So far this year we’ve had 134 inches (11 feet) and we’re two weeks away from August.

Some days, the standard 5-inch rain gauge doesn’t hack it.

Just saying.

Back in May, I noted the early blooming of Miconia rubiginosa after the heavy rains in April.

Now, in July, I’ve seen two plants in bloom that I normally see bloom in August: a tree with large bunches of yellow flowers, Senna hayesiana, and a miniature relative of the Elephant Ear herb, Xanthosoma mexicanum. I’m also seeing flower buds on an unidentified Miconia that usually blooms in September. I’m sure more’s going on along this line than I’m seeing.

Maybe these large swings in time of blooming are relatively normal for the tropics. But I’m starting to think that it’s more than coincidence that different plants from three unrelated families (Senna = Fabaceae or bean family, Xanthosoma = Araceae or arum family, Miconia = Melastomataceae or “black mouth” family)  are blooming immediately after uncommonly large monthly rainfalls.

To refresh your memory,

A Witch’s broom is a disease or deformity in a woody plant, typically a tree, where the natural structure of the plant is changed. A dense mass of shoots grows from a single point, with the resulting structure resembling a broom or a bird’s nest.

First recorded instance in Sapindaceae
The Allophylus tree is in the family Sapindaceae, the soapberry family, and I went looking for other instances of witch’s broom in that family. But Dr. Pedro Acevedo, of the Smithsonian Institution and a specialist in Sapindaceae, wrote to me that this is “…the first time that I know of the occurrence of witches’ brooms in Sapindaceae.”

The agent that causes this witch’s broom is not known, either, unsurprisingly. An expert in fungus, Dr. Meike Piepenbring, wrote to me that she has seen several witches’ brooms on avocado and on native plants here in Panama, but not on Allophylus. She found the presence of, not fungi, but aphids. After studying the literature, she concluded that the most probable agent is for the witch’s brooms that she saw is mites, but she has not yet seen these mites herself.

Ted MacRae, in a comment on my earlier notes on this witch’s broom, had suggested that I might look for mites, and I did. I found one on the first “broom” I examined. I have since, very unscientifically, looked through more than a dozen or so brooms, chopping them up with pruning shears, and have found a few more mites, a couple of tiny beetles, a weird-looking white flat thing that I couldn’t begin to identify, several very small and various spiders, and no fungal spores, at least not any detectable with my 16X hand lens. I don’t have much hope of discovering the causal agent all on my own.

Not so innocent brooms
One little broom all by itself doesn’t look so bad, especially since it has taken the basic shape of the inflorescence and become carried away with it, so that it looks like it might give rise to a robust bloom of small flowers.

But once you know that witch’s broom is a disease and that it could harm the tree (for instance, witch’s broom is a grave threat to cocoa production), they’re not so attractive. Here’s a portion of a tree that is infested with these things.

Maybe even these green brooms don’t look so bad to you, but they look pretty nasty after they’ve “died” or whatever they do after they’ve accomplished their purpose. The brown or black ones may be a little harder to see, even after you click the image on the left. So I’ve circled them in the image on the right, which is also clickable.

No self-respecting inflorescence would end up looking like that!

It is my hope that a graduate student somewhere with an interest in Sapindaceae stumbles across this post and decides to write a thesis on witch’s broom in Allophyllus psilospermus! Wouldn’t that be great?

On the following graph, the blue line is the 17-year average for each month of the year, and the red line represents the rain we’ve had so far this year. Months that have more than 10 inches of rain occur during our rainy season, thus our rainy season extends from May through November, a period of seven months.

March had rainfall pretty close to average, but February and April were way off the average line. Because April was so far above average (it qualified as a rainy season month this year) and because May was so on-the-nose average, I decided to look at just how often do we have average rainfall in any given month.

What is average?

Here’s a graph representing each of 17 years of rainfall, superimposed on the average (thick black line).

On seeing this graph, one person remarked that “It looks like there’s not a single average year on that graph!”

So I wondered – how many months actually have average rainfall? I created a table showing the deviation from average for each month. (You may have to click on the table to see it more clearly.)

I highlighted the months that differed from the average by 1 inch or less and then totaled those months in the last row. A total of 28 months during that 17-year period had within an inch of average rainfall. This is 14% of the months represented. We can therefore expect that we will have non-average monthly rainfall 86% of the time.

Over that 17-year period, August never had near-average rainfall. September had the greatest deviations from the average – more than two feet of rain (24.4 inches) above average in 1999 and 20.4 inches of rain below average in 2009.

Does El Niño have anything to do with this?

