Winter litter disturbance facilitates the spread of the nonnative invasive grass Microstegium vimineum (Trin.) A. Camus

We investigated the impacts of winter litter disturbance on the spread of the nonnative invasive plant Microstegium vimineum (Trin.) A. Camus through experimental removals. We hypothesized that light penetration through the litter layer facilitates the spread of M. vimineum in forested systems. Our objective, therefore, was to quantify M. vimineum spread following litter removal. Linear spread and cover expansion from established M. vimineum patches was documented for one growing season under intact, undisturbed hardwood canopies within plots receiving one of two treatments. Treatments included litter removal (hereafter “removal”) and no litter removal (hereafter “undisturbed”). After one growing season, plots receiving the removal treatment experienced a spread of M. vimineum 4.5 times greater than plots receiving the undisturbed treatment (P < 0.0001; 1.66, and 0.37 m expansion, respectively). Cover expansion (measured as percent cover in 0.5 m² blocks at 0.5, 1, 1.5, and 2 m from established M. vimineum) averaged 16, 4, 0, and 0%, respectively, for the undisturbed treatment and 87, 64, 31, and 9%, respectively, for the removal treatment. Differences existed in cover expansion between treatments at the 0.5, 1, and 1.5 m distances (P < 0.0001, P < 0.001, and P = 0.01, respectively). Our results suggest that winter litter removal as a result of harvest activities, floodwater scour, or animal activities can drastically increase M. vimineum spread and may enhance potential ecological impacts of invasions by increasing M. vimineum percent cover. Previous studies have shown that M. vimineum responds to canopy removal with dramatic increases in biomass. This study suggests one mechanism facilitating rapid expansion of M. vimineum following site disturbance, and indicates that M. vimineum can experience rapid growth in response to site disturbance even in the absence of canopy removal.     

Optimizing seed crops of common bent (Agrostis capillaris) by sowing rate

Abstract

As part of a project to stimulate Norwegian seed production of common bent (syn. browntop, US: colonial bentgrass, Agrostis capillaris L. syn. A.tenuis Sibth.) field trials comparing sowing rates of 2.5, 5.0, 7.5 or 10 kg ha^?1 were conducted at Landvik, south-east Norway, (58°N) from 1989 to 1994. Three trials were laid out of the forage cultivar ‘Leikvin’ and three trials of the lawn cultivar ‘Nor’, each trial being harvested for three consecutive years. While the average per cent ground cover in spring increased from 87% at 2.5 kg ha^?1 to 94–96% at 7.5 kg ha^?1, seed yields decreased with increasing sowing rate in both cultivars. On average for all harvests, quadrupling the sowing rate from 2.5 to 10 kg ha^?1 reduced seed yield by 9% in ‘Leikvin’ and 15% in ‘Nor’, the stronger effect probably being associated with a greater competition between tillers in the lawn cultivar. Seed yield reductions with increasing sowing rate showed no relationship with crop age, but were less accentuated for crops undersown in spring wheat in a dry year than for crops established without cover crop in years with ample rainfall in early summer. Increasing sowing rates reduced plant height and panicle number in ‘Nor’, but had no effect on seed weight or germination in any of the cultivars. It is concluded that seed crops of common bent should be established with a sowing rate of 2–5 kg ha^?1, with the lowest rate in lawn cultivars, under ideal seedbed conditions and when seed crops are sown without cover crop.