@G_N you are absolutely correct given the way you are defining intelligence. We can assume that trees (perhaps) don’t have self-reflection, arguably the ultimate test of intelligence. That said, it is not just stimulus-response behavior that we should focus on. There is more than that. Here is an excerpt from another study (Coast Redwood and Giant Sequoia Mega-Genomes Sequenced | UC Davis)
A coast redwood genome, sequenced only recently at UC-Davis, has 27 billion base pairs of DNA, about 9 times that of humans. A redwood can also live for more than 3000 years, an incomprehensible timescale for us who are lucky if we make it past 70. Usually we are just stupid enough to kill each other. Compared to humans, trees are way more intelligent and strong, the redwoods especially as they have to stay in the same place for thousands of years and fend off every attack – disease, insects, storms.
That last sentence stuck in my head for a long time – the redwoods especially as they have to stay in the same place for thousands of years and fend off every attack – disease, insects, storms – to stay alive for thousands of years, that in itself is an ability that far surpasses any other living thing. Surely, that is a sign of something.
There are other behaviors as well. For example, consider Canopy shyness. This is remarkable. Of course, there is much we have still not discovered. So much to learn