The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 330

loss of surface L layers and O horizons, leaving exposed the uppermost
mineral horizon of the soil (Radley, 1965; Maltby et al ., 1990; Haslam et al .,
1998). Destruction of roots and seeds, depletion of the nutrient stock and
loss of water-holding capacity of the soil all combine to slow down recovery
from severe fires (Haslam et al ., 1999).
Although the conditions under which different fires occur are rarely the
same, comparison of adjacent sites where fires have occurred at different
times allows the investigation of recovery and succession after burning. We
believe that conveniently matched fire sites are rare. This study is based on
research undertaken at sites of severe fires separated by nearly 20 years
in time (1957 and 1976) and 50 m in space in the southern Pennines
of northern England (Haslam, 1999), where we have estimated the rates of
carbon reaccumulation and investigated details of the recolonization by
organisms in the decades since the fires.
Carbon Loss and Reaccumulation
The site we have investigated in the Pennines has been described in detail
elsewhere (Haslam et al ., 1998; Haslam, 1999). It comprises two areas, one
in excess of 3 ha and the other nearly 5 ha, where severe fires in 1957 and
1976, respectively, removed all the L layer and O horizon of what was a
stagnogley podzol. The total C loss was estimated by determining the
amount of C in the L layer and O horizon in the adjacent, unburned soil
at 20 randomly selected positions. The rates of reaccumulation were
estimated from measurements made in 1996 of C in the L layers and O
horizons of soils at 21 randomly selected positions in the sites burnt in both
the 1957 and 1976 fires, the underlying assumption being that this C had
accumulated since the fires. The justification of this assumption is
discussed in more detail by Haslam et al . (1998), but essentially it relies
on the fires having left the uppermost mineral horizon of the soil exposed.
The total C loss was 30 kg C ha −1 or 1.47 t C and 0.93 t C as a result
of the fires in 1957 and 1976, respectively (Haslam et al ., 1998). The
amounts of C in the L layers and O horizons of the burned areas when
measured in 1996 are shown in Table 4.15.1. Initially the organic matter
accumulated in the L layer and consequently there was no recognizable O
horizon at the site burned in 1976. From these estimates of C content, the
mean rates of C accumulation over the period from 1957 to 1996 and from
1976 to 1996 were estimated. The rate of organic matter accumulation
was much slower during the first 19 years after burning than subsequently.
During much of the 0-19 year period, the fire sites did not have plant cover
and did not, therefore, receive organic matter inputs from plant litter.
According to observations in 1984 by one of us (D.W.H.), the 1976 fire site
had only ~50% plant cover 8 years after the fire, whilst plant cover on the