Canopy of the closed-cone pine forest dominated by mature bishop pine (Pinus muricata), just outside the perimeter of the 1995 Vision Fire on the north side of Inverness Ridge, Point Reyes National Seashore. All photographs by Brian J. Harvey. FOREST RESILIENCE FOLLOWING SEVERE WILDFIRE IN A SEMI-URBAN NATIONAL PARK by Brian J. Harvey, Barbara A. Holzman, and Alison B. Forrestel

hen most of us think CALIFORNIA CLOSED- sence of fire is rare. Mature bishop of forest fires, we CONE PINE FOREST pine trees are easily killed by fire, likely invoke images but the synchronous release of most of the 1988 fires in One such ecosystem is the seeds immediately following a fire YellowstoneW or the 2013 Rim Fire in closed-cone pine forest, which ex- allows for abundant post-fire seed- Yosemite—wildfires in national ists in a narrow band of discon- ling establishment. As such, most parks or national forests far away nected populations along the Pa- bishop pine forests are even-aged from urban areas. Over the last half cific Coast of California and Baja stands that originated after fire century, we’ve learned volumes California. Many of these forests are (Sugnet 1985). about the importance of wildfires dominated by bishop pine (Pinus One of the largest native bishop in these large, relatively remote ex- muricata), a medium sized tree that pine forests in the world exists in panses of forest. But what about typically lives to be 80–100 years and around Point Reyes National forests that exist within a morning old before succumbing to disease or Seashore, approximately 30 miles commute from places like San Fran- pests. Bishop pines bear serotinous north of San Francisco. Until 1995, cisco or Los Angeles? What role does cones that remain sealed with resin most forest stands in Point Reyes fire play in the coastal conifer for- until the heat of a fire breaks the had not experienced fire in 60–80 ests that neighbor some of the major cone scales open and releases seeds; years. Many mature bishop pine trees cities in California? therefore reproduction in the ab- were approaching the end of their

14 FREMONTIA VOL. 42, NO.3, SEPTEMBER 2014 lifespan and very few seedlings ex- strated enormous post- isted in the forest understory. This fire resiliency (the ca- all changed abruptly in early Octo- pacity to recover follow- ber 1995 when a wildfire ignited ing fire). Once the pre- just outside the eastern park bound- fire trees were killed, ary on Mount Vision. Over the post-fire bishop pine course of several days, the 5,000 seedling germination hectare (ha) Vision Fire burned and establishment be- through Point Reyes Peninsula dur- came critical for forest ing a period of steady warm, dry persistence. Released winds blowing from the east, even- from cones on burned tually reaching the Pacific Ocean mature trees, bishop Burned and weathered bishop pine cones from a mature just days later. In the bishop pine pine seeds covered the tree killed by the 1995 Vision Fire remain attached to a forest, the fire severity was so high blackened soil within fallen branch in a canopy gap filled by sticky monkeyflower that nearly all pre-fire vegetation weeks of the fire, and (Mimulus aurantiacus) in 2009. was killed. seedlings sprouted The Vision Fire was an impor- within months (Ornduff and Norris ately following fire results from the tant ecological disturbance in one 1997). Shortly thereafter, anyone myriad fire adaptations exhibited by of the most prized natural areas in would be hard pressed to say that the native plants in this forest. While the San Francisco Bay Area, and pro- the forest stands were not on their bishop pines store their seeds high vided a unique opportunity to study way back. One year post-fire, in the forest canopy, blue blossom the role of fire in coastal California Holzman and Folger (2005) recorded ceanothus (Ceanothus thyrsiflorus) ecosystems. Concern over how the an average of 250,000 bishop pine and several manzanita species (Man- ecosystems at Point Reyes would seedlings/ha—greater than a 300- zanita spp.) store theirs in a soil respond to a severe fire was high, fold increase from the pre-fire tree seedbank where they are stimulated although observations suggested density! As seedlings grew into larger to germinate after fire. Less domi- that the bishop pine forest was teem- saplings and then young trees, in- nant tree species such as coast live ing with plant life within months tense competition for resources re- oak (Quercus agrifolia) and Califor- following the fire (Ornduff and sulted in post-fire tree density de- nia bay/California laurel (Umbel- Norris 1997; Ornduff 1998). Here, creasing to an average of approxi- lularia californica) can resprout from we synthesize the scientific findings mately 15,000 live bishop pine trees/ their root crowns or their stems af- from longer-term post-fire research, ha by 14 years after the fire (Harvey ter fire. Small statured plants such focusing on vegetation changes in and Holzman 2014). This process is as yellow bush lupine (Lupinus the bishop pine forest that have oc- referred to as “self-thinning,” and is arboreus) and annual herbs in the curred over nearly two decades since expected to continue as surviving Lotus genus specialize in colonizing the fire. We highlight insights gained individuals grow larger at the ex- recently burned areas, where they from several studies and identify key pense of neighboring plants. gain an early competitive advantage unknowns and priorities for future by fixing nitrogen through a symbi- research. Much of the research we otic relationship with bacteria in describe was supported by a Doc POST-FIRE SUCCESSION their roots. Burr Educational Grant from the AND FOREST STAND The fact that species diversity is California Native Plant Society and DEVELOPMENT at its highest immediately following a small grant from the US National fire illustrates the importance of fire Park Service. Plant community dynamics after in maintaining plant community the Vision Fire demonstrated a pat- structure in bishop pine forests. All THE END AND BEGINNING tern common to many fire-prone species that were recorded at any OF A FOREST Mediterranean ecosystems; that is, point during the first 14 years fol- plant species diversity was highest lowing the fire were present in the The severity of the Vision Fire in the first years following fire. Two first two years, after which some early transformed mature forest stands years after the fire, 34 different plant post-fire specialists were outcom- (approximately 750 trees/ha) into a species were present (Holzman and peted and later disappeared. It is charred landscape with few traces Folger 2005), but by 14 years post- likely that some of these may re- of living vegetation within days af- fire this number had decreased to 21 emerge when the next fire comes ter the fire, but bishop pine popula- species (Harvey and Holzman 2014). through. Some non-native species tion dynamics after the fire demon- The peak in plant diversity immedi- were also recorded in the early post-

