How a Tropical Conifer May Hold the Key to Kākāpō Recovery

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The plight of the kākāpō is a tragedy. Once the third most common bird in New Zealand, this large, flightless parrot has seen its numbers reduced to less than 150. In fact, for a time, it was even thought to be extinct. Today, serious effort has been put forth to try and recover this species from the brink of extinction. It has long been recognized that kākāpō breeding efforts are conspicuously tied to the phenology of certain trees but recent research suggests one in particular may hold the key to survival of the species.

The kākāpō shares its island homes (saving the kākāpō involved moving birds to rat-free islands) with a handful of tropical conifers from the families Podocarpaceae and Araucariaceae. Of these tropical conifers, one species is of particular interest to those concerned with kākāpō breeding - the rimu. Known to science as Dacrydium cupressinum, this evergreen tree represents one of the most important food sources for breeding kākāpō. Before we get to that, however, it is worth getting to know the rimu a bit better.

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Rimu are remarkable, albeit slow-growing trees. They are endemic to New Zealand where they make up a considerable portion of the forest canopy. Like many slow-growing species, rimu can live for quite a long time. Before commercial logging moved in, trees of 800 to 900 years of age were not unheard of. Also, they can reach immense sizes. Historical accounts speak of trees that reached 200 ft. (61 m) in height. Today you are more likely to encounter trees in the 60 to 100 ft. (20 to 35 m) range.

The rimu is a dioecious tree, meaning individuals are either male or female. Rimu rely on wind for pollination and female cones can take upwards of 15 months to fully mature following pollination. The rimu is yet another one of those conifers that has converged on fruit-like structures for seed dispersal. As the female cones mature, the scales gradually begin to swell and turn red. Once fully ripened, the fleshy red “fruit” displays one or two black seeds at the tip. Its these “fruits” that have kākāpō researchers so excited.

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As mentioned, it is a common observation that kākāpō only tend to breed when trees like the rimu experience reproductive booms. The “fruits” and seeds they produce are an important component of the diets of not only female kākāpō but their developing chicks as well. Because kākāpō are critically endangered, captive breeding is one of the main ways in which conservationists are supplementing numbers in the wild. The problem with breeding kakapo in captivity is that supplemental food doesn’t seem to bring them into proper breeding condition. This is where the rimu “fruits” come in.

Breeding birds desperately need calcium and vitamin D for proper egg production. As such, they seek out diets high in these nutrients. When researchers took a closer look at the “fruits” of the rimu, the kākāpō’s reliance on these trees made a whole lot more sense. It turns out, those fleshy scales surrounding rimu seeds are exceptionally high in not only calcium, but various forms of vitamin D once thought to be produced by animals alone. The nutritional quality of these “fruits” provides a wonderful explanation for why kākāpō reproduction seems to be tied to rimu reproduction. Females can gorge themselves on the “fruits,” which brings them into breeding condition. They also go on to feed these “fruits” to their developing chicks. For a slow growing, flightless parrot, it seems that it only makes sense to breed when food is this food source is abundant.

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Though far from a smoking gun, researchers believe that the rimu is the missing piece of the puzzle in captive kākāpō breeding. If these “fruits” really are the trigger needed to bring female kākāpō into good shape for breeding and raising chicks, this may make breeding kākāpō in captivity that much easier. Captive breeding is the key to the long term survival of these odd yet charismatic, flightless parrots. By ensuring the production and survival of future generations of kākāpō, conservationists may be able to turn this tragedy into a real success story. What’s more, this research underscores the importance of understanding the ecology of the organisms we are desperately trying to save.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2]

Life On a Floodplain

Floodplains can be pretty rough places for plant life. Despite readily a available water supply, the unpredictable, disturbance-prone nature of these habitats means that static lifeforms such as plants need to be quite adaptable to survive and persist. Join In Defense of Plants for a brief look at this sort of ecosystem.

Producer, Editor, Camera: Grant Czadzeck (http://www.grantczadzeck.com)

Music by
Artist: Somali Yacht Club
Track: Up In The Sky
http://somaliyachtclub.bandcamp.com

How Trees Fight Disease

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Plants do not have immune systems like animals. Instead, they have evolved an entirely different way of dealing with infections. In trees, this process is known as the "compartmentalization of decay in trees" or "CODIT." CODIT is a fascinating process and many of us will recognize its physical manifestations.

