Final answer:
In an abandoned garden with nutrient-poor soil, first observed vegetation will be hardy pioneer species such as bacteria and lichens leading the ecological recovery through secondary succession. These species improve soil quality, paving the way for more diverse vegetation to take hold over time.
Step-by-step explanation:
An abandoned garden with nutrient-poor soil will most likely first observe vegetation in the form of pioneer species. These are typically hardy species like bacteria and lichens that can survive in marginal conditions. Through a natural process termed secondary succession, these pioneer species begin the process of ecological recovery, amending the poor soil through the decomposition of their biomass, and setting the stage for other species such as grasses, shrubs, and eventually trees to establish themselves.
As more organic matter adds to the soil with the growth and decay of these plants, the soil quality improves and becomes capable of supporting more diverse and complex life forms. This process progresses until an equilibrium state of the local ecosystem is reached, which includes a mixed community of plants and animals that is much different from the original pioneer species. The eventual vegetation observed will depend on a range of factors, including climate, topography, and ongoing soil formation and enrichment.