Fire Ecology Marathon; Nature Red in Tooth and Flame Part-4

The savannas of the southeastern United States are inimitable natural communities that have undergone ecological assembly in the presence of seasonal fire cycles and, as discussed during the first three installments on this topic (available here; Part-1, Part-2, Part-3), are rich in organisms capable of manipulating the regularity, movement and intensity of these wildfires. During the preceding post (Part-3) the phenotypes of two such fire-born species, the longleaf and slash pines, were detailed as exemplars of organisms with traits that not only aid in defending against heat and flame, but also as species that exhibit specific physical structures, chemicals and behaviors that could intrinsically promote fire. In closing that previous discussion, consideration was given to the possible motives behind the longleaf and slash pine’s ability to deliberately provoke fire.

Though it may initially seem to be counterproductive or even a hindrance to survival, through promoting fires the savanna pines obtain benefits that directly enhance their inclusive fitness. Because of the processes that drove the organismal evolution of the longleaf and southern slash pines in geological time, and the processes that propelled community assembly in savannas, the presence of wildfires effectively created a duality in the character of potential pine competitors and that of would-be savanna inhabitants - either they can tolerate fire, or they can’t tolerate fire.

In the absence of wildfires over extended periods of time (i.e. fire suppression) several ecological changes can occur in savannas. Most profoundly, without regular wildfires not only would the already present fire-tolerant plant species survive, but in addition, fire-intolerant species would experience greater fecundity. Without the deterrence provided by fire, resource-rich savannas can quickly become the envy of plants from surrounding hammocks and mixed hardwood forests, thus encouraging invasion and recruitment from these neighboring communities. Such movement of new species into the savannas would contribute to substantial ecological alteration of the natural processes that maintain the system’s predictable boundaries, ecotones and makeup.

Recall from Part-1 of this post that the plants found in hammocks have undergone selection for initial rapid growth and direct competition for sunlight. Just as the natural history of the pines has been shaped by fire, the history of dense-canopy species have evolved to fight for radiance. If unobstructed access to the abundant savanna sun is tantalizingly flaunted, these species would quickly invade, rapidly recruit and hurriedly regenerate to overtake all biologically available space. What was initially a patchwork of invasive species would spread to encompass and overcrowd the savanna, in the process reducing the diversity of appropriate groundcover plants, and adversely impacting the reproductive success of the native inhabitants – slash and longleaf fitness would decline.

In addition to increasing interspecific competition in the savannas, invasive species also create positive feedbacks in the wildfire cycle - magnifying fire suppression. The presence of abundant shrubs and woody species in a normally open savanna formulate densely vegetated landscapes that reduce fine fuel loads on the ground and decrease the likelihood of fire propagation. The lack of fire - in turn - facilitates further invasions, which increases vegetative densities even more, which reduces fire even more, which allows for yet greater invasive proliferation, etcetera…

With continued fire suppression, what was once a savanna, characterized by thinly distributed trees, would transition towards a densely canopied hammock with an impenetrable thicket understory. Growing populations of invasive species would amplify competition for resources, thus pushing the fitness experienced by the longleaf and southern slash pines to dangerously low values. This is precisely why the ‘fire gene’ is so critically important to the pine’s genotype. As crowding increases in this scenario, and essential resources dwindle, hormonal stress responses within the pines intensify. The hormones drive physiological changes in the trees causing leaves to drop and internal hydrocarbon chemistry to move toward increased combustibility. The probability for fire is increased. And, when fire does return, the stems, branches, leaves and roots from newly arrived invasives will serve as kindling for augmented wildfire intensity - to such extremes that only the hardiest of the fire-tolerant will be able to survive.

For clarification, conceptual genes (like the ‘fire gene’) aren’t confirmed as actual chromosomal localities for which variable alleles compete. Rather, conceptual genes are offered as thought-tools for understanding the premise that natural selection operates on phenotypical traits that are the products of genotypical coding. In regards to the ‘fire gene’ specifically, it is a hypothetical genetic compliment that is expressed in such a manner that the physical presence of fire improves the likelihood of that genotype being passed on to future generations. In other words, if a population of trees exist in which some members have a genotype that provides increased fitness in the presence of fire, AND that population is then exposed to fire - ultimately killing a certain percentage of the population - those trees with fire gene advantage will experience higher survivability and greater measures of fecundity compared to those not possessing a fire gene.

Returning to the savanna pines expressly, irregardless or not if there is literally a single gene that provides for all of the phenotypical adaptations to fire described throughout this post, or if these traits are the result of a cooperative epistasis, or if the characters are disparate and independent, it remains likely that their occurrence and continued propagation through evolutionary time has provided a significant advantage.

