PARENT SESSION
Organized Oral Session 25: Dynamics of invasive plants: Individuals to ecosystems
Organizer(s): TM Knight and JM Drake
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal
Non-native grasses impede oak establishment by altering soil conditions.
Davis, Mark*,1, Ungier, Daniel1, Kujala, Brianna1, 1 Macalester College, Saint Paul, MN, USA
ABSTRACT- Establishment of oaks (Quercus ellipsoidalis, Q. macrocarpa,) in old fields at the Cedar Creek LTER site is a very slow process, even though oaks readily establish in openings of native oak savannas and woodlands that border the fields. One difference between the old fields and the native openings is the composition of the dominant grasses, with native grasses dominating the native openings and introduced grasses dominating the old fields. Prior experiments have shown that oak seedling success is considerably reduced by dry soil conditions, and that the drought effect is significantly more pronounced for seedlings growing with introduced grasses. During summers 2003 and 2004, we conducted a series of pot experiments to determine if the different seedling success rates might be due to soil differences associated with the different grass types. In the first experiment, seedlings were grown in pots under wet and dry conditions, some with grass (either native or introduced) and associated soil, and some with just the associated soil (grasses removed). Virtually all seedlings survived under wet conditions, irrespective of the other treatments, but under dry conditions, seedling survival was much lower for seedlings growing in the exotic pots, and success was the same whether the pots contained the soil and the grasses or just the soil. In the second experiment, seedlings were grown in pots containing soil (grasses removed) from the two grass types, and the soil was exposed to one of four treatments: sterilization, a fungicide wash with one of two fungicides, and control. Again, seedling success was uniformly high under wet conditions, irrespective of treatment. In dry conditions, seedling success was highest in the sterilized pots and lowest in the control pots, and the differences were most pronounced in the exotic pots. Our results suggest that part of the explanation for the slow establishment of oaks into Cedar Creek's old fields is due to negative (from the point of view of the oaks) changes in the soil biota fostered by the introduced grasses. These changes could involve the reduction of positive soil biota effects found in the native grass soils, e.g., mycorrhizal interactions, or the increase of, or introduction of new, negative effects, e.g., pathogens.
Key words: old field, oak establishment, non-native species, soil biota