Why are there so few tree species in Europe?

Photo by Susulyka licensed under CC BY-SA 4.0

Take a look at a list of tree species from temperate Europe, North America, and Asia and you will notice a glaring disparity. Whereas North America and Asia are home to something like 1000 tree species each, Europe is home to just about 500 species. Why is this?

The answer may lie partly in the glacial history of the Northern Hemisphere as well as in some quirks of geology. Starting in the late Pliocene, roughly 3 million years ago, the Earth began to cool. As our planet entered into a epoch dominated by massive, continent-wide glaciers, life was responding accordingly.

Historically it was assumed that Europe lost many of its temperate tree species thanks to the east-west orientation of its mountain ranges. As glaciers advanced from the north, species were pushed farther and farther south until they hit physical barriers in the terrain like the Alps. With nowhere to go but up, many species that couldn’t handle either the rate of climate change or the altitude adjustment simply winked out of existence. Fossil evidence from Europe provides plenty of evidence that this region was once home to far more tree species, including relatives of sweetgum (Liquidambar spp.) and tulip trees (Liriodendron spp.) that are still present in North America, and umbrella pines (Sciadopitys spp.), which still exists in Asia. Many temperate tree species in North America and Asia were spared this fate because there were far fewer barriers to successful southern migrations.

This all sounds a bit too simple and indeed, recent studies suggest that it is. Though climate change, glaciers, and mountains certainly played a role in the differential extinction rates of European trees, the story is a bit more complicated than that. It turns out that the European mountain ranges don’t present as impenetrable of a barrier to plant migrations as was once thought. The fact that southern Europe and northern Africa share many similar taxa is proof of this. Instead, the amount of suitable habitat and land area available to trees migrating down from northern Europe may have played an even larger role in the extinction rate of European trees.

Extent of glacial coverage (blue) during the last ice age. Map by Hannse Grobe licensed under CC-BY-2.5

It is a well documented phenomenon in ecology that smaller areas of land support smaller numbers of species. This is the case for Pleistocene Europe. Suitable habitat for temperate tree species during this time would have largely consisted of three peninsulas (Iberia, Italy, and the Balkans) separated by the Mediterranian Sea. Each of these peninsulas boast mountain chains that would have offered small bands of suitable microclimates for temperate tree species to find refuge during glacial advance.

Pushed into tiny pockets of refugia, Europe’s temperate tree species would have been more vulnerable to extinction than tree species in North America and Asia, which had far more suitable habitat available to them in the southern portions of those continents. By looking at which taxa survived and which went extinct, patterns do start to emerge. Tree species that are widespread in Europe today are descendants of trees that were far more tolerant of cooler growing seasons and harsh winters than genera that went extinct. This likely reflects the fact that their ancestors were those species that found refuge high up in the mountains.

Alternatively, present-day Europe also boasts small pockets of what are termed “relictual genera,” which is a fancy way of saying species that were once more common in the past than they are today. These so-called relictual taxa have been found to be far more tolerant of drought than genera that went extinct. This likely reflects the fact that their ancestors found refuge in warmer, low-elevation habitats in southern Europe.

It appears that species on either end of the tolerance curves were the ones that won out in Europe’s extinction lottery. By tolerating either extreme cold or extreme drought, “stress tolerators” were able to not only survive repeated glaciation events, but also provide seed sources for those lineages following glacial retreat.

Only the species that were able to find suitable habitats in southern Europe’s glacial refugia were the ones that were able to recolonize the region after the Ice Age had ended. At this point in time, these are some of the best pieces of evidence we have in explaining the disparity in tree diversity between Europe, North America, and Asia. What’s more, I find disturbing trends in such extinctions because it wasn’t like the glaciers always wiped out species immediately. Instead, many species were able to survive glaciation but were pushed into smaller and smaller pockets of suitable habitat until relatively small disturbances pushed them over the edge.

Today, we humans are changing Earth’s climates at a rate that hasn’t been seen in over 50 million years and all the while we are fragmenting habitats more and more. What is going to happen to species living today in these tiny pockets?

Photo Credits: [1] [2]

Further Reading: [1] [2] [3] [4]

The Sinewy American Hornbeam

Photo by Richard Webb licensed by CC BY-SA 3.0

Winter is when I really start to notice trees. Admittedly, I am pretty poor when it comes to tree ID and taxonomy but there are a few species that really stand out. One of my all time favorite trees is Carpinus caroliniana.

