Tropical Rainforests rainforests are the most complex ecosystems on earth lush, equatorial evergreen forests highest diversity of any terrestrial biome àa belt of green extending ≥10º N & S of equator à has the greatest number of coexisting species receive an average rainfall of 50-260”/yr Today rainforests encompass 6% of earth’s surface plants are so densely packed that rain falling on the (13% of land) canopy can take as long as 10 minutes to reach (30,603,000 km2 = 14 M sq mi) the ground support ~half of all known species of plants and temperature almost always in the 70’s or 80’s F animals average humidity is ~83% eg. 2/3rd’s of all flowering plants rainforests are one of oldest of terrestrial ecosystems some estimate that less than 5% of all tropical once covered 20% of earth’s land surface species have been identified à millions of years ago would have looked very similar from the 1 hectare (2.2 acres) of rainforest supports: air as it does today à fossil evidence indicates tropical rainforests have existed since 42,000 different species of insects the Cretaceous (>60MY ago) up to 800 trees of over 300 species à rainforests once existed on almost every continent Location 1,500 species of other plants Amazon in Brazil – world’s largest central and So America, more biomass and more species than any other Africa ecosystem on earth SE Asia Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 1 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 2 eg. 830 B tons of living matter on earth’s surface descriptions of rainforest ecosystems tend to stress 460 B tons (55%) are in tropical forest the remarkable or unusual ecosystems eg. temperate forests are often dominated by 1 or 2 but standing inside to untrained eye it wouldn’t tree species look particularly distinctive rainforests have many dominant species the diameter of most trees is not unusual eg. lots of local endemics buttresses are found in many large trees eg. 1 hectare (2.2 acres) has >200 species of trees even in temperate forests with trunks >12” diameter [in New England forest ~10-25 species in same vines are commonplace as are epiphytes area] there are several subcategories of rainforests eg. in 300 sq mi of rainforest up to 600 bird species most of the descriptions below refer to wet tropical rainforests were found à more than 4 x’s number that is found in eastern US forests the uniqueness of the rainforest ecosystem is in its eg. 90 species of frogs and toads in a few km great diversity of life and in its complex layering of à more than all species in whole USA habitats eg. 1 ha (2.2 acres) Abiotic Features eg. 1 tree yielded 54 species of ants 1. Climate eg. 2000 sweeps of a net in ground level of Central American forest yielded 500 species of insects; warm constant temperature throughout the year usually much higher diversity in mid and upper level of canopy à no seasonal temperature changes eg. of 19 trees in one panama study 1200 species of beetles were collected and 80% of them were high precipitation almost daily new species (200-450cm: 80-180”/yr) à reservoir for genetic diversity humidity rarely below 95% Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 3 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 4 much of rainfall comes from locally recycled water from forest interwoven, shallow roots quickly absorb transpiration freed minerals from soil àrainforest creates its own climate! most minerals and nutrients are tied up in 2. Soil biomass ancient soil root hairs and micorrhizae actually grow into the litter as it decomposes one paradox of the lush tropical rainforest is that àthe nutrients are held in living organisms the soil is nutrient poor not in the soil soil of rainforest is some of poorest of all soil is just for anchoring the plants forest soil eg. in Northern deciduous forests ~ half of all nutrients when trees are cut and removed most of the in the ecosystem are in soil and the other half in nutrients are removed with them the plants in rainforests, most nutrients are in the plants when land is cleared and converted to agriculture and very little in the soil or other use it can only be used a couple of years without massive additions of fertilizers canopy produces a continuous shower of dead leaves, twigs and blossoms à results in slash and burn; use an area for 2 or 3 years then clear another area organic matter is decomposed rapidly 3. Light à rapid recycling of nutrients intense competition for light ants, termites, fungi and bacteria quickly decompose them leads to stratification of plants and animals into 6 à after 2-3 weeks they are mostly gone or 8 “layers” (temperate decomposition takes ~ 1 yr; conifers ~ 7-10 yrs Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 5 