The False Allure of Garlic Mustard

The West Virginia White (Pieris virginiensis) is highly localized in Ontario. This one is nectaring on a non-native mustard. The presence of non-native mustards is partly responsible for the decline of the this woodland butterfly across much of its range.

Photo: Randy L. Emmitt (Wikimedia Commons)

Eastern Onatrio's Frontenac Arch is home to a wide variety of species at risk, including an unassuming woodland butterfly, the West Virginia White (Pieris virginiensis). It's a butterfly that's notable for a number of reasons: it's truly sylvatic, whereas almost all other Ontario butterflies are found in open habitats; it's restricted to only a handful locations in the province, and it has apparently disappeared from many of those sites in recent years; and perhaps most importantly, it has a taste for mustards (family Brassicaceae). It's a combination of all three of these things that has earned the West Virginia White the designation of a species of special concern in Ontario.

I have fond memories of living among West Virginia Whites, which I could find flying in May only a short bike ride away from my cabin on Opinicon Lake. My favourite West Virginia White colony, was found under a forest canopy composed of some thirty species of trees, where salamanders seemed to reside under every fallen log, and spring wildflowers bloomed in ridiculous profusion. Among the abundant wildflowers were two toothworts: Cut-leaved (Cardamine concatenata) and  Two-leaved (Cardamine diphylla), and it was upon these forest floor mustards that my West Virginia Whites fed. It's been several years since I last had the opportunity to visit my old colony, but I wonder with genuine concern how those rare butterflies are fairing.

In the past, the most pressing threat to West Virginia White populations throughout Ontario would have been loss or fragmentation of the mature forest habitat they and the toothworts require. Happily, my colony was safe from any kind of forestry, tucked away as it was on a large swath of protected land. The there was something else to worry about back then, in those heady days with my butterfly colony, and it's a worry that persists today: the insidious Garlic Mustard (Alliaria petiolata).

Garlic Mustard was intentionally introduced to North American from Europe as an edible herb during the mid 1800's. It has since expanded across the Great Lakes region and throughout much of the northeastern United States. Once established, it spreads like wildfire, choking out native vegetation and turning large areas of forest understory into Garlic Mustard monocultures. It's a terribly invasive species, more deserving of the appellation "weed" than almost any other woodland plant.

Just like the toothworts, Garlic Mustard is a member of the family Brassicaceae, the mustards. The mustard family includes such human favorites such as Broccoli, Cabbage and Cauliflower (Brassica oleracea), Turnip (Brassica rapa), Canola (Brassica napus), Common Radish (Raphanus sativus) and Horseradish (Armoracia rusticana). Many of these garden species are popular foodplants for introduced Cabbage White (Pieris rapae) caterpillars, but for West Virginia Whites the options are fewer because not many mustards grow in its dark forest habitat. The toothworts do and, unfortunately, so does Garlic Mustard. Indeed, I've spent more time than I care to recall pulling up Garlic Mustard in my woodlot. It's an annual chore, but it works to keep the forest floor more or less free of the nefarious weed. I fear however, that no one has been pulling Garlic Mustard at the old colony I used to visit years ago, and that may be cause for concern.

Garlic Mustard can out-compete the native toothworts for sunlight and soil nutrients, effectively eliminating them from the forest floor, leaving West Virginia Whites without their native foodplant. Interestingly, the butterflies will switch to using Garlic Mustard as a foodplant in the absence of toothworts, and may even prefer Garlic Mustard over toothworts. At first glance it seems like a fair trade off: replace one mustard with another and carry on. I mean, wouldn't stand to reason that the spread of Garlic Mustard would lead to a flourishing of West Virginia Whites, just as the planting of Crown Vetch (Securigera varia) along roadsides throughout southern Ontario has led to a drastic range expansion of Wild Indigo Duskywings (Erynnis baptisiae). In the case of the duskywing, which was once restricted to a small portion of southern Ontario, it has recently taken up the non-native vetch as a new larval foodplant and expanding its range as a consequence of this new widely available resource. In western North America, the naturalization of non-native Fennel (Foeniculum vulgare) has allowed Anise Swallowtails (Papilio zelicaon) to produce produce two flights every year, when previously it produced only one. This shift from unvoltinism to multivoltinism in the swallowtail was assisted by the tremendous abundance of Fennel which augmented the supply of natural carrot family (Apiaceae) foodplants. In strong contrast, however, the abundance of Garlic Mustard has actually had a negative effect on West Virginia Whites.

Lab experiments and field observations in the American portion of the West Virginia White's range have shown that caterpillars which feed on Garlic Mustard never reach maturity, usually dying after several days. Garlic Mustard, though attractive as an ovipositing site to adult females, is actually a death sentence to any caterpillar unlucky enough to hatch there. The Garlic Mustard's chemical defenses and a suite of growth inhibitors in the plants kill all caterpillars by the time they reach their second instar. Or at least that's the case in most populations. In at least one Massachusetts  population, however, caterpillars are able to survive until the pupal stage by feeding on Garlic Mustard alone. Though the caterpillars took longer to pupate and were a third smaller than caterpillars that grew up on toothworts, they did survive. Perhaps other populations of West Virginia Whites may also be able to adapt to use Garlic Mustard.

