LAUSR

• Savin juniper is an excellent species for desertification control in arid and semi-arid areas, where it typically establishes under the protection of nurse plants. Ultimately, established plants emerge into full sunlight as they grow, and this transition is accompanied by an increase in the preponderance of scale-like vs. needle-like leaf forms. • To test how age and variable sunlight environments affect shade tolerance in savin juniper, we established a pot study under field conditions with two age cohorts (1- and 4-year-old rooted scions) and three sunlight regimes (10%, 50% and 100% light transmittance). We measured growth, leaf parameters, photosynthesis, chlorophyll fluorescence and foliar pigments on a monthly basis (seven growing months per year, from 2015 to 2017). • Overall, there was little interaction for all variables, and both cohort and light regime had significant effects. Leaf form and spacing varied continuously, tending towards shorter, more closely spaced and more appressed scale leaves with higher dry leaf mass per area in older plants or under higher sunlight. There were no clear age-related patterns in carotenoids but both cohort and light had significant effects on gas exchange and chlorophyll fluorescence variables. • Savin juniper shows an intermediate tolerance to shade that changes with growth in that younger plants were less tolerant of full sun than older plants, consistent with its reliance on nurse plants for ultimate establishment in the open.