Plants are life sustainers, the emergence of green plants on earth produce the air we breathe, the primeval atmosphere would poison present/day life forms. When forests are felled ,erosion spreads, the sun beats down, at night temperatures plummet because the heat is not retained, the air and the soil dry out so the soil is eroded and blows away. When forests are lost a link in the carbon cycle is weakened because through photosynthesis plants catch carbon whilst giving out oxygen so levels of co2 rise causing the greenhouse effect.
Plants are self-sufficient, able to colonize new areas and survive by photosynthesis. Plants produce food ,animals consume it, without plants animals could not exist, plants provide the fabric of our landscape and homes for animal life. Before human dominance natural vegetation was abundant, covering everywhere with a huge bio diversity of tall forest to arctic tundra reflecting changes in climate ,soil and terrain, forming a natural security blanket helping to maintain the balance of gases in the air and nutrients in the soil, stabilizing the climate and river flows .
Trees in tropical rain forests have a shallow root system because the soil is thin and poor, they get their nutrients from the rich organic leaf mould ,because of the high humidity it decomposes quickly, the biomass produced feeds the trees and vegetation. The forest contains a very high bio diversity of species and are arranged in stories according to size, often the trees support each other or have large buttress roots vines also climb and support, small plants live in the trees, some have whole eco systems as big as a car. People come along and slash and burn the eco system down then sow their crops which do not grow because the soil erodes. Without the complex rainforest the thin soil is blown or washed away. People have been cutting down trees for thousands of years, the Mesopotamian civilization and the Indus valley ceased because of excessive deforestation.
The move from living off the natural vegetation to agriculture meant that trees were cut down for pasture to graze animals or to grow crops .When the fields were small and surrounded by hedges that link up with woodlands ,so they form wildlife corridors also wide margins left around fields and wild flower meadows then nature can cope the bio diversity should be enough to sustain animals bugs birds insects etc and BEES.
Large monoculture fields ,void of all biodiversity have to rely on chemicals for nutrients, pesticides and herbicides to control weeds and pests. The soil has very little humus so it erodes causing dust bowls 'America' also the soil level drops. Trees on mountain watersheds safeguard the soil on the steep slopes binding with their roots the soil and absorbing rainfall. If the trees are destroyed the soil is washed away, rain gouges out ravines, exposing the underlying rock causing landslides creating erosion in the valleys below, as seen in Nepal. It has been said that if you want to see the Himalayas, go to Bangladesh.
Indian religious writing - 'A tree is like 10 sons. It gives ten valuable things -oxygen, water, energy, food, clothes, timber, medicinal herbs, fodder, flowers and shade.'