Abstract

There is evidence that wildfire is increasing in frequency and size in the Arizona Upland subdivision of the Sonoran Desert due to the establishment of exotic annuals, consecutive wet winters and urbanization. This increase in fire disturbance has unclear consequences on plant community structure, and may change present species composition, such as removing long lived perennials such as saguaro. A fire records systems has been designed to centralize fire activity information in the Sonoran Desert, and to formulate a base line understanding of fire's role and history in vegetation communities,. This records system currently exists as a prototype and consists of a relational database management system(RDBMS) and a geographic information system(GIS). The prototype is populated with historical fire data from Saguaro National Park in Tucson, Arizona. Use of the World Wide Web will facilitate data sharing and transfer between multiple agencies throughout the Sonoran Desert to generate a regional model of fire history.

Introduction

Wildfire has played an undetermined role in the ecology of the Sonoran Desert. In the Arizona Upland subdivision, characterized by the saguaro-palo verde vegetation series, Robert Humphrey among others, observed that fires in the Arizona Upland were infrequent during the early to mid 1900's(Humphrey 1963, 1974; Phillips 1962; Shreve 1925, 1951; Steenberg & Lowe 1977). They speculated that the average low production and fragmented nature of annual plant biomass was insufficient for carrying wildfire(Humphrey 1963; Shreve 1951) This notion, however, was based on a landscape heavily disturbed by cattle grazing since Anglo settlement of Southern Arizona in the late 1800's. This widespread disturbance kept fuel loads lower than normal for at least 70 years prior to the development of Humphrey's hypothesis. As a result, little recognition and few studies of fire's effects on desert species exist prior to 1980, although review of newspaper articles show reports of desert fires since 1859(Bahre 1985).

There is no question that the Arizona Upland has experienced fire throughout history. Wildfire can be opportunistic based on the combination of wind speeds and increased fuel loads due to wet winters(McLaughlin & Bowers 1982; Rogers & Vint 1987). Amerinds were also known to start large fires for hunting and warfare purposes which must have burned through parts of the desert scrub(Bahre 1985). But what remains unclear is the frequency and effect of these fire events in the Arizona Upland. Tree-ring analysis of woody desert perennials has proven to be an invalid means for determining fire frequency intervals since growth is not limited to one season in the Sonoran Desert, hence growth rings are not indicative of age(Judd et al. 1971; Rogers & Steele 1980). Testing whether fire was as infrequent prior to Anglo arrival as that observed by Humphrey is a difficult if not impossible task.

To understand fire's history in the Arizona Upland, we are in essence restricted to the knowledge contained in our own historical records. These records illustrate a rise in fire events, particularly dramatic in the past decade(McAuliffe 1995; Rogers 1985; Rogers & Steele 1980; Schmid & Rogers 1988; Wilson et al. 1995). The observed change is no doubt related to the control and management of cattle grazing on public lands initiated in the 1970's. Relief from grazing disturbance has allowed as increase in overall biomass as well as facilitated the displacement of native ephemerals with exotic species. Invasive grasses introduced in seed shipments for re-vegetating grazing land are now providing a more continuous and combustible fuel source(D'Antonia 1992; McAullife 1995). Additionally, the past two decades have received higher than normal winter precipitation due to El Nino. This has resulted in greater native and non-native fuel loads. Finally, as the population of cities like Tucson and Phoenix grow at exponential rates, people are more frequently in contact with their environment, increasing the chance for human caused fires.

