The "Base Cation Pump" Idea Revisited: On What Type of Forest Soils Can European Beech Improve Forest Floor Chemistry and Nutrient Cycling Compared to Norway Spruce?.

Deep rooting beech (Fagus sylvatica L.) supposedly produces litterfall that is richer in base cations (especially Ca) when compared to Norway spruce (Picea abies (L.) Karst) growing on the same site. Beech may thus improve the chemical status and lead to less accumulation of the forest floor when admixed to spruce forests. Here, we investigated whether this base cation pump effect of beech occurs over a range of soil buffer ranges, or whether it is restricted to those sites, where beech can access exchangeable cations in deeper soil layers that are not accessible to the commonly shallow-rooted spruce.

In young to mature mixed spruce-beech forests of south-western Germany the concentrations and the contents of base cations in foliar litterfall, forest floor and mineral soil materials were determined for three different soil base saturation (BS) profiles: (1) soils with low BS (<10%) to one meter depth, (2) soils with distinct difference in BS between upper and subsoil, and (3) high BS (>75%) to one meter depth. Litterfall, forest floor and soil were collected beneath groups of pure beech, pure spruce or mixed-species canopies.

The quantities of base cations recycled via litterfall were not higher under beech than spruce. Owing to slower turnover of the forest floor under spruce and small differences in concentration of base cations in litter between the species, forest floor mass and base cation contents increased as follows: beech < mixed < spruce canopy. In addition, no significant difference between species was detected in exchangeable base cation contents in the soil (0–10 cm) within each soil BS profile.

There is no evidence that beech improves base cation cycling when compared to spruce for a range of typical buffer ranges.