Developed most probably as a denfence against forest fires,the bark of the cork...

（由于）最有可能发展成为森林防火的篱笆墙，软木的树皮...（具有防火作用——我猜测的）。

网友过于节俭，就差几个单词写完句子。现依照这个分析：

Developed most probably as a denfence against forest fires：是现在分词短语，作（原因）状语。