Tree Tales: Canada’s Threatened Trees

Canada’s trees have developed some resistance to native diseases and insect pests. However, climate change has been facilitating more forest damage. For example, the native Mountain Pine Beetle (Dendroctonus ponderosae) used to be held in check because it was killed by extremely cold winter temperatures, which occur less frequently now than they used to. Additionally, in the last 125 years, the importation of live trees and untreated wood from other continents has brought in many pests that now threaten not just urban trees, but the integrity and survival of our wild forests as we know them. Likewise, the accidental importation of North American diseases and pests, such as the Pinewood Nematode (Bursaphelenchus xylophilus), threatens forests on other continents. The stories of just three threatened Canadian tree species are recounted below.

(Castanea dentata)

American Chestnut leaves and fruits from the Manitoba Museum’s collection. MM F-38.

(Ulmus americana)

The beautiful Pembina Valley is full of wild American Elm and ash trees.

(Fraxinus spp.)

Manitoba’s Green Ash is being decimated by the introduced Emerald Ash Borer.

There are many things we can do to help protect our trees.

1. Slow the Spread
Follow all biosafety protocols regarding importation of any plant or plant product. Buying locally grown trees and nursery plants, and locally produced wood mulch rather than imported products is the safest option. Consider buying and refinishing antique furniture, and using reclaimed or recycled wood for woodworking and construction projects instead of new wood. To be safe, don’t transport ANY firewood; burn local wood only.

4. Support scientific research
Scientific research that was started 43-years ago at an arboretum at Penn State may hold the key to saving ash trees as some appear to have natural resistance and can be used for breeding resistant stock. In Canada, the University of Guelph has been leading a breeding program for DED-resistant American Elm trees. The National Tree Seed Centre in Fredericton, New Brunswick stores seeds of Canada’s native trees, which can be used to breed resistant plants. In fact, the public is being encouraged to collect and send them wild ash seeds for their seed bank. But public support for research that doesn’t appear to offer any immediate benefit, is not always forthcoming. Real life is not like a Hollywood movie; scientists can’t conjure up cures to diseases overnight. It takes years of research to come up with solutions to new problems. Let your political representatives know you support publicly-funded science.

Trees provide us with so much-oxygen, shade, beauty, wildlife to admire and even food-that we need to give something back. You can report sick trees in Winnipeg by calling 311, the Canadian Food Inspection Agency or the Emerald Ash Borer hotline at 1-866-463-6017. If you lost a tree to disease or the tree-pocalypse storm in October 2019, consider planting a new one as soon as you can. Many Winnipeg greenhouses will even deliver plants right to your door this year. If you would like to see a tree planted on a city-owned boulevard or park, you can ask the city of Winnipeg to plant one. Remember the best time to plant a tree was 20 years ago. The second-best time is now. Enjoy your neighborhood trees this spring!

Parasites and diseases are what population ecologists call density-dependent causes of mortality; factors that only affect an individuals’ survival when populations are at high densities. Other density-dependent factors affecting plant survival include: competition for resources, such as water, light and soil minerals, and intense herbivory (usually by insects). In general, density-dependent causes of mortality are biotic, that is, caused by other organisms. Density-independent factors of mortality are usually abiotic (not alive) or environmental: forest fires, drought and volcanic eruptions that bury vegetation in lava are a few examples.

There are plenty of plant parasites and diseases that evolved right here in North America. However, most native plants have evolved methods to resist these organisms to some degree so it is not always fatal to the plant, unless it is in a weakened state. During droughts for example, trees are much more likely to die of a disease. Since the colonization of North America occurred, species of diseases that were not native to this continent have been accidentally introduced, typically with dire consequences. In my next blog, I will be discussing how three species of native Canadian trees (American Chestnut, American Elm, and Green Ash) are being negatively impacted by introduced diseases, and how we can change our behaviour to protect our forests, both wild and urban.

