Mountain Vegetation - Mountain Geography: Physical and Human Dimensions - page 362

These Afroalpine plants have evolved largely through speciation from the surrounding
lowland vegetation, and thus differ from most other midlatitude floras (Hedberg 1965,
1969, 1971, 1995). Other regional floras that have experienced a similar developmental
process include those of the Andes and the mountains of Malaysia, Indonesia, and New
Guinea (Van Steenis 1934, 1935, 1962, 1972; Troll 1958; Cuatrecasas 1968).
Nested within the broader context of regional climate and geology (e.g., Moser et
al. 2005), local environmental factors largely determine alpine habitat and floristic di-
versity. These factors—including microclimatic conditions (temperature and moisture),
soil characteristics (texture, pH, and nutrient status), snowpack (depth and duration),
disturbance (grazing), and plant interactions (e.g., Callaway et al. 2002; Boyce et al.
2005; Volanthen et al. 2006; Pierce et al. 2007; Löffler and Pape 2008)—create mosaics
of habitat types and local environmental gradients.
Phylogeography of Alpine Plants
Phylogeography is an emerging topic of biogeographic research that combines the spa-
tial and environmental context of historical biogeography with the genetic composition
of individual plant species. Based on many of the ideas developed by early biogeograph-
ers such as Marie Brockmann-Jerosch (Holderegger et al. 2011), recent advances in
genetic research have deepened our ability to explore biogeographic patterns and ori-
gins of alpine plants (e.g., Comes and Kadereit 2003) and ecologically related organisms
(e.g., Garnier et al. 2004). This merger of historical biogeography (dispersal and migra-
tion) combined with the discrete spatial nature of alpine environments (isolation), and
a genetics-based alpine plant genealogy (the study of evolutionary lineages) provides
researchers with an exciting new means to test a broad range of biogeographic assump-
tions and theories essential to our understanding of the past, present, and future dis-
tributions of alpine plants. Moreover, the recent availability of genetic information im-
proves the accuracy of dating for significant evolutionary events related to the origin,
migration, and diversification of alpine floras. As a result, biogeographers are now bet-
ter able to relate episodes of plant migration and dispersal (e.g., Comes and Kadereit
2003), isolation (Schneeweiss and Schönswetter 2011), disjunctions (e.g., Schönswet-
ter et al. 2003), and genetic diversification (e.g., Kadereit et al. 2004) to past climatic
change (e.g., Paun et al. 2008) and orogenesis (Hughes and Eastwood 2006).
The advent of modern genetics has also provided new tools that allow researchers to
test important hypotheses pertaining to biogeography of alpine plants. Phylogeography
now allows us to better assess (1) the genetic contribution of arctic versus low-elevation
plants in specific alpine areas (e.g., Holderegger and Thiel-Egenter 2009); (2) the relat-
ive importance of immigration versus in situ diversification of alpine plant species (e.g.,
Paun et al. 2008); (3) the role of geology, soils, and other physiographic factors in pro-
moting alpine plant biodiversity (e.g., Alvarez et al. 2009); and (4) the role of safe sites
harboring plants during unfavorable conditions, such as habitat refugia and nunataks
(isolated, nonglaciated areas that remained above Pleistocene glaciers and ice sheets)
during oscillating periods of cool glacial and warm interglacial periods (Schneeweiss
and Schönswetter 2011). Carefully designed phylogeography research can also address
several of these types of questions within a single study. For example, recent DNA-based
comparisons by Schönswetter et al. (2006) provide a compelling explanation of the di-