(TSA) induces GFP activation in GFP(؊) cells and can also increase GFP expression in GFP(؉) cells. In the case of the GFP(؊)populations, we found that after removal of TSA, GFP silencing was reestablished in a subset of cells. We used that finding to enrich for stable GFP(؊) cell populations in which viral GFP reporter expression could be reactivated by TSA; furthermore, we found that the ability to isolate such populations was independent of the promoter driving the GFP gene. In such enriched cultures, hCMV IE-driven, but not the viral long terminal repeat-driven, silent GFP reporter expression could be reactivated by the transcriptional activator prostratin. Microscopy-based studies using synchronized cells revealed variegated reactivation in cell clones, indicating that secondary epigenetic effects can restrict reactivation from silencing. Furthermore we found that entry into S phase was not required for reactivation. We conclude that HDACs can act rapidly to initiate and maintain promoter-independent retroviral epigenetic repression and silencing but that reactivation can be restricted by additional mechanisms.

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Two organizations found ways to be more intentional about encouraging participation by a diverse spectrum of attendees at scientific meetings—the scientific community can learn from their experiences.

Urban street trees face adverse growing conditions: compacted soils, extreme heat, lack of nutrients, drought, car damage and vandalism. Limited funding, however, is cited by urban tree-planting organizations as their major obstacle. To maximize budgets, many organizations along the eastern United States have planted bare root trees as a less expensive alternative to balled-and-burlapped (B&B) trees. Existing research indicates equivalent survival rates between bare root and B&B trees; but no research has examined this in community group-planted urban street trees. Bare root trees are additionally advantageous in community-based plantings because they are much lighter and easier for volunteers to handle. This study evaluated the influence of stock and other site factors on street tree survival and growth measures (diameter at breast height, percent canopy cover, and percent live crown), while controlling for species and age. Site factors included street traffic intensity, site type (curbside, park, yard, or commercial corridor), wound presence, and sidewalk pit cut dimensions. 1159 trees (representing ten species) planted by Philadelphia community groups under the guidance of the Pennsylvania Horticultural Society from 2006-2009 were sampled. Overall, trees showed a high survival rate of 95%, with no significant difference between B&B and bare root trees. Species with the highest survival rates were Prunus virginiana (chokecherry), Platanus x acerifolia (London plane tree), and Acer tataricum ssp. ginnala (Amur maple). Heavily trafficked streets exhibited lower survival, percent canopy cover and percent live crown. Larger growth measures were expected and found in B&B trees, as they have historically been planted larger than their bare root counterparts. Findings support planting larger trees (such as B&B and/or larger bare root trees) along commercial corridors. Species in the Rosaceae family (Amelanchier spp., Malus spp, and Prunus virginiana) exhibited lower percents canopy cover. Wound presence and pit cut size were not major factors affecting the 1-5 year old street trees sampled in this study. The major management implication of these findings is that bare root trees are a viable alternative to B&B trees in community-based urban forestry initiatives. Tree-planting campaigns with similar climactic conditions to Philadelphia can use this study to inform selection of stock and species.

Over the last two decades, there has been a substantial increase in street tree plantings across the United States. Many cities have set ambitious planting goals, relying on volunteer community groups to meet them. Existing research demonstrates that community stewardship increases the survival of urban street trees. There is a lack of research, however, on how defining characteristics of community groups affect the survival and growth of the trees they plant. This study explores the significance of community group size (# participants), type (apartment, block watch, church, concerned neighbors, park, public housing, school, and social service), planting longevity (# years active), experience level (# trees planted), and neighborhood (geo-political boundaries). Measured for this study were 1393 trees planted from 1995 to 2007, by 134 groups, through the Urban Resources Initiative’s Community Greenspace program in New Haven, Connecticut, U.S. There was an overall survival rate of 76%. Highest survival and growth was found among trees planted by groups with more planting experience, greater longevity, and more participants. Higher tree survival and growth was observed when trees were planted by groups working in line with their mission (e.g., park groups in parks). Lowest survival and growth was found among yard trees planted by public housing groups. Existing canopy cover and neighborhood percent homeownership had little effect on survival or growth. This research can offer guidance for city managers by suggesting which planting groups require particular assistance in conducting successful, lasting street tree plantings.