Live Fast, Die Young: Evolutionary Outcomes of an Asteroid Impact

Figure 1: (A) "Dryophyllum" subfalcatum, (B) unknown nonmonocot,
(C) "Ficus" planicostata, (D) "Populus" nebrascensis

A new semester has started and with it an influx of new students into the lab has begun. Busy has become my middle name. So when I was looking around for a paper to write about I wanted something different and cool. Not exactly hard to find in science. The asteroid known as 2012 DA14 will narrowly miss Earth this Friday, the closest known asteroid flyby on record. And by close we’re talking within the orbits of many communications satellites. This got me thinking about and looking for recent papers about asteroids. It didn't take me long to come by an interesting new paper about the dino-killing Chicxulub bolide impact.

As of now, it is widely accepted that an epic asteroid collision ended the 135 million year reign of the dinosaurs. The Cretaceous-Paleogene boundary (KPB) extinction event is marked by the Chicxulub (CHEEK-sheh-loob) impact on the Yucatán Peninsula in Mexico. This asteroid or comet is estimated to have been about 6 miles (10 km), releasing as much energy as 100 trillion tons of TNT that caused a crater more can 110 miles (180 km) across! This impact coincides with a mass extinction event that includes the dinosaurs. Dramatic climate swings caused by the dust kicked up into the atmosphere were likely the culprit behind many of these extinctions. Before we go further, take a second to think about what you know about this extinction event. You probably think of the mass die-off of the dinosaurs and the subsequent rise of the mammals, right? But, as I have in the past, I’ll now pose a question: What about the plants?

A new paper published yesterday in PLOS Biology asks just that question. We know that in temperate North America the Chicxulub impact resulted in the extinction of over 50 percent of the plant species. From an evolutionary and ecological stand-point, that’s a lot of competitors that were taken out of the game. However, the environment was dramatically altered as well, changing to a cold and dark “impact winter.” Combined, these factors created a unique selection scenario for certain ecological strategies. The new paper takes a close look at the functional traits associated with these strategies.

The researchers measured fossil leaf assemblages spanning a 2.2 million year interval across the KPB, assessing four differing selection scenarios for functional traits. First, wrap your head around the concept of “functional traits.” These are characteristics that define species in terms of their ecological roles. In the case of leaves, these include leaf mass per area (LMA; Do you make a big, expensive leaf or a light, cheap one?) and leaf minor vein density (VD; Do you have more veins to transport lots of water?), among many others. Because leaves are the food producers, these traits are linked to plant growth and fitness. Next, you can relate these traits to the “leaf economic spectrum” (LES) that contrasts species with inexpensive short-lived leaves with fast returns on carbon and nutrients (deciduous, angiosperm, broadleaf) to costly long-lived leaves with slow returns (coniferous, gymnosperm, evergreen). The former is typically selected for in a less resource variable environment and vice versa. From this, you can get a more global perspective on changes in species composition.

The researchers measured LMA and VD for fossil leaf assemblages spanning the KPB. To do this they digitally photographed specimens that could be measured and confidently reconstructed. Then they used Photoshop to digitally separate the leaf from its rock matrix. For LMA they used ImageJ to calculate leaf area and petiole width, and then ran these numbers through empirical scaling functions (a.k.a. equations). For VD, they used a MATLAB line-counting program to isolate the veins and then manually counted the number of vein-line intersections, computing the mean distance between veins  as the sum of all line counts divided by the sum of all distances (a.k.a. a slightly less complicated equation). They ran a few scenarios to account for site and region plant specificity as well.

They found LMA to decrease and VD to increase across this time period. Even changes just these two traits reflect large physiological and biological shifts in plant functioning over a relatively short period of time. According to their data, the Chicxulub impact led to the selective extinction of species with slow strategies. This caused a directional selection away from evergreen species along with a stabilizing selection of deciduous angiosperms. The authors pose a few hypotheses in their discussion that are worth mentioning. The higher observed VD in angiosperms, and their ensuing selection, could have been driven by declining atmospheric carbon dioxide (CO2), which selects for higher hydraulic capacity. This CO2 hypothesis would, of course, not really hold water (no pun intended) for nonangiosperms and shade species, but the authors suggest that the observed increase in VD is more likely to be a direct consequence of the impact selecting for specific leaf economic strategies rather than ongoing-longer term climate change.

In this case, slow and steady did not win the race.


