Incident rainfall is a major source of nutrient input to a forest ecosystem and the consequent throughfall and stemflow contribute to nutrient cycling. These rain-based fluxes were measured over 12 ...mo in two forest types in Korup National Park, Cameroon, one with low (LEM) and one with high (HEM) ectomycorrhizal abundances of trees. Throughfall was 96.6 and 92.4% of the incident annual rainfall (5370 mm) in LEM and HEM forests respectively; stemflow was correspondingly 1.5 and 2.2%. Architectural analysis showed that ln(funneling ratio) declined linearly with increasing ln(basal area) of trees. Mean annual inputs of N, P, K, Mg and Ca in incident rainfall were 1.50, 1.07, 7.77, 5.25 and 9.27 kg ha-1, and total rain-based inputs to the forest floor were 5.0, 3.2, 123.4, 14.4 and 37.7 kg ha-1 respectively. The value for K is high for tropical forests and that for N is low. Nitrogen showed a significantly lower loading of throughfall and stemflow in HEM than in LEM forest, this being associated in the HEM forest with a greater abundance of epiphytic bryophytes which may absorb more N. Incident rainfall provided c. 35% of the gross input of P to the forest floor (i.e., rain-based plus small litter inputs), a surprisingly high contribution given the sandy P-poor soils. At the start of the wet season leaching of K from the canopy was particularly high. Calcium in the rain was also highest at this time, most likely due to washing off of dry-deposited Harmattan dusts. It is proposed that throughfall has an important 'priming' function in the rapid decomposition of litter and mineralization of P at the start of the wet season. The contribution of P inputted from the atmosphere appears to be significant when compared to the rates of P mineralization from leaf litter.
In the strongly seasonal, but annually very wet, parts of the tropics, low-water availability in the short dry season leads to a semi-deciduous forest, one which is also highly susceptible to ...nutrient loss from leaching in the long wet season. Patterns in litterfall were compared between forest with low (LEM) and high (HEM) abundances of ectomycorrhizal trees in Korup National Park, Cameroon, over 26 months in 1990-92. Leaf litter was sorted into 26 abundant species which included six ectomycorrhizal species, and of these three were the large grove-forming trees Microberlinia bisulcata, Tetraberlinia bifoliolata and Tetraberlinia moreliana. Larger-tree species shed their leaves with pronounced peaks in the dry season, whereas other species had either weaker dependence, showed several peaks per year, or were wet-season shedders. Although total annual litterfall differed little between forest types, in the HEM forest (dominated by M. bisulcata) the dry-season peak was more pronounced and earlier than that in the LEM forest. Species differed greatly in their mean leaf litterfall nutrient concentrations, with an approx. twofold range for nitrogen and phosphorus, and 2.5-3.5-fold for potassium, magnesium and calcium. In the dry season, LEM and HEM litter showed similar declines in P and N concentration, and increases in K and Mg; some species, especially M. bisculcata, showed strong dry-wet season differences. The concentration of P (but not N) was higher in the leaf litter of ectomycorrhizal than nonectomycorrhizal species. Retranslocation of N and P was lower among the ectomycorrhizal than nonectomycorrhizal species by approx, twofold. It is suggested that, within ectomycorrhizal groves on this soil low in P, a fast decomposition rate with minimal loss of mineralized P is possible due to the relatively high litter P not limiting the cycle at this stage, combined with an efficient recapture of released P by the surface organic layer of ectomycorrhizas and fine roots. This points to a feedback between two essential controlling steps (retranslocation and mineralization) in a tropical rain forest ecosystem dominated by ectomycorrhizal trees.
