Carlo Urbinati

Daily weather response of balsam fir ( Abies balsamea (L.) Mill.) stem radius increment from dendrometer analysis in the boreal forests of Québec (Canada)

Daily stem radial growth of balsam fir [Abies balsamea (L.) Mill.] was studied between 1998 and 2001 using automated point dendrometers to investigate meteorological influence. By dividing the dendrometer day-night variation, the diurnal growth pattern was resolved into the three phases of (1) contraction, (2) expansion and (3) stem radius increment (SRI). The entire circadian cycle (4) defined by the three previous phases was considered as a fourth phase. The mean weather conditions of each phase were compared with the SRI using simple correlation and response function analysis. It was found that the weather conditions prevailing from 1600/1700 hours to 0800/0900 hours corresponding with the expansion-SRI phases had greater impact on SRI. Response function results confirmed most of the correlation analyses and explained up to 95% of the variance of the SRI series. Total rainfall in phases 2, 3 and 4 was correlated positively with SRI, and hence verifies the importance of daily water balance. The importance of water was also demonstrated by the negative effect of high vapour pressure deficit of phase 2, decreasing the possibility of cell radial expansion. The maximum temperature of phase 3 was the only temperature variable having a positive impact on SRI suggesting that night temperature was more important than day temperature in controlling radial growth. These results may influence the process of cell enlargement and reflect only the mechanical aspect of growth.

Three centuries of insect outbreaks across the European Alps

Knowledge of the persistence of regular larch budmoth outbreaks is limited in space and time. Although dendrochronological methods have been used to reconstruct insect outbreaks, their presence may be obscured by climatic influences. More than 5000 tree-ring series from 70 larch host and 73 spruce nonhost sites within the European Alps and Tatra Mountains were compiled. Site-specific assessment of growth-climate responses and the application of six larch budmoth detection methods considering host, nonhost and instrumental time-series revealed spatiotemporal patterns of insect defoliation across the Alpine arc. Annual maps of reconstructed defoliation showed historical persistence of cyclic outbreaks at the site level, recurring c. every 8-9 yr. Larch budmoth outbreaks occurred independently of rising temperatures from the Little Ice Age until recent warmth. Although no collapse in outbreak periodicity was recorded at the local scale, synchronized Alpine-wide defoliation has ceased during recent decades. Our study demonstrates the persistence of recurring insect outbreaks during AD 1700-2000 and emphasizes that a widely distributed tree-ring network and novel analysis methods can contribute towards an understanding of the changes in outbreak amplitude, synchrony and climate dependence.

500 years of regional forest growth variability and links to climatic extreme events in Europe

Climatic extreme events strongly affect forest growth and thus significantly influence the inter-annual terrestrial carbon balance. As we are facing an increase in frequency and intensity of climate extremes, extensive empirical archives are required to assess continental scale impacts of temperature and precipitation anomalies. Here we divide a tree-ring network of approximately 1000 sites into fifteen groups of similar high-frequency growth variability to reconstruct regional positive and negative extreme events in different parts of Europe between 1500 and 2008. Synchronized growth maxima or minima within and among regions indicate eighteen years in the pre-instrumental period and two events in the 20th century (1948, 1976) with extensive radial growth fluctuations. Comparisons with instrumental data showed that the European tree-ring network mirrors the spatial extent of temperature and precipitation extremes, but the interpretation of pre-instrumental events is challenged by lagged responses to off-growing season climate extremes. We were able to attribute growth minima in subsequent years to unfavourable August‐October conditions and to mild climate during winter months associated with respiratory carbon losses. Our results emphasize the importance of carry-over effects and species-specific growth characteristics for forest productivity. Furthermore, they promote the use of regional tree-ring chronologies in research related to climate variability and terrestrial carbon sink dynamics.

The “blue ring”: anatomy and formation hypothesis of a new tree-ring anomaly in conifers

Key messageDouble-stained microsections from highaltitudePinus nigrawood cores highlighted unlignified latewood cells possibly linked to abrupt temperature reduction at the end of the growing season. More consolidated detection could increase their role in dendroecology.AbstractCambial activity and wood formation are influenced by environmental factors, primarily climate. During cell wall formation the lignification is mainly controlled by temperature. By staining with safranin and astra blue it is possible to distinguish cell walls richer in lignin (stained in red) from those richer in cellulose (stained in blue). Here we show an uncommon phenomenon observed in 41 transverse sections prepared for anatomical studies of young European black pine (Pinus nigra Arnold) individuals. We detected some layers of incompletely lignified cells that appear blue in safranin–astra blue-stained sections. Growth rings showing this anatomical feature were named “blue rings”. The aims of this preliminary study are: (i) to describe the features of this peculiar anatomical trait, (ii) to enhance its visualization, and (iii) to suggest possible drivers of its formation. First results indicate the influence of low air temperature causing a lack of lignification in latewood cells. The added values provided by the identification of “blue rings” within tree-ring series could be (i) their possible use as pointer year, (ii) cross dating improvement, and (iii) finer assessment of tree sensitivity to environmental and climatic factors.

