Vegetation and Landscape Ecology Lab | Main / Post-Cedar Fire Mixed Conifer-Hardwood Monitoring and Mixed Coniferous Forest Restoration at Cuyamaca Rancho State Park, San Diego County, California

Sponsored by California State Parks, Colorado Desert District, 2004-2009 (overseen by Kim Marsden, Assoc. Resource Ecologist)

The project formed the Masters thesis research of Linnea Spears who completed her degree on December 2005. The main findings are summarized below in the Executive Summary of the project submitted to California State Parks. A follow-on project is determining the locations of natural post-fire conifer regeneration in the Park, and the environmental conditions associated with seedling establishment and survival. This project will form the Masters thesis research of Erin Berman (2007-2009). The proposed work for this phase is outlined below.

Publications to Date

Spears, Linnea Anne, 2005, Tree mortality and forest recovery in Cuyamaca Rancho State Park, San Diego County, California following the 2003 Cedar Fire, Thesis (M.S.)-- San Diego State University (Biology), 45 p.

Spears, L. A. and Franklin, J., 2005, Tree Mortality and Forest Recovery in Cuyamaca Rancho State Park, San Diego County, California after the 2003 Cedar Fire, Year One Report, Department of Biology, San Diego State University, submitted to Kim Marsden, Resource Ecologist, California State Parks, Colorado Desert District, 200 Palm Canyon Drive, Borrego Springs, CA 92004-3427; 1/31/05.

Franklin, J., Spears-Lebrun, L., D. Deutschman, and K. Marsden, 2006, Impact of a high-intensity fire on mixed evergreen and mixed conifer forests in the Peninsular Ranges of southern California, USA, Forest Ecology and Management 235: 18-29. See Publications

Franklin, J. 2008.Post-Cedar Fire Mixed Conifer-Hardwood Monitoring at Cuyamaca Rancho State Park, San Diego, California. Final Report, Interagency Agreement Number C0543025, California Department of Parks and Recreation, Colorado Desert District, Borrego Springs, CA. 26 pp. December 2008.

Post-Cedar Fire Monitoring and Mixed Coniferous Forest Restoration (2008-2009) Ongoing Work

A follow-on project is aimed at determining the locations of natural post-fire conifer regeneration in the Park, and the environmental conditions associated with pine seedling establishment and survival. We are doing this via a stratified sample of locations throughout the Park where locations that were conifer forest pre-fire and that vary in their terrain characteristics (slope, aspect, elevation) and fire severity will be systemtatically surveyed for conifer establishment and survival. We particularly focus on pines (Coulter, Sugar and Jeffrey). This project will yield information about where regeneration is occuring, and under what environmental conditions (terrain position, pre-fire stand density, post-fire vegetation patterns). It will also yield a model of suitable conditions for pine establishment that can be used by the Park to determine sites for forest restoration -- where conditions seem suitable but natural regeneration is not occurring (due to lack of seed, etc.) Patches of natural and planted forest can serve as foci for future natural recruitment. While our previous study (see below) found little evidence of pine recruitment during the first two years following the Cedar Fire, we were pleasantly surprised to locate over 700 2-4 year pine saplings surviving on West Mesa in 2007. This was based on opportunistic observations. Systematic surveys were conducted in 2008.

Surveys in 2008 suggest that pines, especially Pinus coulteri (which is partially cone serotinous), are establishing and surviving in about one third of the formerly forested area – that is, in 425 out of 1231 (2000-m2) quadrats that were searched, at least one juvenile conifer individual was found that has established since the fire.

Pinus coulteri is regenerating, albeit sparsely, throughout its elevational range in the Park, 1182-1930 m. Limited regeneration of incense cedar and sugar pine have been observed in small patches of forest where fire severity was low. However, the extent of mixed conifer forest in CRSP was limited to forested areas above 1500 m, comprising about 1400 ha (14%) of the Park, and including a significant component of P. coulteri. P. coulteri is partially cone serotinous, and therefore expected to respond to fire with some degree of seedling establishment.

Models of conditions associated with pine establishment are being developed.

Post-Cedar Fire Mixed Conifer-Hardwood Monitoring (2007) -- Executive Summary – Findings and Recommendations

The 2003 Cedar Fire burned extensive forested areas of the Cuyamaca Mountains in the Peninsula Ranges of San Diego County, CA, USA. This large fire severely affected these forests. The purpose of this study was to examine the effect of the heterogeneity of both the landscape and disturbance on patterns of post-fire vegetation dynamics. An earlier project (Agreement C0443021) reported that conifer mortality in Cuyamaca Rancho State Park (CRSP) was extremely high and positively related to fire severity, and that early post-fire vegetation dynamics during the first two growing seasons were dominated by the establishment of abundant and diverse native herbs (including fire-obligates) as well as shrub seedlings, and resprouting by shrubs and oak trees. This study reports on the analysis of data from 38 vegetation monitoring plots in West and East Mesas resurveyed in May-June 2007, the fourth post-fire growing season. Vegetation changes in the first four years following a large, severe crown fire in Coulter pine and mixed conifer forests are described.

