This is a great way to build a completely natural exhibit on a budget. Use the existing vegetation and just fence it in. I guarantee this exhibit is better than many artificial exhibits that were much more expensive.
Glad they are getting more height. It takes more than just adding mesh and support poles to hold the mesh up and have the tensile-strength to withstand the elements. Since they are already using mesh around living trees, there are specialized connections to hold the mesh in place. Without constricting the growth and nutrient flow of the trees so they may continue to mature, adding more height and essentially, weight to a less fortified part of the tree takes planning. With the current height, the mesh roof has the support of the base and root system. It takes more engineering, and thought, than just raising the roof, so to speak. We, as Zoo-enthusiasts, always play keyboard designer and architect with our imagination and wishful thinking. I think, we should reel-in our comments and appreciate what is already in use. A nice, spacious enclosure with real vegetation without the use of mock-rock.