There may be some hope for West Virginia Whites if other population can shift to using Garlic Mustard successfully. But that's not likely to happen soon enough to stop the decline of this species all across its range. Evolution is a long and often risky road, after all. It seems that combating Garlic Mustard where it has become established and keeping it from spreading into pristine woodlands in the first place is the best defense we can give West Virginia Whites. So I keep pulling and spraying Garlic Mustard in my woods and I keep hoping that the old colony of mine is still flourishing under those big trees half a province away, and not just in my memories.

Naturescape: Edward's Hairstreak

An Edward's Hairstreak (Satyrium edwardsii) nectaring on a Butterflyweed (Asclepias tuberosa).

Photo: Mark Conboy

Naturescape: Smooth Aster

Smooth Aster (Symphyotrichum laeve) in bloom on a dewy summer morinng in the Canadian Rocky Mountains.

Photo: Mark Conboy

Naturescape: Red Maple

The beautiful early spring flower buds of a Red Maple (Acer rubrum) about to burst.

Photo: Mark Conboy

Naturescape: Golden Shower Orchid

Golden Shower Orchid (Oncidium sphacelatum) is a common flower in the rainforests of Belize.

Photo: Mark Conboy 

Designer Forests

Pawpaw (Asimina triloba) produce the largest fruit of any native North American tree and were probably widely planted and cultivated by first nations people.

Illustration: Mark Catsby

I live minutes away from one of the most biologically diverse patches of old growth forest remaining in Canada. It's a green paradise of endangered Tulip Trees (Liriodendron tulipifera) and imperiled Butternuts (Juglans cinerea), massive American Beeches (Fagus grandifolia), impressive Basswoods (Tilia americana), generous Black Cherries (Prunus serotina), large Large-toothed Aspens (Populus grandidentata), ancient Sugar Maples (Acer saccharum), giant Black Maples (Acer nigrum), sky-high Northern Red Oaks (Quercus rubra), jumbo Eastern Black Oaks (Quercus nigra), broad Common White Oaks (Quercus alba), shaggy Shagbark Hickories (Carya ovata), bitter Bitternut Hickories (Carya cordiformis), stately Black Walnuts (Juglans nigra), substantial White Ashes (Fraxinus americana), towering Yellow Birches (Betula alleghaniensis), shady Eastern Hemlocks (Tsuga canadensis) and wind-sculpted Eastern White Pines (Pinus strobus). Tangled River Grape (Vitis riparia) vines drape over limbs high above the forest floor, while tenacious Poison Ivy (Toxicodendron radicans) and tendrilous Virginia Creeper (Parthenocissus quinquefolia) climb up trunks. Diminutive American Chestnuts (Castenea dentata), fragrant Sassafras (Sassafras albidum), strong Blue-Beeches (Carpinus caroliniana), superstrong Ironwoods (Ostrya virginiana), beautiful Eastern Flowering Dogwoods (Cornus florida), oriental Pagoda Dogwoods (Cornus alternifolia), spreading Witch-Hazel (Hamamelis virginiana), spicy Spicebush (Lindera benzoin), and rare Wahoo (Euonymus atropurpurea) fill out the understory. Slender Black Gums (Nyssa sylvatica), regal Swamp White Oaks (Quercus bicolor), girthy Bur Oaks (Quercus macrocarpa), huge Red Maples (Acer rubrum), stupendous Silver Maples (Acer saccharinum), hefty White Elms (Ulmus americana), modest Slippery Elms (Ulmus rubra) and robust American Sycamores (Platanus occidentalis) ring salamander breeding ponds. Quiet and solitude pervade. In this place, it's tempting to think that this remnant forest is a pristine urwelt, untouched since glacial times. But that's simply not the case; humans have been influencing and impacting the forests in one way or another since time immemorial, including this one.

Since the arrival of Europeans in the Americas, forests have suffered tremendously. In my own patch of forest I see evidence of overharvesting of "medicinal" plants, namely American Ginsing (Panax quinquefolius); recreational vehicle damage; overgrazing by White-tailed Deer (Odocoileus virginianus) caused by poor management practices; the historical overhunting of fur and game animals which has left the woods impoverished of Fisher (Martes pennanti) and Elk (Cervus canadensis) and a host of other species; fragmentation by roads; increased incidences of Brown-headed Cowbird (Molothrus ater) parasitism on nesting birds because of reduced forest area; artificial drainage ditches; sterile conifer plantations; dozens of devastating introduced species like Chestnut Blight (Cryphonectria parasitica), Emerald Ash Borer (Agrilus planipennis) and Garlic Mustard (Alliaria petiolata); forest fire suppression; and the extirpation of top predators like Grey Wolf (Canis lupus). Other forests are impacted still further by industrial and selective forestry, clearing for agriculture, overgrazing by domestic livestock and fragmentation by pipelines, power transmission lines and seismic lines. Most of these impacts would be considered European in origin, perhaps with the exception of clearing land for agriculture. But first nation, especially along the St. Lawrence River and around the Great Lakes, were influencing and impacting forests, sometimes in extreme ways, long before the arrival of European explorers and settlers.