Through 300 million years of natural selection, wildfires have propelled the savanna defending pines to levels of adaptation in which they are capable of wielding fire. ‘Nature, red in tooth and flame’ has fashioned a true ecosystem engineer, one that is capable of establishing and defending the ecotonal boundaries between natural communities.


Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458

Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x

Ecosytem Engineering and Fire Ecology, Part 3

The closing paragraph of ‘Nature, Red in Tooth and Flame Part-2’ mentioned how extrinsic factors in the environment, such as the presence of increased atmospheric oxygen and an abundance of herbaceous plants to serve as fuel, collectively worked to generate frequent and intense wildfires during the Pennsylvanian Period approximately 300 million years ago. It was the presence of these Carboniferous wildfires that positively selected fire-tolerant gymnosperm species for continued development, and initiated their adaptive radiation towards the representative pine trees that occupy the modern-day savannas in the southeastern United States. It is within contemporary savannas that the longleaf pine (Pinus palustris) and the southern slash pine (Pinus elliottii var. densa) express their fiery ancestry; however, the fire ecology observable in these natural communities isn’t limited to wildfires born of purely extrinsic factors. Through, evolution the longleaf and slash pines have developed the ability to intrinsically influence the movement of fire, and they have learned to use this powerful tool as an instrument for customized ecosystem engineering.

During the description of savanna communities in Part-2, it was detailed that the canopies of these systems exist in an open condition that allows for ample access to sunlight by a diverse range of groundcover plants. Ample sunlight, water and soil nutrients can all be found in savannas. So, considering the occurrence of these botanical prerequisites, compounded with the highly competitive, almost war-like, tendencies of nature (as elaborately described in Part-1), one might wonder why trees from the hammocks don’t advance to occupy the promising and resource-rich savannas… The reason for the limited progress of hammock trees in moving to the savannas is that invasions are tightly controlled by the few trees already inhabiting the systems – the few trees usually being longleaf and slash pine.

An open canopy is a characteristic physiognomy of savannas precisely because the ground gaining charge of closed-canopy trees is impeded by the heirs of the Carboniferous gymnosperms. Said differently, the trials-by-fire endured by the antecedents of the modern-day conifers have shaped the phenotypes of the savanna-defending longleaf and southern slash pines. Furthermore, the phenotypes shown by the longleaf and slash pine reach outward to encompass the savanna as a whole, where these phenotypes serve as catalysts for engineering ecosystem towards one purpose – making more pine trees.

The longleaf and southern slash pine exhibit a host of morphological features that facilitate their continued manipulation of fire. For instance, both of these trees have thickly armored plates of bark on the exterior of their trunks; like fire-retardant shields, the plates guard the tree's interrior tissues against excessive heat and all but the most intense of wildfires. Similarly, the undifferentiated cells (meristematic cells) found within the trees, the ones that make-up the growth tissue found in meristems, are safeguard by a casing of heat resistant scales. And, as opposed to a pattern of wide lateral spreading, the roots of the slash and longleaf trees penetrate perpendicularly downward, where they are sheltered from harsh surficial temperatures. These are but a small number of the morphological – anatomical – traits displayed by the fire-scaping pines; their reproduction and growth habits give additional clues as to their natural history.



The reproductive cycle of the longleaf and southern slash pine include strategies that take into account the recurring spring fires described in Post-2; by germinating in the fall and occasionally producing periodic mast crops, young pines are afforded several months of growth before the first ravages of wildfire arrive. In spite of the head start gained through fall germination, the longleaf and slash pine don’t approach growth from a mere lackadaisical standpoint, quite the contrary, both trees posses the ability to quickly establish themselves. Just as the most successful plants of a closed canopy hammock battling for access to solar radiation (see the ‘competition for sunlight’ example provided in Part-1), the savanna pine trees – in addition to a ‘fire gene’ – also hold in their genetic arsenal a ‘rapid growth gene.’ Slash pine, for instance, has a genetic compliment that permits the tree to take advantage of every opportunity to seize real estate; once germinated, it rapidly shoots upward expressing secondary needles in less than six month’s time, and by the time it is two-years old, it is able to survive a wildfire of ‘average' intensity.

The above characteristics depict but a few of the intrinsic phenotypes that improve the survivability and reproduction of the savanna dwelling pines in the presence of fire; but what is truly remarkable is the trees’ ability to channel fire directly – the trees’ ability to shape their ecosystem through offensive tactics.