VOL. 42, NO. 3, SEPTEMBER 2014 FREMONTIA 15 Severe fire renews the bishop pine forest. ABOVE: Bishop pine forest stand that did not burn in the 1995 Vision Fire. Trees are approximately 80 years old and illustrate moderately sparse stand density representative of the pre-fire forest. No tree seedlings are present in the forest understory, indicative of a long interval since the last fire. OPPOSITE TOP: Post-fire bishop pine forest stand in 2009 in an area where all pre-fire trees were killed in the 1995 Vision Fire. Abundant seedlings established immediately following the fire, leading to high, but variable post-fire stand density. fire years. Australian fireweed (Erech- landscape (Harvey and Holzman canopy trees, high shrub cover tites minima) was of particular con- 2014). Pre-fire forest density (ap- (mostly blue blossom ceanothus), cern, as this species can rapidly colo- proximately 750 stems/ha) was fairly and high plant species diversity. This nize burned areas and form a long- uniform across space, but different diversity in vegetation structure lived soil seedbank. Park managers pathways of post-fire forest stand generated by fire is important for and volunteers removed Australian development were evident immedi- wildlife habitat diversity for many fireweed in 1996 and very few plants ately after the fire and have per- animals. were observed up to six years after sisted nearly two decades later. Some the fire. It is not clear if there are any stands that had the highest initial FIRE AND FOREST long-term effects from Australian post-fire bishop pine seedlings (in EXPANSION fireweed on post-fire forest dynam- a few cases over 1,000,000 seed- ics; however, seedbanks of this spe- lings/ha) have since proceeded along In addition to the abundant tree cies may be present in the forest a densely-forested “closed-canopy regeneration within the footprint of soils now, and long-term effects pathway” with low shrub cover pre-fire bishop pine stands, fire may not be evident until another and plant species diversity. Other served as a catalyst for forest expan- fire occurs. stands with initially lower bishop sion into new areas. The forest The Vision Fire also promoted pine seedling establishment (ap- nearly doubled its extent after the diversity in forest structure (tree proximately 40,000 seedlings/ha) fire, encroaching into pre-fire coastal density, shrub cover, and plant spe- have since proceeded along an grassland and coastal scrub. Before cies composition) across the burned “open-canopy pathway” with sparse the fire, bishop pine stands were

16 FREMONTIA VOL. 42, NO.3, SEPTEMBER 2014 restricted primarily to the high- lustrate the importance of pre-fire eventual landscape patterns of for- elevation portions of Inverness legacies—the location of pre-fire in- est versus coastal scrub. Second, Ridge; after the fire, they expanded dividual trees, forest stands, and soil whether the evidence of forest resil- all the way from the ridge top to the seedbanks—in shaping post-fire iency and expansion following the Pacific Ocean (Forrestel et al. 2011). vegetation patterns that may last Vision Fire is broadly representa- Forest expansion occurred close to decades or more. tive of other populations of Califor- both pre-fire stands and around soli- nia closed-cone pines is unknown. tary pre-fire bishop pine trees that KEY UNKNOWNS AND Tracking post-fire trajectories or were at times over 500 meters from FUTURE RESEARCH the edge of a pre-fire contiguous PRIORITIES forest stand (Harvey et al. 2011). These solitary trees were killed by While the research following the the fire, but the seeds released from 1995 Vision Fire provides insights their serotinous cones resulted in into the disturbance ecology of dense post-fire stands that are now coastal California pine forests, sev- greater than 1,000 stems/ha. Simi- eral key unknowns remain. First, lar to the regenerating stands in ar- mechanisms underpinning the pat- eas that were forest prior to the fire, terns we observed over 14 post-fire many of these expanded forest years could be explored through stands are interspersed with thick- careful experiments. Such designs Mature bishop pine cones on a 14-year-old ets of blue blossom ceanothus, could help determine the relative tree that established after the 1995 Vision which increased in extent by more importance of initial seed influx Fire. Bishop pine cones are strongly sero- tinous (they only open and release their than 4,000% across the burned land- (through soil or canopy seedbanks) seeds after being exposed to the heat of a scape. Findings from Forrestel et al. compared to post-fire competitive fire), and are guarded from seed predators (2011) and Harvey et al. (2011) il- interactions in determining the with spines on the tips of cone scales.

