Wildfires are a natural phenomenon in many ecosystems, including forests along the U.S. Pacific West Coast, as natural fires serve to rejuvenate ecological communities. However, from mid-August through mid-September 2020, forests in California, Oregon, and Washington State suffered through unprecedented wildfires caused by extreme weather events that can be attributed to climate change. By September 15, 2020, in Washington state, 700,000 acres (280,000 hectares) had burned; in Oregon, about 1 million acres (405,000 hectares) had burned; and in California, the worst-hit state, more than 7700 fires had burned 3 million acres (1.2 million hectares), damaged or destroyed more than 5000 structures, and killed at least 35 people. The single largest fire to date was the California Complex fire in Northern California, which was still raging on September 15 after it had already burned about 800,000 acres (320,000 hectares). These epic blazes have created some of the worst air pollution in the world from Seattle, Washington, to Southern California, with haze reaching as far east as New York City. See also: Air pollution; Extreme weather events; Forest fire; Global climate change; Wildfire impact on air quality

The Joshua tree (Yucca brevifolia) is a remarkable evergreen, treelike plant found only in the southwestern United States. It was named by Mormon settlers in the early 1800s. Upon seeing the limbs of this plant branching upwards to heaven, the Mormon travelers were reminded of the biblical prophet Joshua, who raised his arms in prayer for guidance to the Promised Land. The Joshua tree is the largest member of the Yucca genus of monocotyledonous trees and shrubs, which is placed in the agave family (Agavaceae; order Asparagales) or the lily family (Liliaceae; order Liliales), depending on the taxonomic system being used for classification. The height of the Joshua tree can reach 15 to 40 feet (4.6 to 12.2 meters) and its diameter ranges from 1 to 3 feet (0.3 to 0.9 meters). Life spans of 150 to 200 years have been documented for this resilient species, with some unverified ages of 500 to 1000 years being estimated. See also: Asparagales; Liliales; Monocotyledons; Tree

It is estimated that 1 gram of soil can be inhabited by up to 10⁹ microorganisms and approximately 60,000 bacterial species. Moreover, soil harbors a vast reservoir of antimicrobial agents, and soil-dwelling bacteria have played a key role in the introduction of antibiotics to treat infectious diseases. Because these resilient bacteria not only produce antibiotics but also are exposed to other antibiotics produced by surrounding strains in the soil, they have developed diverse mechanisms to survive the toxic antimicrobial compounds created around them. Importantly, these mechanisms of robust resistance to numerous classes of antibiotics often resemble the mechanisms of resistance identified in clinical pathogens, including those that infect humans. Thus, scientists are attempting to find possible correlations between antibiotic resistance in soil bacteria and in infectious agents in humans. If correlations can be found, investigators might be able to predict future signs of clinical resistance to certain antibiotics, providing clinicians with methods to circumvent any potential resistance that may emerge. See also: Antibiotic; Antimicrobial agents; Antimicrobial resistance; Bacteria; Clinical microbiology; Drug resistance; Infectious disease; Medical bacteriology; Microbiology; Pathogen; Soil; Soil microbiology

To bolster food security in a warming world, engineers are developing a coating that could better protect seeds, such as beans, from drought in semiarid regions. The coating mimics a mucilage-based hydrogel produced naturally by some seeds, such as basil and chia. The hydrogel traps moisture, regulates nutrient retention, and creates an environment around the seed which promotes the growth of beneficial microorganisms. The artificial coating is accordingly tailored to help protect seeds during germination and early seedling growth. In semiarid regions, water stress caused by a lack of available moisture during these sensitive periods of a plant's development is the highest cause of crop loss worldwide. This water stress on agricultural crops in drought-prone, marginal lands is expected to substantially increase in coming decades because of global climate change. See also: Agricultural engineering; Drought; Farm crops; Global climate change; Mucilage; Seed

