Land-use practices (coppices and dehesas) and management intensity modulate responses of Holm oak growth to drought

Last decades increase in reported events of drought-induced tree mortality evidences how climate-change is transforming forest ecosystems all over the world. The parallel increase in human pressure over the land is also causing major changes in forest functioning but it remains unclear how these two driving forces interact between them. We combined tree-ring data with aboveground cover, leaf area index (LAI), soil variables, and the standardized precipitation evapotranspiration index (SPEI) as water availability indicator to disentangle the existence of linkages between contrasting Holm oak (Quercus ilex L. subsp. ballota [Desf.] Samp) land-use practices and its drought-induced decline and mortality. We selected ten sites covering different soil and climatic gradients, land-use practices (i.e., declining dehesas, DH; declining coppices, FRd; and healthy coppices, FRh), and tree vigour classes (i.e., living, affected, and dead trees) in Spain. DH sites presented lower tree coverage, soil water holding capacity and soil pH than coppice (FR) sites. Dead Holm oaks from DH sites were younger than living ones, whereas dead trees from FRd sites were smaller and showed lower growth rates than living ones. We also found that conservation of traditional land-use practices in FR sites, resulting in less understorey cover but more soil erosion (less nutrients and microbial biomass and more bare soil), may positively affect the growth plasticity and sensitivity to drought of Holm oak trees by alleviating inter-specific competition, but in detriment of vegetation cover and soil health. Further studies should evaluate whether what holds true for FRh sites regarding the maintenance of traditional land-use practices might also apply for healthy DH. In the face of drier and hotter scenarios, our results add robust evidences on how the modulation of the intensity of the traditional uses could be a useful tool to optimize ecosystem services in Mediterranean systems highly vulnerable to climate change. © 2020This research was funded by the Spanish Government projects VERONICA (CGL2013-527 42271-P) and IBERYCA (CGL2017-84723-P). Additionally, it was also supported by the Basque Government through the BERC 2018-2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation (MDM-2017-0714). Ana-Maria Hereş was financially supported by the projects NATIvE (PN-III-P1-1.1-PD-2016-0583) and REASONING (PN-III-P1-1.1-TE-2019-1099), both funded by the Romanian Ministry of National Education and by the Romanian Ministry of Research and Innovation through UEFISCDI ( link ). A. Gazol acknowledges funding by project RTI2018-096884-B-C31 (Spanish Ministry of Science). We thank Daniel García Angulo, Miguel Fernandez, David López Quiroga, Bárbara Carvalho, Matheus Lopes Souza, and Mario Díaz for their priceless support during the field campaigns and the laboratory work

The ecosystem carbon sink implications of mountain forest expansion into abandoned grazing land: The role of subsoil and climatic factors

Woody encroachment is a widespread phenomenon resulting from the abandonment of mountain agricultural and pastoral practices during the last century. As a result, forests have expanded, increasing biomass and necromass carbon (C) pools. However, the impact on soil organic carbon (SOC) is less clear. The main aim of this study was to investigate the effect of woody encroachment on SOC stocks and ecosystem C pools in six chronosequences located along the Italian peninsula, three in the Alps and three in the Apennines. Five stages along the chronosequences were identified in each site. Considering the topsoil (0 30 cm), subsoil (30 cm-bedrock) and whole soil profile, the temporal trend in SOC stocks was similar in all sites, with an initial increment and subsequent decrement in the intermediate phase. However, the final phase of the woody encroachment differed significantly between the Alps (mainly conifers) and the Apennines (broadleaf forests) sites, with a much more pronounced increment in the latter case. Compared to the previous pastures, after mature forest (>62 years old) establishment, SOC stocks increased by: 2.1(mean) ± 18.1(sd) and 50.1 ± 25.2 Mg C·ha -1 in the topsoil, 7.3 ± 17.4 and 93.2 ± 29.7 Mg C·ha -1 in the subsoil, and 9.4 ± 24.4 and 143.3 ± 51.0 Mg C·ha -1 in the whole soil profile in Alps and Apennines, respectively. Changes in SOC stocks increased with mean annual air temperature and average minimum winter temperature, and were negatively correlated with the sum of summer precipitation. At the same time, all other C pools (biomass and necromass) increased by 179.1 ± 51.3 and 304.2 ± 67.6 Mg C·ha -1 in the Alps and the Apennines sites, respectively. This study highlights the importance of considering both the subsoil, since deep soil layers contributed 38% to the observed variations in carbon stocks after land use change, and the possible repercussions for the carbon balance of large areas where forests are expanding, especially under pressing global warming scenarios. © 2019 Elsevier B.V.The project of this work is part of the research activities of the PhD in science, technology and biotechnology for sustainability. The first author received a fully founded scholarship partially by the University of Tuscia (Viterbo - Italy) and partially by the University of Molise . Tommaso Chiti participated in the project by conducting his work with the funding obtained through the LIFE MediNet project (grant number LIFE15 PRE IT/732295 ). Jorge Curiel Yuste was financed in part by the Basque Government through the BERC 2018-2021 (grant code) program and by Spanish Ministry of Economy and Competitiveness (MINECO) through BC3 María de Maeztu excellence accreditation MDM-2017-0714. I.C (grant code)

