Taking in visits to the USA, China, Scotland and South Africa, this episode explores the connections within and between ecosystems. Discover how a single species can influence a landscape, from tiny fireflies to iconic wolves, and how planting trees can reverse the impact of deforestation, help native wildlife to thrive and aid in mitigating the effects of climate change. The programme also examines the complexity within every ecosystem and shows how the wrong species in the wrong place can have catastrophic impacts.