Feral horses dung piles as potential invasion windows for alien plant species in natural grasslands

Abstract

Small scale disturbances could act as patches that provide sites for the colonization of competitively inferior species, promoting the establishment of non-native species in some cases. We analyzed the vegetation associated with feral horse dung piles in montane pampas grasslands in Mid-East Argentina and described the changes following their abandonment, evaluating whether dung piles act as invasion windows, allowing the entrance of alien plant species. We estimated the portion of the study area directly covered by horse manure and dung height was used to estimate the time elapsed after the abandonment of each pile. Vegetation replacement on dung piles of different ages was assessed and compared with grassland controls using discriminant analysis. We used regression analysis to look for changes in vegetation cover, species richness, species diversity and evenness in response to height (age) of the dung piles, and principal component analyses (PCA) to identify groups of plants associated with different successional stages. We compared cover of alien plant species on dung piles with grassland controls using one-way ANOVA. On average, 2.5% of the study area was covered by horse dung. Total vegetation cover, species richness, diversity and evenness increased after the piles were abandoned. Characteristic plant groups were associated with initial, middle and last phases of the studied succession. Vegetation on the dung piles significantly differed from that in grassland controls and two species were consistently associated with dung piles: the invasive Red Star Thistle, Centaurea calcitrapa, and a native grazing-intolerant grass, Nassella clarazii. Non-native species cover was also higher in dung piles than in control plots. Dung piles cover a significant portion of grassland area in our study site, produce significant changes in the vegetation and are associated with some invasive alien plants that could eventually colonize more pristine areas in the vicinity. On the other hand, they might represent refuges for palatable species, since horses seem to avoid them for grazing.

Exotic vertebrate and invertebrate herbivores differ in their impacts on native and exotic plants: a meta-analysis

“…Various other mechanisms through which herbivores may affect plant invasion have, nevertheless, been reported. These include seed dispersal (Janzen 1984;Suarez 1995, 1997;Fischer et al 1996;Campbell and Gibson 2001;Pakeman 2001;Holmgren 2002;Pakeman et al 2002;Vellend et al 2003;Mouissie 2004;Myers et al 2004;Manzano and Malo 2006;Loeser et al 2007;Loydi and Zalba 2008) and soil disturbance (Cushman et al 2004). A future analysis similar to the one we carried out but including other mechanisms described above would help elucidate the most important mechanisms by which the exotic vertebrate herbivores may influence plant invasion.…”

Invasibility of a Nutrient-Poor Pasture through Resident and Non-Resident Herbs Is Controlled by Litter, Gap Size and Propagule Pressure

“…fluctuating resource hypothesis, [9]). This prediction was supported by field experiments showing that high levels of disturbance that were coupled with high fertility were most favourable for the establishment success of non-resident species [10], [16]–[19]. However, the response of different species to gaps and disturbance is idiosyncratic and seems to be related to plant traits such as seed mass [2], [18], [20], [21], life history stage [4] and germination requirements [2], [18] at least initially [22].…”

A global review of weeds that can germinate from horse dung

“…; Cosyns et al . ; Loydi & Zalba ; Törn et al . ) from inclusion in the database, but not from the general review if the dung could have been contaminated with seed from the site where it was deposited, if they repeated data in one of the existing studies or if the study did not find germination of seed from horse dung.…”