Shrubs are woody plants that refuse a single trunk life
A shrub or bush is a small to medium perennial woody plant with persistent stems above ground, evergreen or deciduous. Unlike trees, shrubs usually branch into multiple stems without one dominant trunk, dominating landscapes from fynbos and maquis to moorland and garden shrubberies.
What separates a bush from a tree is mostly height and stem count. Shrubs keep woody stems above ground year after year, unlike soft herbaceous plants, but they usually branch below the soil surface into several stems with no real trunk, and they stay under a cutoff of roughly 6 to 10 metres that varies by species. The line blurs in both directions: oak and ash can grow as multi-stemmed plants tall enough to count as trees, and trees stunted by harsh conditions can pass for shrubs. Plants under about 2 metres, such as lavender, periwinkle and most garden roses, are often called subshrubs. The Greek thinker Theophrastus already divided plants into trees, shrubs and herbs.
Lifespans vary widely. Some species manage only about five years even in good conditions, while bigger, woodier kinds can pass 70; the average shrub species dies at around eight. Some, like hawthorn, drop their leaves in autumn, while holly and others stay green.
Why two woody growth forms coexist has attracted surprisingly little research. One model credits many stems with more bark area for photosynthesis, more cambium and phloem, and more places to resprout than a young tree of equal wood volume, which correctly predicts faster early growth. Spare stems also insure against loss, and seed comes sooner. Flowering trees that are cut or broken often resprout from the base and grow as shrubs for a while. Airborne seeds help willows spread, and shrubs cope in alpine zones where trees thin out; in recent decades warming has driven a marked shrubification of the Arctic.
People use relatively few shrubs directly beyond berries, perfume plants such as lavender and rose, and many medicinal species; tea and coffee come from plants kept shrub-sized that could become small trees. Australian ecologists classify shrublands by height, with 2 and 8 metres as thresholds, and by foliage cover, from closed stands above 70 percent down to open ones below 10.
Source: Shrub