Spatial variability of soil respiration (R<inf>s</inf>) and its controls are subjected to strong seasonality in an even-aged European beech (Fagus sylvatica L.) stand

Uncertainties arising from the so-far poorly explained spatial variability of soil respiration (Rs) remain large. This is partly due to the limited understanding about how spatially variable Rs actually is, but also on how environmental controls determine Rs's spatial variability and how these controls vary in time (e.g., seasonally). Our study was designed to look more deeply into the complexity of Rs's spatial variability in a European beech even-aged stand, covering both phenologically and climatically contrasting periods (spring, summer, autumn and winter). Although we studied a relatively homogeneous stand, we found a large spatial variability of Rs (coefficients of variation &gt; 30%) characterized by strong seasonality. This large spatial variability of Rs suggests that even in relatively homogeneous stands there is a large potential source of error when estimating Rs. This was also reflected by the sampling effort needed to obtain seasonally robust estimates of Rs, which may actually require a number of samples above that used in Rs studies. We further postulate that the effect of seasonality on the spatial variability and environmental controls of Rs was determined by the seasonal shifts of its microclimatic controls: during winter, low temperatures constrain plant and soil metabolic activities and hence reduce Rs variability (temperature-controlled processes), whereas during summer, water demand by vegetation and changes in water availability due to the microtopography of the terrain (i.e., slope) increase Rs variability (water-controlled processes). This study provides novel information on the spatiotemporal variability of Rs and looks more deeply into the seasonality of its environmental controls and the architecture of their causal-effect relationships controlling Rs's spatial variability. Our study further shows that improving current estimates of Rs at local and regional levels might be necessary in order to reduce uncertainties and improve CO2 estimates at larger spatial scales. Highlights: The spatial variability of soil respiration (Rs) and its environmental controls vary seasonally. Seasonal shifts from temperature- to water-controlled processes determine Rs's spatial variability. Besides microclimate, slope and grass cover explain the spatiotemporal variability of Rs. An intense sampling effort is needed to obtain robust Rs estimates even in homogeneous forests. © 2021 British Society of Soil Science.This research was supported by the Forest GHG Management (PN‐II‐ID‐PCE‐2011‐3‐0781), TREEMORIS (PN‐II‐RU‐TE‐2014‐4‐0791), BIOCARB (PN‐III‐P1‐1.1‐TE‐2016‐1508), NATIvE (PN‐III‐P1‐1.1‐PD‐2016‐0583) and REASONING (PN‐III‐P1‐1.1‐TE‐2019‐1099) projects, all financed by the Romanian Ministry of Education and Research through UEFISCDI ( link ). This research was also supported by the IBERYCA (CGL2017‐84723‐P) project and by the BC3 María de Maeztu excellence accreditation 2018‐2022 (Ref. MDM‐2017‐0714), both financed by the Spanish Ministry of Science, Innovation and Universities. The Basque Government also supported this research through the BERC 2018‐2021 programme

Radiocarbon dating reveals different past managements of adjacent forest soils in the Campine region, Belgium

