Invasive Plants

This morning we met up with UNH Natural Resources professor and Forest Ecologist, Dr. Tom Lee to learn about invasive plants.  We started by defining some terms that are often thrown around and used inappropriately:
Native Plant: Plant has been growing in New Hampshire prior to 1600 (before the bulk of European settlers arrived
Non-Native Plant: Plant was brought by people to the area (weather intentional or not). This often includes crossing major geographic barriers such as oceans or mountain ranges.
Invasive Plant: A Non-native plant that moves into native communities and may displace native organisms.  Invasive plants have ecological and economic impact.

It's a common misconception that all non-native plants are bad. In fact many don't spread or try to take over areas and many, such as wheat and many decorative plants are very beneficial. The jury, however is still out when it comes to invasive plants and what the best method of treating them is.

Multiflora rose is an invasive species that has a lot of controversy surrounding it. On the one hand its big boughs shade other plants, eventually out competing them. On the other, multiflora rose provides great shaded thickets, attracts pollinators and its sharp thorns protect small animals from predators, including the cotton tail rabbit which is endangered. 

multiflora rose

Burning bush was a common lawn decoration due to its bright red foliage in the fall, however this invasive plant spreads easily and shades out other plants. It is also difficult to remove because when cut down, the roots will simply send up new shoots. Sale of burning bush is now banned in New Hampshire; instead nurseries are now promoting decorative native plants.

burning bush

Compare these two leaves:

Which is the norway maple and which is the sugar maple?

The one that appears on the Canadian Flag (right) is the sugar maple leaf, the other is the Norway maple, an invasive tree that was often used for landscaping as they make great shade trees. However, being more shade tolerant than sugar maples, they are out pacing sugar maples. The problem is sugar maples are preferred due to their higher quality sap for maple syrup production, higher quality wood and brighter fall foliage. The Norway maple is an example of the economic impact that invasive plants can have. 


Dr. Lee also taught us the three main theories behind why invasive plants tend to be far more aggressive in a non-native region compared to their native region.
1) Natural resistance hypothesis: plants in their native land have developed methods to protect themselves from the plant. Eg. garlic mustard plant secretes toxins that kills the symbiotic fungi of neighboring plants in its non-native areas, does not affect plants in its native area.
2) Enemy release hypothesis: similar to invasive animals, the plant does not have the same predators that it had in its native land ( insects, disease, etc.)
3) Disturbance hypothesis: Disturbed habitats are more likely to be taken over by invasives. (When we were at Warren Farm, Randy pointed out the autumn olive which is invasive in some of the areas that he had cleared.)

There is still a lot for ecologists to learn about invasive plants, including preventing them, how best to control them, why they spread so rapidly and the impacts to the area.

After our time with Dr. Lee we went back to the classroom to participate in Kim's reading facilitation that compared the visible effects of forest fires vs. overgrazing.

It was great to review and make a clear list of the indicators of these past disturbances.


The last portion of the class was spent doing extensive brainstorming on the topics for our projects.  While it could have been a chaos of ideas, Lara stepped us through a process of first brainstorming on our own, then writing our ideas up on the board, then working together to combine and refine our ideas. I think I am leaning towards a project that would study an artificial pond created by a beaver dam where we would be looking at the characteristics of the pond (water temp, pH, DO levels) and the types of plants and animals living in the pond. I think my second choice would be studying the plant and animal species in areas where there has been significant disturbance such as the area where power lines cut across a meadow.

It's crazy to think how we will write our proposals for the project tomorrow, have six full days in the field, three days to prepare our presentations, present and that will be the end of the program.