlights the importance of timely monitoring of both tropical deforestation and the highly dynamic woody carbon stocks of savannah ecosystems for assessments of global carbon stocks.

Journal Reference: Brandt, M., Wigneron, J., Chave, J., Tagesson, T., Penuelas, J., Ciais, P., Rasmussen, K., Tian, F., Mbow, C., Al-Yaari, A., Rodriguez-Fernandez, N., Schurgers, G., Zhang, W., Chang, J., Kerr, Y., Verger, A., Tucker, C., Mialon, A., Vang Rasmussen, L., Fan, L., Fensholt, R. 2018. Satellite passive microwaves reveal recent climate-induced carbon losses in African drylands. Nature Ecology & Evolution, doi: 10.1038/s41559-018-0530-6.

 

 

L’aforestació és un tipus de canvi en els usos del sòl inicialment destinat a la producció de fusta, la conservació d’aigua i sòl, incrementar l’emmagatzematge de carboni i la mitigació del canvi climàtic. Aquest estudi mostra com la reforestació canvia a més una variable clau del sòl, el seu pH. Fotografia: Pixabay

 

El pH del sòl, el qual mesura la seva acidesa o alcalinitat, està associat a moltes propietats dels sòls com ara l’equilibri iònic, les comunitats microbianes, o els continguts en matèria orgànica. El pH del sòl regula també els processos biogeoquímics del sòl i genera efectes en cascada sobre l’estructura i funcions dels ecosistemes terrestres.

L’aforestació ha sigut una eina àmpliament adoptada per tal d’incrementar el segrest de carboni dels sòls i millorar la preservació tant de l’aigua com del sòl. Tot i això, l’efecte de l’aforestació sobre el pH del sòl és encara poc conegut.

Un nou estudi realitzat per un equip internacional de científics i publicat a la revista Nature Communications, presenta els resultats de la seva recerca orientada a avaluar els canvis en el pH del sòl generats per l’aforestació (establir boscos a llocs on no n’hi ha hagut un des de feia molt de temps). Aquesta avaluació l’han realitzada mitjançant la presa de mostres emparellades en 549 localitats aforestades i 148 localitats de control del Nord de la Xina, considerant diferents espècies d’arbres i al llarg de gradient de pH del sòl.

Els autors han trobat una neutralització significativa del pH del sòl deguda a l’aforestació, que disminueix el pH en sòls relativament alcalins i incrementa el pH en sòls relativament àcids. El llindar del pH del sòl (TpH), el punt al quan l’aforestació canvia d’incrementar a disminuir el pH del sòl, són especifiques de cada espècie d’arbre, en un rang que va de 5.5 (Pinus karaiensis) a 7.3 (Populus spp) amb un promig de 6.3.

L’estudi permet una millor comprensió de com l’aforestació genera impactes en el pH del sòl al llarg d’un ampli rang de tipologies de sòl i d’aforestacions amb espècies diverses d’arbres. Aquesta comprensió és bàsica per desenvolupar estratègies de mitigació del canvi climàtic i de plans de sostenibilitat ecològica.

“El nostre estudi indica que l’aforestació, amb una apropiada selecció d’espècies d’arbres, té el potencial de mitigació de l’acidificació del sòl causada per la deposició àcida”, comenta el Dr. Songbai Hong del Sino-French Institute for Earth System Science, Peking University.

“Els resultats d’aquest estudi ens indiquen que l’aforestació pot modificar el pH del sòl si les espècies d’arbres i el pH inicial estan correctament ajustats, el què potencialment pot millorar la fertilitat del sòl i promoure la productivitat dels ecosistemes”, ha dit el Prof. Josep Peñuelas del CREAF-CSIC Barcelona.

Segons els autors, són necessaris més estudis de camp per tal de determinar quines són les millors espècies d’arbres per a l’aforestació segons les propietats del sòl, la disponibilitat d’aigua, la idoneïtat del clima, l’ecosistema i els objectius socioeconòmics.

