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Tuesday - May 25, 2010

From: York, PA
Region: Mid-Atlantic
Topic: Invasive Plants, Non-Natives
Title: Reference for native critical populations from York, PA
Answered by: The Smarty Plants Team


I have recently read a naysayer of native gardening. He states that native garden plants usually do not have the critical population size to be self-perpetuating. He says that one could better help the environment by writing a check to the World Wildlife Fund.I would like to know if there is an easy reference for such critical population sizes. I would certainly like to give any plantings the chance to spread to nearby wild areas and roadsides. As chance would have it, we are in the process of eliminating a stand of Ailanthus and will soon have a sunny, if somewhat stony, space to fill.


How many Ailanthus altissima, Ligustrum lucidum, Triadica sebifera or Melia azedarach plants does it take to create a self-perpetuating population?  Apparently, not very many, since all of these species - often planted as landscape plants - have found a way to cast off their garden shackles and invade the Texas countryside.

Just because a native plant is introduced to a garden setting does not mean that it will be henceforth isolated from others of its species.  Nearly all gardens are relatively close to wild areas of some kind.  Many gardeners are surprised to find, after planting a native in their garden, the same species already thriving in the greenbelt just behind their house.

The number of plants necessary to reach critical mass for population stability varies with species - native and non-native, as well.  Some plant species do need large populations to become self-sustaining.  But, some plants need very few plants of their own species to perpetuate themselves.  Indeed, a surprising number of native plants need only one plant of their species – themselves – to reproduce.

For lots of specific research in this area, do a Google Scholar search using the terms, “minimum viable population” and “metapopulation”.

So, yes there is good stewardship in removing non-natives and gardening with native plants.  Will you repopulate Pennsylvania with a native tree species by planting it in your back yard?  Probably not, but you certainly won’t be adding to the already burgeoning Ailanthus population either.

Contributing to the World Wildlife Fund or the Lady Bird Johnson Wildflower Center are worthwhile acts.  But so is doing your bit in your own garden.


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