All posts by admin

Hairys and Downys

by Don Scallen, Vice-President
Downy Woodpecker - Illustration by Fiona Reid
Downy Woodpecker – Illustration by Fiona Reid

Hairy and Downy woodpeckers frequent backyard feeders at this time of year. Though different sizes – the hairy larger, the downy smaller – their colouration and patterning is well-nigh identical. The bills tell the tale. Hairy woodpeckers brandish large dagger- like beaks; the beaks of Downys are smaller and more chisel-like.

I’ve always assumed that downy and hairy woodpeckers were about as closely related as two species could be – that sometime in the relatively recent past, their lineages diverged from a common ancestor.

This happens when a species of animal or plant becomes geographically isolated through some mechanism, such as an ice age. Each group then proceeds on its own evolutionary trajectory to become a different species.

Interestingly, gene sequencing has proven that this process is not responsible for the similarity between downy and hairy woodpeckers. It turns out that they aren’t closely related at all. They are both, most assuredly, woodpeckers, but they peck on separate branches in the woodpecker evolutionary tree.

One startling theory suggests that mimicry – like the mimicry that explains the similarity between monarch butterflies and viceroy butterflies – is at work. Just as viceroys benefit from their resemblance to toxic monarchs, downy woodpeckers may benefit from looking like hairy woodpeckers.

To explain how, a study in 2012 proposed that the look-alike downys are able to claim space and resources because hairy woodpeckers mistake them for other hairys. The reasoning continues that since hairy woodpeckers know that fighting each other is potentially dangerous – recall the dagger beak — they leave the similar looking downys alone as well.

I don’t think the last words have been written on this topic. For me the idea that downy and hairy woodpeckers developed their striking similarity as a result of mimicry strains credulity, but then the natural world is nothing if not astonishing.

Read more by Don Scallen at his blog, Notes from the Wild

Long-tailed Ducks

Long-tailed Duck (Fiona Reid_
Long-tailed Duck (Fiona Reid_

Personally I prefer their old name, Oldsquaw, but sadly it has been replaced by a more prosaic one. Nonetheless, this bird has always been a favorite of mine, a winter visitor elegantly attired at all times, and as with all the winter ducks, apparently unfazed by cold water and icy winds.

Don Scallen and I had stopped off at the Travelodge Hotel in Burlington to see what the lakeshore had to offer and we enjoyed watching a large group of Long-tailed Ducks diving for food. They swam away from the rocky wall on our approach, but not for long. They returned close to shore to dive under large chunks of rubble and rocks, staying underwater for several minutes at a time. We thought they were probably gleaning mollusks, and in fact this is their main source of food in winter. In summer these ducks also eat aquatic insects, other aquatic invertebrates, and some plant material. They usually feed within 30 feet of the water surface, as they were today, but these ducks can dive more than 200 feet deep at times. Like most ducks they propel themselves with their feet when diving, but they also may swim with their wings partly open. They fly low, with stiff wing-beats, sometimes tilting from side to side. During migration and when flying over land they fly very high in large flocks.

These ducks establish pair bonds in winter or during migration. They nest near water, using a great deal of down that the female supplements as she lays her eggs. Females first breed at two years of age, laying 6 to 11 eggs and incubating for 24- 29 days. The young swim and dive soon after hatching, but are tended by the female who may dislodge food items for them. They start to fly about a month later.

by Fiona Reid
President, Halton/North Peel Naturalist Club

Death of a tree

Two weeks ago one of my favourite trees was felled by a bulldozer. This tree, on Creditview Rd. in Brampton, was graced with the lovely arching form that only mature elms exhibit.

Before Dutch elm disease ravaged the land this beauty was common. The few remaining mature elms are rare treasures.

The lure of this elm was so powerful that I would include Creditview Road on my route to work simply to see it in the morning. The green and gold cropland surrounding it provided a lovely foil for its iconic form.

