Encroachment of shrubs into subalpine grasslands in the Pyrenees changes the plant-soil stoichiometry spectrum

Abstract

We thank all the people who were involved in the field and laboratory work and Jose V. Roses-Díaz for his comments that helped to improve this manuscript. We thank two anonymous reviewers for their contribution to improve this manuscript.

Belowground impacts of alpine woody encroachment are determined by plant traits, local climate, and soil conditions

“…A shift from primarily herbaceous (grasses, sedges, and forbs) to woody plant cover generally increases the quantity and decreases the quality of litter inputs, and may result in slower decomposition of organic matter (Cornelissen et al., 2007). However, this pattern can differ across woody plant species based on chemical and morphological litter traits such as leaf carbon, nitrogen ratio (C:N), leaf dry matter content (LDMC), and specific leaf area (SLA; Cornwell et al., 2008; Gavazov, 2010; Urbina, Grau, Sardans, Ninot, & Peñuelas, 2020). Litter mixing between woody and herbaceous plants can increase the chemical complexity of the substrate pool, enhancing both microbial niche space and diversity (Chapman & Newman, 2010; McGuire, Zak, Edwards, Blackwood, & Upchurch, 2010).…”

Alpine shrubs have benefited more than trees from 20th century warming at a treeline ecotone site in the French Pyrenees

“…High elevation ecosystems have faced unprecedented warming in recent decades, leading to accelerated changes in their productivity and functioning (Carlson et al, 2017;Choler, 2015;Choler et al, 2021;Filippa et al, 2019;Rumpf et al, 2022). Shrub encroachment at the treeline ecotone and beyond, a landscape-scale phenomenon, has been observed on the Tibetan Plateau and in the Himalayas (Brandt et al, 2013;Klein et al, 2014;Lehnert et al, 2016), in the Rocky Mountains (Formica et al, 2014), Scandes (Hallinger et al, 2010;Kullman, 2002;Rundqvist et al, 2011), European Alps (Cannone et al, 2007;Dullinger et al, 2003) and the Pyrenees (Grau et al, 2019;Montané et al, 2007;Urbina et al, 2020). Specifically in the Pyrenees, shrub and tree encroachment has been found to be triggered primarily by land abandonment after centuries to millennia of intense agro-silvo-pastoral activities and by climate change (Ameztegui et al, 2016;Améztegui et al, 2010;Galop and Jalut, 1994;Gartzia et al, 2014).…”

“…Specifically in the Pyrenees, shrub and tree encroachment has been found to be triggered primarily by land abandonment after centuries to millennia of intense agro-silvo-pastoral activities and by climate change (Ameztegui et al, 2016;Améztegui et al, 2010;Galop and Jalut, 1994;Gartzia et al, 2014). Shrub encroachment has direct effects on surface albedo, vegetation roughness, snowpack dynamics and litter input, which in turn has various impacts on alpine tundra carbon balance by increasing ecosystem carbon uptake and altering ecosystem respiration (Mekonnen et al, 2021;Urbina et al, 2020). In the Pyrenees, shrub encroachment plays a complex but important role in the first stage of tree re-colonization at treelines.…”

“…In the Pyrenees, shrub encroachment plays a complex but important role in the first stage of tree re-colonization at treelines. Treeline advance is mainly driven by Pinus uncinata establishment (Améztegui et al, 2010;Camarero and Gutiérrez, 2004), in interaction with the spread of Juniperus communis and/or Rhododendron ferrugineum dominated heathlands (Angulo et al, 2019;Batllori et al, 2009;Gartzia et al, 2014;Pasche et al, 2004;Urbina et al, 2020). Indeed, scattered shrubs have a beneficial effect on tree establishment by sheltering seedlings, but dense, encroached heaths inhibit their development (Angulo et al, 2019;Batllori et al, 2009;Camarero and Gutièrrez, 1999).…”

Fungal Perspective of Pine and Oak Colonization in Mediterranean Degraded Ecosystems

“…Among soil microbes, fungi are fundamental drivers of ecosystems processes owing to their role as decomposers, mutualists, or pathogens of plants and animals [10,11]. The role of soil fungi is, therefore, important for understanding the interplay between below-and above-ground processes and ecosystem functioning [12]. However, the effect of disturbances upon soil fungi has received less attention in comparison to above-ground responses (see: [13,14]), even if disturbances that alter drastically the soil components, and therefore soil fungal communities and networks, can have ecosystemwide implications through their interactions and the biogeochemical process that they sustain [11,15].…”