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Attempts to determine characteristics that render habitats invasible to nonnative species have met with limited success. This may be because most studies focus on modern habitat conditions and do not consider invasibility in the context of a historically dynamic landscape in which both the abundance of a species and the invasibility of a site may change. We surveyed 159 currently forested sites for the occurrence and abundance of Berberis thunbergii (Japanese barberry), an invasive, nonnative shrub in forests of the northeastern United States, relative to modern environmental conditions, contemporary logging activity, and two periods of historical land use. Berberis thunbergii occurred more frequently and was more abundant in post-agricultural forests than in continuously wooded sites. This relationship was stronger for agricultural sites that were abandoned and reforested after B. thunbergii was introduced to the region than for sites that reforested prior to B. thunbergii introduction. In contrast, recent forest harvesting did not influence the occurrence or abundance of B. thunbergii. Modern soil fertility explained a significant portion of the variation in B. thunbergii occurrence, whereas site history considerably improved predictions of population density and helped evaluate potential invasion mechanisms. While land-use history covaries with soil fertility and distance to putative seed sources, the strong relationship between modern abundance patterns and historical agriculture suggests that B. thunbergii colonized recently abandoned agricultural lands in the early 20th century and then persisted and spread locally during subsequent reforestation. Our results indicate that interpretations of both native community composition and modern plant invasions must consider the importance of historical landscape changes and the timing of species introduction along with current environmental conditions.

We investigated current forest composition in relation to land use history at Broad Meadow Brook, a 157 ha urban wildlife sanctuary in Worcester, central Massachusetts. We obtained historical information from aerial photographs dating back to 1938, maps dating to 1831, various published sources, and interviews with long-term residents. We sampled tree vegetation in 35 20 m × 20 m plots and understory vegetation in 140 5 m × 5 m subplots. We obtained ages of several dozen trees by coring. Most of the sanctuary supported dry, mixed-oak forest that has been subject to frequent fires. Disturbed oak woods bore a greater variety of plants than older oak forest, including several non-native species. Mesic forest supported Fraxinus americana, Acer rubrum, and A. saccharum, with an abundant A. platanoides understory, a legacy of nearby residential plantings. Acer rubrum heavily dominated wet woodland. A small, previously cultivated plot supported an open canopy of A. rubrum with a dense understory of herb...

We describe a measurement of the angular power spectrum of anisotropies in the Cosmic Microwave Background (CMB) from 0.3 degrees to ~10 degrees from the North American test flight of the BOOMERANG experiment. BOOMERANG is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a Long Duration Balloon flight. During a 6-hour test flight of a prototype system in 1997, we mapped > 200 square degrees at high galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26 and 16.6 arcmin FWHM respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of ~1 degree with an amplitude ~70 uK., 5 pages, 1 figure LaTeX, emulateapj.sty