26 



CIRCULAR 791, U. S. DEPARTMENT OF AGRICULTURE 



had been kept continuously weeded average 12 inches in height at 

 3 years. Seedlings of the same age on unweeded plots under partial 

 tree cover averaged 3 inches. Early growth in the better quality 

 swamps is at about the same rates under corresponding degrees of 

 cover. 



Reproduction by Layering 



Black spruce propagates by layers as well as by seed (8). Some 

 writers have, in fact, advanced the opinion that reproduction by means 

 of layers is more common than by seed (17, 3). Although there is 

 no question that layers are common, the widespread occurrence of 

 stands of fire origin, where seed is the sole means of reproduction, 

 gives cause for doubting that layers are more abundant than seedlings. 

 Even in typical mature pulpwood stands, seedlings outnumber layers 

 although the layers are of somewhat larger average size and hence 

 have comparatively better chances for survival (table 7). 



Table 7. — Comparative abundance of seedlings and layers, by height 

 class in a mature stand of black spruce in a swamp on the Katoishiwi 

 Experimental Forest, northeastern Minnesota 





Reproduction per acre 



Height class (feet) 



New 

 seed- 

 lings 



Older 

 seed- 

 lings 



Layers 



- - -- --- 



Number 

 133 

 

 

 

 

 



Number 



3,517 



633 



183 



50 



50 



100 



Number 

 83 



1 



283 



2 _-- _- 



33 



3 



17 



4 -_ 







5 + 1 - _ 



117 







Total 



133 



4,533 



533 



1 4.6 feet up to 3.5 inches d. b. h. Actual average height about 10 feet. 



Layers are capable of developing into well-formed vigorous trees 

 when they are released (fig. 18). In understocked stands where live 

 branches persist near the bases of the trees layers are of some signifi- 

 cance in increasing the density of the forest. On uplands, layers are 

 more common on the drier sites and shallower soils than on moist soils 

 where competing vegetation shades out the lower limbs on spruce 

 trees. 



In open stands of young trees it would be possible to encourage lay- 

 ering by weighting down low-hanging branches with sticks or a 

 shovelful of earth or peat. However, for forest management prac- 

 tices in general, seedling reproduction has much wider application 

 for several reasons : ( 1 ) their ability to reproduce at a distance from 

 the parent, (2) their tendency to establish themselves rapidly, and 

 (3) the fact that they occur much more frequently than layers. 