One of the most significant contributions that America’s Indigenous peoples have made is with respect to agriculture. Many of our most beloved foods (e.g. chocolate, potatoes, corn) are native to the Americas, being initially cultivated or domesticated by Indigenous farmers. 

Indigenous agriculture has a long history with the most recent archaeological evidence suggesting it has been practiced in the Americas for at least 10,000 years, almost the same time length of time as in the Fertile Crescent of the Middle East. There were five agricultural centers of origin (i.e. places where multiple species were cultivated or domesticated) in the Americas: three in South America and one each in Central and North America. 

Crop plants cultivated or domesticated in the Americas by Indigenous peoples. 

Cereals & pseudo-cereals: Amaranth, chia, goosefoot, knotweed, little barley, maize (corn), maygrass, quinoa, sunflower and wild rice. 

Legumes & nuts: American chestnut, black walnut, Brazil nut, cashew, common beans (green, black, pinto, navy, etc.), hickory, lima beans, peanut, pecan, scarlet runner beans and tepary bean 

Roots & tubers: Arrachacha, arrowroot, camas root, cassava, hopniss, jicama, leren, mashua, oca, potatoes,  sunroot, sweet potato and yacón 

 Fruits: Acai, avocado, blueberry, chayote, cherimoya, cranberry, feijoa, guava, huckleberry, papaya, passionfruit, peppers, persimmon, pineapple, prickly pear, raspberry, squash,  strawberry, tomato and tomatillo 

Spices, beverages & flavours: Achiote, chicle, chocolate, coca, maple, tobacco,  vanilla and yerba mate 

 The Andes was where the earliest American crops (e.g. potatoes (Solanum spp.) were domesticated, about 10,000 years ago. Corn (Zea mays) and squash (Cucurbita spp.) domestication began in Central America 8,700 years ago and beans (Phaseolus spp.) shortly after. In the eastern U.S., agriculture was being practiced 3,800 years ago. 

Crops that were part of the “Eastern Agricultural Complex” in the southeastern U.S. included a variety of nutritious seed plants such as sunflower (Helianthus annuus), goosefoot (Chenopodium berlandieri), bottle gourd (Lagenaria siceraria), marshelder (Iva annua), little barley (Hordeum pusillum) and squash (Cucurbita pepo). Other domesticates that followed include ragweed (Ambrosia trifida), pigweed (Amaranthus spp.), and knotweed (Polygonum spp.).  After ~200 BCE  (before common era) corn, beans and squash from Mexico were brought to this region, and cold-tolerant varieties (e.g. Northern Flint) bred. The productivity of corn was so high that the traditional seed crops fell out of favour and were gradually abandoned. Sunflowers and squash are the only crop plants left from the original Eastern Agricultural Complex that are still grown today. The other species have largely reverted to their wild state. Some of these species are considered “weeds” in croplands today even though they are still edible. 

Most people are surprised to find out that Indigenous people were practicing agriculture in the Dakotas and Manitoba in the early 1400’s. In 1986, Manitoba Museum Curator Dr. Leigh Syms unearthed evidence that corn, beans, squash and sunflowers were being grown as far north as Lockport during that time (Learn more).  These three plants were traditionally grown close together, with the beans climbing up the corn stalks and the squash helping suppress weeds (Wilson 1987). Raising plants in this manner improved the fertility of the soil as beans harbour special bacteria that turn gaseous nitrogen into a form available to all plants (ammonium or nitrate). Together, these three plants were the foundation of a healthy, vegetarian Indigenous diet. Sunflowers, often called the fourth sister, were typically grown along the edges of Indigenous fields, and provided an additional source of fat and protein (Wilson 1987).  Climatic changes which resulted in a shorter growing season, and population losses due to diseases introduced after European contact in 1492, may have resulted in the abandonment of the cropland in Manitoba. 

