first of all, i think you should keep using your kit lens until a point of time whereby u think there is a need to upgrade.
Secondly, A lot of things out there are related to nature. Be it bird photography, macro, landscape, all of them can be classified under nature.
thirdly, for a start, u might wan to try canon 75-300 III for bird/animal photography. Whereas for macro, the cheapest method is to do lens reversing. As for landscape, i think u cant use your kit lens for the time being until u find a need to upgrade
If you don't know this then you don't need any 2nd lens - that's the simple truth.
As others have pointed out: figure out what you want to shoot. Check how you use your lens and where exactly you run into limitations. First check if it is something about your skills and usage of cam or if it's really a limitation of equipment (e.g. focal length, depth of field, aperture, sharpness etc.). This will also improve your knowledge about equipment and helps deciding what you need to overcome the limitations.
Instead of getting an expensive IS lens you could stick to your kit lens and get a tripod. That helps already a lot to stabilize your camera and it's useful for a lot of nature shoots, low light pictures and others.
There is no need for "constant upgrading" when it comes to equipment, only for your skills