What's killing our trees?

"Our industrial society with its attendant air pollution is slowly killing our forests, as it has the forests of eastern Europe, weakening and stressing trees, and making them more susceptible to cold winters and attack by pathogens."  Paul Donahue, in Tree Death and Forest Decline.

Dying forests in eastern Europe. Photo by Lovecz, posted on Wikimedia Commons. 

Forests in the eastern U.S., the Rocky Mountains, and California are all seeing massive death of forest trees.  This in turn adversely affects the survival of other plants, as well as of animals dependent on those trees, and biodiversity is seriously diminished.  Yet there are misconceptions, put out deliberately by special interests or arising from ignorance, about what exactly is killing our forests. 

Donahue continues:

"One criticism often leveled by opponents of stricter air pollution standards is that acid rain or other pollutants don't kill trees, that they are actually killed by cold winters or by insects or fungus or some such agent." 

Those who lobby for relaxing pollution standards are using carefully selected facts out of context to support a particular agenda (one of the tools of pseudoscience). It is true that the trees in forests like those above are killed by insects, pathogens and extreme weather, but what is carefully ignored is the fact that such death is greatly increased after the trees have been seriously stressed or weakened by air pollution or changing climate patterns.

In the eastern U.S., as discussed in detail by Donahue, the immediate cause of death has often been severe weather, but trees that have been weakened by acid rain are more prone to damage than healthy trees.  Acid rain results from burning sulfur-containing fossil fuels by industry and from the nitrogen oxide component of automobile exhaust.

In the Rocky Mountains, the Sierra Nevada, and elsewhere in the west, the Mountain Pine Beetle is often blamed.  But this a native species of insect that has been here for thousands of years.  Beetle larvae overwintering below the outer bark of the trees are normally killed by cold weather, keeping the populations under control. They are having a much greater impact now because of higher than normal temperatures and lower rainfall in the past ten years, which also stresses the trees. These changes are part of overall global climate change. 

There is a misconception about climate change, voiced frequently by ignorant government officials, that it will be expressed as a uniform and consistent warming everywhere.  Climate change actually results in a complex array of disruptions that include more temperature and precipitation extremes, both up and down.  So vicious winter storms and extreme low temperatures are part of that disruptive pattern.

The planet is indeed warming overall, as is evident in the melting of the polar ice caps, which in itself will result in complex repercussions in oceanic currents and climate patterns, as well as the rising sea levels that threaten coastal human populations and entire low-lying nations.

"Those who deny the existence of climate change and rising sea levels, who want to do away with environmental protection agencies, who oppose treaties on clean air and reduction of carbon emissions, and who want to open up national parks and other wild lands to mining and other economic exploitation, just don't get it, and must be rejected."

This quote is from my October 2016 essay on endangered species and population growth.  Unfortunately, the fears expressed have been chillingly born out. The current governmental leadership in the U.S. is moving rapidly backwards on issues of air quality, climate change, and protection of public lands.  

Americans have another opportunity in the upcoming congressional elections to choose more environmentally supportive representatives.  Can those of us who understand and respect science, and who care about the environment and biodiversity, make a difference?

Given the many highly publicized and polarizing issues grabbing voter attention this year, it may seem hopeless.  But even if we can tip the scales on some tight congressional elections, even helping elect one or two conscientious representatives, we can make a difference.  You can help in a number of ways:

ASK your representatives or candidates what their stand is on air quality standards and other environmental issues.

EDUCATE your current representatives about important environmental issues and urge them to do the right thing.

If they will not be educated, REPLACE them.  Support candidates who understand the issues and will stand up for them.

VOTE for the best available candidates, Democrat or Republican.  

Though environmental protection has in recent decades has been associated primarily with the Democratic Party, an exchange of letters in a recent Sierra Club Magazine demonstrated that many conservatives also cherish our natural heritage and support the Club's fundamental mission.  This was expressed some time ago in a post from the Missouri chapter of the Sierra Club (click here).  In fact, an organization called Republicans for Environmental Protection (now called ConservAmerica) was established in 1995.  

The primary elections in both parties are the first opportunity to bring better candidates forward.  Republican candidates who support the environment particularly need support.

If you are among the many readers of this blog who do not reside in the U.S., do what you can in your own elections when they come up, and best of luck.  All nations must work together to protect our global ecosystem.

Mosses of Central Florida 43. Micromitrium

There are three species of Micromitrium (Ephemeraceae) in our area: M. megalosporum Austin

Micromitrium tenerum at a drying pond edge.  Permission pending from
Okayama University of Science, http://www1.ous.ac.jp/garden

M. tenerum (Bruch & Schimp.) Crosby and M. synoicum (James) Austin.  These are tiny short-lived plants that form sparse colonies on bare soil along drying pond edges.  The plants form rosettes with a single, globose sporangium nestled among the leaves.  Their leaves lack a midrib and the leaf cells are elongate, somewhat curved (worm-like) and smooth.

