Neglecting the natural

This is going to be a short rant, so if you hate rants, please feel free to skip the post.

I am staying in Kissimmee near Orlando in Florida. As some people may know, this city hosts the theme park Walt Disney World. What most may not know is that there is a nearby preserve that is called the Disney Wilderness Preserve, which is maintained by the non-profit Nature Conservancy.   

I visited this preserve and I was amazed at the beauty of the place.

The major part of the preserve is open Pine lands with absolutely gorgeous fields of grasses (dominated by the usual Andropogon and Aristida spp), and sprinkled with multitudes of shrubs and forbs and other plants. Even though it was a scorcher of a day, I barely noticed as I was busy glancing around and taking pictures of the colorful landscape.

The sad part was that there was barely any visitors to the park. A handful of cars dotted the parking lot, and  we did not meet any other hikers in the trails themselves, although a couple followed in our wake for a short while.

Meanwhile, I am sure the nearby theme park was packed with people (or at least semi packed, given the still potent sting of Covid-19), who probably would not give a darn that this preserve exists. We live in a world where artificial pleasures reign supreme; a time when virtual excitement through videogames and other activities far removed from the natural are the norm.

I am not really mad about this. People are free to choose what fulfills their lives. But I am sad that such beautiful places as the Disney Wilderness Preserve barely attract notice in our modern frenetic world.

Update (January 25, 2022): I have had more occasion to visit this place and I am glad to say there are times (especially the weekend) when there are quite a number of people visiting and appreciating the natural beauty of the preserve.

A meeting of giants

Flowerhead of C, purpureus

I admit I am not your typical tourist. Sometimes I like to wander the streets of cities I visit, just looking at all the flora and fauna to be seen. This was the case when I visited Florida City in Florida, which is close to Everglades National Park and Key Largo.

I was walking along the sidewalk of a busy street in this smallish city (ok, it was Route 1, a state highway!), when I had to do a double take. Along a dead-end side street next to one of the many motels in that area was a long row of gigantic grasses! 

Long row of gigantic grasses

They were tightly packed and stretched in an unending row from the start of the street (SE 1st Ave) to its end near the motel back. The grasses rose to 4 meters in height or more, and above some were whitish flowerheads.

Schoolbus parked next to C. purpureus for scale. 

My first thought was that I stumbled on Arundo donax, but a quick inspection of the flowerhead nailed the species as Cenchrus purpureus (syn. Pennissetum purpureum), which has various common names such as Napier grass, elephant grass, and Uganda grass.

Young C. purpureus spreading across a recently fallow lot

The grass had spread from the row to infest a field of trees behind it. The land looked abandoned, but a quick look at Google Street View from previous years showed that it had once been carefully tended, with palms planted in neat rows. Now young Napier grass sprouted from all over the field, and I was thinking that without tending that the lot would soon be filled with it. I also encountered another large stand of Napier grass east of the motels, along with smaller clusters that must have been derived from the larger stands (see image below).

C. purpureus in yellow, N. reynaudiana in red.

Interestingly enough, I spotted other large grass stands in the distance in the empty lot, but a quick look showed that they were a different species!

I trudged into the lot and found out that the new grasses were Neyraudia reynaudiana (Burmareed), their gigantic forms topped by huge plumes of brownish flowerheads. They were scattered in small clusters, and the nearest group was about 30 meters away from the equally tall Napier grass.

Neyraudia reynaudiana

I wondered what would happen when the two species finally met in that empty lot. Would one species be dominant over the other, or would they coexist, the two groups forming a field of gigantic grasses with distinctly different flowerheads? Which grass would prevail in this clash of giants?

Another interesting thing is that I have seen both species all over Southern Florida, but they both become much rarer as one travels north. I have not seen Burmareed in Lake Okeechobee (though I have seen what I took to be Phragmites australis in the distance next to the lake), while Napier grass was quite abundant on the northern lake shore. However, once one gets closer to Orlando, the glimpses of giant grasses becomes rare to non-existent, and I have only seen one cluster of Napier grass in the Orlando area. The specimens were located in Shingle Creek Regional Park, and they seemed a bit unhealthy looking.

