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Does Time Since Fire Explain Plant Biomass Allocation in the Florida, Usa, Scrub Ecosystem?

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Does Time Since Fire Explain Plant Biomass Allocation in the Florida, Usa, Scrub Ecosystem? Fire Ecology Volume 6, Issue 2, 2010 Saha et al.: Fire Effects on Biomass of Florida Scrub doi: 10.4996/fireecology.0602013 Page 13 RESEARCH ARTICLE DOES TIME SINCE FIRE EXPLAIN PLANT BIOMASS ALLOCATION IN THE FLORIDA, USA, SCRUB ECOSYSTEM? Sonali Saha1,*, Alessandro Catenazzi, and Eric S. Menges Archbold Biological Station, 123 Main Drive, Venus, Florida 33960, USA *Corresponding author: Tel.: 001-305-247-6547; e-mail: [email protected] ABSTRACT Although belowground biomass patterns are important in understanding aboveground re- sponses, few studies have quantified how belowground biomass changes in response to fire cycles. In this study, we determined if patterns of time-since-fire (TSF; range 3 yr to 25 yr) affect belowground and aboveground biomass in scrubby flatwoods, a type of Flor- ida, USA, scrub ecosystem. We also examined if plant groups (oaks, palmettos and all other species) show variation in biomass partitioning between belowground to above- ground biomass. We found that TSF had a significant positive impact on shoot biomass of oaks and leaf litter but did not affect total aboveground biomass or the aboveground bio- mass of other species groups. Total belowground biomass was not significantly explained by TSF, although the belowground biomass of oaks showed a significant quadratic rela- tionship with TSF (r2 = 0.45, P = 0.023). Mean belowground to aboveground biomass ra- tios were 3.47 ±0.76 overall, 2.18 ±0.99 for oaks, 7.25 ±1.01 for palmettos, and 4.94 ±0.89 for other species. Management of fire-prone ecosystems can use belowground biomass patterns to avoid too-frequent burns that may reduce belowground biomass and affect the ability of ecosystems to respond to subsequent fires. Management actions should also maintain sufficient belowground biomass to buffer against periodic drought. Keywords: aboveground, belowground, oaks, palmettos, rhizomes, scrubby flatwoods Citation: Saha, S., A. Catenazzi, and E.S. Menges. 2010. Does time since fire explain plant bio- mass allocation in the Florida, USA, scrub ecosystem? Fire Ecology 6(2): 13-25. doi: 10.4996/ fireecology.0602013 INTRODUCTION ecosystems often have higher aboveground biomass accumulation shortly after fire, with Fire regimes play an important role in bio- declining growth rates as time-since-fire (TSF) mass allocation patterns. For example, in fire- increases (Hanes 1971, Wirth et al. 2002, Map- prone ecosystems, total plant biomass, growth pin et al. 2003). A chronosequence approach rates, and distribution of biomass between (holding all variables but time since fire con- roots and shoots is influenced by fire intensity stant; Jenny 1941) is one of the most used and frequency (Pare and Bergeron 1995, de methods to examine long-term ecosystem re- Vinas and Ayanz 2000, Dijkstra et al. 2002, sponse such as fire in a short time frame (Ew- Day et al. 2006, Mack et al. 2008). Pyrogenic ers and Pendall 2008). Fire Ecology Volume 6, Issue 2, 2010 Saha et al.: Fire Effects on Biomass of Florida Scrub doi: 10.4996/fireecology.0602013 Page 14 Ecosystem-level patterns of plant biomass prior work, we made several predictions. First, in relation to TSF, especially for roots and oth- based on theoretical predictions of biomass er belowground organs, are poorly understood distribution in harsh environments experienc- (Williams et al. 2008). Uncertainties in esti- ing frequent fires (Chapin 1980, Iwasa and mation of carbon fluxes are attributed to poor Kubo 1997, Gurvich et al. 2005), we predicted resolution of biomass data, since most data are that Florida scrub plants will allocate greater satellite-derived (Quaife et al. 2008). Under- biomass to belowground storage organs than standing the patterns in biomass distribution aboveground shoots. We also predicted that between aboveground and belowground bio- aboveground biomass will increase with TSF, mass sheds light on ecosystem processes such because plants are top-killed by fires and re- as carbon sequestration and water table dy- sprout with greater vigor after fire in similar namics (Feddes et al. 2001, Day et al. 2006, sclerophyllous shrub-dominated ecosystems Collins and Braas 2007, Rodriguez-Iturbe et (Schmalzer and Hinkle 1987, Dijkstra et al. al. 2007, Sierra et al. 2007). 