Structural response of Caribbean dry forests to hurricane winds: a case study from Guanica Forest, Puerto Rico

Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple-stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance. Methods: Over 2000 stems in five plots were sampled for hurricane effects within 1 week after Hurricane Georges impacted field sites in 1998. Sprout initiation, growth, and mortality were analysed for 1407 stems for 2 years after the hurricane. Soil nutrient pools were measured at the base of 456 stems to assess association between nutrients and sprout dynamics. Results: Direct effects of the hurricane were minimal, with stem mortality at \u3c 2% and structural damage to stems at 13%, although damage was biased toward stems of larger diameter. Sprouting response was high . over 10 times as many trees had sprouts after the hurricane as before. The number of sprouts on a stem also increased significantly. Sprouting was common on stems that only suffered defoliation or had no visible effects from the hurricane. Sprout survival after 2 years was also high (\u3e 86%). Soil nutrient pools had little effect on forest response as a whole, but phosphorus supply did influence sprout dynamics on four of the more common tree species. Main Conclusions: Hurricanes are able to influence Caribbean tropical dry forest structure by reducing average stem diameter and basal area and generating significant sprouting responses. New sprouts, with ongoing survival, will maintain the high frequency of multi-stemmed trees found in this region. Sprouting is not limited to damaged stems, indicating that trees are responding to other aspects of high winds, such as short-term gravitational displacement or sway. Soil nutrients play a secondary role in sprouting dynamics of a subset of species. The short, shrubby forest structure common to the Caribbean can arise naturally as a response to hurricane winds

Trans-ancestry genome-wide association study identifies 12 genetic loci influencing blood pressure and implicates a role for DNA methylation

We carried out a trans-ancestry genome-wide association and replication study of blood pressure phenotypes among up to 320,251 individuals of East Asian, European and South Asian ancestry. We find genetic variants at 12 new loci to be associated with blood pressure (P = 3.9 × 10-11 to 5.0 × 10-21). The sentinel blood pressure SNPs are enriched for association with DNA methylation at multiple nearby CpG sites, suggesting that, at some of the loci identified, DNA methylation may lie on the regulatory pathway linking sequence variation to blood pressure. The sentinel SNPs at the 12 new loci point to genes involved in vascular smooth muscle (IGFBP3, KCNK3, PDE3A and PRDM6) and renal (ARHGAP24, OSR1, SLC22A7 and TBX2) function. The new and known genetic variants predict increased left ventricular mass, circulating levels of NT-proBNP, and cardiovascular and all-cause mortality (P = 0.04 to 8.6 × 10-6). Our results provide new evidence for the role of DNA methylation in blood pressure regulation

Lithospheric evolution in the wake of the Mendocino Triple Junction: structure of the San Andreas Fault system at 2 Ma

As the Mendocino triple junction (MTJ) moves northwards up the North American margin, the tectonic regime changes from subduction to strike-slip. For the first few million years following triple junction migration, the San Andreas Fault system consists of several strike-slip faults distributing deformation over a region ~ 150 km wide. This same region is expected to be affected by a slab gap beneath North America, created by the northward removal of the subducting Gorda plate, and into which asthenospheric mantle is thought to rise to crustal depths. The onshore and offshore Mendocino Triple Junction Seismic Experiment (MTJSE) provides a continuous seismic velocity-reflectivity cross-section across the deforming zone from the Pacific ocean basin to the eastern edge of the California Coast Ranges. The accretionary complex rocks that make up most of the crustal thickness are underlain by a 5-10 km thick high-velocity(6.4-7.2 km s- 1) layer at the base of the crust that extends from the Pacific to at least 50 km, and probably 90 km east of the San Andreas Fault. The top of the lower crustal layer deepens from 7 km beneath the Pacific ocean basin at the west end of the profile to 23 km at the east end by a gentle (5° -10°) eastward dip punctuated by abrupt offsets at the San Andreas and Maacama fault zones. At each fault the top of the lower crust is offset by up to 4 km, down to the east. The Moho is similarly deformed beneath the faults, although by only 2 km. Such localized deformation of the Moho implies that these two strike-slip faults penetrate through the entire crust to the upper mantle. Good agreement between seismic velocity and seismic reflectivity in the vicinity of the faults gives confidence in these results, although details of the offset beneath the San Andreas Fault are better resolved than those under the Maacama Fault. Seismic velocities in the upper mantle show only a small change along the profile, from 8.1 km s- 1 beneath the Pacific to about 7.9 km s- 1 beneath the Coast Ranges. We infer that upwelling of asthenosphere into the slab gap is limited laterally, or a lithospheric lid is present in the slab gap by 2 Ma. Gravity data and crustal density structure show that most of the margin width is in local Airy isostasy with the changes in crustal thickness near the strike-slip faults corresponding closely to changes in surface topography. The crustal blocks defined by the strike-slip faults appear to be independently in isostatic equilibrium, provided that the mantle beneath the Coast Ranges has a somewhat lower density than that beneath the Pacific plate. The densities in the Coast Range upper mantle are consistent with limited temperature elevation, suggesting that the asthenospheric mantle is present beneath the depth of seismic energy penetration from our survey