Unlike a desk which was created by an intelligent designer, a tree is a living thing that replicates though the biological process of evolution. The tree can independently decide to move its leaves to face the sun and grow thicker branches on the side where the sun shines daily. It can even shed it's leaves to save it's energy before the cold winter arrives and grow them back in the spring.
But if all thoughts are merely the result of some material thing, and have no independence from the material world, then we cannot know beforehand or afterward whether we can trust the stimulating forces to create proper conclusions.
Those who make improper conclusions are less likely to live long enough to mate leaving the ones who make proper conclusions to breed the next generation and that's a process that's been going on for a very long time. It's called natural selection and you can read Darwin for more information on how that works.
Those who make a proper inference about sequences of events are more likely to outlive, yes. Those species, from a Darwinistic perspective, that realize that jumping off a cliff = death and thus avoid it will live longer and reproduce. Even a non-lving computer can be programmed to learn this, but it isn't really what we mean by abstract reason. How does one explain why we humans can abstractually consider what forces, both atomic and subatomic, cause one to fall, can propose the theory of gravitation and Newtonian physics, can then refine Newtonian physics with quantum physics, and can search for a GUT. This is not a simple, "I drop a rock on my toe, my toe hurts, therefore I won't drop rocks on my toes." This is a pure abstraction. And far from recognizing natural phenomenon, we actually create natural events via superconductors and things like this to test our abstractions.
Moreover, if my reasoning abilities developed purely randomly, what does that imply as to their trustworthiness?
I admire your ability to note that while a desk is clearly made by an intelligent designer, something much more complex, like a tree, or even an amoeba, developed independent of any outside intelligence, regardless of the means that intelligence may have used (be it theistic evolution or special creation or something else).
I myself find it difficult to hold both opinions simultaneously because I don't believe that I know enough about the universe to make two such seemingly incompatible statements with any certainty as to their mutual validity. I am not here arguing evolution versus creation, but naturalism versus theism. A supernatural power could have used a guided evolutionary process to create, or it could have "spoken" life into existence.
I am saying that I too hold the belief that my desk was created by an intelligent designer. I find it difficult to reconcile this belief about my desk with the idea that something more complex, like a tree or the human brain, developed independently of any intelligence. So I must simply disagree with you and leave it at that.