fallen trees are a kind of dead organism & removing dead organisms from an ecosystem causes available nutrients to be removed from that ecosystem ->  removing fallen trees from an ecosystem causes available nutrients to be removed from that ecosystem  a plant is a kind of organism & a plant / living thing requires nutrients to grow ->  organisms require nutrients to grow  if a living thing requires something then that something has a positive impact on that living thing & a living thing is an organism ->  if an organism requires something then that something has a positive impact on that organism  organisms require nutrients to grow & if an organism requires something then that something has a positive impact on that organism ->  nutrients have a positive impact on organisms  nutrients have a positive impact on organisms & organisms are a part of an environment ->  nutrients have a positive impact on the environment  nutrients have a positive impact on the environment & a plant is a kind of organism0 ->  removing nutrients has a negative impact on the environment  removing nutrients has a negative impact on the environment & harming something has a negative impact on / effect on that something ->  removing nutrients harms the environment  removing nutrients harms the environment & an environment is a kind of ecosystem ->  removing nutrients harms an ecosystem  removing fallen trees from an ecosystem causes available nutrients to be removed from that ecosystem & removing nutrients harms an ecosystem -> removing fallen trees harms an ecosystem by removing available nutrients