Tropical Grasslands (2001) Volume 35, 218–225

Patterns of seedling emergence over 5 years from seed of 38 species placed on the soil surface under shade and full sunlight in the seasonally dry tropics

THE LATE C.J. GARDENER1, L.V. WHITEMAN1 and R.M. JONES2

1CSIRO Tropical Agriculture, Townsville, and
2Indooroopilly, Queensland, Australia

Abstract

Seeds of 50 different seed lots from 38 species (12 tropical legumes, 2 temperate legumes, 10 introduced grasses, 11 native/naturalised grasses and 3 weedy forbs) were placed on the soil surface under either full sunlight or artificial shade transmitting 10% sunlight at Townsville, north Queensland in September 1983. Seedling emergence was measured until January 1988 and data are presented on a yearly basis where a year (Oct 1–Sept 30) includes the wet season and following dry season. In all seed lots, except for Sida acuta under shade, over 50% of all seedling emergence occurred in the first year and, for most seed lots, over 80% of emergence. Most of this emergence occurred in the first 3 months (Oct 1–Dec 31, 1983). Only 10 of 50 seed lots had more emergence in the last 9 months than in the first 3 months of the first year and these included 5 legumes, 4 native/naturalised grasses and 1 forb.
Overall, more legume seedlings emerged in the shade than in full sunlight whereas more seedlings of native/naturalised grasses emerged in full sunlight. No seedling emergence occurred in the fourth and fifth years in full sunlight whereas there were still low levels of seedling emergence under shade, especially of legumes and Sida acuta. No grass seedlings emerged under shade in the fifth and final year. The advantages and disadvantages of a persistent seedbank for herbaceous pasture legumes and for the shrub legume Leucaena leucocephala are discussed.

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