N. reynaudiana on the road to Everglades National Park

It is a change to the landscape that is quite evident, perhaps even to the eyes of laymen. The land of giant grasses transforms into a land filled with Andropogon sp. and Aristida sp., much smaller grass species that nevertheless dominate many areas in a way that even the giants might envy.

Spider lurking in a C. purpureus inflorescence

From googly to reality

The reality

In a previous post I talked about the use of Google Street View and how it can allow one to view the spread of invasive species over time. 

The Googly (from Google Street View)

The example I used was for Neyraudia reynaudiana (burmareed), a tall fire-adapted grass which has been destroying Pine Rockland ecosystems in Florida.

I swear that I was not looking specifically for it, but I somehow ended up in the same place during an exploration in Homestead, FL. In fact, I did not realize it was the same place until I came back to the hotel and mapped the location on Google Maps, where I was extremely surprised to discover the coincidence.

The masses of N. reynaudiana was heaps more impressive in person, their huge 3-4 meter tall forms towering above me like some impenetrable wall, and I stood there for so long that some local started eying me suspiciously as I wondered at the stately grass. Perhaps he thought I was some drug dealer waiting for a rendezvous, or perhaps he was simply wondering why the crazy guy was taking pics of the grasses. 

The world works in mysterious ways, and sometimes it gives a pleasant surprise.

A Slow Motion Carnage

The dried brownish seedheads of Andropogon sp face off with the white fuzzy spikes of Cogon grass (I. cylindrica)

The scenery that lazy afternoon seemed almost pastoral to human eyes, a landscape of tall trees and grasses waving in the breeze. But in reality, such a depiction was quite deceptive.

Grasses and other plants mostly live in slow time. We see them as a green backdrop to the fast movements of the animals that depend and live with them, but they are of course living things. They are dynamic entities, not passive observers. They  fight and cooperate with others and die messy deaths just like animals, albeit at a pace that is glacial relative to our own fast paced lives. They can in fact be every bit as vicious and aggressive as animals.

The forces arrayed. Red arrow shows main cluster of Cogon grass

In this case, the location is Lakes Park in Fort Myers, FL. The combatants are a native grass (Andropogon glomeratus) on one end, and a world-conquering invasive (Imperata cylindrica) at the other end. The situation is dire for the native stand, with the cogon grass massed in an extremely dense cluster next to it. In the photograph above, the erect light-green blades of I. cylindrica are to the right, with its main boundaries marked by the red arrow. To the left are individuals of A. glomeratus, their seedheads rising above the fray like flags set out for battle. Unlike the cogon grass, the native grasses exist in a looser grouping with more forbs in it.

Beautiful seedhead of I. cylindrica

It is easy to tell the two apart. The seedhead on Cogon grass is much slimmer and almost pure white. It is fluffy in texture and quite distinctive. I've seen videos of entire fields of the cogon grass flowers, and they are simply beautiful, notwithstanding the fact the species is a weed in almost every single place where it has taken hold.

Anthers and stigma of I. cylindrica

The battle is joined when the I. cylindrica rhizomes encounter the roots of the native grass. The rhizomes of cogon grass comprise up to 60% of the total biomass of the plant, and not only are their sharp tips capable of piercing through the flesh of their adversaries, but they also inhibit germination and growth of nearby plants through the excretion of allelopathic chemicals. In addition, cogon grass roots are strong competitors for soil nutrients such as phosphorus. 

Cogon grass rhizome

But their most effective attribute is that they quickly allow cogon grass to push into nearby territories as they produce shoots along their length. Established stands of cogon grass can have from 3 to 11 tonnes per hectare of rhizomes, supporting 3 to 6 million shoots.

The battle is joined

It is a silent battle that is waged for nutrients underground, and for light and space above - one whose ferocity and destructiveness is undetectable to passing human beings.

But in the end, this is probably going to be less of a battle than a carnage. The dense cluster of cogon grass will slowly expand into the A. glomeratus territory, following in the wake of the underground rhizomes. When I peered into the area that still had native forbs and grasses in it, I could see numerous cogon grass blades pushing up from the soil (see photo below), the underground rhizomes moving relentlessly outward. 

