Trees have evolved to adapt to disturbance and site condition for success in regeneration

Part 1: Disturbances like wildfire or windstorms that destroy many trees also create conditions to which native trees have developed adaptions for successful regeneration.

Aspen regeneration following timber harvest | Photo by Mike Schira, Michigan State University Extension
Aspen regeneration following timber harvest | Photo by Mike Schira, Michigan State University Extension

Forest stands tend to be accepted as naturally occurring without too much thought given to how forests sustain themselves. The true story is that trees have evolved through time to have developed some remarkable adaptations to help them be more competitive and successful in regenerating themselves.

Forest stands that sustain themselves without human interference are usually referred to as naturally regenerated. If this natural term invokes a vision of a seed fluttering down to earth to be gently engulfed by the soil to germinate into a new beginning of the next generation of forestland, the reality of tree species natural regeneration might be somewhat of a surprise. In many cases this “natural” rebirth is in conjunction with violent acts of nature.

One of the more violence caused episodes of forest renewal is what occurred following the retreat of the glaciers so many eons ago. For the most part, all that was left after the glaciers melted was soil, water and stone; even in this extreme conditions trees were able to repopulate the lands over time through a variety of regenerative adaptions.

In our world today extreme events are more likely to come in the form of wildfire, tornados, hurricanes, straight-line winds, drought and flooding. Some species of trees are adapted to these kinds of violent disturbances. The poplar family (Populus spp.) produces seed that is embedded in a cottony mass that drifts on the wind to be deposited in a site that is hopefully suited for germination and growth. This wind sown seed may end up hundreds of yards or even miles from the parent trees depending on wind conditions.

Poplars also have another adaption that is their primary means of regeneration. Their roots have buds along their length that, given the right conditions, will sprout up from the ground and grow into new trees from the preexisting root system. This root sprouting gives these trees advantage following wildfire. Although the fires may kill most of the above ground vegetation, new sprouts shoot up from the still healthy root systems protected underground. Forest managers may choose to duplicate this natural event by prescribing clearcutting of aspen and other poplar family trees to somewhat duplicate what occurs in a fire situation to regenerate stands.

Another species to have unique adaption to help sustain itself following wildfire is Jack pine (Pinus banksiana). Jack pine has a cone that is labeled as serotinous as they contain excessive pitch which keeps most closed for years, protecting their valuable seed. It takes heat of 122 degrees F to cause the cones to begin to open. Following wildfire, although the parent trees may be scorched and killed, the cones, having been heated by the fire, slowly open, allowing the protected seed to be distributed by the breezes into ash laden seed beds with little or no competition. Post fire, a new stand of pine will emerge from the aftermath.

Michigan State University Extension has publication available through the MSU Bookstore that provide greater insight into these tree regeneration adaptations. Soil type, moisture availability, proximity to the Great Lakes as well as latitude all impact trees ability to reproduce and sustain themselves.

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