Tree mortality: common causes and preliminary statistics

In the Jungle Rhythms project volunteers tag observations with #hashtags on the online forum. One observation in particular is not only informative towards post-processing of the annotations but also has scientific value in it’s own right. Mainly, the cause of death of an observed tree within the Jungle Rhythms project holds information on the ecology of the tree and human and natural stresses it experiences, which lead to it’s demise.

Within this context I ran some quick statistics on the hashtags of the online forum of the Jungle Rhythms project.

Overall, several sources of tree death exist as nicely summarized by @itsmestephanie and I quote:

“Abattu as in abattoir. Felled, cut down.  / Coupé as in coupon. Cut, presumably down. / Passants - passers-by. Coupé par les passants - cut down by passers-by. / Sec as in desiccation. Dry. / Brûlé as in crème brûlée. Burnt. / Cassé: Broken. / Tombé: Fallen. / Vent as in ventilation. Wind. Tombé par le vent = Fallen (rather pushed down) by a really big vent. / Mort: Mortician, mortality, mortuary. Morbidity, moribund, morbid. Jack Mort. Lord Voldemort.”

I counted all instances of the hashtags on subjects in the forum and summed them using both natural or human causes. Double mentions were excluded, not to count hashtags multiple times within the same forum post.

The largest class is the “coupé” class, with a total of 257 occurrences. Second on the list is the “cassé” class with 74 mentions, followed by “mort” (72) and “tombé” (46). All other classes list smaller numbers.

Summing all human caused events results in a total of 264 deaths, while natural causes only account for approximately half this number (133). Both these values account for 10 and 5 % of the total number of observed trees. With the project currently at 90% completion and no incentive to report the events I’ll have to validate the true numbers.

However, a few conclusions can be drawn from these simple statistics. Firstly, the human influence on the experiment was significant (twice as large as the natural deaths). As far as I could tell most trees were located along forest paths. This increased the likelihood of a tree being cut down due to easy accessibility (e.g. more elaborate description such as: coupé par les passants). Within the natural causes the classes “cassé” and “tombe” account for a large fraction of the deaths. In other words, over 50% of the deaths are related to physical instability and tree fall of either the whole tree (tombé) or the bole supporting the canopy (cassé).

Treefall is an important process in forest regeneration, statistics derived from the Jungle Rhythms project therefor not only give insight into seasonal processes of the trees observed but also provides mortality rates and causes.