Beyond bark thickness: multifunctional explanations for variations in relative bark allocation in temperate forest trees

Abstract

While the fire protection function of tree bark has been extensively documented, other critical functions, including storage and mechanical support, have received less attention. In this study we examined: (1) the allometry of bark thickness (and biomass) against wood radius (and biomass) at a disc level, (2) differences in bark allocation between the ratio and the regression approaches, (3) differences between bark thickness and biomass as metrics of bark allocation, and (4) how bark allocation is associated with the evolution of wood from non-porous to diffuse-porous and ring-porous types. Thickness and biomass of bark and wood were measured using trunk discs of 88 individual trees of 36 species in a temperate forest characterized by a long fire interval. Allometric relationships of bark thickness (and biomass) against wood radius (and biomass) explained why both relative bark thickness and biomass decreased with increasing stem diameter. Variations in both among species varied by factors of 3.5 to 7.5 depending on the measurement methods. The ratio approach produced higher estimates of both relative bark thickness and biomass compared to the regression approach, while relative bark thickness was significantly lower than relative bark biomass. Ring-porous species exhibited higher bark thickness based on the ratio approach, which might reflect evolutionary adaptations where ring-porous species have developed thicker bark as protection: thermal insulation against freeze–thaw embolism coupled with carbohydrate reservoirs for hydraulic repair. The regression slope of bark allocation against wood density increased along the wood porosity gradient, demonstrating evolutionary biomechanical coordination between bark and wood. These findings highlight systematic coupling between bark and xylem multifunctionality.

Keywords

Bark thickness / Stem diameter / Relative bark thickness / Relative bark biomass / Bark allocation

References

[1] Chave J, Coomes D, Jansen S, Lewis SL, Swenson NG, Zanne AE. Towards a worldwide wood economics spectrum. Ecol Lett, 2009, 12(4): 351-366

[2] Cornelissen JHC, Lavorel S, Garnier E, Díaz S, Buchmann N, Gurvich DE, Reich PB, ter Steege H, Morgan HD, van der Heijden MGA, Pausas JG, Poorter H. A handbook of protocols for standardised and easy measurement of plant functional traits worldwide. Aust J Bot, 2003, 51(4): 335-380

[3] Dominguez PG, Niittylä T. Mobile forms of carbon in trees: metabolism and transport. Tree Physiol, 2022, 42(3): 458-487

[4] Dong HJ, Wang XC, Yuan DY, Liu D, Liu YL, Sang Y, Wang XC. Radial distribution differences of non-structural carbohydrates in stems of tree species of different wood in a temperate forest. Chin J Plant Ecol, 2022, 46(6): 722-734 in Chinese

[5] Hempson GP, Midgley JJ, Lawes MJ, Vickers KJ, Kruger LM. Comparing bark thickness: testing methods with bark-stem data from two South African fire-prone biomes. J Veg Sci, 2014, 25(5): 1247-1256

[6] Jin Y, Wang CK. Leaf hydraulic traits and their trade-offs for nine Chinese temperate tree species with different wood properties. Chin J Plant Ecol, 2016, 40(7): 702-710 in Chinese

[7] Jupa R, Rosell JA, Pittermann J. Bark structure is coordinated with xylem hydraulic properties in branches of five Cupressaceae species. Plant Cell Environ, 2024, 47(5): 1439-1451

[8] Lawes MJ, Midgley JJ, Clarke PJ. Costs and benefits of relative bark thickness in relation to fire damage: a savanna/forest contrast. J Ecol, 2013, 101(2): 517-524

[9] Li YR, Wang XC, Wang CK, Liu F, Zhang QZ. Spatial variation in diurnal courses of stem temperature of Betula platyphylla and Fraxinus mandshurica and its influencing factors. J Appl Ecol, 2017, 28(10): 3197-3207 in Chinese

[10] Li ZM, Luo DD, Ibrahim MM, Hou EQ, Wang CK. Adaptive strategies to freeze-thaw cycles in branch hydraulics of tree species coexisting in a temperate forest. Plant Physiol Biochem, 2024, 206 108223

[11] Loram-Lourenço L, Farnese FDS, de Sousa LF, Alves RDFB, de Andrade MCP, Almeida SEDS, Moura LMF, Costa AC, Silva FG, Galmés J, Cochard H, Franco AC, Menezes-Silva PE. A structure shaped by fire, but also water: ecological consequences of the variability in bark properties across 31 species from the Brazilian cerrado. Front Plant Sci, 2020, 10: 1718

[12] MacFarlane DW. Highly variable bark-wood density relationships across tree species reflect tradeoffs in evolved tolerances to environmental stressors. Trees, 2024, 38(5): 1223-1239

[13] Martín-Sanz RC, San-Martín R, Poorter H, Vázquez A, Climent J. How does water availability affect the allocation to bark in a Mediterranean conifer?. Front Plant Sci, 2019, 10: 607

[14] Midgley JJ, Lawes MJ. Relative bark thickness: towards standardised measurement and analysis. Plant Ecol, 2016, 217(6677-681

[15] Neumann M, Lawes MJ. Quantifying carbon in tree bark: the importance of bark morphology and tree size. Methods Ecol Evol, 2021, 12(4646-654

