Grasslands And Forests In Nebraska Are Vulnerable To Tree Invasion From Roadsides

Roadsides can be vectors for tree invasion within grasslands by bisecting landscapes and facilitating propagule spread to interior habitat. Current invasive tree management in North America’s Great Plains focuses on reducing on-site (i.e., interior habitat) vulnerability through on-site prevention and eradication, but invasive tree management of surrounding areas known to serve as invasion vectors, such as roadsides and public rights-of-ways, is sporadic. We surveyed roadsides for invasive tree propagule sources in a southeastern Nebraska grassland landscape to determine how much of the surrounding landscape is potentially vulnerable to roadside invasion, and by which species, and thereby, provide insights into the locations and forms of future landcover change. Invasive tree species were widespread in roadsides. Given modest seed dispersal distances of 100-200 m, our results show that roadsides have potential to serve as major sources of grassland exposure to tree invasion, compromising up to 44% of grasslands in the Denton Hills. Under these dispersal distances, funds spent removing trees on grassland properties may have little impact on the landscape’s overall vulnerability, due to exposure driven by roadside propagule sources. A key implication from this study is that roadsides, while often neglected from management, represent an important component of integrated management strategies for reducing grassland vulnerability to tree invasion.

Timescale Analyses of Fluctuations in Coexisting Populations of a Native and Invasive Tree Squirrel

1. Competition from invasive species is an increasing threat to biodiversity. In Southern California, the western gray squirrel (Sciurus griseus, WGS) is facing increasing competition from the fox squirrel (Sciurus niger, FS), an invasive congener. 2. We used spectral methods to analyze 140 consecutive monthly censuses of WGS and FS within a 11.3 ha section of the California Botanic Garden. Variation in the numbers for both species and their synchrony was distributed across long timescales (> 15 months). 3. After filtering out annual changes, concurrent mean monthly temperatures from nearby Ontario Airport (ONT) yielded a spectrum with a large semiannual peak and significant spectral power at long timescales (> 30 months). Squirrel-temperature cospectra showed significant negative covariation at long timescales (> 35 months) for WGS and smaller significant negative peaks at 6 months for both species. 4. Simulations from a Lotka-Volterra model of two competing species indicates that the risk of extinction for the weaker competitor increases quickly as environmental noise shifts from short to long timescales. 5. We analyzed the timescales of fluctuations in detrended mean annual temperatures for the time period 1915-2014 from 1218 locations across the continental USA. In the last two decades, significant shifts from short timescales to long timescales have occurred, changing from less than 3 years to 4-6 years. 6. Our results indicate that (i) population fluctuations in co-occurring native and invasive tree squirrels are synchronous, occur over long timescales, and may be driven by fluctuations in environmental conditions; (ii) long timescale population fluctuations increase the risk of extinction in competing species, especially for the inferior competitor; and (iii) the timescales of interannual environmental fluctuations may be increasing from recent historical values. These results have broad implications for the impact of climate change on the maintenance of biodiversity.

Timescale Analyses of Fluctuations in Coexisting Populations of a Native and Invasive Tree Squirrel

1. Competition from invasive species is an increasing threat to biodiversity. In Southern California, the western gray squirrel (Sciurus griseus, WGS) is facing increasing competition from the fox squirrel (Sciurus niger, FS), an invasive congener. 2. We used spectral methods to analyze 140 consecutive monthly censuses of WGS and FS within a 11.3 ha section of the California Botanic Garden. Variation in the numbers for both species and their synchrony was distributed across long timescales (> 15 months). 3. After filtering out annual changes, concurrent mean monthly temperatures from nearby Ontario Airport (ONT) yielded a spectrum with a large semiannual peak and significant spectral power at long timescales (> 30 months). Squirrel-temperature cospectra showed significant negative covariation at long timescales (> 35 months) for WGS and smaller significant negative peaks at 6 months for both species. 4. Simulations from a Lotka-Volterra model of two competing species indicates that the risk of extinction for the weaker competitor increases quickly as environmental noise shifts from short to long timescales. 5. We analyzed the timescales of fluctuations in detrended mean annual temperatures for the time period 1915-2014 from 1218 locations across the continental USA. In the last two decades, significant shifts from short timescales to long timescales have occurred, changing from less than 3 years to 4-6 years. 6. Our results indicate that (i) population fluctuations in co-occurring native and invasive tree squirrels are synchronous, occur over long timescales, and may be driven by fluctuations in environmental conditions; (ii) long timescale population fluctuations increase the risk of extinction in competing species, especially for the inferior competitor; and (iii) the timescales of interannual environmental fluctuations may be increasing from recent historical values. These results have broad implications for the impact of climate change on the maintenance of biodiversity.

Innovative Model of the Cost Price Calculation of Products from Invasive Non-Native Wood Species Based on the FTDABC Method

Invasive tree species continue to spread, so in addition to strategies to limit this their use in the production of innovative products must be considered. This research aimed to develop and apply a model for calculating the cost price of invasive wood products considering the specificities of materials and production process, and is suitable for quickly assessing the economic feasibility of using the selected tree species for a given product. The TDABC method with the inclusion of fuzzy logic was used to incorporate the uncertainty of time and quality parameters. In the model, the imprecise values of these parameters are represented with triangular fuzzy numbers. Using a furniture product (dining table) made of black locust wood as an example, we demonstrated the applicability of the developed model. We found that the most probable cost price of a table made of black locust wood is comparable to the price of a product made of oak wood. In this way, we proved the potentially high economic value of invasive wood. The innovative products from invasive non-native wood species can achieve a high added value due to their visual characteristics and attractive appearance. Such use could increase interest in the (more efficient) management of invasive tree species, which would help to manage and use them efficiently. For further research, it would be useful to apply the proposed model to other invasive tree species as well as to other products.

Invasion of Celtis tala forests by Ligustrum lucidum in Argentina: impact on soil properties and the arbuscular mycorrhizal community

The arrival of invasive plants can cause drastic changes to ecosystems, such as the displacement of native plant communities and the disruption of ecological functions. <i>Ligustrum lucidum</i> is an invasive tree species that has been registered in numerous regions worldwide. We analysed the effect of the expansion of <i>L. lucidum</i> on the edaphic properties and mycorrhizal fungal communities in forests of <i>Celtis tala</i> located in central-western Argentina. Sampling sites were established along a gradient of invasion, in which we measured the forest structure and soil physical-chemical factors and identified the fungal species using morphological techniques. The analysis of the variance revealed severe changes in the tree structure and a decrease in the concentrations of organic matter and nitrogen in the invaded sites. Thirty-two Glomeromycota species were identified, belonging to 6 families. The abundance of <i>Dentiscutata cerradensis</i> decreased with the invasion, whereas <i>Funneliformis mosseae</i> and <i>Septoglomus constrictum</i> increased. The alpha diversity of the arbuscular mycorrhizal communities showed no differences between sites. The beta diversity decreased at invaded sites, indicating a tendency towards convergence and reduced variability in these communities in the presence of the exotic species.