TAMARACK FOREST COMMUNITIES 193 



species were moving. Such groupings are common among hibernating 

 insects and are believed to keep the temperature a little higher. Baker 

 (100) has studied the wet forest near Shermerville, 111. In his Stations 

 7-1 7 the forests are ecologically older. (For birds and mollusks present, 

 see 100, p. 468.) 



3. THE TAMARACK SWAMP COMMUNITIES 



(Stations 54, 54a; Tables XLIII-XLV) 

 Tamarack swamps develop about deep lakes. Floating plant debris 

 supports first water-lilies and later bulrushes and cattails. Upon these 

 grow shrubs, such as the leather-leaf and the willows; these make condi- 

 tions suitable for the poison sumac and young tamaracks. The semi- 

 aquatic plants are thus succeeded by the shrubs and finally by the 

 tamarack. 



The aquatic communities have not been studied in a typical tamarack 

 lake, but there is no reason to suppose that they differ in any important 

 way from the aquatic communities of other old bodies of water. 



a) Floating bog and forest edge association (Tables XLIII, XLIV). — 

 The floating bog of cattails and bulrushes is usually full of low places in 

 which water is present the year round. Here we find the typical 

 animals of semi-temporary ponds, as described on p. 150. The various 

 frogs of the marsh probably breed here. Another aquatic habitat of 

 some interest is the water-holding leaves of the pitcher-plant (158). 

 The pitcher-plant mosquito (Wyeomyia smithii) is known to breed in the 

 leaves of pitcher-plants only. These are accompanied by the larvae of 

 midges and large numbers of dead insects which crawl into the pitchers 

 and cannot get out on account of the presence of many hairs which pro- 

 ject inward along the wall of the entrance. 



The surface of the bog is frequented by marsh spiders, insects, and 

 frogs, only a few of which belong especially to pre-tamarack bogs. The 

 inhabitants of the vegetation (field stratum) are like those on the vege- 

 tation over other marshes, belonging chiefly to low prairies. The edge 

 of the tamarack woods (Fig. 144) is a characteristic forest margin. 

 Except for the presence of some of the tamarack leaf-feeders, such as 

 the larch sawfly larva and measuring-worm, it possesses few species 

 different from the margins of other marshes (Fig. 145). 



b) Tamarack forest formation (Table XLV). — Pools: The pools 

 within the forest proper contain old-pond animals together with some 

 mosquito larvae (such as those of Culex canadensis) which are char- 

 acteristic of pools in all moist and mesophytic forests (see 99c). 