  Blonder B, Royer DL, Johnson KR, Miller I, & Enquist BJ (2014). Plant Ecological Strategies Shift Across the Cretaceous-Paleogene Boundary. PLoS biology, 12 (9) PMID: 25225914




(image via above citation)

Getting to the Roots (and Fungi) of Carbon Sequestration

This week, I found a paper that I’m calling the best of both worlds. Well, for me at least. This paper combines my past (and lingering) interest in island biogeography with a current interest in climate change and carbon storage.

If you have been reading my blog long enough then you already know my love of islands. They are just so darn useful. In the past, I have focused on oceanic islands, but lake islands are also really neat. These types of islands typically form when lower lying land areas fill with water, effectively cutting off higher areas from the mainland and making them into islands. As such, these islands usually already contain forest as opposed to an oceanic island that emerges from the ocean and must be colonized. A new study, published in journal Science, looks at a fire-driven boreal forest chronosequence on forested lake islands in northern Sweden. Such a chronosequence allows the study of soil carbon sequestration over time scales of centuries to millennia.

This new study looks at roots and their associated fungi (mycorrhizae) as sources of this stored carbon. I’m not going to spend the space to describe mycorrhize, but will, instead, send you over to my Free Market Fungi post for more information, if you need it. It is known that 16 percent of the global carbon stock is sequestered in soils. To date, most carbon studies of this type focus on aboveground leaf litter as the fundamental determinants of this carbon accumulation. But a large portion of photosynthetically fixed carbon is actually directed belowground to the roots and, subsequently, the mycorrhizae. Now, let’s add fire. It has been shown that when a forest doesn't burn, the soil and ecosystem carbon accumulate unabated, and in a linear fashion. Add this information together and it becomes a big deal when it comes to correctly allocating carbon, calculating the long term sequestration rates, and predicting how forests will respond to climate change and other environmental shifts.

The study sites were in two adjacent lakes, Lake Hornavan and Lake Uddjaure, in northern Sweden. The islands in these lakes were formed after the most recent glaciation and come in a variety of sizes. In terms of fire, larger islands burn more frequently because they are larger targets for lightning strikes. As a result, several of the large islands in these lakes have burned in the last century, whereas some of the small islands haven’t burned in at least 5000 years. This lack of fire leads to very thick humus layers (or organic layers towards the top of the soil column) on smaller islands, up to 1 meter thick!

The researchers divided islands into three size classes of 10 islands each: large (over 1 ha), medium (0.1-1.0 ha), and small (less than 0.1 ha). They took soil samples from these islands to look at the organic soil profiles and found that large islands accumulated 6.2 kg of C per square meter belowground with a mean time since fire of 585 years, medium islands accumulated 11.2 kg of C per square meter with a mean time since fire of 2180 years, and small islands 22.5 kg of C per square meter with a mean time since fire of 3250 years. Then they looked at the carbon dynamics across this chronosequence by analyzing bomb 14C. This allowed them to determine the age since fixation of soil carbon. Then they fitted a mathematical model to measurements of carbon mass and age distribution across the soil profiles for six of the islands (3 large, 3 small). This model revealed that the distribution of carbon mass and age could only be predicted when they included carbon from roots. This root-derived carbon accumulation was found to be larger on small islands (70 percent, that's a LOT!) than large islands (47 percent). They were able to explain the entire carbon sequestration difference on small islands from these root-derived inputs. The model also showed that small islands store a major proportion of their soil carbon in the deeper soil layers, those over 100 years old. However, below 20 cm depth, the root-derived carbon inputs were shown to be low and to decompose slowly. So the root-derived carbon input into the upper layers probably contributes to the long-term buildup of humus that is seen on these islands. But, as usual, that's not the end of the story.

We know that fungi play very important roles in forest ecosystems, both as decomposers and in root-assoicated carbon transport and respiration. So the researchers also profiled the relative abundance of major groups of fungi by depth in the soil profiles. They found that the upper soil layers are dominated by free-living saprotrophs (fungi that obtain their nutrition heterotrophically from non-living organic materials), and greater depths were dominated by mycorrhizal and other root-associated fungi. Their model suggests that these mycorrhizae live at the spots where the largest difference in carbon sequestration between the island size classes exists, which also tends to be the areas of highest root mass. When they ran tests for fungal biomass throughout each soil profile they found greater mycelial (the vegetative part of a fungus, consisting of a mass of branching, threadlike hyphae) production on large islands, but less mycelial necromass (dead stuff) on small islands. This suggests that the large production is counterbalanced by faster decomposition of mycelial remains. “Correspondingly, the 14C model indicated faster decomposition of root-derived [carbon] on large islands, despite inputs being conservatively constrained to be equal across all islands.”