The cropland is no more. The soil that gave life to the wheat, the corn and the soybeans has been scraped bare by earth moving equipment. Denuded and sterilized, the land waits sullenly for the homes and strip malls that characterize the inexorable expansion of Brampton.

I knew the destruction of this landscape was imminent. New development announces itself with cheery signs and property stakes. But I harboured hope for the elm. Fencing had been placed around it. I thought – naively it turned out – that “my” elm would be saved.

The elm now lies ingloriously in the mud, its roots ripped from the desolate earth.

I realize that thousands of trees are felled every day in this province to feed various appetites. I realize as well that landowners have certain broad rights to do as they wish with the property they own.

But, perhaps it is time to try to enshrine some protection for trees of character – trees that rate highly for certain features including size, rarity, cultural importance and the admittedly subjective quality of beauty.

The elm will continue to influence the route I take to work. I’ll now avoid the place where it once stood.

by Don Scallen
Vice-President, Halton/North Peel Naturalist Club

Tufa deposits discovered in Credit River watershed

Belfountain CA Tufa Deposit (Photo by Lynda Ruegg)
Belfountain CA Tufa Deposit (Photo by Lynda Ruegg)

In 2012, Credit Valley Conservation inventory staff discovered a provincially and nationally rare phenomenon along the Niagara Escarpment at Silver Creek and Belfountain. This discovery was of tufa, a soft rock, being actively formed at the emergence of select springs. Tufa is a variety of limestone. It differs from typical Escarpment rock formed on ancient sea beds from calcium-rich shells, exoskeletons and coral. Instead, tufa is formed by calcium precipitated out of water. Bits of the precipitated calcium carbonate can amalgamate to create larger rocks.

Ontario’s known tufa deposits are formed at springs and waterfalls, particularly along the Niagara Escarpment. Tufa is only known in Ontario from Brantford, Paris, Dundas, Niagara Falls, and with the discoveries reported herein, Silver Creek and Belfountain. In 2008, the Ontario Ministry of Natural Resources designated a tufa deposit in Brantford as a provincially significant Earth Science Area of Natural and Scientific Interest.

Tufa only forms at springs where just the right conditions exist. First, ground water must contain carbon dioxide picked up from the air, making the water weakly acidic. Second, the ground water must become supersaturated with soluble calcium by dissolving limestone. Third, as the calcium-rich water emerges from the ground, it must release enough carbon dioxide to cause the soluble calcium to solidify into insoluble calcium (rock). The same precipitation process is responsible for the formation of stalactites and stalagmites in caves.

Precipitated Calcium Carbonate in Tufa Pool at Silver Creek Conservation Area (Photo by Leanne Wallis)
Precipitated Calcium Carbonate in Tufa Pool at Silver Creek Conservation Area (Photo by Leanne Wallis)

Tufa was first found in the Credit River watershed by the author and assistant Pete Davis at Silver Creek Conservation Area. The author recognized it based on tufa deposits seen on a Hamilton Naturalist’s Club hike to Spencer’s Gorge (Dundas) led by Dr. Terry Carleton, a forestry professor at the University of Toronto. Dr. Carleton was the first to document tufa deposits at Spencer’s Gorge, which he recognized based on his observations of similar occurrences in England. News of the discovery at Silver Creek led to CVC’s Scott Sampson reporting possible tufa at Belfountain Conservation Area. A visit by the author, CVC’s Dawn Renfrew, biologist Lynda Ruegg, and Dr. Carleton confirmed the report.

Tufa deposits at Belfountain may be more abundant than anywhere else in Ontario. Tufa deposits can be easily observed at this conservation area on north-facing slopes. The best viewing spot is from the foot bridge that spans the West Credit River. The largest and most impressive tufa deposit can be seen from here on the slope on the south side of the river. This tufa deposit is almost completely covered by a blanket of moss in shades of green and red, with a small patch of whitish tufa peeking through.

