Mast is the
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
of
forest
A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
tree
In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
s and
shrub
A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
s, such as
acorns and other
nuts.
The term derives from the Old English ''mæst'', meaning the nuts of forest trees that have accumulated on the ground, especially those used historically for fattening
domestic pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
s, and as food resources for wildlife.
In the aseasonal tropics of Southeast Asia, entire forests, including hundreds of species of trees and shrubs, are known to mast at irregular periods of 2–12 years.
More generally, mast is considered the edible vegetative or reproductive parts produced by woody species of plants, i.e. trees and shrubs, that wildlife and some domestic animals consume as a food source. Mast is generated in large quantities during long-interval but regularly recurring
phenological
Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors (such as elevation).
Examples include the date of emergence of leaves ...
events known as mast seeding or masting.
Such events are
population
Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
-level phenomena hypothesized to be driven by a wide variety of factors, depending on the plant species involved, including availability of nutrients,
economies of scale
In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...
, weather patterns, and as a form of
predator satiation
Predator satiation (less commonly called predator saturation) is an anti-predator adaptation in which prey briefly occur at high population density, population densities, reducing the probability of an individual organism being eaten.
When predati ...
.
In turn, these pulses of masting contribute to many ecosystem-level functions and dynamics.
Types of mast
![Quercus coccifera (acorns)](https://upload.wikimedia.org/wikipedia/commons/e/e7/Quercus_coccifera_%28acorns%29.jpg)
Mast can be divided into two basic types: hard mast and soft mast. Tree species such as
oak
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
,
hickory, and
beech
Beech (''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia, and North America. Recent classifications recognize 10 to 13 species in two distinct subgenera, ''Engleriana'' and ''Fagus''. The ''Engle ...
produce a hard mast—
acorns, hickory nuts, and beechnuts.
It has been traditional to turn
pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...
s loose into forests to fatten on this form of mast in a practice known as
pannage.
Other tree and shrub species produce a soft mast, such as
raspberries
The raspberry is the edible fruit of a multitude of plant species in the genus ''Rubus'' of the rose family, most of which are in the subgenus '' Idaeobatus''. The name also applies to these plants themselves. Raspberries are perennial with ...
,
blueberries, and
greenbriar.
Mast seeding
Mast seeding (or mast reproduction) is defined as the highly variable annual production of
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
by a population of trees and/or shrubs.
These intermittent pulses of food production drive ecosystem-level functions and forest dynamics.
The difference between a mast seeding year and a non-mast seeding year can be thousands of acorns, hickory nuts, beech nuts, etc.
Mast seeding predominantly occurs in
wind-pollinated
Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are many plants in the order Poales, including grasses, sedges, and rushes. Other common anemophilous pla ...
tree species, but has also been observed in
grass
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...
es and
Dipterocarp
Dipterocarpaceae is a family of 16 genera and about 695 known species of mainly tropical lowland rainforest trees. The family name, from the type genus ''Dipterocarpus'', is derived from Greek (''di'' = two, ''pteron'' = wing and ''karpos'' = f ...
s.
Hypotheses for the evolution of mast seeding can broadly be assigned to three categories: economies of scale, resource matching, and proximate cues (i.e. weather).
Economies of scale
The
predator satiation
Predator satiation (less commonly called predator saturation) is an anti-predator adaptation in which prey briefly occur at high population density, population densities, reducing the probability of an individual organism being eaten.
When predati ...
hypothesis states that predator populations may be effectively controlled from year to year by inconsistent pulses of food made available by their prey. For predators of plant communities whose prey are the fruits and seeds produced by the plants, it has been proposed that periodic mast seeding events may be an example of this strategy. Producing excessive quantities of fruits and seeds in mast seeding years may over-satiate seed predators to the point that a small proportion of seeds can escape consumption, while a lack of seed production keeps predator populations low in the intervening years. In plant communities with a local abundance of
frugivores, large seed releases can effectively exceed seed predation and improve the chance of successful establishment of seeds in future seasons.
