Chapter 6: A Summary of Current Ecosystem Conditions

"...a society and its biophysical environment are interactive, interadaptive, and interdependent in a single biosocial system of constant mutual adjustment."

R.W. Behan, 1995

This chapter documents the current status of selected ecosystem indicators for forests and woodlands of the Southwest. The integration and interpretation of these indicators from the conditions described in chapters 3 to 5 provide both a summary for specific biotic communities and a statement of professional expertise and judgment of the team. Ecosystem conditions in this chapter are defined by the following questions:

1. Is adequate provision made for the conservation of biological diversity? The maintenance of biodiversity includes, at a broad scale, maintaining the composition and arrangement of species and ecosystems across the landscape and, at a lower level of organization, maintaining the diversity of gene pools within a species. Diversity is important in forested ecosystems because a loss of species is associated with an increased potential for species extinction or genetic loss of species with known or unforeseen ecological or societal value. Also, diverse ecosystems may be less susceptible to devastation by disturbance events.
2. Is ecosystem integrity and resilience maintained in the long term? These are respectively defined as the ability of the ecosystem: (a) to maintain vital ecological processes, such as energy flows, nutrient cycling, hydrologic cycling, soil development, plant community succession, animal population movements (i.e., migration), and unimpaired flow of genetic material at rates within the range of historic variability and (b) to recover biotic integrity following disturbance.
3. Are human needs for ecosystem resource use and landscape occupancy being adequately accommodated?

WOODLANDS

Biological Diversity

• A decreased diversity in grasses and forbs has resulted from less frequent burning than the historic fire regime.
• Herbivore use is above historic levels (prior to Territorial Period), resulting in decreased biotic and genetic diversity in native species.
• Past land disturbances have permitted increases in introduction and establishment of exotic species.

Integrity and Resilience

• Soil erosion today is greater than in the past, resulting in decreased upland site productivity.
• Soil infiltration rates are below historic levels, resulting in greater overland flows, higher peak flows, reduced length of base flows in intermittent streams, and more confinement of channels.
• Some wildlife populations such as pronghorn have been isolated because of the construction of major highways.
• Culling of dying, standing dead, and downed pinyon and juniper trees through fuelwood gathering and salvage operations has reduced available snags and downed logs needed by many species of wildlife (e.g., insects, woodpeckers, bats, nuthatches, titmice, small rodents, and many reptiles). Opportunities are also lost for other benefits, such as the release of nutrients to the soil and increased plant growth adjacent to these structures.
• Stock tanks and ponds provide for increased habitat for species such as woodpeckers, frogs, elk, bats, and other animals. These waters not only provide water for wildlife, but also attract insects, a source of food, and help disperse populations of wildlife.

Human Needs and Uses

• Coniferous woodlands have changed from a visually diverse mosaic of tree-covered patches and corridors to a matrix of trees with more homogeneous tree cover and reduced overall scenic diversity and quality.
• Roads and utility corridors have changed the appearance of the landscape by adding foreign line elements that span wide areas.
• Past attempts at improving grazing conditions through chaining and pushing resulted in some large, geometric, linear, unnatural-looking patterns on the landscape.
• Controversies resulting from resource allocations between threatened species and traditional community uses, such as firewood gathering, have resulted in disputes between cultures.
• Woodlands are especially rich in heritage sites which have been susceptible to damage from human activities and natural processes such as erosion.

PONDEROSA PINE

Biological Diversity

• Because of changes in fire regime and forest management, there have been significant changes in the diversity of vegetation and wildlife. Many well-spaced groups of large yellow-bark ponderosa pine have been replaced with closed thickets of small, blackjack ponderosa pine or with mesic mixed conifer species.
• These changes have been accompanied by decreased diversity of grasses, forbs, and shrubs and by increased levels of surface organic material.
• Although wildlife species (some small mammals) that benefit from increases in mixed conifer or surface litter are more abundant, many other species dependent on open stands and large trees, and especially on large snags (cavity-dwelling birds and mammals), are found in fewer areas.
• Overall, the loss of large ponderosa pine trees has resulted in a reduction of vegetation and wildlife diversity.

Integrity and Resilience

• Reductions in low-intensity fires, changes in species composition, and increases in stand density have altered both physical and biotic processes in ponderosa pine forests.
• Mortality of large trees by dwarf mistletoe, root disease fungi, bark beetles, and wildfire has replaced the understory thinning action of low-intensity ground fires as the principal forest disturbance.
• In general, the scale at which tree death and regeneration occurs has been altered from that of the rare loss of mature individuals (appearing as a constant, uniform change) to more common destruction of groups of trees (appearing as a more variable or chaotic change).
• Impacts from grazing and browsing of livestock and wildlife have resulted in decreased watershed cover and riparian stability in some areas.

