Changed Southwestern Forests: Resource effects and management remedies (Page 3 of 3)

Author: Marlin A. Johnson. From a paper presented at the Forest Ecology Working Group session at the Society of American Foresters National Convention held in Albuquerque, New Mexico, November. 9-13, 1996.

Impacts of Dense Forests and High Fire Intensities on Other Values

Soil productivity

Dense Southwestern ponderosa pine forests may decrease available nitrogen (N) (Covington and Sackett, 1988). Accumulation of litter blocks recycling of organically bound N available for plant use in organic form. Since N is often a limiting factor, this may reduce productivity of ponderosa pine ecosystems. Where fires burn hottest, the greatest loss of volatile nutrients such as N also occurs (Covington and Sackett, 1988). While fire helps make N available, the duration of benefit is less than four years; therefore, fires must occur on a 2- or 3-year cycle to enhance N availability and productivity (Covington and Sackett, 1988).

Coarse woody debris (CWD) is essential for ectomycorrhizal activity. While too little will reduce productivity, so will too much. Optimum ranges presented by habitat type are most often exceeded in the Southwest in overly dense stands or following wildfires.

Fuller et al. (1955) report that high intensity fires consume much of the duff layer, exposing mineral soil to climatic elements that contribute to accelerated erosion. This makes difficult the reestablishment of many species of conifers. They also report that severe burning raises the pH level of the top two inches of soil by about one unit. Campbell et al, 1977) report that in the year following burning, runoff carried about 1.7 tons per acre of suspended and bedload sediment from severely burned watershed, as compared to a few pounds from the moderately and unburned watersheds. This affects both soil productivity and water quality. Growth on surviving trees will be lower due to crown scorch, and tree regeneration will often be reduced or absent. (Campbell et al, 1977). In some cases, the result of extremely hot fires is a change in the ecosystem from forest to brushfield (Covington et al, 1994).

Stream flow and water quality

The effects of more dense forests on stream flow is well documented. At Beaver Creek on the Coconino National Forest, researchers found that in ponderosa pine forests, on either Brolliar or Siesta-Sponseller soils, stream flow changed as follows with changing basal area (BA) (USDA Forest Service, 1974):

Other researchers have also found increases in water yield after harvest to reduce vegetative density. At Workman Creek in Central Arizona, water yields increased with harvest (Rich and Gottfried, 1976). Baker (1986) found that increases at Beaver Creek diminish and then end in about seven years, due to water use from increased forage plants and young trees. However, a long-term cycle of harvest and prescribed fire should maintain much of the increase.

As discussed above, today's forests are even above the baseline density used in the Beaver Creek study. This shows that they are providing less water for fish, riparian areas, groundwater recharge and downstream users than were the pre-settlement forests.

The results of this are evident in other ways too. Today, streams in the SW that were perennial a century ago do not flow year-round. Low flows in other streams are lower than they once were, with some intermittent streams drying up much earlier in the year. Low flows in turn affect water temperature and are a critical factor for fish and other aquatic life. However, where prescribed natural fire has occurred three or more times in the last two decades in the Gila Wilderness, streams are now flowing again that had not flowed for many years (personal communication, Steve Servis.)

Forest fires also affect many hydrologic processes. A 1978 (USDA Forest Service, 1979) study summarized the following: Water repellency increases with fire intensity, with more intense fires having the most effect. While removing vegetation normally increases soil moisture, Campbell et al. (1977) observed reduced soil moisture in the upper 30 cm. in an area severely burned, due to the repellency after fire. Debris flows increase following severe fires (Jensen and Cole, 1965; Klock and Healvey, 1976). During heavy rains, Campbell et al. (1977) observed an eightfold increase in runoff from a severely burned watershed compared to an unburned watershed during heavy autumn rains. They also report that runoff efficiency (ROE), the ratio of runoff to precipitation, increased from 0.8 percent on an unburned watershed to 3.6 percent on a severely burned watershed. Compared to a moderately burned watershed, ROE on a severely burned watershed was 375 percent greater during the rain season and 51 percent less during the snow season.

Archaeological Resources

Archaeological sites are also affected by hot forest fires. At the Henry Fire site in the Jemez Mountains, no effects were found on lithic artifacts, and ceramic artifacts were lightly sooted on lightly or moderately burned sites. However, in heavily burned sites, severe effects were present on artifacts, construction materials, and ground stone (Lentz et al, 1996). They concluded that where no heavy fuels burn in place, fire effects may be confined to the surface. However, where there is increased fire residence time because of a log or other heavy fuel loads, subsurface artifacts can be severely affected.

Studies after the La Mesa fire of 1977 note several types of damage to archeological resources (Traylor et al, 1990). First, they found damage from fire suppression and rehabilitation. They also found that on-site vegetation intensified the burn and did more damage. They noted some of the fire's greatest damage was to tuff, the major construction material of Pajarito Plateau masonry sites. They feel that the damage to tuff alone is a good indicator of the severity of La Mesa Fire compared to past fires. Especially where fire burned hottest, they found exterior surfaces flaking off and cracking. On one severely burned site, building stones had significantly deteriorated, losing much of their interior strength. Stones were so weak that they could not hold their own weight.

