Hudson A.R., Alfaro-Sanchez R., Babst F., Belmecheri S., Moore D.J.P., Trouet V. (2019) Seasonal and synoptic climatic drivers of tree growth in the Bighorn Mountains, WY, USA (1654–1983 CE). Dendrochronologia. 58: 0-0.EnlaceDoi: 10.1016/j.dendro.2019.125633
In the United States’ (US) Northern Rockies, synoptic pressure systems and atmospheric circulation drive interannual variation in seasonal temperature and precipitation. The radial growth of high-elevation trees in this semi-arid region captures this temperature and precipitation variability and provides long time series to contextualize instrumental-era variability in synoptic-scale climate patterns. Such variability in climate patterns can trigger extreme climate events, such as droughts, floods, and forest fires, which have a damaging impact on human and natural systems. We developed 11 tree-ring width (TRW) chronologies from multiple species and sites to investigate the seasonal climatic drivers of tree growth in the Bighorn Mountains, WY. A principal component analysis of the chronologies identified 54% of shared common variance (1894–2014). Tree growth (expressed by PC1) was driven by multiple seasonal climate variables: previous October and current July temperatures, as well as previous December and current April precipitation, had a positive influence on growth, whereas growth was limited by July precipitation. These seasonal growth-climate relationships corresponded to circulation patterns at higher atmospheric levels over the Bighorn Mountains. Tree growth was enhanced when the winter jet stream was in a northward position, which led to warmer winters, and when the spring jet stream was further south, which led to wetter springs. The second principal component, explaining 19% of the variance, clustered sites by elevation and was strongly related to summer temperature. We leverage this summer temperature signal in our TRW chronologies by combining it with an existing maximum latewood density (MXD) chronology in a nested approach. This allowed us to reconstruct Bighorn Mountains summer (June, July, and August) temperature (BMST) back to 1654, thus extending the instrumental temperature record by 250 years. Our BMST reconstruction explains 39–53% of the variance in regional summer temperature variability. The 1830s were the relatively coolest decade and the 1930s were the warmest decade over the reconstructed period (1654–1983 CE) – which excludes the most recent 3 decades. Our results contextualize recent drivers and trends of climate variability in the US Northern Rockies, which contributes to the information that managers of human and natural systems need in order to prepare for potential future variability. © 2019 Elsevier GmbH
Lucas-Borja M.E., Plaza-Álvarez P.A., Gonzalez-Romero J., Sagra J., Alfaro-Sánchez R., Zema D.A., Moya D., de las Heras J. (2019) Short-term effects of prescribed burning in Mediterranean pine plantations on surface runoff, soil erosion and water quality of runoff. Science of the Total Environment. 674: 615-622.EnlaceDoi: 10.1016/j.scitotenv.2019.04.114
Fires are a complex phenomenon that may generate a chain of responses and processes that affect each part of the ecosystem. Thus, it is important to understand the magnitude of the impacts of fire on soil properties and the response of plants to this disturbance. For the moment, few studies have examined the effects of prescribed fire on large plots in afforested pine plantations in Mediterranean ecosystems. To fill this gap, the effects of a prescribed fire on runoff, soil erosion, and water quality for approximately one year after burning have been evaluated in pine plantations in south-eastern Spain. We constructed six erosion plots in the control area and six erosion plots in the burned area that were 4 m long and 2 m wide, immediately after the prescribed fire. Runoff, soil erosion and runoff water quality were studied after each rainy event in all plots. Our results reveal that prescribed fire did not significantly affect runoff and soil erosion when low intensity precipitations occur at pine plantations. In relation to water quality, water turbidity, salinity, pH, organic matter content and ionic substances concentrations increased immediately after prescribed burn, nevertheless these changes disappeared over time. We can conclude that prescribed fire can be a useful tool for fuel reduction in Mediterranean pine plantations without wide and long-term impacts to soil losses, or water quality. © 2019 Elsevier B.V.
Sagra J., Moya D., Plaza-Álvarez P.A., Lucas-Borja M.E., González-Romero J., De las Heras J., Alfaro-Sánchez R., Ferrandis P. (2019) Prescribed fire effects on early recruitment of Mediterranean pine species depend on fire exposure and seed provenance. Forest Ecology and Management. 441: 253-261.EnlaceDoi: 10.1016/j.foreco.2019.03.057
Prescribed fires are becoming more widely used forest management tool to reduce both fuel load for fire prevention and high-severity wildfires. However, alterations to site conditions and influence on the natural regeneration of these fires in Mediterranean pine forests are still poorly known. Our study investigates how using prescribed fires before or after natural pine seed release could influence changes in germination and individuals’ early survival by altering the composition and structure of these Mediterranean habitats. We ran a seed-sowing experiment to analyse the recruitment patterns of three Mediterranean pine species (Pinus halepensis, Pinus pinaster and Pinus nigra) in three sites where prescribed fires were carried out. In each site, we sowed one representative pine species according to natural habitats. Three treatments (control: sowing without intervention; pre-fire: sowing before prescribed fires; and post-fire: sowing after prescribed fires) were established. In the sown experiment, we tested two biogeographical seed provenances (wetter and drier regions) per species to observe different capabilities of adaptation. Germination and survival of individuals were monitored during one year. We observed that the provenances from drier areas had higher germination and survival rates than those from the wetter ones. The three species seemed to undergo a negative effect in the burned plots. Within the burned area, the pre-fire seeds presented higher germination and early survival rates than post-fire. These outcomes could be useful in fire management planning as a tool to influence forest regeneration. © 2019 Elsevier B.V.
Alfaro-Sánchez R., Nguyen H., Klesse S., Hudson A., Belmecheri S., Köse N., Diaz H.F., Monson R.K., Villalba R., Trouet V. (2018) Climatic and volcanic forcing of tropical belt northern boundary over the past 800 years. Nature Geoscience. 11: 933-938.EnlaceDoi: 10.1038/s41561-018-0242-1
The position of the northern boundary of the tropical belt affects the hydroclimate of many arid and semi-arid regions in the Northern Hemisphere. Widening of the tropical belt since the 1970s has largely been attributed to anthropogenic forcing. However, the relative influence of natural drivers of tropical belt expansion and contraction before this time is poorly understood. Here we use data on tree-ring widths from five mid-latitude regions in the Northern Hemisphere to reconstruct the movement of the northern boundary of the early spring tropical belt over the past 800 years (ad 1203–2003). Our reconstruction explains 45% of the interannual variance in the latitudinal extent of the Hadley circulation, a metric of the position of the tropical belt boundary. We find that the tropical belt contracted (expanded) during positive (negative) phases of the El Niño Southern Oscillation and Pacific North American teleconnection patterns. The tropical belt also contracted significantly following major volcanic events that injected sulfur into the stratosphere. The longest period of persistent tropical belt expansion occurred in the late sixteenth century, during one of the coldest periods of the Little Ice Age. Our results warn of potential socio-economic consequences of future variations in tropical belt width driven by natural climate variability or stratospheric aerosol injections, whether volcanic or artificial. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.
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