Borealization and its discontents: drivers of regional variation in plant diversity across scales in interior Alaska

Abstract

Quantitative studies of regional variation in plant diversity across eastern Beringia (northern Alaska and adjacent areas) are lacking due to an absence of datasets of sufficient scale and scope. We interrogated a landscape-scale plant diversity dataset collected across two regions of interior Alaska with different disturbance, topographic, and climate attributes to investigate hypotheses regarding drivers of plant species richness. Our approach integrated a multi-scale sampling design with an analytical framework focused on quantifying how components of plant diversity (growth forms, biogeographic groups, and dominant species) respond to site factors that vary along landscape gradients. Our results revealed essential similarities in both the composition of the overall floras and the influences on local and meso-scale species richness across both regions. However, these continuities at smaller scales contrasted with differences in landscape-level distribution of plant diversity patterns along elevation gradients. Our findings suggest that local drivers of richness and occupancy interacted with differing macro-scale attributes (e.g., relative continentality) to produce distinctive landscape-level diversity patterns. Our results confirm that high levels of local and meso-scale plant richness in interior Alaska depend on conditions that foster richness of herbaceous and northerly distributed species groups. However, we found that important differences in landscape-level richness patterns were driven by regional differences in climate, topoedaphic variables, and disturbance. In the warmer region, woody species and boreal plant communities extended to higher elevations and common species occupancy showed marginally greater influence of fire. Overall richness was relatively low in alpine areas of the warmer region but heterogeneous edaphic and topographic circumstances stimulated higher species turnover in lower elevations there, increasing landscape-level richness. In contrast, in the cooler region, woody species showed restricted distribution across the elevation gradient while site attributes associated with increased species richness aligned with the elevation gradient and thus peak richness occurred in the alpine zone. Our results show how total and growth-form richness, as well as community composition, vary regionally in relation to important drivers (including growing season warmth) across interior Alaska. Consequently, our study provides new insights into the potential trajectories of future change in biodiversity patterns in this rapidly warming region.

Tree and shrub expansion at treeline drive contrasting responses in a subarctic passerine community

“…We found pronounced topographic and edaphic gradients in conifer and shrub colonization, emphasizing the capacity of portions of boreal‐tundra landscapes to resist woody vegetation expansion (e.g. Raiho et al, 2022; Roland et al, 2016, 2021; Tape et al, 2012). Both shrub and conifer expansion appeared to depend strongly on proximity to propagules or the initial presence of some adjacent, non‐negligible cover.…”

“…We found pronounced topographic and edaphic gradients in conifer and shrub colonization, emphasizing the capacity of portions of boreal-tundra landscapes to resist woody vegetation expansion (e.g. Raiho et al, 2022;Roland et al, 2016Roland et al, , 2021Tape et al, 2012).…”

Evaluating photosynthetic activity across Arctic-Boreal land cover types using solar-induced fluorescence

“…Similar to EC towers, satellite remote sensing techniques indirectly infer GPP. An advantage of satellite remote sensing techniques is a more extensive spatial coverage, enabling the comparison of GPP across heterogeneous land cover (Funk et al 2004, Roland et al 2021 and complex Arctic-Boreal terrain (Roland et al 2019). However, satellite remote sensing techniques also have higher uncertainties due to more assumptions made in the derivation of GPP (Tramontana et al 2015.…”