Exotic vascular plant invasiveness and forest invasibility in urban boreal forest types

The riverine forests of the northern city of Edmonton, Alberta, Canada display strong resilience to disturbance and are similar in species composition to southern boreal mixedwood forest types. This study addressed questions such as, how easily do exotic species become established in urban boreal forests (species invasiveness) and do urban boreal forest structural characteristics such as, native species richness, abundance, and vertical vegetation layers, confer resistance to exotic species establishment and spread (community invasibility)? Eighty-four forest stands were sampled and species composition and mean percent cover analyzed using ordination methods. Results showed that exotic tree/shrub types were of the most concern for invasion to urban boreal forests and that exotic species type, native habitat and propagule supply may be good indicators of invasive potential. Native forest structure appeared to confer a level of resistance to exotic species and medium to high disturbance intensity was associated with exotic species growth and spread without a corresponding loss in native species richness. Results provided large-scale evidence that diverse communities are less vulnerable to exotic species invasion, and that intermediate disturbance intensity supports species coexistence. From a management perspective, the retention of native species and native forest structure in urban forests is favored to minimize the impact of exotic species introductions, protect natural succession patterns, and minimize the spread of exotic species.     

Effects of disturbance intensity and frequency on early old‐field succession

Abstract. Early old‐field succession provides a model system for examining vegetation response to disturbance frequency and intensity within a manageable time scale. Disturbance frequency and intensity can interact with colonization and competition to influence relative abundance of earlier and later successional species and determine, respectively, how often and how far succession can be reset. We tested the joint effects of disturbance frequency and intensity on vegetation response (species richness, abundance, canopy structure) during the first six years of succession by clipping the dominant species (D) or all species (T) in spring and fall of each year (S), once per year in summer (Y1), each two years in summer (Y2), or each four years in summer (Y4). Vegetation response reflected disturbance effects on expansion of a later monospecific dominant perennial herb, Solidago altissima, and persistence of the early, richer flora of annuals. A more abundant and taller top Solidago canopy developed on plots clipped each 2 yr or less frequently. Plots clipped yearly or seasonally were richer, but had less abundant, shorter, and differently stratified canopy. Disturbance mediated the relative abundance of early and later successional species; however, frequency and intensity effects were not completely congruent. Persistence of a richer early successional flora increased through the most frequent disturbance (S), and was magnified by disturbance intensity. Disturbance as extreme as clipping all vegetation twice yearly did not cause a drop in species richness, but maintained the early successional community over the first six years of succession. We conclude that clipping disturbance influenced the rate of succession, but the early community could rebound through the range of disturbance frequency and intensity tested.     

Assessing Risk-Based Policies for Pretrial Release and Split Sentencing in Los Angeles County Jails

Court-mandated downsizing of the CA prison system has led to a redistribution of detainees from prisons to CA county jails, and subsequent jail overcrowding. Using data that is representative of the LA County jail system, we build a mathematical model that tracks the flow of individuals during arraignment, pretrial release or detention, case disposition, jail sentence, and possible recidivism during pretrial release, after a failure to appear in court, during non-felony probation and during felony supervision. We assess 64 joint pretrial release and split-sentencing (where low-level felon sentences are split between jail time and mandatory supervision) policies that are based on the type of charge (felony or non-felony) and the risk category as determined by the CA Static Risk Assessment tool, and compare their performance to that of the policy LA County used in early 2014, before split sentencing was in use. In our model, policies that offer split sentences to all low-level felons optimize the key tradeoff between public safety and jail congestion by, e.g., simultaneously reducing the rearrest rate by 7% and the mean jail population by 20% relative to the policy LA County used in 2014. The effectiveness of split sentencing is due to two facts: (i) convicted felony offenders comprised ≈ 45% of LA County’s jail population in 2014, and (ii) compared to pretrial release, split sentencing exposes offenders to much less time under recidivism risk per saved jail day.     

N-Cadherin is expressed on human hematopoietic progenitor cells and mediates interaction with human mesenchymal stromal cells

Specific cell–cell junctions between hematopoietic stem cells (HSC) and their niche have been shown to regulate stem cell function. N-cadherin was suggested to play a central role in this process, whereas other studies indicated that it did not play an essential role in the murine model. We have analyzed the role of N-cadherin for interaction between hematopoietic progenitor cells (HPC) and supportive mesenchymal stromal cells (MSC) in a human–human setting. Expression of N-cadherin and of cadherin-11 (osteoblast cadherin) was analyzed in HPC by quantitative RT-PCR, Western blot, and flow cytometry. N-cadherin and cadherin-11 were expressed in HPC at a moderate level, whereas they were not detectable in differentiated cells. Confocal laser scanning microscopy revealed that N-cadherin and β-catenin are colocalized at the junction of HPC and MSC. siRNA knockdown of N-cadherin or cadherin-11 as well as treatment with the blocking function antibody decreased adhesive interaction of HPC to MSC. Furthermore, knockdown of N-cadherin or blocking function antibody impaired maintenance of long-term culture-initiating cells (LTC-IC) on coculture of HPC and MSC. These results indicate that N-cadherin is involved in the bidirectional interaction of human HPC with their cellular determinants in the niche.     

Tumor cytotoxicity of 5,6-dimethyl-1,10-phenanthroline and its corresponding gold(III) complex

A gold(III) complex possessing 5,6-dimethyl-1,10-phenanthroline (5,6DMP) was synthesized and fully characterized using standard spectroscopic techniques, as well as X-ray crystallography and elemental analysis. The complex [(5,6DMP)AuCl₂][BF₄] (2) was found to possess a distorted square planar geometry about the gold(III) center, commonplace for d⁸ Au(III) cations possessing sterically un-hindered polypyridyl ligands. Compound 2 was evaluated for its potential use as an anticancer therapeutic. It was determined that the complex is stable in phosphate buffer over a 24-hour period, thought it does undergo rapid reduction in the presence of equimolar amounts of reduced glutathione (GSH) and ascorbic acid. The DNA binding and in vitro tumor cytotoxicity of the title compound 2 were also determined. It was found to undergo weak and reversible binding to calf thymus DNA, and was more cytotoxic towards a panel of human cancer cell lines than the commonly used chemotherapy agent cisplatin. Cytotoxicity experiments with the free 5,6DMP ligand indicate that the ligand has IC₅₀ values that are slightly lower than those observed for the gold complex (2), and coupled with the fact that the ligand appears to be released from the gold(III) metal center in reducing environments, this suggests the ligand itself may play an important role in the antitumor activity of the parent gold complex.     

N-substituted bis-C-alkyloxadiazolones as dual effectors: Efficient intermediates to amidoximes or amidines and prodrug candidates of potent antimalarials

A convenient route to N-substituted bis-C-alkylamidines possessing antiplasmodial activity and their oxadiazolone and amidoxime prodrug candidates, is described. These three families of compounds were available after a key N-alkylation step of the parent oxadiazolone 1a. Testing of the three compound classes in vitro and in vivo is also presented.