By: Becca Badgett, Co-author of How to Grow an EMERGENCY Garden
To the gardener, the most important thing about microclimatesoils is their ability to provide areas where different plants will grow – plantsthat might not grow in your primary landscape because of a lack of sun ormoisture. Soil in microclimates is influenced by various factors, making themdifferent than most of your other soil.
The term microclimate is normally defined as “a smaller area within a generalclimate zone that has its own unique climate.”
Soil is an integral part of the microclimate for thegardener. Does soil affect microclimates, you might ask. It is most often theother way around, as microclimates can affect the soil’s temperature andmoisture. The soil in microclimates can also be influenced by vegetation thatis growing there, such as trees.
Factors may include soil that is cooler or warmer or thatoffers sunnier or shadier conditions with varying degrees of moisture. Forexample, think of the conditions around the foundation of your home. Becausesome areas are shaded and grass likely won’t grow, these areas may be theperfect spot for some shade-loving plants.
If foundation areas get runoff from rain and stay moistlonger, you can grow plants that prefer damp shade and high humidity. Theseplants aren’t likely to perform properly in dry and sunny areas of yourlandscape. Take advantage of microclimate soils for growing different varietiesof specimens you love.
Your microclimate may be dry with loamy soil that getshotter than your mostly shady yard. This gives you an opportunity to growdifferent, heat-loving specimens. Soil in these areas may be different from therest of the property or it may be the same. It can be amended, if necessary,for a particular type of plant.
The wind also affects the soil and microclimate. It mayremove moisture and, depending upon its direction, can make the area warmer orcooler.
Microclimate soils are abundant under groves of trees thatmight grow on a corner of your property or beneath a mixed shrub border. Treesand shrubs shade the soil beneath, again providing a different environment thanthe surrounding landscape. Needle dropping specimens may influence the soil andmicroclimate by adding nutrients.
As an example, we often see shade-loving hosta plants under trees. However, there are many other shade tolerantplants that enjoy those microclimate soil conditions. Try planting solomon’s seal and others not seen in every garden down the street. ConsiderRodgersia,with attractive large leaves and colorful mid-summer plumes.
If there’s enough room in your microclimate soil area, add afew as background for others that grow well in these conditions. Consider shadetolerant fernsor the Brunnerafor plants not so often used.
Now that you’ve learned to recognize the microclimates inyour landscape, take advantage of them by growing different plants.
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Microclimate, any climatic condition in a relatively small area, within a few metres or less above and below the Earth’s surface and within canopies of vegetation. The term usually applies to the surfaces of terrestrial and glaciated environments, but it could also pertain to the surfaces of oceans and other bodies of water.
The strongest gradients of temperature and humidity occur just above and below the terrestrial surface. Complexities of microclimate are necessary for the existence of a variety of life forms because, although any single species may tolerate only a limited range of climate, strongly contrasting microclimates in close proximity provide a total environment in which many species of flora and fauna can coexist and interact.
Microclimatic conditions depend on such factors as temperature, humidity, wind and turbulence, dew, frost, heat balance, and evaporation. The effect of soil type on microclimates is considerable. Sandy soils and other coarse, loose, and dry soils, for example, are subject to high maximum and low minimum surface temperatures. The surface reflection characteristics of soils are also important soils of lighter colour reflect more and respond less to daily heating. Another feature of the microclimate is the ability of the soil to absorb and retain moisture, which depends on the composition of the soil and its use. Vegetation is also integral as it controls the flux of water vapour into the air through transpiration. In addition, vegetation can insulate the soil below and reduce temperature variability. Sites of exposed soil then exhibit the greatest temperature variability.
Topography can affect the vertical path of air in a locale and, therefore, the relative humidity and air circulation. For example, air ascending a mountain undergoes a decrease in pressure and often releases moisture in the form of rain or snow. As the air proceeds down the leeward side of the mountain, it is compressed and heated, thus promoting drier, hotter conditions there. An undulating landscape can also produce microclimatic variety through the air motions produced by differences in density.
The microclimates of a region are defined by the moisture, temperature, and winds of the atmosphere near the ground, the vegetation, soil, and the latitude, elevation, and season. Weather is also influenced by microclimatic conditions. Wet ground, for example, promotes evaporation and increases atmospheric humidity. The drying of bare soil, on the other hand, creates a surface crust that inhibits ground moisture from diffusing upward, which promotes the persistence of the dry atmosphere. Microclimates control evaporation and transpiration from surfaces and influence precipitation, and so are important to the hydrologic cycle—i.e., the processes involved in the circulation of the Earth’s waters.
The initial fragmentation of rocks in the process of rock weathering and the subsequent soil formation are also part of the prevailing microclimate. The fracturing of rocks is accomplished by the frequent freezing of water trapped in their porous parts. The final weathering of rocks into the clay and mineral constituents of soils is a chemical process, where such microclimatic conditions as relative warmth and moisture influence the rate and degree of weathering.
This article was most recently revised and updated by John P. Rafferty, Editor.
The slope and aspect of a vegetated surface strongly affects the amount of solar radiation intercepted by that surface. Solar radiation is the dominant component of the surface energy balance and influences ecologically critical factors of microclimate, including near-surface temperatures, evaporative demand and soil moisture content. It also determines the exposure of vegetation to photosynthetically active and ultra-violet wavelengths. Spatial variation in slope and aspect is therefore a key determinant of vegetation pattern, species distribution and ecosystem processes in many environments. Slope and aspect angle may vary considerably over distances of a few metres, and fine-scale species’ distribution patterns frequently follow these topographic patterns. The availability of suitable microclimate at such scales may be critical for the response of species distributions to climatic change at much larger spatial scales. However, quantifying the relevant microclimatic gradients is not straightforward, as the potential variation in solar radiation flux under clear-sky conditions is modified by local and regional variations in cloud cover, and interacts with long-wave radiation exchange, local meteorology and surface characteristics.
We tested simple models of near-surface temperature and potential evapotranspiration driven by meteorological data with the incoming solar radiation flux adjusted for topography against measurements of temperature and soil moisture at two chalk grassland field sites in contrasting regional climates of the United Kingdom. We then estimated the cumulative distribution function of three key ecological variables (monthly temperature sums above 5 and 30 °C, plus potential evapotranspiration) across areas of complex topography at each site using two separate approaches: a spatially explicit and a spatially implicit method. The spatially explicit method uses digital elevation models of the sites to calculate the solar radiation at each grid cell and hence determines the spatial distribution of environmental variables. The second, less computationally intensive, method uses estimated statistical distributions of slope and aspect within the field sites to calculate the proportion of the surface area of each site predicted to exceed a given threshold of temperature sum or potential evapotranspiration. The spatially implicit model reproduces the range of the explicit model reasonably well but is limited by the parameterisation of slope and aspect, underlining the importance of variation in topography in determining the microclimatic conditions of a site.
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By now, you know how to create a cooler microclimate. By taking advantage of some ideas from good old Mother Nature, you can make things a little cooler for plants that can’t take the heat.
I hope you found this article helpful – if so, please share it with someone who can use the information. Until next time, stay cool and enjoy your garden’s pleasant microclimate!
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