I was asked in the comments recently if I had time to photograph autumn colours. Last week, I was in the Alberta and British Columbia Rockies hoping to do just that, but because of the hot and dry autumn, colours were overall poor. In fact, many trees had crisped brown leaves instead of any sort of colouration. This photograph is from my 2011 trip. It's a good example of how photographs can omit--the split stream flows through a triangular piece of land bordered by roads (which you can see via the Google Map).

The yellow-leaved trees are young black cottonwood or Populus trichocarpa while I believe the conifers in the foreground are Engelmann spruce, Picea engelmannii. The other possibilities for the conifers are Picea glauca (white spruce) or the hybrid between the two species.

It's been a long time since I've shared an image like this. In the past, they have provoked reactions along the lines as to what an image like this has to do with botany. It's hard to argue against that point, so my only excuse for sharing it is that it's a weekend before I'm out of the office for the next week, and I don't have time to write much.

For your reading fix, I suggest visiting the Art Blog of Jonathan Jones, with a recent assertion: Science is More Beautiful Than Art. If I recall correctly (the past week has been a blur), the article was forwarded to me by UBC Botanical Garden's new Artist-in-Residence, Dana Cromie.

Speaking of blurs, that is how today's photograph was made--a long-exposure smooth panning motion on some poplar trees in Jasper National Park.

This photograph is from two autumns ago, when it was a later-than-usual year for autumn colours in eastern North America. Fortunately, one small stretch of Highway 215 near the New Brunswick-Québec border was nearing peak in late September, though I only discovered it on my last day in the area. It's not really a "Natural Landscape" (how I've categorized it), as the shrubs and herbaceous plants in the foreground are trimmed low from time to time (they are along the roadside). It's not really an intentional cultivated landscape, though.

A tentative species identification today, as making a positive identification of a willow is usually a non-trivial matter involving a wide-ranging suite of characteristics. In this case, I have some close-up photographs that more clearly show the leaf shape (obovate), the not-glaucous nature of the branches, and what appear to be yellow buds against the reddish-branches. Combined with the habitat, the known species from the area, and the habit (a small shrub not forming a colony), and I reached the conclusion of Salix bebbiana--but I am entirely willing to be corrected! For more on willow identification, see A Guide to the Identification of Salix (willow) in Alberta (listed in the references).

Assuming the yellow-leaved plant in the photographs is Salix bebbiana, then this is a representative of a species native to much of North America north of Mexico, with the exception of the southeast USA. Bebb's willow or beak willow is also found in far eastern Russia and Siberia. Like the Betula glandulosa from a few days ago, this is an important browse species (though not this particular individual, given its precarious location).

There are somewhere in the vicinity of four hundred willow species, in addition to a number of naturally-occurring hybrids. The majority of these are native to the temperate and arctic northern hemisphere. Unfortunately, when a few species were introduced into Australia for erosion control, they eventually became invasive.

The Canadian Rocky Mountain Parks are on my mind as I prepare for a near-annual trip to the region for autumn colours. While this photo won't win any awards for visual drama, do note the golden colours of the deciduous trees and shrubs at the base of the avalanche chutes (particularly evident in the larger version of the photograph). Looking akin to a flow of golden lava at this time of year, these are plant communities of frequent ecological disturbance from the physical effects of avalanches.

Avalanche ecology is a relatively new field of study (if the dates on cited papers are a good indication). Seemingly, the suppression of avalanches is somewhat like the suppression of fire in changing ecosystem dynamics (see the results of a study in the Swiss Alps: Kulakowski, D. et al. 2005. Changes in forest structure and in the relative importance of climatic stress as a result of suppression of avalanche disturbances (PDF). Forest Ecology and Management. 223:66-74). Fortunately for the biodiversity of the Canadian Rocky Mountain Parks, I don't believe avalanches are suppressed (or, if at all, in only a few areas). For a broad overview of the importance of avalanches, see this video on the benefits of avalanches from the USFS National Avalanche Center, or, to learn about the importance for grizzly bears specifically, read grizzly bear use of avalanche chutes in the Columbia Mountains.

Key to Figures

Figure 1. Rooted cuttings of balsam poplar grown for 10 weeks under different photoperiods. Cuttings under a 16 hour day set bud after ~5 weeks growth, whereas those in the other two treatments did not. This genotype is from Minnedosa, MB (50.3°N).

Figure 2. Balsam poplar shoot tips showing (a) a dormant terminal bud, (b) the opening of a terminal bud in the year of its formation (a second flush), and (c) active growth.

