The effects of 'pebble mulch' on acacia mellifera seedling responses to rain.
Joubert, David F.
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"Pebble mulch" (a layer of quartz and schist pebbles that often forms an almost 100% cover on the slopes of the Highland Savannah in Namibia) influences the dynamics of this vegetation type. A controlled experiment to determine the effects of "pebble mulch" on seed germination and early seedling establishment of Acacia mellifera (ubsp. detinens) was conducted. A. mellifera forms dense thickets in the area. Seeds were germinated under four treatments: A: planted below soil (2 seed widths depth) without pebble cover; B: planted below soil (2 seed widths depth) with pebble cover; C: plated on top of soil underneath a 100% pebble cover; and D: planted on top of a 100% pebble cover. Emergence/germination in all cases was high (overall 82% s.d. 17.5%). Soil moisture was significantly higher in all "pebble mulch" treatments (B, C and D). Although initial establishment was poor in Treatment D (33%), survival thereafter of seedlings whose radicals reached the soil was very high (97%). Seedling survival and vigour were significantly higher in all "pebble-mulch" treatments. The implications of these results for bush encroachment on Highland Savannah rangelands are discussed.