Laboratory-Simulated Grazing: Interactive Effects of Defoliation and Canopy Closure on Serengeti Grasses

摘要: A factorial experiment was performed to evaluate the relationships between defoliation and canopy closure, recognizing that a major effect of grazing in nature is prevent closure. Short (Eustachys paspaloides) mid—height (Themeda triandra) grasses from Serengeti National Park, Tanzania, were grown for 12 wk balanced experiment. Treatments combined clipping simulated by raising an opaque cardboard collar as plant height increased. At harvest, plants separated into morphological parts, dried, weighed, analyzed nitrogen (N) nonstructural carbohydrates (CHO). Simulated closure unclipped reduced photon flux density at base 12% perpendicular light source 55% 45° angle lights. Multivariate analysis revealed experimental treatments produced completely distinct results. Simultated undefoliated more than doubled height, tiller number 65% short grass 90% grass, converted differentiation production many small tillers few very large tillers, changed allocation patterns toward stem sheath, shifted CHO—dominated economy N—balanced economy. The time course yield reached decided maximum 9 but much lower remained comparatively constant grass. Comparing clipped—unshaded (simulating grazing) with unclipped—shaded no that, both grasses, compensation complete total yield, live tissues, crown mass, root leaves. Neither species compensated residual leaf area, area per unit biomass, or mass. Defoliation leaves CHO higher N concentrations. In general, modified clipping. Greater tolerance short—statured due greater tillering, significantly accumulation, blade less root, foliage concentration volume, rate death, ability sustain considerably This indicated growing isolated pots grossly distorts morphology, growth, chemical properties compared experiencing normally encountered ungrazed grasslands. Therefore, failure account self—limiting consequences can mislead conclusions laboratory experiments designed test defoliation.