SHORT-TERM MONITORING OF HARDWOOD RANGELANDS
CDF has monitored oak harvest activities on hardwood rangelands for several years as a part of its IHRMP responsibilities. The objectives of these efforts have been to (1) provide short-term information on statewide availability and condition of hardwood range resources, (2) to identify localized harvest pressures and potential adverse impacts, and (3) to identify opportunities for educational intervention or follow-up research.
Early efforts relied on written reports, largely from casual, ground level observation. While these reports provided some very valuable information and opportunities for input by die public, it was not clear that these reports could provide consistent statewide coverage. Therefore in 1989, CDF added an aerial monitoring program to locate oak cutting sites in wildland areas and to characterize the type and intensity of harvest activities. CDF did not attempt to monitor development, since other methods are being used which should be more accurate and efficient.
Methods
The areas to be flown were identified using hardwood maps produced for CDF from 1981/82 aerial photos. The areas had 10% or more tree canopy cover by oak species such as blue, interior live, Engelmann, coast live, and valley oak. They generally excluded montane hardwood types (black oak, tanoak and madrone) except in areas, such as the north coast, where montane species were intermixed with hardwood range species.
Thirty-seven and 36 counties were flown in 1989/90 and 1991, respectively. These counties contained about 9 million acres or 93% of the non-montane hardwood types according to CDF maps. In general, counties with 50,000 acres or more of oak woodland were flown. Incorporated or urbanized areas in these counties were not monitored, nor were federal lands which have policies prohibiting or limiting harvest of living oak trees.
Cuts of ten acres or more were monitored, since it was assumed that these reflected commercial operations and that small firewood cuts for personal use do not produce significant adverse habitat impacts in most instances. Counties were flown during December 1989 and June 1990, and January-March 199 1, using fixed-wing aircraft flying from 1,500 to 3,000 feet elevation. Observers (1) located sites, 10 acres or larger, of hardwood range oak species which were being harvested or had been harvested over the past 12 months, (2) estimated the total acreage harvested for that year, and (3) estimated preceding tree canopy in percent cover (based on adjacent areas or the observer's knowledge of the area) and residual canopy cover (after harvesting). Generally, two or three observers were used to locate the cuts, and cover estimates were generated by averaging the estimates of the observers.
Results
Table 9 summarizes data for the two evaluation periods. Total harvests observed for wildland and agricultural operations in 1989-90 and 1991 were 8,461 and 5,610 acres, respectively. This represents 0.14% and 0.09%, or about one-tenth of one percent, of hardwood range areas with 10% or more canopy cover. Average sizes of reported harvest sites were 113 and 165 acres.
Average absolute tree canopy cover left after harvest for a given harvest site was 14% the first year and 11% the second. This represented about 80% average removal of the original canopy per site. When agricultural conversions to crops were excluded to examine land uses which retain the wildland use of the land, average residual canopies were about 16% and 14%, and canopy removal rates decreased to 63% and 77%. Additional weighted averages will be generated to reflect the total acres in various canopy classes.
Table 9. Oak tree removal in the years 1989-90, and 1991.
| Statewide Harvest Data: |
1989-90 |
1991 |
| Number of harvests sites |
75 |
34 |
| Total acres |
8,461 |
5,610 |
| Average cut size (acres) |
113 |
165 |
| Avg % canopy cover by residual trees |
14(16*) |
11(14*) |
| Percent of original canopy removed |
79 (63*) |
81(77*) |
(*Excludes sites cleared for conversion to croplands.)
Discussion of Results
Regional and county-based statistics are also available. Statewide harvested acres appear to have decreased in 1991, which was surprising since an increase in activity was expected due to anticipated effects of the gulf war on oil prices. Numerous factors may contribute to decreased firewood harvest, including alternate wood supplies (i.e. orchard wood), high livestock market values, increasing harvest ordinances, and air quality concerns.
Some known harvest sites were missed, probably due to inadequate coverage of the area or to low intensity canopy removal. Follow-up will be done for additional areas to verify and supplement results. Also, harvests in locally significant valley oak stands were probably not reported in this study due to the 10 acre size minimum and the restriction to areas with 10% or more canopy cover.
Regional differences in harvest areas were observed. Counties in CDF Region II (North-Central California), which retain their rural character and rely heavily on natural resource-based economies, had the most numerous and largest operations, and also some of the heaviest harvests. The more intensive canopy removal may reflect the increasing benefits of oak canopy reduction on forage production in northern California, as compared with southern California where forage production levels out once the canopy has been reduced to about 50% cover. Harvest activities in CDF Region I (North Coastal California) were mostly vineyard conversions. CDF Region III (Central and Southern Sierra Nevada) has relatively high land values, healthy economies, and more ordinances which probably result in providing less incentive to harvest firewood. There is, however, an increasing number of vineyard conversions, reducing the size of cuts.
Conclusions
The aerial monitoring method has been very effective when the area is adequately gridded. Harvest activity indicators such as canopy reduction, slash piles, truck and trailer tracks, and stacked wood are quite easy to see at 2,000 ft above ground. If desired, sites smaller than ten acres can also be detected using tight grids.
The percent of the hardwood range area being harvested, about one-tenth of one percent, is very small. Whether this could significantly impact habitat over the long term depends on whether these areas regenerate. Other localized impacts may include erosion and water quality impacts when cutover areas cover large acreage. This study provides opportunities for research on natural regeneration in areas where canopies have been removed.
Plans are to monitor oak harvesting for at least one more year. CDF will also be working with data from the Department of Conservation to monitor agricultural conversions more closely and to monitor hardwood range conversions to development.