It is clear that fire activity in the Arizona Upland has been altered, but what ecological implications will arise from these changes in fire regime? Since wildfire has been ignored in scientific studies during most of this century, little is known about fire's influence on plant community structure. Analysis in the last two decades have shown that most desert perennials do not resprout after fire(Cave & Patten 1984; McLaughlin & Bowers 1982; Rogers 1985; Rogers & Steele 1980; Schmid & Rogers 1988; Thomas 1991; Thomas & Goodson 1986; Wilson et al. 1995), and for populations that do recover several years are necessary for pre-fire densities to return; longer lived species like saguaro and palo verde may take hundreds of years(McAuliffe 1995; Thomas 1991). Sufficient recovery between fires, therefore, is essential to ensure long-term survival of populations. Recurring fire within this recovery period may remove fire intolerant perennials such as foothill palo verde, bursage, saguaro and other cacti, ultimately leading to localized extinctions(Rogers 1985; Thomas 1991). If fire frequency is increasing as fast as recent fires indicate, reference to wildfire may justifiably conjure images of a Sonoran Desert devoid of saguaro and palo verde, the very species which give the Arizona Upland its unique character.

The perception of wildfire in forested areas of the Sonoran Desert, on the contrary is transforming from a historically negative and destructive disturbance into an process that has both positive and protective influences on the landscape. For example, years of fire suppression has lead to fuel build-up threatening to carry fires of large aerial extent and intensity. This has provoked fire managers to conduct prescribed burning and adopt let-burn philosophies to sustain a more natural fire cycle. This "good-in-the-woods", "bad-in-the-desert" dichotomy of fire is not based on statistical evidence, however. Studies have not yet quantified the long-term effect of fire on vegetative community structure in both the Arizona Upland and communities of higher elevations, particularly the effect of shortened fire recurrence intervals. The ecological implications of fire and its ability to change plant community structure in the Sonoran Desert has, therefore, led to controversy among the scientific community, specifically fire managers trying to achieve appropriate administration of fire events which span landscapes with many plant community types.

The first step to solving this dilemma, as well as addressing the role of fire in the Sonoran Desert is to summarize what is known about fire events. Since historical fire records constitute the bulk of our knowledge, organizing this information on an interagency level will generate a baseline of fire history information to document and clarify changes in fire activity such as frequency and size in time and space.

Methods

A relational database management system of historical fire event records has been initiated for the Sonoran Desert. The Historical Fire Events Database (HFED) will contain data from local, state and federal agencies within the Sonoran Desert to complete a regional fire history. Currently, HFED exists as a prototype and is populated with data from the Fire Management archives of Saguaro National Park in Tucson, Arizona. The National Park Service as well as the whole of the Department of the Interior, has used a standardized form for recording fire data since the 1930's. This form known as the USDI 1202 Fire Report has become the logical backbone of the HFED design because of its long-term, interagency use and well documented style of coding. The 1202 Report contains seven categories of fire information. These categories describe general data (date and cause), ownership and size, the reporting agency, suppression techniques, topographic conditions, ignition characteristics and prescribed qualities of reported fires (Fig. 1). Using Microsoft ACCESS for Windows 95 version 7.0 on a Windows NT

Figure 1. A portion of the USDI 1202 Fire Report. Four of the seven categories are shown above: general data (date and cause), statistical data (ownership and size), agency data (reporting agency) and suppression data (suppression techniques). Data pertaining to single fire is recorded on this form with the use of codes. Codes are fully described in a handbook published by the Department of the Interior.

Workstation, the categorical structure of the 1202 Report was transcribed into seven analogous data tables. These tables are respectively named: Main, Statistical, Agency, Suppression, Site, Fire Character and Fuel Type. Each of these data tables contain fields reflecting the data in the corresponding 1202 Report category. The Main data table is unique in that it is composed of several major descriptors such as fire name, cause, and date extracted from the other six tables. Using this structure, 1202 Report data which exists for both the Rincon and Tucson Mountain Districts of Saguaro National Park since 1937 was entered into HFED. In addition to data tables, code look-up tables were also established based on the code handbook published by the Department of the Interior, an instructional document which fully describes the 1202 Fire Report code. One to one relationships were then created between the seven data tables through a common field named Fire ID. Fire ID serves as the primary key by containing a unique identification number for each fire. Likewise, one to many relationships were created between coded fields and their respective lookup tables(Fig. 2).

