Are wood fibres as sensitive to environmental conditions as vessels in tree rings with intra-annual density fluctuations (IADFs) in Mediterranean species?

Forecasted environmental changes are likely to increase the frequency of intra-annual density fluctuations (IADFs) in Mediterranean tree rings. The interpretation of intra-annual anatomical variability of tree rings with IADFs can be useful to understand plant-growth response to environmental changes with seasonal resolution. We analysed the intra-annual variability of quantitative traits of both vessels and fibres in the woods of Arbutus unedo L. and Erica arborea L. to compare the sensitivity of different cell types to environmental variations. We applied digital image analysis on microphotographs of semi-thin sections of tree rings formed at sites with different soil water availability. Wood of both species showed goodadaptability that allows anatomical traits of vessels and fibres to be harmonised by changing the water transport capacity and wood strength, promoting the efficiency or safety of water transport according to water availability during wood formation. The size of fibres showed trends of variation similar to vessels. Not all parameters of vessels were accurate indicators of the IADF presence. In conclusion, parameters of fibres, which offer advantages during automatic measurement, showed the same sensitivity to environmental fluctuations as vessels. Thus, they could be good indicators of summer drought to describe and interpret the ecological meaning of IADFs in tree ringsKey message: Wood fibres are as sensitive to environmental conditions as vessels in tree rings with intra-annual density fluctuations (IADFs) in Mediterranean species. Abstract: Forecasted environmental changes are likely to increase the frequency of intra-annual density fluctuations (IADFs) in Mediterranean tree rings. The interpretation of intra-annual anatomical variability of tree rings with IADFs can be useful to understand plant-growth response to environmental changes with seasonal resolution. We analysed the intra-annual variability of quantitative traits of both vessels and fibres in the woods of Arbutus unedo L. and Erica arborea L. to compare the sensitivity of different cell types to environmental variations. We applied digital image analysis on microphotographs of semi-thin sections of tree rings formed at sites with different soil water availability. Wood of both species showed good adaptability that allows anatomical traits of vessels and fibres to be harmonised by changing the water transport capacity and wood strength, promoting the efficiency or safety of water transport according to water availability during wood formation. The size of fibres showed trends of variation similar to vessels. Not all parameters of vessels were accurate indicators of the IADF presence. In conclusion, parameters of fibres, which offer advantages during automatic measurement, showed the same sensitivity to environmental fluctuations as vessels. Thus, they could be good indicators of summer drought to describe and interpret the ecological meaning of IADFs in tree rings