Expansion of an Invasive Grass Over a Decade as viewed using Satellite Imagery from Google Earth

The field of Imperata cylindrica at ground level (February 2022)

Last year, I found that one can track and view the progress of vegetation over time using Google Street View. This time, I used satellite imagery from Google Earth Pro (Desktop) to examine the expansion of clusters of Imperata cylindrica (cogon grass) as they spread across an open field over almost a decade.

Drone pic of red-hued Imperata cylindrica (cogon grass) clusters from height of 100 m (February  2022)

I used historical satellite imagery from Google Earth Desktop to visualize the progress of the invasion from 2012 to 2021, then made an animated gif (see below) to show clearly how the initial small clusters spread and fused to form contiguous areas of infestation.

Animated GIF showing expansion of I. cylindrica from 2012-2021

As can be seen from the animated gif above, a large cluster slowly expands while multiple smaller clusters develop and grow over the years. Each of the small infestations grows in a circular pattern, which is common during the spread of this rhizomatous species. In 9 years, the area of the field in view that is covered with cogon grass increases to at least five times what it was in 2012, pushing towards 8000 sqm in size  - an area equivalent to almost 2 American football fields!

The gathering of such data shows that the use of online tools like Google Earth and Google Street View holds promise as an informal way of amassing historical data. This is because they allow anyone to derive useful information in an easy and efficient manner. Hopefully, more people learn how to use such tools to advance our knowledge about the world around us.

Well Hello There Cutie Pie: Melinis repens

Masses of Melinis repens (Natal grass) alongside railroad track

In late January, I was walking near the Kissimmee City Hall, when I noticed pinkish-white flowered plants carpeting the side of the nearby railroad track. Being naturally curious, I wandered over to the tracks (making sure there were no incoming trains!) and marveled at the masses of grasses that lined it. Unfortunately, I did not have my macro lens with me, but I took some pics anyways using my 50 mm lens (although I took an inflorescence and later took macros of the spikelets).

Habit of Melinis repens (Natal grass)

I later identified the grass species as Melinis repens (Natal grass), which is originally from Africa and considered an invasive here in Florida, with the potential to push out native species. However, studies have shown that it is somewhat limited to specific microhabitats, and does not seem capable of really invading intact scrub (David and Menges, 2011).

Pretty flowers of M. repens

Using the macro, I could just make out the purple haired glumes  that surround the two closed flowers, one of which is sterile. 

Overall, even though it is non native and might be invasive, I still found the grass to be quite attractive. One of those small grass species with tiny, but pretty flowers. 

Just don't start planting them in your garden and helping them spread!

2-flowered spikelets of M. repens

Literature Citedn

David, A.S., Menges, E.S. Microhabitat preference constrains invasive spread of non-native natal grass (Melinis repens). Biol Invasions 13, 2309 (2011). https://doi.org/10.1007/s10530-011-0044-5

Through the Fire: How Grasses Rise Up from the Flames

Aristida beyrichiana (wiregrass), a resprouter

The fact that the Poaceae use fire to create stable ecological states like grasslands and savannas is well known, but resolving the fine details on the mechanisms underlying these processes is a work in progress.

Grass populations can recover from these fire events via two paths or so-called persistence strategies. Some species die back and resprout from underground rhizomes or undamaged crowns. These are the so-called resprouters. For example, both Imperata cylindrica (cogon grass) and Aristida beyrichiana (wiregrass) come back after a fire from surviving remnants (using tough rhizomes in the case of the former). 

Sharp rhizome of Imperata cylindrica, which is a resprouter

The other way to get a population through a fire is by reseeding. These grasses are the so-called seeders, and they include species like Taeniatherum caput-medusae (medusahead grass), Bromus tectorum (cheatgrass), and Microstegium vimineum (stiltgrass). In this case, the population develops to sexual maturity rapidly, and then sets seed, which can survive past the fire event to form a new population and generation.

