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Mast seeding

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Mast seeding is defined as the highly variable production of fruit by a population[1]. These intermittent pulses of food resources drive ecosystem-level functions and forest dynamics[2]. The difference between a mast seeding year and a non-mast seeding year can be thousands of acorns, hickory nuts, beech nuts, etc[2]. Mast seeding dominantly occurs in wind-pollinated tree species, but has also been observed in grasses and Dipterocarps[1],[3].

Masting, in the strict sense of the term, occurs only in monocarpic (or semelparous) species, whose members reproduce only once during their lifetime, then die.[4]

Hypotheses

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Hypothesis for the evolution of mast seeding can broadly be assigned to: economies of scale, resource matching, and proximate cues (i.e. weather)[5].

Economies of Scale

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The predator satiation hypothesis states that predator populations are controlled by inconsistent pulses of resources, over satiating seed predators in mast seeding years to allow a proportion of seeds to escape, while a lack of resources keeps predator populations low in intervening years[6]. In plant communities with a local abundance of frugivores, large seed releases can effectively exceed seed predation and improve the chance of successful establishment[7]. The pollination efficiency hypothesis states that mast seeding would be selected for to optimize successful pollination and thus fertilization if all individuals within a population synchronized reproductively[8]. This hypothesis is especially relevant for wind-pollinated species, which many mast seeding species are. Both hypotheses are based on the assumption that variable and large reproductive effort is more efficient than small consistent reproductive effort[3] [9], which will lead to higher fitness within a population[3].

Resources and Weather

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The resource matching hypothesis states that reproduction varies with availability of resources[1]. Main limiting resources include water, carbon in the form of nonstructural carbohydrates, and nutrients such as nitrogen and phosphorous[9]. These resources have been shown to be depleted after mast seeding across multiple species[9].

Weather is categorized as a proximate driver of mast seeding, meaning that in combination with resources and economies of scale, various weather parameters can have an effect on the probability of mast seeding occurring[9]. The effect of weather on mast seeding is highly variable depending on species and geographic location. For some species of oak, mast seeding was shown to be influenced by regional weather-related cues on phenology[10]. Cues included spring temperature, summer drought, and spring frost[10]. These weather variables are associated with critical times for fruit maturation and fertilization.

Consequences

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Mast seeding provides food for animals like mice, rats and stoats, whose populations can explode during a mast year, having been reduced by a lack of food in previous non-mast years[2]. In turn, this makes it more likely that birds subsequently will be targeted by the pests,[11] or that rats will invade nearby fields in what is called a "rat flood".[12] Mast seeding has been shown to have both positive and negative effects on an ecosystem. An example of this is the white-footed mouse[13]. When a mast seeding event occurs, the population of white-footed mice also increases, which has shown to increase instances of Lyme's disease since these animals are the main vectors. The positive effect of increased white-footed mouse population is that they predate on Gypsy moths, which are a major forest pest in the eastern U.S.[13]

The interaction between disturbance by fire and mast seeding is key to white spruce regeneration and subsequent stand dynamics in the boreal mixed-wood forest. Peters et al. (2005)[14] found significantly higher densities of white spruce in stands originating from fires that coincided with mast years than from fires coinciding with years of low cone crops. While noting that previous studies had assessed a three- to five-year window of opportunity for obtaining white spruce regeneration after fire before seedbed deterioration closed it, Peters et al. (2005)[14] adduced three lines of evidence to support their claim that the importance of the fire × mast-year interaction hinges on the rapid deterioration of the seedbed, even within one year after fire. Rapid seedbed deterioration is likely to augment the mast-year effect for white spruce as compared with species that are less dependent on short-lived, disturbance-created regeneration microsites. Seed limitation, as well as seedbed deterioration, influences age structure in white spruce. Mast-year effects on the density of white spruce are long-lasting; 40 years after fire, mast-year fires still had 2.5 times more spruce regeneration than non-mast-year fires.[14]

Mast Seeding under Climate Change

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Many mast seeding species are considered foundational species[15]. Predicting how the intensity and frequency of mast seeding may be altered under climate change will help researchers to determine shifts food resources availability to wildlife and forest dynamics[16],[17].