The soils of adjacent first generation monospecific stands of Scots pine (Pinus sylvestris L.) and pedunculate oak (Quercus robur L.) in the Campine region, Belgium, apparently developed under the same forming factors, were studied for carbon dynamics to disentangle eventual different past land uses. In fact, visual observations suggested that the soil under pine experienced substantial addition of organic matter and ploughing, such to be considered a plaggen, opposite to the soil under oak, which is inexplicably much poorer in C. In order to prove this hypothesis, the soil organic carbon was quantified by horizons and, both bulk soil organic matter (SOM) and the least mobile SOM fractions - the humic acid and the unextractable fractions - were radiocarbon dated. Surprising was the marked difference between the mean SOM age from the two stands. In fact, while under oak this age is a few years or decades, under pine it amounts to more than a millennium, so confirming the hypothesis of a confined C supply occurred mainly in the Middle Age, or later using partly humified matter. The mean residence time (MRT) of SOM in the organic layers matches almost perfectly with that estimated via a mass balance approach and, as expected, was much lower in the oaks than in the pines. The humic acid fraction, generally the most stable fraction of SOM, in terms of both mobility and degradability, reflects the behaviour of the bulk SOM, showing higher radiocarbon ages under pine. The findings of this work indicate that the large human-induced additions of organic material in the area now occupied by the pine stand, probably occurred in the Middle Age and it continues to strongly affect the present soil C pools and their dynamics. Any study dealing with budgets and dynamics of C in soil should avail itself of a careful reconstruction of the land uses and management history, in order to provide reliable conclusions about the real role of the current vegetation on soil carbon. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved

Tree vigour influences secondary growth but not responsiveness to climatic variability in Holm oak

Many tree species from Mediterranean regions have started to show increased rates of crown defoliation, reduced groth, and dieback associated with the increase in temperatures and changes in the frequency and intensity of drought events experienced during the last decades. In this regard, Quercus ilex L. subsp. ballota (Desf.) (Holm oak), despite being a drought-tolerant species widely distributed in the Mediterranean basin, it has recently started to show acute signs of decline, extended areas from Spain being affected. However, few studies have assessed the role of climatic variability (i.e., temperature, precipitation, and drought) on the decline and resilience of Holm oak. Here, we measured secondary growth of seventy Holm oaks from a coppice stand located in central Spain. Sampled trees had different stages of decline, so they were classified into four vigour groups considering their crown foliar lost: healthy (0%), low defoliated (25%), highly defoliated (25 70%), and dying (70 100%). Our results showed that during the study period (1980 2009) the highly defoliated and dying Holm oaks grew significantly less than their healthy and low defoliated neighbours, suggesting permanent growth reduction in the less vigorous individuals. Despite these differences, all four vigour groups showed similar responses to climatic variations, especially during winter and late spring early summer seasons, and similar resilience after severe drought events, managing to significantly recover to pre-drought growth rates after only two years. Our findings, hence, illustrate that tree vigour influences secondary growth but not responsiveness to climatic variability in Holm oak. Still, as reduced growth rates are frequently associated with the process of tree mortality, we conclude that the less vigorous Holm oaks might not be able to cope with future water stress conditions, leading to increased mortality rates among this emblematic Mediterranean specie

Cascading effects associated with climate-change-induced conifer mortality in mountain temperate forests result in hot-spots of soil CO 2 emissions

Climate change-induced tree mortality is occurring worldwide, at increasingly larger scales and with increasing frequency. How climate change-induced tree mortality could affect the ecology and carbon (C) sink capacity of soils remains unknown. This study investigated regional-scale drought-induced tree mortality, based on events that occurred after a very dry year (2012) in the Carpathians mountain range (Romania), which caused mortality in three common conifer species: Scots pine, Black pine, and Silver fir. This resulted in hot-spots of biogenic soil CO 2 emissions (soil respiration; Rs). Four to five years after the main mortality event, Rs-related soil CO 2 emissions under dead trees were, on average, 21% (ranging from 18 to 35%) higher than CO 2 emissions under living trees. Total (Rs) and heterotrophic (R H )-related soil CO 2 emissions were strongly related to alterations in the soil environment following tree mortality (e.g. changes in quantity and quality of soil organic matter, microclimate, pH or fine root demography). Moreover, the massive mortality event of 2012 resulted in greater presence of successional vegetation (broadleaf seedlings, shrubland and grasses), which may control the environmental factors that either directly or indirectly affected biotic soil fluxes (Rs and R H ). Besides the well-known direct effects of climate change on soil CO 2 emissions, the cascading effects triggered by climate change-induced tree mortality could also exert a strong indirect impact on soil CO 2 emissions. Overall, climate change-induced tree mortality alters the magnitude of environmental controls on Rs and hence determines how the ecosystem C budget responds to climate change. © 2019 Elsevier LtdThis work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) with the projects VERONICA ( CGL2013-42271-P ) and the project IBERYCA ( CGL2017-84723-P ), and by the Romanian Ministry of Education and Scientific Research through UEFISCDI with the projects TREEMORIS ( PN-II-RU-TE-2014-4-0791 ), NATIvE ( PN-III-P1-1.1-PD-2016-0583 ), and BIOCARB ( PN-III-P1-1.1-TE-2016-1508 ). This research was also supported by the Basque Government through the BERC 2018-2021 program, and by the Spanish Ministry of Economy and Competitiveness (MINECO) through the BC3 María de Maeztu excellence accreditation ( MDM-2017-0714 ). I.C. Petritan was partially funded by the H2020/ERA-NET/ERA-GAS (Project 82/2017, Mobilizing and monitoring climate positive efforts in forests and forestry, FORCLIMIT ). Many thanks to Cosmin Zgremtia, Ionela Medrea, Andrei Apafaian, Raluca Enescu and Marta Ramos for their valuable help during field campaigns and laboratory work