Areas with high cover of Ceanothus shrubs

Dense shrub cover, primarily Ceanothus palmeri, has established on about 40% of the area surveyed, especially in stands with higher former forest cover and fire severity. About half of these stands had lower shrub cover, averaging 32%, and half had high cover, averaging 70%. On a landscape scale I recommend no vegetation management of C. palmeri dominated stands. Ceanothus is a nitrogen fixing genus of California shrubs that serves an important ecosystem function, especially following fire on low-nutrient soils in California’s montane forests. These shrub stands will naturally thin over time, resulting in lower, patchier cover, and allowing establishment of conifers.

Site-specific removal of shrubs over small areas may be required for tree planting projects, but the disadvantage of Ceanothus removal, again, is that it may affect the availability of nutrients for successful tree establishment. Ceanothus is also known to be an intermediate host for mycorrhyzal fungi associated with conifer species and necessary for their survival. In the stands examined that fell at lower elevations in the forested zone (1300-1400 m), shrub cover averaged around 60% and chaparral species dominated vegetation recovery, especially Ceanothus leucodermis. Again, Ceanothus plays an important nutrient cycling role post-fire in California ecosystems. These sites appear to be following a normal trajectory of succession for chaparral-dominated sites. There is no indication that vegetation management is required.

Areas with high cover of invasive, exotic annual grasses and forbs

By 2007, 4 years after the Cedar Fire, exotic annual brome grasses (Bromus spp.) and a mustard, Sisymbrium altissimum, were the most abundant herbaceous species in the areas surveyed. Forested areas of CRSP are interspersed with dry meadows (grasslands) with a history of grazing, and the most abundant brome species have been established there for at least a century. Bromus tectorum, in particular, has been observed to invade following fire in low elevation pine forest. Therefore, it is not surprising that these species were found in abundance following a stand-replacing crown fire. Concerns that are raised, however, are: what is the impact of high exotic herbaceous cover on 1) native herbs, and 2) conifer regeneration? In other words, is there a negative impact on native biodiversity and natural patterns of succession?

Although it is disheartening to see plant diversity dominated by exotic species, I think it is unlikely for these exotic Eurasian grasses to lead to altered fire regimes or type conversion, as has been found elsewhere in sagebrush ecosystems. These grasses are dependent on dispersal in order to establish in forested areas following disturbance because they do not have persistent seed banks. They did not reach potential establishment sites in abundance during the first post-disturbance year, when most resources are available, owing to dispersal limitation. Because of this, they had little impact on the post-fire annuals and bulbs that are a significant component of biodiversity in this forest community. They are shade-intolerant, and therefore I predict that they will not persist in such great abundance in these sites after 5-10 years as the woody canopy closes. Given their temporal and spatial patterns of establishment, they have the greatest potential impact native perennials and opportunistic annuals. They are also likely to re-invade, but only during the same time window (2-10 years after fire), given the proximity of propagule pools, the dry meadows found in the mountains where non-native grasses have long been established. If Sisymbrium altissimum forms a persistent seed bank it could have a greater impact on native plant communities.

I do not know of any practical means to remove these exotic annuals on a landscape scale. Fire has shown to be a particularly ineffective tool for controlling these species, because it tends to promote their establishment (especially low intensity prescribed fire that does not kill seed banks). It fact, one of the biggest challenges to re-establishing fire in western forests is the threat of invasive species. They are likely to persist in these forests, given their establishment in the grasslands (dry meadows) that are interspersed with forest at CRSP, but occur primarily in a short temporal window following fire, after the native post-fire flora has flourished, and before woody cover has re-established. It is not known to what extent exotic annuals interferes with conifer establishment. This will be discussed in the next report (C0643016). Anecdotally, pines are establishing in grass-dominated areas. But it is not known if the amount of conifer establishment would be greater in the absence of competition from exotic annuals.

