Thursday, April 28, 2022

When Kangaroos Came Down from the Trees

by Rileypie

Kangaroos are marsupials, that unique group of mammals that originated in the Americas, then crossed Antarctica 55 million years ago to end up in Australia by around 25 million years ago. Although kangaroos do not belong to a single species, but to several related species in the family Macropodidae, the group is characterized in the mind of the public as all having disproportionately large hind legs and a propensity to hop along the savannas that it inhabits.

But people today would probably not even recognize the ancestors of these iconic mammals, which were opossum-like critters that spent their lives up in the trees and first ate fruits and then tree leaves. The prevailing view at one time was that the kangaroos did not move down from the trees until around 15-5 million years ago, when growing aridity in Australia caused them to gradually evolve to have the attributes we see in them today.

Modern kangaroos loiter about in their grassland home (by By AWS10)

But a new study disputes that theory.

Researchers studied the teeth of more than 1600 kangaroo specimens, both from modern kangaroos and their fossil ancestors. They focused on the crown height and wear on the teeth, which gave them an indication of what the animals ate. Animals that eat relatively soft foods such as leaves and fruit do not have high crowned teeth, and the wear on the teeth is much less than if the animal ate something abrasive such as grass. This is because grasses are filled with silica bodies called phytoliths, which make eating them akin to eating sand, and the high crowned teeth is an adaptation towards eating such tough food.

Modern Tree Marsupial, who remained in the trees, by By Fred Hsu

When these researchers looked at the changes in teeth from the ancestors of kangaroos to their modern counterparts, they found that the change in dentition (from low crowned to high crowned teeth) and explosive radiation of kangaroo species did not happen as the land first grew arid (15-5 million years ago). Instead, this change only happened 3 million years ago, when C4 grasses started pushing back the trees and forests to create the grasslands and savannas that are now so prevalent in that continent.

This tight correlation between the expansion of grasslands in Australia and the evolution of the kangaroo as we know it today again highlights the importance of our old growth grasslands to the rise of so many iconic and magnificent animals. 

In fact, without the grasslands, our own ancestors would not have done the same thing as the kangaroos did, and we might still be lounging lazily in the treetops today, our minds bereft of the keen intelligence that (allegedly) is a hallmark of Homo sapiens.


Couzens AMC, Prideaux GJ. Rapid Pliocene adaptive radiation of modern kangaroos. Science. 2018 Oct 5;362(6410):72-75. doi: 10.1126/science.aas8788. PMID: 30287658.

Monday, April 18, 2022

The Mysterious Origin of Andrews Bald in Great Smoky Mountain National Park

View at Andrews Bald using Panorama setting of Phone Camera

Lying just an hour and a half walk away from one of the most popular tourist destinations in Great Smoky Mountains National Park is a large grassy area that sits atop a mountain. Since it is still below the timberline, all around this open expanse are tall spruce and fir trees, which provide a very shaded environment for hikers who venture out from Clingman's Dome and want to do the 2.5 km trek to this somewhat anomalous area.

The hike itself is moderately easy and quite peaceful, although the almost continuous upward incline on the way back was somewhat strenuous. Recent upgrades to the trail provided nice steps and above-ground planks at certain points that allowed us to move quickly over the sometimes muddy ground.

Narrow boardwalks and steps provide sure footing for hikers

After about an hour and a half we finally burst into the open air and gazed upon an amazing grassy meadow that covered about 1.6 hectares of the mountain top. The change from the dark forested interior to the sunlit top was fairly dramatic, and many people had draped themselves over the lawn-like ground close to the opening, although it was only April and most of the grasses had yet to green and were a dry golden color.

We had finally arrived at Andrews Bald, which at 1800 meters (1.8 km), is the highest so-called "bald" in the Great Smoky Mountains National Park.

Wooden path emerges from forest into Andrews Bald

These "balds" are grassy meadows below the timberline which are found in the southern Appalachian Mountains, and the origins of most are shrouded in mystery. The dominant grass is usually Danthonia compressa, but other grasses such as redtop (Agrostis alba), timothy (Phleum pratense), Canada bluegrass (Poa compressa), Kentucky bluegrass (P. pratense), and red fescue (Festuca rubra) may also be found.

