Effects of experimental shading and competitor removal on vegetative and reproductive performance of Trifolium thompsonii Morton, a rare endemic herb of Eastern Washington
Harrod, R.J. ; Halpern, C.B.
We examine how competitive interactions with associated species in the ground layer and shading by overstory trees may contribute to reduced survival, size, and reproductive allocation of Trifolium thompsonii, a rare native forb of north-central Washington State. We hypothesized that its current rarity reflects long-term exclusion of fire and concomitant increases in vegetation cover and overstory shade. We used field and greenhouse experiments to test whether removal of competing species and experimental shading affected survival, vegetative performance, and reproductive allocation. In 3-y field trials, survival of mature plants was greater in community-removal (89%) than in control plots (69%). Among surviving plants, vegetative performance differed little between treatments, but reproductive allocation was significantly greater in removal plots (average of 5.7 vs. 1.2 flower heads per plant in year 3). Experimental shading (30% ambient light) of estalished plants in the field yielded few significant changes in vegetative or reproductive performance after 2 y of treatment. However, seedling grown under 30% ambient light for 10 wk had less than half the shoot or root mass than did seedlings grown under 70 or 100% light. Our results suggest that competition with associated species and reductions in available light negatively affect particular stages of the life history of T. thompsonii, and may limit its long-term persistence. Future management for conservation of this species should include two strategies: (1) reducing density and cover of conifers in forested habitats through mechanical removal and/or prescribed fire, and (2) limiting development of competing ground-layer vegetation through periodic, low intensity fire. © 2005 Natural Areas Association. Abstract reproduced by permission.
Harrod, R. J., and C. B. Halpern. 2005. Effects of experimental shading and competitor removal on vegetative and reproductive performance of Trifolium thompsonii Morton, a rare endemic herb of Eastern Washington. Natural Areas Journal, v. 25, no. 2, p. 156-164.
abstract okay; age classes; Agropyron spicatum; Bromus tectorum; Ceanothus velutinus; community ecology; competition; coniferous forests; conifers; conservation; cover; Festuca idahoensis; fire case histories; fire exclusion; forest management; grasses; Great Basin and Pacific Slope States; histories; light; low intensity burns; North America; overstory; Pacific Northwest; Pinus ponderosa; plant communities; plant physiology; prescribed fires; seed germination; seedlings; size classes; trees; Trifolium; USA; vegetation surveys; Washington
Great Basin; Northwest
Fire Behavior; Fire Ecology; Fire History; Fuels; Intelligence; Prescribed Fire
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