The environment here is difficult on all types of clothes and footwear. The sun, dirt, mud, thorns, you name it, it's gonna be relentlessly torturing your footwear. I recently replaced my shoes after a year and a half and you can see the wear and tear.
I have to give Merrell some props because the shoes were still in decent shape. The sole was beginning to peel a little and the heel was worn down and getting frequently punctured by thorns but otherwise they were in good shape. I probably could have gone on using them for a few more months but as I found myself out of Tanzania, I went ahead and replaced them. The funniest thing about it, it wasn't the Tanzanian environment that finished them off, rather it was a week in the UK rain. After having my feet sufficiently soaked for a week straight of April rains, my shoes had the classic impenetrable wet sock stench. Even when I took off my shoes, my socks were saturated with the stink.
Thus, I was pleased to replace my shoes and even happier to replace them with the same brand and model. The shoes proved to be sturdy and suit the environment well.