Figure 2. Relationships between data tables and code look-up tables in the HFED database. The seven data tables (DT) are illustrated at the top and linked by the common field Fire ID. The numerous look-up tables (LU) fall below with a network of relationships connecting each LU with the respective coded field.

To facilitate data entry into HFED and ensure integrity and security of this database, a series of data entry forms was developed within Microsoft ACCESS. These forms are launched from a general switchboard(Fig. 3). Each appear similar in design to the 1202 Fire Report for clarity and are complete with drop down pick lists of code options, and input masks to ensure data entered by multiple users is written to the database in a consistent manner (Fig.4). In addition to forms, a report also exists within HFED. This database object has been programmed to access information stored among the data tables, and print data in standard 1202 Report format illustrated in Figure 1.

Figure 3. The switchboard menu for data entry of 1202 Fire Report Data into HFED at Saguaro National Park. This interface regulates access to each data entry form. Main, Statistical and Agency categories have been assimilated into one form, the remaining four categories exist as stand alone forms. Each form is activated by clicking the respective command button, and is opened in add-only format. A preview of data as it appears in 1202 Fire Report format can be conducted as data is being entered.

Figure 4. The Suppression Data Entry Form. Data regarding suppression techniques for a reported fire would be entered using this form. For fields which require coding like Discovery Type, a drop down menu provides a list of descriptive choices. This technique regulates data integrity.

Relational organization of fire attribute data, however, ignores the important issue of its spatial content. To capture the spatial nature of fire events included in HFED, a geographic information system(GIS) was developed. Using facilities provided by the Advanced Resource Technology Group(ART) at the University of Arizona, Saguaro National Park's fire atlas was digitized in host ArcInfo. The atlas is a collection of 15 minute topographic maps illustrating fire point and boundary locations from 1937 to the present. Point and polygon coverages were generated for fire points and boundaries respectively. Both coverages were attributed with the item Fire ID, and each feature labeled with the unique identification number used in HFED. This field, Fire ID, common to HFED and the ArcInfo coverages was used to physically join the two. Due to the extensive nature of this database, only the Main data table was exported from ACCESS in DBASE IV format and converted into an INFO file in ArcInfo for the permanent join. The remaining ACCESS data tables were also exported and converted into INFO files for soft joins or relates with these coverages.

To provide a framework in which to examine fire activity within and around Saguaro National Park, supplemental ArcInfo coverages have been established. Coverages collected from the Arizona General Reference digital library at ART include park boundary of Saguaro National Park, roads, township, range, section, land ownership, geology and GAP analysis vegetation. Coverages derived from 30 meter Digital Elevation Models(DEM's) include topography, slope and aspect. Several coverages were also digitized from 7.5 minute USGS quadrangles. These are hydrology, geodetic control markers, hiking trails, campsites, and picnic areas. The latter three were enhanced with manuscripting from more complete National Park Service maps. Historic vegetation illustrated by the CCC in 1937 of Saguaro National Park and historic grazing allotments have also been digitized from 15 minute topographic maps. All base coverages extend to 1 mile outside of the park boundary.

The use of ArcInfo can require extensive training, placing the dynamic interaction of this GIS data out of the reach of the field fire mangers. For this reason the fire event coverages and their many associated INFO files have been transferred from the host system into ArcView 3.0 for personal computers, along with all supplemental GIS coverages.

Results and Discussion

Transcription of paper fire records into a relational database management system like HFED addresses issues of data preservation and archiving. As nature degrades the fibers of historical documents, the technology of electronic information can provide enhanced vivacity to data sets and alternate means for storage. For example, HFED not only stores data for multiple users, but it allows the 60 years and roughly 600 records of fire information for Saguaro National Park to be juxtaposed, sorted and segregated for investigation and determination of patterns with a few clicks of the mouse. Attributes such as size and cause, for example, can be summarized in queries to clarify changes in these parameters over time. HFED also provides means for updating data and maintaining data security. Data entry forms exist in add-only format and buffer the user from the central body of data housed in the data tables, protecting the core of historical information from potential corruption by the user. The report object in HFED is another advantage by delivering an efficient shortcut for completing hard copy 1202 Fire Reports.

