Distribution Patterns of Great Basin Conifers: Implications of Extinction and Immigration

Abstract

Factors influencing the distribution of scattered montane conifers on mountaintops in the Great Basin of North America were investigated. The sources of data were collections and observations on more than 300 mountain ranges in the region. All mountains in the region with at least one montane conifer species and all adjacent source areas were included in the data set. In all, 164 montane island sites and 40 mainland sites were used in the analyses. Physical data for each site were compiled and regression analyses were conducted to test the predictions of three island biogeography models: immigration, extinction, and equilibrium. These models were treated as alternatives to the Random Placement Hypothesis. The Random Placement Hypothesis was refuted. However, none of the island biogeography models explained the observed patterns because mainland species-area slopes were within the expected range of island slopes. The pattern that emerges is one in which both the ''mainlands'' and islands represent the remnants of a preexisting regional conifer flora. The vertical relief of a site's montane zone is a better estimate of habitat diversity than area, and explains 65% of all variation in species richness on mountain ranges in the region. Although not all predictions of the island biogeography models were supported, it appears that both immigration and extinction of montane and subalpine conifers have occurred in the region during the Late Quaternary. Extinction was more important than immigration in shaping modern conifer distributions because area, not distance to sources, has a stronger influence on species richness.

Mitochondrial DNA haplotype distribution patterns inPinus ponderosa(Pinaceae): Range‐wide evolutionary history and implications for conservation

“…The same may be the case in the Sheep Range of southern Nevada, where three haplotypes coexist in close proximity; interestingly, ponderosa pine appears as a dominant species in a 10000‐yr‐old packrat midden from this area (Van Devender and Spaulding, 1979). Our mtDNA results may suggest that, contrary to the paleobotanical data (Wells, 1983a; Thompson, 1990), ponderosa pine may have existed in the Great Basin prior to the end of the Pleistocene, and may have been a colonization source for other regions (Charlet, 2007).…”

“…It is unlikely either to have evolved since the end of the Pleistocene, or to have migrated from a refugium further south. The high topographic diversity in the Great Basin, however, may have allowed the existence of many habitats on mountains throughout the Quaternary (Charlet, 2007), including places where this haplotype may have survived. The same may be the case in the Sheep Range of southern Nevada, where three haplotypes coexist in close proximity; interestingly, ponderosa pine appears as a dominant species in a 10000‐yr‐old packrat midden from this area (Van Devender and Spaulding, 1979).…”

Long‐term survivorship of single‐needle pinyon (Pinus monophylla) in mixed‐conifer ecosystems of the Great Basin, USA

“…Six of the randomly selected plots were dominated by pinyon, and five of the plots (three randomly located) by ponderosa pine. Although J. scopulorum has been found in the area (Charlet 2007), the only junipers we recorded were J. osteosperma on two of the pinyon-dominated plots. One randomly located plot had no living trees but was covered by shrubs with a few stumps and logs of ponderosa pine still visible (see Table 1 in Cheek et al 2012).…”

“…var. concolor) along with other tree species (Charlet 1996(Charlet , 2007, such as Rocky Mountain juniper (Juniperus scopulorum Sarg.) and bristlecone pine (Pinus longaeva D.K.Bailey).…”

Topographic control of forest species distributions in the Interior West USA

“…Mountains-clearly associated with forests in arid and semi-arid environments (Marston 2008)-are critically important in modifying macroclimate, as the presence, juxtaposition, height, and orientation of mountains directly influence the amount and type of precipitation that is delivered. Indeed, previous work has documented the role of elevation on the occurrence of forests, with the view that mountains are "islands" of suitable habitat among a "sea" of hotter and drier valleys (Wells 1983;Charlet 2007). However, just as non-forested valleys may not be uniformly unsuitable for trees (Kupfer et al 2006), mountain environments themselves are heterogeneous, providing a range of potentially suitable habitat across interacting microclimatic gradients of aspect and steepness.…”