• In a forest grove at Korup dominated by the ectomycorrhizal species Microberlinia bisulcata, an experiment tested whether phosphorus (P) was a limiting nutrient. • P-fertilization of seven subplots ...1995-97 was compared with seven controls. It led to large increases in soil P concentrations. Trees were measured in 1995 and 2000. M. bisulcata and four other species were transplanted into the treatments, and a wild cohort of M. bisulcata seedlings was followed in both. Leaf litter fall from trees and seedlings were analysed for nutrients. • Growth of trees was not affected by added P. Transplanted seedlings survived better in the controls than added-P subplots: they did not grow better with added-P. M. bisulcata wildlings survived slightly better in the added-P subplots in yr 1 but not later. Litter fall and transplanted survivors had much higher concentrations of P (not N) in the added-P than control subplots. • Under current conditions, it appears that P does not limit growth of trees or hinder seedling establishment, especially of M. bisculcata, in these low-P grove soils.
Based on litter mass and litterfall data, decomposition rates for leaves were found to be fast (k = 3.3) and the turnover times short (3.6 mo) on the low-nutrient sandy soils of Korup. Leaf litter of ...four ectomycorrhizal tree species (Berlinia bracteosa, Didelotia africana, Microberlinia bisulcata and Tetraberlinia bifoliolata) and of three non-ectomycorrhizal species (Cola verticillata, Oubanguia alata and Strephonema pseudocola) from Korup were left to decompose in 2-mm mesh bags on the forest floor in three plots of each of two forest types forest of low (LEM) and high (HEM) abundance of ectomycorrhizal (caesalp) trees. The litter of the ectomycorrhizal species decayed at a significantly slower rate than that of the non-ectomycorrhizal species, although the former were richer in P and N concentrations of the start. Disappearance rates of the litter layer showed a similar trend. Ectomycorrhizal species immobilized less N, but mineralized more P, than non-ectomycorrhizal species. Differences between species groups in K, Mg and Ca mineralization were negligible. Effect of forest type was clear only for Mg: mineralization of Mg was faster in the HEM than LEM plots, a pattern repeated across all species. This difference was attributed to a much more prolific fine root mat in the HEM than LEM forest. The relatively fast release of P from the litter of the ectomycorrhizal species suggests that the mat must allow an efficient uptake to maintain P in the forest ecosystem.
Litterfall was measured monthly in ten 1 m2 traps in each of two 0.25 ha plots in the rain forest of Southern Bakundu Forest Reserve, Cameroon for 18 months from 1 July 1982 to 31 December 1983. ...Particular emphasis was placed on measuring species contributions and in relating litterfall to climatic factors; the litterfall data were also used in estimating leaf production. Annual litterfall ranged between 12.9 and 14.1 t ha-1 and was partitioned to leaves (61-66%), branches (23-38%), fruits and flowers (8-12%) and ephiphytes (0.8%). Emergents and top canopy species like Desbordesia glaucescens (evergreen) and Ceiba pentandra (deciduous) contributed more litter than the numerically dominant lower storey species like Cola lepidota and Diospyros spp. Litter fell throughout the year but was greatest during the dry season (November to March); litterfall was thus strongly negatively correlated with environmental moisture variables and could be predicted from its linear regression on time of year, through-fall and relative humidity. By correcting the leaf fall data for leaf weight losses due to grazing and re-translocation, leaf production rates of 10.2 to 11.2 t ha-1 yr-1 were estimated for the forest.
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.
Decomposition of litter on the forest floor and of leaves of five species, Celtis zenkeri, Cola lepidota, Desbordesia glaucescens, Ceiba pentandra and Terminalia superba in nylon mesh bags, as well ...as wood decay were studied in the tropical rainforest at Southern Bakundu Forest Reserve, Cameroon. The rate of loss of dry matter was fastest in Celtis zenkeri which was significantly different from the other species, while potassium was the most rapidly released element from all species with more than 50% being released in the first two months of the experiment. Nitrogen and phosphorus showed initial increases in bagged leaf litter independent of dry weight losses and while nitrogen was later released phosphorus continued to increase reaching 2–3 times the initial concentration. Decomposition constant (k) of litter on the forest floor was found to be 2.23 whereas the mean decomposition constants of the different species were as follows: Celtis zenkeri 4.18, Cola lepidota 2.18, Desbordesia glaucescens 1.60 and Ceiba pentandra 2.16 for the two experiments. Termites were found to have a very great influence on the decay of the wood of Terminalia superba with decay due to micro-organisms being negligible.
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