A puzzling gap

Each summer, Royal B.C. Museum biologists make collections to understand the distribution of plants and animals in British Columbia.

Each summer, Royal B.C. Museum biologists make collections to understand the distribution of plants and animals in British Columbia.

These field collections contribute to the knowledge needed to provide sustainable stewardship of the remarkable plants and animals with whom we share B.C. Each year some surprising discoveries are made, as is to be expected in this vast, diverse and unique province.

For the past 13 years, RBCM botanists have made collections from rarely visited, remote mountains and plateaus in the alpine ecosystems of northern B.C., where many mountains remain unnamed. Vegetation may appear sparse in these habitats, but more than 400 vascular plant species live here. We have collected more than 15,000 specimens from 80 mountains.

In 2014, several significant collections were made during a two week fieldtrip to four provincial parks in the northern Rocky Mountains, north of Williston Reservoir. One of the most interesting plants found was icegrass (Phippsia algida), 200 kilometres east of any previous collections and the first from the Rocky Mountains.

Icegrass has a more or less continuous distribution in northern B.C. and northwards. The plant has not been found in southern B.C., even though extensive suitable habitat is available. The next location to the south is the Beartooth Plateau, at the Montana-Wyoming border, and further south in Colorado, with another gap between these areas.

At least 12 other species have a similar geographic distribution.

What is the explanation for this puzzling gap in the distribution of these alpine plants? Is it complete chance, or are there underlying, historical causes for the similarities in these species’ distributions?

One possible explanation is the seeds of these species were dispersed by wind or animals great distances from one population to the next site of occurrence. This seems unlikely because most of them do not have seeds adapted for dispersal across such great distances.

A more likely explanation is these species once ranged continuously in western North America, thousands or even hundreds of thousands of years ago but their habitat and range was disrupted, leaving the current pattern.

Fossil pollen and other remains reveal that species distributions vary over time, usually in response to changes in climate. For example, we know that tundra occurred as far south as Arizona and as recently as the end of the Pleistocene 13,000 years ago.

During cold periods of the Ice Age, these species may have spread widely when tundra-like habitats occurred at lower elevations than currently.

Tundra zones were certainly disrupted and even obliterated by expanding continental ice sheets. Following the end of the most recent ice advance, more tundra habitat was lost with warming climate and expansion of forests and deserts.

This second explanation doesn’t fully explain why these species do not occur in southern BC, an area from which there is a more thorough, though still incomplete, record of plant distributions.

There is much more to learn about the flora of British Columbia and to do so we intend to visit those regions that have been poorly collected and expect to continue to make new discoveries.

To put this work in a modern perspective, past changing geographic patterns show how important climate is in shaping the distribution of plants and animals. At this time of global climatic change we are likely entering a major re-organization of the distribution of plants on the globe.

•••

Kendrick Marr is curator of botany and Richard Hebda is curator of botany and earth history at the Royal B.C. Museum.

 

 

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