Vegetation response to prescribed fire in the Kenai Mountains, Alaska

The Chugach National Forest has been using prescribed fire as a wildlife habitat management tool since l977. Between 1977 and 1997 about 4,000 hectares have been burned on the Kenai Peninsula to promote regeneration of woody plant species used by moose (Alces alces). Browse species include paper birch (Betula papyrifera), cottonwood (Populus balsamifera subsp. balsamifera and Populus balsamifera subsp. trichocarpa), aspen (Populus tremuloides), Scouler willow (Salix scouleriana), Barclay willow (Salix barclayi) and other tall shrub willows (Salix spp.). The purpose of this study was to evaluate the results of 20 years of prescribed fire in order to assess vegetation response to burning and provide managers with information on future prescribed burn planning. This analysis evaluated relationships among initial vegetation composition, physical site characteristics, browse species abundance, competitive herbaceous vegetation, and fire severity. With few exceptions, browse species increased in abundance after burning where they were present in the initial composition (measurements were made 15 to 20 years post-burn). Early successional grasses and forbs such as Epilobium angustfolium and Calamagrostis canadensis also tended to increase. Late successional species and forest associated species tended to decrease; these species include conifer seedlings, saplings, and trees (Tsuga mertensiana and Picea x lutzii), Rubus pedatus, Linnaea borealis, Drypoteris dilatata, and Menziesia ferruginea. Dwarf shrubs such as Vaccinium uliginosum, V. vitis-idaea, and Empetrum nigrum tended to decrease. Browse species abundance was inversely related to C. canadensis abundance. C. canadensis abundance increases with increasing depth of loamy mineral soil and increasing moisture (but C. canadensis does not occur abundantly on boggy sites with organic soils). Soils with deep loamy surface horizons tend to occur on depositional slopes such as fluvial valley bottoms and toe slopes. Sites with these features generally show large increases in C. canadensis cover after prescribed burning, even when C. canadensis cover is low (3%) prior to burning. The most important pre-burn variables for predicting post-burn browse species abundance are pre-burn C. canadensis cover and type of surficial deposit. Site conditions that are favorable to C. canadensis may be problematic for successful regeneration of browse species, especially if browse species are not present in the initial composition

Somatic mosaicism and common genetic variation contribute to the risk of very-early-onset inflammatory bowel disease

Very-early-onset inflammatory bowel disease (VEO-IBD) is a heterogeneous phenotype associated with a spectrum of rare Mendelian disorders. Here, we perform whole-exome-sequencing and genome-wide genotyping in 145 patients (median age-at-diagnosis of 3.5 years), in whom no Mendelian disorders were clinically suspected. In five patients we detect a primary immunodeficiency or enteropathy, with clinical consequences (XIAP, CYBA, SH2D1A, PCSK1). We also present a case study of a VEO-IBD patient with a mosaic de novo, pathogenic allele in CYBB. The mutation is present in ~70% of phagocytes and sufficient to result in defective bacterial handling but not life-threatening infections. Finally, we show that VEO-IBD patients have, on average, higher IBD polygenic risk scores than population controls (99 patients and 18,780 controls; P < 4 × 10-10), and replicate this finding in an independent cohort of VEO-IBD cases and controls (117 patients and 2,603 controls; P < 5 × 10-10). This discovery indicates that a polygenic component operates in VEO-IBD pathogenesis