Human Needs and Uses

• Ponderosa pine forests have changed from a grass matrix with individuals, clumps, and stringers of various-sized trees (many large), to stands of mostly smaller trees with only an occasional grassy opening. Large trees are no longer found in well-spaced, open groves, but primarily as individuals, surrounded by smaller trees. The visual depth of forest landscapes has decreased due to these changes.
• Increased road densities have resulted in more visual opportunities, but also more visually displeasing road scars.
• Tree decline and mortality due to increased dwarf mistletoe infestations have negatively affected aesthetic qualities at recreation sites and within visual corridors.
• Increased dwarf mistletoe infestations have had a negative effect on timber production.
• Mortality of trees from pine bark beetle outbreaks has resulted in lost opportunities for timber production in the Sacramento Mountains. Outbreaks have occurred in dense stands of ponderosa pine primarily affecting trees of low-vigor, i.e., highly-stressed trees.
• Competition for forage and water between cattle and elk has created controversy over appropriate resource use.
• Controversy over resource allocations between threatened species and timber harvesting has resulted in reduced viability for forest-dependent industries and increased demands for protection.
• Urban development in forested ecosystems has increased risks related to fire.
• Sulfate aerosols and other fine particles and gases in the atmosphere have impaired scenic vistas.
• Scenic and recreation values and expectations are often in conflict with extractive uses and timber management activities.

MIXED CONIFER

Biological Diversity

• The increase in mixed conifer acreage is likely to have slightly increased the diversity of vegetation types and possibly the diversity of wildlife species in some areas.
• With the decline of the aspen component in the mixed conifer, a broadleaf component that is important to some invertebrates such as the western tiger swallowtail and red-spotted purple butterflies is reduced.
• Populations of some bird species have increased due to increased spruce budworm infestations.
• Habitat for cavity-nesting birds has increased following spruce budworm infestations.

Integrity and Resilience

• Due to widespread harvests and fire suppression, younger, multi-storied stands composed of more shade-tolerant trees are more common and more susceptible to western spruce budworm attacks. Sustained heavy defoliation by budworm has resulted in decreased growth, tree deformity, top killing and death. Stand level effects include changes in stand structure, reduction of understory, and a composition shift toward nonhost or less susceptible species.
• Spruce budworm infestations have decreased thermal cover and forage for wildlife but sometimes have increased water yield.
• Forest openings are fewer and smaller than in the past, resulting in reduced snow accumulation and faster spring snow-melt.
• The risks of acidification of high-elevation lakes have increased due to high sulfur or nitrogen deposition. Ozone toxicity to plants, particularly near urban areas, is a concern.

Human Needs and Uses

• The visual diversity in the mixed conifer forests has decreased due to reduced regeneration of aspen stands. Seasonal color and textural contrasts between aspen and conifer have been reduced.
• Due to western spruce budworm infestations, visual quality and recreation use has been affected. Heavy defoliation, discoloration, top-killing, and tree mortality has reduced the visual quality of scenic corridors and heavily used recreation areas. In addition, the presence of large numbers of larvae has been a nuisance in campgrounds, picnic sites, and summer home areas.
• Sulfate aerosols and other fine particles and gases in the atmosphere have impaired scenic vistas.

SPRUCE–FIR

Biological Diversity, Integrity, and Resilience

• Relative to other vegetation communities, little change has occurred in these communities.
• The risks of acidification of high elevation lakes have increased due to high sulfur or nitrogen deposition.
• Ozone toxicity to plants, particularly near urban areas, is a concern.

Human Needs and Uses

• Installations, such as radio towers, microwave facilities, and ski lifts, are the most notable visual changes to the spruce–fir and alpine meadow visual characteristics.
• Sulfate aerosols and other fine particles and gases in the atmosphere have impaired scenic vistas.
• Mountain peaks hold special cultural and religious value for many Southwestern Indian tribes giving rise to conflicts between traditional uses and other uses and development.

ASPEN

Biological Diversity

• There has been a 46 percent decline in the aspen cover type between 1962 and 1986, representing a loss of biodiversity at the landscape level.

Integrity and Resilience

• Aspen regeneration has declined due to continued elk browsing of aspen sprouts, resulting in the death of the sucker root system.
• With the loss of the aspen component in the mixed conifer, we are losing a broadleaf component that is important to some invertebrates such as the western tiger swallowtail and red-spotted purple butterflies.

Human Needs and Uses

• People are concerned about the loss of aspen as they are valued for their scenic beauty. They are also excellent sites for viewing wildlife and wildflowers.
• In many of the mountain towns and villages of northern New Mexico and Arizona, homes are still heated with aspen.
• Many rural people continue to depend on the sale of aspen wood products for part of their livelihoods.

MONTANE RIPARIAN WETLANDS

Biological Diversity

• Grazing and browsing in riparian areas have resulted in decreased diversity and cover in riparian vegetation.
• The number of impoundments and diversions and the level of grazing is greater than in the past, resulting in increases in the number and extent of exotic species in riparian areas.

Integrity and Resilience

• Riparian corridors have been interrupted due to grazing and agricultural practices, resulting in decreased wildlife movement corridors, increased water temperatures, and decreased transport of organic materials.
• Disturbance due to flooding has been reduced below historic levels, resulting in decreased potentials for regeneration and reduced biomass production from native species. Channel stability has also changed due to reduced vegetative cover and changes in sediment transport.
• The risks of acidification of high elevation lakes have increased due to high sulfur or nitrogen deposition. Ozone toxicity to plants, particularly near urban areas, is a concern.

