Photo of American Beech tree
Rick Simek
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You may think you’ve raked up the last of your leaves, but if you’re waiting for those oaks and beeches to drop their leaves, you might be waiting a while!
Although they are deciduous trees, these trees have persistent leaves, which remain on the trees into the spring. At this time of year, oak and beech trees are easy to pick out of a crowd, clutching their leaves while others are boldly showing off their silhouettes. So why do our northern deciduous hardwoods drop their leaves in autumn in the first place?
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One function of leaves is to produce food from sunlight. Back in October, when daylight hours noticeably shortened and temperatures dropped, the process of photosynthesis slowed. Shorter days, and lower sun angle mean that less light reaches the trees. Rather than hang onto leaves that have fulfilled their purpose, trees drop their leaves like the temperatures.
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All living trees shed their leaves at some time. At one end of the spectrum are evergreens, which appear to be fully leafed at all times, and at the other end are deciduous trees that lose their leaves seasonally. Unlike evergreens, such as pine and spruce, deciduous trees create a “shutoff valve” in the stem of each leaf called an abscission layer that allows the leaf to fall when the days begin to shorten and temperatures drop. Oaks and beech lack this shutoff valve, so the leaves may remain on the twigs until spring. (Nantucket Conservation).
Somewhere in between are deciduous trees with persistent, or marcescent leaves. The persistent leaf does not readily form an abscission layer at the base of the leaf petiole (leaf stalk), where it attaches to the twig. Typically, leaf marcescence is seen on oaks (Quercus species), American beech (Fagus grandifolia), as well as hornbeam (Carpinus caroliniana), Eastern hophornbeam (Ostrya virginiana), and witchhazels (Hamamelis species).
Do marcescent leaves benefit the trees or hinder them? The evergreens’ strategy is thought to confer an advantage to a tree by increasing the time available for its leaves (needles) to remain photosynthetic and reducing nutrient losses associated with dropped leaves. Conversely, deciduous leaf fall is considered an adaptation that evolved to reduce water loss and frost damage in regions that experience seasonal changes. These are two strikingly different approaches. Each has its advantages and downsides, and over millennia, most species seem to have settled in to being one or the other.
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Despite the fact that retaining leaves can be a liability in areas prone to heavy snow and ice storms, some ecologists suggest that leaf marcescence has adaptive significance for trees growing on dry, infertile sites. Retaining leaves until spring could possibly be a means of slowing the decomposition of the leaves on the ground and that dropping them in spring delivers organic material at a time when it is most needed by the growing parent tree. Even small amounts at the right time could shift the competitive advantage toward these species on poor sites.
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Other ecologists have hypothesized that persistent leaves might provide some frost protection for buds and new twigs over winter. Additionally, at least one study suggested that marcescent foliage could be a deterrent to browsing by deer and moose. Buds hidden by clusters of dead leaves do not get eaten and thus live to become new shoots and leaves in spring.
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Time may tell if marcescence may indeed be helpful to trees living in dry, cold, environments with high deer populations like our Environmental Study Area. But it may also be simply a sign that beech and oak are evolutionarily delayed, still on their way to becoming fully deciduous from their more evergreen past.
(Photo Minnesota Star Tribune.)
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Stewarding our Center in Action and Spirit |
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How many building custodians look at muddy floors as something to gladden the heart? John Berger, for one. John is responsible for the building upkeep of the EIC. He likes to cheerfully point out that the muddy shoe prints left by groups of school children coming indoors after walking the sloshy nature trails during the maple syruping season indicate that they are directly experiencing that very special tradition in our region. This is but one example of John’s year-round enthusiasm, goodwill, and can-do spirit in support of all of our educational programs.
John's dedication to the EIC extends to the outdoors (pictured below with one of our "mushroom logs") as a long-time Center volunteer. He lends the same high level of care and service to improving the health of the Environmental Study Area. This includes his vital assistance in many habitat rehabilitation efforts, such as invasive plant removal, replanting degraded habitat areas with hundreds of native trees and other plants, planting a large prairie garden, and assembling deer exclosures.
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Having volunteered for decades at the Henry Ford Estate, John also serves as a highly knowledgeable and key resource for helping our staff accurately and effectively integrate Henry Ford history into many aspects of the Center’s programming.
John recently was recognized by the university for his 35 years of staff service. At the EIC, we wish to add to that our own grateful recognition of his many years of generous and dedicated work and volunteer service with a smile.
Thank you, John!
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Parkhurst Natural Areas Fellow Courtney Wagner combined her interests in ecology and geospatial technology to study the extent of aquatic invasive Eurasian Watermilfoil in Fair Lane Lake for a class project in Advanced GIS (Geographic Information Systems). Take a look at her Story Map documenting this exciting project using remote sensing and an "unpersoned" aerial vehicle!
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Eagle Scout Oliver Angel Protects Garden Plots |
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For his Eagle Service Project this past summer, Boy Scout Oliver Angel generously lent his time, skills, fundraising efforts, and substantial physical labor to replace the fence around two large garden plots at the UM-Dearborn Community Organic Garden. Oliver and his intrepid crew of fellow Troop members removed the old, dilapidated fences and followed up by installing new fences.
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The on-site project work scene at the garden on an especially toasty summer day with mosquitoes buzzing about the fence-installation volunteers was surely one of determination, grit, and team effort. Oliver also repaired a seating bench at the edge of the garden that enables folks using the nearby Gateway Trail to stop and rest and relax in the pleasant garden surroundings.
We are very grateful that Oliver chose to do his Eagle Project through the EIC and we congratulate him on his well-earned advancement to Eagle Scout!
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In this unusual time, venturing outdoors and encountering nature is even more important. Our trails are accessible, so please visit our Environmental Study Area. Check out our Remote Learning Activities & Resources page for ideas to create a “Neighborhood Nature Journal” and “Family Nature Walk” activities! |
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Please stay safe, stay tuned, and stay engaged in learning activities while we eagerly wait for the opportunities to share experiences together. In the meantime, watch for our new online activities to satisfy your curiosity about the natural world. |
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Please remember...
The EIC Environmental Study Area is open daily from sunrise to sunset. We would like to remind nature-goers that fishing on site is prohibited and to leave bikes and dogs at home because they cause disruption and stress to the EIC wildlife.
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