Now that the weather has gotten cool and the leaves are off the trees, we humans often think we have to tidy up our landscape. Since there are no more pretty flowers blooming and the colorful red and bronzes of the grasses have subsided, we are tempted to get out the mower and cut everything down. But whoa there! Your natural area still has critical ecological benefits to provide. Here are a few reasons from Minnesota’s Natural Shore Technologies, Inc why it is important to keep your senesced plant material up through the winter and into spring.
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A lonely buck white tail deer walks through the natural landscaping on his way to his morning slumber across the creek. A multitude of animal species are actively looking for food and shelter this time of year. Severe winters present even more challenging conditions. In our urban areas, manicured landscapes, like turf grass lawns, can be considered biological wastelands and make winter tough for animals. On the flip side, restoration areas are critical biological oases. Animals like birds, mice, rabbits and many others rely on native plant seeds for food, and dormant grasses and stalks for shelter to stay warm. Butterflies, bees, moths, beetles, and other insects also use leaf litter and other debris to overwinter, making our native plantings even more important to pollinators.
- Leaving material in your natural landscaping can also be eye-catching when the snow and ice start to fly. Looking outdoors to a winter wonderland and spotting snow-covered Wild Bergamot (Monarda fistulosa) heads and vibrant colored Little Bluestem (Schizachyrium scoparium) along with Red-Twig Dogwood (Cornus sericea) branches seemingly growing out of the snow make us pause and give thanks. Overwintering birds like the Cardinal, Blue Jay and Chickadee also appreciate the nice mix of thanksgiving seeds.
Snow covered native planting left up for the birds and other critters. Photo by Steve Maassen.
- Leaves are a natural fertilizer; phosphorus, nitrogen and other nutrients slowly release into the soil as the leaf material decomposes. Most University Extension Offices now suggest just mulching leaves in lawn areas and letting them sit in natural areas. Taking leaves away, only to add fertilizer to lawns in the summer, wastes resources. Research suggests leaf cover can provide a natural weed barrier.
So fight the urge to cut down and clean up. Instead grab a warm cup of tea, look out the window and know your debris covered natural area will provide very important food and cover for a multitude of animal species, present a pretty picture during a long winter, and provide natural nutrients next spring.
Yes and no. It depends. Heterogeneity rules, some ecosystems require clean up. All the aforementioned positive benefits of leaving biomass seem correct, but as is so often the case in complex systems, such as ecosystems, change affects scale in time and space, and what was once correct is now incorrect. Historically grazing animals and fire (which was conducted to encourage grazing and typically done in the fall to prevent leaf litter from smoothing the grasses, kept much of the land fairly clean and tidy. Grazing and fire were not random, due to landscape features, and some areas were grazed and burned frequently while other areas hardly touched. This maintained a great degree of structural heterogeneity, a cornerstone of diversity.
Leaving biomass to accumulate year after year increases the amount of nitrogen (N) that decomposes into the soils to the point the system become eutrophic. Historically, N was upscaled into complex food webs that imposed strong regulation over millions of pounds of both N and phosphorus (P). Eaten plants evolved to become quite stingy with remaining nutrients, and cycles were tight and closed (e.g. very little N or P allowed into the abiotic environment). Elimination of the second trophic level (300 years ago when the fur-hide-bush meat industry swept through with guns and traps), caused widespread collapse of food webs (i.e. trophic cascades). Likewise, nutrient cycles broke and spilled into the abiotic.
The sudden increase in N favored faster taller growing species. These species, called nitrophytes, share a similair set of functional traits, in being non-edible (even poor pollen nectar sources). Since N isn’t critical, these species aren’t stingy with their nutrients, and actually evolved to rapidly release nutrients upon senescent, so their off-spring are well fed, growing taller and faster.
Eventually, the site becomes dominated by nitrophilic woody species (e.g. red elm, box elder, silver maple, green ash, hackberry, etc.,). And just like a hyper-eutrophic lake, the terrestrial ecosystem soons settles into a dysfunction (poor degradation of solar energy), non-provisional (corrosive of natural capital), high nutrient self-reinforcing ecosystem that supports little if any higher life forms (mammals, birds, etc). Tragically, many of these wooded systems, formerly open grassland-savannas, are seen for the trees and are called forest, and are managed for forest or woodlands, such as the erroneous term “oak forest, oak woodlands, and floodplain forest”; a classic example of “command and control and the pathology of natural resource management”.
So yes, leaving some winter cover is a good thing, but remember, in the historic configuration, the landscape was kept quite tidy by millions of grazing animals (think of how many trees were allowed to dump leaves into lakes when 600 million beaver roamed North America) and later when humans arrived and used fire to encourage grazing. Manage you landscape in ways that mimic biomass harvest by grazing animals and biotic fire.
Thanks for commenting, Stephen. I had to look up the word heterogenity in order to respond to your comment. Heterogeneity refers to the quality or state of being diverse in character or content. In this case biodiversity and the diverse ways in which the various elements within an ecosystem exist, some requiring extra nitrogen from decaying leaves and some not.