Biogeographic, atmospheric, and climatic factors influencing tree growth in Mediterranean Aleppo pine forests

There is a lack of knowledge on how tree species respond to climatic constraintslike water shortages and related atmospheric patterns across broad spatial and temporal scales.These assessments are needed to project which populations will better tolerate or respond to globalwarming across the tree species distribution range. Warmer and drier conditions have been forecastedfor the Mediterranean Basin, where Aleppo pine (Pinus halepensisMill.) is the most widely distributedconifer in dry sites. This species shows plastic growth responses to climate, being particularly sensitiveto drought. We evaluated how 32 Aleppo pine forests responded to climate during the second half ofthe 20th century by using dendrochronology. Climatic constraints of radial growth were inferred byfitting the Vaganov-Shashkin (VS-Lite) growth model to ring-width data from our Aleppo pine forestnetwork. Our findings reported that Aleppo pine growth decreased and showed the highest commoncoherence among trees in dry, continental sites located in southeastern and eastern inland Spain andAlgeria. In contrast, growth increased in wetter sites located in northeastern Spain. Overall, across theAleppo pine network tree growth was enhanced by prior wet winters and cool and wet springs,whilst warm summers were associated with less growth. The relationships between site ring-widthchronologies were higher in nearby forests. This explains why Aleppo pine growth was distinctlylinked to indices of atmospheric circulation patterns depending on the geographical location of theforests. The western forests were more influenced by moisture and temperature conditions drivenby the Western Mediterranean Oscillation (WeMO) and the Northern Atlantic Oscillation (NAO),the southern forests by the East Atlantic (EA) and the august NAO, while the Balearic, Tunisian andnortheastern sites by the Arctic Oscillation (AO) and the Scandinavian pattern (SCA). The climaticconstraints for Aleppo pine tree growth and its biogeographical variability were well captured by theVS-Lite model. The model performed better in dry and continental sites, showing strong growthcoherence between trees and climatic limitations of growth. Further research using similar broad-scaleapproaches to climate-growth relationships in drought-prone regions deserves more attention

Old World megadroughts and pluvials during the Common Era

Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability

Plasticity in dendroclimatic response across the distribution range of Aleppo pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.This work was partially supported by Spanish Ministry of Education and Science co-funded by FEDER program (CGL2012-31668), the European Union and the National Ministry of Education and Religion of Greece (EPEAEK- Environment – Archimedes), the Slovenian Research Agency (program P4-0015), and the USDA Forest Service. The cooperation among international partners was supported by the COST Action FP1106, STREeSS

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

Effects of coppice thinning on growth and yield of Emory oak sprouts in southeastern Arizona.

Emory oak (Quercus Emoryi) is a dominant tree species in San Rafael Valley in southeastern Arizona. However, basic information about the effects of coppice thinning on the growth and yield of this species is lacking. Thus, objectives of the study were to measure the effects of coppice thinning on Emory oak survivor growth, ingrowth, and mortality, which are the basic components of a growth budget. This study determined gross growth, net growth, and yield estimates. In addition, this study evaluated the mean annual growth (MAG) values in relation to the biological rotation age of Emory oak in southeastern Arizona. Coppice thinning treatments were applied to sprouts of different ages. Height and diameter at root collar measurements were taken immediately after thinning and again 5 years later. Sprouts were classified into 5 age groups, 4 stump diameters, and 3 level of coppice thinnings and an unthinned control. The interactions of these treatments and their effect on growth and yield were analyzed. Stump diameters did not significantly affect the growth components, growth estimates, or yield estimates. The number of residual sprouts significantly affected the growth components, growth estimates, and yield estimates. Survivor growth, gross growth, net growth, and yield were lowest for 1 residual sprout, except for net growth of 8-year-old sprouts. There were no significant differences in net growth between the different coppice thinning treatments. At age 8-year-old sprouts, the mean annual growth of individual sprouts increased as the number of residual sprouts per stump reduced. Based on this relationship, it is recommended that 1 residual sprout be left when thinning sprouts. Age of sprouts significantly affected growth. There was an increase in the mortality of the control sprouts in the 6th year. Based on those results, it is recommended that thinning be conducted in the 5th year of the sprout's growth. Proper timing of thinning can reduce the rotation age of Emory oak sprouts, if the rotation is based on achievement of a specified diameter. To draw firm conclusions about the effects of thinning on shortening the rotation age, the study measurement needs to be continued into the future

