Canopy seed bank explained

A seed bank stores seeds from plants and is significant in preserving plant genetic diversity.^[1] Seed banks can be categorized according to their location and the ecological functions they serve. The primary types include soil seed banks, which are found in terrestrial environments; wetland seed banks, located in aquatic habitats; and canopy seed banks, present in the upper layers of forest ecosystems.^{[2] [3]} This process is particularly important for sustainable management and conservation of plant biodiversity.^{[8] [11]} These plant species can store seeds in closed fruits or cones for days to decades until environmental changes are triggered during events such as wildfires and proper growing conditions.^[12] After a year or two, the widely dispersed seed starts the germination process and regeneration of species affected in the disturbed areas.These plant species are often found in fire-prone environments such as Proteaceae species in Australiadioecious species in South Africaand Pine species in the US.

The serotiny levels of species found in specific locations are related to the fire history of those areas as fire is one the most common disturbances faced by plants. These plant species can retain seeds within their canopy for extended periods, eventually leading to the formation of canopy seed banks. Other factors aside from fire disturbances that affect the serotiny levels in plant species include the age of plants, soil quality, environmental stress and season changes in the environment.

Methods of seed bank detection

Research studies, aimed at determining the existence and characteristics of canopy seed banks in plants typically employ a variety of methods, including:

1. Plant species and sample site selection: This involves collecting samples from the canopy of the plant species across various locations of the sample site
2. Seed counting: After collecting the seed from each cone of the sample selected, the number of seeds is counted to calculate the baseline seed density.
3. Density calculation: The density of the canopy is calculated as the total number of seeds in the plot divided by the measured canopy area.
4. Extrapolation: Using the data gathered from the samples collected, the seed density of the selected site can be extrapolated to estimate the seed bank size for the entire canopy.
5. Statistical analysis: Statistical methods are used to analyse the data, compare the means, and determine the seed bank of estimates of plants. These statistical methods include t-test distribution, one-way analysis of variance (ANOVA) and regression modelling.

Significance of Canopy seed bank

Several authors have highlighted the significance of canopy seed bank and their critical roles in ecosystems dynamics, which include preserving crop diversity, protecting the environment from the impacts of climate change, safeguarding against natural and man-made disasters, shielding plants from infectious and destructive diseases, providing seeds for research purposes and ensuring low predation and competition for their species.

Notes and References

1. Jui Ray & Sanjoy Kumar Bordolui. (2021). Role of Seed Banks in the Conservation of Plant Diversity and Ecological Restoration. https://doi.org/10.5281/ZENODO.4922618
2. Leck, M. A. (1989). Wetland Seed Banks. In Ecology of Soil Seed Banks (pp. 283–305). Elsevier. https://doi.org/10.1016/B978-0-12-440405-2.50018-X
3. Enright, N. J., Marsula, R., Lamont, B. B., & Wissel, C. (1998). The ecological significance of canopy seed storage in fire-prone environments: A model for non-sprouting shrubs. Journal of Ecology, 86(6), 946–959. https://doi.org/10.1046/j.1365-2745.1998.00312.x
4. Peeler, J. L., & Menges, E. S. (2018). Effects of fire history, tree age, and canopy seed bank size on serotiny of Ocala sand pine (Pinus clausa var. Clausa) in Florida scrub. Florida Scientist.
5. Tapias, R., Gil, L., Fuentes-Utrilla, P., & Pardos, J. A. (2001). Canopy seed banks in Mediterranean pines of south-eastern Spain: A comparison between Pinus halepensis Mill., P. pinaster Ait., P. nigra Arn. and P. pinea L. Journal of Ecology, 89(4), 629–638. https://doi.org/10.1046/j.1365-2745.2001.00575.x
6. Ayre, D., O'Brien, E., Ottewell, K., & Whelan, R. (2010). The accumulation of genetic diversity within a canopy-stored seed bank. Molecular Ecology, 19(13), 2640–2650. https://doi.org/10.1111/j.1365-294X.2010.04677.x
7. Csontos, P. (2007). Seed banks: Ecological definitions and sampling considerations. Community Ecology, 8(1), 75–85. https://doi.org/10.1556/ComEc.8.2007.1.10 Each type of seed contributes uniquely to plant biodiversity, ecosystem resilience and human well-being. Also, they are unique in the way they retain their seed. For example, in canopy seed banks or aerial seed banks, the seeds are stored in the canopies of trees and plants.^[3]

   Canopy seed banks are defined as the aggregates of the seed that are stored in the upper layer known as the canopy in plants.

   Article body

   Plants with canopy seed bank stores their seeds in branches, pods, and other structures of plants. Ecological disturbances in the ecosystem have led some plants to develop adaptive strategies such as retaining seeds and delaying the seed release.^[4] This ability of these plants to store seeds long-term is one of the main adaptation methods they have developed particularly against recurrent fires.^[5] Additionally, after disturbances, such as fire have occurred, the plant species will release the retained seeds into the ground to germinate at certain seasonal conditions that signal the appropriate time for seedling establishment.^[6]

8. Su, W., Yu, J., Zhang, G., Shi, Z., Wang, L., Zhao, G., & Zhou, R. (2019). Comparison of the canopy and soil seed banks of Pinus yunnanensis in central Yunnan, China. Forest Ecology and Management, 437, 41–48. https://doi.org/10.1016/j.foreco.2019.01.002
9. Bond, W. J. (1985). Canopy-stored seed reserves (serotiny) in Cape Proteaceae. South African Journal of Botany, 51(3), 181–186. https://doi.org/10.1016/S0254-6299(16)31669-6
10. Teste, F. P., Lieffers, V. J., & Landhäusser, S. M. (2011). Viability of forest floor and canopy seed banks in Pinus contorta var. Latifolia (Pinaceae) forests after a mountain pine beetle outbreak. American Journal of Botany, 98(4), 630–637. https://doi.org/10.3732/ajb.1000252 Maternal plants with the ability to maintain canopy seed banks actively store and protect their seeds at an elevated position within the canopy. This strategic placement ensures that in the event of severe disturbances such as wildfires which may result in the death of some or all adult plants, the seeds are well-positioned for dispersal, thereby preserving the genetic diversity of the species.

    The soil seed banks and seeds found on forest floors are less protected compared to the canopy seed banks, particularly during disturbances.^[8] In contrast, seeds stored in the canopy are protected both before and during disturbances. During these severe disturbances, the seed banks within the canopy are expected to be triggered and dispersed widely. After such disturbances, these seeds can be released into the ground, thereby serving as a reliable source for the establishment of new seedlings. This mechanism serves as a critical survival strategy, enabling the species to endure and regenerate following significant environmental challenges and ensure population restoration.

    Serotiny

    Canopy seed bank is often associated with serotinous species. The ability of some plant species to retain seeds in protective structures and delay the release of mature seeds is known as serotiny.^[9]

11. Harris, M. S., & Pannell, J. R. (2010). Canopy seed storage is associated with sexual dimorphism in the woody dioecious genus Leucadendron. Journal of Ecology, 98(2), 509–515. https://doi.org/10.1111/j.1365-2745.2009.01623.x
12. Nadkarni, N. M., & Haber, W. A. (2009). Canopy Seed Banks as Time Capsules of Biodiversity in Pasture-Remnant Tree Crowns. Conservation Biology, 23(5), 1117–1126. https://doi.org/10.1111/j.1523-1739.2009.01235.x