In addition to the defensive phenotypes of the savanna pines, the chemistry of their leaves (i.e. pine needles) have undergone adaptation such that while on the tree, the leaves produce flame resistant chemicals, but when the leaves are shed, their chemical consistency changes to achieve an altogether different effect - they become flammable and easily ignited. As the leaves are shed from branches, they fall to the ground where they accumulate around the circumference of the trees. The piled pine needles are composed of cellulose-laden fibers, which unlike the fire-resistant lignin that evolved during the Paleozoic, serve as excellent fuel for fires. So when on the tree, the pine needles are similar to the armored plates found on the trunks, they help defend against tissue damage when exposed to wildfire; but, in the absence of recurrent fire, the leaves are quickly dropped and their chemistry changes to promote fire. Moreover, pine leaves aren’t the only fire stoking property of the savanna pines. The very structure of the pine’s thin and supra-numerous branches can facilitate the spreading of fire (horizontally and vertically) through increasing the surface area of exposed tissues to flame. And, the flammable hydrocarbons produced in the plant’s resins can incite wildfires or encourage lightening strikes to take hold (for example, the terpenes produced by the conifers in question; think ‘turpentine’).

Though it may initially seem to be counterproductive, or a hindrance to survival, through promoting fires the savanna pines obtain benefits that actually enhance inclusive fitness….

[Continue HERE, PART-4.]


Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458


Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x

Fire Ecology and Cutthroat Ecosystem Engineering, Part 2

The phrase ‘ecosystem engineer’ refers broadly to the ability of an organism to change or modify the physical characteristics of its surroundings. When these environmental modifications resultantly impact the fitness of the engineering organism itself, the feedbacks created can be thought of as functioning like an extended phenotype. In other words, the feedbacks generated between the engineer and the ecosystem contribute to the reproductive success of the organism, and often (directly or indirectly) affect the life history of nearby competitors. In the closing line of ‘Nature Red in Tooth and Flame - Part 1’ the organisms adapted to use fire are personified as ‘cutthroat’ because they possess a genetic compliment that facilitates the shaping of their environment through a two-fold process that could easily be categorized as self-interested. Firstly, through harnessing fire these engineers are able to create a pattern of ecological disturbance that promulgates increased fitness; and secondly, the application of fire eliminates resource pilfering opposition via direct incineration. But, prior to detailing the precise methods in which ecosystem engineering plants employ fire, it is important to set the stage with a description of the battlefield – the savanna community.

In the southeastern United States savannas are typically found on relatively low topographical gradients with poorly drained soils and ample soil nutrients. Similar in biological composition to hydric flatwoods communities, savannas characteristically differ in regards to tree abundance and exhibit a relatively open canopy with a thin understory and a lavish herbaceous groundcover. Both savannas and hydric flatwoods rely on seasonal rain and fire cycles in order to maintain their soil chemistry, floral diversity and faunal components. Yes, these communities depend on fire cycles…

Prior to modern anthropogenic intervention, and the suppression of natural, seasonally occurring fire cycles, the forests, prairies and savannas of the southeastern United States experienced regular ecological disturbance by means of fire. Using Florida as an example, the annual climate cycle here is punctuated by alternating periods of relatively dry and wet weather. More specifically, the months of November through February represent the dry season and accordingly receive comparatively little precipitation. This dry season is followed by dramatically increased amounts of precipitation during summer with heavy rains and thunderstorms (particularly near the coasts) for the period including June, July and August. The spring season, February-through-May represents a transitional period from dry to wet; however the forthcoming summer brings with it thunderstorms; during this period lightening-strikes often ignite wildfires. The wildfires feed on the parched condition of desiccated plants – the wildfires thrive on the fuels remaining behind from the departing dry season. The regularity of this annual climate has resulted in a cyclic ‘fire season’ that has been recurrent for several millennia. The persistence of the fire cycle has thus contributed greatly to the structuring of local natural communities; however to understand the organismal biology of some of the fire adapted plant species a deeper gaze into evolutionary time is required. So, now that a cursory look at the battlefield has been made, a review of the actual players is in order.



Two exemplars of the fire wielding and ecosystem engineering life style are the longleaf pine (Pinus palustris) and the southern slash pine (Pinus elliottii var. densa). These trees both maintain genetic compliments – fire genes – that enable them to prosper in the flame frequented savannas of the southeastern United States. In order to appreciate the natural history of these organisms, a look at their evolutionary past is obligatory.

The longleaf pine (Pinus palustris) and the slash pine (Pinus elliottii) are two species of the genus Pinus (pine tree) which branched from genus Picea (spruce tree) during the Cretaceous Period, somewhere between 87 and 193 million years ago.


NOTE: There are two distinct varieties of slash pine, variety elliotti and variety densa, both of which can be found in southeastern U.S. and although there are several important distinctions, for purposes here both varieties can be considered one and the same, though the southern slash pine (var. densa) displays slightly greater levels of adaptation to fire.