Figure 3. Two subarctic genotypes of balsam poplar at Totem Field. The photo on the left (a) was taken May 11th 2010, while the photo on the right (b), of the same two plants, was taken July 8th 2010. The plant in the foreground is from Fairbanks, AK (65°N), whereas the plant in the background is from Labrador City, NL (53°N). Both trees set bud prematurely in late spring, but the Fairbanks genotype also drops its leaves, whereas the Labrador City genotype retains them until autumn. [courtesy Raju Soolanayakanahally, AESB-AAFC]

The University of British Columbia's Celebrate Research Week series continues today with another entry organized by Claire. Claire introduces today's UBC researcher:

Dr. Rob Guy is a Professor and Department Head in the Department of Forest Sciences. He specializes in the ecophysiology of trees and other plants, with emphasis on the use of stable isotopes (C, H, O & N) at natural abundance levels to field and laboratory problems in plant physiology and ecology. Members of the Tree Physiology Lab focus on material and energy exchange across the plant-environment interface, resource-use efficiencies and environmental stress. Special interests include plant carbon balance, water relations, nitrogen assimilation, temperature acclimation and climate adaptation.This particular write-up discusses how climate and photoperiod interact to control the growth phenology of balsam poplar (Populus balsamifera L.).

Dr. Guy writes:

Balsam poplar (Populus balsamifera L.) is a forest tree with a wide range across the boreal zone of North America, from Colorado to Nunavut, and from Alaska to Newfoundland. To study adaptive variation in this species, and to support tree selection and breeding programs, the AESB-AAFC (Agri-Environment Services Branch - Agriculture Agri-Food Canada) has in recent years established the AgCanBaP collection of 930 native balsam poplar genotypes from 62 locations (provenances) in North America. Just over half of this collection is planted into a common garden at Totem Field, on the UBC campus.

Species with large ranges can exhibit large intra-specific variation in morphology and physiology. For example, in balsam poplar, rates of photosynthesis and peak season shoot growth extension increase with latitude of origin. This is true in outdoor common garden conditions or in the greenhouse. However, when grown outdoors in southern latitudes and particularly at Totem Field, northern trees accomplish much less growth than southern ones, and many end up severely stunted.

It seems paradoxical that northern trees would have higher rates of photosynthesis and shoot extension than southern trees, yet not get nearly as large as southern trees, but this is true only in the field. If the days are kept long in the greenhouse (22 hours long!), the growth of the northern provenances continues to outstrip the south. Through these and other studies, we have established that growth of trees at high latitudes is not limited by intrinsic growth rate or photosynthesis but by day-length, which assures timely growth cessation and eventually leaf senescence and frost hardiness development. In most boreal trees, spring phenology (leaf flush) is controlled by temperature, but autumn phenology is controlled by photoperiod. Bud set for northern provenances is in response to different photoperiods than in southern provenances. This is called "photoperiodic adaptation" and it results in some odd behaviour at Totem Field.

It's not actually the length of day that plants respond to, but the length of night. Figure 1 replicates a classic growth chamber experiment showing how a light break in the middle of the night can maintain height growth in a mid-latitude balsam poplar. In this photo, an 8 hour night (left) has induced growth cessation whereas a 4 hour night (right) permits maximum growth. The tree in the middle received a 15 hour "day" plus a 1 hour light break in the middle of a 9 hour "night". It, too, continues to grow (but not as much the rightmost tree because it receives less light overall). Even just a very short night (<4 hours) will cause northern trees to cease growth and begin getting ready for winter. Within a few days their shoots will set a terminal bud (Figure 2a).

At Totem Field, the mid-latitude and near-arctic trees from northern Canada set bud in response to the longer nights that occur before the summer solstice. In other words, they begin preparations for winter before summer even starts! This explains why they fail to thrive in Vancouver. Spring does not arrive until late May or even June in their native environments, when photoperiods are long. In Vancouver, however, shoots flush and become sensitive to photoperiod long before the solstice. In fact the day-length is never long enough at Totem Field (16¼ hours in Vancouver on June 21) to maintain the growth of the northernmost trees. Mid-latitude trees, if they don't set bud much before June 21, tend not to become fully dormant and can recover with a second flush that occurs near or around this time (Figure 2b). Southern trees do what they're supposed to do and continue to grow steadily until August (Figure 2c).

Like bud set, leaf senescence also occurs earlier in northern provenances, but is separately controlled. This separation is of great adaptive importance to wide-ranging, north-temperate or boreal tree species. Because the climate of North America permits forest growth at a much higher latitude in the west than in the east, quite different photoperiods are needed to trigger events that occur closer to the summer solstice (bud set) than to the autumn equinox (leaf drop). The differences in the latter are nonetheless evident at Totem Field, where in years with an early spring, as in 2010, autumn leaf senescence occurs in May in provenances from the extreme northwest of the continent (Figure 3). In years with later springs, leaf senescence in these genotypes occurs closer to its normal time in late summer.

It is interesting to speculate how climate warming might affect tree phenology in native poplar stands and whether premature bud set may become a problem for our northern trees. Fortunately, there is always the possibility of a second flush. These observations remind us that the natural and/or artificial adaptation of forests to future climate is not just about changes in temperature. It is also about the changing relationships between temperature and the year-to-year constancy of local photoperiodic regime.