The trail continues, with a view to other parts of the Great Smoky Mountains

Some researchers believe Native Americans originally cleared the areas as hunting grounds or lookouts, and there are historical records that seem to indicate that settlers cleared some of the balds for grazing. There are even some who postulate that the balds had been originally founded by prehistoric herbivores, and then maintained by human hands thereafter.

Whatever the case, there is no doubt that the balds had been used as grazing land during the 1800s. The cattle and sheep that were herded up onto these ridgeline areas during the summer months kept the land open, but after the formation of the national park and the cessation of grazing in the 1930s, trees and shrubs have been slowly reclaiming the land.

Andrews Bald, with visitors (dots on far left) sunning themselves on the golden Springtime grass

A quick look at historical satellite imagery from Google Earth shows that Andrews Bald went from being around 2.5 ha in size in 1995 to around 1.6 ha in 2017 (see image below), and if grazing continues to be excluded from the area, then it is probably inevitable that the bald will continue to shrink in the future. 

But for now, visitors can continue to enjoy the relatively open vista possible in Andrews Bald. It may not be the vast green expanse that it used to be, but I still highly recommend it if you ever visit Great Smoky Mountains National Park.

Area of the meadow shrunk from 2.5 to 1.6 ha from 1995 to 2017

Thursday, April 14, 2022

Rushes are Round: Finding Luzula in Great Smoky Mountain

Although this site is focused on the Poaceae, the other members of the order Poales can oftentimes be mistaken for grasses. This is especially true for members of the families Juncaceae (rushes) and the Cyperaceae (sedges), which are sometimes even given common names that mistakenly identify them as grasses. 

In this case, there is an old adage that might help people separate the three. It goes:

Sedges have edges. Rushes are round. Grasses are hollow. What have you found?


Sedges have edges, rushes are round, Grasses have nodes all the way to the ground.

So, if the stems have corners and edges (roll a stem between your thumb and forefinger), then it's likely what you just thought was a grass is actually a sedge, and if the rounded stems are not hollow and have no nodes spaced along their length, then you probably have a rush.

This rhyme helped me during a hike along the Grotto Falls trail in Great Smoky Mountain a couple days back, when I spied some graminoids near the edge of the wet path that had lots of spiky inflorescence at the top. They were notable because this early in the season, almost none of the grasses had any reproductive structures out yet, 

This particular specimen seemed to be a grass on first look, but when I took macro shots of the flowers and felt around the stems, I decided I was probably mistaken. I could not find any solid nodes along the stems (although granted, this early in the season, everything was still pretty low to the ground), and the round stems seemed to have a solid interior.

Now, I am horrible at identification, but I believe what I found on that day was Luzula multiflora, or the common wood rush, a member of the Rush family. The long white hairs on the leaves and stems indicates it belongs to genus Luzula, and the multiple flowers on variable length stalks separates it out from L. acuminata.

It is a circumpolar species but is listed as relatively scarce in this national park, so if I identified it correctly, then I was quite lucky to see it during that hike!

Long white hairs that is typical of Luzula spp.

Sunday, April 3, 2022

Spreading the New Concept of Alternative Biome States (ABS) to Save Our Old Growth Grasslands

Old-growth grasslands are grass-dominated open biomes which are ancient (some are tens of millions of years old), have high endemism and diversity (they are more diverse than rainforests at some scales), and are slow to reassemble once they have been degraded (more than a millennium according to studies). This ecosystem is one of the most endangered in the world, and misguided efforts to fight climate change by mass tree plantings can only hasten their demise.  

One of the major impediments to the widespread acceptance of the concept of ancient grasslands among the general public is the outdated notion that there is only one natural climax community. This wrong idea that ecological succession is a ladder-like process and that closed canopy forests (e.g. rainforests) are the ultimate goal in nature is deeply entrenched in the public consciousness. It promotes the wrong notion that all grasslands are simply forests that are waiting to happen, and are thus exempt from our protection and conservation.

