Trees are memories.
Trees have structure build into them by their very nature. Even within their internal structure, one can tell when drouths occurred, or when there was a bountiful year of rain, or even when a volcanic eruption occurred. And even when the perish by fire or storm, their skeletons remain as sentinels slowly decaying, given a history of what had once been present.
Grass has a structure, but it is fragile. At best it is consumed in the new growth of the coming year; at worst it is burned away by fire or washed away by mud and landslides. It leaves no memory of where it had been in the event it is destroyed, except by its reappearance on the following season
In 2020 in Halltern am See, Germany, a 2,000 year old dagger was unearthed. Whole weapons from that age are rare to unearth; this one originally appeared as a lump of rust:
I am certainly not arguing for the sort of crass consumerism that has been practiced in the past . At the same time, cultures are somewhat defined by the things that the produce - in many cases, the only thing we will know about past cultures are the things they made, the knowledge they left, and perhaps the language or stories they left. Remove the language and knowledge ands stories and we only have the things made - thus the Anasazi exist largely from their buildings and their burial goods, and all we know of the pre-Roman Celts are from from the archaeology we find, the writings of others (Greek and Latin) about them, and the hints of stories and legends we have in their successor cultures.