Referencia: Hong, S., Piao, s., Chen, A., Liu, Y., Liu, L., Peng, S., Sardans, J., Sun, Y., Peñuelas, J., Zeng, H. 2017. Afforestation neutralizes soil pH. Nature Communications, (2018) 9:520. doi: 10.1038/s41467-018-02970-1.

La aforestación es un tipo de cambio en los usos del suelo inicialmente destinado a la producción de madera, la conservación de agua y suelo, a incrementar el almacenaje de carbono y la mitigación del cambio climático. Este estudio muestra como la aforestación cambia además una variable clave del suelo, su pH. Fotografía: Pixabay

 

El pH del suelo, el cual mide su acidez o alcalinidad, está asociado a muchas propiedades de los suelos como el equilibrio iónico, las comunidades microbianas, o los contenidos en materia orgánica. El pH del suelo regula también los procesos biogeoquímicos del suelo y genera efectos en cascada sobre la estructura y funciones de los ecosistemas terrestres.

La aforestación ha sido una herramienta ampliamente adoptada para incrementar la retención de carbono de los suelos y mejorar la preservación tanto del agua como del suelo. A pesar de ello, el efecto de la aforestación sobre el pH del suelo es todavía poco conocido.

Un nuevo estudio realizado por un equipo internacional de científicos y publicado en la revista Nature Communications, presenta los resultados de su investigación orientada a evaluar los cambios en el pH del suelo generados por la aforestación (establecimiento de bosques en lugares en los que desde hacía mucho tiempo no había ninguno). Esta evaluación se ha realizado mediante la toma de muestras emparejadas en 549 localidades aforestadas y 148 localidades de control del Norte de la China, teniendo en cuenta diferentes especies de árboles y a lo largo de un gradiente de pH del suelo.

Los autores han hallado una neutralización significativa del pH del suelo debida a la aforestación, de este modo, la aforestación disminuye el pH en suelos relativamente alcalinos e incrementa en suelos relativamente ácidos. El umbral del pH del suelo (TpH), el punto en el cual la aforestación cambia de incrementar a disminuir el pH del suelo, es específico de cada especie de árbol, con un rango que va de 5.5 (Pinus karaiensis) a 7.3 (Populus spp), y un promedio de 6.3.

El estudio permite una mejor comprensión de cómo la aforestación genera impactos en el pH del suelo a lo largo de un amplio rango de tipologías de suelo y de aforestaciones con diferentes especies de árboles. Esta comprensión es básica para poder desarrollar estrategias de mitigación del cambio climático y de planes de sostenibilidad ecológica.

“Nuestro estudio indica que la aforestación, con una apropiada selección de especies de árboles, tiene el potencial de mitigación de la acidificación del suelo causada por la deposición ácida”, comenta el Dr. Songbai Hong del Sino-French Institute for Earth System Science, Peking University.

“Nuestros resultados indican que la aforestación puede modificar el pH del suelo si las especies de árboles y el pH inicial están correctamente ajustados, lo que potencialmente puede mejorar además la fertilidad del suelo y promover la productividad del ecosistema”, comenta el Prof. Josep Peñuelas del CREAF-CSIC Barcelona.

Según los autores, son necesarios más estudios de campo para poder determinar cuáles son las mejores especies de árboles para la aforestación según las propiedades del suelo, la disponibilidad de agua, la idoneidad del clima, el ecosistema y los objetivos socioeconómicos.

Referencia: Hong, S., Piao, s., Chen, A., Liu, Y., Liu, L., Peng, S., Sardans, J., Sun, Y., Peñuelas, J., Zeng, H. 2017. Afforestation neutralizes soil pH. Nature Communications, (2018) 9:520. doi: 10.1038/s41467-018-02970-1.

