Wednesday, April 22, 2015

After the fires in New Mexico

Valles Caldera Grande, Jemez Mountains, NM
I've been traveling a lot for work lately, and last week I was in Santa Fe NM. I was there to attend a conference on native seeds. The day before the presentations started I was able to attend a field trip touring recovering wildfire sites in the Jemez Mountains, near Bandelier National Monument. Most of the sites we visited had burned twice, once in 2008 (I think), and again in 2011.

wild candytuft (?) in the caldera
We visited the Valles Grande in the Valles Caldera, an active volcano complex 13.7 miles across altogether. This caldera last erupted approximately 1 million years ago. We were given half an hour to explore it, and most of us made a bee-line to the meandering creek dividing the center of the caldera. The problem is it appears deceptively close. I'd guess the Valles Grande is ~3 miles across where we parked. Not one of us made it to the creek by the halfway point, and we were called back short of our goal. Oh well. At least we got to tromp around this montane clearing.

What I didn't understand is this: why no trees? Ponderosa pine and aspen grew at elevations both above and below the caldera, so why not in the caldera itself? Is the ground too saturated with water? The caldera supported a luxurious grass thatch, even with the recent wildfires and historic grazing. Candytuft and marsh marigold (questionable IDs) were the only non-grass plants active at this point in the season.

We could see an abundance of human activity despite the remoteness of the location. The Valles Grande has a (now defunct) ranch within it, and shards of flaked obsidian near the overlooks marked the points where native peoples had sat and worked the stone long ago. The presence of the obsidian shards on the soil surface is a testament to the relative remoteness of the locations we toured. Surely more travelled trails would have had these remains pocketed years ago. It is also possible that the tremendous fires of the past ten years have exposed these remains at the surface.

Unmolested flint knappings at the soil surface
I know that in the tropical rain forests, the first fire marks the beginning of disturbance, but it is the second fire that destroys the ecosystem. This area suffered the same fate. Trees that survived the earlier fire were killed 5 years later when the second fire came through and burned the underbrush and deadwood. Apparently, the smokejumper team from Prescott Arizona that perished in 2013's Yarnell Hill Fire cut their teeth on the 2011 fires in the Jemez.

Compare the brown areas to the green
With this is mind, it was easy to lose myself re-enacting fire behavior in the mountains from the fire scars and standing trees. At its peak it advanced an acre a second. You could see where some (very few) pines had been spared, but you could also see white scars on the earth where the fire had burned so hot the soil had been mineralized, still visible 4 years later. Would my instincts have led me into a trap? I'll never know.

Mineralized soil and dead trees, 4 yrs later

Saturday, April 11, 2015

The monarchs have returned to Texas

Monarch butterfly, probably male
Actually, they returned over a week ago. I believe I saw my first monarch of the year April 1st. It was a female, hopping from milkweed to milkweed. She deposited one egg on each plant. One of her cousins was doing the same nearby. I was impressed with how she homed in on each plant, wasting no time in the search.

side-cluster milkweed w/egg
 Monarch butterflies are incredibly widely distributed, and are found in all lower 48 states.  They even introduced themselves to Hawaii. The Hawaii population is especially unusual because they have developed a unique white morph in contrast to the bright orange we see on the mainland. However, the two major populations are found in the lower 48 states. They can be further split into the western population (approximately 5% of total), and the eastern population (most of the remainder). The eastern population is the subject of the listing petition, and it is the group we see in Texas. This group has seen a 90% decline in overwintering numbers in the past 20 years. While monarchs as a species are secure, this eastern migration is an endangered biological phenomena.

Monarchs have a peculiar life history.  The first 3-4 generations of the year live approximately 4 weeks and grow and reproduce like a standard butterfly. They follow the fresh milkweed and flowers north as the season progresses. However, the last butterflies of the year to hatch live 6-9 months and migrate thousands of miles south from the Upper Midwest to Mexico. These butterflies are in reproductive diapause- that is, they don’t breed- and they focus their energy on gliding south in September, October, and November.  Once they hit Texas (generally in October), their migration slows. Instead they feed, intent on gathering enough fuel to support themselves during the 6 months they spend overwintering in the oyamel fir forests in the mountain highlands west of Mexico City.