In order to understand CODIT, one must know a little something about how trees grow. Trees have an amazing ability to generate new cells. However, they do not have the ability to repair damage. Instead, trees respond to disease and injury  by walling it off from their living tissues. This involves three distinct processes. The first of these has to do with minimizing the spread of damage. Trees accomplish this by strengthening the walls between cells. Essentially this begins the process of isolating whatever may be harming the living tissues.

This is done via chemical means. In the living sapwood, it is the result of changes in chemical environment within each cell. In heartwood, enzymatic changes work on the structure of the already deceased cells. Though the process is still poorly understood, these chemical changes are surprisingly similar to the process of tanning leather. Compounds like tannic and gallic acids are created, which protect tissues from further decay. They also result in a discoloration of the surrounding wood. 

The second step in the CODIT process involves the construction of new walls around the damaged area. This is where the real compartmentalization process begins. The cambium layer changes the types of cells it produces around the area so that it blocks that compartment off from the surrounding vascular tissues. These new cells also exhibit highly altered metabolisms so that they begin to produce even more compounds that help resist and hopefully stave off the spread of whatever microbes may be causing the injury. Many of the defects we see in wood products are the result of these changes.

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The third response the tree undergoes is to keep growing. New tissues grow around the infected compartment and, if the tree is healthy enough, will outpace further infection. You see, whether its bacteria, fungi, or a virus, microbes need living tissues to survive. By walling off the affected area and pumping it full of compounds that kill living tissues, the tree essentially cuts off the food supply to the disease-causing organism. Only if the tree is weakened will the infection outpace its ability to cope.

Of course, CODIT is not 100% effective. Many a tree falls victim to disease. If a tree is not killed outright, it can face years or even decades of repeated infection. This is why we see wounds on trees like perennial cankers. Even if the tree is able to successfully fight these repeat infections over a series of years, the buildup of scar tissues can effectively girdle the tree if they are severe enough.

CODIT is a well appreciated phenomenon. It has set the foundation for better tree management, especially as it relates to pruning. It is even helping us develop better controls against deadly invasive pathogens. Still, many of the underlying processes involved in this response are poorly understood. This is an area begging for deeper understanding.

Photo Credits: kaydubsthehikingscientist & Alex Shigo

Further Reading: [1]

The White Walnut

I must admit, I am not very savvy when it comes to trees. I love and appreciate them all the same, however, my attention is often paid to the species growing beneath their canopy. last summer changed a lot of that. I was very lucky to be surrounded by people that know trees quite well. Needless to say I picked up a lot of great skills from them. Despite all of this new information knocking around in my brain, there was one tree that seemed to stand out from the rest and that species is Juglans cinerea.

Afternoons and evenings at the research station were a time for sharing. We would all come out of the field each day tired but excited. The days finds were recounted to eager ears. Often these stories segued into our goals for the coming days. That is how I first heard of the elusive "white walnut." I had to admit, it sounded made up. Its as if I was being told a folktale of a tree that lived in the imagination of anyone who spent too much time in the forest. 

Only a handful of people knew what it was. I listened intently for a bit, hoping to pick up some sort of clue as to what exactly this tree was. Finally I couldn't take it any longer so I chimed in and asked. As it turns out, the white walnut is a tree I was already familiar with, though not personally. Another common name for this mysterious tree is the butternut. Ah, common names. 

I instantly recalled a memory from a few years back. A friend of mine was quite excited about finding a handful of these trees. He was very hesitant to reveal the location but as proof of his discovery he produced a handful of nuts that sort of resembled those of a black walnut. These nuts were more egg shaped and not nearly as large. Refocusing on the conversation at hand, I now had a new set of questions. Why was this tree so special? Moreover, why was it so hard to find?

The white walnut has quite a large distribution in relation to all the excitement. Preferring to grow along stream banks in well-drained soils, this tree is native from New Brunswick to northern Arkansas. Its leaflets are downy, its bark is light gray to almost silver, and it has a band of fuzzy hairs along the upper margins of the leaf scars. Its a stunning tree to say the least. 

Sadly, it is a species in decline. As it turns out, the excitement surrounding this tree is due to the fact that finding large, robust adults has become a somewhat rare occurrence. Yet another casualty of the global movement of species from continent to continent, the white walnut is falling victim to an invasive species of fungus known scientifically as Sirococcus clavigignenti-juglandacearum

The fungus enters the tree through wounds in the bark and, through a complex life cycle, causes cankers to form. These cankers open the tree up to subsequent infections and eventually girdle it. The fungus was first discovered in Wisconsin but has now spread throughout the entire range of the tree. The losses in Wisconsin alone are staggering with an estimated 90% infection rate. Farther south in the white walnuts range, it is even worse. Some believe it is only a matter of time before white walnut becomes functionally extinct in areas such as the Carolinas. No one knows for sure where this fungus came from but Asia is a likely candidate.

