An experimental manipulation was conducted to test whether germination timing influences the post-germination life-history characters in Amaranthus retroflexus L. and Chenopodium glaucum L. Seeds were sown in spring, late spring, and summer. Life-history characters of both phenology and morphology were measured, and dry masses of roots, stems, leaves, and reproductive organs were determined. Life-history characters showed high plasticity in response to different sowing dates. Later germinating plants had relatively faster growth rates and smaller sizes at reproduction than earlier germinating plants. Delaying germination led to relatively earlier reproduction and a relatively greater allocation to reproduction. Much of the variation (60%) could be explained by a single axis of a principal component analysis. The attributes on this axis were similar to the C–R axis of Grime's C–S–R model. Further, the sowing dates of these two species were aggregated on this axis such that spring germinators tended towards the competitor strategy (C), late-spring germinators tended towards a mixed competitive–ruderal strategy (C–R), and summer germinators tended towards a ruderal strategy (R). Different germination timing led to different life-history strategies in the established phase. This kind of phenotypic plasticity in life history results from the plant adapting to regeneration strategies of different germination timing.Key words: Amaranthus retroflexus, Chenopodium glaucum, phenotypic plasticity, life-history characters, plant strategies, germination timing.

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Silvopastoral systems in New Zealand that incorporate trees planted to control soil erosion on hills largely rely on the productivity of the pastoral system for financial returns. The effect on pasture productivity of increasing the tree canopy height by pruning Italian gray alder (Alnus cordata) was investigated by measuring the response of light, soil moisture, soil temperature, pasture production of major pasture species, and grazing behaviour of sheep. A split-plot design with four replicates was used. The main plot treatments were three levels of shade (81, 23, and 12% of available photosynthetic photon flux (PPF)), created by pruning 11 year old alder grown at the same density. The sub-plot treatments were four pasture mixes: perennial ryegrass (Lolium perenne), Yorkshire fog (Holcus lanatus), and cocksfoot (Dactylis glomerata), each sown with white clover (Trifolium repens), and cocksfoot sown with lotus (Lotus pedunculatus). Soil temperature was highest under light shade. Total herbage yield at 50 mm stubble height from October to May under heavy and medium shade was 60 and 80%, respectively, of the total herbage harvested under light shade. Cocksfoot had the greatest herbage yield, either with lotus or white clover. The tillering of perennial ryegrass was suppressed by shade more than for the other grass species making ryegrass unsuitable for use in this silvopastoral system. More sheep grazed in the light shade than in the heavy shade, but there was no difference in sheep preference for cocksfoot or Yorkshire fog. Lotus was grazed more frequently than white clover. Pruning of alder to increase canopy height has the potential to improve the productivity of the understorey pasture and its acceptability to sheep.

Appropriate pre-sowing methods for the introduc-

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