It turns out that the 2009/2010 El Niño dissipated in May of this year. You may have noticed in the table above that from June through September of 2009, rainfall was below average, usually several inches below average. This is the typical pattern of El Niño in Panama – below average rainfall in the rainy season – leading to droughts – and (slightly) above average rainfall in the dry season. With the dissipation of El Niño in May, our rainfall returned to exactly average.

If El Niños result in less rainfall in Panama during the rainy season, then La Niñas result in more rainfall during the rainy season. Note that the September 2-ft excess rainfall was in 1999 and that rainy season months August through November of that year all had higher than average rainfall. That year, 1999, was a La Niña year.

Back in graduate school, when I first learned about El Niño and atmospheric circulation as a basis for understanding the surface currents of the oceans, we learned that El Niño occurs more or less every 30 years. This gives you an idea about how long ago I was in graduate school! It seems these days that we’re either in an El Niño or a La Niña practically all the time. In fact, NOAA’s Climate Prediction Center states that “Conditions are favorable for a transition to La Niña conditions during June – August 2010.”

Grateful as we may be for average rainfall this May, it looks like average conditions won’t last long, and we may be in for some heavy rain this year.

Update: Carla Black has posted a comment giving the rainfall data from Volcan, which is to the west of us and uphill by a great deal, but still on the Pacific slope side of Volcan Baru. You’ll see that their May rainfall, unlike ours, was far below average.

A lesson from this observation is that local conditions can seem to overwhelm global conditions at any particular time. For instance, last month Carla sent me 13-year’s worth of rainfall data from Aprils in Volcan. This exchange was prompted because here in Potrerillos we had an extraordinarily high rainfall this April. When I plotted all 13 Aprils from Volcan vs. the same 13 Aprils in Potrerillos, I found that there was no correlation between rainfall in the two places whatsoever. Yes, there’s a slope to the line, but the r-squared value, which shows whether there is any significance to that slope, is about 0.2, which says that there is a 20% chance that the data are related. Or an 80% chance that they are not related.

So, if it’s raining in Potrerillos, we cannot predict at all whether it will be raining in Volcan. For example, she wrote that it had been raining for six hours in Volcan – at the moment I received her comment it had only begun to rain here and has now done so for about one hour.

Good lesson!

When it blooms, in June as I said, the whole grove lights up.

But this year it bloomed in early May, nearly six weeks earlier than usual. (Sorry, but my pictures from that day are horrible. The blooms, though, looked like these, above and below, taken in June last year.)

Why such an early bloom?
Plants may not bloom at exactly the same time every year, but it struck me that this year’s early blooms might possibly have something to do with the heavy rains in April.

It has been argued that either moisture availability or sunlight could limit photosynthesis in trees and thus limit the time of year when there is enough energy in the plant available to produce flowers, fruits, and seeds. A study by Zimmerman and colleagues found that, on a community level in tropical forests, sunlight was more important than moisture in triggering the blooms. But at a species level, things were different. Some species found in both seasonal and nonseasonal forests bloomed at roughly the same time of year whereas other species did not. Overall, most species in both places produced flowers, fruits, and seeds when irradiance was highest, but there were some that bloomed when less light and more moisture were available.

My take-away point from this study is that, in general, sunlight provides the energy necessary for a plant to start the reproductive process. However, different species may use different levels of sunlight, whether determined by day length or cloud cover, as a trigger to set flowering in motion. So, does M. rubiginosa look for June day length or June light level to determine when it will bloom?

We are close to the equator. Day length does change throughout the year, but by relatively little. So, for instance, the total day length for the first week in May is about 12 hours and 48 minutes (calculated at the sunrisesunset). The total day length for the first full week in June is about 13 hours. The average difference in day length, then, from early May to early June is 12 minutes. A relatively small difference. Perhaps the flower-triggering clock in M. rubiginosa was a little sloppy this year.

Maybe it’s not so early
However, it is also true that the heavy rains in April caused a reduction in light level for the month. Enough to bring it down nearly to the level that it was in May of 2009. If light level, rather than day length is the trigger, maybe the clock was not so sloppy. Could it be that April’s low light level triggered an early May bloom?

I’ve found no literature on when M. rubiginosa usually blooms, and probably many conditions must be met for the tree to bloom. Maybe it’s just a coincidence that we had much more rain than usual, and much less light than usual, in April of this year and that M. rubiginosa bloomed in early May.

Or perhaps, after all, the clock was simply off. Hey, it happens in this house all the time.

We have two seasons – rainy and dry. Where we live, the rainy season falls in months with more than 10 inches of rain and dry season in months with fewer than 10 inches. Therefore we consider May through November our rainy season (invierno or winter) and December through April our dry season (verano or summer).