[16] Nickolas H, Williams D, Downes G, Harrison PA, Vaillancourt RE, Potts BM. Application of resistance drilling to genetic studies of growth, wood basic density and bark thickness in Eucalyptus globulus. Aust for, 2020, 83(3): 172-179

[17] Paine CET, Stahl C, Courtois EA, Patiño S, Sarmiento C, Baraloto C. Functional explanations for variation in bark thickness in tropical rain forest trees. Funct Ecol, 2010, 24(6): 1202-1210

[18] Pan J, Zhang J, Wang XC, Wang XW, Wang Q, Liu YK, Liu YL, Diao YF, Quan XK, Wang CK, Wang XC. Variations and determinants of tissue carbon concentration of 32 sympatric temperate tree species. J For Res, 2024, 35(1): 113

[19] Pausas JG. Bark thickness and fire regime. Funct Ecol, 2015, 29(3315-327

[20] Pausas JG. Evolutionary fire ecology: lessons learned from pines. Trends Plant Sci, 2015, 20(5): 318-324

[21] Pausas JG. Bark thickness and fire regime: another twist. New Phytol, 2017, 213(1): 13-15

[22] Pérez-Harguindeguy N, Díaz S, Garnier E, Lavorel S, Poorter H, Jaureguiberry P, Bret-Harte MS, Cornwell WK, Craine JM, Gurvich DE, Urcelay C, Veneklaas EJ, Reich PB, Poorter L, Wright IJ, Ray P, Enrico L, Pausas JG, de Vos AC, Buchmann N, Funes G, Quétier F, Hodgson JG, Thompson K, Morgan HD, ter Steege H, Sack L, Blonder B, Poschlod P, Vaieretti MV, Conti G, Staver AC, Aquino S, Cornelissen JHC. New handbook for standardised measurement of plant functional traits worldwide. Aust J Bot, 2013, 61(3): 167

[23] Poorter L, McNeil A, Hurtado VH, Prins HHT, Putz FE. Bark traits and life-history strategies of tropical dry- and moist forest trees. Funct Ecol, 2014, 28(1232-242

[24] Retief E, Stanger TK. Genetic control of wood density and bark thickness, and their correlations with diameter, in pure and hybrid populations of Eucalyptus grandis and E urophyllain South Africa. South For J For Sci, 2009, 71(2): 147-153

[25] Richardson SJ, Laughlin DC, Lawes MJ, Holdaway RJ, Wilmshurst JM, Wright M, Curran TJ, Bellingham PJ, McGlone MS. Functional and environmental determinants of bark thickness in fire-free temperate rain forest communities. Am J Bot, 2015, 102(10): 1590-1598

[26] Rosell JA. Bark in woody plants: understanding the diversity of a multifunctional structure. Integr Comp Biol, 2019, 59(3): 535-547

[27] Rosell JA, Castorena M, Laws CA, Westoby M. Bark ecology of twigs vs. main stems: functional traits across eighty-five species of angiosperms. Oecologia, 2015, 178(4): 1033-1043

[28] Rosell JA, Olson ME, Anfodillo T, Martínez-Méndez N. Exploring the bark thickness–stem diameter relationship: clues from lianas, successive cambia, monocots and gymnosperms. New Phytol, 2017, 215(2): 569-581

[29] Schubert AT, Nano CEM, Clarke PJ, Lawes MJ. Evidence for bark thickness as a fire-resistance trait from desert to savanna in fire-prone inland Australia. Plant Ecol, 2016, 217(6): 683-696

[30] Serra O, Mähönen AP, Hetherington AJ, Ragni L. The making of plant armor: the periderm. Annu Rev Plant Biol, 2022, 73: 405-432

[31] Sevanto S. Phloem transport and drought. J Exp Bot, 2014, 65(7): 1751-1759

[32] Tyree MT, Zimmermann MH. Xylem structure and the ascent of sap, 2013, New York, Springer

[33] Vázquez-Segovia K, Olson ME, Campo J, Ángeles G, Martínez-Garza C, Vetter S, Rosell JA. Tip-to-base bark cross-sectional areas contribute to understanding the drivers of carbon allocation to bark and the functional roles of bark tissues. New Phytol, 2025, 245(5): 1953-1968

[34] Warton DI, Wright IJ, Falster DS, Westoby M. Bivariate line-fitting methods for allometry. Biol Rev Camb Philos Soc, 2006, 81(2): 259-291

[35] Wigley BJ, Charles-Dominique T, Hempson GP, Stevens N, TeBeest M, Archibald S, Bond WJ, Bunney K, Coetsee C, Donaldson J, Fidelis A, Gao X, Gignoux J, Lehmann C, Massad TJ, Midgley JJ, Millan M, Schwilk D, Siebert F, Solofondranohatra C, Staver AC, Zhou Y, Kruger LM. A handbook for the standardised sampling of plant functional traits in disturbance-prone ecosystems, with a focus on open ecosystems. Aust J Bot, 2020, 68(8): 473-531

[36] Wilms F, Duppel N, Cremer T, Berendt F. Bark thickness and heights of the bark transition area of Scots pine. Forests, 2021, 12(10): 1386

[37] Zhang HY, Wang CK, Wang XC. Spatial variations in non-structural carbohydrates in stems of twelve temperate tree species. Trees, 2014, 28(177-89

RIGHTS & PERMISSIONS

Northeast Forestry University