A farmstead carved out of Carolinian old growth near Chatham, Ontario, circa 1838.

Painting: John Philip Bainbrigge

The "untouched" forests that Europeans encountered in the Great Lakes basin were in many cases actually more like carefully designed landscapes, and not deep dark wildernesses. First nations people cleared forests for agriculture, sometimes on impressively grand scales, using fire and by girdling large trees. The fields were then planted up with Corn (Zea mays), beans, squash, tobacco and other medicinal and edible plants. After a decade or so, as local resources such as firewood, game animals and soil quality diminished, settlements were relocated, and fields were burned and left to regrow under natural succession. Where forests were left intact, controlled burns, usually in the form of modest ground fires, were used to clear forest understory of thick shrubs and forbs, promoting the growth of grasses and other forage favourable to game animals. Managing habitat with fire may have imperative to maintaining sustainable game populations around settlements since hunting pressure would have been intense. The legacy of these impacts is difficult to detect in forests today without diving into the pollen or charcoal records of a forest. There is another way, however, that first nations historically influenced forest ecology: sylvaculture of fruit- and nut-bearing trees; in some cases, we can still see evidence of that on the landscape today.

Doubtless, sylvacultural techniques would have differed culturally and geographically, but in general it seems to have included both the management of existing forests to promote the growth of productive old trees, and the planting of new trees in orchards. It was chiefly centered around settlements, where foods could be easily harvested and protected against pests and, no doubt, other humans. Pawpaw (Asimina triloba), oaks, Shagbark Hickory, Shellbark Hickory (Carya laciniosa), Pecan (Carya illinoinensis), American Chestnut, Allegheny Chinquapin (Castanea pumila), hazels, Black Walnut, Butternut, and American Beech were all utilized as food, and may all have been part of sylvacultural practices throughout eastern North America. The reality is, we don't know much about  historical first nations sylviculture, but what evidence we do have comes mainly from studies of witness tree records in the United States. Witness trees were trees marked and noted by surveyors as they laid out plots of land. In theory, witness trees should be representative of the relative abundance of species that were present when surveyors moved through a region, usually sometime in the 1700's and 1800's. Surveyors would have marked whatever tree was closest to corners of the lots they were mapping, so trees were essentially selected randomly (though some bias for selecting trees of certain size or species may have existed). Thanks to this historic record, ecologists have been able to show that a disproportionate number of witness trees around known former first nations settlements are nut-bearing trees.

First nations people may have reduced competition around nut-bearing trees by girdling or otherwise removing adjacent competitors. They also planted trees around settlements, sometimes in large orchards, if historical accounts are accurate. In the course of establishing orchards, trees were sometimes moved well beyond their normal range. I suspect that the few Shellbark Hickories near Long Point, Ontario, may have been moved there (as nuts) by first nations people; the massive nuts of Shagbark Hickory are not likely to have been transported by wildlife over such a long distance from the next nearest populations: 135 km away on the Niagara Peninsula and 200 km away in Essex County. A similarly disjunct population of Pawpaws, again near Long Point, may have been established in the same way. Pawpaw produces the largest fruit of any native tree in North American and were certainly utilized by first nations south of the Great Lakes, so would have been a likely candidate for human-facilitated range expansion. In my childhood haunts of eastern Ontario, there is an isolated population of Bear Oak (Quercus ilicifolia), 200 km distant from the next nearest population in New York State, which is itself disjunct from the species' main range by a similar distance. Was this species brought to eastern Ontario by first nations people? Bear Oak isn't known to have been a particularly important food source, compared to Common White Oak for example, but Bear Oak acorns may have been accidentally transported along with other oaks and either discarded to grow feral or intentionally planted.

I would say that not enough consideration has been given to the influence of first nations on the abundance and distribution of fruit- and nut-bearing trees in North America. Though quantitative evidence is limited, it stands to reason that since other cultures all over the world have been moving useful and valuable plants around the globe for millennia, native Americans would have done the same. Certainly, other first nations' practices such as the widespread use of fire to modify landscapes, has been well documented. The historical legacy of fire use is now being considered in such a way as to cause us to redefine what we mean by untouched wilderness. Very few places on Earth are true wildernesses, truly untouched. Rather, almost everywhere that can support a viable ecosystem has been home to humans at one time or another, and humans, no matter how limited their population, or how conservation-oriented their society is, invariably impact and influence ecosystems in measurable ways. It's time to start looking at humans, both historic and contemporary, as part of forest ecology, not a separate and unnatural or external influence. Only once the human dimension is considered, can we hope to have a complete historic view of forests, and a more holistic approach to addressing modern day conservation concerns.

Columbine Graveyards

Serpentine Columbine (Aquilegia eximia)

Photo: David A. Hofmann (Creative Commons)

The oak savannah and Chamise (Adenostoma fasciculatum) chaparral of California's North Coast Ranges, are interrupted here and there by a unique and altogether surprising floral community: plants that grow on poison. In this case, the poison is serpentine, rocks that are so rich in magnesium and iron that they, and their associated soils, are toxic to most plants. Most, but not all.

