Rainfall input, throughfall and stemflow of nutrients in a central African rain forest dominated by ectomycorrhizal trees

Abstract

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.

Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest

“…Germer et al (2007) (Germer et al, 2007) as well as the distance to industrial pollution emission sources (Levia et al, 2011a) and (for Cl À ), the great distance to the Atlantic and hence low influence by maritime air masses (Germer et al, 2007). Our stemflow concentrations of K þ , NO À 3 , H þ , and Cl À fell within the range of reported values (Abas et al, 1992;Chiwa et al, 2010;Chuyong et al, 2004;Laclau et al, 2003;Liu et al, 2003;Muoghalu, 2003;Olsen et al, 1981;Rodrigo et al, 2003;Tobón et al, 2004;Whitford et al, 1997). Even though this study was based on just nine events, the results are broadly representative for the wet season, because no differences were found in rainfall and throughfall solute concentrations between this study and respective wet season solute concentrations found in a previous study of rainfall and throughfall chemistry at this site based on 22 events that included the nine events from this study ( Fig.…”

“…Throughfall enrichment ratios of K þ greater than 10, as found in this study, are common in tropical forests in Brazil, Cameroon and Venezuela (Chuyong et al, 2004;Dezzeo and Chacon, 2006;Filoso et al, 1999;Forti and Moreira-Nordemann, 1991), secondary tropical forests in Brazil and Nigeria (Hölscher et al, 1998;Muoghalu, 2003), montane evergreen forest in China (Liu et al, 2002), as well as in forests in Japan and Spain (Bellot and Escarre, 1991;Chiwa et al, 2010;Rodrigo et al, 2003). Stemflow enrichment ratios of K þ exceeding 40 as we found are less common, but were found in a lowland Amazon forest (Dezzeo and Chacon, 2006), a montane evergreen forest in the Chinese Ailao Mountains (Liu et al, 2002), a mixed oak-beech forest in the Belgian Ardennes (André et al, 2008a), and a Douglas-fir plantation in the French Beaujolais Mountains (Marques and Ranger, 1997).…”

“…Our high enrichment ratios more likely resulted from comparatively lower concentrations in rainfall than from higher stemflow concentrations compared with other studies. Even though our rainfall K þ concentrations fell within the reported range of comparable studies, our NO À 3 , H þ , and Cl À rainfall concentrations were lower (Abas et al, 1992;Chiwa et al, 2010;Chuyong et al, 2004;Laclau et al, 2003;Liu et al, 2003;Muoghalu, 2003;Olsen et al, 1981;Rodrigo et al, 2003;Tobón et al, 2004;Whitford et al, 1997). The dry season NO À 3 rainfall concentrations at our site (Germer et al, 2007), however, were similar to annual values reported by Tobón et al (2004).…”

“…Moreover, even in forests where the majority of solutes contribute little, the stemflow flux of single solutes can still comprise a considerable share on their overall flux (e.g., K þ in Neary and Gizyn, 1994). These findings imply that stemflow should Chuyong et al (2004). c Neary and Gizyn (1994).…”

Demographic variation and habitat specialization of tree species in a diverse tropical forest of Cameroon

“…The area is a former Pleistocene refugium, and tree species richness and endemism are high (Maley 1987). Mean annual rainfall exceeds 5000 mm, with a dry season from December to February, when average monthly rainfall is <100 mm, followed by an intense wet season (Newbery et al 1998;Chuyong et al 2004b). Soils are skeletal and sandy at the surface, highly leached, and poor in nutrients (Newbery et al 1998;Chuyong et al 2002).…”