Not All Conifers are Evergreen

This is a story about two conifers found in very different habitats in Canada and the United States. Both share one trait that makes them stand out from all other conifers: they are deciduous. Their needles turn golden in the Fall and drop to the soil, or into water, beneath the canopy. Both enjoy “swampy” habitats: one Subtropical, the other Boreal. One is in the Family Cupressaceae, the other in the Family Pinaceae.

There are five deciduous genera among conifers, some with multiple species/subspecies. They are shown in the table below. We will focus on two of them. In years past I did field work in the southern forests of the US (Texas) and in the boreal forest in western Canada (Alberta). Those experiences caused me to appreciate a few of the similarities in the habitats of the two very different genera: Larix (larch) and Taxodium (bald cypress).

References: 1 https://en.wikipedia.org/wiki/Taxodium, 2 https://en.wikipedia.org/wiki/Glyptostrobus, 3 https://en.wikipedia.org/wiki/Metasequoia, 4 https://en.wikipedia.org/wiki/Pseudolarix, 5 https://en.wikipedia.org/wiki/Larch

Larch (Larix laricina, Family Pinaceae.)

Larix laricina (below), often called tamarack in Canada, is where I first encountered this species. It’s a hardy conifer where the climate can be brutal. It has been suggested that the deciduous phenology of conifers evolved millions of years ago at high latitudes and/or elevations. Why support metabolic demand (active vegetation) when maintenance resources are next to nil?

Laricina (tamarack) is part of the “muskeg” (bog, high in organics and acidic) ecosystem, maintained often by sphagnum moss (Sphagnum spp., a source of commercial peat in Canada) and other boreal terrestrial plants, e.g. black spruce (Picea mariana). Frozen hundreds of centimetres below the surface, when sphagnum thaws it may hold up to 30x its weight in water. Therefore, larch is truly a bog species. Fall colours, before needles drop, are shown here before freeze-up in a Canadian bog (muskeg).

Source: https://treecanada.ca/resources/trees-of-canada/tamarack-larix-laricina-2/

Distribution of Larix laricina.

Bald Cypress (Taxodium distichum, Family Cupressaceae )

Bald cypress, (Taxodium distichum), is typical of many locations in the southeastern United States; its northern boundary, however, extends north to Delaware. Its distribution can extend west beyond the humid subtropical habitats (below: eastern swamps high in organics, more acidic and western dryer, riparian, less acidic), where it can be seen growing along river and stream banks in south-central Texas.

The photos below show the seasonal differences in bald cypress’ phenology: summer and fall (after needle drop).

Bald cypress in summer in a swamp. Note the enlarges taper at the base, called “knees”: thought possibly to be important in aeration of the roots.

Bald cypress in a swamp during winter, after needles drop.

Bald cypress thriving along the banks of the Medina River in south Texas (source: Pinterest).

My first introduction to bald cypress was along the shoreline of Caddo Lake (below, east Texas), one of the few naturally occurring lakes in Texas (most are behind dams).

Caddo Lake (summer) in east Texas. Photo: Jay Carriker : note the silhouettes of the “knees”.

Northern larch (L. laricina) and southern bald cypress (T. distichum) are the two genera of deciduous conifers that are found in habitats at opposite ends of the forest spectrum in Canada and the United States. Both occupy either seasonal “bog” conditions (larch) or year round standing water, including riparian sites (cypress). Their fall changes in colour make them unique among the evergreen forests in Canada and the United States.

Thank you for reading my work. If you enjoyed this note, please give it a clap.

Zack Florence ( https://sites.google.com/view/zackflorencebiosketch/?pli=1 )

This note benefited from discussions with M.F. Blakeley and M.K. Florence.