PREMISE OF THE STUDY The Pacific Northwest of North America experiences relatively mild winters and dry summers. For the tall coniferous trees that grow in this region, we predicted that loss in the hydraulic conductivity of uppermost branches would be avoided because of difficulty reversing accumulated emboli in xylem that is always under negative pressure. METHODS To test this hypothesis, w...

Biological invasions pose a significant threat to biodiversity, especially on oceanic islands. One of the primary explanations for the success of plant invaders is direct suppression of competitors. However, indirect interactions can also be important, although they are often overlooked in studies on biological invasion. The shrub Leucaena leucocephala is a widespread island invader with putati...

Aspen (Populus tremuloides) is an early successional tree that has naturally colonized large tracts of land near functioning and defunct smelter sites in the northern Rocky Mountains. This is evidenced by extensive aspen stands on the East Ridge of Butte (MT), behind the smelter stack at Anaconda (MT), near the (removed) smelter in Kellogg (ID), and downwind of the Trail, B. C. smelter (Canada)...

During the past centuries, humans have introduced many plant species in areas where they do not naturally occur. Some of these species establish populations and in some cases become invasive, causing economic and ecological damage. Which factors determine the success of non-native plants is still incompletely understood, but the absence of natural enemies in the invaded area (Enemy Release Hypo...

Question: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)? Location: Subtropical northwestern Argentina. Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographi...

This review explores the long-term role of climate versus human activity on vegetation and fire dynamics in the eastern U.S. Early Holocene warming resulted in a conversion of Picea (boreal) to temperate Quercus and Pinus forests when indigenous populations were sparse but charcoal abundances were relatively high, underscoring the importance of climate. Pyrogenic trees also dominated during the...

Spatial and temporal dynamics of hybridization, in particular the influence of local environmental conditions, are well studied for sympatric species but less is known for native-introduced systems, especially for long-lived species. We used microsatellite and chloroplast DNA markers to characterize the influence of anthropogenic landscapes on the extent, direction, and spatial distribution of ...

Cecropia glaziovi Sneth. (syn. C. glaziovii, C. glazioui) (Cecropiaceae) is a South American medicinal plant whose antihypertensive activity is attributed to its flavonoid and proanthocyanidin contents. The seasonal and intraspecific variations of these two classes of compounds in C. glaziovi leaves were assayed by spectrophotometry in samples of young and mature leaves collected from native, c...