El índice de área foliar es la principal variable biofísica utilizada para modelar muchos procesos vegetales. En el presente trabajo se propone un método para obtener un mapa del índice de área foliar en la Reserva de la Biósfera Mariposa Monarca, basado en el ajuste de una función de transferencia radiativa entre estimaciones del índice de área foliar obtenidas en unos pocos puntos de muestreo con fotografías hemisféricas y los datos radiométricos correspondientes de una imagen del satélite SPOT (satellite pour l’observation de la Terre). Previo al ajuste de la función de transferencia, los datos fueron corregidos del efecto del relieve. Se eligió una combinación lineal de bandas de la imagen SPOT (r = 0.608, RMSE = 0.493). La aplicación de la función de transferencia a la imagen de la reserva permitió construir un mapa de índice de área foliar y evaluar el estado del bosque en una fecha cercana a la declaración de reserva de la biósfera. Este trabajo se llevó a cabo en el marco del proyecto internacional VALERI (validation of european remote sensing instruments).

Chlorophyll is an essential element of photosynthesis and its content in plant leaves indicates their photosynthetic capacity as well as the presence of stress or diseases. The purpose of this work was to evaluate the feasibility of estimating chlorophyll content in the Monarch Butterfly Biosphere Reserve forest (Sierra Chincua sanctuary, México) based on vegetation indices calculated by using hyperspectral reflectance measurements of plant leaves. This study focused on oyamel (Abies religiosa L.) which is the main tree specie of this area. Leaf samples were taken on 140 trees and analyzed for chlorophyll a and b, nitrogen and carbon content. The hyperspectral reflectance spectra were measured on each sample and different vegetation indices were calculated. Results showed that the indices best correlated with chlorophyll content were the red edge position index (r = 0.531) and the red edge position chlorophyll reflectance index (r = 0.506), followed by the MERIS terrestrial chlorophyll index (r = 0.497) and the green chlorophyll reflectance index (r = 0.472). Although there was a significant correlation between nitrogen and chlorophyll content, none of the indices studied here correlated with nitrogen content. The influence of various environmental factors (altitude, slope, vegetation density and aspect) on leaf composition (nitrogen, carbon chlorophyll content and chlorophyll a/b ratio) and on the vegetation indices was studied. Environmental factors had an influence on both leaf composition and vegetation indices. Chlorophyll and nitrogen content were influenced mostly by the altitude and slope of the site while vegetation indices were affected mostly by its orientation.