Diversity and Typology of Land-Use Explain the Occurrence of Alien Plants in a Protected Area

Plant life history and functional characteristics play an important role in determining the invasive potential of plant species and have implications for management approaches. We studied the distribution of 24 alien plant taxa in a protected area in relation to different land-uses by applying ordination analyses and generalized linear models. Taxa richness is best explained by the presence of built-up areas, followed by residential areas, marshlands, and agricultural lands with semi-natural formations. The diversity of land-use within the grid cell proved to be an important explanatory factor, being the only significant variable explaining the richness of wood perennials and vines. The richness of annual herbs and seed-dispersed taxa is explained by a similar set of variables, with the exception of residential areas. The richness of invasive species is explained only by agricultural land and the diversity of land-use. The richness of taxa with predominant vegetative dispersal is best explained by built-up, marshland, and seminatural areas along with land-use diversity. When we consider only the presence of plant groups within grid cells, the results are similar. The results of similar studies may provide an important tool for defining sustainable practices and overall conservation management in protected areas.

The impact of NPK fertilizer on growth and nutrient accumulation in juniper (Juniperus procera) trees grown on fire-damaged and intact soils

Wildfires significantly alter soil properties and result in vegetation shifts; therefore, rapid reforestation activities are needed in the forests affected by wildfires. The decreased nutrient in the soil is the obvious effect of wildfires; however, little is known about the reforestation of Juniper (Juniperus procera) forests with application of NPK fertilizers. Juniper forests are common in Asir and Taif regions of Saudi Arabia and vulnerable to wildfires; thus, reforestation is needed after the onset of fires. This study assessed the impact of different doses of organic NPK fertilizer (0, 5 and 10 g/L) on growth and nutrient accumulation of Juniper trees grown on fire-damaged and intact soils. Data relating to tree height, number of leaves per plant, fresh and dry biomass accumulation in shoot and root, chlorophyll contents and uptake of N, P, K, and Na were recorded. Individual and interactive effects of soil types and fertilizer doses significantly altered all measured traits with minor exceptions. Overall, higher values of the measured traits were recorded for intact soil and 10 g/L fertilize dose. The increasing fertilizer doses improved the growth and nutrient acquisition and application of 10 g/L fertilizer on intact soil recorded the highest values of growth traits. Juniper trees grown on fire-damaged soil accumulated higher amount of nitrogen than intact soil. Similarly, the trees grown on intact soil accumulated lower amount of Na and maintained comparable K/Na ratio to intact soil. It is concluded that supplying 10 g/L fertilizer could improve the establishment of Juniper trees on fire-damaged soil. Therefore, organic fertilizer can be used to improve the reforestation of wildfire-affected Juniper forests in the Asir province.

OUP accepted manuscript

The invasive plant Alliaria petiolata (garlic mustard) has spread throughout forest understory and edge communities in much of North America, but its persistence, density, and impacts have varied across sites and time. Surveying the literature since 2008, we evaluated both previously proposed and new mechanisms for garlic mustard's invasion success and note how they interact and vary across ecological contexts. We analyzed how and where garlic mustard has been studied and found a lack of multisite and longitudinal studies, as well as regions that may be under- or overstudied, leading to poor representation for understanding and predicting future invasion dynamics. Inconsistencies in how sampling units are scaled and defined can also hamper our understanding of invasive species. We present new conceptual models for garlic mustard invasion from a macrosystems perspective, emphasizing the importance of synergies and feedbacks among mechanisms across spatial and temporal scales to produce variable ecological contexts.

Monitoring Invasive Plant Species Using Hyperspectral Remote Sensing Data

The species richness and biodiversity of vegetation in Hungary are increasingly threatened by invasive plant species brought in from other continents and foreign ecosystems. These invasive plant species have spread aggressively in the natural and semi-natural habitats of Europe. Common milkweed (Asclepias syriaca) is one of the species that pose the greatest ecological menace. Therefore, the primary purpose of the present study is to map and monitor the spread of common milkweed, the most common invasive plant species in Europe. Furthermore, the possibilities to detect and validate this special invasive plant by analyzing hyperspectral remote sensing data were investigated. In combination with field reference data, high-resolution hyperspectral aerial images acquired by an unmanned aerial vehicle (UAV) platform in 138 spectral bands in areas infected by common milkweed were examined. Then, support vector machine (SVM) and artificial neural network (ANN) classification algorithms were applied to the highly accurate field reference data. As a result, common milkweed individuals were distinguished in hyperspectral images, achieving an overall accuracy of 92.95% in the case of supervised SVM classification. Using the ANN model, an overall accuracy of 99.61% was achieved. To evaluate the proposed approach, two experimental tests were conducted, and in both cases, we managed to distinguish the individual specimens within the large variety of spreading invasive species in a study area of 2 ha, based on centimeter spatial resolution hyperspectral UAV imagery.