There are some plants that can grow on serpentine deposits and many of those are rare and endemic, not to mention highly adapted, making serpentine flora one of a most intriguing element in California's generous biological endowment. Among the most exquisite serpentine plants is Serpentine Columbine (Aquilegia eximia), which displays large red and yellow flowers to attract the attention of pollinators. In addition to pollinators, Serpentine Columbine attracts great many other insects, but for a totally different reason.

Plants attract animals to help them with all kinds of tasks; the two most obvious, of course, are pollination and seed dispersal. Pollinators are attracted by scents and visually stimulating flowers. Take the elaborate deceptions of the Fly Orchid (Ophyrys insectifera), which wafts bee pheromone-like scents from its bee-shaped flowers. Real bees come not in search of pollen or nectar, as they might at a more conventional flower, but instead they come to mate with the lookalike blossom, in the process getting coated in pollen. The bees pollinate the next orchid they visit in another misguided hope for sex.

Some plants are entirely dependent on animals for dispersing their seeds. In the Rocky Mountains, Clark's Nutcrackers (Nucifraga columbiana) are the near-exclusive disperser of Whitebark Pine (Pinus albicaulis) seeds, transporting them great distances and planting them in suitable habitats.

Examples of animal pollinators and seed dispersers are virtually limitless, but there are lots of other reasons for plants to attract animals. Sometimes it's to eat them. Venus's Flytrap (Dionaea muscipula), is probably the most dramatic of the so-called carnivorous plants, capturing and later digesting insects and even small frogs between snap tap-like leaves. Even the ubiquitous Field Thistle (Cirsium discolor) may capture insects using sticky secretions on its flowers; those same secretions act as digestive enzymes, digesting stuck insects and providing an unusual food source, at least among thistles species.

Other plants feed off animals in more passive ways. The impressive Queen of the Andes (Puya raimondii) offers paramo birds a safe haven among its hooked leaves in exchange for the highly nutritious droppings the birds leave behind. As an added benefit to the plant, a bird occassionally gets hooked among the thorny leaves, dying and providing an even richer source of nutrients for the giant bromeliad.

Some plants attract animals to help them battle damaging herbivores. Azteca ants are provided with living spaces in Ceropia trees and are fed from extrafloral necataries, in exchange for doing battle against caterpillars and other damaging herbivores. Providing shelter and nectar is a pretty conventional way of attracting helpful predators, but there are a few plants, including the Serpentine Columbine, that attract protective insects in a completely different way, and that's by essentially becoming arthropod graveyards.

Serpentine Columbine stems are covered in glandular hair-like trichomes, making them very sticky. So sticky, that they trap insects by the dozens. These trapped insects in turn attract predatory arthropods. The predators come to dispatch trapped living insects or to feed on the corpses of those that have already died. The predators are called upon to primarily combat caterpillars of the Darker Spotted Straw Moth (Heliothis phloxiphaga), which feed on the leaves, buds and even the flowers. The columbine's glandular hairs seem to be of little use in combating this caterpillar, so the plants rally Checker-rimmed Bugs (Pselliopus spinicollis), other true bugs (Order Hemiptera) and even the occasional crab spider (Mecaphesa spp), to help stavse off assault. Between meals of caterpillar, these predators feast on the stuck insects. This buffet style call to arms seems to be effective, columbines with more stuck insects (thus more helpful predators) usually experience greater reproductive success.

The insects that Serpentine Columbines capture aren't, for the most part, pollinators or herbivores that accidentally become stuck, but instead appear to be actively attracted by the plants through some kind of chemical signal. What exactly that signal is remains unclear, but it appears that Serpentine Columbine is the only plant so far known to actively attract insects in this way. Yet another remarkable find from the fascinating serpentine deposits of northern California!

Bromeliad Boroughs

A Giant Tank Bromeliad (Brocchinia micrantha) grows in front of Kaieteur Falls.

Photo: Philina English

 

At dusk, the humid air above Kaieteur Falls comes alive with swifts. First dozens appear, chattering, swooping, rolling, then hundreds, then thousands, zoom with incredible speed and coordination above the Potaro River Canyon. Three species nest and roost behind the falls: the globally rare White-chinned Swift (Cypseloides cryptus), the highly range-restricted White-tipped Swift (Aeronautes montivagus) and the common but fabulously large White-collared Swift (Streptoprogne zonaris). The flocks, in their energetic maneuvering seem to taunt the local Bat Falcons (Falco rufigularis) which sit near the canyon's rim, erect and stoic, looking to snag a wayward swift. After perhaps an hour of impressive display and ceaseless chatter, the swifts finally go to roost. By the dozens, small flocks break away from the main group, and skirt behind the veils of mist and braids of falling water. They cling to the sandstone cliffs in a most awkward manner, betraying themselves as birds of the air, seldom landing but to nest and sleep (and even then, some may sleep on the wing). So loud is the collective chattering from their roost, it can actually be heard above the din of roaring water!

The sunset, the waterfall and the swifts will offer a spectacular end to a day spent exploring the rainforests and savannahs of Guyana's Kaieteur National Park. But it's just the prelude to another show which is about to begin in the growing darkness. It's a show that is fascinating in the extreme even tough it takes place on a much less grand scale: entirely within the watery recesses of a peculiar plant, the Giant Tank Bromeliad (Brocchinia micrantha).

