This week, I start with a closer look at one of the true harbingers of spring, the prairie crocus. It’s more than just a pretty flower, it’s an insect spa. I also look at how climate change means that plants are blooming earlier, but migrating birds aren’t able to keep up with the pace of warming. Finally, I look at how earlier ripening of buffaloberries may not be just what the grizzly ordered. And with that said, let’s get to it!
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Season of the Crocus
It’s funny how people choose to mark the arrival of spring. For some people, it the spring equinox. This year it occurred at 3:58 pm on March 20. Yup, it’s a moment and not a day. For others, it’s the first deck day – the first day warm enough to sit on your patio and enjoy the first warmth of a new season.
For me, it’s the first spotting of Banff’s most famous bear, grizzly 122, better known as the Boss. He’s the biggest, baddest bear in Banff and is usually the last to retreat to his den in the fall and the first to emerge in the spring.
But there’s one other very important harbinger of spring in this area; the first prairie crocuses blooming. Don’t let its name fool you. It’s a prairie flower for sure, but it follows the montane valleys into the front ranges of the Rockies.
If you’ve never seen one of these beautiful spring flowers, you can’t miss it. look for a large blue or purple flower with a bowl-like arrangement of petal-like sepals that stretch 4 cm across. You’ll want to be on the most sun-exposed montane slopes or eastward onto the prairies.
These beautiful flowers are springtime specialists. They have dense hairs on their stems and petals to help protect them from the cold early season temperatures. You’ll often find them poking their purple heads through late season snowfalls.
Blooming early is risky. It can be cold, and late-spring frosts can hamper their ability to produce seeds. There are advantages though as well.
The crocus is perfectly adapted for its role as a harbinger of wildflower season. Dense hairs insulate the flower and as it blooms, it creates a large bowl-like flower. These wide bowls are like a satellite dish. They collect limited spring sunlight and concentrate the warmth into their bowl.
The temperature inside a crocus bowl can be 10C warmer than the surrounding environment. For early-season pollinators, this is an irresistible attraction. The shape of the flower makes it warm and the early blooming means there is less competition from other flowering plants.
If you’ve ever looked to find the perfect warm spot in the sun to bask in its warmth, that’s essentially what the insects are doing inside the yellow centre of the crocus; and while they bask, they get covered in pollen. Tomorrow, they may visit another flower and share that pollen. Crocus flowers provide the perfect place to attract visitors that, in turn, share pollen and assist pollination.
They don’t waste much time either. As an early bloomer, the insects attracted to their warm centre help them produce seeds by early June – well before many other plants have even bloomed.
As a prairie specialist, the seeds are durable. During moist years, they germinate right way, but in drier years, they dry out and wait for the next growing season.
Like many of the earliest of early spring flowers, the blossoms emerge before the leaves. Heavily dissected leaves emerge as the flower fades. The Latin name for the crocus is Anemone patens, and as anemones go, it’s one of the longer-lived flowers. On some of the other anemones in the mountains, like western anemone and windflower, the flowers are short-lived and they are more often recognized by their seed stages.
The seeds are uniquely adapted so they plant themselves. Yup you heard that right. Each seed resembles a barbed spear that uses moisture to point it towards the soil. Imagine a tiny spear with rows of hairs all pointing towards the base, like the quill of a porcupine. At the same time, the structure of the seed absorbs more water near the tip and less towards the tail. This differential absorption of moisture helps to orient the seed downwards. Each time it gets wet, it changes shape as it selectively absorbs and repels water. This slowly moves the seed downward, through leaf litter to get it ever closer to the soil.
If the seed germinates, it creates a deep taproot. Once established, it can reliably bloom for 50 years or more. A single plant can spread 30 cm across and generate 40 flowers at a time.
Crocus flowers are not just a flower, they’re a community of blooms that are part of a large long-lived plant. They provide a spring spa for spring insects and in turn, are rewarded with the benefit of pollination.
Every time you look at a new plant, animal, or bird, ask yourself why is it here? How is it connected to the other members of the community? What does it need to survive and how does it play a role in how other community members survive? Everything is connected, and our next story will illustrate some of the ways in which warming climates are stressing those connections.
