Geoscience Reference
In-Depth Information
(
Pinus
spp). As a result of government policy,
the annual planting rate of 500 000 hectares
in 2005 had doubled by 2010. Annual timber
production in eucalyptus plantations is about
45 m
3
ha
−
2
, although it can reach 70 m
3
ha
−
2
using advanced silviculture techniques, species and
genetic selection. This high productivity is usually
achieved on a rotation period of 6-7 years.
Early studies concentrated on measuring
transpiration from eucalyptus (see Lima, 1993
for a review); the rate was found to be similar
to other tree species and decreased substantially
during the drier periods of the year (Villa¸a and
Ferri, 1954; Mello, 1961). Subsequently, Lima and
Freire (1976), Lima and Reichardt (1977) and Lima
et al
. (1990) used a soil-water balance approach
to estimate the relative water consumption rates
of eucalyptus and pine plantations compared
with natural vegetation cover. The results showed
that the average annual soil water extraction
by transpiration in eucalyptus plantations was
about 215 mm higher than that for open savanna
woodland; it was also higher than the values
measured for pine plantation. Using a hydrological
model, Soares and Almeida (2001) were able
to estimate water movement in the soil under
a
Eucalyptus grandis
plantation in Brazil. They
observed that transpiration used water available
in the root zone during the wet period; in the dry
period, transpiration was reduced and water was
taken from soil layers below the root zone, but at a
rate which balanced the lower transpiration.
land. Stream flow started to decline steadily over
this period, owing to a combination of tree growth
and a reduction in annual precipitation. The
plantation was clear-felled after 7 years and stream
flow ceased that year (1993-1994). Despite a
continuing decline in annual precipitation, stream
flow recovered within 12 months, increasing
by 115 mm compared with the year before
clear-felling (Figure 5.1). Over the 8 year period,
mean annual water balance parameters for the
catchment were: 1327 mm of precipitation; 1186
mm of catchment-scale evapotranspiration; and
141 mm of water yield.
In 1991, a 100 ha experimental catchment
was established at Itatinga in the State of S ao
Paulo. It supported coppice re-growth (about 17
years old) from an
E. saligna
plantation, originally
established about 50 years previously. Stream flow
and precipitation measurements were carried out
during 1991-1998 and the plantation was clear-
felled in 1997. With average values of annual
precipitation and catchment evapotranspiraton
of 1590 mm and 1061 mm respectively, the
average annual water yield was approximately
400 mm (C amara and Lima, 1999). Stream
flow increased by 90 mm in the first year
after clear-felling, as compared with the mean
for the seven years preceding it. However, in
this catchment, streamflow never ceased during
the seven monitored years of plantation growth
(Figure 5.2).
These two initial experimental catchments
marked the beginning of a broader cooperative
programme of hydrological assessment of
plantation hydrology which now comprises
18 locations in several parts of Brazil. Most are
based on single catchments, but three use paired
catchments, whilst one is maintained with native
forest as a control reference. Figure 5.3 shows the
location of 10 of the experimental catchments,
while preliminary overall results are summarized
in Table 5.1.
The pattern of results is consistent with studies
reported elsewhere in the scientific literature.
For example, the increase in evapotranspiration
associated with forest plantations varies according
to local climatic and soil conditions; it is practically
zero
Experimental catchment
studies in Brazil
Experimental studies and monitoring of eucalyptus
plantation hydrology were initiated by The
Institute of Forest Research and Studies (IPEF)
based at the University of S ao Paulo, in
collaboration with forest companies. The first
studies started in 1987 and involved two very
small (7.0 ha) catchments in the hills of the Paraiba
River Valley (Vital
et al
., 1999). Stream flow and
other parameters were measured continuously
for a period of 8 years (1987-1995) following the
planting of
Eucalyptus saligna
on former pasture
in
the
semi-arid
region
containing
the
