Effect of Prescribed Burns on East-African Savanna Small Mammals. Bradley J. Bergstrom, Biology Dept., Valdosta State University, Valdosta, GA 31698 USA

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Mean Dead Grass Stems (hits/10-pin frame)

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Regression R2=68.5%, P=0.00005.CN= Control Non-Glade; 9-ha burn plots B= burned, U= unburned. QuadraticBlack-cotton sites: Z,C,W,WC,MWC = KLEE glade plots; adjacent CG= Control Glade,

Live stems n.s. (P > 0.5)

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Mean Dead Grass Stems (hits per 10-pin frame)

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outside controls = RG-, RB-. Linear Regression R2=54.5%, P=0.006.Inside Red-soil 0.5-ha Exclosures in Glade and Non-glade (Bush)= RG, RB. In adjacent

Live stems, R2 = 35.4% (P = 0.041)

Small Mammal Densities: Ratio by which Unburn > Burn

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ABSTRACT.--The Laikipia Plateau, central Kenya, murid rodent community of black-cotton vertisol grasslands is usually limited to Saccostomus and Mus spp. In red soils, Tatera, Acomys, Aethomys and Mastomys spp. are common co-dominants. In 2006 and 2008, natural small-mammal densities in a variety of sites in both habitats were < 10/ha, but inside large-herbivore exclosures, densities were several-fold higher and species richness doubled. Rodents whose natural refugia were red soils appeared in black-soil exclosures, and vice versa. The diurnal grazer Arvicanthis was common only inside exclosures. Across both habitats in 2006, there was a strong positive effect of grass height and moribund-stem density on small-mammal density. This suggests depleted abundance and diversity of murid rodents resulting from overgrazing and/or long-term fire exclusion. Live trapping of prescribed burns (burn pixels 1 ha and 9 ha) and adjacent unburned controls in black cotton 18-55 months post-burn showed maintenance of taller grass, higher dead-stem density, and higher abundance of small mammals on unburned pixels. In this limited experimental landscape, continued avoidance by predation-risk-averse small mammals of burned patches into the medium term may be perpetuated by cropping by native and domestic grazers in a positive feedback cycle of grazing and nutrient enrichment.

Methods.—Prescribed burns were completed 2002 through 2005 on scattered sites in black-cotton soils. Total area burned per site was 1 ha, 9 ha or 81 ha, with both “continuous” and ”patchy” patterns for each burn area treatment. Small mammal trapping along 1,000-m transects (100 traps; 300-m transects for 1-ha burn treatments) covering burned and unburned pixels was conducted Aug-Dec 2006 and May-Jul 2008. Traps were opened 5 consecutive nights. Distance traveled to burrow upon release at trap was recorded, and average distance traveled was used to determine area sampled by transect. Program CAPTURE was used to choose best density index (or MNA). Every 20 m along transect, a 10-pin frame was randomly oriented and number of hits were recorded for: bare soil, live grass, dead grass. Five measurements of grass height were taken per site. Live trapping and vegetation analyses were repeated inside large-herbivore exclosures (KLEE) and in adjacent controls on both black-cotton and red-soil habitats.

Soil → BLACK RED

Trtmnt ↓ →

Ungrazed

N/ha S

Grazed

N/ha S

Ungrazed

N/ha S

Grazed

N/ha S

Bush n/a 2-7 2 30-50 4-5 181 4

Glade 30-50 3-4 8-12 1-2 50-120 4 4-12 1-2

2006 Results: Rodents >> Abundance & Richness in Ungrazed Exclosures, esp. on Enriched Sites (Glades)

Dead Stem Density: Proportion by which Unburn > Burn

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Small-mammal densities always > on Unburned Controls up to 55 months post-burn—often significantly so up to 35 months.

Why? It appears that cover remains greater on Controls throughout the same period…

And… Grass Height shows a nearly identical pattern—i.e., remains taller on Controls!

Discussion.—Huntzinger et al. (200? ) found rodents avoided areas 4-6 mo post-burn, but in contrast to the present study, Monadjem and Perry (1998; S Afr J Sci 94:89) found a positive effect after a year. Abundant large herbivores of Laikipia are drawn to the burned areas because of enhanced nutrition of grasses and enhanced visibility of openings; their feces/urine extends the nutritional enhancement effect, perpetuating the “grazing lawn” phase for years (similar to abandoned bomas, or glades). Predation-risk averse small mammals avoid these lawn areas. A natural fire regime would affect a far greater area, with patches randomly dispersed (Fox 1982; Ecol 63:1332), and likely not concentrate grazing to the degree seen in this experimental landscape, nor extend the grazing lawn phase for nearly as long.

Acknowledgments.—Fieldwork supported by ROA supplement to NSF grant DEB-0316402 to Truman Young. Ryan Sensenig and Todd Palmer conducted burns. John Mpaiyan and Mathew Nermon assisted in the field. (Background photo Mt. Kenya)

↑ Exclosures

Saccostomus mearnsi

Crocidura sp.