Piles from the harbor of Hamburg show complete water saturation in the bacterial degraded sapwood but only 50% water saturation in the sound heartwood (mc 90% to 110% - heartwood does not sink in water!). Samples were extracted from 4 to 8 m below the water level. The upper parts of the piles were in contact with air. But why aren’t the parts always under water and far from the parts with air contact fully saturated with water? I know, it is somehow the same situation like in standing trees and heartwood is rather impermeable – but if you put smaller pieces of P.sylvestris heartwood under water, they will sink after several weeks to month. Why doesn’t the air in the piles dissolve in water? The water pressure and the cold water temperature should favor this.
This is related to the properties of the heartwood. The conductive properties of cell are shot down by filling the lumens by varies chemicals. As long as it is not rotten this makes wood almost impossible to penetrate by water. The decay process is slower down by lack of oxygen since the wood is submerge.
it is still hard for me to belive that water does not penetrate even into the first cm of heartwood after 140 years. The effective barrier must be extremly thin - from 100% water saturation to 50% water saturation within a few cells. The heartwood chemicals/extractives are mainly deposited in the cell wall, not in the lumen. The cell walls are saturated with water as the moisture content is above 30% but not the lumen. Yes, the pits are blocked - but after 140 years all this sholuld not matter anymore. Wood is really a fantastic and often surprising material .
This is absolutely fascinating! I am by no means a wood science expert... more a hobbyist, so my ability to speak intelligently on this is very limited but I am wondering if your comparisons between small blocks and intact pilings might be the source of the differences observed in water infiltration rates. First, a cut block will likely be from seasoned wood, the pilings were most likely hued and placed green. In a green piling, the resin would likely move toward the cut edges of the tracheids, sealing them off. Secondly, a cut block of heartwood would have lots of surface area of open tracheid ends in direct exposure to water, the only way water could get into a piling would be to first diffuse through the sapwood, and then diffuse through the intact sides of the tracheids, or water could diffuse through the exposed cut ends at the one hand hued point which was driven into the sediment. But again, these are likely sealed with resin.
Regardless, just some thoughts, but a very interesting phenomenon and SOME VERY INTERESTING WOOD! Take care and best of luck deciding who get make something from the samples when you are done:)
Hi Jonathan, thanks a lot for your enthusiasm. Luckily I am not alone to be amazed by the phenomenon. The sealing of the endgrain by resin seems to be a reasonable explanation to prevent axial penetration and the difference to the small blocks. I am going to ask a physicist how to explain the lack of water-air exchange in the radial direction. Dirk
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