Fire Ecology Volume 13, Issue 1, 2017 Lutz et al.: Shrub Communities and Reintroduced Fire doi: 10.4996/fireecology.1301104 Page 104 RESEARCH ARTICLE SHRUB COMMUNITIES, SPATIAL PATTERNS, AND SHRUB-MEDIATED TREE MORTALITY FOLLOWING REINTRODUCED FIRE IN YOSEMITE NATIONAL PARK, CALIFORNIA, USA James A. Lutz1*, Tucker J. Furniss1, Sara J. Germain1, Kendall M.L. Becker1, Erika M. Blomdahl1, Sean M.A. Jeronimo2, C. Alina Cansler2, James A. Freund2, Mark E. Swanson3, and Andrew J. Larson4 1 Wildland Resources Department, Utah State University, 5230 Old Main Hill, Logan, Utah 84322-5230, USA 2 School of Environmental and Forest Sciences, University of Washington, Box 352100, Seattle, Washington 98195-2100, USA 3 School of the Environment, Washington State University, Johnson Hall 177, Pullman, Washington 99164-2812, USA 4 Department of Forest Management, University of Montana, 32 Campus Drive, Missoula, Montana 59812, USA *Corresponding author: Tel.: +1-435-797-0748; e-mail: [email protected] ABSTRACT RESUMEN Shrubs contribute to the forest fuel load; Los arbustos contribuyen en la carga de their distribution is important to tree combustibles de los ecosistemas forestales. mortality and regeneration, and verte- Su distribución es importante en la mortali- brate occupancy. We used a method new dad y regeneración de los árboles y en la to fire ecologyextensive continuous ocupación del espacio por los vertebrados. mapping of trees and shrub patches with- Nosotros usamos un nuevo método en ecolo- in a single large (25.6 ha) study siteto gía del fuegomapeo continuo de parches identify changes in shrub area, biomass, de árboles y arbustos dentro de un sitio de and spatial pattern due to fire reintroduc- estudio (25,6 ha)para identificar cambios tion by a backfire following a century of en el área cubierta por arbustos, su biomasa fire exclusion in lower montane forests y los patrones de distribución causados por of the Sierra Nevada, California, USA. la reintroducción del fuego en bosques mon- We examined whether trees in close tanos en la Sierra Nevada de California, proximity to shrubs prior to fire experi- EEUU. Examinamos si árboles muy próxi- enced higher mortality rates than trees in mos a arbustos antes del fuego experimenta- areas without shrubs. We calculated ban una mayor mortalidad que árboles en shrub biomass using demography sub- áreas sin arbustos. Calculamos la biomasa plots and existing allometric equations, de los arbustos usando patrones de densidad and we developed new equations for y ecuaciones alométricas, y desarrollamos beaked hazel (Corylus cornuta ssp. cali- nuevas ecuaciones para el arbusto Corylus fornica [A. de Candolle] E. Murray) cornuta (Corylus cornuta ssp. californica Fire Ecology Volume 13, Issue 1, 2017 Lutz et al.: Shrub Communities and Reintroduced Fire doi: 10.4996/fireecology.1301104 Page 105 from full dissection of 50 stems. Fire [A. de Candolle] E. Murray) mediante la di- decreased shrub patch area from 15.1 % sección de 50 tallos. El fuego hizo decrecer to 0.9 %, reduced live shrub biomass el área de los parches de arbustos del 15,1 % from 3.49 Mg ha-1 to 0.27 Mg ha-1, and al 0,9 %, redujo su biomasa viva de 3,49 Mg consumed 4.41 Mg ha-1 of living and ha-1 a 0,27 Mg ha-1, y consumió 4,41 Mg ha-1 dead shrubs. Distinct (non-overlap- tanto de su biomasa viva como muerta. Los ping) shrub patches decreased from 47 parches de arbustos no solapados con árboles ha-1 to 6 ha-1. The mean distance be- decrecieron de 47 ha-1 a 6 ha-1. La distancia tween shrub patches increased 135 %. media entre parches de arbustos se incremen- Distances between montane chaparral tó un 135 %. Las distancias entre parches del patches increased 285 %, compared to a chaparral se incrementaron un 285 %, compa- 54 % increase in distances between ri- rado con un incremento del 54 % entre par- parian shrub patches and an increase of ches de arbustos generalistas. La muerte de 267 % between generalist shrub patch- árboles relacionados con el fuego en parches es. Fire-related tree mortality within de arbustos fue marginalmente baja (67,6 % shrub patches was marginally lower versus 71,8 %), mostrando un efecto contras- (67.6 % versus 71.8 %), showing a con- tante de los arbustos en la mortalidad de árbo- trasting effect of shrubs on tree mortali- les entre este ecosistema forestal y los ecosis- ty between this forest ecosystem and temas dominados por vegetación de chapa- chaparral-dominated ecosystems in rral, en los cuales la mayoría de los árboles which most trees are killed by fire. mueren por efectos del fuego. Keywords: allometric equations, Corylus cornuta ssp. californica, Rim Fire, Smithsonian Forest- GEO, Yosemite Forest Dynamics Plot Citation: Lutz, J.A., T.J. Furniss, S.J. Germain, K.M.L. Becker, E.M. Blomdahl, S.M.A. Jeroni- mo, C.A. Cansler, J.A. Freund, M.E. Swanson, and A.J. Larson. 