Abstract
Mountainous areas and their endemic plant diversity are threatened by global climate change and invasive species. Mountain plant invasions have historically been minimal, however, climate change and increased anthropogenic activity (e.g. roads and vehicles) are amplifying invasion pressure. We assessed plant performance (stem density and fruit production) of the invasive non-native forb Linaria dalmatica along three mountain roads, over an eight-year period (2008–2015) in the Greater Yellowstone Ecosystem (GYE), USA. We evaluated how L. dalmatica performed in response to elevation, changed over time, responded to climate and how the climate of our sites has changed, and compared elevation, climate, micro-topography (slope aspect and angle), and fruit production among sites with differing temporal trends. Linaria dalmatica stem density and fruit production increased with elevation and demonstrated two temporal groups, those populations where stem densities shrank and those that remained stable or grew over time. Stem density demonstrated a hump-shaped response to summer mean temperature, while fruit production decreased with summer mean maximum temperature and showed a hump-shaped response to winter precipitation. Analysis of both short and long-term climate data from our sites, demonstrated that summer temperatures have been increasing and winters getting wetter. The shrinking population group had a lower mean elevation, hotter summer temperatures, drier winters, had plots that differed in slope aspect and angle from the stable/growing group, and produced less fruit. Regional climate projections predict that the observed climate trends will continue, which will likely benefit L. dalmatica populations at higher elevations. We conclude that L. dalmatica may persist at lower elevations where it poses little invasive threat, and its invasion into the mountains will continue along roadways, expanding into higher elevations of the GYE.
Highlights
Mountainous areas are often regarded as resistant to invasive plant species due to the harsh climate and a low human footprint (Pauchard et al 2009; Alexander et al 2016)
To address the first part of our third question, we evaluated the effects of 24 climate variables on L. dalmatica stem density and fruit production
Elevation had the strongest relationship with axis 1 of our principal components analysis, which explained 80% of the variance (Table 1) and both stem density (F = 8.09, Den df = 15, P = 0.012; Fig. 1A) and fruit production (F = 10.77, Den df = 15, P = 0.005; Fig. 1B) increased with elevation
Summary
Mountainous areas are often regarded as resistant to invasive plant species due to the harsh climate and a low human footprint (Pauchard et al 2009; Alexander et al 2016). Global climate change, occurring in mountain and high elevation regions, is weakening the strong climate filter (Pyšek et al 2011; Carboni et al 2018), resulting in many species shifting ranges towards higher elevations (Lenoir et al 2008; Chen et al 2011) This shift has been demonstrable for non-native plant species (Walther et al 2002; Kalwij et al 2015; Koide et al 2017), which are spreading upwards in elevation twice as fast as native species (Dainese et al 2017) and anthropogenic propagule sources and roadways are critical for these shifts (Kalwij et al 2008; Kalwij et al 2015; Dainese et al 2017; Lembrechts et al 2017; Lázaro-Lobo and Ervin 2019). Much of the literature, assessing non-native species along elevation gradients, has used frequency or occurrence data to model species distributions or has described community trends (e.g. species richness) across elevation ranges (Kalwij et al 2008; Lenoir et al 2008; Kalwij et al 2015; Dainese et al 2017; Koide et al 2017; Lembrechts et al 2017; Haider et al 2018), with few studies describing non-native abundance or reproductive trends over time along mountain elevation gradients (Pauchard et al 2009; Alexander et al 2016)
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