Pine and spruce trees are grouped together with cycads, gnetophytes and ginkgo as gymnosperms, which had an initial start back in the Pennsylvanian Period of the Carboniferous more than 300 million years ago. The long history of the pine trees, and the slash pine in particular, is significant because these trees have one of the largest and most complex genomes of any organism on the planet today – a result of varied evolutionary forces. Of specific interest in regards to evolutionary history is that gymnosperms arose from the Carboniferous swamps during a period of rapid plant adaptation. In addition to the advent of the bark fiber “lignin,” plants during that period underwent a multitude of morphological changes - many of these changes were adaptations to wildfire. This was the case because unlike the 21% atmospheric oxygen present today, the carboniferous boasted 35% oxygen content, this in conjunction with an abundance of herbaceous material resulted in frequent – and intense – wildfires. Here, ‘intensity’ can be interpreted as being the ratio of a wildfire’s maximum temperature and duration; both of which can vary. The wildfires positively selected for those plant traits that phenotypically exhibited fire-tolerance, and the wildfires also actively worked to eliminate those plants that displayed fire-intolerant characteristics. Through this dualistic mechanism of natural selection, a long passed Paleozoic ecosystem worked to shape and mold the longleaf and the slash pines into masters of pyrogenic manipulation.


[This blog post continues here with installment Number 3.]



Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458


Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x

Nature Red in Tooth and Flame: Fire Ecology and Cutthroat Ecosystem Engineering

Renowned journalist, publisher and geologist Robert Chambers spent the majority of his 19th Century life actively engaged in two - often antagonistic - worlds, the world of science and that of the high-society Scottish elite. It may have been his struggle to maintain balance between these two worlds, one that valued rationality and meticulous observation, the other preferring political correctness and adherence to theological dictates, which helped guide him to the decision to anonymously publish his 1844 work ‘Vestiges of the Natural History of Creation.’ The work was truly progressive by almost any measure and it would go on to influence such diverse individuals as the scientifically minded Charles Darwin and the poetically endowed Alfred, Lord Tennyson.

It was a combination of Vestiges’ theological implications and the loss of a dear friend that motivated Lord Tennyson to pen the following stanza:

Who trusted God was love indeed
And love Creation's final law
Tho' Nature, red in tooth and claw
With ravine, shriek'd against his creed
(In Memoriam A.H.H., Canto 27)

‘Nature, red in tooth and claw’ is an often quoted metaphor for natural selection, and as such, it has been a recurrent theme here at Ecographica. During several previous posts, a harmonious – ‘all is in balance’ - view of nature was contrasted with the perspective of nature as a series of oppositional organisms struggling to gain a competitive edge over rivals. During these comparisons, the ‘red in tooth and claw’ view was the hands-down victor in all cases; being both more analytically accurate, and the more observationally sound perspective. As a case in point, two recently published articles, one appearing in the December edition of The American Naturalist, the other in the July New Phytologist have compelled the issuance of an update to a post made back in April; a post that emphasized the above described contrasting views of nature. Both of the published articles lend further credence to the conceptual “fire gene,” an idea coined in the April blog. One article supports the fire gene concept through development of ecological disturbance feedback models; the other tells the story of an invasive plant with a contrasting and adversarial phenotype to the one detailed in the original post, a phenotype that suppresses fire – it bears what can be called an “anti-fire gene.” As with the original blog post, the re-write begins in the Big Cypress Preserve, with a somewhat overly embellished lead-in…

Nature Red in Tooth and Flame
Gazing across the tranquil landscape of the Big Cypress Preserve, nature seems to be in balance, unchanging and at peace - picturesque beyond any poetic description. Within this serene setting, anthropogenic throngs of sharply angled concrete and glass edifices suspend their battle for roadside commercial dominance and yield themselves to a sea of sparsely treed savannas, rolling prairies of grass, and randomly scattered islands of thickly vegetated hammocks. It’s the perfect environment for a relaxing stroll, a picnic, or, an inquiry into the natural world...

All may appear calm within this enchanting panorama with its diverse array of plants, animals and abiotic ornamentation; however, this perceived tranquility is but a chimera. It is a mere illusion of serenity resulting from shortfalls in the ability of the observer’s photoreceptors to see beyond that narrow range of the electromagnetic spectrum called visible light, an inability to hear sound outside of 22000 Hertz, and the failure of the human olfactory system to nose its way into the vast chemo-landscape of pheromones and other volatile chemicals in which it is continuously assailed. Indeed, if only the sensory apparatus of Homo sapiens was keener – if only it was more finely calibrated – the landscape of the Big Cypress would be seen for what it truly is… How very different it would seem.

