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.
Highlights
Ecuador is a country that is in the top 10 list of countries with the greatest loss of primary forest area between 1990 and 2015 [1], and until recently, exhibited the highest deforestation rate in SouthAmerica [2]
Altitudinal differences among plots were approximately 300 m and plots in the SAN site were at the highest altitude
Measuring stocks of N and P, which is common in many studies, did not improve forest site classification under the present soil acidic conditions
Summary
Ecuador is a country that is in the top 10 list of countries with the greatest loss of primary forest area between 1990 and 2015 [1], and until recently, exhibited the highest deforestation rate in SouthAmerica [2]. In South America, afforestation programs were mainly developed based on the use of exotic species with the early aim of wood production, but later changed into non-wood forest products and for environmental protection [3]. Andean region of Ecuador (Sierra Region), pines and eucalypts have been commonly used for plantations [7,8,9]. The effects of these plantations give evidence of reductions in environmental quality in Ecuador [5,10,11,12,13], and often, they have been shown to be financially non profitable [6,14]
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