Afforestation is a type of land use change project primarily designated for wood production, soil and water conservation, increasing carbon storage and mitigating climate change. This study shows that afforestation changes, moreover, soil pH, that is a key soil variable. Photo by: Pixabay

 

Soil pH, which measures the acidity or alkalinity of soils, is associated with many soil properties such as hydrolysis equilibrium of ions, microbial communities, and organic matter contents. Soil pH regulates soil biogeochemical processes and has cascading effects on terrestrial ecosystem structure and functions.

Afforestation has been widely adopted to increase terrestrial carbon sequestration and enhance water and soil preservation. However, the effect of afforestation on soil pH is still poorly understood and inconclusive.

In a new study in the journal Nature Communications scientists investigate the afforestation-caused soil pH changes with pairwise samplings from 549 afforested and 148 control plots in northern China, across different tree species and soil pH gradient.

Authors find significant soil pH neutralization by afforestation—afforestation lowers pH in relatively alkaline soils but raises pH in relatively acid soils. The soil pH thresholds (TpH), the point when afforestation changes from increasing to decreasing soil pH, are species-specific, ranging from 5.5 (Pinus koraiensis) to 7.3 (Populus spp.) with a mean of 6.3.

The study provides improved understandings on how afforestation impacts soil pH across a broad range of soil types and afforestation tree species, which is critical for developing climate change mitigation strategies and ecological sustainability plans.

“Our study indicates that afforestation has the potential to alleviate soil acidification caused by enhanced acidic deposition with the appropriate selection of tree species and thus could further increase ecosystem productivity and carbon sequestration”, said Dr. Songbai Hong from Sino-French Institute for Earth System Science, Peking University.

 

“Our findings indicate that afforestation can modify soil pH if tree species and initial pH are properly matched, which may potentially improve soil fertility and promote ecosystem productivity”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

According to the authors, further field studies are still needed to determine best tree species for afforestation according to soil properties, water availability and climate suitability, and designated ecosystem and socioeconomic goals.

Journal Reference: Hong, S., Piao, s., Chen, A., Liu, Y., Liu, L., Peng, S., Sardans, J., Sun, Y., Peñuelas, J., Zeng, H. 2017. Afforestation neutralizes soil pH. Nature Communications, (2018) 9:520. doi: 10.1038/s41467-018-02970-1.

 

Large herbivores are a major agent in ecosystems, influencing vegetation structure and carbon and nutrient flows (shattering woody vegetation and consuming large amounts of foliage). Despite the non-negligible ecological impacts of large herbivores, most of the current DGVMs, or land surface models that include a dynamic vegetation module, lack explicit representation of large herbivores and their interactions with vegetation.

During the last glacial period, the steppe-tundra ecosystem prevailed on the unglaciated northern lands, hosting a high diversity and density of megafaunal herbivores. The apparent discrepancy between the late Pleistocene dry and cold climates and the abundant herbivorous fossil fauna found in the mammoth steppe biome has provoked long-standing debates, termed as “productivity paradox” by some paleontologists.

In a new study in the journal Nature Ecology and -Evolution scientists, aiming to address the productivity paradox, incorporated a grazing module in the ORCHIDEE-MICT DGVM model. “This grazing module is based on physiological and demographic equations for wild large grazers, describing grass forage intake and metabolic rates dependent on body size, and demographic parameters describing the reproduction and mortality rates of large grazers”, explained Dr. Dan Zhu from the Laboratoire des Sciences du Climat et de l’Environnement, LSCE CEA CNRS UVSQ, France.

In the study authors also extended the modelling domain to the globe for two distinct periods, present-day and the last glacial maximum (ca. 21 ka BP). The present-day results of potential grazer biomass, combined with an empirical land use map, infer a reduction of wild grazer biomass by 79-93% due to anthropogenic land replacement over natural grasslands.

