© iForest -Biogeosciences and Forestry IntroductionDue to growing needs for timber and wood products, forest plantations have increased around the world and have gained economical relevance. At the same time there has been an increase in concerns regarding the sustainability of planted forests, especially those managed under a regime of short rotations (Nambiar 1995). In particular, the relationship between forest nutrition and sustainable timber production has become an important issue for the management of less studied species in countries such as Costa Rica and China , Arias et al. 2011, Qiong et al. 2011.Teak (Tectona grandis L.f.) plantations have been widely established in Central America, initially in Costa Rica and Panama (De Camino et al. 2002) (Pandey & Brown 2000, De Camino et al. 2002. In this kind of short-rotation, intensively-managed forest plantations, nutrient management is a key issue for attaining sustainability and maintaining yields for future rotations (Poels 1994, Evans & Turnbull 2004. Appropriate knowledge regarding teak nutrition is required to improve plantation management and to attain high productivity and sustainability. Nutrient accumulation increases with the stand's age, mainly due to biomass accumulation; however, nutrient uptake during early years is considered crucial to sustain the high growth rates and the rapid expansion of both crown and roots required to maintain an appropriate nutritional status throughout the entire rotation length (Miller 1981, Laclau et al. 2003. In general, foliage is the tree tissue with the highest nutrient concentration and it is considered to contain 20-40% of total stand nutrients, while tree stems are assumed to have relatively low concentrations of nutrients (Miller 1984(Miller , 1995. However, the high amount of biomass accumulated in the tree stem makes it an important sink of nutrients. As a consequence, the loss of nutrients through wood removal at harvesting is a major cause of impoverishment of forest sites (Fölster & Khanna 1997, Worrel & Hampson 1997. While N, P and Mg are mainly accumulated in the tree stem, bark and roots are considered to be Ca sinks (Nwoboshi 1984). Nutrient uptake depends mainly on the species' demand and its ability to access nutrients, as well as the potential of the site (especially the soil) to supply nutrients. In calcareous soils in India, the most absorbed nutrients by teak were Ca > K > N > Mg > P = S (Negi et al. 1995), while they were K > N > Ca >> Mg ≥ P in less fertile soils in Africa (Nwoboshi 1984) and N > Ca > K > Mg > P > Na > S > Cl in a different study site in India ).In order to understand the relationship between soil and forest nutrition, it has been long recognized that it is first necessary to evaluate the quantities of nutrients taken up by the growing forest and removed from the site during timber extraction (Rennie 1955). However, Fölster & Khanna (1997) pointed out a traditional and general lack of concern of this problem in planted forests. Soil-plant relation research in agricultu...

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REDD+ implementation requires robust, consistent, accurate and transparent national land cover historical data and monitoring systems. Satellite imagery is the only data source with enough periodicity to provide consistent land cover information in a cost-effective way. The main aim of this paper is the creation of an operational framework for monitoring land cover dynamics based on Landsat imagery and open-source software. The methodology integrates the entire land cover and land cover change mapping processes to produce a consistent series of Land Cover maps. The consistency of the time series is achieved through the application of a single trained machine learning algorithm to radiometrically normalized imagery using iteratively re-weighted multivariate alteration detection (IR-MAD) across all dates of the historical period. As a result, seven individual Land Cover maps of Costa Rica were produced from 1985/1986 to 2013/2014. Post-classification land cover change detection was performed to evaluate the land cover dynamics in Costa Rica. The validation of the land cover maps showed an overall accuracy of 87% for the 2013/2014 map, 93% for the 2000/2001 map and 89% for the 1985/1986 map. Land cover changes between forest and non-forest classes were validated for the period between 2001 and 2011, obtaining an overall accuracy of 86%. Forest age-classes were generated through a multi-temporal analysis of the maps. By linking deforestation dynamics with forest age, a more accurate discussion of the carbon emissions along the time series can be presented.

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Background: Soil fertility management and forest nutrition are key factors determining management and productivity of both natural and planted forests. Reference values for foliar and soil nutrient contents and assessment of nutrient balances to evaluate the sustainability of planted forest systems can guide forest managers in determining whether or not additional fertilisation is required.Methods: This review summarises the authors' research into the nutritional requirements for planted teak (Tectona grandis L.f.) forests in Central and South America. Teak is an important species for commercial forest plantations, usually in carefully selected productive sites, with rotations of 20-25 years and commercial volume anticipated to be around 10 m 3 ha -1 year -1 . Results: Foliar nutrient concentration values can be used as a reference to evaluate the nutritional status of planted teak forests. In addition, there may be an association between the dynamics of the concentrations of K, Mg and N with tree age and the age-related declines in teak productivity. Timber extraction by felling constitutes a major nutrient output from the system and repeated nutrient exports during several rotations could be a cause of soil nutrients depletion, especially P and K which typically have low availability in these Central American systems. Multivariate analyses have been shown to be appropriate and helpful tools for grouping forest stands by fertility classes (i.e. soil management zones using the terminology of precision agriculture). Conclusions: The techniques developed can be used as tools for the design of efficient fertilisation programmes, taking into account the inherent heterogeneity of soil fertility across different stands. This is considered as a first step towards a precision forestry scheme. Whether age-related changes in nutrient concentrations are a cause or a consequence of age-related declines in productivity is an important issue for future research.

Vochysia guatemalensis Donn. Smith is a native species commonly used in small-scale reforestation programs in Costa Rica recognized for its fast growth under acidic and unfertile soil conditions. This study aimed to evaluate the nutrient concentration dynamics on individual trees of V. guatemalensis of increasing ages, in order to improve the understanding some aspects of its ecology as well as management of this tree species. Nutrient (N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, and B) and Al concentration in stems, branches and foliage were measured using false time series (also known as chronosequences) in 13 different tree stands (2-21 years) found in the Caribbean lowlands of Costa Rica. N, K and S concentrations in the stems showed a significant inverse relationship with DBH; while P, S, and Cu foliar contents increased with DBH. Average foliar concentrations of N, Ca, K, Mg, Fe, Zn, Mn, B, and Al showed little or no variation with tree growth. Foliar Al concentration (21, 297-28, 826 mg kg -1 ) was higher than previously reported as toxic for non-Al accumulating species (\1000 mg kg -1 ), confirming V. guatemalensis as an Al hyper accumulator. Our results reinforce the possibility of using V. guatemalensis for timber production, especially to improve the income of small farmers farming on very acidic soils. The nutrient concentrations that were obtained for different tree components provide baseline information for further studies where the objective is to evaluate the nutritional status of a site.