i'OEESTS OF PORTO RICO. 25 



Littoral Woodlands. 



The littoral woodlands, although most characteristically developed 

 on the humid side of the island, have certain strong resemblances to 

 the dry deciduous forests of the south coast, the one merging into, 

 giving way to, or overlapping the other at their points of contact. 

 Both formations are forced to struggle continually against the effects 

 of drought. In the case of the littoral woodlands this is occasioned 

 largely by porous and saline soil conditions accentuated by certain 

 adverse climatic factors, strong wind particularly. With the dry 

 deciduous forests, the determining factor is deficient rainfall, to 

 which adverse soil conditions give added effect. The littoral wood- 

 land formation presents two distinct types, namely, the mangrove 

 or wet tidal woodlands below high-water mark and the dry tidal 

 woodlands above high-water mark. 



THE MANGROVE. 



The mangrove, or wet tidal woodland, is a distinctly tropical for- 

 mation. Though unable to withstand unbroken wave action on the 

 open coast, it readily establishes itself in the shallow brackish waters 

 of protected embayments, creeks, and lagoons, where, under favorable 

 cUmatic conditions, it forms dense, almost impenetrable thickets. 

 The Porto Rican mangrove rarely attains a height of over 10 feet 

 above the water, though elsewhere it reaches very respectable forest 

 dimensions. Even in the more or less protected lagoons it is gen- 

 erally exposed to the strong trade winds, which accounts in part for its 

 low stature, while its popularity for fuel and other uses undoubtedly 

 prevents it from attaining its full size. 



The sea, receding at low tide as far as the edge of what seems at 

 high tide a veritable forest rising from the waters, reveals a tangled 

 mass of stiltlike roots anchoring the trees to the blue-black muck 

 along the shore. With every tide new soil material is deposited 

 among the mangrove, which keeps gradually pushing out to occupy 

 new ground, through its remarkable mode of reproduction. The 

 fruit when it reaches maturity remains attached to the parent plant, 

 the seed embryo all the while continuing its development into a 

 new young plant. Having attained a certain size this plant releases 

 itself, falls into the soft mud, strikes root, and becomes firmly fixed 

 within a few hours. 



The mangrove in general attains its most favorable development 

 where the humidity is high, precipitation abundant, and an inter- 

 mittent cloudiness prevails. Its distribution accordingly coincides 

 in general with that of the rain-forest.^ Thus the mangrove in Porto 

 Rico is most abundant along the north and east coasts, is much more 

 restricted on the west coast, and is only sparingly and locally de- 



1 See Schimper's Plant Geography. 