I found these conclusions to be interesting because of the amount of soil carbon from roots and mycorrhizal fungi, especially on small islands. And although they saw less carbon accumulation on large islands, these islands have a greater root density and so should have more carbon allocation to roots and the associated fungi. Did you catch the contradiction? Well, in response to increased carbon dioxide, there will be an increase of carbon inputs to the roots which will accelerate the turnover of soil organic matter. This counteracts carbon accumulation and enhances nitrogen cycling through the microbial pools, an effect these researchers observed when they tested the C:N-ratios in the humus of large islands. This is much lower on small islands, possibly because of impared mycorrhizal nitrogen mobilization and the accumulation of nitrogen in fungal remains. This leads to progressive nutrient limitations, then leads to changes plant productivity, leading to changes in community composition, which leads to changes in total belowground carbon allocation, that leads to changes in fungi.

Definately starting to grasp the importance of the belowground dirty stuff. There’s a whole lot of carbon down there that we need to start looking at, accounting for, and seeing where it goes. We know that changes in the environment such as climate change, soil fertilization, fire suppression, and forest management make big differences to the aboveground stuff. It only makes sense that the belowground stuff is impacted as well.


Clemmensen, K., Bahr, A., Ovaskainen, O., Dahlberg, A., Ekblad, A., Wallander, H., Stenlid, J., Finlay, R., Wardle, D., & Lindahl, B. (2013). Roots and Associated Fungi Drive Long-Term Carbon Sequestration in Boreal Forest Science, 339 (6127), 1615-1618 DOI: 10.1126/science.1231923

If you would like some follow-up reading I suggest:

Treseder, K. K. (2013-03-29) Fungal Carbon Sequestration. Science, 339(6127), 1528-1529. (DOI: 10.1126/science.1236338) 

Also check out the write-up in Nature "Fungi and roots store a surprisingly large share of the world's carbon"

(image via Forest Keepers)

Biological Beta Testing: Altitudinal Edition

Spatial patterns in biodiversity have always been a popular topic in ecology, and understanding these patterns helps us to address the looming threats to biodiversity.

Did you notice how I made the word ‘patterns’ plural? There isn’t a whole separate field of biogeography for nothin’. Biological diversity is difficult (some say impossible) to measure using a single metric. How do you count things? Simply by the number of species? How about rare versus common species? What about species turnover? What geographic scale are you using? How and/or do you define boundaries? Would you like me to keep going or do you get the point?

Lately I’ve noticed a surge in the number of studies that look at diversity gradients that occur along latitude and altitude. We visited the topic of latitude and diversity back in October of last year with the “Dinosaurs, Diversity, Distribution, and the LBG” post. Essentially, latitudinal gradients (LBG or LDG) occur when species richness (a simple count of species) is highest in the tropics and declines polewards (warm areas are more hospitable and produce more food). Altitudinal, or elevational, gradients are nearly as ubiquitous as latitudinal gradients, and they have many of the same characteristics. As you go up in elevation (as on a mountain) the temperature gets colder and habitat areas and the communities they support become smaller and more fragmented. Gradients such as these are overall patterns. Now mix them with diversity indices. In 1960, R.H. Whittaker described the terms alpha diversity (α-diversity), beta diversity (β-diversity), and gamma diversity (γ-diversity). Basically, the total species diversity of a geographic area (γ-diversity) is determined by the mean species diversity at the local, within-site or within-habitat scale (α-diversity) and extent of change in community composition between sites (β-diversity). These definitions have been much argued over (see Tuomisto 2010), and we won’t get in to that. We are going to focus on beta diversity (β-diversity), also called species turnover or differentiation diversity. It is a measure of how different sites are from each other and/or how far apart they are on a gradient of species composition. Factors that drive β-diversity are very important, very poorly understood, and very much argued over. Is it dispersal limitation? Habitat specialization? Environmental heterogeneity? The studies published so far seem to lean toward multiple processes operating at various scales. *sigh* Isn’t that always the way? Observational and experimental studies have shown that impacts on β-diversity vary with productivity. So it would make sense to test this in relation to altitudinal and elevational gradients.

