Remote sensing observations such as normalized difference vegetation index (NDVI) trends can provide important insights into past and present land condition. However, they do not directly provide comprehensive information about our representation of land degradation and the processes at work. This study aimed to analyze vegetation productivity underlying factors in order to assess land degradation and to highlight the impact of definitions on its quantitative assessment, using Mozambique as casestudy. Land productivity change were first analyzed using NDVI time-series (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016), and a two-step framework was then used to understand the main factors of these productivity changes. The impact of land degradation's definition was assessed based on four types of stakeholder, with different priorities in terms of ecosystem services. The results show that 25% of the country display a significant land productivity decrease, while only 3% display a land productivity increase. A large part of these land productivity changes (>61% of the decrease, and >98% of the increase) is directly assigned to human activities, such as native forest growth or tree plantations (for the increase), or forest degradation, deforestation and loss of grassland productivity (for the decrease). We showed that the fraction of degraded land varies according to stakeholders' definitions, ranging from 12% to 20% of the Country, much less than the 39% estimated by Tier 1 United Nations Convention to Combat Desertification. This study provides a sound methodological framework for assessing land degradation status that could help stakeholders to design national and locally relevant land degradation mitigation policies or programmes.
Key message This study demonstrates that Millettia stuhlmannii produces annual growth rings responsive to seasonal climate and should be useful for dendrochronology. Abstract Millettia stuhlmannii is a highly valuable and potentially overexploited timber species indigenous to southeastern Africa. It is of particular economic importance in Mozambique though relatively little is known about its growth rate or response to climate. This study investigates whether M. stuhlmannii is potentially useful for dendrochronology-that is whether this species forms annual growth rings that are responsive to external forcing such as climate. Five methods were used to determine whether M. stuhlmannii growth rings are indeed annual in nature, including analysis of ring anatomy, dating trees of known age, cambial wounding, classical cross-dating, and comparison of annual growth to climate variables. Growth rings of Millettia stuhlmannii are distinct and well formed, young trees from plantations of known age formed an appropriate number of distinct annual rings, trees showed distinct wood reaction to cambial wounding, adding exactly one complete ring in one calendar year, crossdating within and between trees was somewhat successful, and annual growth is significantly correlated with wet season precipitation. Results of this study indicate that M. stuhlmannii is a potentially useful species for dendrochronology. These findings should allow a better understanding of this species' growth dynamics and ecology, as well as its response to climate variability in the past and potentially to future climate change.
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