This study aims at highlighting young children's reasoning about human interventions within a forest ecosystem. Our focus is particularly set on whether preschoolers are able to come up with any basic ecological interpretations of human actions upon forest plants or animals and how. Conducting individual, semi-structured interviews with 70 preschoolers (age 4-5), we first tested their ability to consider the forest as a habitat and recognize simple food chains in it, and then we traced their reasoning about the consequences that human actions upon plants or certain forest animals may possibly have for other animals that also live in the forest. The analysis of our qualitative data with "NVivo" software does reveal an ecological aspect in preschoolers' reasoning, which is thoroughly discussed in the paper.