Picture taken from Turner river Rd - Big Cypress Preserve

Very different indeed; imagine the ecological interplay that could be interpreted if humans could see ultraviolet light through the eyes of a bee, smell pheromones from six-miles’ distance like a moth, or interpret chemical stimuli through soil like a plant… Far from serene, if viewed through time, adaptive maneuvers, survival strategies and arms races would be manifest in every action undertaken by the immense diversity of organisms in the landscape. If these actions could be viewed more directly, if they could be seen in greater detail, the landscape would appear saturated with war; from the birds in the sky to the millions of soil bacteria underfoot, mortal conflict - not harmony - would be identified as the prime mover. Even the distribution of the apparently benign flora, the very plant community boundaries that demarcate prairie-from-savanna-from-hammock in the above described landscape, is maintained by way of fierce battles waged over evolutionary time. These ecosystems, which appear stable and so pleasingly haphazardly scattered, are in fact hordes of competing plants, all struggling for limited resources and their continued existence. It is in these contested boundaries that conflicts incessantly rage, and it is within these envied ecotones that one species has honed a new weapon – it has undergone adaptation to exploit the power of fire.

Before getting to the exploitation of fire, it is important to understand that natural plant communities exist in a continuum of environments and have adapted to inhabit almost every available niche on the planet; from “box thorns” in Death Valley to fully aquatic hyacinths floating around the lakes of Brazil, genetic plasticity in plants is clearly evidenced as a product of natural selection. And although the conquest of diverse habitats represent a surmountable challenge, a multitude of both biotic and abiotic factors conspire to determine the overall abundance (density), composition (diversity) and ultimate success of plant communities at any given location.

For example, looking across the landscape of the Big Cypress, densely concentrated hardwood trees form hammocks which, due to the broad area of their collective canopies, limit the amount of sunlight available to underlying herbaceous groundcover. This is a straight forward relationship, no sunlight reaching the ground means fewer plants on the ground. Following this rationale, if the tree canopy should be opened, say by a storm, hurricane or by the death of older trees, this would permit sunlight to temporarily penetrate to the floor and a rapid emergence (recruitment) of both herbaceous plants and new saplings would be predicted. This is precisely what happens; in this example sunlight is the limiting resource and once made available those plants best able to take advantage of the situation through rapid growth will be able to quite literally overshadow their competitors. Stated differently, plants with genetic compliments favoring a period of ‘initial rapid growth’ are at an advantage and will be positively selected if positioned to compete for sunlight with a species lacking such a genetic compliment.

Similar to the botanical quarrels described for wooded hammocks - those in which plants have undergone selection for rapid growth - plants also engage in conflict to secure access to the resources offered by prairies and savannas. And, just as with the battles for sunlight on the forest floor, contenders occupying hammock-savanna ecotones have evolved specific defensive and offensive phenotypes to aid in their advance; as alluded to earlier, a few have even acquired the ability to harness the power of fire. Like the genetic compliment that allows a plant to undergo a period of initial rapid growth when a break in the hammock’s canopy becomes manifest, some plants possess a genetic compliment that allow for direct modification of local ecology. In short, the genetic compliment allows the plant to apply heat and flame in a cutthroat effort to destroy competitors, and to assert themselves as ecosystem engineers.


[The second installment of this post is available HERE.]



Beckage, B., Platt, W., & Gross, L. (2009). Vegetation, Fire, and Feedbacks: A Disturbance‐Mediated Model of Savannas The American Naturalist, 174 (6), 805-818 DOI: 10.1086/648458


Stevens, J., & Beckage, B. (2009). Fire feedbacks facilitate invasion of pine savannas by Brazilian pepper New Phytologist, 184 (2), 365-375 DOI: 10.1111/j.1469-8137.2009.02965.x

The Fire Gene Described

A lengthy introduction during the initial post on this topic (available Here) contrasted a harmonious view of nature with the perspective of nature as a series of oppositional organisms struggling to gain a competitive edge over rivals. As a model of this outlook, the ecotone boundaries between various sets of differing plant communities were offered as a case study. More specifically, the prairie, savanna and hardwood hammock ecosystems of the Big Cypress Preserve were forwarded along with the proposition that members of these communities actively challenged each other for limited resources. In staging this proposition the question was asked, “Why don’t trees invade - and take over – the prairie communities currently occupied by grasses?” After eliminating the likelihood that densely growing stands of grass crowded-out young saplings by denying them access to sunlight, cyclic wildfire were explained and presented as an alternative explanation. Moving forward with this production, a profile of one of the previously introduced characters is in order – the conifer tree Pinus elliotti.

