stand 表示“忍受”时，后面的 doing sth 是动名词短语作宾语；

stand 表示“站着”时，后面的 doing sth 是现在分词短语作伴随状语。

He （主语）//stood（谓语动词）// looking through some trees（现在分词作方式/伴随状语）, the shadows of whose trunks were spilled out along the ground（为whose引导的非限制性定语从句，修饰前面名词some tress）.（备注“whose trunks=the trunks of which” which指代前面先行词some trees）

正确的理解是：looking through some trees现在分词短语作伴随状语或者方式状语。

(1)looking through some trees作方式状语修饰谓语动词stood，描述以某种方式站着，即以“逐一查看一些树木”的方式站着。

(2)looking through some trees作伴随状语修饰谓语动词stood，描述的是分词动作伴随谓语动词动作同时发生，即以“分词动作为次要动作”“谓语动词动作为主要动作”。

He stood looking through some trees, the shadows of whose trunks were spilled out along the ground.

以上句子可以改为以下一个并列句

He stood and looked through some trees, the shadows of whose trunks were spilled out along the ground.

应该是作伴随状语使用。