Effects of maternal source and progeny microhabitat on natural selection and population dynamics in Alliaria petiolata

PREMISE

The success or failure of propagules in contrasting microhabitats may play a role in biological invasion. We tested for variation in demographic performance and phenotypic trait expression during invasion by Alliaria petiolata in different microhabitats.

METHODS

We performed a reciprocal transplant experiment with Alliaria petiolata from edge, intermediate, and forest understory microhabitats to determine the roles of the environment and maternal source on traits, fecundity, population growth rates (λ), and selection.

RESULTS

Observations of in situ populations show that edge populations had the highest density and reproductive output, and forest populations had the lowest. In experimental populations, population growth rates and reproductive output were highest in the edge, and the intermediate habitat had the lowest germination and juvenile survival. Traits exhibited phenotypic plasticity in response to microhabitat, but that plasticity was not adaptive. There were few effects of maternal source location on fitness components or traits.

CONCLUSIONS

Alliaria petiolata appears to be viable, or nearly so, in all three microhabitat types, with edge populations likely providing seed to the other microhabitats. The intermediate microhabitat may filter propagules at the seed stage, but discrepancies between in situ observations and experimental transplants preclude clear conclusions about the role of each microhabitat in niche expansion. However, edge microhabitats show the highest seed output in both analyses, suggesting that managing edge habitats might reduce spread to the forest understory.

Historic Mining and Agriculture as Indicators of Occurrence and Abundance of Widespread Invasive Plant Species

Anthropogenic disturbances often change ecological communities and provide opportunities for non-native species invasion. Understanding the impacts of disturbances on species invasion is therefore crucial for invasive species management. We used generalized linear mixed effects models to explore the influence of land-use history and distance to roads on the occurrence and abundance of two invasive plant species (Rosa multiflora and Berberis thunbergii) in a 900-ha deciduous forest in the eastern U.S.A., the Powdermill Nature Reserve. Although much of the reserve has been continuously forested since at least 1939, aerial photos revealed a variety of land-uses since then including agriculture, mining, logging, and development. By 2008, both R. multiflora and B. thunbergii were widespread throughout the reserve (occurring in 24% and 13% of 4417 10-m diameter regularly-placed vegetation plots, respectively) with occurrence and abundance of each varying significantly with land-use history. Rosa multiflora was more likely to occur in historically farmed, mined, logged or developed plots than in plots that remained forested, (log odds of 1.8 to 3.0); Berberis thunbergii was more likely to occur in plots with agricultural, mining, or logging history than in plots without disturbance (log odds of 1.4 to 2.1). Mining, logging, and agriculture increased the probability that R. multiflora had >10% cover while only past agriculture was related to cover of B. thunbergii. Proximity to roads was positively correlated with the occurrence of R. multiflora (a 0.26 increase in the log odds for every 1-m closer) but not B. thunbergii, and roads had no impact on the abundance of either species. Our results indicated that a wide variety of disturbances may aid the introduction of invasive species into new habitats, while high-impact disturbances such as agriculture and mining increase the likelihood of high abundance post-introduction.

Windows of opportunity: historical and ecological controls on Berberis thunbergii invasions

Attempts to determine characteristics that render habitats invasible to nonnative species have met with limited success. This may be because most studies focus on modern habitat conditions and do not consider invasibility in the context of a historically dynamic landscape in which both the abundance of a species and the invasibility of a site may change. We surveyed 159 currently forested sites for the occurrence and abundance of Berberis thunbergii (Japanese barberry), an invasive, nonnative shrub in forests of the northeastern United States, relative to modern environmental conditions, contemporary logging activity, and two periods of historical land use. Berberis thunbergii occurred more frequently and was more abundant in post-agricultural forests than in continuously wooded sites. This relationship was stronger for agricultural sites that were abandoned and reforested after B. thunbergii was introduced to the region than for sites that reforested prior to B. thunbergii introduction. In contrast, recent forest harvesting did not influence the occurrence or abundance of B. thunbergii. Modern soil fertility explained a significant portion of the variation in B. thunbergii occurrence, whereas site history considerably improved predictions of population density and helped evaluate potential invasion mechanisms. While land-use history covaries with soil fertility and distance to putative seed sources, the strong relationship between modern abundance patterns and historical agriculture suggests that B. thunbergii colonized recently abandoned agricultural lands in the early 20th century and then persisted and spread locally during subsequent reforestation. Our results indicate that interpretations of both native community composition and modern plant invasions must consider the importance of historical landscape changes and the timing of species introduction along with current environmental conditions.