Maybe the relatively recent logging of the vast majority of Malaysian Borneo's forests might have pushed some species that depend on unlogged ecosystem deeper inland where old forests remain. The old growth forests left in Malaysian Borneo are really the periphery of unlogged forests in Borneo at this point.

I'm still surprised by the results of the study though. I normally think of ecological transition zones as being more diverse.

And I wonder if some of the species in the unlogged forests can't be found in the logged forests.

That would certainly complicate the idea of logging unlogged forests in order to promote diversity.

Is it possible there's less diversity in unlogged forests in Malaysian Borneo because there's very very little area overall left in Malaysian Borneo that's unlogged compared to area that's been logged already?

https://mongabay-images.s3.amazonaws.com/13/0910plos600.jpg

According to this map only a tiny tiny percentage of forest area in Malaysian Borneo is actually unlogged. There is a clear line between the Malaysian territory and the Indonesian territory that is basically coincident with the border between logged and unlogged area on the island, and what's left unlogged in the Malaysian forests are tiny isolated vanishing patches that are disjoined from the rest of the forest in the Indonesian area ... so maybe it's no wonder if the number of species in these areas is a bit smaller at this point. And a comparison to the forests in the Indonesian area of Borneo and to other forests around the world is certainly needed.