2002). Though the fine root biomass in recent- One ecosystem that is shaped by recurrent ly burned scrub shows an immediate (within 1 fire is Florida scrub (Myers 1990, Menges yr) increase after fire (Day et al. 2006, Schafer 2007), a shrub-dominated ecosystem on nutri- and Mack 2009), we posited that belowground ent-poor soils (Myers 1990) harboring several biomass will remain steady with TSF due to endemic and rare plants (Estill and Cruzan two opposing mechanisms—carbon removal 2001). For scrubby flatwoods, a type of Flori- from storage to support resprouting, and addi- da scrub, the optimal fire return interval that tion of photosynthates to belowground com- maximizes species diversity and yields posi- partments (Langley et al. 2002). tive population growth rates of endemic plants is about 8 years to 16 years (Menges et al. METHODS 2008). Biomass patterns in relation to TSF have been described in a coastal Florida scrub Site Description by Schmalzer and Hinkle (1987), and more re- cently by Day et al. (2006). However, these The study was conducted at the ca. 2000 studies do not explicitly consider variation in ha Archbold Biological Station (ABS; 22o11’N, belowground biomass with TSF, and the num- 81o21’W), located at the southern boundary of ber of categories of TSF is limited as well (2, the Lake Wales Ridge in central Florida, USA. 4, 8, and 25 yr in Schmalzer and Hinkle 1987). The climate includes hot, wet summers from Moreover, no estimates of belowground bio- June to September, and mild, dry winters. mass dynamics with TSF exist for interior Typically, temperatures are highest in August Florida scrub ecosystems. and lowest in January (Abrahamson 1984). A main objective of this study was to de- Average annual rainfall is 1.365 mm (ABS scribe TSF-related patterns in total below- weather data, 77 years), with 60 % falling be- ground biomass (rhizomes and roots), total tween June and September; the wet season and aboveground biomass (leaves, stems, and re- intermittent rainfall occurs during the eight- productive parts), litter, and ratios of below- month dry season and may account for 40 % of ground to aboveground biomass in interior total annual rainfall (Chen and Gerber 1990). Florida scrub on the Lake Wales Ridge, Flori- Depth to water table, measured at the main da, USA. We also tested for differences in bio- grounds of ABS, varies from 0.5 m to 1.8 m mass allocation among oaks, palmettos, and all annually (Saha et al. 2008). Soils are coarse- other species; as well as described below- grained, drought-prone, and infertile (Carter et ground biomass in relation to depth. Based on al. 1989, Saha et al. 2008). Fire Ecology Volume 6, Issue 2, 2010 Saha et al.: Fire Effects on Biomass of Florida Scrub doi: 10.4996/fireecology.0602013 Page 15 The ABS area is characterized by a mosaic fire resprouters (Menges and Kohfeldt 1995, of scrub, flatwoods, and seasonal ponds (Abra- Abrahamson 2007). Individual clones of scrub hamson 1984, Menges and Hawkes 1998, oaks often spread over areas of >4 m2 (S. Saha, Menges 1999). Interior Florida scrub vegeta- personal observation) and oaks are particularly tion is divided into several major assemblages persistent in long-unburned scrubby flatwoods described in detail by Abrahamson (1984). (Menges et al. 1993). These include scrubby flatwoods, sand pine scrub, and rosemary scrub. We worked in Biomass Sampling scrubby flatwoods, a type of Florida scrub, and the most common vegetation type at ABS We initially selected 21 20 m by 20 m field (covering about 30 % of ABS area). In partic- sites, all in scrubby flatwoods on flat ground, ular, we chose sites dominated by sandhill oak on Satellite soils dominated by sandhill oak. (Quercus inopina Ashe), as mapped by Abra- We discarded one site dominated by sandheath hamson (1984). Scrubby flatwoods dominated (Ceratiola ericoides Mitchx.). All sites expe- by Q. inopina are characterized by white sands rienced complete burns (all ground burned, all belonging to the Satellite soil series and con- shrubs top-killed) during the last fire. Sites sist of hypothermic uncoated Aquic Quartz- varied in fire history; time-since-fire (TSF) ipsamments (Carter et al. 1989). Soils are was 3, 6, 8, 14, 18, 21 and 25 yr. Thus, our highly infertile with available N and P ranging sample size was three sites per TSF (2 sites for from 0.0 μg g-1 to 2.5 μg g-1 and 0.11 μg g-1 to TSF = 21 years), totaling 20 sites for 7 TSF 0.45 μg g-1, respectively (S. Saha, Institute for categories. We sampled biomass in January Regional Conservation, unpublished data; J. 2007, during the early dry season when all spe- Schafer, University of Florida, unpublished cies irrespective of their leaf phenology had data). Periodic fires, mainly prescribed, have intact leaves present. occurred in these scrubby flatwoods since We conducted biomass excavations in con- 1967, and ABS has maintained spatially ex- junction with excavation for drift fences plicit records of their fire intensity and spatial around lizard enclosures. First, we marked the extent. The ABS fire management plan calls boundary of our sampling plots at the north- for a modal fire return interval of 5 yr to 20 yr western and southeastern corner of each of the for most areas of scrubby flatwoods (Main and 20 m × 20 m enclosures. We then collected Menges 1997). aboveground biomass from within the plot Vegetation in the study area was comprised boundary. After the mechanized trenches were of sclerophyllous shrubs, dominated by clonal excavated, we collected the sand, roots, and oaks (Chapman oak [Quercus chapmanii rhizomes from within our plot boundary.
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