Snow falling on pines might not be the name of a novel, but it is an accurate description of what was happening in early May of 2015 in Arizona’s Sunset Crater Volcano National Monument.
In the generally arid and cool conditions of the higher elevations of Arizona, evergreen conifers are by far more abundant than deciduous trees. Conifer needles have similar properties to other leaves, though packed into a smaller space: conducting tissue for water and nutrients, stomatal chambers for gas exchange, chlorophyll molecules for photosynthesizing, and so on. Other than the reduced size, conifer needles often differ by having a thick and waxy cuticle or outer layer. In most cases, they also persist for more than a year or season, leading to the plants being defined as evergreen. In arid climates, the reduced surface area of the leaves and waxy cuticles are advantageous in reducing water loss. Cool to cold climates can also be desiccating, so the needles are similarly helpful in such conditions. While investing in “evergreen-ness” in temperate or colder climates comes at the physiological cost of producing tougher leaves, it has the benefits of permitting photosynthesis at times of the year when deciduous trees lack leaves and/or increased rates of photosynthesis at cooler temperatures compared to deciduous trees. The integrative science that examines the internal chemical and physical processes of plants in the context of how plants interact with other organisms, including forming broad-scale communities or vegetation types, is called plant physiological ecology.
Nature / language resource link: The word-hoard: Robert Macfarlane on rewilding our language of landscape via The Guardian. “For decades the leading nature writer has been collecting unusual words for landscapes and natural phenomena – from aquabob to zawn. It’s a lexicon we need to cherish in an age when a junior dictionary finds room for ‘broadband’ but has no place for ‘bluebell'”. After reading the article, maybe some of you might like to propose a word (or share one you use!) for the phenomenon in the photograph of “a brief, heavy snowfall where the flakes are large but do not persist because they melt instantly on the warm surfaces”.