17 



THE VEGETATION OF 'SWIDDENS' IN NORTH=EAST 

 YORKSHIRE. 



FRANK ELGEE, 



Middlesbrough. 



As contrasted with other plant associations in Britain, the 

 ericetal flora has probably been less interfered with by man. 

 On moors, and especially those of the wettest types [Sphagneta 

 and Eriophoreta), the interference has been slight, and it is 

 the comparative absence of this interference which renders 

 moorland associations of such great importance and interest 

 to the student of plant ecology. Nevertheless, man does effect 

 changes upon moors, and the following notes refer to the most 

 conspicuous of these changes, and its influence upon the vegeta- 

 tion. But for these alterations, the heath vegetation would 

 present a much more uniform aspect. 



The greater part of the uplands of North Eastern Yorkshire 

 is moorland, usually of the pure Heather type. Everywhere 

 the dependence of the vegetation on the nature of the under- 

 lying rocks is manifest. Differences due to altitude, to slope, 

 to geographical position have to be added to those produced 

 by the strata and their soils, all of which are still further com- 

 plicated by the burning off of the Heather. 



The Heather is fired in the months of March and April in 

 order to obtain a new growth of the plant for the Grouse, To 

 the areas so burnt, the name Swidden is applied in the local 

 dialect. On the newlj^-burnt Swidden, a suite of plants springs 

 up, often totally distinct from the surrounding moorland ; 

 or more correctly, the dominant vegetation clothing a Swidden 

 may be quite different from the dominant plant-association of 

 the vicinity. As a rule, 12-14 years elapse before a Swidden 

 becomes re-clothed with tall Heather, thus enabling other 

 species of quicker growth to obtain a temporary occupation of 

 the ground. What this temporary vegetation will be depends 

 upon a number of factors, viz., the character of the environing 

 plant-association, the nature of the soil and the effect of the 

 burning upon it — also the position of the Swidden in regard to 

 drainage, slope, and other conditions. 



In examining a Swidden, it is important to bear in mind that 

 its age undoubtedly influences the nature of its plant associa- 

 tions, and, although in time a succession is traceable, yet 

 this \aries considerably. As a rule, where Calluna is weakl3'- 



1910 Jan. I. B 



