Pinus contorta Alters Microenvironmental Conditions and Reduces Plant Diversity in Patagonian Ecosystems

Abstract

Pinus contorta is considered one of the most invasive tree species worldwide, generating significant impacts on biodiversity and ecosystems. In several Patagonian ecosystems in southern Chile, it has escaped from plantations established mainly in the 1970s, and is now invading both forests and treeless environments. In this study, we evaluated the impact of the invasion of P. contorta on microenvironmental conditions in Araucaria araucana forest and Patagonian steppe ecosystems, and assessed how these changes related to the richness and abundance of native and non-native plant species. In each ecosystem, 24 plots of 100 m2 were established along a gradient of P. contorta biomass, where 18 environmental variables and the composition of native and non-native vegetation were measured at a local scale. Our results indicated that increased pine biomass was associated with differences in microclimatic conditions (soil and air temperature, photosynthetically active radiation (PAR), and soil moisture) and soil properties (potassium, nitrate, pH, and litter accumulation). These changes were ecosystem dependent, however, as well as associated with the level of invasion. Finally, the reduction in the richness and abundance of native plants was associated with the changes in soil properties (accumulation of leaf litter, pH, and organic matter) as well as in the microclimate (minimum air temperature, PAR) generated by the invasion of P. contorta. Overall, our results confirm that the invasion of P. contorta impacts microenvironmental conditions (i.e., canopy cover, litter accumulation, minimum air temperature, and maximum soil temperature) and reduces native plant diversity. For future restoration plans, more emphasis should be given to how environmental changes can influence the recovery of invaded ecosystems even after the removal of the living pine biomass (i.e., legacy of the invasion).

A single range‐expanding species reshapes alpine ecosystems and their belowground diversity

“…Similar to the loss of mutualists, an increase in the diversity of fungal pathogens could decrease the fitness of native plants. Taken together, these changes in root‐associated fungal communities point towards a potential belowground mechanism by which novel foundation species are restructuring the communities they invade, which could contribute to the commonly observed reductions in aboveground plant diversity associated with novel tree spread and establishment (Bravo‐Monasterio et al 2016, Taylor et al 2016, García et al 2018, 2023, Mogashoa et al 2021).…”

“…Past work clearly demonstrates the ability of novel trees to create microhabitat where they establish, altering abiotic conditions and reducing the diversity of understory plants (Bravo‐Monasterio et al 2016, Taylor et al 2016, García et al 2018, 2023, Mogashoa et al 2021). Here, we show that the belowground abiotic impacts begin only a few years after establishment and are associated with concurrent shifts in the richness, abundance and composition of belowground fungal communities, potentially driven by key changes in soil moisture.…”

“…These belowground impacts may determine the fate of vulnerable alpine and tundra ecosystems threated by range expansion, as long‐term shifts in the diversity of belowground mutualistic and pathogenic fungi can have ecosystem‐wide impacts on nutrient cycling, aboveground diversity and ecosystem services (Körner 2003, Parker et al 2015, Kivlin et al 2017). Although the changes we outline in this study reflect the early stage impacts of single range‐expanding individuals, over time, these effects will likely strengthen as trees multiply and spread, reshaping and transforming alpine and tundra landscapes into forested ecosystems (García et al 2018, 2023), with novel water and fire regimes, increased competition among native species for limited resources, and decreased biodiversity (Simberloff et al 2010, Taylor et al 2016, 2017, Bravo‐Monasterio et al 2016, Franzese et al 2017, Mogashoa et al 2021).…”

“…The disappearance of foundation species can impact a variety, of ecosystem processes as seen during the loss of American chestnut from temperature forests and resulting changes in decomposition, nutrient cycling, diversity and productivity (Ellison et al 2005). Similar to their disappearance, the spread of foundation species into new territories can also impact diversity and ecosystem functioning (Báez and Collins 2008, Collins et al 2018, García et al 2023), but these impacts remain understudied.…”

“…Past work has started to explore the ecological impacts of range‐expanding trees on these biomes, but much of the focus has been on aboveground, rather than belowground, patterns and processes (Lazzaro et al 2015, Siles and Margesin 2016). For example there is strong evidence that novel foundation tree species alter abiotic conditions where they establish (García et al 2023), reduce the area covered by herbaceous alpine and tundra plants (Moiseev and Shiyatov 2003), reduce plant diversity (Moore and Huffman 2004, Bravo‐Monasterio et al 2016, García et al 2023), and impact ecosystem processes (Dickie et al 2011, Rundel et al 2014). However, the belowground consequences of novel trees remain comparatively understudied.…”