Bur Oak: King of the Floodplains

Photos: Diversity of leaf shapes from New Brunswick bur oaks. Leaves were collected from ten different trees. Each tree generally has its own specific leaf shape ‘type’, but the tree-to-tree differences are huge (left). Beds of bur oak seedlings in the nursery (right).

There's so much potential in a tree seedling; given the right conditions and time, a tree you plant today could be feeding wildlife and providing habitat and natural beauty for hundreds of years. There aren't many better examples of this potential than oak trees.

I've been particularly fascinated with growing bur oak (Quercus macrocarpa) for a number of years because of its beauty, rarity, and the special place it occupies in our region's floodplain ecosystem. New Brunswick is home to a disjunct population of bur oak that is isolated from the main continuous range in Eastern and Central North America by at least 500 kilometres. Our bur oaks have incredible diversity in leaf shape, branching structure, and acorn morphology. It seems like every bur oak you come across has something unique about it that distinguishes it from the one next to it.

Photos: Two of the largest bur oaks in the province - a rare sight now (left). Immature acorns on a young bur oak (right).

Bur oaks are a rare sight in New Brunswick now, but they were once common along the lower Wolastoq river and French/Maquapit/Grand Lake basin. Centuries of overharvesting, clearing for agriculture and building have reduced them to a handful of stands and more or less scattered pockets of individuals.  Their decline was lamented as early as 1841 when Edmund Ward published An Account of the River St. John, with Its Tributary Rivers and Lakes.

In his writing on Maquapit lake, Ward wrote:

"The shores of this beautiful lake, have abounded with white [bur] oak, whose quality cannot be excelled, neither equaled by any in the western world. But this invaluable wood has been profusely cut down, for the most trifling purposes; so that it is now nearly all destroyed."

Despite this decline, there is much to be hopeful for.  There are efforts underway that seek to restore it throughout its original range and have it widely recognized and appreciated as an ecologically and culturally important species in New Brunswick.  Some groups have already begun large-scale planting efforts.  The incredible work of the Nashwaak Watershed Association, for example, has led to well over a thousand bur oak seedlings being planted, with more to come.  

Unlike some other threatened floodplain species such as white elm (Ulmus americana) and butternut (Juglans cinerea), bur oak is not under immediate threat from any particular devastating diseases. With a wider public awareness, planting efforts, and protection of key populations, restoration of this species to its former glory can be achieved.

Wanted: Seed Trees

If you or someone you know with property in the historical range of bur oak have acorn producing trees, we'd love to be able to collect from them to grow ourselves and also share with restoration partners (please contact us).  It is important to be able to source seeds from multiple local trees - as many as possible - to preserve the genetic diversity of our local populations.  Knowledge of the location of previously unknown individuals or stands will also be useful to get a better understanding of the current state of the species in the province.

If you are unsure whether a tree is a bur oak, an easy way to identify it is by the shape of it's leaves.  The more common red oak have leaves with sharp teeth, while bur oak has leaves with rounded lobes (see photo above).  The acorns also have fringes on the margins of their caps.

These trees would likely be in or near the floodplains within the area highlighted on the map below:

Map:  Likely range of previously unidentified bur oaks (within drawn borders).