Fire History in Ponderosa Pine and Mixed-Conifer Forests of the Jemez Mountains, Northern New Mexico

A Final Report Submitted to the USDA Forest Service, Santa Fe National Forest and USDI National Park Service, Bandelier National MonumentWe reconstructed fire history in ponderosa pine and mixed-conifer forests across the Jemez Mountains in northern New Mexico. We collected the fire-scarred samples from nine ponderosa pine areas and four mesic mixed-conifer areas. An additional collection was obtained from a bristlecone pine stand in the Sangre de Cristo Mountains. We also reconstructed December-June precipitation from ponderosa pine tree-ring indices that were developed from four different watersheds in northern New Mexico. Prior to 1900, ponderosa pine forests were characterized by high frequency, low intensity surface fire regimes. The mixed-conifer stands sustained somewhat less frequent surface fires, along with patchy crown fires. In both ponderosa pine and mixed-conifer forests precipitation was significantly reduced in the winter-spring seasons preceding fire events. In addition, winter-spring precipitation during the third year preceding major fire years in the ponderosa pine forest was significantly increased. This study provides baseline knowledge concerning the ecological role of fire in ponderosa pine and mixed-conifer forests. This information is vital to support ongoing ecosystem management efforts in the Jemez Mountains.This item is part of the Natural History Reports collection. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about items in this collection, please contact the Lab's Curator, (520) 621-1608 or see http://ltrr.arizona.edu/collection

Role of Dendroclimatology in Water Sustainability in Semi-Arid Regions

From the Proceedings of the 2009 Meetings of the Hydrology Section - Arizona-Nevada Academy of Science - April 4, 2009, University of Arizona, Tucson, ArizonaThis article is part of the Hydrology and Water Resources in Arizona and the Southwest collections. Digital access to this material is made possible by the Arizona-Nevada Academy of Science and the University of Arizona Libraries. For more information about items in this collection, contact [email protected]

Direct Versus Indirect Tree Ring Reconstruction of Annual Discharge of Chemora River, Algeria

Annual river discharge is a critical variable for water resources planning and management. Tree rings are widely used to reconstruct annual discharge, but errors can be large when tree growth fails to respond commensurately to hydrologically important seasonal components of climate. This paper contrasts direct and indirect reconstruction as statistical approaches to discharge reconstruction for the Chemora River, in semi-arid northeastern Algeria, and explores indirect reconstruction as a diagnostic tool in reconstruction error analysis. We define direct reconstruction as predictions from regression of annual discharge on tree ring data, and indirect reconstruction as predictions from a four-stage process: (1) regression of precipitation on tree rings, (2) application of the regression model to get reconstructed precipitation for grid cells over the basin, (3) routing of reconstructed precipitation through a climatological water balance (WB) model, and (4) summing model runoff over cells to get the reconstructed discharge at a gage location. For comparative purposes, the potential predictors in both modeling approaches are the same principal components of tree ring width chronologies from a network of drought-sensitive sites ofPinus halepensisandCedrus atlanticain northern Algeria. Results suggest that both modeling approaches can yield statistically significant reconstructions for the Chemora River. Greater accuracy and simplicity of the direct method are countered by conceptual physical advantages of the indirect method. The WB modeling inherent to the indirect method is useful as a diagnostic tool in error analysis of discharge reconstruction, points out the low and declining importance of snowmelt to the river discharge, and gives clues to the cause of severe underestimation of discharge in the outlier high-discharge year 1996. Results show that indirect reconstruction would benefit most in this basin from tree ring resolution of seasonal precipitation.Center for Hierarchical Manufacturing, National Science FoundationOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]