It must be replaced by the more accurate paradigm of Alternative Biome States (ABS).

African Tropical Grassland (Savanna), by Gossipguy)

What are Alternative Biome States?

New research has shown that open old growth grasslands are a natural alternative to dark shaded forests, and that they can maintain themselves without any human intervention over thousands and even tens of millions of years. Neither grasslands nor forests are the "ultimate" expression and final state of natural succession. Instead, an area whose climactic and soil characteristics can theoretically support both grasses and trees alternates between the two stable biome states depending on other, more local factors.

North American Temperate Grassland (Osage Plains Prairie in Missouri), by Pat Whalen
What local factors keep the two biomes stable over time?

Grasses have harnessed two local factors to help push back forests. Some species have evolved with natural fire, while other grass species have partnered with large herbivores (e.g. elephants, bovids like antelopes, buffaloes, bisons, etc). Both of these "allies" can kill or weaken trees, as well as tree seedlings and saplings. This keeps the grassy biomes sunlit and open, which is the optimum environment for many sun-loving members of the Poaceae.

On the other hand, the dark humid interior of forests is not a welcome environment for most grasses. C4 grasses in particular grow best under the wide open and sunlit skies, and the high humidity and lack of wind also helps keep grass-induced fires from penetrating the inhospitable interior of the forest.

These counteracting forces on both sides stabilize the alternative biomes and allow each one to flourish.

South American Tropical Grassland (Cerrado), by Eliane de Castro)
How are these biomes switched from one state to the other?

Although old growth grasslands and forests are naturally stable over potentially long periods of time, strong perturbations can be enough to tip them over to the alternative state. 

For example, one or two strong forest fires in a region plagued by drought could be enough to quickly turn a closed canopy forest to an open ecosystem, as fire-adapted grasses and other plants colonize the resulting gaps in the forest. This can create a strong feedback mechanism whereby the gaps are widened as the flammable vegetation contributes to more fires going forward, with large herbivores following the grasslands to help keep the trees out.

This scenario created the great savannas in Africa as early as 15 million years ago, when C4 grasses started pushing back the forests to create new and sunlit open landscapes. Evidence of the rise in grass-fueled fires during this period of grass expansion is etched in charcoal deposits, as well as in the phylogeny of savanna-living underground trees, whose lineages increased in response to the rise of the new open biome. It was also around this time when the ancestors of large iconic megafauna like antelopes and other mammalian herbivores radiated into many more species to fill the new ecosystem.
The opposite transition from forest to grassland is usually more gradual, but just as inevitable. If fire and mammalian herbivores are somehow excluded from open ecosystems in areas whose climate and soil can support both biomes, then trees will gradually shade out the grasses and other smaller sun-loving plants. 

African Tropical Grassland (Savanna), by Bjørn Christian Tørrissen
What can you do?

Champion and spread the new paradigm of Alternative Biome States (ABS) as a replacement for the outdated concept that ecological succession is a one directional process towards shaded closed canopy forests. The elevation of open ecosystems as a natural alternative to forests will help protect and conserve our ancient and biodiverse grasslands and the countless other plants and animals that live there.

North American Temperate Grassland (Konza Prairie in Kansas), by Jill Knutson Hauko

Pausas JG, Bond WJ. Alternative Biome States in Terrestrial Ecosystems. Trends Plant Sci. 2020 Mar;25(3):250-263. doi: 10.1016/j.tplants.2019.11.003. Epub 2020 Jan 6. PMID: 31917105.

Tristan Charles-Dominique, T. Jonathan Davies, Gareth P. Hempson, Bezeng S. Bezeng, Barnabas H. Daru, Ronny M. Kabongo, Olivier Maurin, A. Muthama Muasya, Michelle van der Bank, and William J. Bond (2016). Spiny plants, mammal browsers, and the origin of African savannas. PNAS DOI: 10.1073/pnas.1607493113