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North and South Facing Slopes

 

Ranger Steve Mueller

Ranger Steve Mueller

By Ranger Steve Mueller

 

The sun is rising higher in sky, moving farther north and shines in our east facing bedroom window. I speak of appearances instead of accurate occurrences. For most of human history, it was thought that appearances were how things worked in nature niches. We thought the sun rose instead of the Earth rotating to make it appear the sun rises. In the 16th century, Copernicus shared that Earth was not center of universe, and he was placed on house arrest for life unless he recanted and stated his scientific discovery was false. He did not recant his scientific discovery.

An event of great significance for plants and animals is the angle the sun strikes the landscape. Though it is easily observable, many of us have not consciously noticed or considered its importance. Our noses may have noticed skunks begin venturing out in February when days are longer. Day light has been lengthening for two months, even though we receive some of our coldest air at this time of year. We experienced -15 F in mid February.

Cold arctic air masses alternate with warmer southerly air masses sweeping over the region. When clouds are not blocking the sun, higher angle sunrays make more direct contact with the landscape. They warm south facing slopes, melt its snow, and warm the ground to kick-start spring growing conditions earlier than occurs on north facing slopes, where sunlight skims over the slope. Sunray energy concentrates in a smaller area when it strikes south facing slopes perpendicularly. On north-facing slopes, the same amount of energy is obliquely spread widely over a larger area and results in less warming of ground, plants, over wintering insects and other creatures.

Growing seasons on north and south-facing slopes vary depending on the amount of energy they absorb and it creates unique plant and animal microhabitats. As March approaches, notice the variations. The north side of Ody Brook Nature Sanctuary’s big field has exposed bare ground earliest when warm rays reflect infrared heat off forest trees. The middle of the field is slower to lose snow and frozen ground. The south edge of the field is slowest to warm and lose snow because naked winter tree trunks and branches filter light energy and prevent some rays from reaching that edge of the field.

Energy captured by dormant winter trees warms the bark and begins sap flow in February. Look closely at tree buds to notice they swell in advance of spring. It is easier to see changes in trees and shrubs than changes in field plants on north and south-facing slopes. Herbaceous plants have dead vegetation above ground but the warming Earth stimulates unobserved root activity. When spring growth emerges, plants on south-facing slopes bloom earlier than the same species growing on north-facing slopes.

Unfortunately, people often reject science evidence for political or religious reasons as happened with Copernicus. Concerns might stem from human fear of the unknown when we consider changing how to use Earth’s resources. Some people are willing to change behavior to sustain future generations, in addition to caring for our present population, while others focus only on the present. When asked, it appears people are interested in our children’s, grandchildren’s, and succeeding generations sustainability. However, actions are more important than talk, when addressing how we live and strive to sustain a healthy Earth for present and future human generations. It is important that we do not ignore accumulating scientific evidence for how things like the Keystone pipeline or human-caused climate change impact the triple bottom line of economic, social and environmental sustainability. Present and future generations depend on healthy functioning ecosystems. In present day society many are unwilling to accept scientific evidence, much like political and religious leaders were unwilling to accept Copernicus’s discoveries.

Go beyond appearances to discover and understand the importance of evidence-based occurrences.

Natural history questions or topic suggestions can be directed to Ranger Steve (Mueller) at odybrook@chartermi.net Ody Brook, 13010 Northland Dr, Cedar Springs, MI 49319-8433 or call 616-696-1753.

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