The pollination efficiency hypothesis suggests that mast seeding may optimize successful pollination and thus fertilization if all individuals within a population are reproductively synchronized. This hypothesis is especially relevant for wind-pollinated species, which many mast seeding species are. Both hypotheses are based on the assumption that large and variable reproductive effort is more efficient than small, consistent reproductive effort,
which ultimately leads to higher
fitness for the masting population.
Resources and weather
The resource matching hypothesis states that reproduction varies with availability of the resources necessary to reproduce, which is often an energetically and nutritionally expensive action.
The main limiting resources include water, carbon in the form of nonstructural carbohydrates, and nutrients such as nitrogen and phosphorus.
These resources have been shown to be depleted after mast seeding across multiple species.
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 in any given season.
The effects of local weather on mast seeding are 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;
such cues included spring temperature, summer drought, and spring frost.
These weather variables are associated with critical times for fruit maturation and fertilization.
Consequences
Mast seeding provides an abundant food source not only for wildlife but also for domestic animals and animals prone to population explosions such as
mice
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
,
rats, and
stoat
The stoat (''Mustela erminea''), also known as the Eurasian ermine, Beringian ermine and ermine, is a mustelid native to Eurasia and the northern portions of North America. Because of its wide circumpolar distribution, it is listed as Least Conc ...
s, whose populations can increase significantly during a mast year, having been reduced by a lack of food in previous non-mast years.
In turn, this makes it more likely that birds subsequently will be targeted by the pests, or that rats will invade nearby fields in what is called a "
rat flood
Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...
".
Mast seeding has been shown to have both positive and negative effects on ecosystems. An example of this is the
white-footed mouse
The white-footed mouse (''Peromyscus leucopus'') is a rodent native to North America from Ontario, Quebec, Labrador, and the Maritime Provinces (excluding the island of Newfoundland) to the southwestern United States and Mexico. In the Maritimes, ...
.
When a mast seeding event occurs, the population of white-footed mice also increases, which has been shown in turn to increase instances of
Lyme disease
Lyme disease, also known as Lyme borreliosis, is a vector-borne disease caused by the ''Borrelia'' bacterium, which is spread by ticks in the genus ''Ixodes''. The most common sign of infection is an expanding red rash, known as erythema migran ...
, since these mice are hosts for
tick
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...
s, the disease's primary vector. A positive effect of increased white-footed mouse population is that they prey on
Spongy moths, which are a major forest pest in the eastern United States.
The interaction between disturbance by fire and mast seeding is key to
white spruce White spruce is a common name for several species of spruce ('' Picea'') and may refer to:
* ''Picea glauca'', native to most of Canada and Alaska with limited populations in the northeastern United States
* '' Picea engelmannii'', native to the ...
regeneration and subsequent stand dynamics in the
boreal mixed-wood forest. Peters et al. (2005)
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)
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.
The interaction of mast seeding, climate, and tree growth creates notable effects in
tree ring chronologies, and in many tree species reduced growth has been observed in mast years.
Mast seeding under climate change
Many mast seeding species are considered
foundation species
In ecology, the foundation species are species that have a strong role in structuring a community. A foundation species can occupy any trophic level in a food web (i.e., they can be primary producers, herbivores or predators). The term was coined ...
. Predicting how the intensity and frequency of mast seeding may be altered by
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
will help researchers to determine shifts in the availability of food resources to wildlife and forest dynamics.
Mast seeding has become more variable globally during the last century, although the drivers of these long-term changes in mast seeding have not been fully identified. For example, in Europe, mast seeding intensity appears to be linked to the mode of the
North Atlantic Oscillation
The North Atlantic Oscillation (NAO) is a weather phenomenon over the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level (SLP) between the Icelandic Low and the Azores High. Through fluctuations in the ...
, and in tropical south Asia, mast events appear to be linked to the
El Niño–Southern Oscillation
El Niño–Southern Oscillation (ENSO) is an irregular periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. The warming phase of the sea te ...
.
See also
*
Pannage
*
Phenology
*
Seed tree
References
External links
{{wiktionary, mast
Mast Tree NetworkAsh Tree Mast Year
Edible nuts and seeds
Fruit morphology