We investigated the tree growth and physiological response of five pine forest stands in relation to changes in atmospheric CO 2 concentration (c a ) and climate in the Iberian Peninsula using annually resolved width and d 13 C treering chronologies since AD 1600. 13 C discrimination (D % c i /c a ), leaf intercellular CO 2 concentration (c i ) and intrinsic water-use efficiency (iWUE) were inferred from d 13 C values. The most pronounced changes were observed during the second half of the 20th century, and differed between stands. Three sites kept a constant c i /c a ratio, leading to significant c i and iWUE increases (active response to c a ); whereas a significant increase in c i /c a resulted in the lowest iWUE increase of all stands at a relict Pinus uncinata forest site (passive response to c a ). A significant decrease in c i /c a led to the greatest iWUE improvement at the northwestern site. We tested the climatic signal strength registered in the d 13 C series after removing the low-frequency trends due to the physiological responses to increasing c a . We found stronger correlations with temperature during the growing season, demonstrating that the physiological response to c a changes modulated d 13 C and masked the climate signal. Since 1970 higher d 13 C values revealed iWUE improvements at all the sites exceeding values expected by an active response to the c a increase alone. These patterns were related to upward trends in temperatures, indicating that other factors are reinforcing stomatal closure in these forests. Narrower rings during the second half of the 20th century than in previous centuries were observed at four sites and after 1970 at all sites, providing no evidence for a possible CO 2 'fertilization' effect on growth. The iWUE improvements found for all the forests, reflecting both a c a rise and warmer conditions, seem to be insufficient to compensate for the negative effects of the increasing water limitation on growth.

Long-term data on radial increment dynamics in Mediterranean species may identify which climatic variables are the main constraints for radial growth and at which temporal scales they act. To this end, we examined stem radial fluctuations in Quercus ilex L., the dominant evergreen oak species in the Western Mediterranean Basin, over a period of 11 years (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004) at a coastal site in north-eastern Spain. We used manual band dendrometers to record girth changes in trees on north-and south-facing slopes. Annual increments measured by dendrometers showed good agreement with annual tree-ring width. North-facing trees showed a lower long-term cumulative radial increment than south-facing trees. The seasonal radial increment pattern of Q. ilex was bimodal, being characterized by a greater increase in May and a lesser, more variable increase peak in September. Both phases corresponded to warm and moist climatic conditions, whereas radial increase of stems stopped in winter and occasionally in summer. Considering the whole year, mean maximum air temperature was the main factor positively affecting radial increment of Q. ilex from short-(5 days) to-long (30 days) time scales, whereas the accumulated precipitation exerted a similar effect at longer (30 days) scales, but only on south-facing trees. In summer, all trees were positively correlated with precipitation at long-time scales (30 days); however, only stem increment of southfacing trees showed a significant relation to the temperature at short-time scales (10 days). We confirmed the dominant role of temperature as the major constraint on radial increment at short time scales, despite most previous studies were mostly biased towards precipitation effects at monthly scales.

Abstract.A regional study of snow avalanche processes was undertaken in the SE Pyrenees. Dendrogeomorphology was used to date and reconstruct large-scale snow avalanche events that occurred in the last four decades. Dendrochronological analyses yielded the dates of nine winters when avalanches occurred in the recent past in six studied avalanche paths. Some of these avalanches were already known, but others had not been documented. In one case, the existing avalanche path map was improved with the dendrogeomorphological information of a larger past event. As a result of the dendrogeomorphological analyses, evidence for three regional-scale major avalanche years was identified in the SE

ABSTRACT. Historical data about ancient avalanches are scarce in the Pyrenees.Dendrochronology can provide new data about past avalanches and their return period, but up to now little research has been carried out with this purpose. The Aludex project aims to obtain information about the frequency and extent of extreme avalanches, using a dendrochronological and a nivo-meteorological approach. In this paper, we present the results of a dendrochronological study of the Canal del Roc Roig avalanche path which was affected by two extreme avalanches in February 1996. This first dendrochronological study has permitted us to assess the tree-ring signals due to avalanche events in 53 out of 132 dated trees. The trees presented a variety of responses to the 1996 avalanche events. It is shown that the type of tree-ring signal depends on tree age. The methodology has proved successful in detecting the 1996 and 1972 documented avalanche events, and provided outstanding evidence of undocumented past events such as one in 1930.

Aging in trees implies a progressive reduction in the growth rate, related to a shortening of the growing period and changes in the photosynthetic capability and efficiency. These changes may continue during the oldgrowth life stages following the juvenile phase and are reflected in tree-ring properties such as growth increment, density or stable isotopes. We studied possible climate age effects in time series of several tree-ring parameters (ring width, wood density and stable carbon and oxygen isotopes) of mature individuals from two age groups of Pinus uncinata and P. nigra at two locations in Spain. The aim was to test whether age differences in trees in the oldgrowth life stages could lead to diverging climate responses. The results show some differences in response to climate between age groups at a monthly level, but most of these divergences are not significant for seasonal climate variables. Regardless of the age group, the main limiting climate factors constrained tree growth equally. Although our findings do not support the idea of an age-dependent response to climate that may lead to inaccurate climate reconstructions, further studies using tree-ring density and stable isotope series are urgently needed to verify the current results.

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8With the aim of better understanding avalanche risk in the Catalan Pyrenees, the present work focuses on the analysis of 9 major (or destructive) avalanches. For such purpose major avalanche cartography was made by an exhaustive 10 photointerpretation of several flights, winter and summer field surveys and inquiries to local population. Major avalanche 11 events were used to quantify the magnitude of the episodes during which they occurred, and a Major Avalanche Activity 12Magnitude Index (MAAMI) was developed. This index is based on the number of major avalanches registered and its 13 estimated frequency in a given time period, hence it quantifies the magnitude of a major avalanche episode or winter. 14 Furthermore, it permits a comparison of the magnitude between major avalanche episodes in a given mountain range, or 15 between mountain ranges, and for a long enough period, it should allow analysis of temporal trends. Major episodes from 16 winter 1995/96 to 2013/14 were reconstructed. Their magnitude, frequency and extent were also assessed. During the last 17 19 winters, the episodes of January 22-23 and February 6-8 in 1996 were those with highest MAAMI values, followed by 18 January 30-31, 2003, January 29, 2006, and January 24-25, 2014. To analyze the whole twentieth century, a simplified 19 MAAMI was defined in order to attain the same purpose with a less complete dataset. With less accuracy, the same 20 parameters were obtained at winter time resolution throughout the twentieth century. Again, 1995/96 winter had the highest 21 MAAMI value followed by 1971/72, 1974/75 and 1937/38 winter seasons. The analysis of the spatial extent of the different 22 episodes allowed refining the demarcation of nivological regions, and improving our knowledge about the atmospheric 23 patterns that cause major episodes and their climatic interpretation. In some cases, the importance of considering a major 24 avalanche episode as the result of a previous preparatory period, followed by a triggering one was revealed. 25 Key words 26Major avalanche, major avalanche episode, Pyrenees, magnitude, frequency, hazard, risk.

This report describes an international summer course, ''Tree Rings, Climate, Natural Resources, and Human Interaction'', held in Valsaín, Spain, in summer of 2012. The course, with 14 participants from three countries (Spain, Algeria, and Russia), included basic training in dendrochronology skills as well as applied projects in dendroclimatology, dendroecology and dendrogeomorphology.