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Inforestry andecology,understory (American English), orunderstorey (Commonwealth English), also known asunderbrush orundergrowth, includesplant life growing beneath theforest canopy without penetrating it to any great extent, but above theforest floor. Only a small percentage of light penetrates the canopy, so understory vegetation is generallyshade-tolerant. The understory typically consists of trees stunted through lack of light, other small trees with low light requirements, saplings, shrubs, vines, and undergrowth. Small trees such asholly anddogwood are understory specialists.
Intemperate deciduous forests, many understory plants start into growth earlier in the year than the canopy trees, to make use of the greater availability of light at that particular time of year. A gap in the canopy caused by the death of a tree stimulates the potential emergent trees into competitive growth as they grow upward to fill the gap. These trees tend to have straight trunks and few lower branches. At the same time, the bushes, undergrowth, and plant life on the forest floor become denser. The understory experiences greater humidity than the canopy, and the shaded ground does not vary in temperature as much as open ground. This causes a proliferation offerns,mosses, andfungi and encouragesnutrient recycling, which provides favorablehabitats for manyanimals and plants.
The understory is the underlying layer of vegetation in a forest or wooded area, especially the trees and shrubs growing between the forest canopy and the forest floor.Plants in the understory comprise an assortment of seedlings and saplings of canopy trees together withspecialist understoryshrubs and herbs. Young canopytrees often persist in the understory for decades as suppressed juveniles until an opening in the forest overstory permits their growth into the canopy. In contrast understoryshrubs complete theirlife cycles in the shade of the forest canopy. Some smaller tree species, such asdogwood andholly, rarely grow tall and generally are understory trees.
The canopy of atropical forest is typically about 10 m (33 ft) thick, and intercepts around 95% of the sunlight.[1] The understory therefore receives less intense light than plants in the canopy and such light as does penetrate is impoverished inwavelengths of light that are most effective for photosynthesis. Understory plants therefore must beshade tolerant—they must be able tophotosynthesize adequately using such light as does reach their leaves. They often are able to use wavelengths that canopy plants cannot. Intemperate deciduous forests towards the end of the leafless season, understory plants take advantage of the shelter of the still leafless canopy plants to "leaf out" before the canopy trees do. This is important because it provides the understory plants with a window in which to photosynthesize without the canopy shading them. This brief period (usually 1–2 weeks) is often a crucial period in which the plant can maintain a net positivecarbon balance over the course of the year.
As a rule forest understories also experience higherhumidity than exposed areas. The forest canopy reduces solar radiation, so the ground does not heat up or cool down as rapidly as open ground. Consequently, the understory dries out more slowly than more exposed areas do. The greater humidity encouragesepiphytes such as ferns and mosses, and allowsfungi and other decomposers to flourish. This drivesnutrient cycling, and provides favorablemicroclimates for manyanimals andplants, such as thepygmy marmoset.[2]
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