A new study to be published in Global Ecology and Biogeography looks at how local community processes may create an altitudinal pattern of β-diversity. Their study site was the Shiretoko National Park in north-eastern Hokkaido, the northernmost island of Japan. In addition to being one of the richest temperate ecosystems in the world, the area is characterized by sharp altitudinal changes in forest structure and productivity as a result of strong winds on the western side of the mountains. The researchers chose this western side to measure the diversity of woody plants and mites (Oribatida) in mature stands where they set up seven plots (each containing 10 subplots) at different altitudes. For the woody plants they recorded the number of individuals taller than 0.5 m, measured the girth at breast height (GBH), estimated the total basal area (BA), recorded canopy height (CH) of the stand, measured the diameter and length of all coarse woody debris (CWD), measured understory light, took soil cores to extract the mites, removed roots from the soil samples, measured the thickness and dry mass of the soil surface litter (A0 layer), collected leaf litter, measured water content and pH of the litter, and the carbon-to-nitrogen (CN) ratios of the litter and soil. They then calculated the β-diversity of the two organism groups for each altitude. So as to take into account the dependence of β-diversity on gamma diversity (γ-diversity), they used null modeling. This type of modeling “randomly shuffles individuals among subplots while preserving γ-diversity, the relative abundance of each species per plot and the number of individuals per subplot” which enabled them to estimate how much observed β-diversity differed from expected β-diversity. They also calculated a β-deviation value for each altitude. This is equivalent to a standardized effect size, indicating the magnitude of the deviation from what you would expect of a random (stochastic or by chance) assembly process.

First we’ll hit the results for the oribatid mites. These results showed the altitudinal gradient of β-diversity to be less evident than it was for the plants, and β-deviation showed no altitudinal gradient. That said, they found β-deviation to always be greater than expected in all locations for both woody plants and oribatid mites. In woody plants, the magnitude of β-deviation increased with altitude, suggesting that deterministic processes dominate in low-productivity, high-altitude stands, the role of these processes increasing with decreasing productivity in plant communities. The authors conclude that their results support the hypothesis that “the mechanisms underlying community assembly (e.g. niche versus neutral) play an essential role in creating biogeographic patterns of β-diversity.” They found that niche-based processes (species correlate with environmental variables, the conditions in which the species can persist) govern high-altitude stands, particularly when they included the plants growing in lower layers in the analysis. They found similar results when they calculated β-deviation along a stand-structure gradient with basal area, not altitude, particularly when small understory plants were included. This suggests that “given the altitudinal changes in stand structure, the role of understory plants in deterministic assembly becomes more dominant with altitude.” So those little guys really make a difference! Why? Well, considering that light is a precious commodity, low-elevation, structurally well-developed stands have higher competition for available light, especially for those little understory guys. This fierce competition isn’t so fierce in the higher altitude sites where the upper canopy isn't there to usurp all of the light for itself. This favors a greater, more diverse understory in higher elevations. Again, the authors speculate that this greater high altitude diversity is due to fine-scale niche partitioning, which allows more individuals to exist together.

Okay, so that is a pretty good explanation for the high altitude communities. Now what is going on at low altitudes? Well, there you have to take the site’s history a little more into account. What made these stands so “structurally developed” and generated this stochasticity? Consider this: The canopy trees of these forests colonized before the understory individuals, negatively affecting understory species by reducing the availability of space and resources. You then see a relative dominance of these big-ole-bully trees (that’s a technical term, you know) and a one-sided competition scenario.

Did I scramble your brain and make you hate biogeography yet? Can you see any sort of overall conclusion here? Lemme help you out…

β-diversity is dependent on community processes and shaped by local factors within the landscape. The species in a place use what is in a place.

Do you agree?

Mori, A., Shiono, T., Koide, D., Kitagawa, R., Ota, A., & Mizumachi, E. (2013). Community assembly processes shape an altitudinal gradient of forest biodiversity Global Ecology and Biogeography DOI: 10.1111/geb.12058


(image via Japan-Guide.com)

Burn Baby Burn: Fire, Forests, and Carbon

I know, I know. I've been a bit absent over the last few weeks. I'm going to call laying on the beach in South Florida at Christmas enough of an excuse. That and I was finishing up my Wildland Firefighter course. Yep, I'm now all certified to start and stop forest fires. Should you be afraid? Perhaps. But it got me to thinking about prescribed burning, an area of ecology that I know about but don't regularly keep up with the literature. So I decided to take a look at what has recently been published on the topic and found a nice paper in the journal Forest Ecology and Management about the balance of carbon sequestration and habitat conservation as they relate to fire.

