Main Article Content
Soil seed bank evaluation and seedling establishment along a degradation gradient in a semi-arid rangeland
Abstract
The effects of rangeland degradation on the size and species
composition of the seed bank and seedling establishment in the field were
quantified over a two year period (2000–2001 and 2001–2002 growing seasons).
Soil seed bank sampling was carried out at three-monthly intervals from 0.25m2
blocks 50mm deep. Sampling was from rangeland artificially maintained in three
different rangeland conditions viz. good, moderate and poor. The total seedling
establishment in the field for every species was obtained at the end of the
growing season. Soil temperatures at 100mm depth and soil-water content at 50mm
depth intervals were recorded once a week. Due to the lower basal cover with
rangeland degradation, soil temperatures increased significantly both daily and
seasonally, while soil-water content also decreased. Rangeland in poor
condition was characterised by a significantly higher seed density in the seed
bank and more seedling establishment than grassland in good condition. No
climax seedlings were present in rangeland in poor condition, while very few
survived in rangeland in good condition at the end of the season. A mean
seasonal seed bank density of rangeland in good, moderate and poor condition
was respectively: 48, 74 and 98 seedlings m–2 for October; 28, 32
and 40 seedlings m–2 for January; and 58, 172 and 128 seedlings m–2
for April. Rangeland degradation showed a decrease in species richness in both
the seed bank and seedling establishment in the field. A mean number of 1.67,
2.27 and 2.83 seedlings m–2 established in rangeland in good,
moderate and poor conditions respectively at the end of the growing season.
Keywords: germination, grassland degradation, seedling emergence, seed longevity,
seed recruitment, soil temperature, soil-water content
African Journal of Range & Forage Science 2004, 21(1):
37–47
composition of the seed bank and seedling establishment in the field were
quantified over a two year period (2000–2001 and 2001–2002 growing seasons).
Soil seed bank sampling was carried out at three-monthly intervals from 0.25m2
blocks 50mm deep. Sampling was from rangeland artificially maintained in three
different rangeland conditions viz. good, moderate and poor. The total seedling
establishment in the field for every species was obtained at the end of the
growing season. Soil temperatures at 100mm depth and soil-water content at 50mm
depth intervals were recorded once a week. Due to the lower basal cover with
rangeland degradation, soil temperatures increased significantly both daily and
seasonally, while soil-water content also decreased. Rangeland in poor
condition was characterised by a significantly higher seed density in the seed
bank and more seedling establishment than grassland in good condition. No
climax seedlings were present in rangeland in poor condition, while very few
survived in rangeland in good condition at the end of the season. A mean
seasonal seed bank density of rangeland in good, moderate and poor condition
was respectively: 48, 74 and 98 seedlings m–2 for October; 28, 32
and 40 seedlings m–2 for January; and 58, 172 and 128 seedlings m–2
for April. Rangeland degradation showed a decrease in species richness in both
the seed bank and seedling establishment in the field. A mean number of 1.67,
2.27 and 2.83 seedlings m–2 established in rangeland in good,
moderate and poor conditions respectively at the end of the growing season.
Keywords: germination, grassland degradation, seedling emergence, seed longevity,
seed recruitment, soil temperature, soil-water content
African Journal of Range & Forage Science 2004, 21(1):
37–47
