Litter dynamics and phenology of Melaleuca quinquenervia in south Florida

We monitored litterfall biomass at six different sites of melaleuca (Melaleuca quinquenervia (Cav.) S.T. Blake) forested wetlands in South Florida from July 1997 to June 1999. Annual litterfall of melaleuca varied between sites from 6.5 to 9.9 t dry wt ha(-1) yr(1) over the two-year period. Litterfall was significantly higher (p < 0.0001) in scasonally flooded habitats (9.3 t ha(-1) yr(1)) than in non-flooded (7.5 t ha(-1) yr(1)) and permanently flooded habitats (8.0 t ha(-1) yr(1)). Leaf fall was the major component forming 70% of the total litter, woody material 16%, and reproductive material 11%. Phenology of flowering and leaf flush was investigated by examination of the timing and duration of the fall of different plant parts in the litter traps, coupled with monthly field observations during the two-year study. In both years, flowering began in October and November, with peak flowers production around December, and was essentially completed by February and March. New shoot growth began in mid winter after peak flowering, and extended into the spring. Very little new growth was observed in melaleuca forests during the summer months, from May to August, in South Florida. In contrast, the fall of leaves and small wood was recorded in every month of the year, but generally increased during the dry season with higher levels observed from February to April. Also, no seasonality was recorded in the fall of seed capsules, which apparently resulted from the continual self-thinning of small branches and twigs inside the forest stand. In planning management for perennial weeds, it is important to determine the period during its annual growth cycle when the plant is most susceptible to control measures. These phenological data suggest that the appropriate time for melaleuca control in South Florida might be during late winter and early spring, when the plant is most active.

Measures of Plant Surface-areas for Eurasian Watermilfoil and Water Stargrass

Plant surface areas were measured from samples of two common submersed aquatics with widely diverging morphologies: Eurasian watermilfoil ( Myriophyllum spicatum L.) and water stargrass ( Heteranthera dubia (Jacq.) MacM.). Measures for the highly dissected leaves of Eurasian watermilfoil involved development of a regression equation relating leaf length to direct measures of a subsample of leaf parts. Measures for the simple leaves of the stargrass were sums of measured triangles. Stem surfaces for both species were calculated as measured cylinders. Though the means of the stem length and leaf length were larger for stargrass samples, their mean surface area was 95 cm 2 which was less than the 108 cm 2 recorded for Eurasian watermilfoil samples. Relating surface area to dry weight for the stargrass was straightforward, with 1 mg of dry weight yielding an average 0.678 cm 2 of surface area. Biomass measures for the water milfoil were confounded by the additional weight of epiphytic algae persisting on cleaned samples. The results suggest that a lesstime consuming method for surface area measures of plants with highly dissected leaves and a caveat for using biomass measures to estimate surface area in such plants.

Growth rates of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) under cultivation in ponds at Nyegezi, Tanzania

Aquaculture in Tanzania is still on a subsistence level and most of the ponds are maintained as part time job. The ponds are too small, shallow and over crowded with stunted Tilapia spp. In the present paper the results of experiments conducted in ponds at Nyegezi with T. esculenta and T. zillii are presented. This was part of an overall project of developing techniques of fish cultures with Tilapia under the limited existing conditions at Nyegezi. In a mono - species culture experiement with Tilapia zillii in nine month's time an average size of 172.8 mm/115.0 g was attained. In another experiment with T. zillii and T. esculenta in thirteen month's time, T. zillii attained an average size of 180.2mm/106.6 g and T. esculenta 193.6 mm/118.8 g. In another experiment with intensive feeding schedule an average size of 179.3 mm/126.6 g was attained by T. zillii and 191.0 mm/125.0 g by T. esculenta in four month's time. A locally prepared supplimentary feed with local Brewery Waste and Fish Meal (10:1) was readily accepted by both species of Tilapia. T. zillii voraciously fed on Cabbage leaves, Cauliflower leaves, Chinese cabbage leaves, Cassava leaves and on the common weed Comalina sp. Though all the items mentioned above were readily accepted by T. zillii feeding with Comaltna sp. was the easiest and most convenient because of its availability. In an intensive feeding experiment with vegetable leaves/Comalina sp. and the locally prepared supplimentary feed the fishes attained table size in four months time. Cement cistens of 5 X 3 X 1½ m size could be conveniently used for breeding both species of Tilapia. T. zillii had semi adhesive eggs and they were deposited on the sides of the cement wall. The number of young ones in a brood ranged from 160 to 314 in T. esculenta and 687 to 4,356 in T. zillii.

Seasonal Growth of Waterhyacinth in the Sacramento/San Joaquin Delta, California

Waterhyacinth ( Eichhornia crassipes (Mart.) Solms), is a serious problem in the Sacramento/San Joaquin Delta, California. There is little published information on its phenology or seasonal growth in this system. Waterhyacinths were sampled at 2 to 3 week intervals from November, 1995 to July, 1997 and the following measurements were made on individual plants: dry weight, height, number of living leaves, number of dead leaves, and the width of the largest lamina. (PDF has 4 pages.)