Tufa deposits are a challenging growth environment for plants because soil is absent, the substrate is rock, conditions are calcareous, and there is a constant flow of cold water. Few plants can function in such environments; many of those that can are mosses, especially those specializing in seepy, calcareous habitat. Our tufa deposits, if not barren, tend to be either dominated by mosses, or populated by hardy plants such as Watercress (Nasturtium sp.), Jewelweed (Impatiens sp.) and European Coltsfoot (Tussilago farfara). The dominant moss on Silver Creek and Belfountain tufa deposits is Cratoneuron filicinum. It is not a rare moss, however, there are some provincially rare mosses known to grow on tufa that could be found in future inventories. Interestingly, because photosynthetic activity removes carbon dioxide from the spring water, mosses and other plants actually help create more rock once they become established.

In addition to potentially supporting rare mosses, tufa formation areas may also act as amphibian and dragonfly/damselfly breeding habitat. This is because tufa is often formed on slopes, creating terraces on which small pools of water are formed. Evidence suggests that salamanders (some of which are Species At Risk) may breed in these pools, and as some dragonfly/damselfly species restrict their breeding areas to seeps, they may also be found in these tufa pools. These spring-fed pools may also be an important water source for wildlife, especially if they remain unfrozen in winter months.

Tufa formation is a topic only recently receiving attention amongst biologists, and with increased awareness, the author expects more tufa deposits to be found in the future along the Niagara Escarpment.

Leanne Wallis
Credit Valley Conservation

Results of the 2012 Christmas Bird Count

The 22nd annual Christmas Bird Count took place on December 27, 2012. The fresh fall of snow overnight hindered or even prevented the participation of some count volunteers. Overall, there were 18 participants that took part in the field observations.

Generally, the Count produced close to average results based on comparisons with previous counts. The total number of species reported was 51 and the total number of birds was 10,082. The long-term averages for those are 49.9 and 9760 respectively. The results for the individual species are presented in the attached table. A new species for the Count was Cackling Goose seen in Count Week at Fairy Lake in Acton (See report in this issue of the newsletter). Also not previously reported was a Scaup sp. but this may not be entirely new as Lesser Scaup was recorded in 2011. New high counts were reported for Cooper’s Hawk (6), Merlin (2), Hairy Woodpecker (29), Bohemian Waxwing (180) , Dark-eyed Junco (693), and Northern Cardinal (101). Higher than average numbers of Canada Goose (3755), Mallard (682), Cedar Waxwing (159), American Tree Sparrow (591), and American Goldfinch (269) were recorded. Seventeen species had lower than average numbers and this offset the higher numbers mentioned above.

Thanks to the following participants: Ray Blower, Mark Cranford, Betty Ann Goldstein, Megan Kenzie, Lou Marsh, Meryl Marsh, Irene McIlveen, W.D. McIlveen, Fiona Reid, Dawn Renfrew, Teresa Rigg, Don Scallen, Dan Shuurman, Rick Stroud, David Sukhiani, Janice Sukhiani, Patrick Tuck, and Dave Williams.

Many thanks once more to Larry May for arranging access to the Maple Lodge Farms property and to the Halton Regional Police Service for use of the community boardroom for the wrap-up session.

Cackling Geese at Fairy Lake, Acton

On December 23, 2012, Bradley Bloemendal posted the sighting of at least three Cackling Geese at Fairy Lake in Acton was on the ONTBirds hotline. Next day, I went to check out the report. At that time, there was still a fairly large area of open water on the lake. I counted 330 Canada Geese, 32 Mallards, one American Black Duck, 6 Common Mergansers, and 8 Ring-billed Gulls. I could not distinguish any Cackling Geese among the birds there but they could easily have been present among the geese lined up on the ice off to the west side of the lake. Many had their heads tucked in and size differences were impossible to determine under those conditions. On December 26, I went back and found that much of the formerly-open water had frozen. The Canada Goose count was now down to 130 and those were present in the last open water close to the point in Prospect Park. Among them were four Cackling Geese. As can be seen in the accompanying photo, the Cackling Geese are much smaller than the regular Canada Geese and their bills are stubbier. Their presence was therefore confirmed for Count Week for the Halton Hills Christmas Bird Census that took place on December 27, 2012.

