Abies religiosa Seedling Limitations for Passive Restoration Practices at the Monarch Butterfly Biosphere Reserve in Mexico

Abstract

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.

Recent evidence of Mexican temperate forest decline and the need for ex situ conservation, assisted migration, and translocation of species ensembles as adaptive management to face projected climatic change impacts in a megadiverse country

“…In addition, analysis of the abundance and size (as a proxy of age) of seedlings and saplings undoubtedly indicates a recruitment of seedlings that is insufficient to renew the soon-to-be overaged stands (Guzmán-Aguilar et al 2020). Such insufficient seedling recruitment is more evident in the core zone of the MBBR, at elevations from 3301 to 3550 m a.s.l., where only 3% of individuals were seedlings and 97% were saplings (Fig.…”

Reciprocal Common Garden Altitudinal Transplants Reveal Potential Negative Impacts of Climate Change on Abies religiosa Populations in the Monarch Butterfly Biosphere Reserve Overwintering Sites

“…The forests of A. religiosa can be strongly affected by climatic change-it will induce a decoupling between the populations of A. religiosa and the environment suitable for them, such that by the decade 2090, the models project that suitable climatic habitat for A. religiosa will have disappeared completely from the MBBR [26]. Previous studies have reported that A. religiosa presents a high percentage of non-viable seeds (63-79%) [27,28], in addition to very low recruitment and high mortality of sacred fir seedlings, necessitating the implementation of an active restoration program or other management actions [29]. Additionally, so that the populations of this species can remain coupled to their favorable climatic habitat, their upwards altitudinal displacement of between 300 and 500 m will be necessary by 2060 [30], due to the projected increases in temperature and diminution in precipitation.…”

“…However, to date, no experiments have determined what would happen if young A. religiosa seedlings are exposed to greater temperatures and lower precipitation, as projected in scenarios of climatic change [26,34]. There is also evidence that there are serious difficulties in terms of the natural regeneration of young seedlings, because the warm and dry season of March-May is now more dry and hot than usual, causing a severe mortality of seedlings in April [29]. Although an important genetic differentiation has been demonstrated among populations of A. religiosa for resistance to frost damage along altitudinal gradients [20], a significant genetic differentiation has not been demonstrated among populations for resistance to drought, for example, in the differential accumulation of solutes, such as the amino acid proline, that confer physiological resistance to drought [35,36].…”

Assisted Migration Field Tests in Canada and Mexico: Lessons, Limitations, and Challenges

“…Additionally, a more worrisome sign is that forest decline is already well underway in many forests of the world, linked to heat waves, drought stress, and climate-associated insect and disease outbreaks [19][20][21]45]. For A. religiosa, for example, there is already growing evidence of the lack of regeneration at lower elevations of the species' distribution [108,109]. Thus, we need to avoid inaction because that might make us simply witnesses of an upcoming ecological disaster.…”