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To recover the structure and functionality of a deforested ecosystem, two strategies of ecological restoration are considered: active restoration, which eliminates the disturbance agents and implements strategies to accelerate site recovery, and passive restoration, which eliminates disturbance agents, allowing natural regeneration to occur. Prior to choosing passive restoration, a field evaluation of the potential for natural regeneration is important. In this context, seedling and sapling density as well as patterns of recruitment and survival are appropriate indicators of restoration potential.In the present study, we deduced the potential of sacred fir (Abies religiosa) forest of the Monarch Butterfly Biosphere Reserve to recover by natural regeneration through seedling and sapling density and mortality, since A. religiosa is the dominant tree species in wintering sites of monarch butterfly. In 2015, we evaluated seedling density in 53 sites along an elevational gradient (3050-3550 m above sea level; m a.s.l.). There was a higher density of seedlings and saplings established in canopy gaps, compared to sites under dense forest canopy. Seedling recruitment was higher in sites at intermediate elevations (3050 to 3300 m a.s.l.) than in those at higher elevations. In a second survey, we studied A. religiosa seedling mortality over the dry season of 2016 to identify the environmental variables that cause the high seedling mortality and very low recruitment. Recently emerged seedling mortality was 49.2% at the end of the dry season (June 2016). The highest monthly mortality (14.3%) was recorded in April, a dry and warm month with the lowest values of moss thickness and soil moisture. We found no negative effects of moss layer on seedling mortality; indeed, moss appears to slow soil moisture reduction at the critical end of the warm and dry season. Soil and moss moisture values in April seem to be a critical factor for A. religiosa seedling recruitment, and we expect this condition will deteriorate under projected climatic change scenarios. Thus, the potential of MBBR A. religiosa forest to recover by passive restoration is highly constrained and will require management actions to achieve successful restoration outcomes.

Introducción: Los bosques de Abies religiosa (Kunth) Schltdl. & Cham. en la Reserva de la Biosfera Mariposa Monarca (RBMM) sirven como refugio para la mariposa monarca. Objetivo: Determinar la viabilidad del crecimiento de plántulas de regeneración natural de A. religiosa en vivero y la variación genética asociada al gradiente altitudinal entre poblaciones. Materiales y métodos: Se recolectaron plántulas recién germinadas de manera natural en un transecto altitudinal (2 960 a 3 450 m) que abarcó seis poblaciones de la RBMM. Las plantas crecieron durante 18 meses en un vivero a 3 000 m de altitud. Resultados y discusión: La supervivencia promedio de A. religiosa fue de 75 %. Las plantas mostraron diferencias significativas en la supervivencia (P < 0.0001), altura (P = 0.0430) y diámetro basal (P < 0.0001) entre procedencias; las poblaciones de los extremos altitudinales tuvieron los valores más altos.  Conclusión: El trasplante de plantas germinadas de manera natural en el bosque a envases para su crecimiento en vivero es viable. El patrón altitudinal fue atípico, ya que las poblaciones de los extremos altitudinales tuvieron el mejor crecimiento.

Evaluation of the physiological performance of plants as an environmental response is crucial to understand the ecological succession in plant communities and to implement strategies that increase plant survival and growth for restoration efforts and commercial plantations; however, evaluating plant physiology often requires complex and expensive technical equipment not normally accessible to all researchers and non-specialized people. In the present study, we explored the relationship of the visual condition of the needles with an indicator of their photosynthetic capacity related to chlorophyll content in Abies religiosa. A visual stress index was developed to evaluatethe response to environmental stress in seedlings of A. religiosa during a reforestation effort, and the correlation between leaf chlorophyll content and different categories of the stress index. The replicability of the index was also tested to determine its applicability by non-specialized people. A high correlation was detected between the index and chlorophyll concentration (r2 = 0.76; P < 0.0001). Additionally, there was a significant agreement on the index among several observers (W = 0.95; P < 0.0001). Overall, the stress index is related the physiological condition of the plants and can be adopted by people, after training, to make evaluations of the physiological status of A. religiosa seedlings.

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