As the global climate warms, increased aridity is expected to become a major determinant of forest productivity and tree growth. In gymnosperms, wood density quantified at seasonal to annual scales can be related to changes in tracheid lumen size due to alterations in soil water availability. In this way, minimum wood density (MND) has been shown to respond negatively to early growing-season precipitation in several conifers because dry conditions reduce tracheid lumen size and consequently increase MND. We investigated if this relationship between spring precipitation and MND applies to four conifer species (Abies alba, Pinus sylvestris, Pinus nigra, Juniperus thurifera) in NE Spain from mesic (A. alba, P. sylvestris) to xeric (P. nigra, J. thurifera) conditions. We further assessed how climate, precipitation, and drought-affected tree-ring width (TRW) and MND at several time scales to test if water shortage in spring increases MND and decreases TRW over time and seasonally. Lastly, we quantified the post-drought MND recovery. We found the strongest negative correlations between MND and spring precipitation in P. nigra followed by J. thurifera. In these two species, the associations between MND and 9-month long droughts peaked in early spring (P. nigra, r=−0.73; J. thurifera, r=−0.50). Juniperus thurifera presented a better post-drought recovery (decrease in MND), followed by P. nigra and P. sylvestris. We conclude that MND is a reliable and accurate proxy of drought severity during spring in conifers subjected to seasonal water shortage. MND can be used as an early-warning indicator of short- and long-term changes in the responses of trees to water shortage. ; Spanish Ministry of Economy "Fundiver" project (CGL2015-69186-C2-1-R). FEDER Funds, Andalusia Regional Government, Consejería de Economía, Conocimento, Empresas y Universidad 2014–2020 (PinCaR project UHU-1266324).
Drought stress causes a reduction in tree growth and forest productivity, which could be aggravated by climate warming and defoliation due to moth outbreaks. We investigate how European gypsy moth (Lymantria dispar dispar L., Lepidoptera: Erebidae) outbreak and related climate conditions affected growth and wood features in host and non-host tree species in north-western Spain. There, radiata pine (Pinus radiata D. Don) plantations and chestnut (Castanea sativa Mill.) stands were defoliated by the moth larvae, whereas Maritime pine (Pinus pinaster Ait.) was not defoliated. The gypsy moth outbreak peaked in 2012 and 2013, and it was preceded by very warm spring conditions in 2011 and a dry-warm 2011-2012 winter. Using dendrochronology we compared growth responses to climate and defoliation of host species (radiata pine, chestnut) with the non-host species (Maritime pine). We also analyzed wood density derived from X-ray densitometry in defoliated and non-defoliated trees of radiata pine. We aimed to: (i) disentangle the relative effects of defoliation and climate stress on radial growth, and (ii) characterize defoliated trees of radiata pine according to their wood features (ring-width, maximum and minimum density). Radial growth during the outbreak (2012-2013) decreased on average 74% in defoliated (>50% of leaf area removed) trees of radiata pine, 43% in defoliated trees of chestnut, and 4% in non-defoliated trees of Maritime pine. After applying a BACI (Before-After-Control-Impact) type analysis, we concluded that the difference in the pattern of radial growth before and during the defoliation event was more likely due to the differences in climate between these two periods. Radiata pines produced abundant latewood intra-annual density fluctuations in 2006 and 2009 in response to wet summer conditions, suggesting a high climatic responsiveness. Minimum wood density was lower in defoliated than in non-defoliated trees of radiata pine prior to the outbreak, but increased during the outbreak. The pre-outbreak difference in minimum wood density suggests that the trees most affected by the outbreak produced tracheids with wider lumen and were more susceptible to drought stress. Results of this study illustrate (i) that the pattern of radial growth alone may be not a good indicator for reconstructing past defoliation events and (ii) that wood variables are reliable indicators for assessing the susceptibility of radiata pine to defoliation by the gypsy moth. ; Funding for this research was provided by the Local Government of Cubillos del Sil (Spain) through the contract Seguimiento y bases para la gestion de las masas forestales afectadas por defoliacion de Lymantria dispar en el municipio de Cubillos del Sil.
