Cost of Bark Thickness

[jkshuman]

@rosiealice and I have been discussing the cost of bark thickness in regards to fire resistance/tolerance. Thicker bark trees have a greater resistance to cambial damage by fire than thinner bark trees of the same DBH. Per Lawes et al. (2013) which draws on the work of Bill Hoffman: Because bark area scales as an exponential function of bark thickness and as a linear function of tree diameter for a given bark thickness , relatively thin-barked trees need far greater cross-sectional bark area to achieve a given bark thickness. The net effect is that species with relatively thin bark incur greater allocation costs to achieve a threshold bark thickness for protection from heat damage.

FATES does not currently have a cost for thicker bark, and we should add something. Possibilities include 1) a modification to the height DBH relationship, 2) a carbon cost of thicker bark coming directly from carbon stores. We wanted to put it out to the larger community. Thoughts on implementing the cost of bark thickness?

[rgknox]

@jkshuman, are the material costs to build bark different from stem-wood (is resins, tannins, etc)? Also, I'm guessing there is also bark turnover too, so a plant would need to keep re-building the bark as some sloughs off? We could incorporate bark turnover into the model, if that is a desired thing.

[jkshuman]

@rgknox will look into the answer to those questions. Hadn't considered bark turnover...

[ckoven]

@jkshuman my thoughts were along the lines of @rgknox's: do thicker-barked trees have thicker bark because they allocate a greater fraction of a given year's growth to their bark, or because their bark lasts longer?

[jkshuman]

Will report back. Found some good references. Such as Rosell et al in New Phytologist (2014) 201: 486–497doi: 10.1111/nph.12541 Bark functional ecology: evidence for tradeoffs, functional coordination, and environment producing bark diversity

[tompowell9]

Have you seen this paper: doi.org/10.5194/bg-2017-336? Also explores bark thickness trade-off. TP

[jkshuman]

@rosiealice and @rgknox summarizing my call with Ryan here. Basic themes from a few papers (not in any particular order) 1) cost of bark increases as diameter increases. (Fig 1 Lawes et al 2012, Fig 1 Poorter et al 2014). 2) Larger trees allocate less to bark (allometric power relationships show slow down in bark accumulation as diameter increases) (Fig 2 Poorter et al 2014). 3) Dense wood = dense bark = low water storage in bark (Fig 5c Poorter et al 2014). 4) Increased hydraulic conductivity: thick bark = high water content = lower density. thick bark favors water storage (Rosell et al 2014)

From call with Ryan: Plan is to implement a bark pool with % investment using Fig 1a from Pooter et al 2014 as a start. Bark density is correlated with wood density. Bark that is more dense would be built at a higher cost. Initially this will not affect water transport, but need to discuss implications for water transport. Multiple papers reference water content of thicker bark. In particular Rosell et al 2014 discusses that hydraulic conductivity is correlated with bark density and water content, and that thick bark is favored for water storage. Thus thick bark in a seasonally dry forest may reflect selection favoring water storage (Rosell et al 2014 and Mendez-Alonzo et al 2012).

relevant papers: Poorter, L., McNeil, A., Hurtado, V.-H., Prins, H. H. T. and Putz, F. E. (2014), Bark traits and life-history strategies of tropical dry- and moist forest trees. Funct Ecol, 28: 232–242. doi:10.1111/1365-2435.12158

Rosell, J. A., Gleason, S., Méndez-Alonzo, R., Chang, Y. and Westoby, M. (2014), Bark functional ecology: evidence for tradeoffs, functional coordination, and environment producing bark diversity. New Phytol, 201: 486–497. doi:10.1111/nph.12541

Lawes, M. J., Midgley, J. J. and Clarke, P. J. (2013), Costs and benefits of relative bark thickness in relation to fire damage: a savanna/forest contrast. J Ecol, 101: 517–524. doi:10.1111/1365-2745.12035

Rosell, J. A. (2016), Bark thickness across the angiosperms: more than just fire. New Phytol, 211: 90–102. doi:10.1111/nph.13889

[glemieux]

We checked in on this at May 23 meeting and decided to keep this open for future work goals.