Nature: It giveth and taketh away

When a young McGill University botany professor named Paul Maycock surveyed the nature reserve of Mont Saint-Hilaire near Montreal at the end of the 1950s, he recorded many kinds of plants: 485 species, in fact, everything from wild heather to quillworts.

Little did he know that, in as little as half a century, 70 of those species that covered the floor of the primeval 1,000-hectare forest owned and managed by McGill – a UNESCO biosphere reserve – would disappear.

In their place, according to a new Université de Montréal study, came dozens of new but less distinctive species: everything from spurges and clovers to wild grasses and mustards, brought in on the wind or by hikers or on the hooves of wild deer.

The discovery was made between 2012 and 2015 by Tammy Elliott, then a doctoral candidate in plant biology at McGill and now a postdoctoral researcher at UdeM, and Jonathan Davies, now an associate professor at the University of British Columbia.

Their study was published last month in Biodiversity and Conservation.

'Risk of local extinction'

The many plants lost since 1960 "were often species of special conservation concern [that] tended to be more evolutionarily distinct than species gained and more often associated with the forest understory and wetland habitats," write the authors.

"Our results suggest a process of biological homogenization is reshaping the flora of the reserve, and that there is a danger that native species of conservation concern are at risk of local extinction from the site."

Located 40 kilometres east of Montreal and surrounded by residential suburbs and farms, Mont Saint-Hilaire is the only old-growth forest in the St. Lawrence River Valley and one of only a few left in eastern North America. It was bequeathed to McGill in 1958 by Andrew Hamilton Gault, an ex-Canadian brigadier-general of Irish descent whose family made a fortune in industrial textiles.

In the summer of 1959 and the growing season of 1960, when Maycock made his survey, Mont Saint-Hilaire had a wide variety of vascular plant species: ferns, conifers and flowering plants. Some were common then and are even more common today: grasses and asters, for instance. But there were rarer species, too, orchids, twinflowers and bunchberries and other examples of the heath, rose and other botanical families.

Since he collected them, Maycock's specimens have been stored at the McGill and Marie-Victorin herbaria in Montreal. Elliott and Davies wanted to compare them with their own specimens, and went the extra step of taking tiny molecular pieces of each one, known as DNA barcodes, to be more precise in their analyses and paint an accurate portrait of changes in the park’s plant life over time.

Making a 'family tree'

"We put them together and made a 'family tree' showing the evolutionary relationships of all the species collected on the reserve between our study and Maycock's," recalled Elliott, a Saskatchewan native who now divides her time between UdeM, working with associate professor Simon Joly, and the University of Cape Town, in South Africa. "With that, we were able to look at how the plants had changed over time."

The goal was to see how plant diversity evolves and what different factors are driving that evolution: "more humans around the reserve because of agriculture and suburban development, more white-tailed deer that thrive on that suburban/forest divide because they can get food in both places, eating away the understory," said Elliott, whose research is supported by the Fonds de Recherche du Québec – Nature et technologies.

"The result has been an increase of plant species, no question, but what kind of species? The new ones tend to be non-indigenous to Quebec and also closely related, whereas the old ones, the ones Maycock saw but that we couldn't find anymore, were more evolutionary diverse. We're losing the more native species for what I'd call the more 'weedy' ones that are common all over North America."

Changing people's behaviour

One lesson for the general public – and for environmental policymakers – is that this biological homogenization can be mitigated, in a number of ways:

• Visitors should keep to the trails and respect the reserve’s rules. For example, walking off trail can further trample sensitive plant species and introduce foreign plant seeds to the area. Dogs are also prohibited from the reserve, for the same reasons.
• Hikers can be more careful about what they bring in to the reserve, including food (Elliott has found tomato plants and wheat growing in the forest that likely germinated from sandwich waste left behind);
• Suburbanites around Mont Saint-Hilaire can be more careful about what they grow in their gardens and try to favour more indigenous plants (Elliott has found hydrangeas and yellow day lilies growing on the edge of the reserve);
• Local and provincial governments can continue to support 'forest corridors' in the area that are off-limits to developers and insulate Mont Saint-Hilaire and its native plant species from outside influence.

"Mont Saint-Hilaire is a special area," Elliott concluded. "It's important to support how it's managed and prevent further loss."