Here's Pyxie!

Pyxie (Pyxidanthera barbulata), near Zuni, Va (3/16/19)

I was able to shout that on a recent weekend in southeast Virginia, but was certainly not the first to do so. That "honor" goes to Bayard Long in 1936.  Long was a botanist most associated with the Philadelphia Botanical Club, collector of approximately 80,000 plant specimens, and long-time friend and associate of Dr. M.L. Fernald (an account of Long's career, and publications, as well as the following image of Long, can be found in Rhodora 72:130-136)

Bayard Long was part of an infamous botanical collecting excursion near Franklin, Virginia that resulted in nine "new to Virginia" or state record plants being found.  Long was later quoted as saying, "this is real botanizing!" in the fascinating recount of the trip (Fernald, M.L. 1937, Rhodora 39: nos 465-468) (Also reprinted by Fernald in; Contributions from the Gray Herbarium of Harvard University, 1937, and selected excerpts included in Frost & Musselman 1987: Castanea 52:16-46.)



One wonders if Pyxidanthera would have gone unnoticed had it not been for Long.  In an earlier paper on the "Plants from the Outer Coastal Plain of Virginia" (Rhodora 38: nos. 455-466), Fernald credited Long as follows, "...with his detailed knowledge of Coastal Plain plants and their proper habitats and his unequalled (sic) persistence and skill in finding them, no critical botanizing in eastern Virginia can be wholly successful without him". 

In terms of the overall significance of their botanical finds, Fernald said, "We had stumbled into what we had sought for four years, real unspoiled pine barren in Virginia".

View of "mature" longleaf pines at Blackwater Ecological Preserve, VA
perhaps not unlike what Fernald and Long would have seen if they looked up!

Today, Fernald & Long's collecting site is protected and being actively managed as Blackwater Ecologic Preserve.  Longleaf pine (Pinus palustris) is a prominent tree in parts of the Preserve, which for Virginia, is really significant. At the extreme northern edge of it's natural range, the Commonwealth is believed to support fewer than 200 INDIVIDUAL mature, native longleaf pines (Virginia Department of Forestry 2014, Status Report).

Pyxidanthera range map; 
Kartesz, J.T., The Biota of North America Program (BONAP). 2015
Taxonomic Data Center. (http://www.bonap.net/tdc). 

But back to Pyxie (Pyxidanthera barbulata). Sometimes known as Pyxie-Moss or other related and confusing common names, Pyxie is restricted to the Atlantic Coastal Plain of eastern North America.
Sorrie and Weakley 2001 (Castanea 66:5-82) recognized Pyxie as a coastal plain endemic with a bimodal phytogeographic pattern, as shown to the left.




Pyxie's distribution has a large spatial disjunction that was significantly larger until Fernald's team found it in Virginia, or as they stated, "the first station discovered between southern New Jersey and North Carolina".  According to Fernald, "Pyxidanthera barbulata literally carpeted the ground in many areas".  The best approximation of that pattern I could see today, is shown on the image below, although at this distance (and due to my lack of photographic skill) the Pyxie clumps appear almost as bare "sugar sand".

Pyxie as an abundant ground cover at Blackwater Ecologic Preserve, VA

Pyxie covered by pine needles

Frost & Musselman used Pyxidanthera as a nominal in one of the community types they recognized at Blackwater in 1987 (See citation above), while noting it only"at this one spot".  They referred to this community as "Pond Pine Flat" with both Pond Pine (Pinus serotina) and Turkey Oak (Quercus laevis) as dominants and nominals.  Interestingly, in my experience, these species usually occur in fairly different habitats and soil moisture regimes.  Fernald referred to the habitat as "thin woods of Pinus taeda and Quercus laevis".  He indicated (with a footnote) that they found this oak "to be the regular species of the area" at its northern range limit.  Much like longleaf pine, this range limit has not been significantly extended northward since then.  Turkey Oak is still found at the site but is, perhaps, not as abundant as suggested by Frost & Musselman. (I hope to address this in detail in the future).

Turkey Oak (Quercus laevis) buds (3/16/19)

Turkey Oak (Quercus laevis) stump sprouts (3/16/19), approximately 2 years after last fire; note main trunk
broken off and fallen to right of image

Pond Pine (Pinus serotina) stump sprout, same site as previous;
also approximately 2 years since last fire; note main stem still standing but dead

Since 1986, there have been approximately 16 prescribed fires here with undoubtedly significant effects. 

Structural and density differences at Blackwater Ecologic Preserve
Right: burned on ~ 2 year average return interval since 1986
Left: unburned during same interval

For now, Pyxie seems to be doing just fine! 

The Long Awaited Summer (Fire) - Will it save our savannas?