With the incorporation of GIS, queries of fire event data can be taken a step beyond sorting records for temporal and non-spatial analyses; they can now be spatially represented within a georeferenced landscape(Fig.5). Saguaro National Park's fire history can be viewed in conjunction with vegetation, ownership, elevation, and proximity to trails, roadways and urbanization for developing hypothesis about this history and it's impacts ecologically. For example, when distributions of

fires are viewed among vegetation types, assessment of frequency and size of fire activity in each community can lead to acknowledgment of changes in these parameters over time(Fig. 6). A chronicle of change in fire occurrence will assist in correlating factors which may influence fire activity, specifically exotic species, weather and urbanization. Relationships which result from this type of analysis could be used to predict areas prone to future fire activity as well as the spread of invasive, non-native species(McAuliffe 1997). Fire effects on community structure could also be investigated. In the Arizona Upland for example, areas demonstrated to have a pre-disposition to burning can be identified and its vegetation characteristics compared with those in areas burned less frequently. Such analyses, when supported with information provided from field studies quantifying the effects of fire on desert species, could facilitate understanding fire's role and predict outcomes of changes in fire recurrence intervals like the loss of saguaros and palo verdes. HFED is not limited to fire event data for the Arizona Upland, however. All communities of the Sonoran Desert are represented for fire history examination, which may ultimately influence management strategies such as fire suppression, prescribed burn and prescribed natural fire programs.

By running this GIS database from ArcView, the power of data manipulation and interaction is returned to those who stand to gain the most practical information, the fire managers. Users with minimal GIS experience, for example, can conduct spatial analyses such as theme-on-theme, point-in-polygon, and point-near-line selections(Fig. 7). Spatial joins, basic statistics, merging processes and digitizing are just a few of the many applications available to these users.

Summary

The development of HFED and its GIS component is meant to provide a system for centralizing regional fire information for use at the field or park level. To depict fire history on a regional scale, efforts need to be concentrated in gathering information from other field based offices of federal, state and local activity. Only by pooling these data resources can the predictive power of this system enlighten mangers about natural fire frequencies, fire's effects, exotic species and appropriate management strategies. To facilitate data sharing and transfer between agencies, a fire history web site will be on-line through the USGS Cooperative Park Studies Unit, University of Arizona homepage. The HFED design will be available for downloading by interested parties for organization of their own data sets. These complete databases will in turn be posted to provide access to other users. By providing the essential tools for database management, agencies within the Sonoran Desert will have a means for standardizing fire history information. By utilizing the power of the Internet and establishing a dynamic switchboard of interagency and regional information, a central source of fire data will be at the finger tips of fire managers, scientists and the like.

Acknowledgments

I wish to acknowledge the guidance and support provided by Todd C. Esque, Craig Wissler, Michael Kunzmann, Myles M. Flynn, Michelle M. Hawks, David W. Anning, Rick Anderson, and Chuck Scott. I am also greatly indebted to Michelle Nijhuis, Ann McLuckie, Tom Barett, Sarah Von Schrader and Andrea Butterworth for their diligent patience and participation in populating the HFED database, and assistance in creating ArcInfo coverages.

Literature Cited

1. Bahre, C. J. Wildfire in southeastern Arizona between 1859 and 1890. Desert Plants. 1985; 7(4):190-194.

2. Cave, G. H. and D. T. Patten. Short-term vegetation responses to fire in the upper Sonoran Desert. Journal of Range Management. 1984; 37(6):491-496.

3. D'Antonia, C. M. and P. M. Vitousek. Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annual Review of Ecology and Systematics. 1992; 23:63-87.

4. Humphrey, R. R. Fire in the deserts and desert grasslands of North America. in: T.T. Kozlowki and C.E. Ahlgren (eds.). Fire and Ecosystems. New York: Academic Press; 1974; pp. 366-400.