Most people tend to think Fire = Bad. In many situations that's true, but in others fire is actually a natural, healthy process. In the past, various federal and state agencies have instituted wildfire suppression policies because they thought it was the best way to preserve the natural state of the land. All it really did was create a massive amount of fuel loading - lots and lots of fuel (dead logs, leaf litter, etc.) around to burn - which created even larger, more destructive fires. Now we know better, and the idea of a more natural fire regime is being used to control fuels and keep the balance of natural habitats.

Today's paper takes a look at woodlands, a subset of forests that are composed of low density, short trees  that typically have an open canopy with a ground layer made up of shrubs, grasses, and forbs. They can be economically important for lumber and livestock grazing, but they are also naturally important as significant carbon (C) sinks and as a biologically diverse habitat. Fire is known to be an important process in this ecosystem and is managed such that willdfires are allowed to burn unhindered, landscape level fuel management helps contain fire spread, and prescribed burning reduces fuels. This study investigates the effects of past fires on carbon storage, woody vegetation community composition, and habitat suitability. They do this by utilizing a "chronosequence" approach. This means that they grouped and compared stands of trees at different successional stages following fire events. These stands were located in the woodlands of Balcones Canyonlands National Wildlife Refuge (BCNWR), located northwest of Austin, Texas, USA. The dominant woody vegetation in this area is the evergreen Ashe's juniper (Juniperus ashei), with subdominant species including several oak (Quercus spp.) species and Escarpment Black Cherry (Prunus serotina var. eximia). These woodlands are also inhabited by the golden-cheeked warbler (Dendroica chrysoparia), an endangered bird species they used to assess habitat suitability. The mixed juniper-oak are critical for this warbler as they use the stringy, sloughed bark from the mature Ashe's juniper exclusively for nesting material and requre Lepidopteran (Geometridae) larvae that feed on broadleafed foliage during the spring breeding season.

The researchers established 60 plots next to trees that had been used for a previous dendrochronology (tree rings) study. That means that they had the history of the tree from the tree rings, this history including fire scars that could be pinned to exact years. The fires were low-intensity, surface burns that mostly consumed the ground layer, seedlings, and saplings. From this they were able to pick sites with single fire events and then assign their plots into three groups: recent-fire (less than 40 years), old fire (greater than 40 years), and no fire. Then, for each plot, they identified tree species and measured their diameter and heights, collected data on woody debris and leaf litter depths, and collected soil samples for carbon and nitrogen analysis.

The authors found significantly different total aboveground biomass C averages for the 60 study plots. Recent-fire showed 5.25 kg m-2, old fire averaged 6.86 kg m-2, and no fire had 9.18 kg m-2 of C. Previous studies have shown that low to moderate intensity fires have less effects on live biomass, stabilize carbon fast afterwards, and primarily affect trees in an age-specific and density-related way. This study found that "the impact of low-intensity fire on C storage increases for sites with higher proportions of biomass in small trees" (greater than 20cm in diameter) as these are more greatly impacted by surface fires.

 This study's results support that periodic surface fires maintain many forests by favoring fire-tolerant species, such as oaks, and decreasing the density of fire sensitive species, such as juniper. They found that sites with a single fire disturbance had a higher density of oak seedlings than juniper seedlings (though not significantly so), especially in years that had low precipitation in the summer. The densities of mature trees was found to be mainly influenced by differences in topography, herbivory, and historical climate.

I would like to say that all of this added up to a good conclusion about habitat suitability for the golden-cheeked warblers but, unfortunately, they found significant differences. Fire reduces mature tree density, which has a negative impact on habitat suitability, but high intensity fire is related to higher oak recruitment (food source for their food source). Managing these woodland for the golden-cheeked warbler may require both mechanical treatment and the use of fire. The critical core breeding habitat for this warbler includes old-growth stands composed of large, mature junipers and about a 40 percent oak species mix. These stands should be protected from intense fire through the mechanical thinning of the understory and the removal of heavy fuels.

Overall, the authors conclude that fire management can achieve multiple outcomes on a single site. This means that detailed ecological information about the species composition and population structure of an area are needed in order to assess conditions and projections on restoration.

