PARENT SESSION
Contributed Oral Session 40: Forest Understories
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
Deer and sedge: Bottlenecks to seedling regeneration in northern hardwood forests.
Randall, Jesse*,1, Walters, Michael*,1, 1 Michigan State University, East Lansing, Michigan, USA
ABSTRACT- Shifts in forest floor composition including increased Carex pensylvanica (sedge) density is occurring in Great Lakes northern hardwood ecosystems affected by high white-tailed deer densities. The combination of high sedge densities and deer herbivory could negatively impact tree seedling survival and growth to a greater degree than either factor alone. With vegetation removal (selective C. pensylvanica removal, glyphosate (i.e. total removal), glyphosate + scarification, control) and deer exclosure treatments we examined deer and forest floor vegetation effects on the size and survival of planted and naturally established tree seedlings in managed forests with high deer densities (12-16 deer/km2) in Michigan, USA. Both in and out of exclosures sedge biomass was still significantly lower than controls in all three vegetation removal treatments four years after treatments (P<0.05), whereas herb biomass rebounded to levels equaling or exceeding controls within two years. Survival, total height, and stem mass were significantly greater for planted sugar maple in deer exclosures (68%, 23.6cm, 1.05g , respectively) compared to open areas (25%, 13.1cm, 0.5g respectively). Compared to controls, vegetation removal increased sugar maple size, but only when deer were excluded. In addition sedge removal increased seedling size as much as complete vegetation removal. Furthermore, in exclosures sedge removal interacted with light availability such that sedge decreased seedling size more at high light than low light. Naturally established seedling responses to deer and vegetation competition were similar to planted seedling responses. However, taller, potential canopy recruit seedlings in sedge removal and control treatments in exclosures were dominated by Ostrya virginiana that established before treatments and not canopy dominant A. saccharum. This suggests that past selective browsing by deer could have legacy effects on forest composition. Collectively these results suggest that in our study area deer strongly limit tree regeneration, and high sedge densities become limiting only if deer are removed.
Key words: Carex pensylvanica, Acer. saccharum., Seedling growth & survival, Herbivory