Sunday, October 12, 2014

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.  

(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.

Wednesday, October 8, 2014

Purple Mountain Pitcher Plants - New & Improved!

Purple Mountain Pitchers grow well in naturally occurring beds of Sphagnum moss
like these growing wild in Transylvania County, NC

Ron Deterrmann, has been tireless in his efforts
to secure conservation for Purple Mountain Pitchers  

                                                               Purple Mountain Pitcher Plants occur naturally only in a small region of the southern Appalachians (western NC, adjacent SC and GA).  There has been relatively little conservation attention focused on this narrow endemic, in part due to the relatively recent recognition of its distinctiveness. Schnell & Determann (Castanea 1997) published the new varietal status, thereby bringing needed attention to these unique plants.  

The NC Plant Conservation Program "protects" portions of two of the 8 known populations in the state (although perhaps more populations will become known as the NC Natural Heritage Program is just beginning to keep documentation on this plant for the first time (2014).

One of two protected populations mentioned above has approximately 150 clumps of pitchers and comprises what is thought to be the largest known population in the state. It is unclear why this population is so large compared to others in the region.  We do know that Sarracenia purpurea spreads slowly; Ellison & Parker (American Journal of Botany 2002) documented only a 5 cm median dispersal distance for pitchers in the northeastern US.  Further, Gotelli and Ellison (Ecology 2002) found that Purple Pitchers don't reproduce until individual rosettes reach 10 cm in diameter.  Our Southern Apps variety grows vigorously and flowers profusely in sunny & open habitats, as shown in the following image. In contrast, pitchers subjected to heavy

Mass flowering in an open, sunny, yet constantly moist habitat
shade lose vigor, diminish in size, and cease flowering.  The example shown below displays etiolated leaves typical of shading. This clump is actually smaller than the surrounding Galax foliage and has little chance of flowering or trapping insects. The site where it occurs has been heavily shaded for 20 + years.  It is unclear how long an individual pitcher clump or rosette can survive in dense shade.  Gotelli & Ellison (Ecology 2002) suggest rosettes may persist for 30-50 years, but this longevity is likely to be strongly affected by shading.  In any case, the diminished vigor translates to loss of reproduction, perhaps a significant reason other known populations are much smaller.  

Our large population was almost certainly larger at one time. We have documentation that the pitchers were "once so plentiful they sold for 50 cents a piece".  Even today, pitchers continue to be taken or poached hindering population expansion.  The first image below shows where an entire rosette was taken (depressed area directly in front of the remaining clump). The second image shows a clump partially removed (note the bud forming).  I guess in both cases the losses could have been far worse, eco-conscious poachers?

In spite of the poachers, we have extensively re-opened the site by removing dense shrubs.  Precise demographic data are lacking but we counted 32 flowers in 2012, 94 flowers in 2013, and 114 flowers in 2014. The majority of these flowers seem to be producing seed heads. It has been estimated that Northern Pitchers produce approximately 1000 seeds per head (Gotelli and Ellison, Ecology 2002). Although germination rates may be low, if seed production continues the population could begin to rebound. In fact, on a recent visit Ron Determann pointed out a few true seedlings..... with luck, continued management, patience, and support of our local poaching community the population may continue to rebound!
Purple Mountain Pitcher seed capsule 

Seedling Purple Pitchers