Glossary

Phloem (FLOH-em) is the living vascular tissue in a plant’s stems and roots that transports sugars produced during photosynthesis from the leaves down to the roots, buds, and other growing or storage tissues. Unlike xylem, which moves water upward, phloem moves food downward and outward, feeding the parts of the plant that can’t photosynthesize for themselves.

This sugar transport underpins far more than plant growth. Root exudates delivered through phloem feed mycorrhizal fungi and soil microbes, sustaining the underground food web that so much of the Santa Cruz Mountains’ forest health depends on. In coast live oak and California bay, phloem is also the tissue that bark beetles and boring insects target — and in turn, the layer that woodpeckers and bark-foraging birds probe for those insects.

Phloem sits just beneath the bark, which is why girdling — cutting through bark all the way around a trunk or stem — kills a plant by severing this tissue and cutting the roots off from their food supply, even while water still moves up through the xylem for a while.

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