EPOW - Ecology Picture of the Week

Arrayán (Luma [Myrceugenella] apiculata), Family Myrtaceae
Llao Llao Municipal Park, Bariloche, Argentina

Explanation:  This tree has no clothes!  More accurately, as it has grown, it has shed its outer bark, revealing a beautiful red wood that is smooth and surprisingly cold to the touch.  

This is one of the characteristic trees of Andean Patagonia of southern Argentina and Chile:  an arrayán ... locally pronounced "arra-JHAN." 

Part of the southern beech (Nothofagus) Valdivian forests of Patagonia, the arrayán is a myrtle that commonly grows close to water.  Why would it shed its bark so readily?  One theory is that this prevents the growth of epiphytes such as climbers and vines, that are common on other trees in these forests; perhaps some epiphytes had reduced the tree's fitness and ability to reproduce and survive, so those arrayáns that could shed bark and lose the epiphytes had greater survival value.  

Another theory is that many trees, such as eucalypts and madrones, evolved bark-shedding as an adaptation to cold climates, but how this aids in survival is unclear; bark usually serves to protect the tree from fire, insects, and freezing.  It may be that having no bark at all is better than having fibrous bark that is flammable or prone to insect pests or fungal infection.  

So why would the naked wood be so cold to the touch?  I could find no studies on this.  I speculate that it is a secondary result of the dense wood that thwarts invasion by insects.  In fact, I saw little evidence of any boring insects on any of the arrayáns trunks.  

The arrayán keeps its aromatic leaves throughout the year.  It produces black round berry fruits that are dispersed by some birds and mammals.

Arrayáns are found only in Patagonia, and are most dense in a protected forest in Los Arrayánes National Park on Quetrihué Peninsula on Nahuel Huapi.  Arrayáns there are the largest in the world.  Indeed, the place name gives it away:  quetri means arrayán or myrtle in Araucano, and Quetrihué means the place of arrayánes or myrtles.  

Arrayáns may have medicinal use for the local Mapuche people.  Tea made from the leaves can help reduce toothaches and aid digestion, and the roots are used as astringents.  The fruits are edible, the wood is used in art for carvings, and the tree has high ornamental value.  

Information:
     Bisheimer, M. V., and E. M. Fernández. 2003. Árboles de los parques nacionales del sur: Árboles autóctonos caracteristicos de los bosques Andino-patagónicos de la Argentina. Segunda edición. Impreso en Gráfica Pinter S.A., Buenos Aires, Argentina. 176 pp.
     de la Vega, S. G. 2003. Patagonia: the laws of the forest. Third edition. Contacto Silvestre, Buenos Aires, Argentina. 127 pp.