I may be of some help.
FeralHeart already comes with a some African trees and default rocks, but if those don't work...
>HayleyHails (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&action=profile&u=169737/) has a default mesh priderock (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=30569.0/) that would look good in the center of any African map, plus some other cool objects you could use.
>The Original Hammy (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&action=profile&u=1947/) has a ton of meshes here (http://onelittlecorner.proboards.com/index.cgi?board=fhdownloads&action=display&thread=6/). They're all really nice, and there's a bit of everything. That includes rocks, plants, caves, and anything else you may need.
>Thierry (http://www.feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&action=profile&u=28190/) also has a ton of cool meshes on this (http://feral-heart.com/index.php?option=com_jfusion&Itemid=2&jfile=index.php&topic=8174.msg196067#msg196067/) thread. There are a gazillion foliage packs near the bottom of the thread, but they're all converted from WoW if that matters.
I can go look more later, but that's all I've found for now.