Dried seedheads of Taeniatherum caput-medusae, a seeder

The two types of persistence strategies significantly affect the various morphological and physiological traits of each species, as listed in the table below.

Trait	Relationship with resprouting ability
Photosynthetic pathway	Resprouters are more likely to be C4 than C3 (Moore et al., 2019). C4 species are highly efficient in fire-prone environments and may therefore have greater stored resources to resprout (Tix & Charvat, 2005; Ratnam et al., 2011)
Bud position	Resprouters are more likely to have buds below the soil surface (rhizome resprouters) where they are protected from intense heat (Pausas & Paula, 2020)
Specific leaf area (SLA)	Resprouters will have lower SLA than seeders (Forrestel et al., 2014). High SLA will aid the rapid growth of seeder species
Leaf nitrogen (N) content	Resprouters will have lower leaf N contents than seeders. Resprouters may experience fire multiple times in their lifetime and thus low-N availability (due to N volatilisation during fire; Reich et al., 2001; Hernández & Hobbie, 2008). In these conditions, a high N-use efficiency (low leaf N content) may be advantageous (Wedin & Tilman, 1990; Reich et al., 2001)
Leaf C : N ratio	Resprouters will have higher leaf C : N ratios than seeders. High leaf C : N ratio, which is linked to low decomposition rates and the accumulation of a highly flammable fuel load (Aerts, 1997), may be advantageous to shade-intolerant resprouting species in maintaining an open canopy (by aiding the removal of standing dead and woody biomass; Everson et al., 1988)
Life history	Resprouters are more likely to be perennial than seeders. Perennial-grass species have buds from which to regrow, which annual species may lack

Table 1. From Simpson et al, 2021

These persistence strategies in grasses have a complex and fascinating relationship with the existing fire regime, but in order to understand it, the different characteristics of an existing fire regime have to be defined.

Fire Frequency is the time between fires in an area. More frequent fires tend to be more damaging to a plant.

Fire Intensity refers to the amount of energy released by the flames. Higher amounts of released energy increases the probability of severe damage or death to a plant.

Fire Severity is an index of the damage caused by a fire by measuring the amount of organic matter lost.

These three attributes are related in a simple manner. The less frequent fire events are, the more biomass can be accumulated, which leads to more intense fires and a corresponding increase in the severity of the event.

Grass seeders proliferate under fire regimes of high frequency and low intensity, whereas resprouters dominate when the fires are more intense after a longer period between fire events. The rapid sexual maturity of seeders allows them to seed quickly, and these grasses can persist even in fire frequencies that are as short as a year!  

However, if fires do not occurs frequently, this leads to a larger accumulation of fuel biomass, and more intense fires. In this case, reprouters have an advantage and will dominate an area because they do not need to pass through the more vulnerable seed and seedling stages. 

The golden hued seeder T. caput-medusae (medusahead) carpets an area

Knowledge about the relationship between fire regimes and persistence strategy is not only fascinating, but can also be used to predict community composition in a habitat given specific changes in the fire regime. For example, changes in fire regimes due to climate change can cause dramatic alterations in the ecology. It may also be possible to use this knowledge to dent the advance of invasive grasses that hew to a particular persistence strategy.

References

Simpson, K.J., Jardine, E.C., Archibald, S., Forrestel, E.J., Lehmann, C.E.R., Thomas, G.H. and Osborne, C.P. (2021), Resprouting grasses are associated with less frequent fire than seeders. New Phytol, 230: 832-844. https://doi.org/10.1111/nph.17069

What Strange Beasts: The Hidden Armageddon in Sagebrush Country

What strange beasts slither across the hidden landscapes?

There is a war going on. 

It is a war with devastating consequences and monumental importance, but one which slides below the attention of most people who otherwise care about the natural state of the world. It is a war of a scope that beggars the mind, where an entire ecosystem that has existed for millennia is rapidly being destroyed.

