Comparative analyses of multiple tree-ring parameters of beech along latitudinal gradients in different climatic regimes
Author(s)
Rezaei Sangsaraki, Negar
Date Issued
June 28, 2016
Type
Doctoral Thesis
Abstract
European beech represents one of the most important European forest tree species, hence possible adverse factors affecting productivity and management of this species can have strong ecological and economic impacts in Europe.
Rising atmospheric CO2 concentration, higher temperatures and changes in precipitation are likely to have significant effects on the vegetation period, growth, health and distribution of trees as well as on forest ecosystems, and thus on the goods and services provided by forests.
In the 21st century, the Mediterranean Basin could be most sensitive to climate change due to global warming among the European regions and most of the current climate projections for Central Europe predict increased temperatures that are expected to cause an increase in the frequency and duration of intense summer droughts. Owing to its sensitivity towards low water availability and longer drought periods, physiological performance, growth and competitive ability of European beech may be adversely affected by such changing environmental conditions.
Most European Beech forests have been historically managed trough different silvicultural systems, which acting directly on structure affect many ecophysiological processes.
Tree rings are uniquely widespread relative to all comparable natural archives of climate signals and beech has been concerned extensively in tree ring studies, taking advantage of its widespread distribution, sensitivity to climate and longevity.
Air (CO2) and water absorbed by a tree are subtly modified by physiological processes and in response to the varying environment in which the tree lives, and these small changes affect isotopic ratios of elements into the uptaken molecules (CO2, H2O, nutrients).
In this context the objectives were to: (1) assess the relationship of climatic parameters, growth and carbon isotope discrimination (Δ13C), (2) evaluate the effect of different types of forest management on tree physiology and growth, (3) assess the response to recent atmopsheric CO2 concentration increment of trees growing in different sites.
Hence, we selected four beech forests along a latitudinal gradient: central and southern Apennines (Pian di Limina, CAL1 and Collelongo ABR1, Italy), pre-Alps (Pian del Cansiglio VEN1, Italy), and middle European lowlands (Zoolithenhöhle ZOO, Germany). At each site, co-dominant trees were sampled to build tree ring site chronology and five trees were selected to develop the site Δ13C chronology.
At all sites, our results suggested a negative effect of the temperature of the previous summer on the growth of the current year. This demonstrates that reserves are mobilized at bud break to sustain spring growth and that a severe drought period affecting reserve accumulation and partitioning may also influence phenology and spring growth rate in the subsequent year.
The effect of summer temperatures was significant in the Apennine sites, but in recent times a similar effect appeared also in the North sites of our transect.
In the cold sites we observed a positive relation between spring temperature and Δ13C, suggesting an "earliness effect". The increasing temperature causing the early onset of photosynthetic activities allowed trees to make a substantial part of their growth during the favorable spring conditions (i.e. soil water availability). At the same time increasing temperature affected the summer growth.
In all our sites we observed an active response of trees to the increase of atmospheric CO2 concentration, that is reflected in increasing water use efficiency (iWUE). The increase of iWUE from 1950 to 2013 was different among the sites, showing decreasing sensitivity from north to south, suggesting that trees adaptability involved both genetic and physiological mechanism. Despite higher iWUE, the expected increase in growth rates in response to rising atmospheric CO2 was observed only in the Zoolithenhöhle and Collelongo, where important silvicultural treatments occurred immediately before the study period. Probably, the increase of iWUE after silvicultural treatments is related to the increase of photosynthesis rate. In these sites we observed a negative correlation between Basal Area Increment (BAI) and Δ13C. In general the canopy is “organized” to maximize carbon fixation and thinning modified the ratio between
shade and light leaves, increasing the amount of light leaves that have a higher photosynthetic rates. This produced a reduction of internal CO2 concentration (Ci) in the canopy and a decrease of Ci/Ca producing an enrichment in 13C (less negative δ13C and lower Δ13C). After that canopy closed the gaps, the ratio between shade and light leaves changed again but this time with an increasing fraction of shade leaves, with an overall lower photosynthesis rate, that caused an increment of Ci, so our results suggested a reduction of growth related to an overall lower photosynthesis rate.
In conclusion, we observed that climate is changing (i.e. increase of temperature, increase of atmospheric CO2, changes in precipitation regimes) causing consequent effects on forest growth and tree physiology. Hence, a sustainable and adaptive forest management can have a central role in climate change mitigation and adaptation through preserving and enhancing forest carbon uptake.
Additional information
Dottorato di ricerca in Scienze e tecnologie per la gestione forestale e ambientale
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