Dry deposition of air pollutants on trees at regional scale: A case study in the Basque Country

There is increased interest in the role of trees to reduce air pollution and thereby improve human health and well-being. This study determined the removal of air pollutants by dry deposition of trees across the Basque Country and estimated its annual economic value. A model that calculates the hourly dry deposition of NO2, O3, SO2, CO and PM10 on trees at a 1 km x 1 km resolution at a regional scale was developed. The calculated mean annual rates of removal of air pollution across various land uses were 12.9 kg O3 ha-1, 12.7 kg PM10 ha-1, 3.0 kg NO2 ha-1, 0.8 kg SO2 ha-1 and 0.2 kg CO ha-1. The results were then categorised according to land use in order to determine how much each land use category contributed to reducing air pollution and to determine to what extent trees provided pollution reduction benefits to society. Despite not being located in the areas of highest pollutions, coniferous forests, which cover 25% of the land, were calculated to absorb 21% of the air pollution. Compared to other land uses, coniferous forests were particularly effective in removing air pollution because of their high tree cover density and the duration of leaf life-span. The total economic value provided by the trees in reducing these pollutants in terms of health benefits was estimated to be 60 million yr-1 which represented around 0.09% of the Gross Domestic Product of the Basque Country in 2016. Whilst most health impacts from air pollution are in urban areas the results indicate that most air pollution is removed in rural areas. © 2019 Elsevier B.V.Silvestre García de Jalón, Jorge Curiel Yuste and Aline Chiabai acknowledge support from the Basque Government through the BERC 2018-2021 program and from the Spanish Ministry of Science, Innovation and Universities through the BC3 María de Maeztu excellence accreditation ( MDM-2017-0714

Looking deeper into the soil : biophysical controls and seasonal lags of soil CO2 production and efflux

Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 20 (2010): 1569–1582, doi:10.1890/09-0693.1.We seek to understand how biophysical factors such as soil temperature (Ts), soil moisture (θ), and gross primary production (GPP) influence CO2 fluxes across terrestrial ecosystems. Recent advancements in automated measurements and remote-sensing approaches have provided time series in which lags and relationships among variables can be explored. The purpose of this study is to present new applications of continuous measurements of soil CO2 efflux (F0) and soil CO2 concentrations measurements. Here we explore how variation in Ts, θ, and GPP (derived from NASA's moderate-resolution imaging spectroradiometer [MODIS]) influence F0 and soil CO2 production (Ps). We focused on seasonal variation and used continuous measurements at a daily timescale across four vegetation types at 13 study sites to quantify: (1) differences in seasonal lags between soil CO2 fluxes and Ts, θ, and GPP and (2) interactions and relationships between CO2 fluxes with Ts, θ, and GPP. Mean annual Ts did not explain annual F0 and Ps among vegetation types, but GPP explained 73% and 30% of the variation, respectively. We found evidence that lags between soil CO2 fluxes and Ts or GPP provide insights into the role of plant phenology and information relevant about possible timing of controls of autotrophic and heterotrophic processes. The influences of biophysical factors that regulate daily F0 and Ps are different among vegetation types, but GPP is a dominant variable for explaining soil CO2 fluxes. The emergence of long-term automated soil CO2 flux measurement networks provides a unique opportunity for extended investigations into F0 and Ps processes in the near future.Data collection was possible thanks to NASA, the NSF Center for Embedded Networked Sensing (CCR-0120778), DOE (DE-FG02-03ER63638), CONACyT, UCMEXUS, NSF (EF-0410408), NSF-LTER, KAKENHI (12878089 and 13480150), the Academy of Finland (213093), the Austrian Science Fund (FWF, P18756-B16), the Kearney Foundation, the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), and the Natural Science and Engineering Research Council of Canada (NSERC). R. Vargas was supported by grant DEB-0639235 during the preparation of this manuscript

