The effects of climate stability on northern temperate forests

Ziyu Ma

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

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Life's display of diversity and evolutionary histories is intertwined with climate on Earth.
In this Ph.D. study, I explored the influence of both the past and ongoing climate change on forest trees north of the tropics using large geospatial data sets. Phylogenetic structure of species assemblage and change of tree cover was analyzed. The results indicated the importance of climate stability in maintaining the forests that were familiar to us.
For Quaternary climate change, I demonstrated that areas with long-term stable climate allowed special evolutionary heritage and diversity of trees. The evolutionary relationship among species is known as phylogeny. Tree diversity was mapped using a phylogenetic supertree, covering species in the temperate forests of North America, Europe, and China. I found that Quaternary climate fluctuations limited phylogenetic endemism, which quantified unique evolutionary histories in confined spatial extents. In Europe and North America, with their extensive Pleistocene glaciations, effects of glacial-interglacial climate change on phylogenetic structures of species assemblages were more pronounced than in China, with the results indicating that glacial forest refugia have served as both museums and cradles for old and new species, respectively. Moreover, comparing gymnosperm to angiosperm trees in North America, I found that gymnosperm phylogenetic diversity patterns were more linked to historical than to current climate. However, I also documented effects of modern climate in all analyses, with more diverse and distantly related species in warmer and wetter areas, confirming the Tropical Niche Conservatism hypothesis, which predicts that because tropical climate dominated the Earth's past, non-tropical species should be relatively young descendants from a small subset of phylogenetic lineages.
For current climate change, I examined the broad-scale dynamics of climate-sensitive boreal forest on a decadal time scale. Using global remote sensing data and machine learning, I tested for associations between spatial patterns of tree cover change with possible drivers, i.e., climate anomalies, permafrost, fire, and human activities from years 2000 to 2010. The results showed tree cover change links to fire prevalence and rising temperature in permafrost zones, suggesting impacts of permafrost thawing on large-scale tree cover dynamics in the boreal zone for the first time.
Antal sider103
StatusUdgivet - 29 mar. 2016


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