Giant Tank Bromeliads are enormous succulents, resembling a 2-3 m tall Pineapple (Ananas comosus) top. They are among the dominant plants in Kaieteur's savannah, lording over Yellow-eyed Grasses (Xyris spp.), tiny carnivorous Red Sundews (Drosera kaieteurensis) and a great diversity of fruiting Clusia shrubs. The so-called bromeliad savannahs are alive with shimmering orchid bees, enormous red and black grasshoppers, microcosmic armies of ants, and a pantheon of birds, such as the Guianan Cock-of-the-Rock (Rupicola rupicola) which display their fabulous orange costumes with absurd extravagance. But for me at least, the most interesting species is the little Golden Rocket Frog (Anomaloglossus beebei), whose association with Giant Tank Bromeliads represents a case of extreme specialization. Not only will you find Golden Rocket Frogs only on Giant Tank Bromeliads, but you'll also find them only in the vicinity of Kaieteur Falls.



Golden Rocket Frog (Anomaloglossus beebei), yellow morph.

Photo: Philina English

The entire world-wide range of the Golden Rocket Frog encompasses less than 20 square km and is centred right on Kaieteur Falls itself. It's no coincidence that these frogs have gathered around the falls like worshipers around an idol. Kaieteur Falls spills half a million litres of water over a precipitous 225 m drop every second (during its peak flow). This fantastic volume, making it one of the world's most powerful waterfalls, creates a permanent mist that blankets the rugged sandstone gorge below the falls, and periodically shrouds the cliff tops and savannah above it. The microclimate caused by Kaieteur's humidity is what allows Golden Rocket Frogs to spend their entire lives entirely within those over-sized bromeliads.

Again, recall the Pineapple top-like form of the tank bromeliad, but unlike a Pineapple the leaves are not stiff and armoured with spines, but are instead smooth and often gracefully arching. The broad bromeliad leaves radiate out from a central stalk, forming loose fractal-like whorls. In the axis of each leaf, right where it attaches to the bromeliad's central stalk, a small reservoir of stagnant water forms. Filled up by rain and the condensed mists of Kaieteur Falls, each of these eponymous tanks (or phytotelmata) is a world unto itself, supporting a wide assortment of organisms. The shady, slightly acidic waters are a favourite breeding site for mosquitos and midges. Bromeliad crabs, dragonfly and damselfly larvae hunt other bromeligenous inhabitants. The world's largest bladderwort, the purple flowered Humboldt's Bladderwort (Utricularia humboldtii), sucks up tiny invertebrate prey. And of course there are the frogs.

Like most other dart poison frogs (family Dendrobatidae), Golden Rocket Frogs seem to explode with colour; or rather, about half of them do. Anomaloglossus beebei is a polymorphic species, with yellow frogs found among a bromeliad's fresh green leaves, and brown frogs found among the dead and dying ones. Since each morph is strongly associated with a specific leaf colour it stands to reason that they derive some kind of advantage, likely camouflage, in their respective habitats. Juveniles actually change colour, appearing green during the night and yellow-green during the day, again presumably as a form of camouflage.

Golden Rocket Frog (Anomaloglossus beebei), brown morph.

Photo: Philina English

 

Regardless of colour, both males and females set up and defend territories around bromeliad tanks. With few exceptions, such as when females wander to find mates, they'll spend their whole lives within these territories. Although adult frogs may use the numerous phytotelmata in their territories for foraging or cover, the primary function of the tanks is to serve as nurseries. After mating, females deposit eggs on the underside of a leaf that overhangs a tank. When the egg hatches, the tadpole falls into the water where if everything goes according to plan, it will find a well appointed menu of detritus, algae and small invertebrates to dine upon. Kaieteur's generous mists normally keep water levels topped up and humidity high, but during times of low humidity, and in locations more distant from the falls, further parental care may be needed to combat desiccation. Male frogs will water their eggs by squirting them with liquid from their cloaca. When food is scarce, females will lay non-fertilized trophic eggs for their tadpoles to eat. Generally speaking though, the small yellowish pollywogs subsist on their own.

Finding these small yellow and brown frogs  among the whorls of bromeliad leaves can at first be difficult, but their calls, which resonate through the evening air (just as the swifts go to roost behind the falls), reveal their abundance. If there's one aspect of the Golden Rocket Frog's life history that has been studied (and can be easily observed) it's their calling behaviour.

In Golden Rocket Frogs, calls play two roles. First, males sing an advertisement song to attract mates. That's chiefly what you'll hear as you wend your way across the darkening savannah, watching your every step for Bushmasters (Lachesis muta) and other venomous surprises coiled beneath the bromeliads. Females seek out calling males, looking particularly for big boys with faster call rates than their neighbours. Like in many other dart poison frogs, courtship is somewhat elaborate, involving a little snuggling (tactile interactions, in the dry language of the herpetologist), a slow guided tour of the male's territory and finally the actual mating.

