Ecosystems

An ecosystem consists of a community of organisms together with their physical environment. Ecosystems can differ in size and can be marine, aquatic or terrestrial. Ecosystem comprised of biotic (living things) and abiotic (non-living things, such as climate, and topography) components. Broad categories of terrestrial ecosystems are called biomes.

Watch the video below for a summary of ecosystem ecology

What Is An Ecosystem? | Ecology & Environment | Biology | FuseSchool

Interactions occur in ecosystems between biotic and abiotic factors. An essential part of these interactions lies within ecosystem energetics, such as primary production, energy transfer and important cycles such as the carbon and nitrogen cycle. The next few pages will discuss these topics in more depth. In this section we will be discussing different biomes.

Terrestrial Biomes

The biome concept organizes large-scale ecological variation. Terrestrial biomes are distinguished primarily by their predominant vegetation and are mainly determined by temperature and rainfall. Differences in climate will determine what plant groups can grow in a given area, biome distribution can be plotted on two-dimensional axis between rainfall and temperature, which can be seen in the figure below.

Biome distribution map.jpg

Biome distribution shows a clear spatial pattern across the Earth.

Tropical Forest Biome

Tropical forests, specifically rainforests are located near the equator where the climate is hot and wet and shows little seasonal variation. Central and South America possess half of the world’s tropical forests. The dominant plants are trees, lianas (climbers), and epiphytes (plant that grow on top of plants – like some orchids). Tropical rainforests have an emergent layer of tall trees over 40 m tall – some trees can be as tall as 80 m high, an overstory of trees up to 30 m tall, a sub-canopy layer of trees and tall shrubs, and a ground layer of herbaceous vegetation.

Tropical rainforests have the highest biodiversity and primary productivity of any of the terrestrial biomes. Net primary productivity ranges from 2–3 kg m^-2 y^-1 or higher. This high productivity is sustained despite heavily leached, nutrient poor soils, because of the high decomposition rates possible in moist, warm conditions. Litter decomposes rapidly, and rapid nutrient uptake is facilitated by mycorrhizae, which are fungal mutualists associated with plant roots.

The tropical forest biome is estimated to contain over half of the terrestrial species on Earth. Approximately 170,000 of the 250,000 described species of vascular plants occur in tropical biomes. As many as 1,209 butterfly species have been documented in 55 square kilometers of the Tambopata Reserve in southeastern Peru, compared to 380 butterfly species in Europe and North Africa combined.

The tropical forest biome is composed of several different sub-biomes, including evergreen rainforest, seasonal deciduous forest – these forest tend to be located much further away from the equator where the climate becomes seasonal. There are also tropical cloud forests, and mangrove forests, which occur with changes in elevation or substrate.

In the last few years the exceptionally tall yellow meranti trees (Shorea faguetiana) have been discovered growing in Sabah, a Malaysian state on the island of Borneo. The record height of an individual is over 90-meters

tallest tree.jpg

Watch this video below for more information on tropical forests

Rainforests 101 | National Geographic

Desert Biome

Deserts generally occur in a band around the world between 15–30° N and S from the equator. The climate of deserts is dominated by low precipitation, generally below 250 mm yr^-1. However, there is a lot of variability in desert types, with hot deserts, cold deserts, high elevation deserts, and rain shadow deserts. Consequently, there is a great deal of variation in the biodiversity, productivity and organisms found in different types of desert.

The dominant plant biomass in most deserts is composed of perennial shrubs with extensive roots and small, grey or white leaves. However, in warm deserts, therophytes (annual plants) can make up most of the species diversity. Desert annuals can survive unpredictable dry periods as seeds. Seeds may remain viable in the soil for several years, until the appropriate rainfall and temperature conditions occur, after which they will germinate. These annuals grow rapidly, completing their life cycle in a few weeks, then flowering and setting seed before soil water reserves are depleted. Winter desert annuals in North American deserts can generate over 1 kg m^-2 of biomass in a wet year.

With the exception of large blooms of annuals, net primary productivity in most deserts is low and extremely variable.

deserts in bloom_from Jstor daily.jpg

Desert in bloom in southern California.

Watch this video for more detail on deserts

Deserts 101 | National Geographic

Tundra Biome

Tundra is the coldest of all the biomes. Tundra is a treeless landscape due to it plain. It is noted for its extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. Arctic tundra is located in the northern hemisphere, encircling the north pole and extending south to the coniferous forests of the taiga. The arctic is known for its cold, desert-like conditions. The growing season ranges from 50 to 60 days. The average winter temperature is -34° C, but the average summer temperature is 3-12° C which enables growth. Annual precipitation, including melting snow, is 15 to 25 cm. Soil is formed slowly. A layer of permanently frozen subsoil called permafrost exists, consisting mostly of gravel and finer material. When water saturates the upper surface, bogs and ponds may form, providing moisture for plants. There are no deep root systems in the vegetation of the arctic tundra, however, a variety of plants such as, low shrubs, sedges, mosses, grasses and herbaceous plants grow in this biome.

Watch this video for more information on the tundra biome

What Are Tundras? | National Geographic

Temperate Deciduous Forest Biome

Temperature deciduous forests occur in mid-latitudes where there is distinct seasonality with cool winters, warm summers, and high annual rainfall. Net primary productivity ranges from 600–1500 g m-2 yr-1 with high leaf litter production from trees dropping their leaves during the winter. Litter serves as a major pathway for nutrient recycling in this biome. These forests may have an overstory of 20–30 m tall trees, an understory of 5–10 m trees and large shrubs, and a ground layer of herbaceous plants. Biodiversity is relatively high in this biome (though nowhere near biodiversity levels of tropical rainforests) due to the niche and seasonal partitioning allowed by the multiple forest layers.