I think there are some obvious costs for trees to grow tall. Carbon and other nutrients costs, maintenance cost, energy cost (for growing, to bring water (and nutrients) up to the higher leaves, etc...). So what are the main reasons that cause some trees to grow so tall?, For what purposes is the adaptation of being tall?
Here are three hypotheses I can think of:
- Competition for sunlight
- Better dispersal
- protection against predation
- Some birds (maybe especially those that are potentially good seed dispersers) prefer to land on high trees (avoiding the cost of regaining altitude). Being high attract these birds which eat the fruits and disperse the seeds.
What are the others hypotheses/reasons?
I am currently in Bali, Indonesia looking at palm trees that seem to have a very low competition for sun light (the forest is not dense, the light is intense), there are no tall predators (but being tall might be a protection against climbing predators as well and there are indeed monkeys and other potential climbing predators) and looking at coconuts, papaya and banana I can hardly think that being tall helps to disperse further away (seeds dispersal by barochory). So, why (evolutionary reasons) are palm trees so high?