Riding in the northeast US, I find myself encountering a lot of overgrown mountain bike trails in the spring. Many of these trails are bordered by briars / brambles / jaggers. I can't totally avoid them, so what can I do to protect my legs from them while not subjecting myself to overheating in hot weather with high humidity?
I have used shin guards since the 1980s, growing up in Hawaii and now riding in Utah (both get pretty hot) and I found that wearing knee high socks help with the "heat" factor, but even then, as long as I am wearing shorts, I dont even think about my legs being warm.
I have been using the LizardSkin shinguards (http://bit.ly/L188ZV) for about 15 years now and will continue to use them as long as I ride! (I am still riding the same pair, they are frekn durable!) For the shin-whacks nothing protects better, they have a V-shaped insert that virtually eliminates any hit. And if you want to ride without that layer of protection (or to wash it) you can take that insert out really easily. Even without the insert, it has a pretty durable front with some padding that would help with any sticks or whatever slapping you. The neoprene has holes for ventilation but not really a big help, but the back gives me a gap of about 2 inches, and I have skinny legs. I have ridden a lot of downhill trails and they have helped a lot through the brush. They even come down low enough to give your ankles some protection.
You could try soccer socks, with or without shin guards. They cover the part of legs usually affected by vegetation, and are somewhat sports-oriented.
At least since soccer players usually get covered with sweat on hot days, I guess these equipment are design to handle that.
The shin guards are usually worn inside the socks, but if the vegetation damages the socks too much, it could be adviseable to wear the guards over the socks.
Hope this helps