Logging Impacts

Logging Truck Logging operations on the national forests of the Sierra Nevada continue to have a significant detrimental impact on the ecological health of these vital forest systems. Nevertheless, we also know that in some cases a responsible thinning operation is needed to reduce the fuel profile to promote fire resiliency. A fire resilient forest is one that can survive regular fire, as these forests once did before the era of intensive logging and fire suppression.

However, irresponsible and misguided logging prescriptions are not only bad public policy but are also likely to degrade the ecosystem functions of our national forests, increasing the likelihood of future severe fires, increasing greenhouse gas emissions, and impacting other resource values. Below are some of the negative impacts that logging operations can have on the forests of the Sierra Nevada.

Impacts of Road Building

Road building during logging operations directly leads to many negative consequences for wildlife, aquatic health, and the ecological integrity of the forest. Roads fragment and divided the forest, creating barriers for wildlife dispersal and migration. Many species are unable to cross these barriers and therefore have their range and distribution altered, oftentimes leading to drastic consequences on a local scale. There are more miles of roads in our national forest system than in the rest of the entire continent.

The creation of logging roads also greatly impacts the aquatic systems on the forest by introducing increased erosion and sedimentation into the area. Roads break-up the existing soil and remove the ground cover that assists in the natural distribution of rainfall and runoff. Roads direct and increase the runoff of soils into area streams and rivers adding a high volume of sediment and pollutants onto these watersheds. Aquatic species dependent on clean, clear water, are greatly impacted by this sudden change to the aquatic environment.

Road creation also leads to the increased prevalence of non-native species and diseases. The increased traffic and activity on these logging roads allows for the introduction of invasive species which can quickly overrun native species and thus greatly altering the natural balance of the forest ecosystem. Roads also serve as vectors for the spread of disease by allow an easy access point for a potential threat that otherwise would not have been able to access this intact forest.

Watersheds and Aquatic Environments

Logging activities have numerous impacts on aquatic systems in the Sierra Nevada. The end result of logged landscapes is a highly altered forest system which creates significant problems related to erosion, sedimentation and altered stream flow patterns. Logging removes large trees that normally fall into streams and provide shelter and thermal cover, raises water temperatures and pH, and degrades the chemical and ecological conditions and food webs that fish need to survive. Logging and the roads created to facilitate logging also significantly degrade stream ecosystems by introducing high volumes of sediment into streams, changing natural streamflow patterns, and altering stream channel morphology. Areas that have been logged are far more likely to suffer from major landslides and erosion events which deposit abnormally high levels of sediment into area streams. Roads, ditches, and newly created gullies form new, large networks of flow paths across the landscape. These logged areas therefore, sustain much higher discharge volumes after a storm event than they ever did when the forest was intact.

The changes in stream habitat caused by this increase in sediment loads greatly affects the health of aquatic organisms. The survival rates of many fish species are known to significantly decrease as fine sediment levels and temperatures in the water increase. The deposition of fine sediment on the stream bed degrades spawning areas, reduces pool refuge habitat, decreases winter refuge areas for juveniles, and impedes feeding visibility. Likewise, sensitive amphibian and invertebrate species are also adversely affected by increased sediment loads, decreasing in abundance and diversity as sediment levels rise. The drastic changes in the health of aquatic species brought on by logging has far reaching impacts for general forest ecology as well. Invertebrates, amphibians, and fish are important prey species for many mammals, birds and bats that are vital to the biological integrity of the forest.


Clearcut Logging in the Sierra Nevada has a devastating effect of the health of the soils of the forest. Forest soils serve as the primary building block of the entire forest ecosystem. The road construction which occurs during logging operations leads to compacted soils, disturbed organic layers, and excessive rates of soil erosion. Soil compaction which can last for decades restricts root growth and greatly minimizes the nutrients available to vegetation in these areas. Soil compaction also reduces the oxygen and water available to vegetation and has a significant detrimental effect on microorganisms found in the soil. The loss of organic layers affects mycorrhizal fungi, which are important to many tree species in accessing nutrients. As a result of this damage to vital soil resources, trees suffer from moisture stress, reduced growth rates, inability to establish seedlings, and reduced resilience in the long term.

Compacted soils are also much more susceptible to surface erosion. The frequency of erosion events, such as debris slides, increases in areas that have logged and therefore roaded. Total soil loss in logged forests is significant and continues well beyond the initial road construction and logging operations. Runoff and increase surface flow will persist in areas that have been logged for years, ensuring that increased sediment loads reach local streams and rivers, greatly impacting aquatic systems and species. This loss of nutrient rich soils impacts the forest ecosystem for decades after a logging operation occurs.

Disturbed soils also promote establishment of invasive non-native plant species. Logging skid trails and landings are typically covered with invasive weed species such as Scotch broom, yellow starthistle, bull thistle, wooly mullein, and cheat grass in the Sierra Nevada.

Biological Diversity

The logging program on our national forests often centers around an even-aged management protocol. This approach to forest management directly reduces the biodiversity on a forest by encouraging a plantation-like prescription to recently logged landscapes. As long as our forests are managed with a goal of timber production and not with the goal of ecosystem health, we will continue to see a decrease in the biological diversity of our forests.

Logging programs as they are currently operating promote species extinction by homogenizing the forest and introducing non-native species which compete for forest resources. Biologically vital and threatened habitats such as old-growth forests are still targeted by logging operations even though these habitats offer a haven where many old-growth dependent species reach their highest population levels. The viability of species found throughout the Sierra Nevada in habitats such as old-growth depends upon the cessation of logging in these areas which provide immeasurable ecological benefits to biological diversity.

