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 are needed to make paper  cut trees are a kind of resource that are needed to make paper & recycling reduces the resources needed to make something ->  recycling paper reduces the amount of trees that need to be cut  recycling paper reduces the amount of trees that need to be cut & fewer means a reduced amount ->  recycling paper causes fewer trees to be cut  cutting down trees has a negative impact on an ecosystem / organisms living in an ecosystem & decreasing something negative has a positive impact on a thing ->  decreasing the amount of trees cut has a postive impact on an ecosystem  decreasing the amount of trees cut has a postive impact on an ecosystem & fewer means a decreased amount ->  cutting fewer trees has a positive impact on the environment  recycling paper causes fewer trees to be cut & cutting fewer trees has a positive impact on the environment ->  recycling paper has a positive impact on an ecosystem by causing fewer trees to be cut  recycling paper has a positive impact on an ecosystem by causing fewer trees to be cut & an impact is a kind of effect -> a positive effect of recycling paper is that it causes fewer trees to be cut