2017. Shrub communities, spa- tial patterns, and shrub-mediated tree mortality following reintroduced fire in Yosemite National Park, California, USA. Fire Ecology 13(1): 104–126. doi: 10.4996/fireecology.1301104 INTRODUCTION erts et al. 2008, Fontaine et al. 2009, Fontaine and Kennedy 2012). In shrub-dominated Shrubs constitute a small proportion of chaparral systems, fire behavior is character- forest biomass, but their spatial arrangement ized by rapid and complete combustion of can amplify local effects of fire on surrounding shrubs (e.g., Keeley 2000, 2006). Large, con- vegetation by propagating fire and increasing tiguous patches of montane chaparral are often fire intensity (Collins and Stephens 2010). mixed with forests in the Sierra Nevada, Cali- Through their ability to persist in a wide range fornia, USA (Nagel and Taylor 2005, Lauvaux of light and moisture regimes, and their et al. 2016), and these patches can inhibit for- fire-adapted life history traits such as vegeta- est development through repeated high-severi- tive reproduction (van Wagtendonk and Fites- ty burns (Lauvaux et al. 2016). Kaufman 2006), shrubs provide structural ele- Fire effects in the shrub understory of ments for invertebrate (Marra and Edmonds closed-canopy forests remain poorly under- 2005) and vertebrate habitat (North et al. stood, especially where the area and continuity 2005, Fontaine et al. 2009), as well as food for of montane chaparral species are constrained birds and rodents (Smucker et al. 2005, Rob- by light and nutrient limitations (Conard et al. Fire Ecology Volume 13, Issue 1, 2017 Lutz et al.: Shrub Communities and Reintroduced Fire doi: 10.4996/fireecology.1301104 Page 106 1985, Halpern and Lutz 2013, Lutz et al. fire, however, the severity of fire in riparian 2014b). Although the aboveground portions shrub communities could be higher due to of most shrub species in Sierra Nevada forests greater fuel loads (e.g., Olson and Agee 2005, are killed in fire, they often regenerate asexu- Van de Water and North 2011). Finally, al- ally by sprouting from root crowns in the though the aboveground portion of shrubs spring following fire. The immediate fire-in- burns, some patches would likely remain un- duced reduction in aboveground portions of burned in isolated refugia (e.g., Hylander and shrubs could facilitate tree seedling develop- Johnson 2010; Kolden et al. 2012, 2015), ment through a reduction in competition (Oak- making the net effect of shrubs on tree mortal- ley et al. 2006), and a concurrent reduction in ity unclear. shrub reproductive output during the time re- Recognizing that distinct shrub communi- quired for tree seedlings to gain sufficient stat- ties arise depending on microenvironment ure. Sprouting shrubs do not generally flower (North et al. 2005, Lutz et al. 2014b), we in- in periods following wildfire, effectively re- vestigated the relationship between fire-in- ducing food resources for invertebrates and duced tree mortality and shrub communities vertebrates. Therefore, post-wildfire land- characterizing xeric, moist, and intermediate scapes could enhance tree recruitment and re- environments. We hypothesized that more xe- duce the distribution and abundance of inver- ric shrub communities would burn at higher tebrate and vertebrate species. intensity, while riparian shrub communities In the Sierra Nevada, shrub community would burn at lower intensity. We further hy- composition and structure vary along a soil pothesized that post-fire tree mortality in drier moisture gradient (North et al. 2005, Kee- upland areas characterized by montane chapar- ler-Wolf et al. 2012), with moister vegetation ral species would be higher within shrub communities correlating positively with tree patches because shrub combustion produces vigor and negatively with fire intensity (Van considerable heat that could damage tree cano- de Water and North 2011, Kane et al. 2015b). pies (Weise et al. 2005, Collins and Stephens The distinct shrub communities of xeric areas 2010, Smith et al. 2016b). We also hypothe- could be positively correlated with higher se- sized that riparian areas would have more vig- verity fire and greater tree mortality. Shrubs, orous trees that could resist fire, or less active even in discontinuous patches in the forest un- fire behavior, resulting in lower post-fire tree derstory, could exacerbate local fire effects by mortality. We compared pre-fire and post-fire spreading fire through the understory (e.g., shrub maps of a closed-canopy forest and used Weise et al. 2005) and heightening fire intensi- species-specific allometric equations in combi- ty (Collins and Stephens 2010). Shrub com- nation with tree demographic data to explore bustion is characterized by large and rapid re- the relationship between fire effects on the lease of heat that rises through tree canopies area of shrubs, shrub biomass, continuity of and damages leaves (Smith et al. 2016b). The shrubs, and the contribution of shrubs to long burning times for the woody stems of fire-induced tree mortality.