Abstract:
Forest site classification adapted to the respective site conditions is one prerequisite for
sustainable silviculture. This work aims to initiate the forest site classification for pine plantations
in the southern Andean region of Ecuador. Forest productivity, estimated by the dominant height
of 20-year-old trees (DH20), was related to data from climate, topography, and soil using 23 plots
installed in pine plantations in the province of Loja. Forest site productivity was classified as:
low (class C: 13.4 m), middle (class B: 16.6 m), and high (Class A: 22.3 m). Strong determinants
to differentiate the forest site classes were: the short to medium term available Ca and K stocks
(organic layer + mineral soil standardized to a depth of 60 cm), soil acidity, the C:N ratio, clay and
sand content, forest floor thickness, altitude, and slope. The lowest forest productivity (Class C)
is mainly associated with the lowest short to medium term available K and Ca stocks. Whereas,
in site classes with the highest forest productivity, pines could benefit from a more active microbial
community releasing N and P, since the soil pH was about 1 unit less acidic. This is supported by the
lowest forest floor thickness and the narrowest C:N ratio.