A sad and all too common story to say the least. It was starting to look like I was not going to get a chance to meet this tree in person... ever. My luck changed a few weeks later. My friend Mark took us on a walk near a creek and forced us to keep our eyes on the canopy. We walked under a tree and he made sure to point out some compound leaves. With sunlight pouring through the canopy we were able to make out a set of leaves with a subtle haze around the leaf margins. We followed the leaves to the branches and down to the trunk. It was silvery. There we were standing under a large, healthy white walnut. The next day we stumbled across a few young saplings in some of our vegetation plots. All is not lost. I can't speak for the future of this species but I feel very lucky to have seen some healthy individuals. With a little bit of luck there may be hope of resistance to this deadly fungus. Only time will tell. 

Photo Credit: Dan Mullen (http://bit.ly/2br2F0Z)

Further Reading:
http://bit.ly/2b8GiMV

http://bit.ly/2aLUdMD

Parasitic Protection

Strangler figs are remarkable organisms. Germinating in the canopy of another tree, their roots gradually wrap around the host, growing down towards to forest floor. Once in the soil, the interwoven structure of the fig begins to grow and swell. Over time, the strangler fig does what its name suggests, it strangles the host tree. Strangling is bad news for the host, however, new research suggests that strangler figs may actually provide some benefit to larger host trees, at least for part of its life. 

Cyclones are a force to be reckoned with. Their punishing winds can quickly topple even the sturdiest of trees. This is exactly what happened in 2013 when Cyclone Oswald struck Lamington National Park in Australia. Many trees fell victim to this storm but not all. Survival was not random and an interesting pattern started to emerge when researchers began surveying the damage. 

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

The hollow center of an ancient strangler fig where its host tree once grew and has long since rotted away.  

They found that large trees hosting strangler figs survived the storm whereas those without were more likely to be uprooted. It appears that hosting these parasitic figs just might have some benefits after all. There are a handful of mechanisms with which strangler figs could be helping their hosts. First is that figs spanning multiple trees may provide stability for the host and its neighbors. Another could come in the form of additional leaf area. The canopy of both the fig and its host tree may help reduce the impact of the cyclone winds. Additionally, once they make it to the soil, the roots of the strangler fig may act as guy-wires, keeping the host tree from uprooting. Finally, The interwoven roots of the strangler fig may act as scaffolding, providing additional structural integrity to the host tree. 

More work will be needed to see which of these are the most likely mechanisms. The mere fact that this parasitic relationship might not be so one-sided after all is quite interesting. What's more, by keeping large tree species alive through devastating cyclone events, the figs are essentially keeping legacy trees alive that can then reseed the surrounding forest. This could explain why host trees have not evolved any obvious mechanism to avoid strangler fig infestation. 

Further Reading: [1]

America's Trees are Moving West

Understanding how individual species are going to respond to climate change requires far more nuanced discussions than most popular media outlets are willing to cover. Regardless, countless scientists are working diligently on these issues each and every day so that we can attempt to make better conservation decisions. Sometimes they discover that things aren't panning out as expected. Take, for instance, the trees of eastern North America.

Climate change predictions have largely revolved around the idea that in response to warming temperatures, plant species will begin to track favorable climates by shifting their ranges northward. Of course, plants do not migrate as individuals but rather generationally as spores and seeds. As the conditions required for favorable germination and growth shift, the propagules that end up in those newly habitable areas are the ones that will perform the best.

Certainly data exists that demonstrates that this is the case for many plant species. However, a recent analysis of 86 tree species native to eastern North America suggests that predictions of northward migration aren't painting a full picture. Researchers at Purdue University found that a majority of the species they looked at have actually moved westward rather than northward.

Of the trees they looked at, 73% have increased their ranges to the west whereas only 62% have increased their ranges northward. These data span a relatively short period of time between 1980 and 2015, which is even more surprising considering the speed at which these species are moving. The team calculated that they have been expanding westward at a rate of 15.4 km per decade!

These westward shifts have largely occurred in broad-leaf deciduous trees, which got the team thinking about what could be causing this shift. They suspected that this westward movement likely has something to do with changes in precipitation. Midwestern North America has indeed experienced increased average rainfall but still not nearly as much as eastern tree species are used to getting in their historic ranges. Taken together, precipitation only explains a small fraction of the patterns they are observing.

