Longleaf Pine Sandhills - fire and wiregrass

The "sandhills region" of North Carolina supports some of the most extensive stands of longleaf pine remaining in the state. The preponderance of deep sandy soils not only gives the region its name, but helps explain why so much longleaf pine remains here given the even more substantial declines elsewhere in the state. The coarse, droughty sands are less conducive to most types of agriculture and, when forested, are not as easily overrun by other vegetation.  However, even when longleaf pine is present, regular burning is needed to maintain high quality stands.

Well-burned longleaf pine stand@Sandhills Gameland, NC
Note scorched boles, uneven spacing and diameters

Thankfully, certain land managers and owners are committed to the use of prescribed burning. They have maintained the best upland longleaf in the region through frequent and regular burning. These stands have open canopies, with minimal hardwoods, above dense swards of wiregrass (Aristida stricta).

Heavily fire-suppressed longleaf stand in Moore Co, NC
Note dense Turkey Oaks and absence of wiregrass

The vast majority of remaining stands are heavily altered due, in part to insufficient burning. On dry, sandy uplands these stands may become densely invaded by hardwoods like turkey oak (Quercus laevis), and wiregrass is sparse and barely evident. Such stands carry fire less readily and larger hardwoods become fire resistant and harder to control.

Moderately fire-suppressed longleaf stand in Moore Co., NC
Note patches of wiregrass, those in left foreground show greatly diminished vigor

Less severely fire suppressed stands retain patches of wiregrass and other herbaceous species. Hardwoods are less dominant, patchier, and often smaller. These smaller hardwood stems contribute less shade and litter, thus having less impact on fire dynamics and understory composition.

Wiregrass is a keystone species with a huge ecological impact. It flowers and seeds in the same season, primarily after being burned in the spring or summer, with upright flowering stalks emerging with the characteristic "three-awn" seeds. This happens only rarely in most stands where finds are either excluded or conducted only in the "dormant" season.

Wiregrass (Aristida stricta) flowering
@Pondberry Bay Plant Conservation Preserve, Sampson Co, NC

Wiregrass is a clump-forming bunchgrass whose narrow densely packed culms dry rapidly and carry fire even shortly after rain. In most relatively intact stands, wiregrass forms nearly continuous, dense ground cover. This density and continuity enhances the spread of low intensity fire which ultimately limits the establishment of woody stems.  Although we may imagine it take considerable time to convert an open, savanna-like stand to a dense, closed forest the changes occur surprisingly rapidly.

Dense swath of Wiregrass, note overlapping and draping culms
creating continuous fuel matrix for fire spread

Fire spreading across dense wiregrass layer

Longleaf pine - Turkey Oak Sandhill with suppressed and low density wiregrass,
stand has experienced infrequent, dormant season fire@Moore Co, NC

Longleaf pine - Turkey Oak Sandhill with dense wiregrass in good condition@Moore Co., NC
stand has experienced regular, somewhat frequent fire, but not recent growing season burning

Longleaf pine - with dense wiregrass after regular & frequent prescribed fire,
including growing season. Turkey Oak layer "burnt out" 

A few Southeastern Coastal Plain endemics

Shiny Woodoats (Chasmanthium nitidum)
Wet hardwood hammock,
limestone close to surface
St. Marks NWR, July 2014 

Probably the rarest Woodoats grass or Chasmanthium species in North America, the natural range of Shiny Woodoats (Chasmanthium nitidum) is almost entirely found in Florida. The grass barely finds its way into NC where it is considered threatened, being known only from Pender County. 

Chasmanthium latifolium;
the most widespread member of the genus

Scareweed (Baptisia simplicifolia)
Pine Flatwoods, regularly burned
St. Marks NWR, July 2014

One of the Wild Indigos,  or sometimes called "Scareweed", Baptisia simplicifolia is a narrow endemic confined to a couple counties in north Florida's panhandle.

Limited to open pinelands, this is one of the many fire-adapted species found in longleaf pine flatwoods. At the end of the growing season, stems break off above ground and the plant blows around like tumbleweed, helping to distribute seeds still found in the capsules. The vast majority of the world's population is found on the Apalachicola National Forest.

   

Eurybia eryngiifolia 
Apalachicola National Forest
July 2014

Bristly heads and leaves of Eurybia eryngiifolia

                                                                                                                     












Thistle-leaved Aster (Eurybia eryngiifolia) is nearly endemic to the Florida panhandle, just barely extending into adjacent Georgia & Alabama. It is another pine flatwoods & fire-adapted species, closely associated with longleaf pine.  The scientific epithet (eryngiifolia) is a clear reference to the vegetative similarity to Rattlesnake Master (Eryngium yuccifolium)

Green Silky Scale

Green Silky Scale (Anthaenantia villosa) is a southeastern coastal plain endemic grass species, ranging from eastern Texas to Florida and northward into NC.

A. villosa upright habit and dense, flowering panicle
Note charred longleaf bole and open wiregrass dominated habitat
Image date: Nov 06, 2012

In our area I have observed it only in recently burned longleaf-wiregrass habitats in the inner coastal plain and sandhills regions. Within these generally dry, deep sandy soil sites, the grass occurs in gentle depressions (sometimes called "bean dips") or gentle, almost imperceptibly subtle slopes which are slightly moister than the surrounding uplands.

It occurs in dense swards of grasses where it can be easily overlooked unless flowering. Like a number of other species in these habitats, it may only flower (or at least most profusely) the growing season immediately after burning and may increase as a result. Kush et al. 2000 (in Alabama longleaf pine) documented much greater frequency for this species in biennially burned stands as compared to unburned stands with the greatest frequencies in summer and winter burn units.

Green Silky Scale (foreground), amidst dense wiregrass (Aristida stricta)
Sampson Co., NC (October 20,2011)

Silky Scale clumps turning color in Fall
Nov 06, 2014

                                                                       

Silky scale develops small rhizomatously spreading clumps which appear to expand slowly. Basal leaves are narrow, smooth, and tapering to a narrow tip. According to Grelen & Duvall (1966) leaves are nutritious and palatable forage.

Inflorescences form tight, narrow panicles on upright stems (maybe 3.5' tall) late in the growing season. Individual spikelets are densely pubescent and tightly packed along the upper 8 or so inches of the stem (See image right).

References:

Grelen and Duvall 1966, Common Plants of Longleaf Pine - Bluestem Range, Southern Forest Experiment Station Publication

Kush, J.S., R.S. Meldahl, and W.D. Boyer. 2000. Understory Plant Community Responseto Season of Burn in Natural Longleaf Pine Forests. Tall Timbers Fire Ecology Conference 21:33-39

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.