This year our rainy season began in April. The blue line is the average, the red line is 2010.

The reason for the seasonal pattern is found in global atmospheric circulation. Because the Earth receives more heat from the sun at the equator than elsewhere, the warm air at the equator rises, leaving a low pressure zone behind. That air, having risen, moves away from the equator toward either pole, cools, and sinks back down to the Earth at the Horse Latitudes, creating a high pressure region. The surface air at the Horse Latitudes rushes back down toward the equator, creating the Trade Winds. [image from wikimedia commons]

The Earth is tilted, of course, and in its annual travel around the sun, regions north, then south of the equator receive the maximum heat from the sun. Therefore this low pressure zone, called the Intertropical Convergence Zone (because air masses from the northern and southern hemispheres converge there), moves up and down the latitudes of the earth. [image from wikimedia commons]

The nautical term for the Intertropical Convergence Zone (ITCZ) is The Doldrums. Sailing ships, having enjoyed the trade winds on their journey from, say, Europe, to the Caribbean, suddenly had no wind (that is, no horizontal movement of air – all the air in this region moves vertically upward) and plenty of rain.

The rain falls because the warm air, loaded with moisture, is unable to hold onto that moisture when it reaches the cooler upper atmosphere and therefore the moisture falls back to earth.

These days, the ITCZ is regularly tracked by NASA. The chart below is the Caribbean Sea graphic posted a few hours ago. The ITCZ appears as a red hatched line, crossing Costa Rica, just west and north of Panama. Earlier today, the red hatch crossed Panama itself. As I write, it is raining at the rate of 1.34 inches per hour.

So, we’re in the Doldrums, and forecasters say we’ll be there for at least the rest of the month. Of course, we should be there from sometime in May through sometime in November, so perhaps our rainfall will trend toward normal this month. Our rain right now, of course, is nowhere near the catastrophe now playing out due to the flooding in Tennessee and Kentucky, but it is predicted that we will have flooding in the weeks to come, if for no other reason than that the ground is prematurely saturated.

Next up, sometime this week: Can rainfall trigger the blooming of a tree?

Here it is, from Juan:

I feel so grateful for this piece of information. It [the tree] is highly valuable for the honey industry in Panamá. I am responsible of a Beekeeping Development Project in the Panama Canal Basin thru a USAID grant.

I am very happy reading about the palo blanco. This plant is important for honey production. Recently we harvested honey from palo blanco at an apiary site in Nuevo Ocú area. It has a great taste and character.

My family owns a beekeeping business at Chiriqui Province (West border). We manage 3,000 beehives.

In the past we gave logistical support to a STRI project regarding to plants visited by bees: Estudio Apibotánico de Panamá. David Roubik and Bob Schmalzel.

This plant is found in the Paraguay River at El Pantanal area, Caceres, Brazil in the border with Bolivia. The honey taste the same as in Panama.

When our own palo blanco was in bloom, I saw bees around the flowers, just as I’ve seen bees around many other plants in bloom. It never occurred to me that the honey from these aster family flowers might have “great taste and character,” in Juan’s words.

Let this message be a heads-up to potential beekeepers in Panama!

While the a broad swath of the US experiences storms and flash flooding, the dry season still has a firm grip on our part of Panama. We now have a weather report for April 2009 based on data from our relatively new weather station, put into some context by looking at the 16-year rainfall record of Ricardo Espinosa from Potrerillos Arriba.

I thought at first the small tree (in the Fabaceae family, Mimosa subfamily, but not yet identified) had suddenly developed thorns. A closer look, though, showed this collection of insects:

Some quick research at What’s that Bug suggested that this insect is a “thorn treehopper,” possibly Umbonia crassicornis or Umbonia spinosa. After piecing together the information from various sources, I gather that these insects pierce the plant stem to eat sap and also to lay their eggs in the plant tissue. Aggregations are usually of females guarding the eggs of their young. This activity does weaken the branches of the trees, but little other damage is done, according to what I have read so far.

Sorry, Umbonias, after the recent plague of beetles, we were quick on the draw with a pyrethrin-derivative spray. Next time we’ll watch a little longer and see what happens.

In January we set up a WeatherHawk station on our site, and after running it for some time, I feel it’s fair to go public with the data. The website is Potrerillos Arriba Weather, and current weather conditions are shown at Today’s Weather.

As of today we began broadcasting to Weather Underground, as well. The weather widget in the right-hand column points to our data. In addition, for this special announcement, I decided to include the gaudiest weather icon I could find, just for this particular post.

Enjoy!

PS – I forgot. This post is actually not an April Fools’ Day joke, though you might think so, since that’s about the only thing going around today.