Abstract
Invasive plant species can produce many impacts on native communities. Impacts can be especially important when the non-natives reach high densities, producing monospecific stands where little grows besides the non-native species. We propose three basic pathways by which monospecific stands of invasive tree species are formed: (i) gradually from the propagule source, (ii) via synchronous establishment and (iii) following several pulses of synchronous establishment. Different patterns can produce different impacts through time and may require different management techniques. This study aims to further our understanding of how monotypic stands of invasive species arise. We documented how monospecific stands are formed during invasion processes by studying patterns of spatio-temporal establishment of several monospecific stands of Douglas fir in Patagonia. We obtained data on tree density, year of establishment, size, distance to the seed source and other related measurements for this tree species along transects from the original seed source (80-year-old plantations) to the edge of the monospecific stand. We found that these monospecific stands arose in a more complex way than expected. While individuals established on average simultaneously over all distances from the seed source, there was substantial variation in time of establishment at all distances. Also, tree density was higher near the source than far from it. Different factors can account for the observed pattern of tree establishment, including seed dispersal, mycorrhizal facilitation and herbivory. Our results elucidate the complexities of spatio-temporal pattern of formation in monospecific stands. This understanding can improve management strategies and techniques for this invasion and other plant invasions in different regions.
Highlights
Non-native plant species have notable effects on native communities, ranging from changes in fire regimes to changes in soil nutrients, water and light availability, which may alter species dominance and diversity of the native biota (Pyšek et al 2012)
Monospecific stands are common among invasive plant species and have been described in many different ecosystems
Tree-ring samples show that P. menziesii plantations were initiated in 1937.5 ± 2.7, and the establishment of the first trees within the invasion belt started by the mid-1960s
Summary
Non-native plant species have notable effects on native communities, ranging from changes in fire regimes to changes in soil nutrients, water and light availability, which may alter species dominance and diversity of the native biota (Pyšek et al 2012). Perhaps the most notorious effect is when populations of non-native plants become superabundant and form monospecific stands in which only the non-native species thrive. Nuñez and Paritsis – How are monospecific stands of invasive trees formed?. Grasses and ferns form monodominant stands when invading (Asner and Beatty 1996; Kittelson and Boyd 1997; Portela et al 2009; Cavaleri et al 2014). Once the invasive species has formed a monodominant stand, it becomes extremely difficult to restore the area. This may hold true even after the exotic species has been eradicated, because the legacy of a monodominant stand often results in soil and other key structural alterations (Jordan et al 2008)
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