The taxonomy of birds that most people would recognize as Canada Geese has been in debate for many years. Splitting into various races was mentioned by Tavener over 90 years ago. Over the years, the number of recognized races or sub-species has stood at ten to twelve different forms. Distinction between these is blurred at best but size is one of the main features. There is much overlap and intergrading between the races as well as hybridization, not to mention size differences caused by diets and food supply, and thus distinction in the field is nearly impossible. It was no surprise though that American Ornithologist’s Union’s Committee on Classification and Nomenclature decided to split Canada Goose (Branta canadensis) into two species: Canada Goose (B. canadensis) and Cackling Goose (Branta hutchinsii). This became official in 2004 in the 45th supplement to the Check-list of North American Birds. Greater Canada Goose contains six subspecies, namely canadensis [Atlantic], interior [Interior], maxima [Giant], moffitti [Moffit’s], parvipes, fulva [Vancouver], and occidentalis [Dusky]. The smaller Cackling Goose (Branta hutchinsii) group includes the subspecies hutchinsii [Richardson’s], [Bering], leucopareia [Aleutian], taverneri [Taverner’s], and minima. The asiatica are already extinct.

Cackling Geese
Cackling Geese

The Cackling Goose was first recognized as a separate species when Sir John Richardson collected a specimen in 1822 north of Hudson’s Bay. He named it Branta hutchinsii after a man by the name of Hutchins who was employed by the Hudson Bay Company. For this reason, it is sometimes referred to as Hutchins’s Goose but now it is identified as the Richardson’s subspecies of Cackling Goose. The geese at Fairy Lake appear to be of this subspecies as their breasts are light coloured, unlike the Cackling Cackling Goose (minima) which usually has a much darker breast.

Nomenclature of Canada and Cackling Geese is far from settled and we can expect further changes. There has even been a recent proposal that the group be divided into six species with 200 subspecies. This classification would be quite unworkable for field biologists even though DNA analysis might justifiably distinguish that many true species. It is simply not feasible to recognize that number of subspecies without access to DNA laboratory testing. We are only now just learning to separate out the Cackling Geese. Let’s not go too far in the taxonomic splitting exercise. There is always a possibility that while there may be genuinely different genetic groups, the differences may not be enough to separate the species and in the end, we might still be looking at one large but diverse species of Canada Goose.

by W.D. McIlveen
Halton/North Peel Naturalist Club

LaSalle Park, Burlington

Black-crowned Night Heron (Jim Hughes)
Black-crowned Night Heron (Jim Hughes)

A small group of club members joined me for an outing to La Salle Park back in November. We were fortunate to have very good weather – so often it is extremely cold on the lakeshore! We saw all the more common ducks and swans, and were happy to watch a large group of Ruddy Ducks and with them were some White-winged Scoters, a nice bird to see up close.

Yellow-rumped Warbler (Jim Hughes)
Yellow-rumped Warbler (Jim Hughes)

I spotted two Yellow-rumped Warblers, quite late to be around foraging for insects in the willows. After we all had a look at the warblers we went over to see the Trumpeter Swans up close on the beach. We almost missed a juvenile Black-crowned Night Heron perched above our heads!

La Salle always seems to have something good to offer and this day was no exception.

by Fiona Reid
President, Halton/North Peel Naturalist Club

Dust devils

Earlier this Spring on two successive days, I was driving along our gravel road and noticed a ‘dust devil’ at the same location each time. I am sure that everyone has seen such things at some point in their lives. Seeing one is not at all unusual but noting two in the manner that they occurred prompted me to prepare this little note.