Slash Pine Growing from a Log

Slash Pine is a species of the genus Pinus (pine tree) which branched from genus Picea (spruce tree) during the Cretaceous Period, somewhere between 87 and 193 million years ago. There are two distinct varieties of slash pine, variety elliotti and variety densa, although there are several important distinctions, for purposes here both varieties can be considered one and the same. Pine and spruce trees are grouped together with cycads, gnetophytes and ginkgo as gymnosperms, which had a start back in the Pennsylvanian Period of the Carboniferous more than 300 million years ago. The long history of the pine trees, and the slash pine in particular, is significant because these trees have one of the largest and most complex genomes of any organism on the planet today – a result of varied evolutionary forces. Of specific interest in regards to evolutionary history is that gymnosperms arose from the Carboniferous swamps during a period of rapid plant adaptation. In addition to the advent of the bark fiber “lignin,” plants during that period underwent a multitude of morphological changes - many of these changes were adaptations to wildfire. Unlike the 21% atmospheric oxygen present today, the carboniferous boasted 35% oxygen content, this in conjunction with an abundance of herbaceous material (remember Carboniferous = “coal age”) resulted in frequent – and intense – wildfires.

Wildfires…

So, do wildfires prevent trees, such as slash pine, from invading prairie strongholds held by grasses? Not really, some especially intense (“intensity” being a measure of a fire’s maximum temperature and duration) wildfires may destroy slash pine, but fires capable of doing so are relatively rare. The typical “fire seasons,” as described in the first post, may have sufficient intensity to kill some young saplings, but remember - slash pines also have “initial rapid growth genes” which provide a solid head start in defending themselves. Essentially, any sapling greater than two years old has a good chance of getting through the “average” wildfire. As for the periodic “non-average” wildfire, one that is of an unusually high intensity, slash pines may need to rely on evolutionary adaptations other than “initial rapid growth genes” – they may need to lean on morphological phenotypes resulting from a “fire gene.”

A fire gene is a genetic compliment possessed by an organism that is expressed in such a manner that the presence of fire improves the likelihood of that genotype being passed on to future generations. In other words, if a population of trees exists in which some members have a genotype that provides phenotypical resistance to fire, and that population is then exposed to fire, killing a certain percentage of the population, those trees with fire gene advantage will have higher survivability and greater measures of fitness than will those not possessing a fire gene. Through this process of “selection by fire,” the fire gene would become more prevalent in the population, eventually becoming so common as to be called characteristic.

This is precisely what has occurred with the pine trees of the Big Cypress. Through millennia of “trial by fire,” only those trees expressing the most fire tolerant phenotypes have survived. Morphological features such as thickly armored plates of bark shield the trunk from heat, scale plated meristems guard against flames and the pine’s reproductive strategies take into account spring fires by germinating in the fall and producing periodic mast crops. However, these products of natural selection are merely defenses, what is truly remarkable is that another aspect of the fire gene contributes to offensive maneuvers.

As a thought experiment only, image being a tree with the cognitive function of a human and the knowledge that you have an inherit resistance to fire; a resistance that many of your competitors do not posses. If locked in a battle for survival, and you had a match in hand, (or rather, a match in “branch”) would you start a fire?

Of course, matches are of little use to trees outside of thought experiments, but what if there was an adaptation that would provide not only defense, but also allow trees to harness naturally occurring fires to their advantage? Genes don’t exist in isolation; frequently they form partnerships to gain mutual advantage. Epistasis, the interaction between genes, has occurred in pine trees to accomplish the same goal. Not only do the trees have defensive morphologies, they have also adapted the chemistry of their leaves (i.e. pine needles) such that while on the tree the leaves produce flame resistant chemicals, but when wildfires are absent for extended periods of time leaf chemistry changes. In the absence of wildfires leaves are randomly shed, accumulate in the area around the tree and - as opposed to being flame retardant - they become easily ignited at low temperatures and burn at an intensity that, well… An intensity that only a slash pine would love…

Some fires do adversely affect slash pine, but the presence of a “fire gene” provides both defensive and offensive adaptations that can –and have been – utilized to survive. So, why don’t trees such as slash pines invade prairies? It’s a “one-two punch.” Through heat stressing the trees, fires slow down advancing slash pines; however it is what happens after the fire season that stops them cold in their tracks – flooding. Summer rains pile on additional stress to what has already accumulated due to fire defense investment. Grasses are in the same boat, but due to a better water tolerance they can bounce back more readily. The slash pine can survive fires or flood, but taken together these two modes of environmental disturbance overwhelm the trees and limit their prairie-ward charge. This is, however, a function of seasonality, climate and cyclic wildfires; with climate change and alteration of these natural processes all bets are off. (But that’s a topic for another time…)

Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2

Nordlund, D., & Lewis, W. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions Journal of Chemical Ecology, 2 (2), 211-220 DOI: 10.1007/BF00987744

Morse, A., Peterson, D., Islam-Faridi, M., Smith, K., Magbanua, Z., Garcia, S., Kubisiak, T., Amerson, H., Carlson, J., Nelson, C., & Davis, J. (2009). Evolution of Genome Size and Complexity in Pinus PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004332

Platt, W. J., J. M. Huffman, M. G. Slocum, and B. Beckage. In press. Fire regimes and trees in Florida dry prairie landscapes. In: Noss, R. & Singh, S. (eds.) Land of fire and water: The Florida dry prairie ecosystem. Avon Park Air Force Range and Department of Defense, Avon Park, FL,

US.Kabrick, John M.; Dey, Daniel C.; Gwaze, David, eds. Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium; 2006 November 7-9; Springfield, MO. Gen. Tech. Rep. NRS-P-15. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 28-32.