Human Needs and Uses

• Riparian uses such as grazing, recreation, and agriculture frequently result in water quality not meeting standards for designated beneficial uses.
• Grazing and browsing in riparian areas has had a negative effect on scenic qualities and recreation experiences in some areas.
• Increasing competition for scarce water resources has resulted in conflicts between traditional uses, such as community acequias, and other uses and developments.

FLOODPLAIN–PLAINS RIPARIAN WETLANDS

Biological Diversity

• Riparian area structure and composition have changed due to irrigation diversions, reservoirs, farming, grazing, and human settlement. Consequently, some species diversity has been lost, and channel functions such as sediment transport have changed.
• Due to changes in larger river channel dynamics, many of the native fish species have been lost.

Integrity and Resilience

• Riparian corridors have been interrupted due to grazing, agriculture, recreation, industrial, and urban uses, resulting in decreased wildlife corridors, increased water temperatures, increased sediment transport, and decreased transport of organic materials.
• Due to channel confinement and floodplain constrictions, peak flows have been frequently higher, velocity has been increased, and flood residence time has decreased, thus decreasing groundwater recharge.
• Disturbance due to flooding has been reduced below historic levels, resulting in decreased potential for regeneration of native species and reduced biomass production from native species. Channel stability has also changed due to reduced vegetative cover and changes in sediment transport.
• Agricultural conversion, livestock grazing, invasion of exotic plants, structural alterations of habitats, pollution, and replacement of native cottonwood, willow, mesquite, and marshes by urban environments and croplands have influenced the availability of foraging, breeding, and wintering habitats and food resources for migratory birds. These impacts have also altered the composition, structure, and dynamics of plant and animal communities in riparian ecosystems.
• Increased presence of saltcedar has resulted in increasingly drier riparian systems. The salt residue in the leaf litter tends to prevent native plants from re-establishing. Dense saltcedar thickets form barriers to wildlife, livestock, and human access to water. Bird species richness and abundance in saltcedar-dominated communities are substantially lower than in native plant communities.
• The spread of saltcedar and other exotic woody ornamentals such as Russian-olive and Siberian elm has resulted in the creation of new plant communities with different vertical and horizontal layers, understory species composition, age class distribution, and mixes of native and exotic overstory species.

Human Needs and Uses

• Use of riparian areas, such as grazing, recreation, agriculture, industrial, and urban uses has frequently resulted in water quality not meeting standards for designated beneficial uses.
• American Indian communities along the Colorado River and in northern Mexico have been concerned that their mesquite is not regenerating well enough to ensure sustained supplies for religious and commercial needs.

CONCLUSION

The history of human occupation in the Southwest has resulted in many changes that are pervasive across all provinces. Many forest health issues are problems at scale levels below the province level. However, at a broad analysis resolution, we can address the following questions on the status of forest ecosystems:

Is Adequate Provision Being Made for the Conservation of Biological Diversity?

Species numbers for many species that are intensively managed appear to be stable or even increasing. However, the population dynamics of many less intensively managed species are unknown; others are considered to be on the decline. Habitat fragmentation of the landscape appears to have increasingly isolated many plant and animal populations to the degree that their long-term viability is in question. As intensive human use of ecosystem resources increases with a corresponding rise in our population, the survival of these species will remain in doubt.

Is Ecosystem Integrity and Resilience Being Maintained in the Long Term?

Generally, yes. However, in certain ecosystems such as deciduous riparian forests along major rivers, integrity and resilience has declined to a degree that seriously jeopardizes ecosystem structure and function. Similar degradation has occurred in coniferous woodlands (pinyon–juniper), where loss of understory plant cover has greatly accelerated soil erosion rates beyond historical levels. In coniferous forests (i.e., ponderosa pine), stand structure has changed to conditions that place these forests increasingly at risk of loss from catastrophic (stand replacement) fires than in past time periods.

Are Human Needs for Ecosystem Resource Use and Landscape Occupancy Being Adequately Accommodated?

Human population has been growing and human interest in and demands upon ecosystem resources have expanded and caused a geometric rise in pressure upon the landscape. Increased human occupancy of the land has resulted in greater numbers of people being adversely impacted by disasters such as fires and floods. Increasing human presence upon and use of the land by a wide variety of groups often holding contrasting views and values concerning the land have resulted in a heightened degree of conflict. This is especially true between groups who favor traditional utilitarian uses of the land and those for which preservation and protection are highest priorities. Traditional extractive uses of land resources have declined, resulting in the closing of forest-based industries. American Indian tribes are speaking out more forcefully on traditional cultural and religious concerns. The clash of cultures, whether rural versus urban or utilitarian versus protection, appears driven by our inability to resolve issues related to balancing the needs and desires of humans with the biological needs of nonhuman organisms in the ecosystem. Thus, it seems that human needs are inadequately accommodated.