Wednesday, April 29, 2015

Signs of Spring: Leaf buds and robin (Turdus migratorius) - Bourgeons et merle d'amérique

A classic harbinger of spring, of course, is the American robin (Turdus migratorius).

This is the first one I've seen this year, spotted in the Notre-Dame-des-Neiges cemetery in Montreal on April 25th. T. migratorius is often one of the first migratory birds to return from winter territories.

T. migratorius on a gravestone; note the A. saccharinum blooming in the foreground and the leaf buds on the shrub in the background
Interestingly, this widespread bird is apparently a major carrier of West Nile virus, contributing to the virus' spread across the continent.
T. migratorius
This particular individual didn't seem at all fazed by our presence, and in fact ended up calmly observing us in return.

Leaf bud opening
The leaves are just starting to emerge now. Here are a few photos of leaves beginning to emerge. The species I've seen already opening buds here in Montreal are Acer negundoFraxinus pennsylvanica, and Syringa vulgaris.

More leaf buds
The weather is warming quickly now.

Tuesday, April 28, 2015

Is Scilla siberica invasive?

I've noticed the crocuses, daffodils, and even some early tulips blooming in the neighbourhood gardens this week. But the most eye-catching flower out right now is Scilla siberica (siberian squill).

S. siberica
Scilla siberica is an introduced species, native to Russia, which was introduced here as an ornamental plant. It is attractive and easy to cultivate, as it spreads widely with very little encouragement or care needed. This species is a member of the Asparagaceae (asparagus family).

A friend of mine asked me a question this week that has no easy answer: Is S. siberica an invasive species? There are now some places in the United States where S. siberica is certainly listed as an invasive species [1], though there also appears to be some debate about this listing. At present S. siberica is not found on Canadian invasive species lists [2].

S. siberica
Disagreement about whether or not to list a species as 'invasive' arises from the difficulty of determining what precisely an 'invasive' species is, and the philosophical and moral debate about what we should do about it. In ecological terms, in order to qualify as invasive, a species must be (a) outside of its native range and (b) spreading to the detriment of native species. The first criterion is easy enough to judge, provided there is a historical record or some other straightforward evidence of the species' native status. The second criterion is much harder. It takes a lot of research to establish that (a) native populations are suffering and (b) the suffering is caused by the introduced species.

For example, in some places S. siberica is forming high-density populations in sites which have been previously occupied by native spring ephemerals (eg Trillium spp, Sanguinaria canadensis, etc). These native spring ephemerals are showing drops in population density and other metrics of health.

Knowing these two facts does not establish a causal link; because we're dealing with an open system, it's not so easy to tease apart potential causes of observed effects. Maybe the native spring ephemerals are suffering because of deer predation, or habitat disturbance, climate change, insect predation, fungal infection, or any number of other potential causes -- and more likely several causes including competition from the introduced species. It will take time effort to determine what, precisely, is the cause of the documented decline.

S. siberica flower - note the blue anthers and central stripe along the petals; I certainly can't dispute the aesthetic appeal of this species
And this is where we get to the non-scientific aspect of this whole issue: deciding at what level of proof we should take action. Listing a plant as an invasive species is not just a scientific statement: it's a policy decision, too. So we have to consider the policy; while scientific standards of proof shouldn't be overly impacted by practical concerns, practicality is central to policy decisions and will affect how evidence is assessed.

On the one hand, we don't want to take action without understanding the causes. This could lead to wasted or misdirected efforts, or unintended harm. But by the time we meet the scientific standards for proof, it may be too late to take any useful action. We must find ways to balance the need for good evidence with the unfortunate reality of haste, financial limitations, and culture.

All species which meet the scientific criteria for invasiveness are invasive in both senses (as this is the stricter definition), but some species which do not yet meet the scientific criteria may still qualify as invasive for the purposes of policy-making. The degree of proof to qualify for policy-oriented 'invasiveness' is in principle less strict. Exactly where we draw the line is currently unclear, and may always have to be decided on a case-by-case basis (this is never an attractive option politically; nobody likes to hear the answer "it depends" when we talk about rules, policy, and enforcement).

I believe that this issue will eventually have to be settled politically, as part of a much broader public discussion about what we, as a society, will do to address environmental issues.

So: Is S. siberica an invasive species?

