Return of the aliens in 2011
In the past years the importance of garden escapes (deliberately introduced non-native plants that run wild) has steadily increased in Belgium (see Verloove 2006). "Genuine" aliens (unintentionally introduced non-native plants), on the contrary, have much decreased lately. Wool aliens are no longer seen since the 1970's in Belgium while grain aliens still occur but often in small amounts and confined to a restricted number of localities (mainly in port areas). An obvious explanation for this decline is lacking but one might think of the following:
1) the use of herbicides in the areas of origin is more effective;
2) port areas in Belgium (and a fortiori the surroundings of grain stores, unloading quays, etc.) are less accessible than they used to be in the past;
3) unloading quays and adjacent waste ground are now more often asphalted; as a result, the possibilities for germination of foreign seeds dramatically decreased;
Moreover, grain aliens have been thoroughly studied in the past decades in Belgium. When goods and their areas of origin remain identical, the possibilities for new discoveries are relatively small.
Despite this, 2011 turned out to be an unusually interesting year for "genuine" aliens in Belgium, without clear-cut explanation. Climatological circumstances surely were favourable, especially during spring. The relatively high temperatures from early April onwards enabled foreign seeds to germinate much earlier than they usually do. As a consequence many aliens were able to flower and fruit before they were killed by herbicides in May or June (in "normal" years many species only germinate shortly before they are killed and hence remain unidentifiable). In addition, the nature and/or area of origin of some of the foreign goods might also have changed: several grain aliens that were found in 2011 doubtlessly originated in Russia and the Middle East while Belgian grain aliens in the past decades mostly came in from the Mediterranean area and the Americas. Several species were recorded for the first time in Belgium; others were recorded after an absence of several decades or even a century.
Remarkable records from three areas are concisely enumerated and illustrated below:
1) grain aliens from various origin (including Russia) in the port area of Gent
Artemisia sieversiana (Russia): scattered plants, never recorded before;
Consolida hispanica (Medit.): very common in the entire area; formerly only exceptionally seen (also in recent years);
Descurainia brachycarpa (Am.): a single plant; previous records date back to 1894;
Euclidium syriacum (Medit.): a single plant; previous records date back to 1909;
Geranium divaricatum (Eur.): seen in several places in the port, also elsewhere in Belgium; the previous records date back to 1900;
Taeniatherum caput-medusae (Medit.): scattered plants; previous records date back to 1954;
Tordylium maximum (Medit.): rather frequent in one locality (since 2010); only once previous Belgian record (in 2004).
Further interesting records included, among others, Aegilops cylindrica, Anchusa procera, Anthemis austriaca (common), Asperugo procumbens, Bupleurum rotundifolium, Caucalis platycarpos, Centaurea melitensis, Consolida regalis, Crepis pulchra, C. setosa, C. tectorum, Glaucium corniculatum, Myagrum perfoliatum, Orlaya grandiflora, Ranunculus arvensis, Trifolium diffusum, etc. Some of these are natives (or archaeophytes) but (nearly) extinct as such.
2) grain aliens from various origin at the SAMGA grain mill at the Amerikadok in the port of Antwerpen (including aliens from the Middle East)
Pulicaria paludosa (Medit.): scattered plants, never recorded before;
Tripleurospermum decipiens (Middle East): rather frequent, never recorded before;
Zingeria pisidica (Middle East): rather frequent, never recorded before.
Further interesting records included, among others, Agropyron cristatum, Agrostis scabra, Anacyclus clavatus, Anthemis austriaca (common), Caucalis platycarpos, Centaurea diluta, C. melitensis, Chamaemelum mixtum, Consolida hispanica, C. regalis, Glebionis coronaria, Phalaris minor, P. paradoxa, Piptatherum miliaceum, Plantago afra, Podospermum laciniatum, Ridolfia segetum, Silene conoidea, S. stricta, Torilis nodosa, Turgenia latifolia, etc. Some of these are natives (or archaeophytes) but (nearly) extinct as such.
3) wool aliens from an exposed seedbank along river Maas in Boorsem
Geranium divaricatum (Eur.): a single plant;
Heliotropium europaeum (Medit.): few plants; rarely seen before;
Malvastrum americanum (Am.): a single plant, recorded once before as a wool alien in 1892;
Medicago laciniata (Medit.): a single plant; formerly a typical wool alien but now only exceptionally seen;
Nicotiana glauca (S-Am.): a single plant, never recorded before;
Trigonella caelesyriaca (Middle East): a single plant, only few previous records.
Verloove F. (2006) Catalogue of neophytes in Belgium (1800-2005). Scripta Botanica Belgica 39: 89 p. [available online at: http://alienplantsbelgium.be/sites/alienplantsbelgium.be/files/tabel_2.pdf].