Sagebrush covers a huge swath of the American West

The sagebrush ecosystem in the Great Basin of the Western USA is characterized as having a shrub overstory of Artemisia spp, with sagebrush steppe areas having a large component of perennial grasses and forbs, and sagebrush shrublands dominated by larger sage species with fewer grasses and forbs. It spreads over 11 western states and occupies 62 million hectares, and it is home to a multitude of plant and animal species, some of which are threatened or endangered.

Artemisia tridentata (Big Sagebrush). From Wikipedia. 
By Peemus - Own work, CC BY-SA 3.0 

It is in this gargantuan stage that a fight to the death has been ongoing for decades, although mostly hidden from the eyes of people. Hordes of invasive annual grasses are sweeping through the landscape like a scythe, rapidly converting sagebrush into a sea of low lying grasses. One study estimates that more than 200,000 ha of sagebrush are destroyed and replaced by exotic annual grasses every year (Smith et al, 2021). This is a mind boggling number, an area that is twice the size of Los Angeles and nearly triple the land area of New York City!

Intact sagebrush habitat. Wikipedia. By Famartin

Conversion to a sea of exotic annual grasses

Yet typical invasive species groups in social media almost never mention the rapid destruction of these expansive ecosystems, and perhaps this is understandable. People tend to focus on invasives that are closer to home, and those that blight their day to day lives or their recreational activities. The sparsely inhabited and pristine sagebrush areas are thus a blind spot when it comes to most. The most ferocious winter annual grasses that are swallowing up the Great Basin are relative unknowns, and include species such as Bromus tectorum (cheatgrass), Taeniatherum caput-medusae (medusahead grass), and Ventenata dubia. 

Taeniatherum caput-medusae (medusahead grass) 

Yet the consequences of our blindness may just be as dangerous as the spread of more well known invasives in the suburbs and rural areas. Not only does the sagebrush ecosystems support major endangered species like the Sage Grouse, but this annual grass invasion results in major economic losses as rangeland is lost. 

 

Bromus tectorum (cheatgrass) sprawls along hillside in Bandelier National Monument in New Mexico

In addition, the annual winter grasses use fire as a way to increase and maintain their stranglehold on the land by increasing the frequency and intensity of wildfires (see diagram below). This makes their spread dangerous for human lives and habitation, and in fact these grasses contribute to the huge wildfires that are engulfing the American West and destroying not only our homes but irreplaceable national treasures as well, such as the iconic and ancient Sequoias trees. 

How one winter annual invasive achieves dominance

It is far too late to eradicate these annual winter invasives, and efforts to reclaim land dominated by them have failed to yield fruitful results on a large scale, so land managers are now exploring various other options to mitigate their spread by focusing only on areas that have so far escaped this armageddon  (Maestas et al, 2022). 

We can only hope that it is not too late.

Bromus tectorum

Aegilops truncialis

Maturing Taeniatherum caput-medusae

Literature Cited

Jeremy D. Maestas, Mark Porter, Matt Cahill, Dirac Twidwell (2022). Defend the core: Maintaining intact rangelands by reducing vulnerability to invasive annual grasses, Rangelands, ISSN 0190-0528, https://doi.org/10.1016/j.rala.2021.12.008.

Smith, J.T., Allred, B.W., Boyd, C.S., Davies, K.W., Jones, M.O., Maestas, J.D., Morford, S. L., Naugle, D.E., 2021. The elevation ascent and spread of exotic annual grasslands in the Great Basin, USA. bioRxiv 2021, 425458

The Symbolism of the Bamboo Planet as Home of the New Jedi Temple (Star Wars: The Book of Boba Fett Episode 6)

SPOILERS WARNING!

Do not read if you are about to watch episode 6 of the Boba Fett Saga.

What a great episode in the new Star Wars series on Disney Plus!

Not only did we get to see many of the major characters in Star Wars come back, but the setting for most of the new episode is on a planet that seems to be dominated by various bamboo species!

