Ecological Study of Epiphytic Cryptogams on Populus deltoides in Northeastern South Dakota and Adjacent Minnesota

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Abstract
Epiphytic cryptogams were sampled quantitatively along both north and south exposures of 87 trees of P. deltoides growing singly and exposed in northeastern South Dakota and adjacent Minnesota [USA]. Coverage was estimated for each species occurring in 10 adjacent 1 .times. 2 dm plots placed 0-2 m along each exposure of every tree. Based on coverage and constancy data 3 epiphytic unions are described, including the Physcia ciliata-P. stellaris union on young trees (average diameter = 5.9 d.b.h [diameter breast height]), the Candelariella subdeflexa union on intermediate sized trees (average diameter = 7.1 d.b.h.) and the P. orbicularis-Candelaria concolor union on large (average diameter = 8.9 d.b.h.). Two objective classification methods: agglomerative method and weighted pair group method, confirmed the presence of the epiphytic unions. North exposures supported considerably more luxuriant epiphytic vegetation than south exposures, but trees of a particular size class generally supported the same epiphytic vegetation on both north and south exposures. Though bark moisture holding capacity was higher and bark pH was lower in samples from young trees than old trees, these factors are less important than bark texture in determining the composition of epiphytic unions on P. deltoides. The quantitative method used in sampling also revealed trends of biotic succession among epiphytic vegetation. The Physcia orbicularis-Candelaria concolor union is the apparent climax on old P. deltoides in our region.

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