The conditions that must exist to form the dust devils will likely occur many times but they remain invisible. We only see them when they cause fine dust, leaves, paper and similar light materials, rarely snow, to be swept up into a circular funnel. Without the telltale visual evidence, we pay no attention for we simply cannot detect them. Similarly, we seldom have the opportunity to photograph them. They typically only last a few seconds so unless we have a camera already at hand, we don’t get a fair chance to document their existence.

Dust devil photographed at Lake Bogoria, Kenya, 2001 (Photo by W.D. McIlveen)
Dust devil photographed at Lake Bogoria, Kenya, 2001 (Photo by W.D. McIlveen)

In many respects, they are like miniature tornados with a spinning vortex. ‘Whirlwind’ is a fairly good description. They may be as small as meter wide and ten meters high to rare ones that might be ten times as wide and one hundred times as tall. The motion is nearly always upwards in the form of a swirling updraft under sunny conditions during fair weather. A basic requirement is that there are areas with a differential in heating of different air pockets. The devils form when hot air near the ground surface rises quickly through a small pocket of overlying cooler, low- pressure air. Under the right conditions, the air may begin to rotate. As the air rapidly rises, the column of hot air is stretched vertically, causing intensification of the spinning effect. A fully-formed dust devil is a funnel-like chimney through which hot air moves, both upwards and in a circle. Additional hot air rushes in toward the developing vortex to replace the air that is rising As the hot air rises, it cools, loses its buoyancy and eventually ceases to rise. As it rises, it displaces air which descends outside the core of the vortex. The spinning motion cause the dust devil to move forward. The upward speed of the air within the vortex has been reported to be at least 40 km/hr. On occasion, wind speed in the rotating air can reach as high as 120 km/hr.

Dust devils are most evident in flat terrain that lacks vegetation, or in fields, deserts, or tarmac. Such conditions favor the build-up of heat near the ground surface as well as the increase the chance that dust or sand may be swept up. Clear, or relatively clear, skies enable solar energy to easily reach the ground to warm the surface yet have cooler air above. Ambient wind needs to be very low or absent or else there would be too much mixing of the cooler upper air with the heated air at ground level. If two distinctly different air temperature regimes cannot be established, then a dust devil cannot form.

Somewhat similar vortices form in the center of large fires like forest fires where there is a rather obvious source of heated air and smoke. Vortices also occur in the lea of buildings that are exposed to winds, depending upon the size and shape of building and other characteristics of the surrounding environment. The latter are notably different in origin, arising from mostly lateral winds. The swirling motion can cause snow to form drifts and other debris to form circular piles on the downwind side of the structures. These materials fall to the ground in the centre of the vortex which lacks the air speed to keep the materials suspended.

Dust devils seldom cause significant damage or injury, simply because they are limited in size and do not last. On occasion, they might do limited damage if the particular conditions allow the wind speed to be unusually high. The wind movement could potentially move materials from one place to another and this may be undesirable from a human perspective. Dust might become entrained in the wind and this might be quite undesirable. They could cause the components of the dust or creatures nearthe ground surface (e.g. insects, plant pathogens, weed seeds) to become airborne and moved to new locations. Occasionally small rodents could be forcibly moved from one place to another. In general though, dust devils are mostly just fleeting visible indicators of the fact that our physical environment is constantly in flux.

by W.D. McIlveen
Halton/North Peel Naturalist Club

Bobolinks and Forks of the Credit Provincial Park

In mid-July I watched a flock of bobolinks at Forks of the Credit Provincial Park. They were gathering prior to their incredible 10 000 km journey back to the pampas of Argentina.

Male Bobolink
Male Bobolink

The bobolinks of Forks of the Credit Provincial Park are good news for a species in sharp decline in Ontario and beyond.

Breeding Bird Survey data indicate an alarming 52% drop in Ontario’s bobolink population over the last fifteen years. In part this is because of their penchant for nesting in hayfields – hayfields that are often cut in June when bobolink young are still in their nests.

At the Forks bobolinks needn’t worry about whirring blades. But alas, even here, the future of bobolinks may be in jeopardy.

