There are some general principles in botany that are widely held and applicable: plant communities change through time; plants moved by people can and do establish in new areas; and those introduced plants can affect local plants that are already present, thereby changing plant community compositions.
Those principles are by no means new or only newly understood, but as with any ideas, they had to arise at some time, and had to be articulated by someone…
In 1832, Lewis David de Schweinitz presented his “Remarks on the Plants of Europe which have become naturalized in a more or less degree, in the United States”, and these remarks were published, after his death (in 1834), in Volume 3 of the Annals of the Lyceum of Natural History of New York.
He opens with:
“The fact, that a number of European plants have become naturalized in the United States since the original forests have yielded to cultivation, is generally known and perfectly natural. Their number, however, especially of those which are so introduced that they would be considered indigenous, if their foreign origin was unknown, is comparatively much smaller than it would appear on the superficial view.“
He goes on to note that some of these plants had been brought intentionally, for cultivation – for horticulture, for agriculture – and also unintentionally – basically, as weed seeds. Some of those plants persisted as weeds only in cultivated areas, while:
“Others again have only straggled from the gardens, and are met with exclusively in the vicinity in which they are, or formerly were cultivated.”
But it is a third category of plant that is the prime focus of Schweinitz’s interest here, and he gets to this group when he states that “it is not without interest to note those few … which have followed the steps of cultivated man, nay, in some cases have even preceded him into the wilderness.”
And he precedes that by putting forth what may well be the first formal statement of the concept that introduced plants have the potential to displace and negatively impact native plants (i.e, that non-native plants could become invasive), when he notes that “our native plants would have stood as little chance of maintaining their ground” if introduced plants were (in the early 19th century, that is – at the time of Schweinitz’s writing) “prone to establish themselves” [I will note here that this statement is edited down here, in the interest of clarity and concision – and anyone interested is strongly encouraged to read the complete paper, as it is linked to in the 3rd paragraph, above]
While introduced plants as weeds in and near cultivated fields and gardens were of course quite well known, and acknowledged by Schweinitz for that matter, I am not aware of previous writing on impacts of introduced plants on wild plants.
Schweinitz then goes on to discuss specific examples – starting with “Plants which have become more or less generally naturalized in the United States” including “Plants introduced by cultivation for agricultural and other purposes”, such as timothy [Phleum pratense], “Widely spread in advance of cultivation”, and Queen Anne’s Lace [Daucus carota], and dandelion [as Leontodon taraxacum], “Spread to an incredible extent and preceding cultivation”, and chickweed [Stellaria media], “This, at least in Carolina, was intentionally introduced, as food for Canary birds; and spread, in ten years, upwards of fifty miles.” And also plants “Introduced fortuitously with agricultural seeds” such as yellow foxtail [Setaria glauca], “In the remotest regions”, and doorweed [Polygonum aviculare], “Absolutely every where”, Butter-and-eggs [as Antirrhinum linaria], “Not yet beyond Pittsburg, nor southwardly frequent.”
He also notes “Plants but partially spread” – including orchard grass [Dactylis glomerata], green foxtail [Setaria viridis], bittersweet nightshade [Solanum dulcamara], “sparingly in the northern states”, star of Bethlehem [Ornithogalum umbellatum], “spreading greatly in the northern states”, chicory [Cichorium intybus], “Northwardly, in some localities”, poison hemlock [Conium maculatum], “Here and there in the northern states”.
His final category of plants, “Introduced only in the vicinity in which they are or were cultivated”, includes Jerusalem artichoke [Helianthus tuberosus] and day lilies [Hemerocallis fulva].
Some of the plants that Schweinitz listed had already been documented to have been growing here on their own – for example, chickweed and dandelion and doorweed are all listed in John Josselyn’s 1672 list “Of such Plants as have sprung up since the English Planted and kept Cattle in New-England“. And Henry Muhlenberg, in his 1793 Index Florae Lancastriensis indicates dandelion as growing wild – and chicory as being cultivated (“never found growing wild”).
Schweinitz also mentions plants that hadn’t spread – such as Bellis perennis, which was common in Europe (and continues to be so today), or members of the genus Viola (violets, that is), and states:
“…it is certainly worthy of remark, that among upwards of four thousand species of plants in the United States, not more than from 120 to 130 foreigners should have obtained any thing like a permanent and extensive footing.”
And to close here, while Schweinitz mentions that migration of a plant may be impeded by a river or an unsuitable (to the plant) tract of land:
“The circumstances which prevent some plants, that are naturalized to a great extent in certain localities, from extending generally, are often not to be discovered.”
This is still true today