Yao, J., Murray, D., Adhikari, A., & White, J. (2012). Fire in a sub-humid woodland: The balance of carbon sequestration and habitat conservation Forest Ecology and Management, 280, 40-51 DOI: 10.1016/j.foreco.2012.05.042

More on wildland fires and prescribed burning:
GeoSTAC's Wildland Fires page
University of Florida IFAS Extention's "Benefits of Prescribed Burning"
National Interagency Prescribed Fire Training Center


(image from Texas Department of Agriculture)

Drinking the Clouds

I don’t often talk about water movement in plants even though I work in a lab that studies water movement in plants. I should probably ruminate on that but won’t. Instead, I’ll start out by putting a complex problem into the simplest of terms: Plants drink water with their roots. Okay, that’s true but perhaps it is a bit too elementary. I think that, in this case, I need to explain it in more detail so that you can really appreciate why a certain research paper caught my attention.

For water to do all the important things it should, it needs to get in and around the plant. This is one of the most basic plant physiology…no, basic biology mechanisms we know. Water diffuses in near the tip of a growing root (you know, the hairy part) and makes its way to the xylem. The xylem is the vascular tissue that conducts water and dissolved nutrients to all parts of the plant. Considering that plants grow up, this water must be moved against gravity. This is where transpiration, root pressure, and capillary action come in. Transpiration (like evaporation, it is the loss of water vapor from parts of a plant, usually the leaves) causes tension and pressure that pulls water up, and root pressure pushes water up when transpiration is low, the soil is moist, and when the roots are absorbing lots of water. Capillary action helps it all as it allows water to flow up the narrow channels of the xylem. The leaves are where the plant usually loses water. Leaves have many, small structures called stomata that function in gas exchange. Guard cells open and close a stoma, and when the carbon dioxide is let in water vapor can be let out. Plants can lose a lot of water through transpiration and have various methods (that I won’t go in to) to try and combat it. Now, this sounds like a lot of info but I’m really just barely scratching the surface (see some links below if you want to know more) of this process. What makes the paper I read today so interesting is that it adds another layer to what we already know about water movement in plants.

The authors of a new paper, published online in Ecology Letters, take a look how plants function in cloud forests. These forests are unique and super neat! Tropical montane cloud forests (TMCF) are among Earth’s most rare and endangered ecosystems occupying just 1.4 percent of the world’s tropical forest area. They are like rain forests in that they receive high levels of precipitation. Where they differ is that much of this precipitation comes directly from clouds, through the cloud filtering of the trees. Lateral cloud filtering is a process where clouds blow among the trees and the moisture condenses as it touches the leaves, forming water droplets. This process reduces the vapor pressure deficit (VPD) and photsynthetically active radiation (PAR), decreasing plant water demand and suppressing leaf-level transpiration. When regular, vertical precipitation is limited in the dry season these cloud water droplets can become an important water source. The researchers in this study looked a phenomenon referred to as foliar water uptake (foliar uptake), where this condensed water is taken in through the leaves, and its occurrence in TMCFs.

The researchers compared neighboring tropical montane and pre-montane cloud forests along the Pacific slope of the Cordillera de Tilarán mountains near Monteverde, Costa Rica. They characterized the cloud cover using remote sensing and created an environmental characterization of the forest by looking at factors such as humidity, temperature, soil water content, rainfall, and leaf wetness. Then they characterized and compared foliar uptake in situ in both forest types, measuring sap flow on the small branches of woody plants using the heat ratio method. They also measured the capacity for foliar uptake in several woody plant species by collecting leaves, rehydrating them, and measuring them individually in the lab.

The researchers found that during the dry season, the pre-montane cloud forests (which are further west and at a lower elevation) are subject to greater rain shadow and less cloud immersion. These forests experienced, on average, a lower number of hours of leaf wetness per day and a shorter duration of each individual leaf wetness event when compared with the tropical montane cloud forests. The higher cloud cover frequency of the TMCF resulted in more, longer leaf wetting events resulting in foliar uptake. They found the prevalence of foliar uptake to be quite high and widespread among species, occurring independently of phylogeny, morphology or growth habit. This foliar uptake also took a significant role in the plants’ water status both in the field and in the lab, resulting in greater water deficit reductions. Furthermore, the results showed that the TMCF plant community demonstrated a higher capacity for foliar uptake than did the pre-montane plant community. This is interesting because foliar uptake benefits the drier, pre-montane forest more and yet these forests are unable to capitalize on them physiologically to the same extent as the TMCF plant communities. This may be a result of the presence or frequency certain leaf traits that facilitate the uptake (cuticle, trichomes, hydathodes) or the ability of water to enter the stomata.