Forks of the Credit Provincial Park is gradually returning to its primeval state – forest. Ash, maple and choke cherry are reclaiming the meadowlands cleared by intrepid farmers long ago. Left alone, trees will prevail and the bobolinks will be gone.

Bobolinks though, are only one patch in the quilt of the glorious grassland ecosystem that exists at the Forks. Many other birds such as meadowlarks and a wealth of sparrow species including savannah, grasshopper and clay-colored will disappear as the trees return. And the extensive milkweed stands will vanish along with their famous patron, the monarch butterfly.

Forks of the Credit in Fall (photo by Fiona A. Reid)
Forks of the Credit in Fall (photo by Fiona A. Reid)

Park officials here (and I’m sure in other jurisdictions in Eastern North America) face difficult choices in the management of former agricultural lands in their care.

Should they honour the natural inclination of the land and allow trees to return along with the birds, animals and wildflowers that depend on them? Or should they intervene and kill the trees to save grassland and the myriad species it supports?

We need to start a conversation about the future of the grasslands at the Forks and elsewhere.

This story appeared originally in Notes from the Wild at inthehills.ca/blogs

by Don Scallen
Vice-President, Halton/North Peel Naturalist Club

Weather-related Stress on Plants, 2012

So far, the year 2012 has seen some disruptions in normal weather patterns. In March, we experienced some rather warm days that caused many wild flowers to appear early, foliage on trees and shrubs to emerge early, and for amphibians to start breeding early as well. This was followed by a relatively cool April. Then in June and July there were days with high temperatures and dry conditions. This report examines some of the impacts of those weather conditions on plants.

Temperature and water availability are two of the most important environmental factors that control the welfare of plants. When these are present at high or low values, then we can expect that certain stresses will start to occur or that the plants will perform at less than optimum growth rates. Not all plants will respond in exactly the same way for some are adapted for low temperatures while others prefer warmer temperatures for example.

The conditions that prevailed in the spring 2012 had major consequences for some crops, notably the McIntosh cultivar of apples. Specifically this was because of a frost or low temperature event at a critical time in flowering. As a consequence, the pollination rate was extremely low and little fruit was set. Other cultivars fared somewhat better. It is uncertain whether weather (i.e. frost) was the main factor but it was rather obvious that wild fruit loads on trees and shrubs through Northeastern Ontario were extremely poor and mostly zero by late this summer. A conversation with a wild blueberry seller confirmed that the blueberry harvest was extremely poor and pickers had a very difficult time finding enough fruit to collect and sell. Aside from the very high prices that could be commanded for the limited fruit that was available, it is easy to appreciate that wildlife such as birds and bears will have a difficult time finding food this year.

Figure 1. Ice and cold temperature injury to Alternate-leaved Dogwood, Acton, May 2, 2012
Figure 1. Ice and cold temperature injury to Alternate-leaved Dogwood, Acton, May 2, 2012

Locally, the effect of low temperatures in the early growing season did not appear to have significant impacts for native plants. Most native plants do retain some tolerance to short periods of low temperatures. Even at this, the young foliage on Alternate-leaved Dogwood showed a reddish-brown discoloration along the margins and between the veins. Reddish coloration often accompanies a physiological phosphorous deficiency that is induced by cold temperatures. This gradually disappeared as the growing season advanced. There was a small amount of acute necrosis of some Dogwood leaves but this only occurred where ice formed when rain runoff from the house roof froze on the foliage (Figure1).

Weather-stress conditions occurred later in the growing season in the form of drought. It was reported that the timing of the drought was particularly bad for corn producers. Although corn plants were widely seen to be suffering (leaves rolled up) in many parts of the Province, the plants remained alive for a long time. The yield though was impacted since the silks could not be pollinated during the critical short window when silks and pollen must come together. The overall effect was a low rate of pollination and this in turn will impact upon the amount of seed that gets set. The true impact can only be known after the harvest has been completed. It is expected that the price for corn for animal and human food will be quite high due to shortages in the crop through much of the corn-producing parts of North America.