The second call type is one that territorial males sing to dissuade rival males from encroaching on their turf. Golden Rocket Frogs are highly territorial but their approach to it is nuanced. Males seem to exhibit a curious form of territoriality sometimes known as "dear enemy". In essence, a male gets to know the individual calls of all his immediate neighbours. After a period of sorting out territories, the neighbourhood finds itself in a state of more or less peaceful equilibrium, with each male generally respecting each other's claims. But when an unfamiliar frog enters the neighbourhood and begins calling, the local settled males react strongly, changing their calls from a more subdued version they use among their settled peers, to a more strident and aggressive version when an interloper is about. The reason for this is probably that an interloper may throw the whole neighbourhood into turmoil if he were to try to squeeze in a territorial plot of his own or usurp one of an already settled male. Should this happen it may be necessary for the whole process of staking out territorial boundaries to happen all over again, taking away energies from a more important activity - making new frogs.

That's not to say that Golden Rocket Frogs are entirely antisocial outside of the breeding season, rather they appear to engage in nonaggressive visits between territories. This kind of non-breeding sociality is somewhat unusual among frogs and the purpose of it is not at all understood. Clearly, Golden Rocket Frogs, like so many other tropical organisms, have a vast and unusual natural history just waiting to be discovered.

Bromeliad savannah habitat at Kaieteur Falls National Park

Photo: Mark Conboy



Two Days with Bruce

Massasauga Rattlesnake (Sistrurus catenatus).

Photo: Mark Conboy

A wrong turn on an unfamiliar trail can lead to confusion, frustration and the unenviable job of backtracking across some slippery talus slope or through a knee-deep swamp. On the other hand, it can also lead to a wonderful discovery. By way of example, I took a wrong turn off a Bruce Peninsula trail earlier this month, and I was rewarded for my buffoonery by an encounter with one of Ontario's least often seen and most misunderstood reptiles: the Massasauga Rattlesnake (Sistrurus catenatus). I went to the Bruce Peninsula specifically in search of rattlesnakes and much to my delight what I found was a land full of additional surprises.

The focus of my explorations was Lion's Head Provincial Nature Reserve, the real treasure of the Bruce Peninsula, with one of most dramatic coastlines on the Great Lakes: shinning white cliffs that support ancient forests of stunted Eastern White Cedars (Thuja occidentalis). The cliffs plunge into a band of forest which in turn sweeps down to the crystalline waters Georgian Bay. Upon the cliff tops themselves, the forest, dense with Eastern White Cedar and Balsam Fir (Abies balsamea), hides a geological wonderland of glacial potholes, acid-worn caves, bottomless crags, overhanging rock faces, and erosion-sculpted boulders of ten thousand different forms.

I started on the trail at six o-clock one evening, into a forest alive with the ethereal whistling of Swainson's Thrushes (Catharus ustulatus), which lent the evening air a subdued and angelic texture. I worked my way east along the ridge top from one spectacular lookout to another. To the north I could see the peninsula stretching far off, a vast swath of seemingly undisturbed forest and coastline. Not a breath of sound, not a light, not a tower, not a road, not a cabin betrayed the illusion of vast and insurmountable wilderness. I knew what truly lay out there, hidden by distance, green forest, and heaving geology. Of course I knew of the towns and cottages, the lighthouses, the roads and their stinking cars. But I let my mind imagine a world unsullied by humans, a wild land stretching from Lion's Head to the tip of the peninsula and beyond to Manitoulan Island, to the North Shore, across the boreal hinterlands, to the freezing waters of Hudson Bay. A world teeming with game and fish and winding trails. The cries of a raven brought me back to reality. And so I lifted my pack, and hit the trail once again.

The cliffs upon which I walked dropped down for ninety or one hundred metres into the forest below. Far from smooth, the cliffs were undercut, overhanging ominously, inviting me to stand upon many a narrow slab, as though to dare fate. The cliff faces were pocked by small depressions and shelves, and it was upon those little natural balconies their existed a most remarkable community of ancient trees, a vertical forest of centuries-old Eastern White Cedars. Many of the cedars, though small and spindly, more like shrubs than proper trees, were two, three, four or even eight centuries old. The oldest yet discovered at Lion's Head is over 1,300 years old and for all its age is only about seven metres tall.

Dolostone cliffs at Lion's Head Provincial Nature Reserve with Eastern White Cedars (Thuja occidentalis).

Photo: Mark Conboy

The cliff-side cedars are natural bonsais, sculpted by centuries of extraordinarily slow growth on water- and nutrient-poor dolostone, twisted by driving winds, polished by blowing snow, and cracked by frost. Their trunks and limbs are gnarled, knotted and ropy. They do look truly ancient, truly sage-like. Many of the cedars appear to be half dead, and indeed they are. Eastern White Cedars, perhaps unique among Ontario trees, grow in sections; one portion of the root mass feeds one portion of the crown. In this way the left side of a cedar may die as the roots which feed it run low on nutrients while the right side of the tree continues to thrive, its roots having managed to find sufficient resources. This segmenting, may be one of the reasons why cedars have such staying power, where other less versatile species simply can't survive. Over the past 10,000 years, fire has periodically burned along the cliff tops, but the cliff faces appear to have been spared, and so the trees were allowed to grow old, excessively old. Even that zealous craze for wood and civilization, the rampant forest clearing, left the difficult-to-access vertical forests unmolested. The longevity of the ancient cedar forests it would seem, is a lucky coincidence of topography: safe there on the cliff sides from the ravages of fire and man. But not entirely safe.

