Though they rarely thrive in tropical conditions, they can be grown onthe sides of taller hills and mountains there.
虽然它们在热带环境中极少长得非常茂盛，但在热带地方较高的山坡和高山旁还是可以成长。
Several species of wildlife forage for berries, the largest of these being the bear.
有的类型的野生动物以采食浆果为生，其中以熊的体积最大。
Several species of wildlife forage for berries, the largest of these being the bear.
=Several species of wildlife forage for berries and the largest of these is the bear.
有的类型的野生动物以采食浆果为生，其中以熊的体积最大。
备注：forage 为动词，搜寻食物/尤指动物觅食
解答：你的理解时正确的：the largest of these being the bear为独立主格结构作补充性状语，the largest of these为目前分词逻辑主语。等于The largest of these is the bear =The bear is the largest of these.
