The reconstruction of Holocene environmental changes in lakes on the plateau region of southwest China provides an understanding of how these ecosystems may respond to climate change. Fossil diatom assemblages were investigated from an 11,000-year lake sediment core from a deep, alpine lake (Lugu Hu) in southwest China, an area strongly influenced by the southwest (or the Indian) summer monsoon. Changes in diatom assemblage composition, notably the abundance of the two dominant planktonic species, Cyclotella rhomboideo-elliptica and Cyclostephanos dubius, reflect the effects of climate variability on nutrient dynamics, mediated via thermal stratification (internal nutrient cycling) and catchment-vegetation processes. Statistical analyses of the climateediatom interactions highlight the strong effect of changing orbitally-induced solar radiation during the Holocene, presumably via its effect on the lake’s thermal budget. In a partial redundancy analysis, climate (solar insolation) and proxies reflecting catchment process (pollen percentages, C/N ratio) were the most important drivers of diatom ecological change, showing the strong effects of climateecatchmentevegetation interactions on lake functioning. This diatom record reflects long-term ontogeny of the lake-catchment ecosystem and suggests that climatic changes (both temperature and precipitation) impact lake ecology indirectly through shifts in thermal stratification and catchment nutrient exports.

The variations in macronutrient concentrations of the leaves of Terminalia superba and Pycanthus angolensis were studied and the concentrations of nutrients in leaves before abscission were compared with those after abscission. The amounts of nutrients returned to the forest floor were also computed from litter fall data at the start of maximum annual fall in the Reserve. With the exception of potassium in Pycanthus angolensis, there were significant variations in the nutrient concentrations of the two species with the time of year. With increasing leaf age the concentration of nitrogen, phosphorus, potassium and magnesium declined in Terminalia superba while magnesium concentration decreased in Pycanthus angolensis leaves. Furthermore, calcium showed an increasing concentration in Terminalia superba with increase in leaf age. The concentrations of nitrogen, phosphorus and potassium decreased before leaf fall. Estimated losses in nitrogen phosphorus and potassium before abscission were 44, 53 and 50%, respectively, whereas generally there was an increase (40%) in the concentration of calcium at leaf fall. Magnesium did not follow a definite pattern. The return of calcium through litter fall to the forest floor was the greatest of all the major elements. The distribution and variation of foliar nutrient concentrations in the leaves of Terminalia superba and Pycanthus angolensis and the importance of the amount of litter and the concentration of the various nutrients in the influencing soil fertility are discussed.

The demographic history of a flower-cohort of the tropical tree Dicymbe altsonii (Caesalpiniaceae) was studied by collecting litter from flowers, fruits and seeds, and by monitoring seedling survival. Flower production was estimated at 137 to 172 m−2 in a plot of 1 ha. Four percent of the flowers yielded a pod, which contained an average of 2.0 seeds. Post-dispersal mortality over 3 mo was 39% of the initial number of dispersed seeds. Most flowers and fruits were aborted. Insect and vertebrate predation in the tree and on the ground was very low. Reproductive litter production of this species was estimated to be equal to leaf litter production. The amount of phosphorus lost in litter from fruits and flowers was much larger than in leaf litter. This implies that the impact of the biennial flowering events on the nutrient dynamics of the trees and of the ecosystem may be large. It is argued that the reproductive cycle and the pre-dispersal demography of Dicymbe seem to be determined by a scarcity of nutrient resources, and possibly by pollinator limitation.