Disentangling the effects of spatial proximity and genetic similarity on individual growth performances in Norway spruce natural populations

Cambial growth is a phenotypic trait influenced by various physiological processes, numerous biotic and abiotic drivers, as well as by the genetic background. By archiving the outcome of such complex interplay, tree-rings are an exceptional resource for addressing individual long-term growth responses to changing environments and climate. Disentangling the effects of the different drivers of tree growth, however, remains challenging because of the lack of multidisciplinary data. Here, we combine individual dendrochronological, genetic and spatial data to assess the relative importance of genetic similarity and spatial proximity on Norway spruce (Picea abies (L.) Karst.) growth performances. We intensively sampled five plots from two populations in southern and central Europe, characterizing a total of 482 trees. A two-step analytical framework was developed. First, the effects of climate and tree age on tree-ring width (TRW) were estimated for each individual using a random slope linear mixed-effects model. Individual parameters were then tested against genetic and spatial variables by Mantel tests, partial redundancy analyses and variance partitioning. Our modelling approach successfully captured a large fraction of variance in TRW (conditional R2 values up to 0.94) which was largely embedded in inter-individual differences. All statistical approaches consistently showed that genetic similarity was not related to variation in the individual parameters describing growth responses. In contrast, up to 29% of the variance of individual parameters was accounted by spatial variables, revealing that microenvironmental features are more relevant than genetic similarity in determining similar growth patterns. Our study highlights both the advantages of modelling dendrochronological data at the individual level and the relevance of microenvironmental variation on individual growth patterns. These two aspects should be carefully considered in future multidisciplinary studies on growth dynamics in natural populations.

Climate Influence on the Expansion and Tree-Ring Growth of Pinus nigra L. at High Altitude in the Central Apennines

Scattered expansion of European black pine (Pinus nigra Arnold) has been observed above the current timberline in the central Apennines. We aimed to detect possible common pattern of structure and growth dynamics of pine regeneration in treeline sites. Over 700 black pine samples growing above the timberline were sampled at four sites in the limestone Apennines of Marche and Abruzzo regions. For each tree we measured basal stem diameter, total height and annual height increments; a wooden core was extracted from the stem near the ground for cambial age determination and detection of intra-annual density fluctuations (IADF). We used multivariate analysis to assess patterns of the main tree structural attributes and dendrochronological analysis for age structure and growth dynamics. Expansion of European black pine started about 35 years ago featuring similar germination peaks, tree structure and growth patterns in all the sites. IADF have similar frequencies and peaks and occur in mid-late summer. These similar patterns occur at all sites besides the local differences and grazing histories suggesting the presence of an overall climate driver.

Tree-Ring Growth Trends of Abies alba Mill: Possible Adaptations to Climate Change in Marginal Populations of Central Italy

A dendroclimatic analysis was used to assess the climate-growth relationships of Abies alba Mill. over the last century in marginal populations of Central Italy. Tree-ring cores were collected in five mixed silver fir forests at low and high-elevation sites of the Apennines range in Tuscany and Marches. Regular and moving correlations functions were applied to tree-ring width series and monthly climate gridded data. Principal component analysis displayed groups of chronologies with similar growth patterns, discriminating for altitude and geographical location. Climate-growth relationships showed the positive influence of late-spring and summer precipitations and the negative effect of summer temperatures. Stands growing within the optimal altitude range for the species showed a positive and a decreasing negative influence of spring and summer temperatures, respectively. At the highest site (1375 m asl) the positive effect of previous year spring-summer precipitation and summer temperature of both previous and current year became scarce or null. Results suggest that the shifting influence of summer precipitation on tree-rings growth from July to August of the previous year is a possible response of silver fir to the significant reduction of spring precipitation and general temperature increase throughout the 20th century.

Effetti della temperatura e del fotoperiodo sulla xilogenesi al limite superiore del bosco

Tempi e dinamiche della xilogenesi in ecosistemi forestali di ambienti freddi sono aspetti fondamentali per la comprensione dei cambiamenti climatici perche rappresentano la finestra temporale nella quale i fattori ambientali influenzano direttamente l’accrescimento. La fenologia cambiale e la differenziazione cellulare dello xilema sono state monitorate fra il 1996 ed il 2004 in larice, cembro e abete rosso al limite superiore del bosco nelle Alpi orientali mediante l’uso di dendrometri automatici ed analisi cellulari. La divisione cellulare nel cambio inizia a maggio e si protrae fino ad agosto mentre la differenziazione delle tracheidi si conclude ad ottobre. Fra le specie, sono state osservate simili dinamiche di formazione del legno ed una concentrazione della produzione cellulare nella prima parte della stagione vegetativa con una sincronizzazione dell’attivita cambiale con il fotoperiodo ed una culminazione della produzione legnosa al solstizio d’estate. Le soglie di temperatura necessarie per il mantenimento della xilogenesi variano fra 5.6 e 8.5°C dimostrando cosi l’esistenza di specifici limiti termici nella produzione cellulare in ambienti freddi. Questi studi rappresentano il primo tentativo di associare l’accrescimento con i fattori ambientali in zone di limite superiore del bosco sia a livello annuale sia intra-annuale per avere una comprensione globale del fenomeno della crescita radiale delle piante.