Cambial phenology, wood formation and temperature thresholds in two contrasting years at high altitude in southern Italy

Xylogenesis was monitored during 2003 and 2004 in a timberline environment in southern Italy to assess links between temperature, cambial phenology and wood formation on a short-time scale. Wood microcores were collected weekly from May to October from 10 trees of Pinus leucodermis Ant., histological sections were cut with a rotary microtome and anatomical features of the developing and mature tracheids were observed and measured along the growing tree ring. Spring 2003 was hotter than spring 2004, with temperatures up to 2.6 degrees C above historical means. The hotter conditions resulted in an earlier onset of cambial activity and all differentiation phases of about 20 days, resulting in an increased duration of xylogenesis of about 23 days. Air and stem temperatures at which xylogenesis had a 0.5 probability of being active were calculated with logistic regressions fitted on binary responses. In both years, similar thresholds were estimated with daily mean values of 8.2 and 9.5 degrees C for air and stem temperatures, respectively. The observed convergent responses of cambium phenology to temperature during the two contrasting springs confirm the key role of this environmental factor in determining the onset and duration of wood formation in timberline areas. The intra-annual dynamics of ring-width increase differed between years, with significantly narrower rings formed in 2004 than in 2003. These differences were mainly related to cell size because larger earlywood tracheids were produced in 2003. This study demonstrates the plasticity of tree-ring formation in response to high temperatures as a result of modifications in the onset and duration of differentiation.     

Climatic signal from <Emphasis Type="Italic">Pinus leucodermis</Emphasis> axial resin ducts: a tree-ring time series approach

Developing long-term chronologies of tree-ring anatomical features to evaluate climatic relationships within species might serve as an annual proxy to explore and elucidate the climatic drivers affecting xylem differentiation. Pinus leucodermis response to climate was examined by analyzing vertical xylem resin ducts in wood growing at high elevation in the Apennines of peninsular Southern Italy. Early- and latewood tree-ring resin duct chronologies, spanning the 1804–2010 time period, were constructed. We analyzed the relationships between resin duct chronologies and climate over the last century using correlation and response function analyses. Overall, results showed that ring width and resin duct relationships differed between early- and latewood, which indicated conditions affecting growth were not associated with resin duct production. Results also revealed differential responses to climate between early- and latewood resin duct chronologies. A notable observation was a positive and stable relationship between latewood resin duct number chronology and July maximum temperature throughout the twentieth century. This result suggested resin ducts might be a suitable proxy to evaluate P. leucodermis response to climate in the study area.     

Coordination of morphological and physiological traits in naturally recruited <Emphasis Type="Italic">Abies alba</Emphasis> Mill. saplings: insights from a structural equation modeling approach

Key message

Apical dominance ratio (ADR), reported as a suitable indicator for the growth and development of Abies alba , is concurrently determined by morphological and functional plant traits. Structural equation modeling (SEM) proved here to be an effective multivariate technique to represent the contribution of different variables in explaining ADR variability.

Context

During the natural recruitment of understory tree saplings, the light environment and competition among individuals may change drastically as well as their growth patterns. To cope with this, saplings have a remarkable ability to accordingly modify their physiology and morphology. Therefore, understanding the ecological significance of plant structural patterns requires an integrated view of morphological, architectural, and physiological attributes of plants.

Aims

Here, we applied a SEM approach to understand the mechanisms influencing the ADR, recently reported as suitable indicator of the growth conditions favoring silver fir (Abies alba Mill.) natural regeneration in Mediterranean areas.

Methods

A series of plant traits (e.g., root-collar diameter, leaf mass per area, and isotope composition) were combined into two main latent variables, namely Morphology and Physiology, to account for their relative contribution in explaining the ADR variability.

? Results

Our results underline the importance of variables accounting for the photosynthetic capacity and leaf economics in determining ADR; among them, leaf mass per area (LMA) emerged as an important driving variable.

? Conclusion

SEM proved to be an effective multivariate technique to represent the coordination of different morphological and functional variables in explaining ADR variability in silver fir.

     

Plot size and shape for the early assessment of post-fire regeneration in Aleppo Pine Stands

Aleppo pine stands account for a third of the burned forests in the Mediterranean basin. The early assessment of post-fire regeneration is essential for the management of such stands. The assessment should be based on reliable and objective methods. In the Mediterranean basin, plot size and shape applied in regeneration survey designs and sampling schemes differ considerably. A study involving twelve stands (7 unharvested and 5 harvested) in the Province of Taranto (southern Italy) was carried out 38 months after a fire, by comparing plots of different shape and size within a plot-count sampling frame. The relative efficiency method was used to compare the efficiency of each size and shape. Early regeneration of Aleppo pine proved to be best assessed by 8m × 2m plots, i.e. by a plot size four times wider than the most commonly used one (2m × 2m). The need for such wide plots depends upon the typical spatial arrangement of the seedlings whose clustering is associated with the presence of seed bearing trees.