2020/12/05 by Cabal, Sheena, Kellerman, Gavin, McKillop-Herr, Shannon
#Pacific madrone (Arbutus menziesii) #bark exfoliation #epiphyte #liana #western poison oak (Toxicodendron diversilobum)
paper · doi:10.21973/n3rq24
Bark provides trees with many important functions, such as nutrient transport and protection, yet the Pacific madrone (Arbutus menziesii) regularly exfoliates its bark. The mechanism for this exfoliation is largely unknown, but is possibly due to biotic pressures, such as epiphyte or poison oak (Toxicodendron diversilobum) growth, or abiotic pressures, like solar radiation exposure. In order to test potential drivers of shedding, we surveyed 49 madrones and neighboring oaks at Hastings Natural History Reserve. For each sampled tree, we counted surrounding poison oak stems, poison oak vines, estimated epiphytic cover, and measured total height and bark height of madrones. We found no association between poison oak and madrone bark exfoliation, and no differences between the bark cover on the north and south sides of madrones. Epiphytic cover was lower on oaks than madrones, but the epiphytic cover on oaks had no effect on the amount of bark shed on neighboring madrones. Epiphytic pressure does not directly influence exfoliation, but bark may be shed to proactively remove epiphytes. The cause of madrone bark exfoliation is still unknown, and could be due to a number of untested mechanisms, such as mammal or invertebrate predation prevention.