Invasive Impatiens glandulifera: A driver of changes in native vegetation?

Abstract

Biological invasions are one of the major threats to biodiversity worldwide and contribute to changing community patterns and ecosystem processes. However, it is often not obvious whether an invader is the “driver” causing ecosystem changes or a “passenger” which is facilitated by previous ecosystem changes. Causality of the impact can be demonstrated by experimental removal of the invader or introduction into a native community. Using such an experimental approach, we tested whether the impact of the invasive plant Impatiens glandulifera on native vegetation is causal, and whether the impact is habitat‐dependent. We conducted a field study comparing invaded and uninvaded plots with plots from which I. glandulifera was removed and plots where I. glandulifera was planted within two riparian habitats, alder forests and meadows. A negative impact of planting I. glandulifera and a concurrent positive effect of removal on the native vegetation indicated a causal effect of I. glandulifera on total native biomass and growth of Urtica dioica. Species α‐diversity and composition were not affected by I. glandulifera manipulations. Thus, I. glandulifera had a causal but low effect on the native vegetation. The impact depended slightly on habitat as only the effect of I. glandulifera planting on total biomass was slightly stronger in alder forests than meadows. We suggest that I. glandulifera is a “back‐seat driver” of changes, which is facilitated by previous ecosystem changes but is also a driver of further changes. Small restrictions of growth of the planted I. glandulifera and general association of I. glandulifera with disturbances indicate characteristics of a back‐seat driver. For management of I. glandulifera populations, this requires habitat restoration along with removal of the invader.

Growing and Flowering in a Changing Climate: Effects of Higher Temperatures and Drought Stress on the Bee-Pollinated Species Impatiens glandulifera Royle

“…Himalayan balsam ( Impatiens glandulifera ) is an annual, entomophilous plant with large zygomorphic pink flowers that originated from the Himalayas and has spread worldwide as an ornamental. Impatiens glandulifera is one of the most invasive annual species in the world [ 91 ]. It has spread in the majority of temperate communities in Europe, growing in riparian biotopes and in other disturbed sites with good water and nutrient supply [ 36 , 80 ].…”

Sewage Pollution Promotes the Invasion-Related Traits of Impatiens glandulifera in an Oligotrophic Habitat of the Sharr Mountain (Western Balkans)

“…U. dioica might be equally capable of suppressing local diversity as I. glandulifera [38]. In perspective, it could be expected that the main effect of the extreme increase in size of this invader would be a replacement of nitrophilous species (U. dioica in particular) in "C" stands, as demonstrated for the communities with very high cover of I. glandulifera [14,31,39].…”

“…Further, a positive correlation of plant height and soil concentrations of ammonium and organic carbon-Corg-was reported from five populations of Himalayan balsam in Ireland [29]; the tallest population had a mean height of 164 cm (less than both "A" and "B" stands, Figure 3). With respect to the general effect of habitat types on growth performance of this species, lower values were reported for aboveground dw and plant heights in alder forest compared to meadow habitat [31], while [32] found about 4-fold lower biomass in roadside compared to riparian habitats.…”

“…In nature (non-manipulative) experiments, it is often not possible to establish causal relationships among the considered factors [31]. In fact, often only a sum effect of a set of factors can be identified, while their complex interactions remain in the domain of a "black box" [33,34].…”

“…In the same line, it has remained so far ambiguous whether the presence of this species causes changes in resident vegetation or if it occurs in already degraded vegetation. It has been suggested that this species might be more of a "passenger" or a "back seat driver" (sensu [35]) of environmental change, a symptom rather than a direct cause of ecosystem disturbance [14,31,36,37]. Nutrient enrichment per se can decrease species richness of riparian communities and lead to a replacement of grasses and sedges by nitrophilous herbs such as Urtica dioica ( [20]; Figure 4a, Table 3).…”