Understanding the vulnerability of individual trees to climate requires moving from population to individual level. This study evaluates individual tree response in a mixed forest by assessing how size and neighbourhood density modulated growth responses to climate among coexisting tree species. To understand the complete variation in growth responses to climate, it is necessary to consider intrapopulation variability. Trees respond as individual entities, and their response is modulated by their characteristics and neighbourhood context. To assess the individual climate sensitivity, all living Iberian birches, European beeches, and pedunculate oaks trees located in a temperate mixed forest were cored in four 40 m × 40 m plots. Standard ring-width chronologies were built at tree and species level for the 1977–2007 period. Chronologies were related to climatic variables (monthly precipitation, hailstorm and mean temperature, and summer (June–August) precipitation). Growth response to climate varied among species and individual trees. Differences in climate–growth relationship among species could be partially attributed to the different xylem anatomy, since secondary growth of ring-porous pedunculate oak ( Quercus robur L.) was mainly dependent on the previous-winter climatic conditions (January temperature), while for the diffuse-porous Iberian birch ( Betula celtiberica Rothm. and Vasc.) and European beech ( Fagus sylvatica L.), spring temperature and summer precipitation were the major constraining factors of growth. Tree features and identity of neighbourhood modulated climatic response, especially for Iberian birch and pedunculate oak. Dominant trees in less crowded neighbourhoods responded more intensely to climate factors. Understanding the individual variability of growth responses to climate will provide more realistic predictions of forests response to climate change. ; Special thanks to Silvia Martínez de Olcoz for assistance with the fieldwork and the measurements of the tree-rings. Urkiola Natural Park provided the facilities for field work. Urkiola Natural Park provided the facilities for field work and financial support. Additional financial support was provided by a Basque Government (Grupo de Investigacion Consolidado: Grupo Estudio en Flora, Vegetación y Ecosistemas Terrestres). Furthermore, this work has been supported by the projects CGL2012-34209 and CGL2015-69186-C2-1-R (Spanish Ministry of Economy and Competitivity) and by the Excellence Network "Ecometas" (CGL2014-53840-REDT).
16 páginas, 3 tablas, 4 figuras ; Windstorms are forest disturbances which generate canopy gaps. However, their effects on Mediterranean forests are understudied. To fill that research gap, changes in tree, cover, growth and soil features in Pinus halepensis and Pinus sylvestris plantations affected by windthrows were quantified. In each plantation, trees and soils in closed-canopy stands and gaps created by the windthrow were sampled. Changes in tree cover and radial growth were assessed by using the Normalized Difference Vegetation Index (NDVI) and dendrochronology, respectively. Soil features including texture, nutrients concentration and soil microbial community structure were also analyzed. Windthrows reduced tree cover and enhanced growth, particularly in the P. halepensis site, which was probably more severely impacted. Soil characteristics were also more altered by the windthrow in this site: the clay percentage increased in gaps, whereas K and Mg concentrations decreased. The biomass of Gram positive bacteria and actinomycetes increased in gaps, but the biomass of Gram negative bacteria and fungi decreased. Soil gaps became less fertile and dominated by bacteria after the windthrow in the P. halepensis site. We emphasize the relevance of considering post-disturbance time recovery and disturbance intensity to assess forest resilience within a multi-scale approach ; This research was funded by Ministerio de Ciencia y Tecnología, grant number RTI2018- 096884-B-C31, and Junta de Castilla y León, grant number CLU-2019-05 (co-financed by the European Union ERDF "Europe drives our growth"). ; Peer reviewed
