Understanding of the involved issues in nutritional dynamics process in eucalyptus stands is
the base to sustainable management. Objective this study was to determine the nutritional
dynamic in Eucalyptus urophylla x Eucalyptus globulus stand, Eldorado do Sul - RS. For this,
was available: a) litter production (leaves, twigs – diameter ≤ 1.0 cm, miscellaneous and thick
branches – diameter > 1.0cm) and nutrients uptake, from 6.5 to 9.5 years-old stand (2007 at
2010); b) leaf litter decomposition and nutrients release by litterbags method (adding 12g of
dried leaves in nylon bags), for three years (2007 to 2009); c) aboveground biomass and
nutrients amount in the eucalyptus (wood, bark, branches and leaves) and underground (wood
and leaves) to ten-year-old stand (June 2010); d) interfere of different intensities of biomass
removal (all aboveground biomass removal – eucalyptus + underground; eucalyptus removal;
wood with bark removal and only wood removal) in relation nutrients stock and; -
silvicultural alternative for sustainable forestry management. Litter production was increasing
with stand age increasing, showing seasonal behavior with deposition increasing with the air
temperature increasing and being mainly composed by leaves fraction that also is main
fraction nutrients return through litter. Accumulated litter showed decomposition coefficient
of 0.54 with 1.86 years how time average renewal and 1.29 and 5.59 years to disappear 50 and
95% of the litter. Mass loss leaf showed positive correlation with nutrients concentration,
indicating that the higher mass loss, higher the nutrients concentration in litter remaining.
Litter leaf decay initially showed P, Fe, Mn and Zn immobilization and release of the others,
in the second year occurred P release and in the third year occurred Mn and Zn release, with
Fe exception. Eucalyptus biomass was allocated predominantly to stem (Wood + bark) with
93.7% and with the largest nutrients stock. Biomass components had different chemical
composition, being generally higher in leaves and bark and smaller in wood and branches
biomass. With the harvest of wood with the bark all the nutrients removal would suffer more
than 45% of the total amount accumulated in aboveground biomass. However, removed just
the wood, which has the highest nutrients utilization rate, the nutrients removed percentage,
except by Cu and Zn, will be less than 50% and up to 10% in the case of Ca in relation the
total biomass contained. Phosphorus and calcium can be the main nutrients became limiting in
next rotation productivity, because the potential rotation estimates are close to one, when in
the harvest of wood with the bark. Nutrients output through forestry harvest must be take
account by companies during the planning of activities. Avoiding productivity decreasing
with the next rotations, and also contributing sustainable management, because the nutrients
exportation, Ca mainly, is high due to wood with bark harvest.