Although a smoking gun still has not been found, the researchers are quick to point out that just because changes in climate can not explain 100% of the data, it nonetheless plays a significant role. It's just that in ecology, we must consider as many factors as possible. Decades of fire suppression ,changes in land use, pest outbreaks, and even conservation efforts must all be factored into the equation.

Our world is changing at an ever-increasing rate. We must do our best to try and understand how these myriad changes are going to influence the species around us. This is especially important for plants as they form the foundation of every major terrestrial ecosystem on this planet. As author John Eastman so eloquently put it "Since plants provide the ultimate power base for all the food and energy chains and webs that hold our natural world together, they also form the hubs of community structure and thus the centers of our focus."

Further Reading:  [1]

Invasion of the Earthworms

As an avid gardener, amateur fisherman, and a descendant of a long line of farmers, I have always held earthworms in high regard. These little ecosystem engineers are great for all of the above, right?

Not so fast! Things in life are never that simple! Let's start at the beginning. If you live in an area of North America where the glaciers once rested, there are no native terrestrial worms in your region. All of North America's native worm populations reside in the southeast and the Pacific northwest. All other worms species were wiped out by the glaciers. This means that, for millennia, northern NoNorth America's native ecosystem has evolved without the influence of any type of worms in the soil.

Shading = Glaciers  [1]

Shading = Glaciers [1]

When Europeans settled the continent, they brought with them earthworms, specifically those known as night crawlers and red wigglers, in the ballasts of their ships. Since then, these worms have been spread all over the continent by a wide range of human activities like farming, composting, and fishing. Since their introduction, many forests have been invaded by these annelids and are now suffering quite heavily from earthworm activities.

As I said above, any areas that experienced glaciation have evolved without the influence of worms. Because of this, forests in these regions have built up a large, nutrient-rich, layer of decomposing organic material commonly referred to as "duff" or "humus." Native trees, shrubs, and forbs rely on this slowly decomposing organic material to grow. It is high in nutrients and holds onto moisture quite well. When earthworms invade an area of a forest, they disrupt this rich, organic layer in quite a serious way.

Worms break through the duff and and distribute it deeper into the soil where tree and forb species can no longer access it. Worms also pull down and speed up the decomposition of leaves and other plant materials that normally build up and slowly create this rich organic soil. Finally, earthworm castings or poop actually speed up runoff and soil erosion.

All of this leads to seriously negative impacts on native ecosystems. As leaves and other organic materials disappear into the soil at an alarming rate via earthworms, important habitat and food is lost for a myriad of forest floor organisms. In areas with high earthworm infestations, there is a significant lack of small invertebrates like copepods. The loss of these organisms has rippling effects throughout the ecosystem as well. It has been shown that, through these activities, earthworms are causing declines in salamander populations.

It gets worse too. As earthworms speed up the breakdown of the duff or humus, our native plant species are suffering. They have evolved to germinate and grow in these rich, organic soils. They rely on these soils for survival. As the nutrient rich layers get redistributed by earthworms, native plant and tree populations are suffering. There is very little recruitment and, in time, many species are lost. Our spring ephemerals have been shown to be hit the hardest by earthworm invasions. Earthworms have also been shown to upset the mycorrhizal fungi networks which most plant species cannot live without.

Top Left: Forest soil horizons without earthworms; Top Right: Forest soil mixed due to earthworms; Bottom Left: Forest understory diversity without earthworms; Bottom Right: Forest understory diversity with earthworms. Credits: [1]

So, what can we do about this? Well, for starters, avoid introducing new populations of earthworms to your neighborhood. If you are using earthworms as bait, do not dump them out onto land when you're done. If you must get rid of them, dump them into the water. Also, if you are using worm castings in your garden, it has been recommended that you freeze them for about a week to assure that no eggs or small worms survive the ride. If you are bringing new plants onto your property, make sure to check their root masses for any worm travelers. Remember, no worms are native if you live in a once glaciated region.

Sadly, there is not much we have come up with at this point for dealing with the current earthworm invasion. What few control methods have been developed are not practical on a large scale and can also be as upsetting to the native ecology as the earthworms. The best bet we have is to minimize the cases of new introductions. Earthworms are slow critters. They do not colonize new areas swiftly. In fact, studies have shown that it takes upwards of 100 years for earthworm populations to migrate 1/2 mile! Armed with new knowledge and a little attention to detail, we can at least slow their rampage.

Photo Credit: Peter Hartl

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Why Trees?

