Factors associated with alien plant richness, cover and composition differ in tropical island forests

Abstract

Aim To examine how native plant native communities, environment and geography are associated with alien plant species invasion in tropical island forests. Location Four US national parks in Hawai'i and American Samoa. Methods We analysed the richness, coverage and composition of alien plant species communities located across 204 plots, five islands and two archipelagos. We used generalized linear mixed‐effects models and generalized dissimilarity models to determine the relative importance of native plant species communities (richness, structure and composition), environment (temperatures, precipitation, and soil age) and geography (elevation, geographical distance between plots, identity of islands and archipelagos) on alien plant species communities. Results Alien plant species were found in >90% of plots with on average four species covering ~15% of the understorey. Variation in alien species richness and coverage was primarily explained by archipelago and island identity and elevation. Plots located on younger islands tended to exhibit higher richness and coverage of alien plants. Native tree density and canopy height were negatively correlated with alien species coverage but not with alien species richness. Elevation was negatively correlated with both the richness and coverage of alien species. Differences in elevation, mean annual precipitation and geographical distances explained about 40% of the observed spatial turnover in alien species composition with differences in elevation being the main driver. Turnover in alien species composition was weakly correlated with turnover in native species. Main conclusions In the studied islands, higher elevations seem to be relatively spared from alien species invasion so far. However, our results suggest that the negative effect of elevation on alien species coverage may be larger than on alien species richness. Maintenance of tall and dense canopy may limit the coverage of alien species but not the number of alien species. Our results also support that alien species invasion may be particularly high on isolated archipelagos and younger islands.

Impact of Grazing on Diversity of Semi-Arid Rangelands in Crete Island in the Context of Climatic Change

“…This is in agreement and supports the theory that species richness and diversity decrease along the altitude gradient [ 27 , 96 , 97 ]. Altitude probably has the strongest effects on species richness, abundance, and ground cover [ 98 ]. Nevertheless, other studies found that overgrazing affects functional diversity more than climate, and species diversity declines with an increase in grazing intensity in areas with different climatic conditions [ 41 , 46 , 99 ].…”

Predicting invasion potential of Senna didymobotrya (Fresen.) Irwin & Barneby under the changing climate in Africa

“…Similarly, our ensemble model predicted precipitation variables which are accounting for 26.8% (bio12, annual precipitation; bio14, precipitation of driest month; and bio17, precipitation of driest quarter) as the third most important environmental variables affecting S. didymobotrya distribution. Ibanez et al(2019) also reported positive effects of mean annual precipitation on alien species coverage. Similarly, Averett et al (2016) confirmed that temperature variables (minimum temperature records over 30 years) are the most predictor variables limiting the distribution of non-native species richness.…”

“…Under future climate change scenarios, suitability for S. didymobotrya will expand toward lower elevations. Higher species richness of invasive alien species was reported in the lower elevation ranges than higher elevation (Averett et al 2016;Ibanez et al 2019;Pauchard and Alaback 2004). Similarly, some invasive species are shifting their geographic distribution toward high altitude as the climate warms (Bradley et al 2010;Shrestha et al 2018), and new invasive species are adding to those currently being successfully controlled.…”

Rarity patterns of woody plant species are associated with life form and diversification rates in Pacific islands forests

“…Non-native species are widespread in the studied parks (Ibanez et al, 2019) and can affect rarity/commonness patterns (e.g., Hughes et al, 2012). Therefore, we excluded from analysis all plots in which >50% of all recorded individuals were non-native, or in which >25% of the large tree individuals were non-native.…”