区别 climb up, climb to, climb up to

有一读者问： A Junior English-Chinese Dictionary （商务印书馆出版）中， climb 词条有例： to climb （up）a mountain / tree。可是人教社出版的 Senior English Book I 第13课中则有两句：

(1)Every day he climbed to a high rock near his cave to keep watch.

(2)Early one morning, before starting work, he climbed up to his lookout.

这两句 climb 后均有介词 “to”，不知 to 可否省略？ climb (up)加上 to 再带宾语，与不带 to 直接带上宾语，二者有无区别？

climb up a tree 的意思是“沿着树向上爬”， climb to a high rock 是意谓“爬到一块很高的石头上”， climb up to a high rock 则意谓“向上爬到一块很高的石头上”。