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Cascading Effects of a Wet Spring


As much as warm and sunny weather is enjoyed by us humans in Jackson Hole, many plant communities and wildlife throughout northwestern Wyoming are adapted to wetter and cooler conditions. On cool and rainy days this spring and summer, it is good to remember how happy the trees and shrubs are – and the cascading ecological effects of their happy condition.

Generally, for plant-eating mammals like deer, elk, moose, pronghorn, etc., nothing more strongly correlates to the number and survival rates of offspring than the moisture from the previous year. During a wet and lush summer, females are on a better nutritional plan, so to speak, and therefore produce better milk for their young while maintaining their own body fat during lactation. As a result, they are more “fecund” or likely to get pregnant during the fall mating season. In addition, offspring born in wet years are typically larger and have more fat available to help them survive their first winter.

The fat reserves of pregnant adult females going into winter similarly help them and their yet-unborn offspring to get through the tough winter season. As a result, the following spring, there is often an uptick that can be seen in both the number and birth weight of offspring, which translates to better survival in the first year. Such are the cascading positive effects of lush years.

We had a relatively easy winter this year for plant-eating mammals at low elevations. This has kept more of last year’s well-nourished offspring around to see their first birthday this coming June. However, the lackluster snowfall at lower elevations this winter also puts the upcoming year’s offspring at the mercy of our spring and summer rains to keep the vegetation lush and nutritious. These cycles of moisture and nutrition are often reflected in a one to two year time lag in population sizes and reproduction rates.

While there is very little that private landowners can do about these cycles – and so far, we have been fortunate to have an incredibly lush spring – at a smaller scale, there are some land management actions that can be taken (or refrained from) that contribute to the health of the land and the wildlife it sustains. For example, avoiding disturbing plant communities and soils is especially helpful during dry years, because each time moisture-capturing vegetation is reduced or the soil surface is “opened”, its moisture content trends toward further dryness.

To benefit forested lands, landowners can leave (rather than clean out) dead and downed woody debris. Not only does this support biodiversity and carbon recycling, it also helps to sustain moisture and temperature regimes that benefit trees and shrubs – providing micro-shady spots as well as a sponge-like effect after it rains.

If irrigation water is sourced from a main river in which flows will be determined by our high elevation snowpack, water for irrigation should be reliable for the growing season ahead. If irrigation systems and water features are linked to smaller tributaries, the land’s productivity will depend on rainfall throughout the upcoming months. It helps me to keep the health of the land and wildlife in mind on spring and summer days when my plans get rained out!

–Tom Segerstrom, Land Steward and Staff Biologist

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