Yes. And no. And we don't all agree what to do about it.

Naturalized S. siberica population in a public park in Montreal

Monday, April 27, 2015

Hypoxylon Canker

I've noticed a surprisingly large number of hypoxylon cankers on trees during my walks in the Mont-Royal park this spring.

A hypoxylon canker is a fungal infection of a tree caused by one of a number of species of fungi in the genus Hypoxylon.

Hypoxylon canker
This fungal infection tends to take hold on a tree which is already stressed (weakened) in some other way [1]. Given that the infections I saw in the park were primarily in smaller trees, especially in the aspen family, which were adjacent to footpaths, I suspect that the trees were either suffering from wind/snow damage (aspens are brittle), light deprivation (from being overshaded by taller trees), or root compaction (from the passage of a large number of people over the season). Many of these individuals were also on a heavily eroded slope, so it is also possible that they were suffering from water deprivation or erosion around their roots. The fungal infection takes hold beneath the bark and, over the course of its growth, causes a bubbling and eventual sloughing off of the bark of the tree.

Hypoxylon canker
The cankers I'm seeing at this time of year are of course mature cankers, likely from last year; it is likely, given their black colour, that these stromata emitted their spores last year, which will infect new targets. The photos I have here show the fungus at the end of its life cyle, where the bark has sloughed off to reveal the 'bubbly' surface of the fungus, the spores have been emitted, and the fruiting body has hardened and darkened.

The best method to control this type of infection is to address the underlying cause of weakness in the tree.

Sunday, April 26, 2015

Geology of Mont-Royal : The Trenton Limestone Strata and the Monteregian Hills

Disclaimer: I am not educated in geology. I have simply gone searching for some information about a topic that caught my attention when I was wandering in Mont-Royal park.

Those who have had the pleasure of hiking in the Mont-Royal park may have noticed what I did on a recent trip: there are a large number of sedimentary rocks (rocks formed of layers of material which have gradually compressed together into stone) which have quite a distinctively striped appearance:

Sedimentary rock in Mont-Royal Park
Sedimentary rocks are usually only a relatively thin layer, formed by deposits on top of igneous or metamorphic rocks.

Some internet research and the very handy interactive park map available on the Les amis de la montagne website revealed that this particular sedimentary rock is apparently part of the Trenton limestone strata, which apparently formed approximately 450 million years ago (which would place its formation in the Paleozoic era). Unfortunately, I haven't yet been able to obtain any other information about the Trenton limestone strata at all. If anybody has more information about this rock formation, I would be delighted to hear from you!

It is my understanding that the Mont Royal was formed by magmic activity below the surface along the Great Meteor hotspot track which produced a number of upshoots of igneous rock, pushing the rock above it into hills and mountains.  The Monteregian hills are all considered to have been formed from the same magmic activity.

As near as I can tell without an expert to explain it to me, the Mont-Royal and other Monteregian hills were formed when a bunch of magma pushed up and lifted the sedimentary rocks above. The igneous rock that formed as a result of this activity is apparently less prone to erosion, and so as the land around eroded, these more durable hills made of igneous rock have remained.

So what began as idle curiosity about the striped rock I saw turned into a rather extensive crawl through Wikipedia and other sites, resulting in the discovery that the sedimentary rock that caught my attention in the first place was lifted up and now sits on the shoulders of igneous rock that formed below it. Cool.

I need to take a geology course.

Saturday, April 25, 2015

Mourning Cloak - Nymphalis antiopa - Morio

I spotted quite a few Nymphalis antiopa individuals in the Mont-Royal park on April 19th. It is often one of the earliest butterflies spotted in the spring. This species is globally distributed, but tends to prefer colder, forested environments.

N. antiopa
There is some evidence that this butterfly may overwinter instead of migrating to warmer climates in winter. This may allow the species to mate and reproduce at the earliest possible time in the spring, leaving more time available for their offspring's development throughout the season.

N. antiopa exhibits some very interesting mating behaviour. The males engage in lekking, where they congregate in a general area and establish individual territories where they perform their mating displays, attempting to mate with as many females as possible. The females seek out these congregations and select mates among the choices there.

