Fjölrit RALA - 05.12.1999, Page 139

KEVIN F. 0’CONNOR ETAL.
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Comparative nutrient pools for biomass compartments and soil layers have also
been compiled for N and P for three degradation sequences in Table 3, as well as
comparative biomass compartment pools for K and Ca, and exchangeable K and Ca in
soil layers. Reductions in nutrient pools in live biomass compartments, especially in
above-ground tissue (including wood), but also in roots, that accompany the transfor-
mation of forest to grassland vegetation are far in excess of what is shown for later
transformations of the tall tussock grasslands themselves. There is a clear indication,
however, that soil pools of N, P and K are higher under grassland than they are under
forest.
In respect to N, P and K, degradation of tall tussock grassland to weedy, short
grassland has been accompanied by a reduction in above-ground nutrient pools, both
live and dead. By use of the three localities as replicates, analysis of variance showed
highly signifícant differences between tall tussock grasslands and weedy short grass-
lands for above-ground N (p=0.008), for above-ground K (p=0.000), and almost so for
above-ground P (p=0.013). These differences in nutrients in above-ground pools are
not matched by consistent reductions in N, P and K pools in roots. When roots are in-
cluded for total biomass nutrients, differences are less significant for N (p=0.024), and
for P (p=0.089), but they are highly significant for K (p=0.010). In the case of Ca,
evidence for nutrient decline with ecological degradation is much less plain, except in
the above-ground dead compartment, where the characteristic persistence of Ca is
demonstrated. For difference in above-ground Ca, p=0.058, and for total biomass Ca,
p=0.033.
Soils show no consistent differences in nutrients associated with ecological degra-
dation sequences, apart from the appreciable enhancement of soil N, P, and K, which
seems to accompany the conversion of forest to grassland. This is consistent with the
substantial difference in favour of forest in all nutrients in biomass. As a consequence
of the substantial contribution of soil N and P to the whole system in grasslands, when
tall tussock grassland systems as a whole are compared with short grassland systems,
differences in total system nutrients are negligible and never approach significance
(p>0.5 for N and P).
Changes in nutrient pools with cultural renewal of vegetation
Limited opportunities exist to measure nutrient pools in soils and biomass compart-
ments of cultural vegetation, in comparison with reference areas established in sites
documented in the earlier tables. An intensive study of soil nutrient pools in Tekapo
soil under comparative pastoral cultures over nearly two decades has recently been
compiled and will be reported separately (D. Scott, in prep.). Likewise the degraded
ecosystem on Pukaki soil in the Tekapo sequence in Table 3 is being used as a refer-
ence point for forestry and pastoral development.
At two sites in the Craigiebum subalpine zone, lodgepole pine (Pinus contortd) was
planted in the early 1960s and biomass and nutrient pools were determined in 1978
(Nordmeyer 1980ab). From one of these sites, live and dead above-ground and below-
ground nutrient pools in 13 year old P. contorta are presented in Table 4, in compari-
son with the corresponding values for the Festuca-Agrostis-Hieracium community in
which trees had been planted.