In this episode, the Mandalorian travels to where he believes Luke Skywalker has taken Grogu.

When he lands, the first thing he meets is the venerable R2-D2, who guides him through a bamboo forest to a clearing, where ant-like robots are building what looks to be a stone structure. 

R2-D2 guides the Mandalorian

When the Mandalorian presses him on the whereabouts of Grogu, R2-D2 shuts down and the Mandalorian is forced to rest on a bench that the ant-like robots made for him using stones and bamboo poles.

The bamboo bench

Meanwhile, we cut to Luke Skywalker and Grogu in the bamboo forest. Luke is teaching Grogu how to become a Jedi, and there are many scenes of them in various settings surrounded by bamboo.

In one scene, they are walking along a trail through the bamboo forest, and Luke asks Grogu whether he wants to remember what happened to him in the past. When Grogu seemingly gives assent, Luke places his hand on top of Grogu and we suddenly see scenes of battle, with Clone Troopers killing Jedi and Grogu staring in horror at the devastation.

Luke Skywalker and Grogu walking along a bamboo grove

In another scene, Luke takes Grogu on his shoulders, just like he did Yoda when he himself was being trained as a Jedi, and Luke runs through a forest filled with huge bamboos, before climbing nimbly up to the top of the canopy. 

Luke Skywalker climbing up bamboo stand with Grogu on his shoulders

There Luke tells Grogu about the Force, and how the world exists in balance, and that through the Force Grogu will find balance as well.  It is a moving moment, with the two staring out towards the wider world, and bamboo leaves fluttering around them in the breeze.

Feeling the Force

Finally, we cut to a small clearing surrounded by gigantic bamboo, and we see Grogu balancing successfully on a bamboo culm, while Luke draws his lightsaber and displays his swordsmanship. It is another moving moment in an episode with so many deep emotional currents.

Grogu balancing on a bamboo culm

My favorite character Ahsoka Tano then suddenly shows up. There is no fanfare, no big reveal. The Mandalorian suddenly realizes he is not alone, and when he stands quickly from his rest and draws his gun, he is confronted by Ahsoka, who is casually leaning on some bamboo culms and waiting for him. 

Ahsoka Tano talks to the Mandalorian

She tells him that the structure being built is going to be a new Jedi temple, and that Grogu will be its first pupil. When the Mandalorian insists on seeing Grogu, she leads him through the bamboo groves and tells him he has the option of seeing Grogu, but that this meeting would only cause more difficulty for the child. After some thought, the Mandalorian decides that he will not see Grogu, but he asks Ahsoka to give the child a suit made from Mandalorian armor.

Near the end, we see Ahsoka and Luke talking by a lake, bamboo trees behind them, as Luke asks her what he should do with Grogu. Ahsoka responds that he should trust his instincts, and when she turns to leave, Luke wonders whether he would see her again. She says "perhaps" and wishes him farewell in that most time honored of fashion: "May the Force be with you."

Luke Skywalker 

The continuous use of scenes with bamboo in this episode is likely not accidental. 

In many Asian cultures, bamboo symbolizes harmony and balance, mainly due to the fact this grass features an unmatched combination of flexibility and strength in the structure of its culm. This is analogous to the balance that Luke tells Grogu is inherent in the Force. George Lucas had been heavily influenced by Eastern mysticism in his creation of the Star Wars Jedi ethos, and especially by Taoism, and the series continues to hew to this bias by using bamboo as the primary setting for Grogu's training.

The fact that the planet will also be home to the new Jedi Temple is also heavily symbolic. Bamboos are the fastest growing plants in the world, and they can also be used to symbolize the nascent growth of the Jedi after their decimation by the Sith Emperor.

I cannot emphasize enough how cool this episode was, not only because of the introduction of many of the most beloved characters in the Star Wars universe, but also because of the many beautiful scenes of bamboo that surrounded (and perhaps defined) them.

Go watch it!