The Fire Gene: One Organism’s Ability to Exploit Fire

Gazing across the tranquil landscape of the Big Cypress Preserve, nature seems to be in balance, unchanging and at peace - picturesque beyond any poetic description. Here, anthropogenic throngs of sharply angled concrete and glass edifices suspend their battle for roadside dominance and yield themselves to a sea of sparsely treed savanna, rolling prairies of grass, and randomly scattered islands of thickly vegetated hammocks; the perfect environment for a relaxing stroll, a picnic, or even a quick nap. All may appear calm within this enchanting panorama; however, the perceived tranquility is but a chimera. A mere illusion of serenity resulting from shortfalls in the ability of Homo sapiens’ photoreceptors to see beyond the narrow range of the electromagnetic spectrum called visible light, an inability to hear sound outside of 22000 Hertz, and the failure of the human olfactory system to nose its way into the vast chemo-landscape of pheromones and other volatile chemicals in which it is continuously assailed. If the sensory apparatus of Homo sapiens was keener - more finely calibrated – the landscape of the Big Cypress would appear very different.

Very different indeed, imagine the ecological interplay that could be interpreted if humans could see ultraviolet light through the eyes of a bee, smell pheromones from six-miles’ distance like a moth, or interpret chemical stimuli through soil like a plant… Far from serene, if viewed through time, adaptive maneuvers, survival strategies and arms races would be manifest in every action undertaken by the immense diversity of organisms on Earth. If these actions could be viewed more directly, the landscape would appear saturated with war. Even the plant community boundaries which demarcate prairie from savanna from hammock in the above described landscape are maintained by way of fierce battles waged over evolutionary time. These ecosystems, which appear stable and so pleasingly haphazardly scattered, are in fact tightly ordered armies of competing plants struggling for resources and existence. In these recurrent ecotonal conflicts one species has honed a new weapon – it has adapted to exploit the power of fire.

Naturally existing plant communities exist in a continuum of ecosystems which through evolution have adapted to almost every available habitat on the planet; from “box thorns” (Lycium pallidum) in Death Valley to fully aquatic hyacinths (Eichhornia paniculata) floating around the lakes of Brazil, genetic plasticity in plants is the product of natural selection. Although diverse habitats represent a surmountable challenge, a multitude of both biotic and abiotic factors determine the overall abundance (density), composition (diversity) and ultimate success of plant communities at any given location.

For example, looking across the landscape of the Big Cypress, densely concentrated hardwood trees form hammocks which, due to the broad area of their collective canopies, limit the amount of sunlight available to underlying herbaceous groundcover. This is a straight forward relationship - no sun reaching the ground means fewer plants on the ground. Following this rationale, if the tree canopy should be opened (by a storm, hurricane or by the death of older trees) and sunlight is able to temporarily penetrate to the floor, a rapid emergence of both herbaceous plants and new saplings would be predicted. This is precisely what happens; sunlight is the limiting resource, once made available, those plants best able to take advantage of the situation (through rapid growth) will be able to literally overshadow their competitors; plants with genetic compliments favoring a period of “initial rapid growth” are at an advantage and will be positively selected.

Extrapolating this scenario to the prairies of Big Cypress begs the question – why aren’t there any trees in the prairie?

Prairies, typically found on relatively low topographical gradients in Florida, have an abundance of soil nutrients and water; at least enough to support the enormous quantity of grasses and herbaceous plants currently found there. Additionally, from the perspective of a tree, grasses present little competition for sunlight. So, what is it that prevents trees from invading the prairie?

One often suggested possibility is that because prairies are occupied by dense populations of grasses - some of which more than six feet in height - young trees are prevented from taking hold; sort of like a reverse hammock scenario in which the grasses overshadow the young trees thereby starving them of sunlight instead of vice versa… This is plausible, but why wouldn’t trees take hold after wildfires? Wildfires have been historically inevitable in Florida and have the effect of clearing grasses long enough for those trees possessing an “initial rapid growth gene” in their arsenals to stake a claim.

Slash Pine (Pinus elliotti), for example, has just such an initial rapid growth gene. This permits the tree to take advantage of any opportunity to seize real estate, whether it is in a forest or a prairie. Slash Pine is even capable of expressing secondary needles in less than six month’s time – seedlings grow rapidly. Once present, this conifer could easily out-compete grasses for sunlight.

