if something is required to create something else then that something is needed to make that something else & creating paper requires cutting down trees ->  cut trees are needed to make paper  cut trees are needed to make paper & trees are a kind of resource ->  cut trees are a kind of resource that is needed to make paper  cut trees are a kind of resource that is needed to make paper & recycling reduces the resources needed to make something ->  recycling reduces the trees that need to be cut to make paper  decreasing something negative has a positive impact on a thing & cutting down trees has a negative impact on an environment ->  decreasing the amount of trees that are cut down has a positive impact on the environment  recycling reduces the trees that need to be cut to make paper & decreasing the amount of trees that are cut down has a positive impact on the environment -> recycling has a positive impact on the environment by reducing trees that are cut