VOL. 42, NO. 3, SEPTEMBER 2014 FREMONTIA 17 examining fire histories in other ity. Understanding the potential in- into systems that extend beyond closed-cone pine forests could fill teractions between introduced dis- their borders. Parks such as Point this knowledge gap. Third, with cli- ease and subsequent wildfire is an- Reyes National Seashore, which are mate change likely to increase fire other priority for future research. within or close to urban areas, are frequency, understanding the con- The vegetation response follow- especially unique as they offer an sequences of short-interval fires on ing the Vision Fire illustrates the opportunity for visitors to under- the bishop pine forest is needed. If importance of wildfire in shaping stand the important processes that fires were to occur before the trees one of the emblematic forest ecosys- shape their local ecosystems. accumulate a sufficient aerial seed- tems in coastal California. Post-fire bank and shrubs and herbs accu- research spanning two decades at REFERENCES mulate a sufficient soil seedbank, Point Reyes has demonstrated high post-fire resilience may be compro- natural resilience following severe Forrestel, A.B., M.A. Moritz, and S.L. mised. Finally, young post-fire wildfire in closed-cone pine for- Stephens. 2011. Landscape-scale bishop pine stands in Point Reyes ests—information that is critical to vegetation change following fire in have been recently impacted by pine the conservation of this ecosystem. Point Reyes, California, USA. Fire pitch canker disease, leading to National Parks serve as vital scien- Ecology 7:114–128. Harvey, B.J., and B.A. Holzman. 2014. pockets of locally high tree mortal- tific laboratories that provide insight Divergent successional pathways of stand development following fire in FIGURE 1. BISHOP PINE FOREST EXPANSION CATALYZED a California closed-cone pine forest. BY FIRE. Journal of Vegetation Science 25(1): 88–99. Harvey, B.J., B.A. Holzman, and J.D. Davis. 2011. Spatial variability in stand structure and density-depen- dent mortality in newly established post-fire stands of a California closed- cone pine forest. Forest Ecology and Management 262:2042–2051. Holzman, B.A., and K. Folger. 2005. Post-fire vegetation response in the bishop pine forest at Point Reyes National Seashore. In Vision Fire, Lessons Learned from the October 1995 Fire, ed. S.G. Allen and W. Shook. U.S. Department of the Inte- rior, Washington, DC. Ornduff, R. 1998. Three years after the Vision Fire in Point Reyes. Fremontia 26: 26–27. Ornduff, R., and V. Norris. 1997. Re- birth of a bishop pine forest: First year after the Mount Vision fire. Fremontia 25: 22–28. Sugnet, P.W. 1985. Fire history and

LEFT: Map of pre-fire (above) and post-fire (below) vegetation within the perimeter of the post-fire stand dynamics of Inver- 1995 Vision Fire, illustrating the substantial change in spatial distribution of plant ness bishop pine populations. communities. In particular, the bishop pine forest (light green) expanded to the southwest. Master’s thesis, University of Califor- nia, Berkeley, CA. RIGHT: Aerial photos taken in July 1993, two years before the Vision Fire (above), and August 2012, 17 years after the Vision Fire (below). Photos illustrate the dual modes of post-fire bishop pine forest expansion from pre-fire contiguous stands (dashed red line) Brian J. Harvey, 434 Birge Hall, Univer- and isolated pioneers (dotted yellow line). In both photos the lighter/non shadow-casting sity of Wisconsin, Madison, WI 53706, vegetation is grasses or shrubs whereas the darker/shadow-casting vegetation is bishop [email protected]; Alison B. Forrestel, pine tree crowns. Fort Cronkhite Building 1061, Sausalito, NOTE: Black arrows connect the aerial photos to their corresponding location on the pre- CA 94965, [email protected]; Bar- and post-fire vegetation maps. bara A. Holzman, HSS 265, San Fran-

SOURCE: Maps are modified from Forrestel et al. (2011). Aerial photo data: Google, US cisco State University, San Francisco, CA Geological Survey, and DigitalGlobe. 94132, [email protected]

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