F. W. Oliver 33 



gation in the waters concerned; in addition there are several economic 

 applications to which Spartina may lend itself. 



1 . Navigation. 



Though other navigable waters will doubtless be involved it is con- 

 venient to restrict the present discussion to the case of Poole Harbour, 

 where Spartina has been steadily spreading for 20 years. 



After the object lesson of the great war no one is likely to question 

 the assertion that it is a national interest that Poole Harbour should 

 remain a place primarily for ships and fishermen. And yet the idea of 

 extensive reclamation is hard to resist in view of the great Spartina 

 meadows which are everywhere appearing. As a Poole fisherman put it, 

 after helping to harvest a sample of the grass for a paper making trial, 

 "You'll see, me and my brother will be farmers yet." 



The danger to navigation inherent in reclamation is this. When 

 parts of a tidal estuary are banked off and removed from tidal action, 

 by so much is storage space for water diminished ; and this amount will 

 be lacking for scour at the ebb. The result is that the channels become 

 choked and navigation suffers. 



Suppose for example five square miles of the estuary carrying on the 

 average a depth of 2 ft. of water at the spring tides to be banked off. 

 This would mean a deficit of about 280 million cubic feet — a volume of 

 water far from negligible in this connection. The history of not a few 

 decayed ports shows that there exists eternal antagonism between agri- 

 culture and navigation. When ^p rices of produce rule high the land tends 

 to encroach on the waters. The immediate gain is obvious and tangible, 

 the ultimate consequences remote and shadowy. Amid a multiplicity 

 of authorities the frontagers are apt to help themselves unless the com- 

 munity is unusually vigilant. 



No one can foretell with absolute certainty what will happen as a 

 consequence of the spread of Spartina. There is an unknown factor, 

 the persistence of this new invader. At the same time there are no signs 

 of respite and it will be safest to assume the worst. 



The action of Spartina may be pictured as follows. The plant spreads 

 rapidly on the mud flats and tends to fix such mobile mud as may be 

 drifted over it. In this way in proportion as the flats are colonised by 

 Spartina their level rises. 



The immediate source of the mud which Spartina is fixing will be 

 the sides and bottoms of the channels, though a certain very small 

 amount of this will be made good by new mud entering the harbour by 



Ann. Biol, vn 3 



