Seed Dispersal
Autumn is a season of travelers. Birds migrate south. Deer, elk and antelope move to their wintering grounds. Many plants finish maturing seeds designed for transport to favorable new habitats. Seeds come in a kaleidoscope of shapes and sizes: their structure reveals their means of dispersal.
Many plants rely on the wind to loft their seed to fertile ground. Due to wind’s fickle nature, few of these seeds actually make it to a suitable site, so to compensate they are produced in abundance. Some seeds, like those of dandelion and milkweed, have a downy fluff which floats aloft with the slightest breeze. Others utilize wing-like appendages on the seed capsule, as in maple, ash and pines. The seed is heavier than the blade shaped wing, causing a spiraling motion which propels seeds farther than mere drifting.
Another strategy for seed dispersal is to entice animals to ingest the seed. Some plants like cherries, junipers and grapes do this by imbedding their seeds in a nutritious and tasty pulp. Others, like many grasses, achieve the same end by the placement of the seeds. As grazers consume the foliage, they inadvertently ingest seeds at the same time. Hopefully the seeds end up some distance from the parent plant, deposited in their own dollop of manure to aid seedling growth. Some seeds require a trip through the digestive tract, where the impervious seed coat is eroded away so that the seed can absorb water and germinate. Ants disperse seeds that have a patch of nutritious tissue, the aril, that they gnaw off before discarding the seed.
Another means of dispersal relies on a chance encounter to hitch a ride in an animal’s fur. The seed coat has clinging hooks, hairs or spines that latch onto fur or clothing. Many noxious weeds including burdock, hound’s tongue and cheatgrass use this type of dispersal, so be careful where you groom and dispose of their seed.
Grasses don’t run and pines don’t roam, but plant seeds have many tricks to gain mobility.
This is Linda Kervin for Bridgerland Audubon Society.
Credits:
Images: Courtesy & Copyright Jim Cane &
Courtesy & Copyright Linda Kervin
Text: Linda Kervin, Bridgerland Audubon Society
Additional Reading:
Seed Dispersal
https://andromeda.cavehill.uwi.edu/Dispersal.htm (archived link)
Wind Dispersal
https://www2.palomar.edu/users/warmstrong/plfeb99.htm
Seed Dispersal by Animals
https://www.cnr.uidaho.edu/range556/…
Amazing Adaptations of Utah’s Desert Plants
Hi, this is Mark Larese-Casanova from the Utah Master Naturalist Program at Utah State University Extension.
Anyone who lives in Utah knows that it’s a dry state. In fact, around three-quarters of our state is considered desert. A desert is often characterized as an area that receives less than ten inches of precipitation each year. But, high levels of evaporation, which are influenced by temperature, wind speed, and solar radiation, also contribute to creating a dry desert ecosystem.
So, how exactly are plants able to survive in Utah’s deserts, which are so dry? It turns out that the plants that grow and flourish in Utah’s deserts have an amazing array of adaptations for survival.
Many shrubs and trees, such as desert willow, and certain species of sagebrush and mesquite, have thick taproots that grow deep into the soil to reach groundwater. This helps the plants survive the hot, dry summer. Some mesquite taproots have been found to grow as deep as 200 feet to reach a constant water supply.
Cacti, such as the various types of prickly pear, have almost an opposite adaptation. They produce dense tufts of fibrous roots just below the surface of the soil. This allows cacti to quickly absorb water from brief rainstorms, and then store the water in their thick, succulent leaves.
As temperature increases, desert plants face the danger of excessive water loss from their leaves. A thick, waxy coating on the outside of leaves often helps to retain water. The shiny wax also reflects sunlight to keep the leaves relatively cooler. To further reduce leaf temperature and water loss, some plants, such as brittlebush, grow light-colored dense ‘hairs’ on their leaves and stems. These trichomes not only shade the plant, but also aid in absorbing water from morning dew.
If temperatures get too hot, and drought stress too great, some plants, such as creosote bush and ocotillo, may drop their leaves several times each year to ensure survival. Some of these plants have green chlorophyll in their stems so they can still produce food through photosynthesis when there are no leaves on the plant.
While this is just a sample of an amazing collection of adaptations, it’s clear that desert plants are champions of survival in a harsh ecosystem where water is so scarce.
For Wild About Utah, I’m Mark Larese-Casanova.
Credits:
Images: Courtesy & Copyright Mark Larese-Casanova
US FWS images.fws.gov
Text: Mark Larese-Casanova, Utah Master Naturalist Program at Utah State University Extension.
Additional Reading:
Utah’s Desert Dwellers: Living in a Land of Climate Extremes. Wildlife Review. Utah Division of Wildlife Resources
wildlife.utah.gov/wr/0706desert/0706desert.pdf
Deserts. James MacMahon. The Audubon Society Nature guides. 1985. https://www.amazon.com/Deserts-National-Audubon-Society-Nature/dp/0394731395
Natural History of the Colorado Plateau and Great Basin, Harper, St. Clair, Thorne, and Hess (Eds.), 1994. https://www.amazon.com/Natural-History-Colorado-Plateau-Great/dp/0870815113
The Biology of Deserts, David Ward, Oxford University Press, 2009. https://www.amazon.com/Biology-Deserts-Habitats/dp/0199211477