Carpinus caroliniana goes by a handful of common names including ironwood, musclewood, and American hornbeam. All of these names have been applied to other trees so I'll stick with its scientific name. Finding C. caroliniana is rather easy. All you have to do is look for its unmistakable bark.

Photo by Rob Duval licensed by CC BY-SA 3.0

With smooth, sinewy striations and ridges, it is no wonder how this tree got the name "musclewood." The wood is extremely close-grained and is therefore very hard, earning it another nickname of "ironwood."They are generally small trees, rarely exceeding a few meters in height, though records have shown that some individuals can grow to upwards of 20 meters in rare circumstances. I hope that someday I will be able to meet one of these rare giants.

Carpinus caroliniana is also an indicator of fairly rich soils. Due to their high tolerance for shade, they are often a tree of the mixed hardwood understory. Their foliage resembles that of the family in which they belong, the birch family (Betulaceae).

Photo by Katja Schulz licensed by CC BY 2.0

The caterpillar of the io moth (Automeris io)

An adult io moth (Automeris io). Photo by Andy Reago & Chrissy McClarren licensed by CC BY 2.0

A multitude of insect species utilize C. caroliniana as a larval food source including the famed io moth. In the spring, male and female catkins are born on the same tree and, after fertilization, they are replaced by interesting looking nutlets covered by leaf-like involucres. The seeds are an important food source for a variety of birds, mammals, and insects alike.

The male flowers of Carpinus caroliniana. Photo by Philip Bouchard licensed by CC BY-NC-ND 2.0

Carpinus caroliniana is a tree I could never get bored with. Not only does it have immense ecological value, it is aesthetically pleasing too. Its small size and shade tolerance also makes it a great landscape tree in areas too cramped for something larger. Why this species isn't more popular in native landscaping is beyond me.

Photo Credits: [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3]

A Very Strange Maple

Photo by Abrahami licensed under CC BY-SA 2.5

I love being humbled by plant ID. Confusion usually means I am going to end up learning something new. This happened quite recently during a trip through The Morton Arboretum. Admittedly trees are not my forte but I had spotted something that seemed off and needed further inspection. I was greeted by a small tree with leaves that screamed "birch family" (Betulaceae) yet they were opposite. Members of the birch family should have alternately arranged leaves. What the heck was I looking at?

It didn't take long for me to find the ID tag. As a plant obsessed person, the information on the tag gave me quite the thrill. What I was looking at was possible the strangest maple on the planet. This, my friends, was my first introduction to Acer carpinifolium a.k.a the hornbeam maple.

Photo (c)2006 Derek Ramsey (Ram-Man) licensed under CC BY-SA 2.5

The hornbeam maple is endemic to Japan where it can be found growing in mountainous woodlands and alongside streams. Maxing out around 30 feet (9 m) in height, the hornbeam maple is by no means a large tree. It would appear that it has a similar place in its native ecology as other smaller understory maples do here in North America. It blooms in spring and its fruits are the typical samaras one comes to expect from the genus.

It probably goes without saying that the thing I find most fascinating about the hornbeam maple are its leaves. As both its common and scientific names tell you, they more closely resemble that of a hornbeam (Carpinus spp.) than a maple. Unlike the lobed, palmately veined leaves of its cousins, the hornbeam maple produces simple, unlobed leaves with pinnate venation and serrated margins. They challenge everything I have come to expect out of a maple. Indeed, the hornbeam maple is one of only a handful of species in the genus Acer that break the mold for leaf shape. However, compared to the rest, I think its safe to say that the hornbeam maple is the most aberrant of them all. 

Photo by Qwert1234 licensed under CC BY-SA 3.0

Not a lot of phylogenetic work has been done on the relationship between the hornbeam maple and the rest of its Acer cousins. At least one study suggests that it is most closely related to the mountain maple of neartheastern North America. More scrutiny will be needed before anyone can make this claim with certainty. Still, from an anecdotal standpoint, it seems like a reasonable leap to make considering just how shallow the lobes are on mountain maple leaves.

Regardless of who it is related to, running into this tree was truly a thrilling experience. I love it when species challenge long held expectations of large groups of plants. Hornbeam maple has gone from a place of complete mystery to me to being one of my favorite maples of all time. I hope you too will get a chance to meet this species if you haven't already!

Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

Red or White?

Photo by Msact at English Wikipedia licensed under CC BY-SA 3.0

Who doesn't love a nice oak tree? One cannot overstate their importance both ecologically and culturally. Although picking an oak tree out of a lineup is something many of us are capable of doing, identifying oaks to species can be a bit more challenging. This is further complicated by the fact that oaks often hybridize. Still, it is likely you have come across some useful tips and tricks for narrowing down your oak choices. One such trick is distinguishing between the red oaks and the white oaks. If you're anything like me, this is something you took for granted for a while. Is there anything biologically or ecologically meaningful to such a split?

In short, yes. However, a true appreciation of these groups requires a deeper look. To start with, oaks are members of the genus Quercus, which belongs in the family Fagaceae. Globally there are approximately 400 species of oak and each falls into one of three categories - the red oaks (section Lobatae), the white oaks (section Quercus), and the so-called "intermediate" oaks (section Protoblanus). For the sake of this article, I will only be focusing on the red and white groups as that is where most of the oak species reside. The intermediate oak group is made up of 5 species, all of which are native to the southwestern United States and northwestern Mexico.

As is common with oak identification, reliable techniques for distinguishing between the two groups can be tricky. Probably the most reliable feature is located on the inner surface of the acorn cap. In white oaks, it is hairless or nearly so, whereas in red oaks, it is covered in tiny hairs. Another useful acorn feature is the length of time it takes them to germinate. White oak acorns mature in one season and germinate in the fall. As such, they contain lower levels of tannins. Red oak acorns (as well as those of the intermediate group) generally take at least two seasons to mature and therefore germinate the following spring. Because of this, red oak acorns have a much higher tannin content. For more information on why this is the case, read this article.

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Tyloses in white oak xylem. Photo by Dr. Michael Rosenthal, Technische Universität Dresden via Rosenthal, M.; Bäucker, E. (2013): Zur Anatomie des Holzes der Weiß-Eichen. Rasterelektronenmikroskopische Bildtafeln zu den drei holzanatomischen Schnittrichtungen. licensed under CC BY-SA 3.0

Less apparent than acorns is the difference in the wood of red and white oaks. The wood of white oaks contains tiny structures in their xylem tissues called tyloses. These are absent from the wood of red oaks. The function of tyloses are quite interesting. During extreme drought or in the case of some sort of infection, they cut off regions of the xylem to stop the spread of an embolism or whatever may be infecting the tree. As such, white oaks tend to be more rot and drought resistant. Fun fact, tyloses are the main reason why white oak is used for making wine and bourbon barrels as it keeps them from leaking their contents.

More apparent to the casual observer, however, is leaf shape. In general, the white oaks produce leaves that have rounded lobes, whereas the red oaks generally exhibit pointed lobes with a tiny bristle on their tips. At this point you may be asking where an unlobed species like shingle oak (Quercus imbricaria) fits in. Look at the tip of its leaf and you will see a small bristle, which means its a member of the red oak group. Similarly, the buds of these two groups often differ in their overall shape. White oak buds tend to be smaller and often have blunted tips whereas the buds of red oaks are generally larger and often pointed.

Tricky leaves of the shingle oak (Quercus imbricaria). Note the bristle tip! Photo by Greg Blick licensed under CC BY-NC-ND 2.0

Despite this broad generalizations, exceptions abound. This is further complicated by the fact that many species will readily hybridize. Quercus is, after all, a massive genus. Regardless, oaks are wonderful species chock full of ecological and cultural value. Still, oak appreciation is something we all need more of in our lives. I encourage you to try some oak identification of your own. Get outside and see if you can use any of these tricks to help you identify some of the oaks in your neighborhood.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

On Fungi and Forest Diversity

One simply can't talk about plants without eventually talking about fungi. The fact of the matter is the vast majority of plant species rely on fungal interactions for survival. This mutualistic relationship is referred to as mycorrhizal. Fungi in the soil colonize the root system of plants and assist in the acquisition of nutrients such as nitrogen and phosphorus. In return, most photosynthetic plants pay their mycorrhizal symbionts with carbohydrates. 