  1. ^ a b c Norton, D. A.; Kelly, D. (1988). "Mast Seeding Over 33 Years by Dacrydium cupressinum Lamb. (rimu) (Podocarpaceae) in New Zealand: The Importance of Economies of Scale". Functional Ecology. 2 (3): 399. doi:10.2307/2389413. ISSN 0269-8463.
  2. ^ a b c Ostfeld, Richard S.; Keesing, Felicia (2000). "Pulsed resources and community dynamics of consumers in terrestrial ecosystems". Trends in Ecology & Evolution. 15 (6): 232–237. doi:10.1016/s0169-5347(00)01862-0. ISSN 0169-5347.
  3. ^ a b c Kelly, Dave; Sork, Victoria L. "Mast Seeding in Perennial Plants: Why, How, Where?". Annual Review of Ecology and Systematics. 33 (1): 427–447. doi:10.1146/annurev.ecolsys.33.020602.095433.
  4. ^ Strobilanthes callosus; Botany Photo of the Day. Notes posted by Daniel Mosquin. January 13, 2009.
  5. ^ BURNS, K. C. (2011-06-06). "Masting in a temperate tree: Evidence for environmental prediction?". Austral Ecology. 37 (2): 175–182. doi:10.1111/j.1442-9993.2011.02260.x. ISSN 1442-9985.
  6. ^ Koenig, Walter; Knops, Johannes (2005). "The Mystery of Masting in Trees". American Scientist. 93 (4): 340. doi:10.1511/2005.4.340. ISSN 0003-0996.
  7. ^ Kelly, Dave; Sork, Victoria L. "Mast Seeding in Perennial Plants: Why, How, Where?". Annual Review of Ecology and Systematics. 33 (1): 427–447. doi:10.1146/annurev.ecolsys.33.020602.095433.
  8. ^ Kelly, Dave; Hart, Deirdre E.; Allen, Robert B. (2001). "Evaluating the Wind Pollination Benefits of Mast Seeding". Ecology. 82 (1): 117. doi:10.2307/2680090. ISSN 0012-9658.
  9. ^ a b c d Pearse, Ian S.; Koenig, Walter D.; Kelly, Dave (2016-08-01). "Mechanisms of mast seeding: resources, weather, cues, and selection". New Phytologist. 212 (3): 546–562. doi:10.1111/nph.14114. ISSN 0028-646X.
  10. ^ a b Sork, Victoria L.; Bramble, Judy; Sexton, Owen (1993). "Ecology of Mast-Fruiting in Three Species of North American Deciduous Oaks". Ecology. 74 (2): 528–541. doi:10.2307/1939313. ISSN 0012-9658.
  11. ^ Reich, Josh (16 January 2009). "Trappers face pest population explosion". The Nelson Mail. Retrieved 2009-02-11.
  12. ^ Normile, D. (February 2010). "Holding back a torrent of rats". Science. 327 (5967): 806–7. doi:10.1126/science.327.5967.806. PMID 20150483.
  13. ^ a b Ostfeld, Richard S.; Jones, Clive G.; Wolff, Jerry O. (1996). "Of Mice and Mast". BioScience. 46 (5): 323–330. doi:10.2307/1312946. ISSN 0006-3568.
  14. ^ a b c Peters, Vernon S.; Macdonald, S. Ellen; Dale, Mark R. T. (2005). "The interaction between masting and fire is key to white spruce regeneration". Ecology. 86 (7): 1744–1750. doi:10.1890/03-0656. JSTOR 3450618.
  15. ^ MCSHEA, WILLIAM J.; HEALY, WILLIAM M.; DEVERS, PATRICK; FEARER, TODD; KOCH, FRANK H.; STAUFFER, DEAN; WALDON, JEFF (2007). "Forestry Matters: Decline of Oaks Will Impact Wildlife in Hardwood Forests". Journal of Wildlife Management. 71 (5): 1717–1728. doi:10.2193/2006-169. ISSN 0022-541X.
  16. ^ Graumlich, Lisa J. (1993). "Response of tree growth to climatic variation in the mixed conifer and deciduous forests of the upper Great Lakes region". Canadian Journal of Forest Research. 23 (2): 133–143. doi:10.1139/x93-020. ISSN 0045-5067.
  17. ^ Koenig, Walter D.; Knops, Johannes M. H. (2013-10-12). "Environmental correlates of acorn production by four species of Minnesota oaks". Population Ecology. 56 (1): 63–71. doi:10.1007/s10144-013-0408-z. ISSN 1438-3896.
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