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I'm well aware of the Gardening/Horticultural approach of "a weed is any plant that you don't want in its current location".

But I think most people would agree that there's a more useful interpretation of "weed" that relates to its growth.

I would say that weeds are the plants that would be extremely easy to introduce if you wanted to them in a particular place, and extremely hard to remove if you didn't want them.

Common properties that I can think of, of the top of my head, for such plants include:

  • quickly growing.
  • quickly reproducing.
  • self-seeding.
  • re-growing from roots even if the above-ground plant is removed.
  • not particularly sensitive to ground conditions.

Question:

Why don't all plants exhibit these behaviours?

It feels relatively "obvious" that the plants that exhibit these behaviours should be able to out-compete plants that don't, since they reproduce faster and are more resilient.

And yet the slightest glance outside demonstrates a wide variety of plants that I think would trivial die if I attempted to attack / damage them.

What gives?

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    $\begingroup$ Crops have been bred to have certain characteristics like quantity and quality of yield. Often that breeding process has made them less competitive because they don't spend most of their resources on reproduction but on yield. $\endgroup$
    – Roland
    Aug 21 '20 at 10:28
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every advantage has a disadvantage.

self seeding means less genetic diversity, fast growing also means more energy requirements and even a structurally weaker plant, fast reproducing means tiny sieeds so individual seeds have a very small chance of survival. Biology is all about cost vs benefit, there is no such thing as universal advantage.

regrowing is actually something all plants can do provided they have enough resources, this is one way humans replicate crops. Weeds are often more sensitive to ground conditions, and don't do well in places where humans have not cleared and irrigated the land. weeds are often pioneer species good at taking over open land, one effective way to deal with weeds is to plant a cover crop because weeds can't actually compete well when there is already healthy grass. Many crops on the otherhand are being grown in sub-optimal conditions, in climate/soil other than the the one they evolved for while weeds tend to be native plants already adapted for the local conditions.

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