Treerow vegetation abundance and biodiversity were measured in response to six orchard floor management strategies in organic peach in northern Utah for three growing seasons. A total of 32 weed species were observed in the treerow; the most common were field bindweed, dandelion, perennial grasses (e.g., red fescue and ryegrass), clovers, and prickly lettuce. Weed biomass was two to five times greater in unmanaged (living mulch) than in manipulated treatments. Tillage greatly reduced weeds for approximately one month; however, vegetation rebounded midseason. Tillage selected for species adapted to disturbance, such as common purslane and field bindweed. Straw mulch provided equivalent weed suppression to tillage in the early season. Straw required annual reapplication with material costs, labor, and weed-seed contamination (e.g., volunteer grains and quackgrass) as disadvantages. Plastic fabric mulch reduced weeds the most, but had high initial costs and required seasonal maintenance. Weed biomass declined within seasons and across the three years of the study, likely due to tree canopy shading. Neither birdsfoot trefoil nor a perennial grass mixture planted in the alleyways influenced treerow weeds. Our results demonstrate several viable alternatives to tillage for weed management in treerows of organic peach orchards in the Intermountain West.

Fire is unlikely to be a simple, deterministic process that will result in increased rates of invasion by nonnative plants. Relative dominance of nonnative plants at any postfire site likely results from a combination of factors, including propagule pressure (aboveground and belowground), time since invasion, interspecific competition, disturbance history, rainfall patterns, soil nutrients, environmental heterogeneity, land use, plus the actual fire dynamics. Consequently, the role different factors play in nonnative plant invasion is still relatively unexplained, and the possibility that wildfire may promote nonnative plant species remains a concern. Our aim was to evaluate the state of knowledge concerning how nonnative plant species establish, survive, and spread following wildfire in wildland areas for the main vegetation types of the Intermountain West. Although the particular invading species varied with vegetation type, the most frequently reported species were annual grasses (e.g., downy brome [Bromus tectorum], Japanese brome [Bromus japonicus]) and long-distance, dispersing forbs (e.g., Canada thistle [Cirsium arvense], common dandelion [Taraxacum officinale], and prickly lettuce [Lactuca serriola]). Overall, many of the reviewed studies found an increase, followed by a long-term decline, in nonnative species after wildfire, particularly when other disturbances were minimal. Regardless of this finding, many people consider rapid detection and control of new, nonnative plant populations after wildfire one of the most effective management activities. That axiom may be correct, if the nonnative propagule pressure is high and the anthropogenic disturbances are frequent, but if this is not the case the question to answer is whether immediate management, including reseeding, will benefit the system or whether off-target effects could make that approach undesirable. Continued investigation and increased quantitative analysis of the complex factors that likely contribute to changes in nonnative plants dynamics following wildfire should improve our understanding of the issue and assist managers in allocating limited resources.