Monitoring Recommendations

The established monitoring stands are an excellent framework for long term monitoring of post-fire vegetation succession. I recommend that the stands be resurveyed at 3-5 year intervals in the absence of fire. After the first five post-fire years, vegetation change is likely to occur more slowly, and annual monitoring is not necessary in the absence of fire. These stands provide detailed baseline data on fire effects and species establishment following fire. It will probably also be necessary to establish additional monitoring locations in order to track conifer establishment because conifer regeneration is so sparse on the landscape that it is not adequately captured in this set of vegetation stands whose locations were based on a random stratified sample.

post-fire annuals

Post-Cedar Fire Mixed Conifer-Hardwood Monitoring (2004-2006) -- Executive Summary – Findings and Recommendations

In late October 2003 the Cedar Fire, the largest wildfire in southern California in over 100 years, burned almost all of Cuyamaca Rancho State Park (CRSP; 10,000 ha) at high severity. CRSP, situated in the Peninsular Ranges, harbors one of southern California’s unique sky islands of montane conifer habitat surrounded y a sea of foothills shrublands (chaparral). The landscape looked like scorched earth to anyone who drove through CRSP after the fire. However, many ecosystems in California are fire adapted – their plants have traits that allow them to survive or regenerate after fire, or even that require fire for regeneration.

The purpose of this study was to measure thee effect of the Cedar Fire on the forested lands of Cuyamaca, and to monitor the early recovery of the plant community. We selected the West Mesa area of the Park (about 1100 ha) for study because a previous forest survey was conducted there 11 years before the Cedar Fire, and because it appeared to be less completely burned than other areas (Middle Peak). This selection was ironic for two reasons. First, the previous survey did not locate all sample plots precisely enough that they could be relocated exactly. Therefore, before and after comparisons of forest structure can only be made at an aggregated level. Secondly, we determined that in fact fire severity for all but five of the 37 plots revisited was very high. While this in itself is useful information, it limited our ability to determine the effect of fire severity on forest recovery.

However, we found the following in the first post-fire year (2004):

Almost all pines and other conifer trees were killed by the fire. The greater the fire severity in a location the higher the mortality. Most trees measured in our study area were Coulter Pine but there were also Jeffrey Pine, Incense Cedar and White Fir. Coulter Pine is partially serotinous meaning that some cones on some trees are sealed with resin that is melted by fire, releasing seeds. Only five pine seedlings were found in our plots, or less than 20 seedlings per hectare.
Most oak trees were killed above-ground but were resprouting from the base – the individual survived the fire but the mighty oak was replaced by a few stems. Resprouting was unrelated to characteristics of the environment or the fire.
Shrub species found in chaparral patches and under forest were regenerating vigorously by resprouting and/or establishing thousands of seedlings.
Over 100 species of native wildflowers (annual and perennial) flowered prolifically in 2004, in spite of low rainfall, producing a typical flush of post-fire biodiversity. Non-native plant species were not very abundant or diverse.

The 2003-04 rain year was extremely dry, followed by the extremely wet year of 2004-05. Continued monitoring in 2005 revealed the following:

Even fewer new pine seedlings established and we estimate that survival of those establishing in 2004 to 2005 was low (<20%). Pines are not reestablishing.
In a single stand where several Incense Cedar trees survived the fire we found thousands of seedlings, highlighting the importance of small unburned patches to forest regeneration.
Cover of resprouting oaks, shrubs and of shrub seedlings increased.
A group of “fire-following” herbs, predictably, disappeared in the second year, and unseen to us remain as seeds in the soil waiting for the next fire.
Cover of other herbs increased, presumably in response to the high rainfall.
Unfortunately, a large portion of that cover was non-native (exotic) grasses that are known to be invasive (displace native plants in California ecosystems) and alter fire cycles.
We added new survey plots in an area of East Mesa, part of which had been burned by Park officials in a fuel-reducing prescribed burn one year before the Cedar Fire. East Mesa had much lower fire severity and lower conifer mortality than West Mesa (50% versus 95% mortality). It is not known if this is due to previous fire history, specific behavior of the Cedar Fire, or stand conditions, but it is a dramatic difference. East Mesa is drier, with more open forest stands dominated by Jeffrey Pine.

Predictions and Recommendations

We predict that severely burned forest in CRSP will be dominated by shrubs and oaks for decades to centuries. The expanding cover of these species may prevent pine seedling survival even if pines can disperse seed to these areas naturally.
A review of ecological restoration and plantation forestry projects would provide an estimate of the cost versus effectiveness of promoting pine forest reestablishment by large-scale seeding or planting
More worrisome is the expansion of exotic grasses of forbs following the rains of 2005. This should be closely monitored. These species are known to be detrimental to native plant communities.
Other exotic plant removal programs should be reviewed to determine the feasibility of a removal program. Specifically, there may be strategic places on the landscape where, if done, this would be most effective.

Finally, to paraphrase Professor Paul Zedler, is may be fruitless to debate the natural fire cycle in this region when climate and human use of fire have varied at the time scale of the fire regime itself – hundreds to 10,000 years. Instead, as Wheeler in his book on fire ecology remarked, resource managers must determine what elements of biodiversity, ecosystem function or resource production they want to manage with fire, and then determine how, when and where to use fire (prescription, suppression, let-burn) to achieve their resource management goals.