Pool: THE VEGETATION OF THE SANDHILLS OF NEBRASKA 265 



nated by the linden-cedar-ironwood-ash combination. This is simi- 

 lar to the subdivision called the "Linden-Cedar-Ironwood Formation" 

 in the Phytogeography of Nebraska. 



Because of the narrowness of many of the springbranch canyons 

 the trees are frequently more abundant upon the higher slopes and 

 bluffs about the canyons than deep down near the very narrow 

 canyon bottom. The ironwood is often found in its characteristic 

 low, dense aggregation upon the lower more shaded slopes as well 

 as more scatteringly in almost every situation. The dominants are, 

 however, as a whole distributed more evenly over the upper slopes 

 and margins of the canyons. 



Composition of the Linden-Cedar-Ironwood-Ash Association 

 dominant species 

 Fraxinus lanceolata Ostrya virginiana 



Juniperus virginiana 



Tilia americana 



Acer negundo 

 Celtis occidentalis 

 Gymnocladus dioica 

 Juglans nigra 

 Popidus sargentii 

 Quercus macro carpa 



other common trees 



Salix amygdaloides, 

 Salix longifolia 

 Ulmus americana 

 Ulmus puhescens 

 Ulmus racemosa 



Cornus amomum 

 Crataegus occidentalis 

 EuonymrUs atropurpureus 

 Opulaster opulif alius 



THE SHRUBBERY LAYER 



Rhus radicans 

 Ribes gracile 

 Samhucus canadensis 

 Xanthoxylum americanum 



EXTRA-FORMATIONAL THICKETS 



Amelanchier alnifolia 

 Amorpha fruticosa 

 Cornus asp eri folia 

 Cornus stolonifera 

 Lepargyraea argentea 

 Primus americana 

 Prunus melanocarpa 



Clematis Ugusticifolia 

 Parthenocissus quinquifolia 



Rhus glabra 



Rhus trilobata 



Ribes aureum 



Rubus occidentalis 



Salix longifolia 



Salix nigra 



Symphoricarpos occidentalis 



LIANAS 



Smilax herbacea 

 Vitis vulpina 