Fungi provide important forest ecosystem services worldwide. In Mediterranean pine forests, predicted warmer and drier conditions could lead to a decline in mushroom yields. Climate is a key factor regulating both tree growth and fungal yields, particularly in drought-prone Mediterranean ecosystems. However, the responses of forest growth and mushroom production to climate depend on the differences among tree and fungal species and functional groups (e.g., mycorrhizal vs. saprotrophic), forest types, as well as depending on site conditions. Here we investigate how climatic conditions drive seasonal wood formation (earlywood −EW− and latewood −LW− production) and mycorrhizal mushroom production, to disentangle if growth and fungal yields are related. This assessment was done in Mediterranean forests dominated by four pine species in two areas located in Catalonia (NE Spain) representing mesic and xeric conditions and encompassing wide ecological gradients. The data consisted of 7-year to 13-year long inventories of mushroom production. EW production was favoured by cold and wet climate conditions during the previous fall and winter, and during the current spring and summer. LW production was enhanced by warm and humid conditions from spring to early fall. Mushroom yield was improved by wet late-summer and fall conditions, mainly in the most xeric area. This study confirms the ample differences found in tree growth and fungal production along ecological and climatic gradients. Clear relationships between mycorrhizal fungal yields and tree growth were mostly observed in specific sites characterized by severe summer drought. Specifically, latewood production seems to be the tree-ring variable most tightly linked to mycorrhizal fungal yield in drought-prone areas. ; This study was partially funded by the research projects AGL2012-40035-C03-01 and AGL2015-66001-C3-1-R (Ministerio de Economía y Competitividad of Spain, Secretaría de Estado de Investigación, Desarrollo e Innovación), by the European project 'StarTree—Multipurpose trees and non-wood forest products: a challenge and opportunity' under grant agreement No. 311919. Irantzu Primicia work was supported by a STSM Grant from the COST Action FP1203 (European Non-Wood Forest Products). Sergio de Miguel's work was supported by the European Union's Horizon 2020 research and innovation programme within the framework of the MultiFUNGtionality Marie Skłodowska-Curie Individual Fellowship (IF-EF) under grant agreement No 655815.
Density is an important wood mechanical property and an indicator of xylem architecture and hydraulic conductivity. It can be influenced by forest management and climate. We studied the impact of thinning and climate variables on annual stem radial growth (ring width and ring density, and their earlywood and latewood components) in two contrasting Scots pine ( Pinus sylvestris L.) stands in northern Spain (one continental, one Mediterranean). At each site, three thinning regimes (control or T0, removing 20% basal area or T20, and removing 30% or T30) were randomly applied to nine plots per site (three plots per treatment) in 1999. Thinning was repeated at the Mediterranean site in 2009 (increasing thinning intensity in T30 to 40%). Eight trees per plot were cored in spring 2014. Second thinning at the Mediterranean site and first thinning at the continental site generally caused significantly wider ring (RW), earlywood (EW) and latewood (LW) widths, although no differences between T20 and T30/40 were found, supporting in part the common observation that radial growth is enhanced following thinning as competition for water and nutrients is reduced. At the Mediterranean site, values of latewood density (LD) and maximum density (Dmax) relative to pre-thinning conditions were significantly lower in T0 than in T30. However, at the continental site, relative changes of ring density (RD) and LD were significantly higher in T0 than in T20 and T30. Climate significantly affected not only RW but also RD, with significant RD drops during or right after unusually warm-dry years (e.g., 2003, 2011), which were characterized by LD reductions between 5.4 and 8.0%. Such RD decreases were quickly followed by recovery of pre-drought density values. These results indicate trees temporarily reduce LD as a way to enhance hydraulic conductivity during dry summers. However, climate effects on wood density were site-dependent. We also detected that the thinning effect was not intense enough to prevent drought-induced changes in wood density by altering water availability, but it could help to reduce wood properties fluctuations and therefore maintain more homogeneous wood mechanic features. ; E.G.A. was funded through a Spanish Predoctoral Research Grant (ref. BES-2013-066705). Funding for this research has been provided by the Spanish Ministry of Economy and Competitiveness (project AGL2012-33465), which also funded Y.-H.L. J.A.B. was funded through a Ramón y Cajal contract (ref. RYC-2011-08082) and a Marie Curie Action (ref CIG-2012-326718-ECOPYREN3), which also funded D.C.-P. Funds to cover the costs of publishing in open access were provided by the OpenAIRE pilot program of the European Union 7th Framework Programme
