You can make a lot of speeches, but the real thing is when you dig a hole, plant a tree, give it water, and make it survive. That's what makes the difference.
Good compost is key to thriving garden, it's zero-carbon (possibly even carbon-negative), free, and has positive ecological benefits.
Building up soil organic matter helps retain moisture and improve drainage, improves retention of nutrients, and even makes them more acessible to plant roots. Micro-fauna & flora populations are increased and these provide the basis of a rich food web where invertebrate numbers are boosted which provide meals for birds, hedgehogs and amphibians.