Fuel loads, fire severity, and tree mortality in Florida Keys pine forests

Transcription

1 Fuel loads, fire severity, and tree mortality in Florida Keys pine forests Jay Sah, Mike Ross, Danielle Ogurcak SERC, Florida International University, Miami, FL & Jim Snyder USGS, Florida Integrated Science Center, Ochopee, FL

2 The Pine Rocklands of South Florida Subtropical forests dominated by slash pine (Pinus elliottii var. densa) An endangered ecosystems Rich in flora including many endemic plant taxa. Key Deer (Odocoileus virginianus clavium) The Pine rocklands in the Lower Florida Keys: Habitat of the endangered

3 The Pine rocklands and fire: Fire is important in shaping the structure and function of ecosystems. The endemic herb species require fire for their existence, survival, and reproduction. Without fire: Fire behavior depends on: Stand age & fuel availability Understory fuel types Season of prescribed burning succession towards a closed hardwood canopy loss of the characteristic pineland herb flora

4 Time since last fire + Pre-burn fuels + + / - intensity Season of burn (S/W) Hurricane/ Storm surge + Tree mortality Stand structure A conceptual model showing hypothetical relationships among fuel loads, fire behavior and tree mortality

5 BPK Experimental Plots 2.0 Ground elevation (m) BC BS BW DC DS DW IC IS IW LC LS LW OC OS OW PC PS PW

6 Orchid Site Plot code Burn Year Poisonwood Iris Dogwood Locustberry Buttonwood BPK Experimental burns & Tree monitoring OC (2004) OS OW 1998 (S) 1998 (W) PC PS PW 1998 (S) 1998 (W) IC IS 1999 (S) Post-burn Yr-1 IW 2000 (W) 2001 DC DS 1999 (S) DW LC LS LW 2001 (S) 2001 (S) BC BS BW 2001 (S) 2001 (S) Post-burn- Yr-2 Post burn- Yr PosthurricaneYr3 2008

7 Methodology Fuel estimates Fire severity Char height Scorch percent Shrub and Saplings (Ht >1m, dbh <5 cm) 0.25 m 2 Radius = 4 m 0.25 m 2 50 m 2 shrub plots Ground fuel plot Shrubs and Pine allometric equations height and crown area or dbh Palms Crown area and number of leaves Ground layer (Height <1m) Harvest method

8 Results Understory Total fuels Pine saplings Palms Shrubs Ground layer 25 Fuel (Mg/ha) Iris-8 Orchid-8 Dogwood-11 Poisonwood-12 Iris-14 Locustberry-14 Buttonwood-30 Sites

9 Palm Fuel HW Shrub Fuel Ground Fuel 0.94 U Char height Path diagram showing the relationships among fuel types, fire intensity and fuel consumption U Ground fuel Consumption (The thickness of lines indicates relative strength of significant correlations) 0.78 U Season Sah et al. (2006) Variable Direct Indirect Total Ground fuel Palm fuel HW shrub fuel Char height Season Not modeled

10 Season and fire severity HW shrub fuel vs Ground fuel consumption

11 Char height Scorch % Site - Poisonwood Summer burn Winter burn

12 Tree size, fire severity & pine tree mortality

13 Tree size, char height & pine tree mortality Tree size & Char height 1 P( m) = 1 + e ( * DBH * CharHt) Probability of tree mortality in relation to DBH and Char height DBH (cm) Char height (m) > >

14 Mean ground elevation vs fire and storm surge (2005) induced cumulative pine tree mortality

15 Logistic model tree mortality in relation to dbh

16 Stand structure in BPK Pine forest Change in stand density index (SDI) Change in average stand diameter (cm) Change in average stand diameter MSD (2008)= 9.1 to 17.2 cm BC BS BW DC DS DW IC IS IW LC LS LW OC OS OW PC PS PW Plots Change in SDI SDI ( 5 cm; 2008) = 5 to 255 BC BS BW DC DS DW IC IS IW LC LS LW OC OS OW PC PS PW Plots

17 Conclusions Fire intensity increased with surface fuel loads, but was negatively related to the quantity of hardwood shrub fuels. probably because these fuels are associated with a moist microenvironment within hardwood patches, and therefore tend to resist fire. Winter fires were milder than summer fires, however effects of season on tree mortality varied among sites. Fire-induced mortality was higher in small tree classes, whereas storm surge effects were concentrated on large trees. The stand structure pine forests in Big Pine Key has changed quantitatively over the decade, primarily due to effects of both fire and storm surge-caused tree mortality.

18 Acknowledgements Fire Project Interns/Field assistants: Sahara Moon Chapotin, Joanne Singfield, Jenny McCune, Jana Mott, Christie Whelan, Sarah Naylor, Elizabeth Bergh, Tina and Dennis Henize, Marianna Bradley, Mark Knowles, Wendy Miller Lab crews: Pablo Ruiz, Susana Stoffella Hillary Cooley (ENP), Dave Reed (FIU) USFWS National Key Deer Refuge The Nature Conservancy-Florida Keys Initiative Fire crew from the Panther Refuge