A diverse alpine species pool drives a ‘reversed’ plant species richness–elevation relationship in interior Alaska

Abstract

Aim We evaluate whether vascular plant species richness in interior Alaska is highest in the alpine zone. We test the proposition that historical dynamics have influenced the sizes of species pools inhabiting different segments of the landscape by quantifying the contrasting responses of five phytogeographical elements within the flora to changes in elevation and topography. Location Denali National Park and Preserve, Alaska, USA. Methods We developed Bayesian hierarchical models for total plant species richness and the richness of five phytogeographical elements with data from a systematic‐grid sample containing 1022 plots. We also used rarefaction and extrapolation techniques on these data to estimate species richness for more extensive landscape segments, including across seven elevation bands in the study area. Results Plot‐level species richness had a unimodal response to elevation, reaching its peak in the alpine zone. Overall plant species richness across more extensive areas was also higher in the alpine zone, even though this zone occupies less area overall in interior Alaska. Species richness of Alaska endemic and amphi‐Beringian phytogeographical elements showed particularly strong positive responses to elevation, whereas that of the North American and incompletely circumpolar elements declined with elevation. Main conclusions Our results document a unique pattern in the study of variation in species‐pool sizes with elevation, revealing that sparsely vegetated alpine areas contained a larger species pool than adjacent extensive lowlands. This pattern was driven by pronounced increases in phytogeographical elements whose distribution patterns suggest that they evolved or persisted in the region during full‐glacial intervals. The persistence of tundra and/or similar open, treeless vegetation in interior Alaska contrasts with the simultaneous periodical elimination of boreal lowland ecosystems in the region. We posit that this has resulted in a regional species pool relatively enriched in alpine species and impoverished in boreal lowland taxa, causing a ‘reversed’ relationship between species richness and elevation. Increased habitat heterogeneity in high‐relief areas of the mountainous landscape are also likely to have contributed to the reported patterns.

Proliferating poplars: the leading edge of landscape change in an Alaskan subalpine chronosequence

“…Only two species were present in four or more plots in 1958, but absent from the sample in 2012 (species “lost”; Table ), whereas eight species that occurred in four or more of the 35 full plots measured in 2012 were not observed in the 1958 full plots (species “gained”; Table ). The two species lost from the sample are alpine taxa, whose minimum elevations in the Denali systematic sample (Roland and Schmidt ) were higher than the study area and mean elevations were much higher (Table ). In contrast, the eight species that were new to the sample in 2012 all had minimum elevations more than 300 m below the elevation of our study area in the same systematic plot data set (Table ).…”

“…We compiled the minimum and mean elevational range of these species in Denali, as quantified by a randomized landscape‐scale systematic plot vegetation data set (Roland et al. , Roland and Schmidt ) to investigate the elevational distribution of vascular plant species lost from the 1958 sample or gained in the 2012 sample.…”

Species richness of multiple functional groups peaks in alpine tundra in subarctic Alaska

“…A recent study in interior Alaska revealed that alpine areas support larger vascular plant species pools across multiple scales than do adjacent lowland areas (Roland and Schmidt ). Similar studies in Scandinavia show decreasing and “humped” relationships between vascular plant species pools and elevation, with highest diversity occurring at mid‐elevations (Grytnes et al.…”

Relationships between Plant Species Richness and Terrain in Middle Sub-Tropical Eastern China

“…Topography was regarded as the important factor for governing the biodiversity pattern at landscape and regional scales [3][4][5]. Topographic variables, such as altitude, slope and aspect, were often used as predictors to analyze the biodiversity-topography association [6][7][8][9][10]. In recent years, instead of incorporating topographic metrics as predictors to analyze the relationship between species richness and topography, geodiversity was used as a comprehensive indicator to represent environmental heterogeneity [11][12][13].…”

“…However, there still exist conflicting views on the relations between species richness and topographic variables. For example, at least three patterns of species richness along altitude were reported: negative [6,15], positive [16,17] and hump-shaped [7][8][9][10]18]. Recently, some research works provided quantitative proof to underpin positive Environmental Heterogeneity (EH) -species richness relationships across EH subject areas, habitat types, taxonomic groups and …”