Sylvie-Annabel Sabatier

Deciphering the developmental plasticity of walnut saplings in relation to climatic factors and light environment

Developmental plasticity, the acclimation of plants to their local environment, is known to be crucial for the fitness of perennial organisms such as trees. However, deciphering the many possible developmental and environmental influences involved in such plasticity in natural conditions requires dedicated statistical models integrating developmental phases, environmental factors, and interindividual heterogeneity. These models should be able to analyse retrospective data (number of leaves or length of annual shoots along the main stem in the present case). In this study Markov switching linear mixed models were applied to the analysis of the developmental plasticity of walnut saplings during the establishment phase in a mixed Mediterranean forest. In the Markov switching linear mixed models estimated from walnut data sets, the underlying Markov chain represents both the succession and lengths of growth phases, while the linear mixed models represent both the influence of climatic factors and interindividual heterogeneity within each growth phase. On the basis of these integrative statistical models, it is shown that walnut saplings have an opportunistic mode of development that is primarily driven by the changing light environment. In particular, light availability explains the ability of a tree to reach a phase of strong growth where the first branches can appear. It is also shown that growth fluctuation amplitudes in response to climatic factors increased while interindividual heterogeneity decreased during tree development.

Retrospective analysis of tree architecture in silver fir (Abies alba Mill.): ontogenetic trends and responses to environmental variability

ContextUnderstanding the effects of exogenous factors on tree development is of major importance in the current context of global change. Assessing the structure development of trees is difficult given that they are large and complex organisms with lifespan of several decades.AimsWe used a retrospective analysis to derive the ontogenetic trends in silver fir development and assess the effects of climate or light environment on tree architecture.MethodsThanks to the identification of relevant growth markers (bud cataphylls and pseudo-whorl branches), a retrospective analysis allowed to record annual shoot extension and to date them on silver firs of various sizes under different environmental conditions.ResultsThe length of successive annual shoots located on different axes clearly show gradual trends related to the physiological age of meristems. Within- and between-tree variations are noted due to the plasticity of development and growth induced by light environment and climate.ConclusionRetrospective analysis is an efficient method for getting information on the history of trees architecture and subsequently to relate it to environmental factors.

Climate Change Impact on Tree Architectural Development and Leaf Area

The response of forests to the forecasted increase in climate stress occurrence is considered a key issue in climate change scenarios [1]. Although forest productivity increased in most ecosystems during the 20th century [2,3], a review by Allen et al. [4] underlined an emerging trend of heat and drought induced forest decline and dieback at global scale. Several and generally combined physical and biological causes contribute to observed tree decline or die-off [4-7]. Apart extensive insect outbreaks [8], understanding the respective role of hydraulic failure and carbon starvation due to excessive or long lasting water stress is one of the major research goal in order to predict forest response to climate change [9].