There are two major categories of mycorrhizal fungi - ectomycorrhizae (EMF) and arbuscular mycorrhizae (AMF). Though there are a variety of different species of fungi that fall into either of these groups, their strategies are pretty much the same. EMF make up roughly 10% of all the known mycorrhizal symbionts. The prefix "ecto" hints at the fact that these fungi form on the outside of root cells. They form a sort of sheath that encases the outside of the root as well as a "hartig net" around the outside of individual cells within the root cortex. AMF, on the other hand, literally penetrate the root cells and form two different kinds of structures once inside. One of these structures looks like the crown of a tree, hence the term "arbuscular." What's more, they are considered the oldest mycorrhizal group to have evolved. 

[SOURCE]

The type of mycorrhizal fungi a plant partners with has greater implications that simple nutrient uptake. Evidence is now showing that the dominant fungi of a region can actually influence the overall health and diversity forest ecosystems. The mechanism behind this has a lot to do with the two different categories discussed above. 

Researchers have discovered that trees partnering with AMF experience negative feedbacks in biomass whereas those that partner with EMF experience positive feedbacks in biomass. When grown in soils that previously harbored similar tree species, trees that partnered with AMF grew poorly whereas trees that partnered with EMF grew much better. Additionally, by repeating the experiments with seedlings, researchers found that seedling survival was reduced for AMF trees whereas seedling survival increased in EMF trees. 

What is going on here? If mycorrhizae are symbionts, why would there be any detrimental effects? The answer to this may have something to do with soil pathogens. Thinking back to the major differences between EMF and AMF, you will remember that it comes down to the way in which they form their root associations. EMF form a protective sheath around the roots whereas AMF penetrate the cells.  As it turns out, this has major implications for pathogen resistance. Because they form a sheath around the entire root, EMF perform much better at keeping pathogens away from sensitive root tissues. The same can't be said for AMF. Researchers found that AMF trees experienced significantly more root damage when grown in soils that previously contained AMF trees. 

The differences in the type of feedback experienced by EMF and AMF trees can have serious consequences for tree diversity. Because EMF trees are healthier and experience increased seedling establishment in soils containing other EMF species, it stands to reason that this would lead to a dominance of EMF species, thus reducing the variety of species capable of establishing in that area. Conversely, areas dominated by AMF trees may actually be more diverse due to the reduction in fitness that would arise if AMF trees started to dominate. Though they are detrimental, the negative feedbacks experienced by AMF trees may lead to healthier and more diverse forests in the grand scheme of things. 

Infographic by [1]

Further Reading: [1]

Bark!

Photos by SNappa2006 (CC BY 2.0), nutmeg66 (CC BY-NC-ND 2.0), Eli Sagor (CC BY-NC 2.0), and Randy McRoberts (CC BY 2.0)

Say "tree bark" and everyone knows what you're talking about. We learn at an early age that bark is something trees have. But what is bark? What is its purpose and why are there so many different kinds? Indeed, there would seem to be as many different types of bark as there are trees. It can even be used as a diagnostic feature, allowing tree enthusiasts to tease apart what kind of tree they are looking at. Bark is not only fascinating, it serves a serious adaptive purpose as well. To begin to understand bark, we must first look at how it is formed.

To start out, bark isn't a very technical term. Bark isn't even a single type of tissue. Instead, bark encompasses several different kinds of tissues. If you remember back to Plant Growth 101, you may have heard the word "cambium" get thrown around. Cambium is a layer of actively dividing tissue sandwiched between the xylem and the phloem in the stems and roots of plants. As this layer grows and divides, the inside cells become the xylem whereas the outside cells become the phloem. 

Successive divisions produce what is known as secondary phloem. This is where the bark begins. On the outside of this secondary phloem are three rings of tissues collectively referred to as the "periderm." It is the periderm which is responsible for the distinctive bark patterns we see. As a layer of cells called the "cork cambium" divides, the outer layer becomes cork. These cells die as soon as they are fully developed. This layer is most obvious in smooth bark species such as beech. 

Similar to insect growth, however, the growth of the insides of a tree will eventually outpace the bark. When this happens, the periderm begins to split and cracks will begin to appear in the bark. This phenomenon is most readily visible in trees like red oaks. When this starts to happen, cells within the secondary phloem begin to divide. This forms a new periderm underneath the old one. The cumulative result of this results in alternating layers of old periderm tissue referred to as "rhytidome." 

This gives trees like black cherry their scaly appearance or, if the rhytidome consists of tight layers, the characteristic ridges of white ash and white oak. Essentially, the distribution and growth pattern of the periderm gives the tree its bark characteristics. But why do trees do this? Why is bark there in the first place?