Introduction of Disease

Logging increases the likelihood of the introduction and spread of lethal tree diseases through a variety of methods. Stumps left behind after logging operations have a much higher incidence of infection than do living trees. Once a disease enters an area through a stump it is likely to spread to surrounding trees that otherwise would not have been exposed to such threat. The debris left behind after logging operations, often referred to as slash, also invite disease and insect pests.

Trees that are stressed by disease are more susceptible to attack by bark beetles and other insects. While insect infestation within a forest is for the most part a natural aspect of forest ecology, the spread of certain infestations can have a serious impact on the health of an individual tree species and a forest as a whole. Biologists predict that logging and the subsequent habitat destruction will increase the severity of a variety of insect outbreaks because the loss of habitat diversity and old-growth forest has meant a decrease in the diversity of natural pest predators. The natural predators of many of these pest insects are found within a healthy forest. Once the integrity of the forest is shattered these natural predators may not be around to deal with the pests which have been introduced due to those very operations which removed the predators.

Introduction of Invasive Species

The creation of roads, along with the intense activity conducted throughout a logging operation, greatly increases the possibility of the introduction of non-native species into areas where they have previously not existed. Logging operations are generally conducted over the course of weeks, not days. These logged forests and the areas surrounding them are visited hundreds of times during the operations by logging trucks, water trucks, administrative vehicles, herbicide trucks, and so on. All of these trips into these newly exposed areas greatly increase the likelihood of an invasive species being introduced into an area which is ill-prepared for its detrimental effects. Not only can vehicles transport the seeds of non-native plants to these areas but the reduction of canopy cover along with disturbed soils allow these species a chance to take root and begin competing with native species for limited resources.

Invasive species disrupt natural ecosystem processes and the native species that have depended upon them for millennia. Non-native plants are exceptionally effective at out-competing native species and replacing the understory vegetation of a forest. These species often cause an increase in fire risk, higher erosion rates, and a decline in the vegetation utilized by wildlife species for food, habitat, and cover.

Habitat Fragmentation

As mentioned above in the section dealing with roads, logging operations can greatly impact the connectivity of habitat and lead to a fragmented forest which leaves many species on an island and unable to migrate from an ideal feeding ground to their denning locations for example.

Separate from the creation of roads, logging operations also lead to habitat fragmentation by changing large areas of forest from one highly utilized habitat type to another that may be less useful to a certain species. The open spaces and edges created during logging operations inhibit movement by many wildlife species that were otherwise at home in the preexisting forest landscape. Species that typically live in the forest interior which has higher levels of old-growth and mature forest will find themselves having to adjust to conditions that are no longer compatible with their natural habitat needs. In the Sierra Nevada, a species such as the American marten or Northern flying squirrel will have a difficult time adapting to and recovering from a logged forest which has reduced the forest characteristics required for their survival. Scientific research is also quite convincing in documenting the impact of logging on the habitat needs of many bird species. The edges created by logging operations can introduce rarely encountered predators and competitors for resources.

Forest Structure

Logging operations greatly alter the natural structure of a forest by changing the amount of downed woody material, the incidence of snags or standing dead trees with cavities that provide wildlife habitat, and reducing the canopy cover of the immediate area, with the result of a homogenized or less diverse forest structure. A reduction in canopy cover also increases the amount of sunlight reaching the forest floor which can reduce the moisture content of the forest. Many aspects of forest health are impacted by this including a change in local conditions such as air temperature and wind patterns, and an alteration in the behavior and distribution of wildlife species that require the conditions of a closed canopy forest.

The change in the amount of downed woody material also impacts forest ecology by removing dying and decaying logs and stumps which serve as habitat and help maintain the natural structure of the forest floor. Removal of these important legacy materials along with the opened canopy increases the temperature of the forest and leads to an altered ecological system including patterns of fire and fire behavior.

Wildfire Risk

According to the Sierra Nevada Ecosystem Project's (SNEP) report in 1996, "Timber harvest, through its effects on forest structure, local microclimate, and fuels accumulation, has increased fire severity more than any other recent human activity. If not accompanied by adequate reduction of fuels, logging (including salvage of dead and dying trees) increases fire hazard by increasing surface dead fuels and changing the local microclimate. Fire intensity and expected fire spread rates thus increase locally and in areas adjacent to harvest." This conclusion supports the consensus view of fire ecologists that logging operations greatly increase the fire risk on a forest.

In addition, plantations that are planted with densely packed, single species conifers after clearcut or salvage logging also contribute to additional wildfire risk. The structure of these even aged tree farms are among the most fire prone configuration in the forests. Plantation management also requires an increase in fire suppression, because managers need to protect the investment. This leads to a vicious cycle of unnatural fire regimes, the build-up of fuels, and the inevitable return of large forest fires with devastating consequences. Such practices interrupt the natural fire regime, leading ultimately to higher carbon emissions that contribute to global warming.

Read more about the relationship of fire to forest ecology here on our website.

Global Warming

Logging old forests also contributes to global warming through removing significant sources of sequestered carbon. After logging, the local microclimate is also altered, resulting in hotter and drier conditions which contribute to increased fire hazard. These and other types of feedback loops can hasten rapid climate change. Research shows that old-growth forests in the Northern Hemisphere sequester large amounts of carbon for many centuries, whereas the disturbance associated with logging and planting conifer monocultures creates net carbon emissions for decades. When added together, the cumulative impacts of logging in the Sierra Nevada as currently practiced is not sustainable and if allowed to continue, will endanger not only the fish and wildlife, plants and ecology of the region, but will harm human health and welfare as well.

Read more about the relationship between forest management and global warming, here on our website.

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