1st Summertime prescribed fire conducted in Brunswick Co, NC
Longleaf Pine relict (right), middle sized trees are mostly Pond Pine
no Longleaf Pine regeneration is present

Vegetation response several weeks later (same site as previous)
Longleaf Pine unfazed but significant needle loss on all Pond Pines 

It has been known for decades that regular or frequent fire facilitates the development of open, grassy longleaf pine (Pinus palustris) savannas. Restoring such conditions in existing longleaf pine stands has become virtual dogma across the southeastern United States. However, relatively few sites actually receive the frequency of fire needed to maintain or recreate open savannas, and even fewer receive fires during the growing season when lightning fires would have occurred historically. This has certainly been the case at the Boiling Spring Lakes Plant Conservation Preserve in Brunswick Co., North Carolina where we have been working, with the help of The Nature Conservancy and the NC Forest Service (NCFS), for approximately 10 years to restore fire prone landscapes.  This summer (2014), the NCFS and our small team conducted the first known summer fire in the region (special thanks to Bill Walker, Shane Hardee, Mike Malcolm & Miller Caison for making the burn a reality)

For decades, typical controlled burns across the southeastern NC and the US occurred during the dormant or winter season.  However, it has been recognized that significant parts of the landscape, especially areas dominated by longleaf pine, developed under eons subject to fires started by lightning. Lightning strikes, especially those most likely to start fires, are mostly associated with summer thunderstorms. In North Carolina July is the peak for these storms (1).                                    
                                                                                                                     

Outcalt (2) showed that the largest, tallest trees were preferentially hit by lightning in longleaf stands. These strikes often leave telltale marks (left), sometimes extending to the ground. In certain cases hot strikes ignite the tree itself and the flammable ground cover nearby (right).



Given dry conditions, available fuels, wind to push the fire, and an unbroken landscape, such lightning ignited fires could have extended for miles.  Large, old longleaf pines tend to have concentrated resins that allow them to burn hot, even when drenched with water. These can easily ignite fires even after the passage of rain fall events.

There is some evidence that lightning season fires produce different ecological effects than fires at other seasons; at least 3 syntheses of these differences have been attempted  (3,4,5).  One benefit is the creation of  "seedbeds" for longleaf pines, which drop their seeds in late Fall.  These seeds (which are produced relatively infrequently, and primarily from older, larger trees) need to access mineral soil and are easily "hung up" in understory grass or shrubs. Ironically, typical winter burns occur almost immediately after seeds have dropped thereby destroying many seed crops. Therefore, managing longleaf stands with regular winter fires could eliminate regeneration of the dominant trees. Further, non-lightning season fires (especially if infrequent as they are in most areas) tend to favor development of dense shrub stems which may further hinder longleaf regeneration.

A perfect seed bed for longleaf pine seeds to establish

Serotinous Pond Pine Cone
Immediately after fire

Serotinous Pond Pine Cone
Just opened after fire

In contrast, Pond Pine (Pinus serotina) produces much smaller seeds, produces them at much younger ages, and holds them on the tree for several years until hot fire opens them.

Fires during any season, including winter, could potentially heat the serotinous cones and cause seeds to drop into freshly prepared seed beds.  Pond Pine also has the capability to reprout after even intense fires that could kill similar sized longleaf pines.  Taken together, these factors provide an environment where tree dominance shifts from longleaf pine to pond pine.

Pinus serotina resprouting after summer fire;
in addition to "main" epicormic sprout there are 3 others emerging (front right, back left)
Several previous stems (now blackened and top killed) were present from previous fire

Savanna in Brunswick Co., NC with a rare regenerating Longleaf pine (foreground) amidst taller saplings of Pond Pine
larger trees (rearground) are also Pond Pine

BELOW: Longleaf Savanna replaced by Pond Pine Flatwoods
Lone Pinus palustris persists near middle; dense shrub layer has developed






Longleaf pine relict indicating previous stand composition and open structure
One fire reduced some immediately adjacent & "invading" Pond Pine stems but
high fuel loads remain and threaten remaining Longleaf

BELOW: Longleaf Pine stand decimated by wildfire after heavy midstory development as in previous image;
standing dead are longleaf pines,Pond Pine present were killed and have not reemerged into midstory or overstory
dense tall shrub layer is still present

Although growing season fires are often thought to be important for various ecological reason one of the most important, yet least understood, may be the reversal of longleaf pine savanna replacement from dense, flammable stands of Pond Pine.  

References:
(1) http://www.wunderground.com/blog/weatherhistorian/thunderstorms-the-stormiest-places-in-the-usa-and-the-world
(2) Outcalt, K. 2008. Lightning, fire and longleaf pine: Using natural disturbance to guide management. Forest Ecology and Management 255.
(3) Robbins, L.E. and R.L. Myers. 1992. Seasonal effects of prescribed burning in Florida: a review. Tall Timbers Research Station. Misc. Publ.
(4) Streng, etal. 1993. Evaluating effects of season of burn in longleaf pine forests: a critical literature review and some results from an ongoing long-term study. Proceedings Tall Timbers Fire Ecology Conference 18.
(5) Knapp etal. 2009. Ecological effects of Prescribed Fire Season: A Literature Review and Synthesis for Managers. USDA General Technical Report PSW-GTR-229.