I knew that if nothing were done about it, that these small blades of grass would ultimately engulf the remaining natives. The doomed natives would put up a fight, but I thought that the next time I visited the park that I would most likely see a much larger mass of white seedheads, and perhaps only a few scattered individuals of Andropogon left. 

The young yellow-green blades of I. cylindrica pushing into enemy territory

The Major Grasses of the Pine Flatwoods and Sandhills of Florida

Any corrections to the identification of the species are always welcome. I do not pretend to be an expert at it.

It's quite interesting to hike and see the various habitats in central and southern Florida.

In addition to the hardwood hammocks which contain broadleaved trees, the most common ecosystem I've seen are the mesic pine and scrubby flatwoods, as well as the pine sandhills, which contain various dominant grasses. 

Shrub and Scrub understory at Oscar Scherer State Park

When I hiked, one of the most common understory denizens of these ecosystems were the very distinctive Saw Palmetto (Serenoa repens), which forms the shrubby layer below the taller pines and Sabal palmetto.

Grasses at Oscar Scherer State Park

But there were also vast areas covered with various grasses in these ecosystems, and it was quite amazing to see them waving in the wind below the tall stately pines and Sabal palms. Although there were smaller stands of grasses in area with a denser canopy, the really large stands occurred when the canopy was more open.

Andropogon along the path at Ocala National Forest

One of the more distinctive species I saw while hiking was Aristida beyrichiana (wiregrass), which is one of the common denizens of these sandhills and flatwoods. This species is a major component of the ecosystem and is so reliant on fire in that it only produces viable seeds when a fire goes through the area during the growing season.

A. beyrichiana at Ocala National Forest

The other grasses all tended to be from the genus Andropogon, with A. virginicus dominating in some areas, in addition to being quite obvious as weedy occupiers of roadsides all over the central and southern portions of the state.

A. virginicus at Ocala National Forest

Another Andropogon that looks somewhat similar, although with much thicker and profuse seedheads was Andropogon glomeratus, although some botanists consider this to be a subspecies of A. virginicus.

A. glomeratus

In addition to the major native grasses, I also stumbled on a few pockets of Imperata cylindrica (cogon grass), which is usually treated when found by workers in the parks.

I. cylindrica (Cogon grass) at Oscar Scherer State Park (straight blades in foreground)

In Oscar Scherer State Park for example, I found a small cluster somewhat hidden close to the periphery of the park. It had probably escaped detection due to being off the main path.

I. cylindrica (Cogon grass) at Ocala National Forest Campsite (in foreground)

At Ocala National Forest,  I found spreading clusters near the area reserved for camping, where it looked to be slowly muscling aside the other understory vegetation.

I also saw some interesting animal species during my hikes. One of the most memorable was when I accidentally bumped into a Gopher Tortoise that was crossing the trail at Oscar Scherer State Park. My wife had passed by a few minutes earlier, and the tortoise must have thought it was safe to cross the road, not knowing that I was lagging behind her (taking pics of everything).

Grasses flank the trail at the Disney Nature Preserve

It withdrew into its shell and would not come out until I had moved far away from it, whereupon it continued to trundle to the opposite side of the road, perhaps muttering about the inconsiderate humans that share its world. 

Grass understory at Ocala National Forest

A Lost Bamboo in Tampa

We were walking along the paved path in Rowlett Park in Tampa Bay, FL when I stopped in surprise.

The trees in the park were a mixture of hardwoods, including oak trees covered in Spanish Moss, as well as pine hammocks. The oaks in particular were quite enchanting in their epiphytic finery. 

But what stopped me in my tracks was a sight that seemed quite out of place in that genteel surroundings Rising up like some mountainous upthrust from between bent hardwood trees and a small palm were the beautiful culms of a large bamboo grass! 

It was as if the trees had been pushed to the side by the more aggressive bamboo, as can be seen in the image above, where I marked the trunk of one tree with a yellow arrow.

I examined the bamboo, and found that its leaves were quite delicate looking, and the culms were an attractive dark green. The bamboo reared up from the surrounding foliage of the hardwoods and clearly had no problem gaining access to the sun.

