Geoscience Reference
In-Depth Information
In looking at the fauna inhabiting these humus profiles, Bal distinguished char-
acteristic groups of organisms that had a dominant influence in creating the different
types of moder. Fly larvae, mites and enchytraeid worms were common to both,
though the population size and species differed. Both the oak and conifer litter had
first to be rendered palatable by microbial attack but the fir needles needed a longer
period before they were acceptable.
A similar trend of humus profile development is characteristic of Brown Pod-
zolic Soils in Britain, under, for example, birch and oak woodlands in the uplands,
or some woodlands and heaths on acidic soils in the lowlands. On the less acid and
more fertile soils of lowland Britain, woodland litter is incorporated faster and more
thoroughly. This results in the mull humus forms characteristic of Brown Earths and
Calcareous Soils. The rapid recycling of nutrients that is a feature of mull humus soils
is important in maintaining natural fertility. In his work on the biology of woodland
soils, K.L.Bocock pointed out that 75 percent of the annual nutrient requirements of
trees in closed canopy woodlands could be met by the decomposition of one year's
litter fall. His colleague J.Satchell estimated that the annual nitrogen turnover due to
earthworms in a fertile mull soil under mixed woodland was four times greater than
the nitrogen in the annual litter fall.
Other early work by the Nature Conservancy in the Lake District compared the
respective attack by organisms on freshly fallen oak and ash litter placed on the soil
surface in nylon mesh bags. One site was mixed deciduous coppice (mainly ash and
hazel) on a mull humus over limestone; the other was oak-birch coppice on a more
acid moder over slaty rocks. At the mull site, ash leaflets had been skeletonized with-
in the first six months, and some had even been dragged from the nets by large earth-
worm species. On the moder humus site, the leaves remained in the nets and were ex-
Oak leaf litter showed similar contrasts between sites, but with a delay before sub-
stantial faunal attack occurred. Again, some initial weathering and microbial attack
was needed to remove some of the tannins and render these palatable.
Turning to a Northamptonshire site, Bedford Purlieus near Peterborough is a
complex woodland with a mixture of coppice regrowth, planted deciduous and con-
ifer species, and naturally regenerated trees. The wood is notable not only for its di-
verse flora and fauna but also for providing important benchmark examples of undis-
turbed lowland soils which overlie strongly contrasting parent materials. At one end
of the soil chemical range, calcareous Rendzinas are disturbed by high populations
of earthworms and moles. The worms incorporate the humus deeply into the profile
and contribute to a strong granular crumb structure, while the moles continually bring
limestone fragments up from below.
