Rangelands are arid and semiarid wildlands that make up to 60% of the world’s land mass; composed of native vegetation of grasslands, shrublands, and open woodlands. For various reasons (low precipitation, rough topography, cold temperatures, etc) Rangelands are unsuitable to grow timber and crops. Rangelands provide multiple ecosystem goods and services such as grazing for livestock and habitat for wildlife, serving as a watershed, improving soil and water quality, providing clean air, open spaces, and recreation.
Grasslands can be defined as land composed mostly of grass species, members of the family Poaceae, with little or no woody vegetation. Sufficient precipitation is needed to be able to support grasses, but not trees and shrubs, in this biome. Grasslands occur on every continent and are around 23% of total land cover.
Grasslands are important economically because of grains from cereal grasses that provide food for animals and humans: wheat, rice, corn, oats, barley, rye. Grasses also provide hay and pasture for livestock. Grasses are important ecologically because they have an extensive root system that improves soil quality and prevents erosion. They also influence sequestration of CO2. They are worth studying because of the ecosystem goods and services grasses provide.
Grasslands are threatened by a variety of human activities including agriculture, fragmentation, invasive species, lack of fire, desertification, urbanization, and livestock. Grasses are being converted to cropland and infrastructure, suppressed of fire, and overgrazed by different animals. All of these things contribute to the loss and degradation of grasslands. It is important to conserve grasslands because of the regulating, provisioning, and cultural services that they provide. Grasslands provide food and habitat, improve soil and water quality, play a role in nutrient cycling, and have cultural value. It is important that we manage grasslands sustainably so that these goods and services continue.
E.O Wilson identified two laws in biological/ecological systems: properties of life are obedient to laws of chemistry and physics, and all biological processes and differences that distinguish species are evolved from natural selection. Species originate from the evolution of some difference that adapts them to the environment. Natural selection is the process by which organisms that have physical/molecular traits that better adapt them to their environment will tend to survive and reproduce. Speciation is the formation of new and distinct species, from the splitting of one evolutionary lineage into two. Natural selection is the primary influence driving evolution, and therefore speciation.
Grasses are in the division Magnoliophyta, class Liliopsida, in the order Cyperales, part of the family Poaceae (Gramineae), have 600 genera, and have around 9000 species. They occur in arid or semi-arid environments. They are annual (reestablish by seed each year) or perennial (persist from year to year) herbs that have noded stems. The have leaves with two parts: sheath surrounding stem and a linear, flat blade. Flowers are formed by inflorescence subdividing into spikelets, which other flowering plants do not have. The dry fruit is called caryopsis (grain). Grasses have rhizomes, stolons, basal leaf meristems, high shoot/root density, underground nutrient reserves, deciduous roots, and rapid transformation/growth.
The main adaptations of grasses involve responses to the disturbance of drought and open space. They have evolved to be wind pollinated and drought resistant. Grasses are able to spread during periods of increasing drought because of traits such as Basal meristems, small stature, high root and shoot density, deciduous roots, underground nutrient reserves, and rapid transformation and growth. Rhizomes and Stolons are used as growth strategies to extend the root system laterally. Other adaptations include how rhizomes evolved because of trampling by large herbivores, basal leaf meristems evolved as an adaptation to grazing, and wind pollination evolved due to open conditions of savannas.
Grasslands are abundant because of the genetic traits that have evolved that help them better fit their environment, to survive and reproduce. Therefore, natural selection has influenced Poaceae to survive throughout history due to specific beneficial differences evolving in response to disturbance and environmental change, and thrive in today’s biosphere. The specific traits that grasses have evolved through natural selection is basal leaf meristems, high root/shoot density, underground nutrient reserves, deciduous roots, and rapid transformation/growth, rhizomes and stolons. All of these characteristics contribute to drought resistance. As an adaptation of moving from woodland to open landscapes, grasses evolved to be wind pollinated and can reproduce more efficiently. Rhizomes and stolons produce lateral growth without the use of seeds, increasing distribution and abundance. The morphology of grasses is important to grassland abundance because without the evolutionary process forming this vegetation type, Poaceae would have never developed traits that help them better adapt to their changing environment; and they would eventually go extinct. Basically, the current state of grass species morphology is produced by species adaptation to environmental change. Overall, grasslands are abundant because of their resistance and resilience to environmental change; because of their ability to easily adapt to disturbance because of traits they evolved due to natural selection and speciation.