After Europeans arrived in the Americas, crops from Eurasia (e.g. wheat, barley, oats) were brought here while American crop plants were transported to Africa, Asia and Europe; this process was known as the Columbian Exchange. Sometimes the new American foods were embraced readily (e.g. beans) but others were not, particularly those in the nightshade family (e.g. tomatoes, potatoes and peppers). In Europe, nightshade plants are mainly poisonous rather than edible, so people were suspicious of them. In France, people initially rejected the potato (they thought it caused leprosy) but King Louis the 16th was convinced by the agronomist Antoine Parmentier that it was a good food plant to grow. Apparently, Parmentier had potatoes planted in the Kings’ gardens and then set guards around them to prevent thefts (although the guards were told to accept bribes). This reverse psychology apparently worked and after some people got their hands on the potato, its cultivation spread. Many American crops are now an integral part of European, African and Asian food culture. However, introduction of these new foods did cause some problems. 

The knowledge of how to prepare American foods did not always accompany the food, possibly because Europeans of that time period were generally disdainful of Indigenous knowledge, customs and food culture. Unfortunately, this attitude ended up causing a lot of unnecessary deaths. 

People in warmer parts of Europe and Africa readily adopted corn because it was so much more productive than other crops. But after doing so, a strange new disease began affecting poor people who were relying mainly on corn for food. This disease is pellagra, a condition that causes dermatitis, diarrhea, dementia and eventually, after four or five years, death. Physicians were confused about this new diet-related disease because they noticed that even though Mexicans ate a lot of corn, they rarely got pellagra. The answer to this puzzle was in Indigenous food culture. Corn was often softened by soaking it in an alkaline solution. This softened corn, known as hominy, is then eaten as is, or dried and ground to make masa, the flour used to make tortillas and tamales, among other things. This process, known as nixtimilization, increases the bioavailability of niacin (vitamin B3) and tryptophan in corn. Pellagra is caused by a deficiency in niacin and tryptophan in the diet. In Europe, Asia, Africa and, even among poor, non-Indigenous people in the southern U.S. , people were just drying the corn, grinding it up and cooking it in dishes like cornbread or polenta. Eaten in this manner, with no other foods containing niacin in the diet, pellagra is the result. Another aspect of Indigenous food culture that was not taken to heart was the custom of eating corn with niacin-containing beans, resulting in a balanced diet. 

Racism, and the intellectual and cultural arrogance that accompanies it, has caused tremendous human suffering. Colonization and the discouragement of traditional Indigenous agricultural practices and cooking, resulted in the near loss of ancient varieties of crop plants such as quinoa, as well as the memory of how these foods should be grown and prepared. It is heartening to see Indigenous peoples embracing their gastronomic legacy by planting Three Sisters gardens, writing cookbooks featuring pre-colonial foods (e.g. The Sioux Chef’s Indigenous Kitchen, Cooking with the Wolfman, and tawâw) and opening innovative restaurants (e.g. Ishkode Indigenous Pop-up ). Part of reconciliation is simply accepting that Indigenous culture is valuable. Another part is supporting the efforts of Indigenous peoples in keeping their culture alive. Food has a way of bringing people together so maybe the path forward is to sit down and share a meal together. 

Reference 

Wilson, G. 1987. Buffalo Bird Woman’s Garden: Agriculture of the Hidatsa Indians. Minnesota Historical Society Press, MN. 

Plants with fruits that ripen late in the year often rely on flocks of migratory birds for dispersal. Birds are particularly good seed dispersers because they lack teeth, typically swallowing fruits whole. In bird stomachs, the fleshy part of the fruit is digested but the tough seeds usually excreted intact. In fact, the seeds of many plants need to pass through the guts of animals before they will even germinate. However, some fruits are toxic to mammals (like rodents) but not birds.  This is because mammals tend to chew the seeds as well as the fleshy parts, killing the baby plant. For that reason, berries that birds can eat are not always safe for people!  Therefore, make sure you have correctly identified and researched the toxicity of any fruit before you eat it.