Effects of Soil Properties, Temperature and Disturbance on Diversity and Functional Composition of Plant Communities Along a Steep Elevational Gradient on Tenerife

Elevational variation of vegetation has been of interest for centuries, and a prominent example for such pronounced vegetation changes can be found along the steep elevational gradient on Tenerife, Canary Islands, 200 km off the West-African cost. The 3,718-m ascent to the peak of the island volcano, Teide, offers a unique opportunity to investigate associated changes in vegetation. However, elevation is not a directly acting factor, but represents several natural environmental gradients. While the elevational variation of temperature is globally rather uniform and temperature effects on plant communities are well understood, much less is known about the region-specific elevational change of chemical soil properties and their impact on plant communities along elevational gradients. Because human interference takes place even at high-elevation areas, we considered human-induced disturbance as important third factor acting upon plant community assemblages. In our study, we compared the effects of soil properties, temperature and disturbance on species richness, functional identity and functional diversity of plant communities along the elevational gradient on Tenerife. We used pairs of study plots: directly adjacent to a road and in natural vegetation close by. In each plot, we did vegetation relevées, took soil samples, and installed temperature loggers. Additionally, we collected leaf samples to measure leaf functional traits of 80% of the recorded species. With increasing elevation, soil cation concentrations, cation exchange capacity (CEC) and pH decreased significantly, while the soil carbon to phosphorus ratio slightly peaked at mid-elevations. Temperature had the strongest effects, increasing species richness and favoring communities with fast resource acquisition. Species richness was higher at road verges, indicating the positive effect of reduced competition and artificially generated heterogeneity. However, we did not detect road effects on plant functional characteristics. Vice versa, we did not find soil effects on species richness, but increased concentrations of soil cations favored acquisitive communities. Surprisingly, we could not reveal any influence on community functional diversity. The importance of temperature aligns with findings from large-scale biogeographic studies. However, our results also emphasize that it is necessary to consider the effects of local abiotic drivers, like soil properties and disturbance, to understand variation in plant communities.

Quantifying the effects of road width on roadside vegetation and soil conditions in forests

Context The majority of ecological studies of roads have focused on their deleterious effects, and these preconceptions have hampered a full evaluation of the ecological functions of roads. As an integrated indicator, road width represents comprehensive effects, including anthropogenic and natural disturbances. Objectives We try to explore the different effects produced by various road widths by considering changes in forest vegetation and soil. Methods We selected six study forests spanning from Shandong Province in the north to Guangdong Province in the south of China, and we assessed the influences of wide and narrow roads on plant species diversity, biomass, and soil properties along transects running from the forest edges and adjacent forest interior. We used a “shape-dependent model” to explain the factors that determine the magnitude of road effects on forests. Results Three variables measured in this study changed significantly with increasing distance from the road to the forest interior along wide roads: tree biomass, herbaceous plant biomass, and soil pH. However, no measurable biological or environmental effects were found from narrow roads. The different shapes of glades in a forest may be one reason for the various effects caused by roads of different widths. Conclusions Forest roads of different widths may have quite different ecological effects. While wider roads with large glades tend to have substantial negative impacts, small-enough roads may cause little disturbance to the forest. This suggests that not all forest roads should be perceived as the same, and narrow roads may be compatible with forest conservation.

Road and landscape-context impacts on bird pollination in a Mediterranean-type shrubland of the southeastern Cape Floristic Region

Road verges can provide important habitats for plants, especially in transformed landscapes. However, roads and their associated traffic have several adverse impacts on ecosystems that can disrupt vital ecological processes, including pollination. In transformed landscapes, road effects on pollination might be complemented by impacts of large-scale habitat modification. In these landscapes, road verge populations of plants that rely on pollinators for pollen transfer could thus be at risk of pollination failure. This study investigates the pollination of a reseeding, bird-pollinated shrub,Erica glandulosa, in road verges of a fragmented and transformed rural landscape in the southeastern Cape Floristic Region. We test for road impacts on pollination by comparing number of ruptured anther rings—a proxy for pollination—in fynbos vegetation fragments at different distances from the road (0–10, 20–30 and 40–50 m). We also test whether different land-cover types (intact fynbos, alien thickets and rangelands/pastures) next to road verges influence the number of ruptured anther rings. After controlling for robbing rate and plant density, fewer flowers were pollinated near the road than farther away, and fewer flowers were pollinated where road verges occurred next to alien thickets or pastures/rangelands compared to intact fynbos. However, bird pollination was not excluded in road verges: on average, ca. 20–30% of flowers were still visited by birds near the road. These findings potentially call into question the suitability of road verges as refugia for seed-dependent, bird-pollinated plant species in transformed landscapes.

Genomic Data from an Endangered Amphibian Reveal Unforeseen Consequences of Fragmentation by Roads

Roads fragment landscapes and can cause the loss of metapopulation dynamics in threatened species, but as relatively new landscape features, few studies have had the statistical power to genetically examine road effects. We used DNA sequence data from thousands of nuclear loci to characterize the population structure of New York-endangered Eastern tiger salamanders (Ambystoma tigrinum) on Long Island and quantify the impacts of roads on population fragmentation. We uncovered highly genetically structured populations over an extremely small spatial scale (approximately 40 km2) in an increasingly human-modified landscape. Geographic distance and the presence of roads between ponds are both strong predictors of genetic divergence, suggesting that both natural and anthropogenic factors are responsible for the observed patterns of genetic variation. Our study demonstrates the value of genomic approaches in molecular ecology, as these patterns did not emerge in an earlier study of the same system using microsatellite loci. Ponds supported small effective population sizes, and pond surface area showed a strong positive correlation with salamander population size. When combined with the high degree of structuring in this heavily modified landscape, our study indicates that these endangered amphibians require management at the individual pond, or pond cluster, level. Particular efforts should be made to preserve large vernal pools, which harbor the greatest genetic diversity, and their surrounding upland habitat. Contiguous upland landscapes between ponds that facilitate natural metapopulation connectivity and demographic rescue from future local extirpations should also be protected.