Wildfires, also termed bushfires or forest fires, are currently devastating large swaths of land in Australia. Detrimental ecologic consequences of these uncontrolled combustions of forest fuels and vegetation are numerous. One of the most serious issues pertains to the survival of the koala, which is a small marsupial (pouch-bearing mammal) found only on that continent. Conservationists and scientists are concerned that the hundreds of fires presently raging in Australia, which were brought about by hotter and drier conditions exacerbated by anthropogenic climate change, may cause significant enough reductions in the population of koalas to threaten the continued existence of this species. See also: Australia; Forest fire; Global climate change; Global warming; Koala; Marsupialia

The American beech (Fagus grandifolia) is native to forest regions east of the Mississippi River and is a key tree species in the United States. In particular, it is very abundant from Ohio to the New England states. The tree is also found in the southernmost portions of eastern Canada, especially southern Ontario. Since 2012, though, American beech trees have been distressed by a lethal leaf disease—termed beech leaf disease—that has spread rapidly from Ohio into the other aforementioned geographical areas. Most cases of the disease have been detected in forest regions, but landscaped locations also have been affected. The external symptoms of the disease include striped banding and shriveling of tree leaves, aborted budding, reduced production of leaves, and premature leaf drop. More importantly, beech trees with beech leaf disease often die within a relatively short span of time after being inflicted by the disease—within 2 to 3 years for saplings and within 6 years for larger and older trees. See also: Beech; Forest; Forestry; Leaf; Tree; Tree diseases

Biocontrol, or biological control, is the natural or applied regulation of populations of pest organisms—especially insects—through the role or use of natural enemies. In other words, biocontrol uses living organisms to reduce and eliminate pest abundance and damage. The agents through which biocontrol is accomplished are varied. For example, biocontrol agents can be consumers of pests; thus, herbivores are used to reduce weeds, whereas predators or parasites are employed to diminish the number of insect and other animal pests. In addition, pathogens and competitors that interact with pests are often utilized in biocontrol. Typically, agricultural and forest pests are the major targets of biocontrol. Notably, biocontrol operates as an alternative to the use of pesticides that may be harmful to the environment. See also: Agricultural science (animal); Agricultural science (plant); Agricultural soil and crop practices; Agriculture; Biological insect control; Forest; Forestry; Insecta; Parasitology; Pathogen; Predator-prey interactions; Weeds

Many questions concerning the sustainable production of biofuels have emerged over recent years in terms of land and water use, pollution from fertilizer and pest-control chemicals, greenhouse-gas production, net energy production, and whether enhanced land-use and climate benefits would result from simply planting trees and eschewing biofuels altogether. According to researchers reporting in the Proceedings of the National Academy of Sciences (September 2020), the answer depends, in part, on optimizing land-use policies and bioenergy production systems. Researchers have concluded that sustainable biofuels could make an important contribution toward reducing greenhouse-gas emissions and stabilizing the global climate if we produce bioethanol from biomass sources, such as perennial grasses, that are grown without affecting the carbon already stored in the ecosystem. See also: Biomass; Ethyl alcohol; Global climate change; Greenhouse effect; Land-use planning; Reforestation

Humans have used dried bovine dung (manure) as a fuel source since prehistoric times. In India, for example, many people burn cow or buffalo dung for cooking fuel. This bioresource provides a low-cost fuel as well as an efficient means of waste disposal. However, in rural India, the burning of dung is simultaneously a source of hazardous indoor and outdoor air pollution, resulting from the emission of fine particulates that are 2.5 micrometers or less in diameter (PM_2.5). Such combustion byproducts are considered the most dangerous to human health, because PM_2.5 can be inhaled deep into the lungs, impairing lung function as well as and affecting other organs, such as the heart and brain, or causing cancer. See also: Air pollution; Indoor air pollution

Many trees enjoy extremely long lives in comparison to humans and other animals. Yet one group of trees, the bristlecone pines, stands out as the most ancient of all, with individual trees that commonly live for thousands of years, including one that has survived more than 5000 years. See also: Tree