The dominant role of bark is protection. Without it, vital vascular tissues risk being damaged and the tree would rapidly loose water. It also protects the tree from pests and pathogens. The cell walls of cork contain high amounts of suberin, a waxy substance that protects against desiccation, insect attack, as well as fungal and bacterial infection. Thick bark can also insulate trees from fire. 

Countless aspects of the environment have influenced the evolution of tree bark. In some species such as aspen or sycamore, the trunk and stems function as additional photosynthetic organs. In these species, cork layers are thin and often flaky. Shedding these thin layers of bark ensures that buildup of mosses, lichens, and other epiphytes doesn't interfere with photosynthesis. The white substance on paper birch bark not only inhibits fungal growth, it also helps prevent desiccation while at the same time making it distasteful for browsing insects and mammals alike.

When you consider all the different roles that bark can play, it is no wonder then that there are so many different kinds. This is only the tip of the ice berg. Entire scientific careers have been devoted to understanding this group of tissues. For now, winter is an excellent time to start noticing bark. Take some time and get to know the trees around you for their bark rather than their leaves.

Photo Credits: Eli Sagor (bit.ly/1OTnA8H), Randy McRoberts (bit.ly/1PgzH35), Lotus Johnson (bit.ly/1JyVt1E), SNappa2006 (bit.ly/1TkjHil), and nutmeg66 (bit.ly/1QwyZQ8)

Further Reading:
http://www.botgard.ucla.edu/

html/botanytextbooks/generalbotany

/barkfeatures/typesofbark.html

http://dendro.cnre.vt.edu/forestbiolog

y/cambium2_no_scene_1.swf

http://life9e.sinauer.com/life9e/pages

/34/342001.html

http://www.botgard.ucla.edu/html/bo

tanytextbooks/generalbotany/barkfe

atures/

Hyperabundant Deer Populations Are Reducing Forest Diversity

Photo by tuchodi licensed under CC BY 2.0

Synthesizing the effects of white-tailed deer on the landscape have, until now, been difficult. Although strong sentiments are there, there really hasn't been a collective review that indicates if overabundant white-tailed deer populations are having a net impact on the ecosystem. A recent meta-analysis published in the Annals of Botany: Plant Science Research aimed to change that. What they have found is that the overabundance of deer is having strong negative impacts on forest understory plant communities in North America.

White-tailed deer have become a pervasive issue on this continent. With an estimated population of well over 30 million individuals, deer have been managed so well that they have reached proportions never seen on this continent in the past. The effects of this hyper abundance are felt all across the landscape. As anyone who gardens will tell you, deer are voracious eaters.

Tackling this issue isn't easy. Raising questions about proper management in the face of an ecological disaster that we have created can really put a divide in the room. Even some of you may be experiencing an uptick in your blood pressure simply by reading this. Feelings aside, the fact of the matter is overabundant deer are causing a decline in forest diversity. This is especially true for woody plant species. Deer browsing at such high levels can reduce woody plant diversity by upwards of 60%. Especially hard hit are seedlings and saplings. In many areas, forests are growing older without any young trees to replace them.

What's more, their selectivity when it comes to what's on the menu means that forests are becoming more homogenous. Grasses, sedges, and ferns are increasingly replacing herbaceous cover gobbled up by deer. Also, deer appear to prefer native plants over invasives, leaving behind a sea of plants that local wildlife can't readily utilize. It's not just plants that are affected either. Excessive deer browse is creating trophic cascades that propagate throughout the food web.

For instance, birds and plants are intricately linked. Flowers attract insects and eventually produce seeds. These in turn provide food for birds. Shrubs provide food as well as shelter and nesting space, a necessary requisite for healthy bird populations. Other studies have shown that in areas that experience the highest deer densities songbird populations are nearly 40% lower than in areas with smaller deer populations. As deer make short work of our native plants, they are hurting far more than just the plants themselves. Every plant that disappears from the landscape is one less plant that can support wildlife.

Sadly, due to the elimination of large predators from the landscape, deer have no natural checks and balances on their populations other than disease and starvation. As we replace natural areas with manicured lawns and gardens, we are only making the problem worse. Deer have adapted quite well to human disturbance, a fact not lost on anyone who has had their garden raided by these ungulates. Whereas the deer problem is only a piece of the puzzle when it comes to environmental issues, it is nonetheless a large one. With management practices aimed more towards trophy deer than healthy population numbers, it is likely this issue will only get worse.

