They're in different fields. Almond trees are more susceptible to soil moisture and need better drainage. Pest control is different, and having them all together means farmers would have to spray both crops for a problem only one of them has, and a given pesticide may be allowed for almond trees but not for olive trees (e.g. the insecticide phosmet is not allowed in olive trees destined for olive oil; lambda-cyhalothrin applications are limited to two per campaign in olive orchards; many recommend against using glyphosate for weed control in the first years of an almond orchard.)

There are some annuals that might be interesting, such as clover, that help with erosion and nitrogen fixation. Native plants serve as buffers for auxiliary species and some (Brassicaceae) act as a prophylactic against fungal infections (Verticillium). Innoculation with mycorrhizae also helps.

Perennials might be interesting in riparian zones, to help with drainage and unusual surges of flow.