Warming Climates are altering Food Availability for Wildlife
Ecosystems are delicately balanced systems which evolved over thousands, and in some cases, hundreds of thousands of years. Over these vast timespans, patterns emerged around normal seasonal changes. Springtime in the mountains is a time of rebirth. The first crocus and coltsfoot flowers are now blooming, and soon the grass will begin to turn green, new leaves will sprout, and the poplar fluff will all combine to set off the seasonal patterns that kickstart the new growing season in the mountain west.
Every plant has evolved to sprout, leaf, flower, fruit, seed, and then either die or go dormant for winter. The timing of these stages has developed through the ages and is closely tied to local climate and temperature. When climates are stable, the timing of these important life-stages is also relatively stable.
As you explore the mountains this spring, take careful note of when you first notice important seasonal landmarks. The first crocus flowers are one of the most exciting moments in the mountains. Surely, spring must be here when their fuzzy purple or pink flowerheads emerge.
Come late-April or early May when the first leaves sprout, the landscape suddenly looks greener than you remember from previous years. New colours are brilliant colours. Take note when the first poplar fluff fills the air and when the first conifer pollen clouds initiate the first sulphur storms.
These are only a few of the critical events that are part of the annual cycle of life, death, and rebirth that northern ecosystems go through on an annual basis.
With warming climates, the timing of critical seasonal events is shifting. In a 2011 study, researchers Elisabeth Beaubien and Andreas Hamann of the University of Alberta studied the blooming times of the prairie crocus (Anemone patens), trembling aspen (Populus tremuloides), Saskatoon Berry (Amelanchier alnifolia), choke cherry (Prunus virginiana), wolf willow or silverberry (Elaeagnus commutata), northern bedstraw (Galium boreale) and finally yarrow (Achillea millefolium). These are just a few of the representative plants of the central parkland ecoregion in central Alberta.
They looked at how their blooming times varied over the period of 1936 and 2006 in response to warming temperatures. This study is interesting in large part because there aren’t too many locations in North America with long records of spring blooming dates. This is also one of the first studies to specifically look at higher latitude plant ecosystems.
Spring blooming is not solely a reflection of temperature. A number of factors determine the moment when a plant first blooms. While early blooming allows a wildflower like a prairie crocus to take maximum advantage of the shorter growing seasons at higher latitudes, it also puts it at higher risk of late-spring frosts. For other plants, the amount of available daylight may limit when they can bloom. For other plants and/or locations, the amount of snow on the ground adds an additional limiting factor.
In episode 76, I look at a new report showing that Canada is warming up at twice the global average. Unfortunately, the further north you travel, the more drastic are the effects of human-caused global warming.
Research has shown that in northern latitudes, at least for the prairie crocus, the risk of frost is a secondary selector for blooming when compared to the length of the growing season. The need to bloom as early as possible overpowers the risk of potential late-season frost events. So over time, the crocus blooms earlier and earlier as the climate warms.
When biologists talk about growing seasons, terms like “growing degree days” are bandied about extensively. In most studies, a growing degree day reflects a day when the average daily temperature is above 5ºC. Differing plants need different numbers of growing degree days. This study specifically chose plants that historically have sequentially bloomed one after the other on successfully later dates.
Early bloomers like crocus and aspen can flower shortly after the snow melts. In fact crocuses, with their furry flowerheads, are often seen literally poking their purple heads through the last bits of snow. For the crocus, earlier spring means earlier flowers.
This study looking into more than just blooming dates. It looked at a range of species in an attempt to determine what influenced blooming in each one. There were three goals.
- The first was to see if the plants had any reaction to global warming. Warmer temperatures are irrelevant if there are other constraints on flowering that are more of a limiting factor. The first step is to determine if warming has any impact on blooming.
- Second, it looked to see if changes in blooming patterns reflected the corresponding changes in temperatures. Alternatively, it was also trying to determine if temperature was or wasn’t the primary factor determining changes in blooming dates.
- Finally, it looked at whether earlier blooming increased the risk of late-season frost damage.
