36 CIRCULAR 791, U. S. DEPARTMENT OF AGRICULTURE 



(Chrysomyxa cassandrae) which causes little injury to the health and 

 growth of the trees, 24 but like the needle miner temporarily spoils them 

 for use as Christmas trees. 



Response of Black Spruce to Swamp Drainage 



About 1915, after the best farm lands in Minnesota had been settled, 

 extensive areas of swamp lands were drained for agricultural purposes. 

 In many instances the projects failed even before the forest cover had 

 been removed (fig. 8). Later, studies were undertaken to determine 

 to what extent forest growth had benefitted from the lowering of the 

 water tables (2). 



It was found that black spruce, as well as the other swamp trees, 

 tamarack and white-cedar, had accelerated in both height and diameter 

 growth rates close to the ditches, but the drainage effect did not extend 

 on the average more than about 330 feet from the ditches. Imme- 

 diately adjacent to the ditches, where the greatest stimulation occurred, 

 volume growth of black spruce after drainage averaged 0.48 cord per 

 acre per year in contrast to 0.21 cord before drainage. However, most 

 of the areas studied were on poor or submerchantable sites and a large 

 part of the volume was contained in very small trees. Hence, these 

 volumes must be scaled down considerably to conform with usual 

 standards of timber utilization. 



It was concluded that the widely spaced deep agricultural drainage 

 ditches needed to be supplemented by shallower lateral ditches spaced 

 from one-eighth to one-quarter mile apart in order to accomplish a 

 general, effective lowering of the water table. However, the estimated 

 additional expenditure could not be justified on the basis of the in- 

 creased growth. 



More and more of the ditches are being dammed by beavers and it 

 is expected that in time the drainage systems in forested swamps will 

 become almost totally inoperative. Considerable areas of spruce tim- 

 ber have been killed as the result of flooding by water that has backed 

 up behind beaver dams. The restoration of natural conditions on 

 drained areas evidently is not a simple matter. Some ditches also have 

 been dammed by work relief organizations as a conservation measure, 

 although the wisdom of this may be questioned in view of the harm 

 that has resulted from the activities of beavers. 



SILVICULTURAL OPERATIONS— CUTTING AND 

 REGENERATION 



The previous sections on the occurrence, natural succession, repro- 

 duction, and growth rates of black spruce provide the basic informa- 

 tion from which recommendations for silvicultural management of 

 the species have been developed. The more important features of black 

 spruce that have a direct bearing on its management for timber pro- 

 duction are: (1) It occurs on two sharply different kinds of habitats, 

 swamps and upland: (2) it reproduces readily following forest fires 



24 Hodson, A. C, and Cheistensen, C. M. Minnesota forest insect and disease 

 survey for 1941. Minn. Agr. Expt. Sta. Paper No. 1997. Scientific Journal Series, 

 12 pi>. [No date, mimeographed.] 



