Spatial and temporal dynamics of two cacti seed banks in a xerophytic shrubland in Mexico City

Background: Soil and aerial seed banks directly affect recruitment in plant populations. Soil banks result as the balance between seed inputs and outputs. Seed bank dynamics vary by species and environmental conditions. Few records on cacti seed banks are available. Questions: What types of seed banks do two cacti genera form in a lava-field reserve? Does seasonality influence the seed bank dynamics? Are inputs and outputs associated to the microenvironment? Studied species: Opuntia tomentosa, O. lassiacantha, Mammillaria haageana subsp. san-angelensis, M. magnimamma. Study site and dates: Xerophytic shrubland in the “Reserva Ecológica del Pedregal de San Ángel” in Mexico City. 2016 to 2018. Methods: We collected soil samples from four microenvironments during the rainy and the dry seasons, searched for seeds and tested their viability. We compared the number of inputs, outputs and viable seed by microenvironment and season. For M. magnimamma, each month we registered fruit maturation and searched for seeds remaining between tubercles. Results: Opuntia seed bank inputs occurred in all microenvironments and in both seasons. Rain favored inputs in hollows by secondary seed dispersal. We registered a large number of outputs caused by germination, granivory and loss of viability. Opuntia seed bank was developed in headland, plain and slope. No Mammillaria seed inputs were found, neither an aerial bank in M. magnimamma. Conclusion: Opuntia seed banks were restricted to microenvironments that provided “safe sites” which stored viable seeds. Mammillaria seed dynamics may hinders recruitment for their populations.

Seed bank persistence and germination of chinee apple (Ziziphus mauritiana Lam.)

Chinee apple (Ziziphus mauritiana Lam.) is a thorny tree that is invading tropical woodlands of northern Australia. The present study reports three experiments related to the seed dynamics of chinee apple. Experiment 1 and 2 investigated persistence of seed lots under different soil types (clay and river loam), levels of pasture cover (present or absent) and burial depths (0, 2.5, 10 and 20 cm). Experiment 3 determined the germination response of chinee apple seeds to a range of alternating day/night temperatures (11/6°C up to 52/40°C). In the longevity experiments (Expts 1 and 2), burial depth, soil type and burial duration significantly affected viability. Burial depth had the greatest influence, with surface located seeds generally persisting for longer than those buried below ground. Even so, no viable seeds remained after 18 and 24 months in the first and second experiment, respectively. In Expt 3 seeds of chinee apple germinated under a wide range of alternating day/night temperatures ranging from 16/12°C to 47 /36°C. Optimal germination (77%) occurred at 33/27°C and no seeds germinated at either of the lowest (11/6°C) or highest (52/40°C) temperature regimes tested. These findings indicated that chinee apple has the potential to expand its current distribution to cooler areas of Australia. Control practices need to be undertaken for at least two years to exhaust the seed bank.

A reaction–diffusion model of forest boundary with seed dynamics

The density of forest cover based upon reaction–diffusion model for mono-species of two age classes with seed dynamics is to be attempted. The prevailing densities of young, old species and airborne seedlings are resolved by homotopy perturbation method which is applied in reaction–diffusion model. This model is utilized to verify the effect of the density of forest cover with the following variables namely seed reproduction, seed deposition, seed establishment rates, coefficients of aging of old tree and coefficients of mortality on the space variable.

Seed dynamics of two fire-dependent Geranium species in the boreal forest of southeastern Sweden

We analyzed critical life-history variables for two rare fire-dependent annual Geranium species in southern Sweden, which are today threatened because of effective fire suppression. At recently burned sites with abundant recruitment, seedlings occurred only where the humus layer had been completely removed by smoldering fire. Emergence depths ranged 1–6 cm in the mineral soil. Soil sampling at four sites revealed that in unburned soil Geranium seeds were located only in the mineral soil. Surprisingly, residual seeds were still present where fire had burned away the humus layer. An experiment showed that both species deposit seeds relatively evenly within a radius of 5–6 m, through ballistic dispersal. Repeated sampling in the field over a 2-year period after seed dispersal at one site indicated a low rate of seed depletion, corroborated by an indoor incubation of seeds. Our results show that successful management of these species depend on deep-burning prescribed fire, which can only result after severe drought. On the other hand, the seed bank is extremely long-lived, as viable seeds were present at a site last burned 200 years ago. This well-protected seed bank will likely buffer against both ill-timed fires and occasional failure in the recruiting seedling populations.