They are similar to Ephemerum crassinervium, which is in the same family, but that species has leaves with  distinct midribs, more ovoid capsules, and papillose cells near the tip of the leaf.

The ranges of the three species overlap, as they all occur throughout eastern North America. M. tenerum has been also reported from British Columbia, and M. synoicum from Oregon.  In Florida, they are all found primarily in the panhandle region, with reports from as far south as Polk County. None are collected very often, however, as they are short-lived and hard to see.

In M. megalospermum the leaves are broadly ovate and the spore capsule opens irregularly, while in M. synoicum and M. tenerum the leaves are lance-shaped, and the capsules open along a distinct ring around the middle or above.

In M. synoicum the leaves are erect, with smooth, somewhat incurved margins and have distinct stems below the crown of leaves, while in M. tenerum the leaves are spreading, with flat margins, and teeth at the tips, and the plants are stemless.

Mosses of Central Florida 42. Papillaria nigrescens

Papillaria nigrescens (Hedwig) A. Jaeger (Meteoraceae) occurs on tree bark in shaded, humid hammocks.  It's leaves are scale-like and pressed against the stem, giving the yellowish to blackish leafy shoots the appearance of tiny juniper twigs.  Some shoots have drooping, whip-like extensions with sparser, smaller leaves, or are nearly naked with a small tuft of leaves at the ends.  This species is not known to produce spore capsules in our area.

Dried specimen of Papillaria nigrescens, collected in Hillsborough River State Park on bark of hardwood tree (Griepenburg 10, USF) 

The main leaves are ovate, but gradually narrowing to a sharp tip.  Leaf cells are narrowly-ovate and tapered, and somewhat wavy (worm-like) with papillae (hard, translucent bumps). The midrib reaches to about mid-leaf, though may not be very distinct.

The scale-like leaves of Papillaria gradually taper to a sharp
tip. A faint midrib extends a little more than half the leaf
length.

This species has been found throughout Florida, but collected only occasionally.  It occurs throughout the New World tropics, and elsewhere in the U.S. it has only been found in southern Louisiana. It has previously been known as Meteorium nigrescens.

Leaf cells in Papillaria are elongate, tapered and somewhat wavy.  The papillae (hard, translucent dots) can be seen lined up along the length of each cell.

Mosses of Central Florida 41. Tortella

The genus Tortella (Pottiaceae) includes two species found in Florida.  The genus is distinguished from other members of the family, such as Barbula or Hyophiladelphus by the distinctive V- or U-shaped boundary between the large basal region of clear cells and the upper green cells.  It shares with them the elongate leaves with strong midrib, and the upright spore capsules with long twisted teeth around the opening.  Leaf cells in the upper part of the leaf are small, round and papillose.

Leaves of Tortella densa illustrate the distinctive leaves of the genus.  Note the V-shaped boundary between the large clear cells at the base and the smaller green cells of the tip.  Photo by Hermann Schachner, posted on Wikimedia, Creative Commons license.

The long, twisted teeth around the opening
of the spore capsule, characteristic of
Tortella and several other genera of the
Pottiaceae.  Photo courtesy the Western
New Mexico University, Department of
Natural Sciences and the Dale A.
Zimmerman Herbarium,
Plants of the Gila Wilderness.

Tortella flavovirens (Bruch) Brotherus and T. humilis Hedwig both form low colonies of upright leafy shoots, with leaves distributed uniformly around the stem (radially symmetrical).  Capsules arise from the tips of the shoots. In T. humilis the stems are  elongate, forming loose tufts, while in T. flavovirens, they are more compact, forming dense mats of rosettes.

In Florida, both species occur scattered throughout the state. Tortella humilis is found throughout eastern North America and in scattered mountain locations from New Mexico to British Columbia. It is found inland on soil, tree bases, and rocks. T. flavovirens has a more southern distribution, from Texas to North Carolina. It is tolerant of salt spray and is confined to coastal vegetation.

Mosses of Central Florida 40. Vesicularia vesicularis

Vescicularia vesicularis growing at Castellow Hammock,
Miami-Dade County. Photo by Scott Zona

Vesicularia vesicularis (Schwagrichen) Brotherus (Hypnaceae) is a creeping
moss found on moist soil, logs, rocks, and sometimes submerged in running water.  The ovate, smooth-edged leaves lack a midrib, but may have two very short ribs at the base. Leaf cells are oval to diamond-shaped in the upper leaf, somewhat smaller and roundish at the base.  The spore capsules are symmetrical and short-cylindric, becoming constricted below the opening when dry, and are nodding by a bend in the upper stalk.