Wildlife

Because of the highly varied environmental gradients and disturbance regimes, wildlife communities were diverse before settlement (Covington et al, 1994). Since then, some species have been extirpated, others have declined, and yet others increased in abundance. For example, antelope are believed to have declined as ponderosa pine forests became denser (personal communication, Dave Patton). Other species that prefer open forests and may have declined include Grace's Warbler, Rock Wren, Western Woodpewee, and Chipping Sparrow (Finch et al, 1977). Today's dense forests should favor red squirrels and Mexican spotted owls. Some feel snag-dependent species may have declined; however, inventories today indicate that there may still be more snags than there were in 1910 when Woolsey found about 0.2 snags per acre greater than 18" in diameter.

The Southwestern Region of the Forest Service has a wildlife data base called RMWILD. This shows which species and groups of species use various habitats. It is notable that each canopy closure category and stand structure is used by large numbers of species. However, during this century, the amounts of grass/forb/shrub, seed/sap, and zero- to 40-percent canopy closure have drastically declined. It could be inferred from this that species that prefer vegetative stages and densities that have declined may also have declined. However, more work is needed to determine what specific changes have occurred.

Susceptibility to insect and disease

Trees that are close together, like other organisms, are more susceptible to disease and to attack by insects than are wider-spaced trees (Sartwell and Stevens, 1975). This spacing was one mechanism that kept presettlement forests from being more severely attacked. Researchers have found that bark beetles, mountain pine beetle, Douglas-fir beetle, spruce budworm, and dwarf mistletoe are among those pests that expand as forests become more dense (Johnson 1994). Mistletoes were always present but were kept in check by recurring fire (Alexander and Hawksworth, 1975).

Management Needs for Sustainability

There is no one simple solution to returning Southwestern forests to healthy, sustainable conditions; many techniques must be used. And, these techniques must be applied in a patchwork of small and large blocks to create diversity, which has been largely lost over the past century (Pyne, 1996). Miller (1996) points out that a management philosophy is needed that incorporates a range of stand density and structure, and that activities must be carried out in a variety of block sizes. Following are some actions that can be used to treat these forests for sustainability:

Prescribed fire. Where prescribed fire can be properly controlled, it is a valuable tool in forest restoration. It is successfully used to reduce fuel loads and remove patches of trees.

Wildfire. Wildfires will occur. While some of the results will be negative, others will not and will help rectify the situation. For example, in many habitat types, they will help restore aspen to the ecosystem.

Thinning. Both pre-commercial and commercial thinning can reduce tree densities and, equally important, can remove or reduce lower canopy layers and thus reduce the likelihood of crown fire. Especially if done in a patchy pattern and in various size areas, it can greatly reduce homogeneity and enhance spatial and structural diversity (Edminister and Olsen, 1996). It proves useful in second-growth, even-aged stands, in overstocked, uneven-aged stands, and also in overstocked old-growth stands (Fiedler et al, 1996).

Harvests to mimic natural disturbances. Thinning and prescribed fire are most often mentioned when looking for ways to improve conditions in Southwestern forests. However, we have to consider how each habitat type functioned naturally to know if we can perpetuate a forest. Group selection may be most appropriate for ponderosa pine, but not mixed-conifer. Howe (1995) points out that single-tree or small-group selection can result in dysgenic effects to the long-term genetic makeup of forests that regenerated naturally as even-aged such as SW mixed-conifer forests. He also states that pioneer species can be maintained in an uneven-aged condition only with very low stocking. In the southwest, aspen and ponderosa pine on white and Douglas-fir habitat types could suffer in the long term with uneven-aged management unless stocking is maintained at low levels.

All of the above. In the end, we must give all of the above tools to the on-the-ground manager rather than establishing regional or national policies about using any one or a certain combination of them. Based on conditions on a landscape, and on individual sites within that landscape, decisions can be made to enhance that area's sustainability and productivity. I include productivity here because for eons, humans have counted on their forest lands to provide for their needs and most land owners continue to expect that. It can be done along with sustaining the long term health of the ecosystem (Johnson et al, in review).

Before many of these activities can be undertaken, socio-political change must occur. Prescriptive direction, such as the Mexican spotted owl (MSO) Recovery Plan and Northern Goshawk Guidelines, need to be adjusted or applied with flexibility considering pre-settlement condition and function of our forests. Where attitudes exist about meeting harvest targets in large trees, they must change. Current laws such as the Endangered Species Act (ESA), National Environmental Policy Act (NEPA), and National Forest Management Act (NFMA) can be used successfully by a handful of people to delay and stop activities that must be carried out. These laws were all passed with good intentions to provide protection for the environment, but change is needed in interpretations that, to date, have taken them beyond their authors' original intentions.

Conclusion

Forests in the SW have lost much of their diversity; they have far more trees today than ever before, an unsustainable condition. This leads to severe, stand-replacing fires, followed by damage to resource values and decreased soil productivity. Water, sometimes considered the gold of the SW, is being used by the dense tree stands, reducing stream flows. Stand-replacing fires will increase flooding rather than restore normal flows. Wildlife populations change, favoring one suite of species over another. Cultural resource sites are damaged and sometimes destroyed by the hot fires.

We know what needs to be done to improve the situation--thinning, prescribed burning, harvest to mimic natural disturbances, and a combination of these. Society has the resolve to suppress wildfires and provides hundreds of millions of dollars for this effort. This same resolve is needed to take the actions necessary to improve the health of our forests which in turn will reduce the need for firefighting. Power has been given to the few who want little to happen. This leads to future destruction of our forests if action is not taken soon.

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