How ideas come together

I've always been fascinated by the idea of sentient trees.  I've written a short story about humans interacting with them, but I want to write a whole novel.

I've never been able to find the right angle to write this story from - until I read a book this week.  Sue Burke's Semiosis is the tale of humans co-existing with sentient plants.  The book follows a group of colonists struggling to survive on a hostile world.  They are kept alive and aided by a sentient bamboo.  And later they defend themselves against hostile aliens, with the aid of the bamboo.

How could I translate that to trees?  Well, trees are long-lived, so perhaps they'd seen an earlier group of colonists land on the planet.  That way they could already have a knowledge of human language. They have their Rosetta Stone that allows them to understand the newcomers.

Then I started thinking about whether the trees could have mobile branches.  I decided I might be able to work out a system to move young and whippy shoots, but I need to do more research to work this out. 

Was there some way the trees could generate an electrical signal the colonists could use to communicate?  Trees are connected via the wood-wide web, a vast network of filaments that link the trees in a forest.  They transmit nutrients, but what if they could evolve to transmit and receive electrical signals?  The human body runs on electrical pulses, there's no reason why trees couldn't have evolved elsewhere to use electricity for communicate.

Perhaps they transmit in chemical language too.  What if they communicate with the local big cats that way?  And what if the big cats are telepaths, and can communicate with the human telepaths among the colonists?

Once I started asking what if? a whole cascade of interlocking ideas appeared.  I've had odd glimpses of how to write this story in the past, but haven't seen how to link the desperate elements together.  Now, thanks to Sue Burke's example, I at last have the whole ecosystem.  Now all I have to do is sit down and write the book.