S tudies of the effects of climate change on forests have focused on the ability of species to tolerate temperature and moisture changes and to disperse, but they have ignored the effects of disturbances caused by climate change (e.g., Ojima et al. 1991). Yet modeling studies indicate the importance of climate effects on disturbance regimes (He et al. 1999). Local, regional, and global changes in temperature and precipitation can influence the occurrence, timing, frequency, duration, extent, and intensity of disturbances (Baker 1995, Turner et al. 1998). Because trees can survive from decades to centuries and take years to become established, climate-change impacts are expressed in forests, in part, through alterations in disturbance regimes (Franklin et al. 1992, Dale et al. 2000). Disturbances, both human-induced and natural, shape forest systems by influencing their composition, structure, and functional processes. Indeed, the forests of the United States are molded by their land-use and disturbance history. Within the United States, natural disturbances having the greatest effects on forests include fire, drought, introduced species, insect and pathogen outbreaks, hurricanes, windstorms, ice storms, and landslides (Figure 1). Each disturbance affects forests differently. Some cause large-scale tree mortality, whereas others affect community structure and organization without causing massive mortality (e.g., ground fires). Forest disturbances influence how much carbon is stored in trees or dead wood. All these natural disturbances interact with human-induced effects on the environment, such as air pollution and land-use change resulting from resource extraction, agriculture, urban and suburban expansion, and recreation. Some disturbances can be functions of both natural and human conditions (e.g., forest fire ignition and spread) (Figure 2).

Although coronavirus disease 2019 (COVID-19) causes cardiac dysfunction in up to 25% of patients, its pathogenesis remains unclear. Exposure of human induced pluripotent stem cell (iPSC)-derived heart cells to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) revealed productive infection and robust transcriptomic and morphological signatures of damage, particularly in cardiomyocytes. Transcriptomic disruption of structural genes corroborates adverse morphologic features, which included a distinct pattern of myofibrillar fragmentation and nuclear disruption. Human autopsy specimens from patients with COVID-19 reflected similar alterations, particularly sarcomeric fragmentation. These striking cytopathic features in cardiomyocytes provide insights into SARS-CoV-2-induced cardiac damage, offer a platform for discovery of potential therapeutics, and raise concerns about the long-term consequences of COVID-19 in asymptomatic as well as severe cases.

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A central question concerning the response of terrestrial ecosystems to a changing atmosphere is whether increased uptake of carbon in response to increasing atmospheric carbon dioxide concentration results in greater plant biomass and carbon storage or, alternatively, faster cycling of C through the ecosystem. Net primary productivity (NPP) of a closed-canopy Liquidambar styraciflua (sweetgum) forest stand was assessed for three years in a free-air CO 2 -enrichment (FACE) experiment. NPP increased 21% in stands exposed to elevated CO 2 , and there was no loss of response over time. Wood increment increased significantly during the first year of exposure, but subsequently most of the extra C was allocated to production of leaves and fine roots. These pools turn over more rapidly than wood, thereby reducing the potential of the forest stand to sequester additional C in response to atmospheric CO 2 enrichment. Hence, while this experiment provides the first evidence that CO 2 enrichment can increase productivity in a closed-canopy deciduous forest, the implications of this result must be tempered because the increase in productivity resulted in faster cycling of C through the system rather than increased C storage in wood. The fate of the additional C entering the soil system and the environmental interactions that influence allocation need further investigation.

α-Aminoisobutyric acid (Aib) is a Cα-tetrasubstituted amino acid that strongly favors helical structure. Most of the conformational trends established for Aib-rich peptides have been determined by X-ray crystallography. Whether these conformational trends carry over to protic solvents is an open question. In order to develop a general strategy for probing the properties of peptides containing Cα-tetrasubstituted amino acids, the hexameric sequences Boc-TOAC-Ala n -TOAC-Ala4-n-OtBu were synthesized where n = 0−3 and TOAC is a spin label Aib analog. The peptides were studied by electron spin resonance (ESR) in four alcohols:  MeOH, EtOH, TFE, and HFIP. Biradical J-coupling and dipolar interactions between the TOACs within each peptide were used to determine peptide geometry as a function of solvent. In MeOH, strong biradical interactions were observed consistent with the geometry of a 310-helix. The solvents displayed differing tendencies to support helical structure with the ranking MeOH > EtOH > TFE > HFIP. In HFIP, there were no indications of residual helical structure. While Cα-tetrasubstituted amino acids do favor the helix, these data demonstrate that such amino acids do not “lock in” the helical conformation. Qualitative analysis of the line width variations for the hexamers in MeOH suggests that the interconversion time for helix → coil is several nanoseconds. Additional peptides were prepared in order to explore the effects of peptide length, N-terminal blocking group, and insertion of an additional Aib.