Photo Credit: tuchodi (http://bit.ly/1wFYh2X)

Further Reading:
http://aobpla.oxfordjournals.org/content/7/plv119.full

http://aobpla.oxfordjournals.org/content/6/plu030.full

http://www.sciencedirect.com/science/article/pii/S0006320705001722

Cooksonia: A Step Into the Canopy

Photo by Steel Wool licensed under CC BY-NC-ND 2.0

For plants, the journey onto land did not happen over night. It began some 485.4–443.4 million years ago during the Ordovician. The best evidence we have for this comes in the form of fossilized spores. These spores resemble those of modern day liverworts. Under high powered microscopes, one can easily see that they were indeed adapted for life on land. These early plants were a lot like the hornworts, liverworts, and mosses we see today in having no vascular tissues for transporting water, an adaptation that would not come along for another few million years. 

Without vascular tissues, plants like liverworts and mosses cannot transport water very far. They instead rely on osmosis and diffusion to get water and nutrients to where they need to be, which severely limits the size of these types of plants to only a few centimeters. This growth pattern carried on well into the Silurian. Until then, the greening of our planet happened in miniature. 

Photo by Sabrina Setaro licensed under CC BY 2.0

Around 415 million years ago, however, plants became vascularized. This changed everything. It set the stage for the botanical world we know and love today. Paleobotanists place the fossil remains of these newly evolved vascular plants in the genus Cooksonia. Based on what we would call a plant today, Cooksonia probably pushes the limits. However, in some species the branching structure is full of dark stripes, which have been interpreted as vascular tissues. It still wasn't a very tall plant with the tallest specimen standing only a few centimeters but it was a major step towards a much taller green world. 

Cooksonia did not have any leaves that we are aware of but some species certainly had stomata (another major innovation for water regulation in plants). Each branched tip ended in a sporangium or spore-bearing capsule. It has been suggested that Cooksonia may not represent an individual photosynthetic plant but rather a highly adapted sporophyte that may have relied on a gametophyte for photosynthesis. This hypothesis is supported by the diminutive size of many Cooksonia fossils. They simply do not have enough room within their tissues to support photosynthetic machinery. Because of this, some botanists believe that vascularization sprang from a dependent sporophyte that gradually became more and more independent from its gametophyte over time. Until an associated gametophyte fossil is found, we simply don't know. 

Photo Credits: Steel Wool (http://bit.ly/1AjLYh8) and Sabrina Setaro (http://bit.ly/16mdyxw)

Further Reading: [1] [2] [3]

A Fungal Net in the Canopy

It is easy to think that a falling leaf usually has to hit the ground before fungi go to work turning it into the soil. All of our conceptions about fungi seem to be, quite literally, grounded. We tend to forget that fungi are everywhere. Their spores travel like smoke in the slightest breeze and carry them throughout the globe. In moist tropical jungles around the world, some fungi don't wait for plant debris to hit the ground before they go to work on it. There are species of fungi out there waiting in the canopy for their next meal. What's more, they form a vast net-like community to do so. 

As far as we know, these arboreal fungi all belong to the genus Marasmius. Though they are hard to see, anyone hiking through a tropical jungle has likely encountered some of these. These nondescript little mushrooms send out a network of mycelia called a "rhizomorph net." The threads are quite sticky so leaves and small branches easily get caught in them. The fungi don't waste any time making quick work of these aerial meals. In some instances, these arboreal fungi can capture so much detritus that very little makes it to the forest floor. 

This has some major ramifications throughout the entire ecosystem. Tiny critters flock to these suspended soil factories. Their energy rich contents and more than suitable microclimates offer a haven for a whole community of insect life. Experiments have shown that these fungi are responsible for upwards of 70% of the insect diversity in a given hectare of tropical forests. These are some impressive stats when you consider the sheer numbers of insects in the tropics. Despite their importance, these arboreal fungal nets have gone largely unnoticed. Entire communities rely on these fungi yet we know very little about them. 

Photo Credit: Bernard DUPONT (http://bit.ly/1Ie2pun)

Further Reading:
http://rsbl.royalsocietypublishing.org/content/8/3/397