Effects of an experimental ice storm on forest canopy structure

Intermediate disturbances are an important component of many forest disturbance regimes, with effects on canopy structure and related functions that are highly dependent on the nature and intensity of the perturbation. Ice storms are an important disturbance mechanism in temperate forests that often result in moderate-severity, diffuse canopy damage. However, it has not previously been possible to distinguish the specific effect of ice storm intensity (as ice accretion) from predisturbance stand characteristics and physiographic factors. In this study, we utilized a novel experimental ice storm treatment to evaluate the effects of variable ice accretion levels on forest canopy structure. Our results verified significant impacts of ice storm disturbance on near-term canopy structural reorganization. Canopy openness, light transmission, and complexity increased significantly relative to predisturbance baselines and undisturbed controls. We documented variable impacts with disturbance intensity, as significant canopy changes largely occurred with ice accretion levels of ≥12.7 mm. Repeated ice storm disturbance (two consecutive years) had marginal, rather than compounding, effects on forest canopy structure. Our findings are relevant to understanding how ice storms can affect near-term forest canopy structural reorganization and ecosystem processes and add to a growing base of knowledge on the effects of intermediate disturbances on canopy structure.

Native Species Abundance Buffers Non-Native Plant Invasibility following Intermediate Forest Management Disturbances

The biotic resistance hypothesis (BRH) was proposed to explain why intermediate disturbances lead to greater resistance to non-native invasions proposing communities that are more diverse provide greater resistance. However, several empirical data sets have rejected the BRH because native and non-native species richness often have a positive relation. We tested the BRH in a mature loblolly pine (Pinus taeda) forest with a gradient of disturbance intensities including canopy reduction, canopy reduction + fire, and canopy reduction + herbicide and fire. We analyzed data from the study using a combination of Pearson’s correlation and beta regressions. Using species richness, we too would reject BRH because of a positive correlation in species richness between native and non-native plants. However, native species abundance was greatest, and non-native species abundance was lowest following intermediate disturbances. Further, native and non-native species abundances were negatively correlated in a quadratic relation across disturbance intensities, suggesting that native species abundance, rather than richness, may be the mechanism of resistance to non-native invasions. We propose that native species abundance regulates resistance to non-native invasions and that intermediate disturbances provide the greatest resistance because they promote the greatest native species abundance.

Assessment of Mountain Ecosystems Changes Under Anthropogenic Pressure in Latorica River Basin (Transcarpathian Region, Ukraine)

The Carpathian mountain ecosystems have been changed under anthropogenic pressure during last decades. The different types of anthropogenic pressure affect the ecosystem characteristics and functioning. The species composition, species richness and ecological indicator values of 12 ecological factors were compared among 14 habitats: natural, semi-natural, degraded and ruderal ecosystems in different altitude zones. The results show that anthropogenic pressure and altitude gradient influence indices of edaphic and climate conditions. The anthropogenic pressure also affects biodiversity: the highest species richness and Shannon-Wiener index are observed in habitats with ‘intermediate’ disturbances level, while high level of disturbances cause decrease in bio-diversity. The disturbances cause the ecosystem to become susceptible to invasion of alien species, while native species, especially rare, become vulnerable and can disappear.