Life strategies in intra-annual dynamics of wood formation: example of three conifer species in a temperate forest in north-east France

Abstract

We investigated whether timing and rate of growth are related to the life strategies and fitness of three conifer species. Intra-annual dynamics of wood formation, shoot elongation and needle phenology were monitored over 3 years in five Norway spruces (Picea abies (L.) Karst.), five Scots pines (Pinus sylvestris L.) and five silver firs (Abies alba Mill.) grown intermixed. For the three species, the growing season (delimited by cambial activity onset and cessation) lasted about 4 months, while the whole process of wood formation lasted 5-6 months. Needle unfolding and shoot elongation followed the onset of cambial activity and lasted only one-third of the season. Pines exhibited an 'extensive strategy' of cambial activity, with long durations but low growth rates, while firs and spruces adopted an 'intensive strategy' with shorter durations but higher growth rates. We estimated that about 75% of the annual radial increment variability was attributable to the rate of cell production, and only 25% to its duration. Cambial activity rates culminated at the same time for the three species, whereas shoot elongation reached its maximal rate earlier in pines. Results show that species-specific life strategies are recognizable through functional traits of intra-annual growth dynamics. The opposition between Scots pine extensive strategy and silver fir and Norway spruce intensive strategy supports the theory that pioneer species are greater resource expenders and develop riskier life strategies to capture resources, while shade-tolerant species utilize resources more efficiently and develop safer life strategies. Despite different strategies, synchronicity of the maximal rates of cambial activity suggests a strong functional convergence between co-existing conifer species, resulting in head-on competition for resources.

The effects of thinning intensity and tree size on the growth response to annual climate in Cedrus atlantica: a linear mixed modeling approach

“…This result, which we interpreted as the effect of size-related constraints on cedar growth, agrees with a previous study reporting that Pinus with greater growth were proportionally more affected by drought (Martínez-Vilalta et al 2012). The interpretation of this higher sensitivity from the viewpoint of the ability of cedar to cope with drought effects is not straightforward, and we still lack a conceptual framework linking the growth signal features to life traits (Cuny et al 2012) and demography (Martínez-Vilalta et al 2012). Indeed, previous studies produced seemingly contradictory results, reporting higher mortality rates for trees showing highly variable growth (Suarez and Ghermandi 2004) or a weaker correlation between the growth of the dying trees and the climate variables (Linares et al 2010).…”

“…Plots with a "*" differed significantly from the others (at the 5 % probability level in a pairwise Tukey test). Bottom numbers (X) means "X years since the last thinning" drought (Eilmann et al 2009) or in the capture of resources (Cuny et al 2012) are associated with distinct growth responses to environmental factors among species. Collectively, our results confirm that the increased water availability in recently heavily thinned stands of Atlas cedar allows trees to maintain higher growth during drought in our site.…”

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…Soil drought, for instance, has been suggested to hasten the cessation of cambial activity (Dünisch and Bauch 1994;Gričar and Čufar 2008), though this result is not systematically observed (Gruber et al 2010). Day length, which likely modulates the rate of cambial division (Rossi et al 2006;Cuny et al 2012), may also act as a cue for the cessation of cambial activity, but this hypothesis remains to be tested. Finally, the ending of xylem differentiation, which marks the end of annual wood formation, occurs at similar temperatures to the prevailing temperatures during the onset of cambium cell division .…”

“…In certain ring-porous species (deciduous oaks), the onset of cambial division is the first step of spring resumption (Gričar 2010;González-González et al 2013), whereas in others (e.g., Fraxinus excelsior), overwintering vessels start to enlarge before budburst (SassKlaassen et al 2011) and cambial division is resumed after budburst (Frankenstein et al 2005). In conifers, the resumption of cambium activity generally occurs before budburst (Rossi et al 2009;Gruber et al 2010;Cuny et al 2012;Michelot et al 2012;Huang et al 2014).…”

Wood formation in Norway spruce on a lowland site in Slovenia in 2015 and comparison with other conifers all over Europe

“…Plants try to maximize the use of resources while minimizing the effects of various harmful events. Growth occurs when the condiAons are favourable (Cuny et al, 2012). In temperate and boreal biomes, cold temperatures are the main limiAng factor of growth (Rossi et al, 2008), and cambium is usually acAve from spring unAl autumn, with a shorter growth period in boreal ones.…”