The capsules of Vesicularia are nodding or slightly skewed to the side, but not asymmetric like
Isopterygium.  Photo by Scott Zona.

This species is similar in habit and general appearance to the common Isopterygium tenerum, which is also in the Hypnaceae, from which it differs most clearly by the shape of the leaf cells and the spore capsules.  In Isopterygium, the leaf  is more drawn out into a narrow tip, which is somewhat toothed, and the leaf cells are elongate and worm-like.  The capsules in Isopterygium are asymmetric and bent to the side like a bird's head.

This is a tropical species found throughout the new world tropics. In the U.S. it is found only in Florida and Louisiana. In Florida it has been collected in scattered locations throughout the peninsula and in Santa Rosa County.

Mosses of Central Florida 39. Barbula indica

A dried specimen of Barbula indica,
showing the leaves twisted around the
stems. (from  Merner s.n. 20 Sep 1970,
USF)

Barbula indica (Hooker) Sprengel (Pottiaceae) forms cushions of upright stems as high as 1.2 cm, mostly on limestone rocks. The leaves are narrow-ovate in shape and clearly grooved on the upper surface along the strong midrib, spreading when wet but rolled together and twisted when dry.  Leaf cells are roundish and papillose, with larger clear cells at the base.  Spore capsules are rarely seen in Florida, but when present are upright, more or less symmetrical, and have  long, twisted teeth around the opening.

A piece of limestone with Barbula indica and Hyophiladelphus agraria (with orange capsule stalks near the top) From Newberry s.n. 25 Feb 1971, USF.

This species, usually differentiated as Barbula indica variety indica, is found throughout the world, including much of eastern North America, Alaska and the Canadian Northwest Territories.  In Florida, it has been collected spottily throughout the state.  Another variety,  B. indica var gregaria is found widely in tropical America, but oddly only in Alberta, Canada in North America.

The family Pottiaceae, at least in central Florida, can be recognized by its upright, radially symmetrical shoots, with papillose leaves, and most often occurring on limestone.  Other central Florida genera in the Pottiaceae include Weissia, which has short, rosette-like leafy shoots with narrow, sword-shaped leaves that are strongly inrolled at the edges, and capsule teeth that are short and straight. It is also more likely found on soil.  Hyophiladelphus occurs also on limestone rocks, sometimes mixed with Barbula, and also has long twisted teeth around the opening of the capsule, but has short, rosette-like shoots, and leaves that are only rarely papillose. Tortella  is also similar but the leaves have a very distinctive V-shaped pattern of clear basal cells.

Mosses of Central Florida 38. The genus Neckeropsis

A single leafy shoot of Neckeropsis
disticha, showing the broad, blunt-tipped
leaves, arranged alternately on the two
sides of the stem. Photo from a rehydrated
herbarium specimen, (Lassiter 892
(USF))

Two species of Neckeropsis (Neckeraceae) occur in Florida: Neckeropsis disticha (Hedwig) Kindberg (Neckeraceae) and Neckeropsis undulata (Hedwig) Reichardt. The two species have a similar growth form, what has been described as "shelf-forming," with flattened, fern-like  leafy shoots that extend horizontally from their attachment to the sides of tree trunks, logs, and sometimes rocks.

The leaves are broad and blunt-tipped, with midribs that don't reach the tip. Leaf cells are roundish near the tip, but more elongate further down. The spore capsules, shaped like champagne glasses, are essentially stalkless, and located along the leafy shoots, nestled within crowns of narrow, bract-like leaves.

The leaves of Neckeropsis undulata are distinctively rippled. Photo by Elizabeth Lavocat Bernard.

The spore capsules of Neckeropsis disticha are scarcely
pushed beyond the leaves by their very short stalks.
Photo by Elizabeth Lavocat Bernard.

Both species of this pantropical genus are found in Florida from Citrus and Semiole Counties southward.  They differ most conspicuously in their leaves.  Those of Neckeropsis undulata are rippled, like crisped ribbons, while those of N. disticha are more or less flat when wet, or slightly wavy when dry.

The spore capsules of Neckeropsis undulata are distinctly
larger than those of N. disticha.  Photo by Elizabeth
Lavocat Bernard.

I am grateful to Elizabeth Lavocat Bernard for permission to use photographs from a blog article on the bryophytes of Guadaloupe on the website MOVECLIM (MOntane VEgetation as listening posts for CLIMate change).

An additional interesting photo displaying the shelf-like growth pattern of this genus can be viewed at:
Neckeropsis undulata by Scott Zona