Forest transition to grasslands just a tipping point away

Accumulating evidence suggests that forests, communities dominated by trees, can quickly become grasslands with only some small changes in the environment particularly temperature (higher) and rainfall (lower), which often vary together. This comes as no surprise because one of the best long-term studies with which the Phactor is familiar, the still ongoing research that has been mentioned in this blog before, the monitoring of tropical forests by David and Deborah Clark, suggests the exact same thing. Tipping points are the big problem that looms by ignoring climate change and pretending that nothing needs to be done. What this means is that nothing much will happen as the trend of temperatures rising and rainfall dropping continues, and then in very short order, a forest becomes a grassland maintained by fire ecology. For a grassland to change back into forest takes falling temperatures and a lot more rain. But for people who live in the area, everything changes, plants, animals, agriculture. And even worse all that carbon locked up in wood gets released in short order, carbon dioxide that will help exacerbate the trend that caused the change. So tipping points will catch humans with their pants down around their ankles even though they are not unexpected. Unfortunately by the time you get to say "I told you so!" to do-nothing politicians it's too late, a cheerful thought.

Rainforest in the rain

Rainforest always looks its best just after a rain or during a light rain; in a real heavy rain you just can't see anything. Took our traveling companions of a field trip to see some rain forest in a light rain. This particular forest was in a national park at about 900 m above sea level. Here's a nice picture of the forest profile, a particularly difficult type of picture to get because you are seldom in the right place to see the forest like this. The primary vine in this forest is rattan palm, not one of the Phactor's favorite plants as it is forever trying to rip your head off. In just showing people the darned thing it ended up planting some of its grappling hooks in my hand. It's why the locals call it "lawyer cane" because once it gets its hooks into you it never lets go. Our temperate forests have fewer layers and are deciduous. Next blog another nasty denizen will be introduced.

Of fish and figs

One of the more interesting aspects for tropical forests are fish that function as seed dispersers. In Costa Rica the machacas (pictured, ~35-50 cm long) have excellent eyesight above the water and a quite a number will race out from under the over hanging tree crowns to snag a chunk of banana or a fig much to the delight of each year's class of students. In the Amazon other members of the same family, the characins (tetras, piranha), have proven to be excellent dispersers, especially in flooded forests, because fruiting trees are an island of resource, a patch of food, so foragers must move from place to place to find the patches. Fruit-eating fish in that ecosystem can move seed up to 5.5 km, dispersal on a par with large birds and mammals. However, over fishing could have an impact on tree reproduction, an excellent example of interconnections not at first evident.

Friday Fabulous Flower - Thanksgiving Cactus

The extreme seasonality of north central Lincolnland produces three months of tropical weather, three months of arctic weather, and two 3 month periods of very changeable transition. Long ago the Phactor discovered that his tropical plants performed very well if they were quartered outside, hanging from arbors and tree limbs, mostly in light shade, with short sunny periods for the warmer months, usually from late May until September, or like this year, October. Once the nights start getting cold they get unhappy. The shorter days and cooler weather of early fall are quite good at promoting flowering, and people who complain about their house plants not flowering invariably leave them inside year around, and keeping them in well-lit rooms (long nights stimulate flowering). So a month after moving back inside, right on cue, the Thanksgiving cactus (probably Schlumberger truncata, or a similar species, or even a hybrid of this species) began flowering. This particular group of cacti is native to tropical forests of Brazil where they grow as epiphytes. As adaptions to this habitat of frequent rain and rapid drying, tropical or so-called orchid cacti lack the thick spiny stems that most people think are characteristic of cacti and have flattened, leaf-like stems. Certainly the flower is quite spectacular and clearly adapted for hummingbird pollination. You can see how a hummingbird flying in to prob this flower for a nectar reward will upon arrival have its head and neck contact the exerted stigma (red nob)and stamens, both delivering and picking up pollen in that order. Unfortunately this cactus never flowers early enough to interact with our native ruby-throated hummingbirds before one migrates south and the other moves indoors.

From carbon dioxide to carbon dioxide - lesson from the tropics

Here in the rain forest life is a pretty dramatic process. While the great towering giants of wood have a aura of permanence about them, the tree turn over in a wet tropical forest is 2 to 3 times as fast as in temperate forests. Trees are great store houses of carbon dioxide, relatively short term reservoirs, and it is hard for people to rap their brains around the fact that all that stuff is primarily built out of a colorless, tasteless gas that only makes up a fraction of one percent of the atmosphere.

In the temperate zone we are used to seeing mushrooms pop up out of the ground, reproductive structures that are dwarfed by the huge filamentous organisms hidden from sight. And of course such fungi are the primary recyclers of cellulose and the other stuff trees and plants are built from. So you might expect to see lots of fungi on the ground in rainforests, but such is not the case. Decomposition is so fast here, no organic material builds up in or on the soil. Most of the fungi you see are growing right out of decomposing plant material. The fungi shown here are called "dead man's fingers", cute, eh? And they are growing out of a log that is pretty far along in terms of decomposition. The Phactor is not an expert on fungi, but he seems to remember that this fungus is called appropriately enough Xylaria, after xylem, wood. And so after being stored in this log for decades or in some cases even centuries, all that carbon dioxide is going back into the air. And if, as some of the best data indicates (see for link), even a slight increase in temperature causes a higher rate of tree mortality, then you have a very scary scenario where an increasing concentration of carbon dioxide is driving an increase in tree mortality and more carbon dioxide is being released.