Infrastructure Development Accelerates Range Expansion of Trembling Aspen (<i>Populus tremuloides</i>, Salicaceae) into the Arctic

Abstract

ABSTRACT. Interacting forces of climate change and increased human activity in the Arctic are driving rapid changes in ecosystem structure, function, and biodiversity. One such change is the northern range expansion of tree species. We present the first account of the boreal tree species trembling aspen (Populus tremuloides, Salicaceae) growing beyond the latitudinal treeline in the northern foothills of the Brooks Range, Alaska. The four trembling aspen stands described in this paper are located on abandoned gravel roads or pads created for construction purposes. We hypothesize that gravel pads create islands of substrate suitable for tree growth within the Arctic by providing greater rooting depth, well-drained microsites, an extended growing season, and acid-buffering capacity. Further, traffic along the south-to-north oriented Dalton Highway from the boreal forest in Interior Alaska to the Arctic may aid seed dispersal across the topographic barrier of the Brooks Range. Therefore, increased development in the Arctic will likely accelerate the establishment of trees as climate becomes more favorable for tree growth. Tree colonization associated with infrastructure development would contrast sharply with prior conceptual models of gradual treeline advance following disturbance.Key words: trembling aspen; Populus tremuloides; Arctic treeline; range expansion; infrastructure development; human activity; climate change; Brooks Range; Alaska RÉSUMÉ. Dans l'Arctique, les forces interactives du changement climatique et de l'activité humaine accrue donnent lieu à des changements rapides dans la structure, la fonction et la biodiversité de l'écosystème. Un de ces changements prend la forme de l'expansion des espèces d'arbres dans l'aire de répartition septentrionale. Nous présentons le premier compte rendu au sujet de l'espèce boréale du peuplier faux-tremble (Populus tremuloides, Salicaceae) qui pousse au-delà de la limite forestière latitudinale dans les piémonts du nord de la chaîne de Brooks, en Alaska. Les quatre peuplements de peupliers faux-trembles décrits dans ce texte se trouvent sur des routes ou des remblais de gravier abandonnés créés à des fins de construction. Nous formulons l'hypothèse selon laquelle les remblais de gravier produisent des îlots de substrat qui conviennent à la croissance des arbres dans l'Arctique en raison de la plus grande profondeur d'enracinement, de la présence de microsites bien irrigués, d'une saison de croissance prolongée et de la capacité de tamponnage de l'acide. De plus, la circulation le long de la route Dalton, orientée du sud au nord, depuis la forêt boréale de l'intérieur de l'Alaska jusqu'à l'Arctique pourrait favoriser la dissémination des graines à l'échelle de la barrière topographique de la chaîne de Brooks. Par conséquent, le développement accru de l'Arctique accélérera vraisemblablement l'établissement d'arbres, au fur et à mesure que le climat deviendra plus favorable à la croissance des arbres. La colonisation des arbres liée au développement de l'infrastructur...

Arctic shrub growth trajectories differ across soil moisture levels

“…These are conservative estimates that account only for accelerated individual growth, not the proliferation of new shrub stems across the landscape. However, we emphasize that factors besides soil moisture, such as topography, biotic interactions, or disturbance, may modify shrub growth trajectories (Ackerman & Breen, 2016;Christie et al, 2015;Olofsson et al, 2009;Ropars et al, 2015;Schuur et al, 2007). As reviewed by Myers-Smith et al (2011), biomass increases like those predicted here will likely have significant impacts on surface energy balance, primary productivity, and soil temperature and gas exchanges.…”

“…These are conservative estimates that account only for accelerated individual growth, not the proliferation of new shrub stems across the landscape. However, we emphasize that factors besides soil moisture, such as topography, biotic interactions, or disturbance, may modify shrub growth trajectories (Ackerman & Breen, ; Christie et al., ; Olofsson et al., ; Ropars et al., ; Schuur et al., ). As reviewed by Myers‐Smith et al.…”

“…However, a relative scarcity of landscape‐scale investigation has made it difficult to connect plot‐level experimentation to regional greening trends (Hobbie & Kling, ). Landscape factors like topography, disturbance, and biotic interactions may modulate rates of shrub expansion (Ackerman & Breen, ; Christie et al., ; Olofsson et al., ; Ropars, Levesque, & Boudreau, ; Schuur, Crummer, Vogel, & Mack, ). A poor understanding of the heterogeneity of shrub expansion across arctic landscapes inhibits accurate incorporation shrub feedbacks into mechanistic climate models such as dynamic global vegetation models (e.g., Sitch et al., ).…”

“…biotic interactions may modulate rates of shrub expansion (Ackerman & Breen, 2016;Christie et al, 2015;Olofsson et al, 2009;Ropars, Levesque, & Boudreau, 2015;Schuur, Crummer, Vogel, & Mack, 2007). A poor understanding of the heterogeneity of shrub expansion across arctic landscapes inhibits accurate incorporation shrub feedbacks into mechanistic climate models such as dynamic global vegetation models (e.g., Sitch et al, 2003).…”

Human‐mediated dispersal as a driver of vegetation dynamics: A conceptual synthesis

“…The different aspects of HMD are often interwoven in any particular situation and in many dispersal scenarios involving human activities, more than one process may apply. For example, accidental transport of non‐native Populus tremuloides seeds along roads into arctic regions (Ackerman and Breen, 2016) is a form of HVD but also illustrates enhancing HAD along green infrastructure (in this case road verges).…”