Figure 2. Total monthly precipitation reported at Pearson Airport from March through July, 2012.
Figure 2. Total monthly precipitation reported at Pearson Airport from March through July, 2012.
Figure 3. Monthly precipitation reported at Pearson Airport from March through July, 2012 excluding the rain events on June 1 and July 31
Figure 3. Monthly precipitation reported at Pearson Airport from March through July, 2012 excluding the rain events on June 1 and July 31

The reported monthly totals of precipitation for the study period (March through July) may be a somewhat misleading. As shown in Figure 2, the monthly totals at Pearson Airport for March, April and May are not much more than half of the normal amounts for each month. The amount for June is very close to average while that for July is about 30% above average. But timing is everything. Of the total of the 76.4 mm for June, nearly half (37.4 mm) fell on the very first day of the month. In July, the largest rainfall that measured (38.8 mm) fell in a thunderstorm on the very last day of the month. There were a couple of light rains on July 22 and July 25 but these were not even seen in many parts of our area. This means that there was an extended time (over seven weeks from June 2 to July 21) where practically no rain fell at all. In combination with some days with rather high temperatures, most plants without an irrigation source would have been subjected to some very severe drought stress. Figure 3 shows the same data as Figure 2 but the amounts of rain that fell on June 1 and after July 22 have been excluded to provide a more realistic image of the conditions that plants would have experienced. Some native plants in our area did exhibit symptoms of weather (drought) stress. Such symptoms included drooping of the foliage and later, complete drying of the foliage. (Figs. 4 and 5).

The normal growth of plants includes uptake of water from the soil and transpiration of that water through the foliage. When there is an inadequate supply of water, the plant has several responses to help cope with the shortage. A prime reaction is to close the stomates to reduce the loss of water through the leaves. While water loss may be reduced by this action, it also reduces the amount of nutrients that can be absorbed from the soil and transported to the leaves. Closure of the stomates reduces the amount of carbon dioxide that can be taken up to become involved in the photosynthetic process. Reducedtranspiration means that the foliage does not get cooled through evaporation of the water. As a result, the leaf temperatures get raised above optimum and so the plant cannot grow at an optimal rate. Overall though, it is most desirable to the plant to conserve the water it has, rather than grow large. To compensate for the lack of water, many plants will shed their excess foliage. This effectively cuts down on the total leaf surface that is transpiring at any given time.

Figure 4. Temporary wilting of foliage of Green-headed Coneflower due to drought
Figure 4. Temporary wilting of foliage of Green-headed Coneflower due to drought

Hormones produced in the roots trigger the mechanisms that lead to abscission of excess leaves, much like the normal fall of foliage each Autumn. Stressed trees for example might show a high proportion of yellowed foliage (often older leaves and leaves lower on the stem. Another clue to the drought stress is an excess of recently-fallen foliage on the ground much earlier than would normally take place. Sometimes, totally dried or dead foliage will be retained on the branches.

Figure 5. Foliar necrosis due to drought stress on Wild Raspberry, Acton, July 25, 2012
Figure 5. Foliar necrosis due to drought stress on Wild Raspberry, Acton, July 25, 2012

Late in August, large patches of totally brown, necrotic trees and shrubs were seen in the area south of Parry Sound. This area has rather shallow soil soil and therefore the water reserve in the soil is quite prone to drought stress but the degree of stress in the summer 2012 in that area is the most severe that the author has witnessed in over 35 years. Whether or not the affected vegetation was killed outright will become known in 2013; however, there is little doubt that there will at least be a notable impact on the affected sites for several years to come. Locally, the stress observed will not likely have an observable enduring impact on perennial species but cumulative stress from similar conditions in future years could produce notable effects, likely as smaller plants with less flowering, lower seed set, or greater incidence of insect and disease attacks.

by W.D. McIlveen
Halton/North Peel Naturalist Club