Of the plants in this study, the first to bloom is the crocus. Usually, within just a few days of the crocus flowers emerging from the last snows, the trembling aspen begins to produce pollen and leaf out. Things stay fairly quiet for a little over three weeks until the Saskatoon berry blooms. From this moment, in 8-day intervals, the chokecherry, then the wolf willow, followed by the northern bedstraw and finally the yarrow bloom, or at least that’s how it used to work.
Curiously, over the 70-year period covered by this research, the mean February temperature rose by an astounding 5.3ºC, March by 2.7ºC, and April by a still incredible 1.8ºC. When researchers reviewed the average blooming dates of the 7 plants in this study, they noticed the early blooming flowers like crocuses advanced blooming by two weeks between 1936 and 2006. Later blooming plants like wolf willow and bedstraw only advanced by 1 to 6 days.
When it came to the risk of late-season frost vs blooming date for crocus, they found an interesting result. The report states:
“Late-spring frosts of -10ºC occurred earlier, at a rate of 0.7 days per decade, and very severe frosts of -20ºC occurred earlier, at a rate of 1.1 days per decade over the study period. This is a considerably slower rate than the advance in bloom times for the early-blooming species which occurred at a rate of 2 days per decade. This discrepancy raises the question of whether early-blooming species might be exposed to increased risk of late-spring frosts because of climate change.”
In essence, the blooming dates of crocus were outpacing the end of winter. While the air was warm most of the time, late-season frosts actually became a bigger risk for the plants over time. Winters are becoming shorter, but the timing of spring is not merely a reflection of temperatures. Just because daytime highs increase, lingering spring frosts are now an even bigger risk for crocus flowers.
In 2006, the cold frosts that hit crocus blooms were on average 4ºC colder than they were in 1936. For crocus, the higher risk of frost is worth the risk if the growing season is a few days longer. This study also showed for the first time that earlier blooming comes with a higher risk of frost.
Beaubien and Hamann’s study helped biologists understand how warming climates impact blooming dates, but what it didn’t do was offer a good way to forecast the blooming stage of particular plants remotely.
Plants blooming earlier is a very big deal ecologically. Blooming signals the emergence of plant-eating insects. Nesting birds rely on these insects in order to raise their young, but increasingly the arrival of migratory birds is getting more and more out of sync with the spring green-up.
A recent study looked into the increasing difference between spring green-up and the arrival of migratory birds across North America. While plant emergence is determined by varying climatic conditions, many bird migrations are triggered by less variable conditions like the amount of daylight in their wintering grounds.
If birds arrive at the wrong time, they risk missing the peak availability of food for their nestlings, and in turn, risk reduced reproductive success. Birds are responding to changes in the arrival of spring in their nesting grounds, but it appears that in many cases, they aren’t responding quickly enough over time.
This study looked at a very short timespan, just the years between 2001 and 2012, but even in that short period, warming climates were having big impacts on a number of migratory birds.
The good news is that birds are responding to warming climates by migrating and nesting earlier. As winters get shorter and shorter, birds able to adjust their migration and nesting times at a similar pace will be more likely to weather the rapid changes to their historic nesting patterns.
On first glance, it would seem that the simple act of migrating would mean that a particular bird species was pretty adaptable, after all, simply migrating IS an adaptation to changing availability of foods over the course of a year. The problem arises when the annual events that trigger migration, like hours of daylight don’t change, but the conditions at the nesting sites are changing dramatically from one year to another.
Timing is everything when it comes to balancing migration and nesting. Birds that arrive too early to their nesting grounds need to fight cold temperatures, and eggs hatching before enough food is available. Arriving in the nesting grounds too late risks missing peak food supplies, and fewer mates with strongly defended territories. It’s a delicate balance that is being shaken up more and more as climates warm.
This study looked at 48 perching birds across North America. While spring green-up is not a definitive indicator of food availability, it is a good indicator for arrival times of perching birds for several reasons. As the report states:
“we view green-up as a strong index point for arrival timing of migratory insectivorous birds, for the following reasons. First, green-up predicts the increase in availability of insects as bird resources. Most foliage-gleaning birds consume primarily herbivorous insects, whose biomass, in turn, increases as a direct response to green-up.