A quick word about wildfires: Florida’s climate cycle is punctuated by alternating dry and wet periods. November to February is the dry season, with relatively little precipitation, and is followed by heavy rains and thunderstorms (particularly near the coasts) during the months of June, July and August. The spring season, February through May, represents a transition from dry to wet, but during this period lightening strikes often cause wildfires due to the parched conditions of plants – parched, having just come out of the dry season. Regularity of climate has resulted in a cyclic “fire season” arriving during the early spring.

Speaking of wildfires… Being a regular occurrence, they are often offered as another explanation for limiting the advance of trees into prairies. Although this suggestion is partially correct, it isn’t the whole story - in some instances trees have even wielded fire as a weapon to destroy its grass competitors.


4-19-09 UPDATE: The Second Half of this Post can be Viewed HERE.

Beckage, B., Gross, L., & Platt, W. (2006). Modelling responses of pine savannas to climate change and large-scale disturbance Applied Vegetation Science, 9 (1) DOI: 10.1658/1402-2001(2006)9[75:MROPST]2.0.CO;2

Nordlund, D., & Lewis, W. (1976). Terminology of chemical releasing stimuli in intraspecific and interspecific interactions Journal of Chemical Ecology, 2 (2), 211-220 DOI: 10.1007/BF00987744

Morse, A., Peterson, D., Islam-Faridi, M., Smith, K., Magbanua, Z., Garcia, S., Kubisiak, T., Amerson, H., Carlson, J., Nelson, C., & Davis, J. (2009). Evolution of Genome Size and Complexity in Pinus PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004332

Platt, W. J., J. M. Huffman, M. G. Slocum, and B. Beckage. In press. Fire regimes and trees in Florida dry prairie landscapes. In: Noss, R. & Singh, S. (eds.) Land of fire and water: The Florida dry prairie ecosystem. Avon Park Air Force Range and Department of Defense, Avon Park, FL,

US.Kabrick, John M.; Dey, Daniel C.; Gwaze, David, eds. Shortleaf pine restoration and ecology in the Ozarks: proceedings of a symposium; 2006 November 7-9; Springfield, MO. Gen. Tech. Rep. NRS-P-15. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 28-32.

Ecosystem on a Log and Scarab Beetles - Field Photos

I wanted to share couple of interesting snapshots taken during the past week – well the snapshots themselves aren’t all that great, but what is depicted in them is pretty cool.

First, a section of an old log that now serving as a microcosm of biodiversity:

The fallen log is of the species Pinus elliottii (Slash Pine), as you can see from the photo, a new P. elliottii sapling has sprouted mid span. The sapling’s roots haven’t penetrated the base of the log and are fully contained within the rotting wood.

And if you take yet a slightly closer look,


You’ll notice that near the base of the sapling several other species of plants, grasses and mosses (including this week’s Wetland Plant of the Week - L. lucida) have made the log home. Though it’s difficult to see from the above images, there are also several ants, spiders and chiggers using the plants as habitat.

Using the fallen pine log for nutrients and structural support is interesting enough, but the story gets even better!

What is truly remarkable is that if you take a look to the right of the log in the first photo, you’ll notice a clearing of the foliage associated with a slight topographical depression. This depression actually functions as a waterway during periods of seasonal flooding!

Taking a look at the surrounding trees,


you’d find water stain lines more than a foot in elevation above the ground surface.

Considering that this entire site is less than five miles from the Gulf of Mexico and letting my imagination run a little wild (but not too much), I can easily envision a scenario in which such a log-microcosm serves as a platform in “rafting” plants and animals to far off places, thereby driving Natural Selection via a founding effect… It even has a ready made sail - the leaves of the pine sapling!

The other snapshot I felt deserved posting was a couple of Scarab Beetles (Family Scarabaeidae) battling for the privilege of rolling dung.


Being a still photo as opposed to a video, you may not be able to read the whole story in the above image, but what’s happening is that three "Tumblebugs" (Canthon spp.) are maneuvering a well-rounded ball of dung.

Male Scarab beetles proactively assist the females in collecting dung to be used for nest building. In exchange for help with rolling the dung balls back to the burrow, males may receive the opportunity to mate with the female, who will in turn lay a single egg on the dung ball.

Rolling the dung helps compact the material into a more stable base for larval development and at the same time provides a method for the most fit males to demonstrate their paternal skills in hopes of wining the affections of a potential mate.

In the picture above two males, both vying for an opportunity to mate, are attempting to impress the female – unfortunately for her, their back-and-forth rolling has landed her on her back under the ball of dung! She can just be made out under the upper left corner of the dung ball.