Monarch ovipositing on milkweed
The monarchs arrive at their overwintering grounds in Mexico around the first of November most years. Their arrival coincides with the Day of the Dead celebrations, and monarchs are taken to represent the visiting souls of departed loved ones. Once the monarchs arrive, they become dormant and roost in high density “shingles” entirely coating the trees in their chosen forests. They don’t feed or breed, and spend most of their time resting on the branches and trunks of these oyamel firs. It is at this time that the monarchs are counted. Because the monarchs roost socially in high numbers, you can get a population estimate based on the area occupied. The lowest ever numbers were recorded in the winter of 2013, when the entire eastern population, ~95% of the world’s population, only occupied 1.7 acres.

Fresh monarch egg
By mid-March, spring returns to the Mexican highlands and monarchs break dormancy. They mate and begin their migration north. Monarchs return to south Texas in late March, making the thousand mile trek from Mexico in about a week. Once they reach Texas, they search out fresh milkweed sprouts on which to lay their eggs.  It was these tired, 9 mo old females I observed ovipositing earlier this month. After breeding, this generation dies. It is their offspring which continue the journey north to recolonize their North American range. Each subsequent generation moves a little farther north, until September when the “methuselah” generation hatches and the cycle begins again.

2nd instar monarch caterpillar
Texas is crucial to the monarch habitat for two periods of the year- those first monarchs returning to the states, and the last generation to leave. In March and April, the returning females nectar on wildflowers and lay their eggs on milkweed, the only food plant which can support their caterpillars. Texas becomes important again in September and October, when migrating monarchs stop to re-fuel on wildflower nectar before their long slumber in Mexico. Without nectar in the fall, these monarchs will not survive the winter. Without milkweeds in the spring, their offspring will starve. We can support monarchs as they funnel through our state by planting milkweed and fall blooming nectar plants. We cannot control what happens to these butterflies across the entirety of their range, but by working in our own backyards we can support the start and end of their migration.

Photo credits: Figures 2 & 4: Philip Barbour, CNTSC; Figure 1 & 3: Anne Stine; Figure 5: Rosanna Brown, CNTSC.

Tuesday, April 7, 2015

Fighting slime with slime

Or: the tale of two gastropods, slime and punishment, etc etc...
A curious brown garden snail
I've often noticed large round snails clinging to plant stems in the shade or on wet mornings. They seem to be everywhere. Known as the the brown garden snail, these beefy vegetarians are native to the mediterranean. They were originally imported to North America to serve as escargot. Edible, though perhaps not palatable to American tastes, these snails now range across most of the southeast and California.

These introduced snails are a minor garden nuisance, but high populations in California have vexed the citrus industry. The best snail management plan has a multi-pronged approach. Removal of daytime hide-outs, snail baits and traps, using copper barriers, and releasing another non-native mollusk: the decollate snail [1, 2] are used in tandem to knock back populations. Unlike the brown garden snail, the decollate snail is a predator. It hunts other snails.

Releasing one non-native to control another is called "classic" biological control, and has a storied history. In Australia the cane toad was introduced to control a pest beetle, but has since become a much larger threat to ecological stability than the beetle ever was. Closer to home, in North America a parasitic fly introduced to control gypsy moths has directly contributed to the scarcity of our own beautiful silk moths. The luna, the cecropia, the polyphemus, and the promethea are all much rarer than they once were. A little bit of magic left our eastern forests. On the other hand, biological control is our last best hope in the case of the hemlock woolly adelgid and purple loosestrife , so it cannot be discounted completely.

While the UCANR Integrated Pest Management (IPM) guide noted that releases of the carnivorous decollate snail are prohibited outside certain areas (because the decollate snail is a generalist, and will eat native snail eggs as readily as those of a pest), I have not heard of the decollate snail causing problems. Of course, how would we know. I can count the number of individuals I know who can even identify snails on one hand, let alone track and monitor native population dynamics.

But, what's done is done. When I turn the soil in my garden bed, the shells of both non-native snails surface in abundance. Eradicating either species is likely an exercise in futility at this point. However, their history piques my interest in our native snails! I'll have to keep a look out for these tough survivors.

Foreground: decollate snail shell. Background: brown garden snail shells