Second, green-up occurs at comparable temperature thresholds to the flight of many insects and degree-day models predict both leafing phenology of plants and flight of insects.
Third, birds incur costs for later arrival. While it has not yet been established whether edible arthropod biomass generally decreases at times beyond early spring, anti-herbivore allelopathic chemicals tend to increase throughout the growing season and birds may face additional costs with later arrival such as fewer available nest sites and fewer available mates with territories.”
Essentially, green-up tends to sync with the maximum availability of food insects, the insects are more mobile, and therefore more available for hungry birds, at the temperatures associated with green-up, and finally, late arrival may mean that plant-eating insects have had more time to accumulate distasteful chemicals which deters birds from feeding on them.
This study showed that for 27 species, green-up averaged 0.952 days earlier each year. Surprisingly, for 4 western species, the opposite occurred. Green-up occurred some 1.52 days later each year. It found that bird arrival times were changing to better match the actual green-up dates.
Unfortunately, the pace with which birds were adapting their arrival and nesting times didn’t keep pace with warming. For 7 species, the timing of green-up exceeded the arrival time of the birds by an additional 0.63 days each year. This means the birds are falling behind by a little more than half-a-day each year. Over 12 years, that’s more than 6-days more out-of-sync with the emergence of insect foods.
Biologists are constantly looking for better ways to estimate the seasonal availability of foods while also looking at how local animal populations are able to adapt to those changes.
As climate change becomes a bigger and bigger player in our ecosystems, scientists need to be able to create computer models that will better help them to predict the timing of plant cycles over time. While aerial photographs can tell us a lot about the forest canopy, it reveals very little about what’s happening on the forest floor.
A new study by Ph.D. candidate David Laskin is looking to change this – in particular for one critical mountain plant, the Canadian buffaloberry. This low shrub of montane and lower subalpine landscapes is one of the most critical foods for black and grizzly bears in the central Rockies.
The study was designed to test a method that would allow biologists to reliably predict what stage plants would be in at any given time, despite the fact they’re hidden from satellite view by the forest canopy above them.
Ground level growth patterns are difficult to predict using visual aerial instruments so Laskin devised a way to combine growing degree days, or the number of days above +5 C along with satellite measurements of under-story temperatures to estimate the seasonal progression of buffaloberry from flower to fruit with almost real-time accuracy. As interesting as this might be, you might ask why it’s important to be able to predict the exact timing of flowering, fruiting, or even leaf fall so accurately.
In the central Rockies, there isn’t a huge diversity of available foods for black and grizzly bears. Buffaloberries are the most important food every year and provide the vast majority of the bears fat reserves as they head into their winter hibernation. When it comes to reproductive success, female bears need at least 20% body fat before they become pregnant.
When buffaloberries ripen, a large grizzly can eat up to 200,000 berries every single day. That’s the equivalent of you eating 75 Big Macs every day for 6-8 weeks while the berries are available. When the first frost arrives, the berries drop from the plant and the season is over.
Laskin’s study was able to predict fruit ripening within an error of just +2.4 days, and since the prediction relies on data that can be added to computer models, it can predict when berries will ripen in varying climate scenarios.
They looked at conditions in the year 2080 based on current climate models. This showed a stark change in all stages of the plant’s seasonal development. It showed that in low-elevation montane valleys, ripe berries would occur 19-days earlier than they do today. At higher elevations, the changes were even more astounding, with berries predicted to ripen 37-days earlier in the lower subalpine. During this same period, the range will decrease by 8%, indicating a loss of 4,510 km2.
With earlier ripening, the berries are more likely to wither if left uneaten as opposed to being killed off by frost as is normal under today’s climate.
So what does this mean for black and grizzly bears? It will impact both bears, and our relationship with them. As berries ripen earlier and earlier, this also means that bears will be attracted to trails, roads, and townsites earlier as well. Buffaloberries need sunlight to grow, and so they need openings in the canopy where sunlight can percolate down to the forest floor. This means our low elevation trails and roads are lined with these tasty berries (at least the bears like them). Townsites also create lots of openings in the canopy and so there are usually plentiful berries near large accumulations of people.