Perhaps the single biggest threat that the ancient cedars face todays is rock climbers. The cliffs of Lion's Head are a popular sport climbing destination. It's easy to spot the most well-climbed routes: lichens have been rubbed away, duff has been swept from the tiny ledges, and in some rare cases, cedar branches have been cut. It seems that most of the pruning, and it hasn't been excessive, was done before the agelessness of the cedars was discovered. Though, if a saw-wielding climber had bothered to look at the annual growth rings of the limbs they were pruning it may have been obvious just how old those trees were. Today, the climbing community has more awareness of the ancient trees, and thankfully, disturbance is less of an issue as it was in the past. To share the cliff faces with age-old trees, that can only add to the exhilaration of the climb, can it not?

Cryptoendolithic organisms (not from the Bruce Peninsula in this example) growing inside a rock.

Photo: Guillaume Dargaud (Wikimedia Commons)

Eastern White Cedar belongs to the family Arborvitae, from the Latin, tree (arbor) of life (vitae). Indeed a fitting appellation for this long-lived species. The cedars though are not the only ancient cliff dwellers. The roughly textured dolostone supports an array of lichens, tiny symbiotic organisms that give colour to the cliff faces. Hidden within the pores of the rocks themselves is even more unlikely and more bizarre life, cryptoendolithic organisms. Nine species of cyanobacteria and 13 species of green algae living 1-5 mm deep within the porous rock have been recorded on the Bruce Peninsula. From the right vantage point these colonies of microorganisms can be seen as black stains on the white dolostone. The cyanobacteria and algae aren't just innocuous cliff dwellers, but instead play a role in the nutrient cycling of the cliff ecosystem, absorbing sunlight through the semi-translucent rock, and imputing nutrients into an otherwise depauperate ecosystem. The Bruce Peninsula is one of only a handful of places on Earth where cryptoendolithic organisms have been studied.
After several kilometres of fairly rugged trail I began a descent towards the coastline past thick slabs of dolostone that fell from the cliffs centuries ago, each now supporting their own garden of trees and shrubs. The Swainson's Thrushes sang all around as I dropped further and further down. Just before reaching the cobble beach, the trail passed below a massive overhanging slab. The slab protruded from the forest like a great bird's beak. Eight metres long and almost as wide, it sheltered a patch of bare soil, starved of rain water and sunshine, nothing grew there, a stark contrast to the thick forests that surrounded the outcrop. It's a fantastic natural sculpture, unexpected along this trail, while simultaneously not out of place in this land of geological wonder.

Earlier on the trail I came across several potholes, including one with the whimsical name, the Giant's Cauldron. These potholes or kettles were formed beneath glacial ice, where free flowing water formed a small whorlpool. Stones gathered up by the whirlpool were spun around and around wearing holes into the rock. The potholes stopped growing when the water flow subsided or the stones that chiselled them eroded to nothing. The Giant's Cauldron was about the size of, well, a very large cauldron, but just down the trail was an even more impressive one, the Lion's Head Pothole. This one was at least three metres deep and about a metre and half in diameter. There was a wonderful little portal in its side, that allowed one to squeeze right inside of the pothole. From within, the smooth stone wall directed your out of a sky light towards a canopy of Sugar Maple (Acer saccharum) and American Beech (Fagus grandifolia). Standing literally within the rock, an eerie silence prevailed.

The Lion's Head Potholes claims another curious naturalist.

Photo: Mark Conboy

The trail stepped over dozens of grykes, joints in the rock widened by weathering of the basic dolostone by slightly acidic rainwater. Small caves peaked out of the leaf litter; I wondered if they led to larger caves, caverns, perhaps as yet unexplored. The trail was rocky and never flat, each step either up or down over pock-marked rock. The pocks, or vugs in geological parlance, were formed as the dolostone itself was formed. Dolostone is essentially limestone that has been infused with magnesium. The original limestone, the precursor to the dolostone I navigated over all evening, was laid down in a massive coral reef sometime during the Silurian period (443 to 416 million years ago). This reef, which essentially forms the backbone of the Niagara Escarpment (of which the Bruce Peninsula is the northernmost extension), was formed by the growth and death of countless generations of corals and other sea creatures whose calcium carbonate shells became consolidated into solid limestone over eons. That limestone was eventually pushed underground where it was infused with highly saline magnesium-rich groundwater. The magnesium replaced the lime, changing the limestone to dolostone. That conversion resulted in some loss of rock volume, and that's how the vugs were formed. Had this dolomitization process not occurred we might not have the dramatic scenery of the Bruce Peninsula we see today. Dolostone, though it can be weathered, as evidenced by the potholes, grykes and caves along the trail, and large piles of talus below the cliffs, is far less resistant to erosion than limestone. Perhaps the limestone would have been eroded millennia ago, leaving a more or less flat shoreline, similar to the Peninsula's western shore. But the dolostone has persisted, giving us the dramatic views and ancient cedar forests of the Lion's Head.

The trail lead to a pleasant campsite under the shade of cedars and Red Maples (Acer rubrum). I pitched my tent near the cobble beach and settled in for a night apart from the rest of humankind.

