Plastic responses of Abies pinsapo xylogenesis to drought and competition

Abstract

Radial growth and xylogenesis were studied to investigate the influence of climate variability and intraspecific competition on secondary growth in Abies pinsapo Boiss., a relic Mediterranean fir. We monitored the responses to three thinning treatments (unthinned control -C-, 30% -T30- and 60% -T60- of basal area removed) to test the hypothesis that they may improve the adaptation capacity of tree growth to climatic stress. We also assessed whether xylogenesis was differentially affected by tree-to-tree competition. Secondary growth was assessed using manual band dendrometers from 2005 to 2007. In 2006, xylogenesis (phases of tracheid formation) was also investigated by taking microcores and performing histological analyses. Seasonal dynamics of radial increment were modeled using Gompertz functions and correlations with microclimate and radiation were performed. Histological analyses revealed it as fundamental to calibrate the dendrometer estimates of radial increment and to establish the actual onset and end dates of tracheid production. The lower radial-increment rates and number of produced tracheids were observed in the trees subjected to high competition in the unthinned plots. The growing season differed among the plots, and its duration ranged from an average of 78 days in unthinned plots to 115 days in thinned ones (T60). Variations in the beginning of the growing season (13 April to 22 May) and earlywood-latewood transition (early August) were mainly determined by the temperature pattern, while the onset and the end of the growing season were related to both annual precipitation and tree-to-tree competition. The tracheid-formation phases of radial enlargement and cell-wall thickening showed similar patterns in the trees from thinned and unthinned plots subjected to low and high competition, respectively, but the mean number of tracheids in each phase was always higher in the trees from the thinned plots. The reduction of competition through thinning induced a longer growing season and enhanced the radial growth in A. pinsapo.

Effects of thinning intensity on radial growth patterns and temperature sensitivity in Pinus canariensis afforestations on Tenerife Island, Spain

“…Deterioration of growth conditions will arise for many Mediterranean species if heat and water stress are intensified (Andreu et al 2007). As Linares et al (2009) reported, drought stress is probably the main reason for the current growth decline of coniferous woodlands in southern Europe.…”

Regulation of Water Use in the Southernmost European Fir (Abies pinsapo Boiss.): Drought Avoidance Matters

“…During spring and autumn, and sometimes in summer, foggy and rainy days were frequent, which impeded the use of equipment in the field; otherwise, during winter, the temperatures were usually low and the study area was sometimes covered by snow [19]. In addition, the inaccessibility of the study sites necessitated the transport of the sampling devices by mules.…”

“…Nonetheless, trees located at the lower elevation (1200 m) exhibited earlier symptoms of water stress, while trees located at 1550 m showed systematically higher values of stomatal conductance, as well as improved daily-scale recovery of xylem water potential and growth [11]. Regardless, both populations showed a seasonal response to increasing drought, similar to that of typical Mediterranean species, with spring maximums and low summer stomatal conductance values [19,[30][31][32].…”

“…[19]. This relict tree is perhaps among the most vulnerable to climate change within the Mediterranean mountain forests.…”

“…This relict tree is perhaps among the most vulnerable to climate change within the Mediterranean mountain forests. Indeed, several recent studies focusing on tree growth and stand dynamics have reported extensive A. pinsapo forest decline related to temperature rises and increasing drought [11,12,19].…”