Bare soil is vulnerable soil. We think of cover crops as the living skin of the land.
Diversity is particularly valuable. Legumes such as clovers, vetches, peas, lupins and fava beans can support biological nitrogen fixation. Grasses such as oats, rye and barley produce abundant roots and biomass. Brassicas such as daikon radish and mustard provide different rooting structures and nutrient-cycling functions. Flowering plants such as phacelia, buckwheat and borage can provide resources for pollinators and beneficial insects.
In Monchique, winter-growing mixtures are especially interesting because they can make use of seasonal rainfall before summer drought becomes dominant.
Keep the land covered, rooted and alive for as much of the year as the climate allows.