As with everything we do now, look at this through your climate change lenses. What are the consequences of climate change in these ecosystems? Tropical mountains are projected to experience high rates of climate change, increasing dry season surface air temperatures 3.8°C and decreasing precipitation by 14 percent. All of this could increase cloud frequency and cloud base height causing a higher water demand in these plants.

All in all, this new layer to the water movement mechanisms we all know and love is pretty thought-provoking. I know it set out to shed light on the prevalence and role of foliar uptake, but, with me, it had a greater impact in thinking about its consequences. The effect of drought on plants is a hot topic in the plant physiology world, and this paper is an interesting way to look at it.


Goldsmith, G., Matzke, N., & Dawson, T. (2012). The incidence and implications of clouds for cloud forest plant water relations Ecology Letters DOI: 10.1111/ele.12039

More on water movement in plants:
Bellevue College's "Transport in Plants" notes
Univ of Illinois at Chicago's "Transport in Plants" lecture notes
Science Mag's "Transpiration: Water Movement in Plants" (Flash player animations that are good)

About cloud forests:
Community Cloud Forest Conservation
Canopy in the Clouds

On this story:
Science Daily: "Cloud Forest Trees Drink Water Through Their Leaves"
UC Berkeley's "Cloud forest trees drink water through their leaves"

(image via Buncee.com)

Tales from the Road: South Florida Cypress Dome

To keep with, or rather develop a, pattern for this segment of blog posts here are some pictures from a beautiful cypress dome we walked through. These systems are typically isolated forested areas that occur on flat land that has developed a depression that holds water. They get their name because when viewed from afar they have a characteristic dome shape due to large trees growing in the center and tree size getting smaller towards the edges. Due to the depression of the land, the center of these areas is the wettest part, so wet that the soil and roots are completely submerged for prolonged periods of time (tip: look up cypress knees). Adult cypress trees are tolerate of this inundation but need dry periods so that their seeds can germinate, and fire is often an important component to ecosystem health. Although cypress trees (pond and bald cypress) tend to dominate you will also see red or swamp maple (Acer rubrum), swamp tupelo (Nyssa sylvatica var. biflora),  saw palmetto (Serenoa repens), coco plum (Chrysobalanus icaco), pond apple (Annona glabra), pop ash (Fraxinus caroliniana), and herbaceous plants such as Sphagnum moss (Sphagnum spp.), Spanish moss (Tillandsia usneoides), sawgrass (Cladium jamaicense), resurrection fern (Polypodium polypodioides), and many many other species. It is an important area that provides habitat for many species including amphibians and birds.

A look out on some of the edge of the cypress dome.

One of the palms that you will see scattered throughout.

Epiphyte diversity can be quite high in these areas.

Another look out through the center-edge of the dome.

Some links about cypress domes:

The actual place where these pictures were taken is located in the Big Cypress Preserve in South Florida and run by the Seminole Indian Tribe. They have a beautiful, well maintained boardwalk through the area with very education signs and labeled plants. Stop by or schedule your own tour or just look around their website:
http://www.ahtahthiki.com/big-cypress-tours/index.cfm

From the School of Forest Resources and Conservation at the University of Florida. Here is a page on the plants of Florida swamps, including cypress domes:
http://www.sfrc.ufl.edu/4h/other_resources/contest/highlighted_ecosystem/swplants.htm

The Florida Nature website has some good information on various habitats found in the state including South Florida:
http://www.floridasnature.com/florida_habitats.htm

Also, here are some old but good references on this topic:

Brown, S. (1981) A comparison of the structure, primary productivity, and transpiration of cypress ecosystems in Florida. Ecological Monographs: 51, 403-427. (Link)

Ewel, K.C., and W.J. Mitsch. (1978) The effect of fire on species composition in cypress dome ecosystems. Florida Scientist: 41, 25-30. (Link)

Ewel, K.C., and L.P. Wickenheiser (1988) Effect of swamp size on growth rates of cypress (Taxodium distichum) trees. American Midland Naturalist: 120, 362-370. (Link)

Kurz, H., and K.A. Wagner. (1953) Factors in cypress dome development. Ecology: 34, 157-164. (Link)

Vernon, R.O. (1947) Cypress domes. Science: 105, 97-99. (DOI: 10.1126/science.105.2717.97)

Tales from the Road: The Florida Everglades

My recent hiatus from the blog is due to a trip to South Florida. Day one of the trip was all about the beautiful, subtropical landscape that is the Florida Everglades. The Everglades is one of the largest wetlands in the entire world. The "River of Grass" is characterized by a shallow sheet of water that flows over and through the system amid blades of sawgrass. This ecosystem is very rich, hosting many species of plants and animals, 14 of which are endangered and 9 threatened. I've included some useful links at the bottom of this post if you are interested in learning more about this ecosystem.