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 6 tropical forests have more leaves/area than mosses, lichens and even small ferns other forests leaves commonly have “drip tips” à hastens the drainage of water à almost no direct sunlight reaches the àslows growth of epiphytes forest floor in mature rainforest trees grow continuously; no dormant period àmake optimal use of sunlight à no growth rings in wood Biotic Features (except in seasonal rainforest with dry/wet periods) Plants timing of leaf fall, flowering or fruiting is most Trees closely related to seasonality in rainfall, not temperature rainforests contain ~1/3rd (80,000) of the known flowering plant species roots often shallow (<1’) and form dense interconnected mat general features that characterize the tropical rainforest plants: many actually grow above the soil into the leaf litter trees characterized by long straight trunks buttress roots & prop roots help support taller that may not branch below 100’ trees almost all rainforest plants are perennials vines trees are the predominant lifeform, shrubs are over 2500 species of vines grow in the erainforests rare eg. Lianas begin life as small shrubs trees usually evergreen flowering plants sends out tendrils that attach to sapling trees (not conifers) both grow together to reach canopy old leaves often have a film of cyanobacteria, green algae, Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 7 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 8 the vines grow from one tree to another and may comprise 40% of all the canopy leaves seeds produced by canopy trees are often eg. rattan vines have spikes on underside of its leaves to small and dispersed by wind grab onto trees canopy trees support lots of epiphytes eg. strangler vines use trees as support and grow thicker and thicher as they reach the canopy eg. bromeliads eventually kills its host tree epiphytes can’t use roots to absorb water epiphytes so many are succulents or hold water eg. some of the largest bromeliads can Rainforest Strata hold several gallons of water become small aquatic ecosystems for aquatic a fully developed rainforest has 3 or 5 layers fauna and frogs, etc (strata): eg. strangler fig A. canopy (>50M; >160’): starts life as an epiphyte tall, straight, disproportionately slender some roots grow quickly down trunk to the ground tree trunks as roots develop they surround the trunk canopy tree trunks rise 60-80’ before and fuse into a rigid cylinder that branching into flattened crowns restricts further growth of “host” tree eg. some grow to over 200’ tall fig’s branches and leaves overshadow the tree’s foliage entirely exposed to sun eventually host dies and rots leaving strangler fig freestanding exposed to more wind and air movements eg. lianas more temperature and humidity extremes stems of lianas hang from upper branches of giants and grow in great loops between trees often buttressed at base canopy trees Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 9 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 10 shade and seedlings of taller trees thicken and become woody but flexible à become highways for wildlife generally few low growing species on forest floor à bind the canopy together but when old tree falls sometimes other lots of bare areas healthy trees are pulled down with it àits very open except around “holes” where an old tree has fallen, or at road cuts and some trees grow adventitious roots to river edges absorb water and nutrients from these pads of epiphytes (the old TV versions of hacking through dense undergrowth is an exaggeration) B. middle story (30-40M; 100-130’) little forest litter since it is rapidly dense, forms continuous canopy of leaves decomposed that trap most of the remaining sunlight seedlings of large trees must adapt to conditions of each level as they grow air currents are blocked so humidity is toward the canopy greatly increased tropical vines grow up trees to find light C. understory (ground level to several m) (when young grow away from light!) have very low light (<5%) year round dark, humid à somewhat rivals a cave in constancy almost all understory trees are perennials lots of algae, lichens and mosses growing on plants à better adapted to low light understory plants often have leaves that are smooth annuals generally need lots of light to and slick and drooping to allow water to run off complete life cycle in one year and discourage growth of algae, lichens and mosses shrubs and herbs specialized for life in the Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 11 Ecology: Terrestrial Ecology –Tropical Rainforests, Ziser Lecture Notes, 2017.11 12 little or no wind in understory locomotion and ability to conceal vary greatly àseeds of understory plants are most often eg.