Safe microsites for Symphoricarpos microphyllus (Caprifoliaceae) germination, a shrub species with seed dormancy

Abstract

Background and Aims: Temperate forests suffer continuous deforestation and other anthropogenic disturbances. Additionally, some types of forest management, such as secondary vegetation removal ("chaponeo"), can be another disturbance that negatively affects the values of some environmental variables important for seed germination. Light, soil temperature and moisture characterize microsites and determine germination percentages. These variables are also affected by slope orientation and vegetation structure. The aim of this study was to characterize microsites for Symphoricarpos microphyllus seed germination in a temperate forest, its response to light qualities in germination cameras, and seed viability during two years.Methods: Twenty-four microsites that differed according to their position in north/south (N/S) facing slopes, and by the presence/absence of secondary vegetation (“chaponeo”) due to forest management (U-undisturbed/P-perturbed) were characterized for light, soil temperature, moisture, pH and nitrogen. We also studied germination under different light qualities (white light, red light, far red light -FRL-, darkness) in germination cameras and seed viability for two years.Key results: All microsites were different in light, temperature and soil moisture. Microsites with the highest germination percentages were those US (undisturbed south) and UN (undisturbed north), where higher soil moisture and lower temperatures were registered, favoring embryo growth of seeds, since they possess morphophysiological dormancy. In cameras, germination percentages were the highest in FRL (32%). Seeds of S. microphyllus can remain viable for two years (60%).Conclusions: We do not recommend secondary vegetation removal because it affects variables of soil moisture (decreasing it) and temperature (increasing it) in microsites. This negatively influences this species germination, which needs a filtering of light and an alternation of high-low temperatures for dormancy breaking. These findings are important if we consider that the populations of this species are reducing due to overexploitation.

Germination Response of Two Shrub Species Under Controlled Conditions and to Secondary Vegetation Removal (Weeding) in the Magdalena River Basin, Mexico

“…However, GSF did show significant effects for A. glabrata meaning that as most secondary species, it is highly responsive to gap openings (Redwood et al, 2016), In terms of the light requirements for the germination of both species, S. angulifolius showed the highest germination percentages in FR light conditions in growth chambers. Other shrub species in this study area have been reported to germinate in high percentages in FR light as well (Martínez-Camacho et al, 2018;Martínez-Orea et al, 2019). In field conditions, germination was the highest for both species at US microsites, where RL values were higher than FRL.…”

“…Although seeds were sown when mature and right after collection and during dispersal times, the best temperatures for germination are most likely reached in June, when temperatures of 20-25°C have been recorded (Vázquez-Santos et al, 2019 in press) at this study site and when soil moisture values reach 100%, during the onset of the rainy season, therefore seed germination can vary between seasons independently from seed maturity (Baskin and Baskin, 1998). Although seeds of many species will germinate at constant temperatures, the germination of many shrub species increases due to temperature fluctuations (Zambino, 2010;Martínez-Orea et al, 2019). Another factor that could explain the low germination percentages registered could be the presence of primary seed dormancy.…”

“…According to some authors, in small seed species (~3 mm long, such as the studied species), a microsite may be no more than a few centimeters in diameter (Fowler, 1988). Microsites do not form a continuum in a forest, and differences in micro environmental variables will arise due to forest complexity at different scales, which can occur naturally but also, they can be influenced by some silvicultural practices and disturbances (Caviedes and Ibarra, 2017;Martínez-Orea et al, 2019).…”

“…Germination and establishment of secondary species are crucial for forest regeneration and will respond to environmental variables, such as the light that reaches the forest floor through canopy gaps, soil temperature, moisture (Matlack, 1993) as well as the structure and texture of forest floor that often represents an obstacle for seeds for reaching the soil (Benvenuti and Mazzoncini, 2019). Although secondary species have been reported as abundant or common under some perturbation regimes (Calderón and Rzedowski, 2005); the characterization of safe microsites for their germination might be important for conservation plans (Evans and Young, 1984;Martínez-Orea et al, 2019). Not only slope orientation but also some disturbances can influence microsites causing differences in moisture, temperature, and light compared to conserved sites (Linding and Zedler, 2002;Martínez-Orea et al, 2019).…”

“…Although secondary species have been reported as abundant or common under some perturbation regimes (Calderón and Rzedowski, 2005); the characterization of safe microsites for their germination might be important for conservation plans (Evans and Young, 1984;Martínez-Orea et al, 2019). Not only slope orientation but also some disturbances can influence microsites causing differences in moisture, temperature, and light compared to conserved sites (Linding and Zedler, 2002;Martínez-Orea et al, 2019). For example, Chen et al (1999) found differences in air temperature of up to 6 °C between conserved sites and forest edges in a Pseudotsuga menziesii forest in North America (Washington).…”