A Tham field is the background magical radiation field that exists throughout the universe. Nature magic involves accessing this field in order to produce effects in the real world. A user does this by channeling the energies of the field into themselves, using their body as a fulcrum for the energy to pass through. Channeling is done through chanting, body movement, as well as using certain runes or sigil relevant to the culture in question.
Natural magic is always done in groups of several people. The more powerful the effect, the more people are used to perform it. The users channel a certain amount of energy into themselves, each performing their own separate part to complete the spell. However, a single person is able to perform this magic by themselves. An individual can access these energies using the same methods with no help from others. Doing this would make the spell more powerful because they do not need to spread the energy that they channel to the other users.
Why would performing nature magic be safer in a group of people?