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Accueil du site → Doctorat → États-Unis → 2011 → Cryptogam communities in forest and steppe ecosystems of Oregon, USA

Oregon State University (2011)

Cryptogam communities in forest and steppe ecosystems of Oregon, USA

Root, Heather T.

Titre : Cryptogam communities in forest and steppe ecosystems of Oregon, USA

Auteur : Root, Heather T.

Université de soutenance : Oregon State University

Grade : Doctor of Philosophy (Ph. D.) in Botany and Plant Pathology 2011

Résumé partiel
I focus on addressing knowledge gaps relating to management of cryptogams in Oregon’s public lands in Pseudotsuga menziesii-Tsuga heterophylla forests on the west side of the Cascade Range and dryland steppe in the Cascade Range’s rainshadow. While a great deal of research has illustrated the importance of late-successional forests for maintaining biodiversity in the Pacific Northwest of North America, over 76% of the forests in the region are less than 100 years old. To preserve landscape-level biodiversity, forest managers are increasingly interested in how young stands can be manipulated to favor late-successional species. At two sites in moist conifer forests of western Oregon, lichen community monitoring plots were established prior to treatment and resampled approximately 10 years after alternative thinning treatments aimed at promoting late-successional strucural characteristics. At both sites, hardwood gaps and open-grown trees were positively associated with cyanolichen species richness. At one site, thinned plots hosted more Bryoria, Candelaria concolor, Leptogium polycarpum, Peltigera collina, Nephroma laevigatum and Physcia tenella than had been observed prior to thinning. I concluded that thinning treatments retaining remnants, open-grown trees and hardwood gaps have potential to favor lichen communities rich in cyanolichen and alectorioid species. In the same sites, I sought to understand how stand-level gradients in canopy structure relate to dominant forest floor bryophyte and lichen species composition and abundance. At the one site, I found no strong associations between forest floor communities and stand structural characteristics. At the the other, lichens, particularly Cladonia, were negatively associated with canopy cover whereas bryophyte abundance was positively associated with Tsuga basal area. This relationship was stronger in the thinned stands, which had a different community composition than those left unthinned. Overall, the forest floor communities were fairly homogeneous at both sites and relationships with stand structural variables were subtle, indicating that thinning did not have a strong impact. Biological soil crusts are ecosystem engineers in arid and semi-arid habitats ; they affect soil chemistry, stability, and vegetation. Little is known about regional variation in biotic crust communities of North America. I explored how biotic crust lichen community composition and richness related to vascular plant, soil and climate characteristics in Oregon. In 59 0.4-ha plots, I found 99 biotic crust lichen taxa, one-third of which were observed only once, 33 of which occurred in only one plot and seven of which were new to Oregon. I compiled records from herbaria and other studies to evaluate the rarity of 124 biotic crust lichen species and conclude that 37 are rare or uncommon. Many of these appear to be associated with calcareous substrates.

Mots clés : Lichen — Ecology — Biotic Crust — Forest Structure — Bryophytes — Steppe


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