Walking through the forest is my favorite activity in the world. It is where I feel truly myself. There is something about towering trees that calms me. The thought of why forests are even there often jumps to mind during my strolls. Plenty of plants seem to do just fine hanging out closer to the ground. Why have trees (and some forbs) taken to this vertical realm. Why do forests exist?

In essence, forests are a prime example of an evolutionary arms race. It is one that these organisms have been fighting since the Devonian, roughly 385 million years ago. As plants left the water and began covering the land, some inevitably grew taller than others. There are pros and cons to growing tall. Competition is likely the prime driver for most tree species. Getting above your neighbors means more sunlight. Not every plant is as content as an herb to live out its life in the understory.

Height also means better pollinator visibility and seed dispersal for many tree species. Out in the open, gametes and propagules can be carried great distances by the wind. Colorful blooms would prove to be more exposed and easier for pollinators to locate. Growing tall can also get you out of harms way, removing sensitive growing parts from many different kinds of hungry herbivores and all but the worst forest fires.

There are many downsides to growing tall as well. For one, trees are exposed to the elements and are often victims of strong winds or lightening strikes. What's more, all of that wood takes a lot of energy to produce and, at least for most species, gives nothing back in the way of photosynthesis. It is a rather hefty investment. However, the cost of getting shaded out by your neighbors is definitely not worth the risk of staying small for sun-loving species.

Pumping water is another serious issue. The laws of physics suggest that redwoods are pushing the limits for how tall a tree can grow and still be able to lift water to leaves way up in the canopy. Of course, humidity can assist with such issues but for a majority of the water needs of a tree, water must be able to travel against gravity via weak hydrogen bonds. Water forms an unbroken chain within the vascular tissues of plants. As it evaporates from the leaves, it pulls more water up to fill in the void. It is possible that in today's world, a tree would not physically be able to grow much over 400 feet.

Despite the seemingly lavish waste of limited resources that a forest of trees would suggest, they are nonetheless a common occurrence all over the globe and have been for millions of years. The pros must certainly outweigh the cons or else tallness in trees would never have evolved. The next time you find yourself hiking through a forest, think of how the struggle for survival has led these towering organisms from lowly green stains on rocks to hulking behemoths racing towards the sky.

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

On Orchids and Fungi

It is no secret that orchids absolutely need fungi. Fungi not only initiate germination of their nearly microscopic seeds, the mycorrhizal relationships they form supplies the fuel needed for seedling development. These mycorrhizal fungi also continue to keep adult orchids alive throughout their lifetime. In other words, without mycorrhizal fungi there are no orchids. Preserving orchids goes far beyond preserving the plant. Despite the importance of these below-ground partners, the requirements of many mycorrhizal fungi are poorly understood.

Researchers from the Smithsonian Environmental Research Center have recently shone some light on the needs of these fungi. Their findings highlight an important concept in ecology - conservation of the system, not just the organism. Their results clearly indicate that orchid conservation requires old, intact forests.

Their experiment was beautifully designed. They added seeds and host fungi to dozens of plots in both young (50 - 70 years old) and old (120-150 years old) forests. They continued to monitor the progress of the seeds over a period of 4 years. Orchid seeds only germinated in plots where their host fungi were added. This, of course, was not very surprising.

The most interesting data they collected was data on fungal performance. As it turns out, the host fungi displayed a marked preference for older forests. In fact, the fungi were 12 times more abundant in these plots. They were even growing in areas where the researchers had not added them. What's more, fungal species were more diverse in older forests.

The researchers also noted that host fungi grew better and were more diverse in plots where rotting wood was added. This is because many mycorrhizal fungi are primarily wood decomposers. Nutrients from the decomposition of this wood are then channeled to growing orchids (as well as countless other plant species) in return for carbohydrates from photosynthesis. It is a wonderful system that functions at its best in mature forests.

This research highlights the need to protect and preserve old growth forests more than ever. Replanting forests is wonderful but it may be centuries before these forests can ever support such a diversity of life. Also, this stands as a stark reminder of the importance of soil conservation. Less obvious to most is the importance of decomposition. Without dead plant material, such fungal communities would have nothing to eat. Clearing a forest of dead wood can be just as detrimental in the long run as clearing it of living trees.

Research like this is made possible by the support of organizations such as the Native North American Orchid Conservation Center. Head on over to www.indefenseofplants.com/shop and pick up an In Defense of Plants sticker. Part of the proceeds are donated to this wonderful organization, which helps support research such as this! As this research highlights: What is good for orchids is good for the ecosystem.

Further Reading:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2012.05468.x/abstract;jsessionid=3385C965FF5BA4CB83290005DFD47FD1.f01t02