The thickness of the bark is a trait of paramount importance in trees living in ecosystems with frequent surface (understory) fires (e.g., some coniferous forests, savanna woodlands, etc.). This is because the bark is a good insulator protecting vital tissues from the heat of the fire. Having a bark few millimeter thicker provide an advantage in such fire-prone ecosystems. Thus there has been a selection for thick barks in surface fire ecosystems . A prominent example of a tree with a very thick and insulating bark is the Cork oak (Quercus suber) that growth in the western part of the Mediterranean Basin . In such species the thicker is the bark, the better is the response after fire [3, 4]. This bark is so thick and insulating that it is used not only as bottle tops, but also as insulating material in many industrial applications. However the Mediterranean Basin has been densely populated from long ago and it is very difficult (if possible) to find Cork oak woodlands in “natural” conditions, and thus it is not easy to know how thick the bark of Cork oak could attain in natural conditions. Most trees are frequently debarked for obtaining cork (frequencies ranging from every 9 to every 12 years, depending of the site conditions).
Few days ago I visited an ethnographic museum in Aggius (Sardinia) and found a piece of Cork oak bark of about 22 cm thick (see picture below), which is pretty thick. I only know of one record of a thicker bark: 27 cm in a 140 years-old Cork oak that was never debarked . Do you know of any tree (of the same or another species) in the world with a thicker bark? Is Cork oak the world record on bark thickness?
Figure: Piece of bark from a Cork oak (Quercus suber), in the ethnographic museum of Aggius (Sardinia).
 Pausas J.G. 2009. Convergent evolution. jgpausas.blogs.uv.es, 8/Nov/2009. [link]
 Aronson J., Pereira J.S., Pausas J.G. (eds). 2009. Cork Oak Woodlands on the Edge: conservation, adaptive management, and restoration. Island Press, Washington DC. [link]
 Natividade J.V. 1950. Subericultura. Direçao Geral dos Serviços Florestais e Aquícolas Lisbon, Portugal.