How can plants and animals affect neighboring cells directly?

Releasing hormones is one way this can happen. Hope this helps.

Labor costs would be a large factor holding production of shade-grown coffee back. if it requires higher labor costs to receive a smaller benefit per hectare, then these costs would be prohibitive on expanding this practice to all coffee growing.

True because work is more professional and you need specific skills. in your personal life you need different skills such as maintaining relationships.