So what is tropical dry forest?

So what is tropical dry forest? In trying to compile a list of recent dry forest-related literature that question comes to the fore. It's a very familiar question - I spent a lot of time wondering about that early in my grad school career when I thought that I should get a handle on all the literature related to tropical dry forest. (What can I say, I was ambitious naive.) Part of the problem comes from relying on Holdridge's definition - if you define dry forest in relation to precipitation and potential evapotranspiration (which basically boils down to precipitation and temperature), you end up including riparian forests and some forests dependent on ground water - forests that which resemble wetter forests in terms of physiognomy and species composition. When it boils down to it, regardless of rainfall, they don't function as dry forests. In addition, there's the issue of savannas - many savannas fall within the dry forest life zone, but if you look at them as "former" or "potential dry forest" you ignore the fact that they have been grassland for thousands and years. (Other grasslands though, are recent human creations.) Then there are areas that function as dry forest, but get too much rainfall.

In selecting literature I am trying to use broad criteria. I'm including deciduous and semi-deciduous forest even if they seem to be a bit on the wet side. I'm also including savannas. In a case like this, it's probably more useful to use a broad definition.