The food chain starts with plants.Plants convert the energy of the sun and atmospheric carbon into a biomass that is the beginnings of all food for all living creatures.
Energy and nutrients enter the food web in plants.Even in death plants recycle nutrients through decomposition.Insects, fungi, and microbes break down all this dead material into humus. Decaying organic matter and humus in soil retain moisture and nutrients within the root structure of growing plants.
Water and nutrients are absorbed by the roots then the water moves the nutrients in solution through the plants vascular system,where some is transpired through the leaves back into the atmosphere.The plant uses this as a cooling mechanism losing more water the warmer the air temperature. Trees and large areas of plant material influence a gardens comfort level and on a large scale, global weather patterns.
As evaporation of water from plants, moisture laden soil and bodies of water,collects in the atmosphere it is then released as rain. Where plant life is abundant and the soil has much organic matter rain moves through the soil into the groundwater where it moves back into the watershed.Not coming into contact with pavement, roads or sewer systems the water is less polluted and is filtered further by the earth.
So that pretty garden helps to feed life on earth, protect the waterways and influences weather.
Not bad for a hobby...