For the last glacial maximum, authors find that the larger mean body size of mammalian herbivores than today is the crucial clue to explain the productivity paradox, due to a more efficient exploitation of grass production by grazers with a larger-body size. Evidences from fossil and extant mammal species have shown a long-term trend towards increasing body size in mammals throughout the Cenozoic, this indicates selective advantages of larger body sizes, such as larger guts of herbivores that allow microbes to break down low-quality plant materials, and higher tolerance to coldness and starvation. “Our results show quantitatively the importance of body size to explain the productivity paradox, as a larger-body size enables grazers to live on the mammoth steppe in substantial densities during the LGM, despite colder temperatures and shorter growing seasons than today”, said Dr. Philippe Ciais from the Laboratoire des Sciences du Climat et de l’Environnement, LSCE CEA CNRS UVSQ, France.

For the authors large herbivores might have fundamentally modified Pleistocene ecosystems; therefore, “to bring them into large-scale land surface models would help us better understand the intricate interactions among climate, plants and animals that shaped the biosphere”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

Journal Reference: Zhu, D., CIiais, P., Chang, J., Krinner, G., Peng, S., Viovy, N., Peñuelas, J., Zimov, S. 2018. The large mean body size of mammalian herbivores explains the productivity paradox during the last glacial maximum. Nature Ecology & Evolution

_{This study presents a new approach to quantify ecosystem functioning at scales relevant for policy makers. Photo by Pixabay.}

 

Forests provide a number of functions related to key services such as timber production, climate regulation and recreation, and are important for the conservation of many plant and animal species. Thus humans require multiple services from ecosystems, but it is largely unknown whether trade-offs between ecosystem functions prevent the realisation of high ecosystem multifunctionality across spatial scales.

In a new study in the journal Ecology Letters scientists combined a comprehensive dataset (28 ecosystem functions measured on 209 forest plots) with a forest inventory dataset (105,316 plots) to extrapolate and map relationships between various ecosystem multifunctionality measures across Europe. These multifunctionality measures reflected different management objectives, related to key services (timber production, climate regulation and biodiversity conservation/recreation).

Authors found that different measures of forest multifunctionality tend not to tradeoff with each other, at both local and continental scales. “Within some areas there were strong synergies between different multifunctionality measures, indicating that even though they are currently uncommon, ‘win-win’ forest management strategies are possible and could be promoted in the future. “Using one of the most comprehensive assessments so far, our study therefore suggests a high but largely unrealised potential for management to promote multifunctional forests in Europe”, said Dr. van der Plas from Institute of Plant Sciences, University of Bern, Switzerland.

For the authors this study is a first step in reaching the ultimate goal of predicting how future ecosystem functioning and service provision will be altered by ongoing global trends, such as climate change), eutrophication and acidification or land-use change “Future studies could combine this approach with models on climate change, biodiversity change or management scenarios to investigate the impacts of these global trends for the future functioning and service provisioning of forests and other ecosystems”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

 

Journal Reference: van der Plas, F., Ratcliffe, S., Ruiz-Benito, P., Scherer-Lorenzen, M., Verheyen, K., Wirth, C., Zavala, M.A., Ampoorter, E., Baeten, L., Barbaro, L., Bastias, C.C., Bauhus, J., Benavides, R., Benneter, A., Bonal, D., Bouriaud, O., Bruelheide, H., Bussotti, F., Carnol, M., Castagneyrol, B., Charbonnier, Y., Cornelissen, J.C., Dahlgren, J., Checko, E., Coppi, A., Muhie Dawud, S., Deconchat, M., De Smedt, P., De Wandeler, H., Domisch, T., Finér, L., Fotelli, M., Gessler, A., Granier, A., Grossiord, C., Guyot, V., Haase, J., Hättenschwiler, S., Jactel, H., Jaroszewicz, B., Joly, F., Jucker, T., Kambach, S., Kaendler, G., Kattge, J., Koricheva, J., Kunstler, G., Lehtonen, A., Liebergesell, M., Manning, P., Milligan, H., Müller, S., Muys, B., Nguyen, D., Nock, C., Ohse, B., Paquette, A., Peñuelas, J., Pollastrini, M., Radoglou, K., Raulund-Rasmussen, K., Roger, F., Seidl, R., Selvi, F., Stenlid, J., Valladares, F., van Keer, J., Vesterdal, L., Fischer, M., Gamfeldt, L., Allan, E. 2018. Continental mapping of forest ecosystem functions reveals a high but unrealized potential for forest multifunctionality. Ecology Letters 21, Issue 1, 31–42, doi: 10.1111/ele.12868.

