Chlorophyll galore

July 13 1:30PM 84F

A sea of green remains, feels like the height of summer though the season technically only began a few weeks ago. It's hot, muggy, buggy, and the forest is quickly approaching peak biomass. Spring ended hot, broke lots of global records for high temps in June, but the last few weeks have also been dry. The understory here has lost a little bit of its lushness, presumably due to the lack of rain. It's been very green and thick with skunk cabbage and non-native Japanese stiltgrass (Microstegium vimineum), a frequent invader of forested floodplains just like the mandala. This riparian area seems to support an abundantly green understory. Right now, there's a distinct lack of color, nothing obvious is flowering (so where have the pollinators gone?). All of this green, this chlorophyll depends on a complex cycle of microbial activity in the soil. Nitrogen is one of the key chemical building blocks of not only chlorophyll but also of the photosynthetic machinery. Thinking of N awakens memories of my grad school days in which I extensively studied patterns of soil N cycling. I suspect that some of the differences between this lush, green understory here compared to the predominantly brown understory farther uphill include a more favorable soil microclimate (wetter but not saturated) and greater detrital inputs due to greater plant productivity and litterfall, both of which likely contribute to enhanced microbial biomass and activity. This in turn yields greater rates of N turnover and availability for plant uptake and growth. This positive feedback between plant production and soil N is further driven by plants like the annual stiltgrass that I'm guessing are N-rich. Plants with high leaf N then have relatively low N resorption leaving more N in litterfall which contributes to higher rates of soil N mineralization as soil bacteria are relatively short on C supply. Then soil N tends to be readily available for plant uptake and to maintain high leaf N. The cycle continues. This pattern in the mandala is all speculative but offers an interesting comparison between the green understory here versus the brown forest floor in the upland oak forest just uphill. I suppose that it could be as simple as greater soil water availability but plant resource demand extends well beyond water or even N.

My focus today has been drawn to the unseen interaction behind the plants and the soil but lots of other critters are out and about. I hear birds chipping and a woodpecker but they are all mostly hidden in the foliage. There are bugs flittering about including both white and dark-colored spastic butterflies, big black ants, tiny brown ants on the skunk cabbage, and more. Despite the lush greenness of the understory, there's little green between 2-7 feet aboveground, except in bunches dominated by [likely] unpalatable shrubs, due to deer browse. I recently finished reading Where the Wild Things Were by William Stolzenburg and while much of it wasn't new to me, it reinforced the ecological significance of deer in the absence of large predators. Certainly, deer represent one of the greatest threats to forest health and reproduction. The trees that have been able to escape deer browse and made it beyond their reach are very straight and tall with few branches beneath the canopy as they compete for light. My attention is caught by a cicada buzzing above me. It fell or maybe flew out of the canopy and landed 10' above me in a tulip tree. It crawled on the leaves, bouncing in the breeze, then worked its way back to the bole and crawled up and out of sight. I expected to hear more cicada buzz but only heard this one. In looking up annual cicadas, I find that there are 14 species of annuals in Maryland, an impressive number to me.

Before I leave the mandala, I visit the stream. The water is low and very clear as a result of the lack of rain. From my vantage point on the bank, I count at least 7 crayfish. The largest one scurries back and forth on the silty stream bottom, comes of a small rock, pulls out another crayfish from underneath and takes its place without a fight. A few of our students have been researching crayfish including in this stream, finding both native and non-native species including perhaps hybrids.