In the morning, I found myself ascending to the cliff tops once again. Black-throated Green Warblers (Setophaga virens) were singing in profusion; it seemed that I was never out of earshot of one all morning. The woods were simply overrun with those pretty little songsters, but it wasn't long before my attention turned from the birds to the trailside plants. The Bruce Peninsula supports over forty species of orchids, most of which I didn't expect to find the Lion's Head; they are inhabitants of bogs, fens, swamps and alavars - habitats I simply didn't pass through on my hike. But these high and dry cedar woods do support a handful of species, including two biogeographical oddities: Menzies' Rattlesnake Plantain (Goodyera oblongifolia) and Alaska Orchid (Piperia unalascensis).

The tiny flowers of an Alaska Orchid (Piperia unalascensis), a western species with a disjunct Great Lake population.

Photo: Mark Conboy

Both the rattlesnake plantain and the Alaska Orchid are western disjunct species. Both are primarily distributed in western North America, but they can also be found in pockets isolated pockets elsewhere. The Alaska Orchid is the more extreme example of this pattern. Its main distribution extends from southern Alaska to Baja California. Disjunct populations occur on the Great Plains, in eastern Canada and of course, in the Great Lakes Basin. It's likely that Alaska Orchid enjoyed a much broader prehistoric distribution, that linked all of the disjunct populations to the species' main western range. For some reason, the Alaska Orchid's range contracted into the discrete populations we see today. Though less dramatically, the rattlesnake plantain also has a similar  disjunct pattern and probably has a similar biogeographic history. Perhaps it was the presence of such disjunct species that caused American botanist M.L. Fernald in the 1920's, to hypothesize that the Bruce Peninsula was an unglaciated relict, harbouring species that once enjoyed a wide preglacial distribution in an ice-free refugium. We now know that unequivically, the Peninsula was completely ice-covered for several thousand years and that the disjunct distribution of orchids and other species must be explained by other means.

Another plant caught my attention on several occasions throughout the hike. The Northern Holly Fern (Polystichum lonchitis) is a relatively rare species in Ontario, but evidently there is a healthy population on the Bruce Peninsula. Beyond ancient trees, disjunct orchids, and unusual ferns, the Bruce Peninsula harbours other botanical treasures, including significant concentrations of range-restricted Dwarf Lake Iris (Iris lacustris), Lakeside Daisy (Hymenoxys herbacea), and Tuberous Indian-plantain (Arnoglossum plantagineum).

Northern Holly Fern (Polystichum lonchitis) and Maidenhair Spleenwort (Asplenium trichomanes).

Photo: Mark Conboy

But as I said, the Massasauga Rattlesnake was the main reason I visited the Bruce Peninsula. Rattlesnakes were extirpated from my home county of Norfolk and most of the rest of Southwestern Ontario long ago, although there are remnant isolated populations at either end of Lake Erie. The species' last true haven is the Bruce Peninsula and the Georgian Bay coast. In the case of Ontario's Massasauga Rattlesnakes, there is a significant amount of genetic differentiation and geographical isolation between the Bruce Peninsula and Georgian Bay populations. Even though these two rattlesnake populations exist in close proximity, they are actually rather isolated from one another, and that can have some important biological consequences. 

Gene flow is important to maintaining genetic diversity, and good genetic diversity can help with disease resistance and adaptation to changing environmental conditions. Isolated populations of snakes and other organisms tend to have limited genetic diversity because of a lack of immigration from other populations (immigrants bring new genetic materials) and inbreeding.

Massasauga Rattlesnake (Sistrurus catenatus).

Photo: Mark Conboy

The snakes of the Bruce Peninsula are isolated from those of eastern Georgian Bay by water (and also intensive agriculture and road development on the southern part of the peninsula). Massasaugas, despite their fondness for wetlands, are unable or unwilling to undertake long distance swims, so the Bruce Peninsula snakes are effectively stuck on their own island, separate from their conspecifics to the east. Indeed open water is such an effective barrier to rattlesnake dispersal that Lyal Island, a mere 1.3 km off the western shore of the Bruce Peninsula, harbours its own genetically distinct population of Massasaugas. At some time in the past, Masassaugas colonized the island, but since that time, emigration from the main peninsula population has been all but nonexistent, allowing the Lyal Island snakes to develop their own genetic identities, apart from the Bruce Peninsula snakes.

 

Isolated populations are not necessarily a bad thing, especially if they are large, and genetic diversity can be maintained to some degree through mutations; so the Bruce Peninsula rattlesnakes are not likely to disappear because of inbreeding or something like that, at least not any time soon. What is most interesting about the isolation and genetic uniqueness of the peninsula's rattlesnakes (and it's orchids too, no doubt), is that it demonstrates a simple biological fact: not all members of one species are the same. I argue that each and every distinctive population should be conserved as though it were a distinctive species. In the case of Massasauga Rattlesnakes, we need to insure that the Bruce Peninsula population is receives proper conservation, and so too does the Lyal Island population and the many genetically discrete populations on Georgian Bay's east coast, each as though they were a different species. It would certainly be a tall order, but it would be the right conservation approach.