Density is an important wood mechanical property and an indicator of xylem architecture and hydraulic conductivity. It can be influenced by forest management and climate. We studied the impact of thinning and climate variables on annual stem radial growth (ring width and ring density, and their earlywood and latewood components) in two contrasting Scots pine (Pinus sylvestris L.) stands in northern Spain (one continental, one Mediterranean). At each site, three thinning regimes (control or T0, removing 20% basal area or T20, and removing 30% or T30) were randomly applied to nine plots per site (three plots per treatment) in 1999. Thinning was repeated at the Mediterranean site in 2009 (increasing thinning intensity in T30 to 40%). Eight trees per plot were cored in spring 2014. Second thinning at the Mediterranean site and first thinning at the continental site generally caused significantly wider ring (RW), earlywood (EW) and latewood (LW) widths, although no differences between T20 and T30/40 were found, supporting in part the common observation that radial growth is enhanced following thinning as competition for water and nutrients is reduced. At the Mediterranean site, values of latewood density (LD) and maximum density (Dmax) relative to pre-thinning conditions were significantly lower in T0 than in T30. However, at the continental site, relative changes of ring density (RD) and LD were significantly higher in T0 than in T20 and T30. Climate significantly affected not only RWbut also RD, with significant RD drops during or right after unusually warm-dry years (e.g., 2003, 2011), which were characterized by LD reductions between 5.4 and 8.0%. Such RD decreases were quickly followed by recovery of pre-drought density values. These results indicate trees temporarily reduce LD as a way to enhance hydraulic conductivity during dry summers. However, climate effects on wood density were site-dependent. We also detected that the thinning effect was not intense enough to prevent drought-induced changes in wood density by altering water availability, but it could help to reduce wood properties fluctuations and therefore maintain more homogeneous wood mechanic features. ; E.G.A. was funded through a Spanish Predoctoral Research Grant (ref. BES-2013-066705). Funding for this research has been provided by the Spanish Ministry of Economy and Competitiveness (project AGL2012-33465), which also funded Y.-H.L. J.A.B. was funded through a Ramón y Cajal contract (ref. RYC-2011-08082) and a Marie Curie Action (ref CIG-2012-326718-ECOPYREN3), which also funded D.C.-P. Funds to cover the costs of publishing in open access were provided by the OpenAIRE pilot program of the European Union 7th Framework Programme.
40 Pags., 11 Figs., 3 Tabls. The definitive version is available at: http://journals.ametsoc.org/loi/eint ; In this study, the authors provide a global assessment of the performance of different drought indices for monitoring drought impacts on several hydrological, agricultural, and ecological response variables. For this purpose, they compare the performance of several drought indices [the standardized precipitation index (SPI); four versions of the Palmer drought severity index (PDSI); and the standardized precipitation evapotranspiration index (SPEI)] to predict changes in streamflow, soil moisture, forest growth, and crop yield. The authors found a superior capability of the SPEI and the SPI drought indices, which are calculated on different time scales than the Palmer indices to capture the drought impacts on the aforementioned hydrological, agricultural, and ecological variables. They detected small differences in the comparative performance of the SPI and the SPEI indices, but the SPEI was the drought index that best captured the responses of the assessed variables to drought in summer, the season in which more drought-related impacts are recorded and in which drought monitoring is critical. Hence, the SPEI shows improved capability to identify drought impacts as compared with the SPI. In conclusion, it seems reasonable to recommend the use of the SPEI if the responses of the variables of interest to drought are not known a priori. ; This work has been supported by the research projects CGL2008-01189/BTE, CGL2011-27574-CO2-02, CGL2011–24185, CGL2011-26654 and CGL2011-27536 financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, "Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés" financed by "Obra Social La Caixa" and the Aragón Government and "Influencia del cambio climático en el turismo de nieve" (CTTP01/10) financed by the Comisión de Trabajo de los Pirineos. JJC acknowledges the support of ARAID. ; Peer reviewed