From an airboat zooming through the Glades

Some beautiful cypress trees and pop ash

Some larger trees found among the marshy, grassy areas of the Glades.

You can see that this area has been cleared due to water flow and the passage of airboats.

 The Everglades Digital Library via Florida International University. It includes resources relating to the South Florida environment including scientific and technical reports, natural history writings, educational materials, datasets, maps, photos, etc.
http://everglades.fiu.edu/

The Wetlands Page of the Environmental Protection Agency (EPA). It gives some very useful information on wetlands in general and legislation concerning them.
http://water.epa.gov/type/wetlands/index.cfm

The homepage of the South Florida Water Management District. It has good info on water conservation and the restoration of the Everglades.
http://www.sfwmd.gov/portal/page/portal/sfwmdmain/home%20page

The website of the Comprehensive Everglades Restoration Plan (CERP). It has videos and lots of information about the Everglades and the on-going restoration.
http://www.evergladesplan.org/index.aspx

Florida PantherNet via the Florida Fish and Wildlife Conservation Commission. A close look at this very endangered animal and its conservation.
http://www.floridapanthernet.org/

Under Cover

While working on my masters thesis I got really interested in the rates of forest and species loss. As a result, articles relating to these topics still catch my eye. So when I saw this article published online in PNAS I knew I couldn't pass it up.

If you are reading this blog then you are probably aware of the massive forest loss in the topics and other places around the world. Forests that aren't completely cut down are fragmented into ever smaller islands and refugia. We can see this happening, but putting a rate to it can be difficult. Typically, rates are calculated by such methods as putting together a large meta-analysis or collecting lots of satellite images. This study does the latter in that the researchers took data from the MODIS sensor to look at stratification for forest cover loss. MODIS (Moderate Resolution Imaging Spectroradiometer) is an instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites that orbit around the Earth. Terra passes from north to south across the equator in the morning, and Aqua passes in the afternoon. This allows the satellites to view the entire surface of the Earth every 1-2 days. The authors also used the Landsat ETM+ to quantify gross forest cover loss (GFCL) for the entire planet. With these data they were able to compare GFCL among biomes, continents, and countries. Note that "GFCL is defined as the area of forest cover removed because of any disturbance, including both natural and human-induced causes."

"GFCL was estimated to be 1,011,000 km2 from 2000 to 2005, representing 3.1% (0.6% per year) of the year 2000 estimated total forest area of 32,688,000 km2." The results showed that Russia had the most extensive forest loss. Next in line were Brazil, Canada and the USA. If you break it down by type then you see the most loss in boreal forests, Russia being the biggest offender again - 60% of boreal forest loss can be blamed on them. Tsk tsk. Humid tropical forests rank next, especially in the countries of Brazil, Indonesia and Malaysia. Although, in terms of smallest proportion lost they actually rank pretty well. Mweh, still not exactly a comforting figure. Sticking with the tropics, dry tropical forests rank next, especially in the countries of Australia, Brazil, Argentina and Paraguay. Temperate forests have been hacked at for hundreds of years and, as of this study, still managed to have the second higest proportional loss (after boreal forests, which I mentioned above), with North America being the biggest offender -- 30% of the blame for global loss (5.1% proportional loss) lies there. Also, I would be remiss if I did not mention that the processes driving GFCL, and rates of recovery from it, vary regionally. If you look at the boreal system you will find that naturally induced fire is important, and in other systems additonal factors are key. But all in all, everybody needs to step back -- to a global scale, as in the picture at the top -- and see what this fragmentation is doing to these regions. (insert finger waggle and head shaking here)

Here's the article:
Hansen, M.C., S.V. Stehman, and P.V. Potapov (2010) Quantification of global gross forest cover loss. Proceedings of the National Academy of Sciences: published online. (DOI: 10.1073/pnas.0912668107)

(Both images are credited to NASA's MODIS website: http://modis.gsfc.nasa.gov/gallery/ and more spectactular images can be found there. Check it out!)