The Knife Edge of Spring

"To what purpose, April, do you return again?

Beauty is not enough.

You can no longer quiet me with the redness

Of little leaves opening stickily."

-from Spring by Edna St. Vincent Millay

In AZ, the spring green up of grasses and trees makes use of a narrow window of time between declining winter moisture and increasing summer heat.  Our redbud trees blooms for three or four days (this year, from April 26-29), the lilac bushes hardly last much longer, and the spring green up of weedy lawns is over by the end of May.  June is the dry season in Arizona.  June is when spring dies.

The knife edge of spring in Arizona can be seen in the biomass production.  For example, the Rangeland Analysis Platform shows that peak spring growth in Dugas, AZ in 2020 lasted approximately 3 weeks, from 4/1 to Earth Day 4/22.  By May, the growth of the annual green up was already in freefall.  More examples can be seen in this previous blog post using RAP to investigate biomass production variability from year to year.  

Phenology Mapping

The National Phenology Network's Visualization Tool can be used to follow the spring green up via Accumulated Growing Degree Days (AGDD), which work by adding up all of the days and temperatures above some minimum threshold for growth, usually 32 F for cool season plants (winter annuals, cool season grasses, willows and cottonwoods and other early spring plants) or 50 F for warm season plants (mesquite, acacia, and other warm season trees like Chilopsis, walnut, and warm season grasses and forbs).

AGDD Details

A "growing degree day" (GDD) is calculated by subtracting the threshold temperature (T) from the average temperature for each day when the minimum temperature is above the threshold temperature of 32 or 50 degrees. 

Average T = (Maximum T - Minimum T)  / 2

GDD = Average T - Threshold T

 Accumulated growing degree days (AGDD) simply adds up all of the GDD since the beginning of the year.

AGDD = GDD (January 1) + GDD (January 2) + … + GDD (yesterday)

To use the NPN Visualization Tool for AGDD, choose Map>Base Layer>Category: Daily temperature accumulations>Layer:Current Day.

AGDD Example - 32 F

The figure below shows AGDD around Prescott, AZ from a threshold temperature of 32 as 5/2/24.  Most of the map shows AGDD of about 2,000; since there have been about 120 days since the beginning of the year, that works out to an average daily temperature of 48 degrees F (2,000/120 + 32 =  48).  Of course, some areas have been warmer than that and some have been cooler:  

Phenology AGDD from 32 F 

1,600 - cottonwoods leafed out (Prescott)

1,800 - still winter grasses not green (Kirkland junction)

2,200 -  annual grasses very green, early spring wildflowers blooming (Dugas)

2,245 - mesquite not leafed out yet, annual grasses still somewhat green (Yava)

2,500 - mesquite leafed out, annual grasses brown (Date)

2,800 mesquite flowering (Congress)

AGDD Example 50 F

Or maybe a 50 degree threshold better shows mesquite and grass green up? The average daily temperatures, of course, are the same, but the different threshold yields much lower AGDDs, mostly in the low 100's.  On this map, light green area are grasses already brown and mesquite leafed out, green areas actually are green fields of annual grasses, whereas white and blue are areas where willows, cottonwoods, and elms have leafed out, but herbaceous plants are just barely getting started.

Phenology AGDD from 50 F 

240 - oaks turning brown (Kirkland)

350 - mesquite not greened up yet, annual grasses and forbs green (Dugas)

400 - mesquite not leafed out yet, annual grasses still somewhat green (Yava)

550 - mesquite leafed out, annual grasses brown (Date)

800 - mesquite flowering (Congress)

AGDD Anomalies

The examples above of specific phenology AGDD values can be used in conjunction with NPN's Visualization Tool to predict plant growth stage.  Also, it is possible to use NPN's Visualization Tool to highlight geographic areas that may be ahead or behind the usual spring green up using the "Anomaly" visualization.  In the figure below, anomaly from 32 F AGDD, it can be seen that the Kirkland valley, Black Canyon City, and the Verde valley are behind (blue) normal phenology, whereas Prescott valley and especially the area north of Bagdad are ahead (red) normal phenology.  

"Life in itself 

Is nothing,

An empty cup, a flight of uncarpeted stairs.

It is not enough that yearly, down this hill,

April

Comes like an idiot, babbling and strewing flowers."

-from Spring by Edna St. Vincent Millay

El Nino in the Spring

March, April, May and the first week of June have been quite wet for the East slopes of the Rockies and the Western Great Plains, with large regions receiving more than three or four times normal precipitation.  Meanwhile, the West has continued its drought, with CA looking especially dry.

NM has significant regions above 400% of normal precipitation.  While there is lush growth in some areas, other areas are not appreciably greener than they might otherwise be.  Sometimes this can be attributed phenology (e.g. to summer grasses not responding to early spring rains, or perhaps the exact timing is important for annual germination), but some must also be due to the severe productivity reduction of overgrazed and eroded soils.

El Nino has strengthened in recent months.  An active fall hurricane season supplyied NM with abundant moisture in the fall, In the winter a steady progression of Pacific storms brought an average amount of precipitation.  And since late May we have already experienced large moisture plumes from yet more unusually-strong Eastern Pacific hurricanes,  Andres and now, currently, Blanca.

Expanding Ethics to Include Animals?

Source.

Tonight is another night in a hotel room somewhere in a small town in New Mexico, bordered by train tracks and highway. I hear calves lulling in the trailer parked back of my bathroom window, and I can hear the train long after it is gone, singing on tracks miles up the mountain.




The sun sinks low over green hills and high cumulus clouds tilt and light on fire and everything tumbles into purple ashes until the stars come out. The cows say moo over and over again. There are ten each in the upper and lower half trailer lined with hay; they look innocent in a manger scene.




In the ecologist literature (article by David Barash) I read that we are all one, that every atom in me was once in other creatures, and every action I take affects everything else. Of course, we all know this from interacting with other humans, but the key to understanding our current culture is that we don't (yet) interact with rain like we do with a human.




We listen to weather forecasts of the rain's behavior, what experts think it might do. No one does that for other people. We know other people are too complex for 3-dimensional weekend forecasts. Or, take earthquakes. Great beyond comparison to a human body, but in scale of effect like a governor or a president or a war, maybe. Sure its possible to speculate about their arrival, but when they do arrive only their presence matters. Or cherry blossom season, when everyone goes outside to say hello to mother nature, a homecoming parade for a season and a life-force, back after a long sojourn to more southern climes. The Navajo consider it extremely rude to not greet the rising sun. Would you ignore your own grandmother?




"If we see individuals, we don't see that they are only intersections of an infinite tapestry of connections. So ecologists do not speak of the bear or the forest, but the bear-forest ecosystem."

A Mississippi River Wetland National Park?

http://www.osu.edu/news/newsitem3123