Carbon fluxes resulting from land-use changes in the Tamaulipan thornscrub of northeastern Mexico

Information on carbon stock and flux resulting from land-use changes in subtropical, semi-arid ecosystems are important to understand global carbon flux, yet little data is available. In the Tamaulipan thornscrub forests of northeastern Mexico, biomass components of standing vegetation were estimated from 56 quadrats (200 m2 each). Regional land-use changes and present forest cover, as well as estimates of soil organic carbon from chronosequences, were used to predict carbon stocks and fluxes in this ecosystem

Predicting aboveground forest biomass with topographic variables in human-impacted tropical dry forest landscapes

Topographic variables such as slope and elevation partially explain spatial variations in aboveground biomass (AGB) within landscapes. Human activities that impact vegetation, such as cattle grazing and shifting cultivation, often follow topographic features and also play a key role in determining AGB patterns, although these effects may be moderated by accessibility. In this study, we evaluated the potential to predict AGB in a rural landscape, using a set of topographical variables in combination with indicators of accessibility. We modeled linear and non-linear relationships between AGB, topographic variables within the territorial boundaries of six rural communities, and distance to roads. Linear models showed that elevation, slope, topographic wetness index, and tangential curvature could explain up to 21% of AGB. Non-linear models found threshold values for the relationship between AGB and diffuse insolation, topographic position index at 19 × 19 pixels scale and differentiated between groups of communities, improving AGB predictions to 33%. We also found a continuous and positive effect on AGB with increased distance from roads, but also a piecewise relationship that improves the understanding of intensity of human activities. These findings could enable AGB baselines to be constructed at landscape level using freely available data from topographic maps. Such baselines may be of use in national programs under the international policy Reducing Emissions from Deforestation and Forest Degradation

Estrés hídrico en Pinus engelmannii Carr., producido en vivero

The effect of water stress was evaluated in relation to the water potential and growth of five-month old seedlings of Pinus engelmannii Carr. The essay was conducted from September 21st to October 27th, 2003; in this period of time three water stress cycles were completed. Significant differences between water supply treatments were found (p < 0.01) in regard to the seedlings water potential after the third day of watering. The seedlings under water stress reached final water potentials from –1,96 to –2,29 MPa, while the seedlings without water stress showed values between –0.13 and –0.20 MPa. The morphological response of the seedlings presented two well-defined trends. First, the seedlings irrigated without humidity restriction showed larger growth rates in height (20.7%), collar diameter (69.4%) and total phytomass production (144.1%). On the other hand, the seedlings under water stress showed smaller increments in height (1.3%), collar diameter (9.8%) and total phytomass (73.1%). It is concluded that the seedlings were sensible to the evaluated levels of water stress, therefore allowing management to promote their hardening. Key words: humidity deficit, seedlings quality, growth, preaconditioning phase.Se evaluó el efecto del estrés hídrico en el potencial hídrico y en el crecimiento de plantas de Pinus engelmannii Carr. de cinco meses de edad, sometidas a dos tratamientos de riego (con y sin estrés hídrico). El experimento comprendió del 21 de septiembre al 27 de octubre de 2003, tiempo en el que se aplicaron tres ciclos de estrés hídrico. Se encontraron diferencias significativas entre tratamientos (p < 0,01) en el potencial hídrico a partir del tercer día después del riego. Las plantas sometidas a estrés hídrico alcanzaron valores de –1,96 a –2,29 MPa al final de cada ciclo de estrés hídrico, mientras que los del tratamiento sin estrés variaron entre –0,13 y –0,20 MPa. La respuesta morfológica de las plantas mostró dos vertientes bien definidas; en el tratamiento sin restricción de humedad las tasas de crecimiento fueron mayores en altura (20,7%), diámetro del cuello (69,4%) y producción total de fitomasa (144,1%); mientras que en la condición de estrés los incrementos fueron menores en altura (1,3%), diámetro del cuello (9,8%) y fitomasa total (73,1%). Se concluye que las plantas fueron sensibles a los niveles de estrés hídrico evaluados, lo que permitiría su manejo para favorecer su preacondicionamiento