Grandis Forest Research Articles

Soil microbial indicators sensitive to land use conversion from pastures to commercial Eucalyptus grandis (Hill ex Maiden) plantations in Uruguay

Commercial forest plantations have increased during the last decade in Uruguay in soils of low cropping capability. Eucalyptus grandis (Hill ex Maiden) has been the main species planted due to its fast growth and adaptability to climate fluctuations. Assuming that the conversion from natural grazed pastures to commercial Eucalyptus plantations generates significant changes in the soil biological properties, we compared microbial enumeration and variables directly related to microbial activity to characterize these changes, as well as to determine the extent to which these soil biological properties change seasonally and with soil depth. The soil use conversion from pasture to forest land did not have a significant effect on the number of cellulolytic aerobes, P-solubilizers and Azotobacter spp. communities. Soil respiration, the C-mineralization coefficient, dehydrogenase, fluorescein diacetate hydrolysis and acid and alkaline phosphatase activities were affected significantly. Microbial enumeration of cellulolytics, P-solubilizers and Azotobacter spp., and parameters related to microbial biomass, soil respiration and the C-mineralization coefficient showed marked effects of sampling season. This, however, was not the case for the relative levels of the enzyme activities evaluated. These results indicated that the enzyme activities evaluated were sensitive and reliable indicators of the biochemical changes generated by the soil use change. Spring appeared to be a better time for sampling than summer or winter because enzyme activities tended to be higher. Soil sampling depth was shown to be an important factor for obtaining consistent results, especially for the measurement of enzyme activities. For the last indicators, as well as the others, better results were obtained sampling and analyzing the upper 10 cm of the mineral soil profile. Our work suggested that microbial biomass, soil respiration, and enzyme activities are useful tools to assess biological soil quality changes due to the conversion of pasture land to planted E. grandis forest.

Population Size of the Wedge-tailed Shearwater Puffinus pacificus Population in Pisonia grandis Forest on Heron Island in 1992

Repeated counts of Wedge-tailed Shearwater Puffinus pacificus burrows were made in two 30 × 30 m permanent plots in Pisonia grandis forest on Heron Island in 1978,1979 and 1992. The results support the population estimates of Hill & Barnes (1989) and their suggestion that the shearwater population almost doubled (to c. 16 000 pairs) between 1983 and 1985. However, due to the wide confidence limits on most estimates, a more gradual increase (of c. 3% per annum) cannot be ruled out. The 1992 population estimate was 16 503 ± 3427 pairs. Because shearwaters are supposedly faithful to nesting sites, the increase poses questions about inter-island movement and social organisation within colonies. It may also present problems for management of the Heron Island population.

Population increase and nesting patterns of the black noddy Anous minutus in Pisonia forest on Heron Island: Observations in 1978, 1979 and 1992

Abstract Estimates of the population size of black noddy Anous minutus on Heron Island were made by counting nests in permanently marked plots in Pisonia grandis forest in 1978, 1979 and 1992. The results, and published data, indicate that the population has been increasing at ca 7% per annum since early this century and currently is ca 63 000 ± 7000 pairs. The continued exponential increase in bird numbers poses interesting ecological questions and potential management problems, as more of the island is occupied by the birds and interaction with the vegetation intensifies. Pisonia is by far the most common tree on the island and most nests are in this species. However, there is evidence that Ficus opposita is preferred over Pisonia and the high mortality of this species in the marked plots may be due to excessive use by noddies. Pisonia trees which reach the forest canopy and are in the 40–60 cm stem diameter class have more nests than smaller trees. Larger stems (>60 cm diameter) are also underutilized relative to their size, and it is suggested that this is because they are more liable to windthrow in cyclones.

The population biology of Bromus tectorum in forests: effect of disturbance, grazing, and litter on seedling establishment and reproduction.

The effect of tree canopy, understory, herbivores, and litter depth on seedling establishment, survival, and reproduction of the alien grass, Bromus tectorum (cheatgrass), was examined in a series of experiments in four forest habitat types in western North America. Higher recruitment, survival, and reproduction on clearcuts, which would be expected if the overstory alone is limiting the distribution of cheatgrass in forests, were not observed. Removing the understory in an otherwise undisturbed Pinus ponderosa forest did, however, increase the emergence of B. tectorum, but plants in these experimentally-created openings were more vulnerable to grazing by small mammals. In contrast, removing the sparse understory in an Abies forest neither enhanced recruitment nor increased the incidence of grazing of B. tectorum seedlings. Regardless of the forest habitat, most grazed plants died before maturity; even fewer grazed plants produced seeds. Litter depth influenced both recruitment and biomass production: both the rate of germination and the size of resultant seedlings were lower on thick litter (6 cm) compared to results on thin litter (1.5 cm). In the more open Pinus ponderosa and Pseudotsuga menziesii forests, cheatgrass colonization may often occur in openings in the understory alone. Colonization in the more shady A. grandis and Thuja plicata forests is unlikely, however, unless the opening extends through both the understory and the overstory. As a result, cheatgrass is unlikely to increase in any of these forests unless the scale and incidence of disturbance increases substantially.