Thanks for your interest. All of Costa Rica is "somewhat mountainous" except for small coastal plains, but certainly there is a huge difference in soil from the ridges to the richer soil washed to the bottom of ravines where most of my images are from, however Costa Rica, like much of Central America has volcanoes as a ubiquitous feature. Volcanic soil is famous for it's fertility and even on the ridge tops there is rather rich soil where often huge trees are able to grow, such as the Kapok relative (Pseudobombax septenatum) with it's peculiar photosynthesizing bark. As the landscape is younger than land in the Eastern US, the hill soil is not as leached of nutrients. It is difficult to know how much of the difference between some of the uphill landscapes and ravine gallery forest landscapes is a result of human intervention because there has been so much conversion of somewhat dry forests to pastures, and because there is so much variation in mineralization and climate micro systems. Some uplifted limestone karst topography is also found in a couple of places on the pacific slopes, and annual rainfall can be quite different in slightly different locations. I do hope however that a geologist who may know more about this situation might have more illuminating comments than mine.
All this said, there is no question that the hills, which you can see on my other posts on Central/South America viewtopic.php?f=44&t=2008 viewtopic.php?f=156&t=3746
, were much more forested before European settlement of Costa Rica, but I believe there is a remnant of what used to be there in the less accessible parts of the ravines albeit most of the valuable timber trees are probably no longer there. The gigantic Wild Cashews do have a relatively soft wood, and hence they were not highly coveted by loggers. There are so many other species of interest that there was simply not time to key them all out, and the Cashews were generally the largest trees and therefor got my attention.
On a different subject, I will be posting images today on some of the creatures that live in the trees, and in later days an extensive post on big trees of Amazonian Peru on my big tree hunt there this last September.