This has always been a challenge in both bear and human-use management. If you live and play in the mountains, it’s important that you understand just how critical this single plant is to the survival of black and grizzly bears. The quest for this single berry, and people’s refusal to stay out of legal closures designed to allow bears to feed is ultimately what led to the translocation and death of Canmore’s Bear 148.
With earlier ripening, these conflicts will likely become more common.
There is another potentially more important impact that earlier ripening will have on bears. At first glance, earlier ripening should be a good thing for bears. They’ll have longer to feed on them and more time to fatten up. Instead of being killed by frost, the berries may persist, but in the end, they will dry out naturally.
One thing that many of us haven’t considered in the past is that the timing of the ripening can also be critical to bears. Just like nesting birds try to coincide nesting with available insects for food, bears also have a strong connection to WHEN the berries ripen. While potentially more berries in their belly IS a good thing, having them ripen ever earlier is not.
Currently, berries ripen just when they’re needed most. During the summer months, the amount of food available to bears in the central Rockies isn’t sufficient to help them build their fat layers for winter. Buffaloberries ripen just at the perfect time. The bears have lost significant weight and whammo…suddenly there is an almost endless supply of nutritious berries.
The timing is critical because the berries allow them to gain weight at the perfect time; just before winter denning season. While females mate in the spring, they aren’t technically pregnant yet. Mating fertilizes their egg, but it doesn’t implant into the uterus and begin to develop into cubs until the late fall. If she doesn’t have enough fat reserves than her body will just reabsorb the egg and she won’t actually become pregnant.
If the berries ripen too early, bears may fatten up, but with a longer lag time between berry season and hibernation, they may head into their dens in poorer condition. It turns out its not just the right amount of calories, but the right calories at the right time that is critical.
Bear populations are seeing changes in their primary foods across their western ranges. In episode 42, I look at a study that showed bear populations in Alaska abandoning salmon streams to feed on red elderberry bushes. Historically the salmon run occurred prior to the elderberries ripening. This was ideal for the bears because they could feed on the salmon first, and when the salmon run was fading, the berries were ripening.
Unfortunately, the salmon run occurs at the same time each year, but the berries are ripening earlier and earlier. Given the choice, the bears chose elderberries over salmon, and the biologists lost their minds. No scientist ever believed that bears would choose berries over meat protein but it turns out that it’s not about the amount of protein, but about the right protein.
Bears not feeding on salmon has a huge impact on the wider ecosystem. Bears eat salmon, but they also carry fish into the forests and leave much of the meat behind. They focus on the more fatty parts of the fish, the eggs, the brain, and the skin. The parts you and I might want, they may toss away. When you have an unlimited amount of food, you don’t have to clean your plate, you can just eat your favourite parts.
As bears dragged salmon into the forest and left remains behind, they provided food for an ecosystem of animals that scavenged on these remains. Whatever was left provided nitrogen to the plants and trees growing along the rivers. This role as a disperser of nutrients along the salmon streams is at risk as food availability changes and cycles get out of sync. You can check out the story at MountainNaturePodcast.com/ep042.
Before this story, I had never really heard the word phenology before. According to Wikipedia:
“Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate.”
I remember when I was a kid and I first learned about the idea of the web of life. It talked about how everything was connected. Pulling on one strand would affect countless other strands as so many plants, animals, birds, invertebrates, and other living things were connected.
What I never considered was time! Each of those strands was only connected to each other at the right time. If caterpillars don’t coincide with birds that need them for food than the system goes out of balance. Birds miss out on their optimum feeding time, and if insects aren’t being fed upon, then they also have a greater opportunity to spread and become pests.
Ecology now has a much more important scientific specialty. I’m sure we’ll be talking about this more and more down the road
In the past few weeks, the first robins have begun singing at sunrise in the mountain west. Why not begin paying attention to natures milestones as you explore the mountain landscape. When did you hear the first robin song? How about last year? When did the first buffaloberry ripen? I for one plan on taking much more careful notes about not just what I see, but when…