TITLE: Making bark thickness punches
DATE: 2022-01-05
AUTHOR: John L. Godlee
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Trees in savannas often have thick corky bark to insulate the
vascular cambium, buds and meristem tissue from fires
(Pérez-Harguindeguy et al. 2016). Outside of fire-prone savannas,
bark thickness still varies a lot among species. The English Oak
for instance has very thick bark, but doesn't occur in fire-prone
regions. Various theories have been put forward to explain
functional variation in bark thickness among species in
non-fire-prone ecosystems, like resistance to frost, mechanical
stability in windy environments, and buffering against fluctuations
in water potential (Rosell et al. 2014). Interestingly, it doesn't
look like bark thickness is necessarily associated with other "slow
economic" plant traits like thick leaves, wood density and leaf
mass per area (Richardson et al. 2015). Trees in tropical
rainforests often have very thin and smooth bark. It has been
suggested that thick bark may be a disadvantage in these ecosystems
as it provides shelter for invertebrate enemies (Pausas 2015).
[Pérez-Harguindeguy et al. 2016]:
https://doi.org/10.1071/BT12225_CO
[Rosell et al. 2014]:
https://doi.org/10.1111/nph.12541
[Richardson et al. 2015]:
https://doi.org/10.3732/ajb.1500157
[Pausas 2015]:
https://doi.org/10.1111/1365-2435.12372
In the SECO project, I'm interested in bark thickness as a measure
of resistance to fire. Differences in bark thickness might explain
variation in carbon dynamics among ecosystems based on their fire
regime and tree community composition.
[SECO project]:
https://blogs.ed.ac.uk/seco-project/
My Dad found some steel pipe that used to be used in the dairy for
milk. The pipe had a 23 mm external diameter and a 16 mm internal
diameter, meaning the wall thickness was ~7 mm. Punch diameter
varies, but 10-15 mm seemed common across the literature I found.
The SEOSAW traits manual, originally written by Carla Staver
recommends 15 mm. We cut the pipe out using hacksaws, and then cut
it into 8 inch lengths. About 1 inch from the top of each section
of pipe, I drilled a hole all the way through the pipe. At the
other end of the pipe we used a bench grinder to sharpen the pipe,
with a bevel on the outside.
[SEOSAW traits manual]:
https://bitbucket.org/miombo/seosaw/raw/master/doc/manuals/traits_ma
nual/versions/seosaw_traits_manual_latest.pdf
We found some metal rod in the farm buildings attached to a rusting
piece of farm machinery called a Lely Cock Pheasant. This machine
is also known as a tedder and is used to turn hay, kind of like a
mechanised pitchfork. We used an angle grinder to remove the rods,
then I cut the rod into 9 inch lengths with a hacksaw, slightly
longer than the punch. The rod fits into the drilled hole to use as
a handle to pull the bark punch back out of the tree trunk. The rod
can also be used to push the bark plug out of the pipe so it can be
measured.
[tedder]:
https://en.wikipedia.org/wiki/Tedder_(machine)
Finally, I cut a small piece of wood to protect the top of the pipe
when hammering the pipe into the tree trunk.
I tested the bark punch on a piece of fresh ash that came down in
storm Arwen a few weeks back, fresh enough that I can pretend it's
a living tree trunk. It worked pretty well, though I did notice a
couple of nicks where the cutting edge had rolled over. I will
reset the angle of the bevel so that it is steeper, and possibly
try to temper the metal somehow.