N. antiopa - this particular individual very obligingly held still while I got close to photograph it. At some point I may be better to acquire a telephoto lens for my camera, if I don't want to have to sneak up on insects hoping they will hold still while I stick a camera within a few inches of them
N. antiopa isn't much of a pollinator, as it feeds primarily on foliage and sap -- and there are some reports of its caterpillars stripping entire trees with their appetite.

Thursday, April 23, 2015

Colt's Foot - Tussilago farfara - Tussilage

On our walk on Sunday, E and I encountered Tussilago farfara (colt's foot, fr: tussilage) already in bloom, even though there was still snow on the ground in some places.

Tussilago farfara
T. farfara is a spring ephemeral, a plant which blooms in the brief period between snow melt and the closure of the forest canopy (the emergence of leaves on the trees), when there is light in the forest understory.

This plant is among the first bloomers this year. It often is, as it actually sets its flower buds in the fall prior to the season, a strategy which allows for the earliest possible emergence of flowers. Indeed, at this stage T. farfara does not have any leaves out. They will emerge only later, once the flowers have matured (and once the plant has been exposed to enough sunlight to produce new leaves). T. farfara is a rather unassuming plant later in the season, producing short, heart-shaped leaves in clusters.

Tussilago farfara inflorescence. Note the absence of leaves at this stage of the season.
The flowers are actually a cluster of florets, of which the long ones are fertile, and the ones in the inner disc are infertile. After pollination, they produce seeds which superficially resemble those of dandelions. They have a tuft of light material attached which assists in wind dispersal.

T. farfara is an introduced species in North America, being originally native to Europe. It was brought over as a medicinal plant, but note that we have since determined that it is a toxic plant which can cause serious liver damage. Some varieties without the toxic chemicals have been cultivated in Europe, but these are only in commercial settings; the wild plants are toxic.

This plant is also listed in the Ontario weed registry. It occurs primarily in disturbed areas, particularly along roads.

Wednesday, April 22, 2015

Silver Maple - Acer saccharinum - Érable argenté

So E and I went for a stroll over the weekend and enjoyed the sight of the maples beginning to bloom. Acer saccharinum (silver maple) appears to be the most forward of the maples in our area, already blooming exuberantly.

Abundantly blooming Acer saccharinum
Acer saccharinum is an interesting plant. Although it is a member of the angiosperm (animal-pollinated) lineage, this particular group has returned to wind pollination as a reproductive strategy (pollination syndromes). This fact shows very clearly in the floral morphology (flower shape).

Acer saccharinum - staminate (male) inflorescence. Note the absence of large petals or sepals, and the long stamens which expose the anthers to wind currents. The pollen produced is small and lightweight, which improves its airborne distance.

Acer saccharinum - pistillate (female) inflorescence. Yes, those little fuzzy red protrusions are pistils. They are fuzzy and relatively large in order to best sift pollen from the air.
Anemophilous (wind-pollinated) plants lack sepals, petals, nectar, and perfumes (note that some, like these, can have small or underdeveloped petals or sepals). This is because all of these function to attract pollinators and take up a lot of metabolic energy to produce. So, plants which don't need to attract pollinators will quickly see selection pressure favour inconspicuous, lower-energy flowers. Instead, they invest energy in producing larger quantities of pollen, since wind dispersal is a very imprecise method of fertilization. As a result, the staminae tend to be long and exposed, putting the anthers (pollen-producing portion) in the way of potential wind currents. The pistillae tend to be large and fuzzy in order to better sift and capture airborne pollen.

Acer saccharinum staminate inflorescences
Acer saccharinum is a monoecious plant, but is flowers are unisexual. This means that male and female gametes (pollen and eggs) are both produced on the same plant, but each flower produces either male or female gametes. Note that so far in my observations the trees produce either male or female flowers but not both, but this may vary from year to year; I will defer to the various experts who indicate that this species is monoecious and assume that the individual trees can produce flowers of either sex, and but may express only one in any given year; this also is monoecy. This kind of sex alternation by season has been observed in a number of plants including Arisaema triphyllum.

Acer saccharinum staminate inflorescences
They may not be the showiest flowers in the world, but I love the fluffy, fuzzy appearance of maple trees in full bloom. I find them quite beautiful. Of course, that means that I wouldn't survive long as a pollinator -- I'd waste all my energy visiting flowers that have no reward!

Fortunately for me there's a grocery store nearby, so my poor choice in flower won't reduce my own fitness.