I wondered who had planted it, and when. Was it there by design, a gift from the landscapers who populated the park? Did some itinerant local gardener lovingly plant it during one of his sojourns? Or perhaps it was even a natural event, a consequence of some seed or bamboo fragment being deposited into this unlikely spot.

I also wondered whether any of the joggers and walkers and passers-by even noticed this unusual resident of their local community park, something almost miraculous in the heart of their thriving urban jungle.

For anyone interested, the coordinates of this unusual bamboo are: 28.02272,-82.43262

Diversity is not the panacea for resisting all invasions

Andropogon virginicus and Aristida beyrichiana in longleaf pine sandhill near Lake Apopka, Florida

Diversity in either species or function has been usually touted as a way for natural communities to resist encroachment by invasive species. This so-called Elton Hypothesis postulates that invasion is favored in areas with lower resident diversity, and that the greater the diversity, the less probability there is for an invasive to gain traction in the community.

There are several mechanisms by which such communities can have this feature. First, a diverse assemblage of species or functional types can use the surrounding resources more completely, and thus prevent invasives from easily being able to exploit an empty niche. Second, a diverse community has a greater degree of interspecific competition, which again means that it will be more difficult for invasive species to gain a foothold.

Imperata cylindrica smothering a roadside in Kissimmee, Florida

Imperata cylindrica (cogongrass) is a tropical and subtropical species that is one of the worst invasive plants in the world, blanketing up to 500 million hectares worldwide and costing governments millions in preventative and eradication efforts.

The species is of particular concern for pine ecosystems (both natural and artificial) in the southeastern USA. In one case, it threatens a forest community called the Florida longleaf pine sandhill, which is anchored by a pine called Pinus palustris, with an understory of oak species and a ground layer of perennial grasses and other herbaceous plants. The major grasses include Aristida beyrichiana (wiregrass) and Andropogon virginicus (broomsedge grass).

The distinctive fluffy seedhead of I. cylindrica in amongst the foliage  in Kissimmee, Florida

Cogongrass invasion of this community not only alters the lower herbaceous and shrub layer, but it slowly destroys the entire pine community by killing pine seedlings and smaller trees due to soil resource competition and an altered fire regime (which is not only more frequent but also significantly larger and hotter than normal). For example, the biomass of pine seedlings after 3 growing seasons in competition with cogongrass was only an astounding 2.4% that of pine seedlings with no competition, and 18% of pine seedlings in competition with only native vegetation (Daneshgar et al, 2008).

Distinctive fluffy seedheads of Imperata cylindrica in gated community in Kissimmee, FL

In order to determine whether plant diversity hinders the invasion patterns of cogongrass, some researchers did a series of experiments in Northern Florida. They selected 5 understory native grasses, forbs, and shrubs, then created mixtures and monocultures of each of the test species. Cogongrass was introduced into these 40 mesocosms, and the amount of biomass and cover of the invasive grass was then monitored (Daneshgar and Jose, 2009).

Contrary to expectations, the most diverse environments did not resist the cogongrass best. Instead, monocultures of the grass A. virginicus (broomsedge) were the most resistant to invasion.  In addition, mixtures that contained broomsedge resisted cogongrass better than mixtures that did not contain this species. 

The authors attributed the ability of broomsedge to compete effectively against cogongrass to its formidable underground root system, which was able to persist even in the midst of the dense roots and rhizomes of the invader, and they suggested that this native species be used to deter cogongrass from overwhelming Florida pine sandhill ecosystems.

Literature Cited

Daneshgar P and Shibu Jose (2009). Broomsedge Communities Are Resistant to Invasion by Cogongrass (Florida). Ecological Rest. December 2009 27:383-385

Pedram Daneshgar, Shibu Jose, Alexandra Collins, Craig Ramsey, Cogongrass (Imperata cylindrica), an Alien Invasive Grass, Reduces Survival and Productivity of an Establishing Pine Forest, Forest Science, Volume 54, Issue 6, October 2008, Pages 579–587, https://doi.org/10.1093/forestscience/54.6.579