Climate change is a lot of different things. For the statement that the count matters and a "tree is a tree",

Carbon sequestration? A giant redwood stores more carbon than a fir.

Healthy ecosystems? Different trees fit into different roles in a healthy forest.

The loss of biodiversity? Once a forest dies, a new forest somewhere else doesn't bring back the lost biodiversity.

In theory, Carbon sequestration is the closest to "a tree is a tree", you can plant large amounts of fast growing trees can capture more carbon over time, but that's specifying the later tree, which then matters.

Why did you mention ecosystems and biodiversity? Is the idea that those store more carbon, too, or was it just gratuitous?

Edit after downvote: but why though? It looks like conflation of climate change with the entirety of environmentalism. That is a misleading thing to do.