It refers solely to trees, and Vallombrosa is the place "where th' Etrurian shades / high overarch't imbow'r."

这个比喻指的就是树木，地点是瓦隆布罗萨,“在瓦隆布罗萨，厄特鲁利亚的光辉逐渐暗淡“

耶鲁公开课 - 弥尔顿课程节选

This is the initial part of the simile that describes the leaves: "thick as Autumnal Leaves that strow the Brooks / in Vallombrosa, where th' Etrurian shades / high overarch't imbow'r."

这是描写落叶的比喻的开始部分：,“他们人数众多，稠密得像秋天的繁叶,/在瓦隆布罗萨，厄特鲁利亚的光辉逐渐暗淡“

耶鲁公开课 - 弥尔顿课程节选