Tuesday, June 11, 2013

Sunlight and Plant Aggressiveness


A plant's behavior one year is not a sure indicator of how it will behave the next. This light green wave engulfing the plants around it seemed mild-mannered the first few years.

Fringed loosestrife (Lysimachia ciliata)--a native not to be confused with purple loosestrife--has modest flowers facing downward, and grows beside streams or in other consistently moist areas. It's rarely seen around Princeton. So, why the sudden show of aggression?

One cause may be the tendency of some wildflowers to seem well behaved the first few years, then start quickly expanding once they've established a strong root system. Here, the fringed loosestrife has completely enveloped blueflag iris and marsh marigold, with which it had been peacefully cohabiting.

Turtlehead and sensitive fern, too, are getting run over. A bigger factor in this sudden expansion is likely the extra sunlight the loosestrife is getting since a big pin oak had to be taken down a year ago. Add extra hours of sunlight, and a plant admired last year for its quiet beauty has become this year a menace to the balance of the garden, and must be pulled out.

A similar dynamic appears to be at work at Rogers Refuge, in an area where the shade of stunted ash trees curtails the cattails enough that they remain a scattered presence, allowing a more diverse understory of tussock sedges and ferns room to grow.

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