5. ---. The role of fire in the desert and desert grassland areas of Arizona. Proceedings of the Tall Timbers Fire Ecology Conference; 1963: 45-62.

6. Judd, B. I. et al. The lethal decline of mesquite on the Casa Grande National Monument. Great Basin Naturalist. 1971; 31:153-159.

7. McAuliffe, J. R. The aftermath of wildfire in the Sonoran Desert. The Sonoran Quarterly. 1995; 49(3):4-8.

8. ---. Burning Issues in the Sonoran Desert. Bajada. 1997; 5(2):12-13.

9. McLaughlin, S. P. and J. E. Bowers. Effects of wildfire on a Sonoran Desert plant community. Ecology. 1982; 63(1):246-248.

10. Phillips, W. S. Fire and vegetation of arid lands. Proceedings of the Tall Timbers Fire Ecology Conference; 1962: 81-93.

11. Rogers, G. F. Mortality of burned Cereus giganteus. Ecology. 1985; 66(2):630-632.

12. Rogers, G. F. and J. Steele. Sonoran Desert Fire Ecology. Proceedings of the Fire History Workshop; 1980; Tucson, Arizona. University of Arizona: 15-19.

13. Rogers, G. F. and M. K. Vint. Winter precipitation and fire in the Sonoran Desert. Journal of Arid Environments. 1987; 13:47-52.

14. Schmid, M. K. and G. F. Rogers. Trends in fire occurence in the Arizona upland subdivision of the Sonoran Desert, 1955-1983. The Southwestern Naturalist. 1988; 33(4):437-444.

15. Shreve, F. Ecological aspects of the deserts of California. Ecology. 1925; 6(93-103).

16. ---. Vegetation and flora of the Sonoran Desert. Vol 1 Vegetation. Washington, DC: Carnegie Institute; 1951.

17. Steenberg, W. F. and C. H. Lowe. Ecology of the Saguaro: II. Reproduction, Germination, Establishment, Growth and Survival of the Young Plant. US National Park Service, Science Monograph Series No 8; 1977.

18. Steenbergh, W. F. and C. H. Lowe. Critical factors during the first years of life of the saguaro (Cereus giganteus) at Saguaro National Monument, Arizona. Ecology. 1969; 50(5):825-834.

19. Steenbergh, W. F. and P. L. Warren. Preliminary ecological investigation of natural community status at Organ Pipe Cactus National Monument. Cooperative National Park Resources Studies Unit. 1977; Technical report no. 3, National Park Service contract no. CX 8000-4-0033. 1-152.

20. Thomas, P. A. Response of succulents to fire: a review. International Journal of Wildland Fire . 1991; 1(1):11-22.

21. Thomas, P. A. and P. Goodson. How do succulents cope with fire? British Cactus and Succulent Journal. 1986; 4(4):111-112.

22. Wilson, R. C. M. G. Narog A. L. Koonce and B. M. Corcoran. Postfire regeneration in Arizona's giant saguaro shrub community. Biodiversity and Management of the Madrean Archipelago: The sky islands of southwestern United States and northwestern Mexico; 1994 Sep 19-1994 Sep 23; Tucson, Arizona. USDA Forest Service; 1995: 424-431.

Author Information

Pamela J. Swantek, Graduate Assistant, USGS Cooperative Park Studies Unit, BioSciences East Room 125, The University of Arizona Tucson, Arizona 85721. (520)621-1174 phone, (520)670-5001 fax, email: swantek@u.arizona.edu

William L. Halvorson, Unit Leader, USGS Cooperative Park Studies Unit, BioSciences East Room 125, The University of Arizona Tucson, Arizona 85721. (520)670-6885 phone, (520)670-5001 fax, email: halvor@srnr.arizona.edu

Cecil R. Schwalbe, Research Ecologist, USGS Cooperative Park Studies Unit, BioSciences East Room 125, The University of Arizona Tucson, Arizona 85721. (520)621-5508 phone, (520)670-5001 fax, email: cecils@srnr.arizona.edu