Some Changes in the Weed Flora of Whatcom County, 

 Washington 



W. C. MUENSCHER 



When the timber is removed from a forested region and the 

 land is cleared for agricultural purposes, usually only a few 

 weeds are present to contend with during the first few years. 

 The native woodland species that are accustomed to the reduced 

 sunlight, moist humus cover, higher atmospheric humidity, 

 and other factors and conditions associated with a woodland 

 environment, usually are unable to persist very long after the 

 land has been cleared. Soon however, exotic weeds arrive, es- 

 tablish themselves and frequently multiply and spread rapidly. 

 The interval between the time when most of the native species 

 disappear from the arable land and the time when the foreign 

 ones arrive, while somewhat variable with local conditions, as 

 a rule is very brief. 



After a number of years many of these introduced species 

 may become very troublesome. Indeed, they may even form 

 the most conspicuous part of the vegetation of waste land and 

 roadsides. The less common species often go unnoticed until 

 they are more widespread, when it is usually difficult to obtain 

 much information concerning their first appearance. 



At various times the writer has had opportunities for making 

 observations and records of the flora of Whatcom County, 

 Washington, the most northwestern county in the United 

 States. Some of the more important changes observed in the 

 weed flora of this county are recorded here.^ 



The eastern portion of Whatcom County lies in the Cascade 

 mountains and, for the greater part, is still covered with virgin 

 evergreen forests. This discussion refers only to the western 

 portion of the county, extending from sea level on Puget Sound 

 eastward for about 30 miles to the foothills of the Cascade 

 mountains. The annual rainfall in this region averages about 

 40 inches, very little of which falls between July and September. 

 The soils consist mostly of sandy and silty loams. Clay soils 



^ Based largely upon observations and records made by the writer as 

 follows: 1900-1911; June-Sept. 1912; Sept. 1913; June-Sept. 1914; Aug.-Sept. 

 1915; Aug.-Sept. 1916; May-June 1918; Jan.-Sept. 1919; June 1929. Specimens 

 of most of the species reported have been deposited in the herbarium of Cornell 

 University. 



130 