Legacies of past forest management determine current responses to severe drought events of conifer species in the Romanian Carpathians

Worldwide increases in droughts- and heat-waves-associated tree mortality events are destabilizing the future of many forests and the ecosystem services they provide. Along with climate, understanding the impact of the legacies of past forest management is key to better explain current responses of different tree species to climate change. We studied tree mortality events that peaked in 2012 affecting one native (silver fir; growing within its natural distribution range) and two introduced (black pine and Scots; growing outside their natural distribution range) conifer species from the Romanian Carpathians. The three conifers were compared in terms of mortality events, growth trends, growth resilience to severe drought events, climate-growth relationships, and regeneration patterns. The mortality rates of the three species were found to be associated with severe drought events. Nevertheless, the native silver fir seems to undergo a self-thinning process, while the future of the remaining living black pine and Scots pine trees is uncertain as they register significant negative growth trends. Overall, the native silver fir showed a higher resilience to severe drought events than the two introduced pine species. Furthermore, and unlike the native silver fir, black pine and Scots pine species do not successfully regenerate. A high diversity of native broadleaf species sprouts and develops instead under them suggesting that we might be witnessing a process of ecological succession, with broadleaves recovering their habitats. As native species seem to perform better in terms of resilience and regeneration than introduced species, the overall effect of the black pine and Scots pine mortality might be compensated. Legacies of past forest management should be taken into account in order to better understand current responses of different tree species to ongoing climate change. © 2020 Elsevier B.V.We thank the Forest District staff of Sacele, Kronstadt, Rasnov, Teliu, Codlea, and Intorsura Buzaului for all their support and for giving us access to the Forest Management Plans. This work was financed by the NATIvE ( PN-III-P1-1.1-PD-2016-0583 ) and TreeMoris ( PN-II-RU-TE-2014-4-0791 ) projects through UEFISCDI (link; Romanian Ministry of Education and Research ) and supported by the BERC 2018-2021 ( Basque Government ), and BC3 María de Maeztu Excellence Accreditation 2018-2022, Ref. MDM-2017-0714 ( Spanish Ministry of Science, Innovation and Universities ). We also thank Antonio Gazol for interesting discussions on the study and Ionela-Mirela Medrea, Andrei Apafaian, Maria Băluţ, and Florin Dinulică for assistance during field and laboratory campaigns. Silver fir, black pine, and Scots pine figures included in the graphical abstract are reproduced with the authorization of the designer Luiza Anamaria Pop (©2020) who drew the three conifer species and processed the drawings in Adobe Illustrator® CS5 (v. 15.0.0)

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. © Copyright © 2021 Lasso, Matheus-Arbeláez, Gallery, Garzón-López, Cruz, Leon-Garcia, Aragón, Ayarza-Páez and Curiel Yuste.Special thanks to David Campos, Fabian Salgado, Luis Fernando Rojas, Ewen Dano, Jorge Acosta, Juliana Portilla, and Michelle Guevara that helped with field and lab work. We would like to thank the Sabogal family for allowing the establishment of the OTC and collection of samples in the p?ramo ?Parque Ecol?gico Matarredonda? and to the Lieutenant Colonel Edgar Riveira, Commander of the High Mountain Battalion No. 1 in Sumapaz and all the commanders that follow him and who provided us with accommodation and food in the battalion as well as logistic support in all our field campaigns. Thanks to all the soldiers who always enthusiastically helped us in the field work in Sumapaz. This research was also supported by the Basque Government through the BERC 2018?2021 program, and by the Spanish Ministry of Science, Innovation and Universities through the BC3 Mar?a de Maeztu excellence accreditation (MDM-2017-0714). Funding. Funding for this research comes from the ?Patrimonio Aut?nomo Fondo Nacional de Financiamiento para la Ciencia, la Tecnolog?a y la Innovaci?n Francisco Jos? de Caldas?Colciencias,? grant number 120471451294, granted by Colciencias (today?s Colombian Ministry of Science, Technology and Innovation), from Eloisa Lasso?s FAPA (Fondo de Apoyo para Profesores Asistentes) grant number P12.160422.001 from the Universidad de los Andes, and from the Research Fund to support faculty programs at the Faculty of Sciences at the Universidad de los Andes grant number INV-2019-84-1805