 

 

The 2015 climate summit in Paris galvanized global commitments to an ambitious yet vaguely defined goal of climate stabilization. The Paris Agreement is based on emission scenarios that move from a sluggish phase-out of fossil fuels to largescale late-century negative emissions. At the same time, some scientists argue that the model based scenarios with 1.5 °C and even 2 °C temperature change targets seem unattainable and detached from current political realities. Alternative pathways of early deployment of negative emission technologies need to be considered to ensure that climate targets are reached safely and sustainably

In a new study in the journal Nature Climate Change, authors scrutinize the dominant climate mitigation scenario archetype that projects low global decarbonization rates in the first half of this century followed by large negative emissions in the second half, thanks to carbon dioxide removal (CDR) technologies. Authors call this approach to mitigation the ‘Late- Century CDR’ scenario archetype.

This archetype is consistent with nearly all of 2 °C scenarios covered by the IPCC’s Fifth Assessment Report (AR5), 87% of which deploy CDR technologies in the second half of the century. The authors consider that, following this predominant archetype might not only turn out to be a risky strategy, but may lead to significant environmental damages and may also be economically inefficient. In Late-Century CDR scenarios, CDR mostly in the form of bioenergy with carbon capture and storage (BECCS) typically removes the equivalent of 20 years of current GHG emissions to reverse the temporary GHG budget overshoot that is tolerated earlier on. The authors point out that the challenges and uncertainties associated with CDR are well described in the scientific literature, yet the scientific and political debate addressing the consequences of large-scale and late deployment of CDR as a backstop strategy is only at an early stage.

Authors argue that a new set of scenarios needs to be generated and analysed to inform the policy process on robust timing of climate mitigation, with the aim of avoiding negative side effects. “Essentially, three attributes characterize such budget-constrained scenarios: the timing and magnitude of global peak net emissions and the speed of decline thereafter; the maximum amount of allowable deployment of biomass-based CDRs; and an admissible risk threshold associated with a temperature overshoot”, noted Prof. Obersteiner from the Ecosystems Services and Management Program, International Institute for Applied Systems Analysis (IIASA) Laxenburg, Austria.

The study concludes that the timing of mitigation actions, in particular of negative emission technologies, needs to be urgently revisited in the analyses of ambitious climate targets. They argue that considerations of both intergenerational equity and climate/environment safety motivate early and moderate — rather than extreme — deployment of negative emission technologies as well as a timely peak in net carbon emissions as early as 2020. As a consequence all of the near-term and mid-century net emission reduction, targets should be, according to the authors, reformulated to include targets of early action on CDR technology portfolios.

“Transforming the 570 million farms to be climate smart and incentivizing 1.6 billion people who economically depend on forests to become early movers in No Overshoot and Minimize CDR scenarios is a formidable global policy challenge. We call for a discourse on effective strategies, starting with more detailed global gap assessments of the archetypes, and then mainstreaming the gained insights into Nationally Determined Contributions and implementation plans”, said Prof. Josep Peñuelas from CREAF-CSIC Barcelona.

Journal Reference: Obersteiner, M., Bednar, J., Wagner, F., Gasser, T., Ciais, P., Forsell, N., Frank, S., Havlik, P., Valin, H., Janssens, I.A., Peñuelas, J., Schmidt-Traub, G. 2018. How to spend a dwindling greenhouse gas budget. Nature Climate Change 8, 7-10. doi: 10.1038/s41558-017-0045-1