Climate Change and...
Effects of Climate Change
- Climate Variability
- Climate Models
Effects of Climate Change
Dale, V. H., Joyce, L.A., McNulty, S., Neilson, R. P., Ayres, M. P., Flannigan, M. D., Hanson, P. J., Irland, L.C., Lugo, A.E., Peterson, C. J., Simberloff, D., Swanson, Frederick J., Stocks, B. J., Wotton, M. (2001). Climate change and forest disturbances. BioScience 51 (9): 723-734
INTRODUCTION: Studies of the effects of climate change on forests have focused on the ability of species to tolerate temperature and moisture changes and to disperse, but they have ignored the effects of disturbances caused by climate change (e.g., Ojima et al. 1991). Yet modeling studies indicate the importance of climate effects on disturbance regimes (He et al. 1999). Local, regional, and global changes in temperature and precipitation can influence the occurrence, timing, frequency, duration, extent, and intensity of disturbances (Baker 1995, Turner et al. 1998). Because trees can survive from decades to centuries and take years to become established, climate-change impacts are expressed in forests, in part, through alterations in disturbance regimes (Franklin et al. 1992, Dale et al. 2000).
Disturbances, both human-induced and natural, shape forest systems by influencing their composition, structure, and functional processes. Indeed, the forests of the United States are molded by their land-use and disturbance history. Within the United States, natural disturbances having the greatest effects on forests include fire, drought, introduced species, insect and pathogen outbreaks, hurricanes, windstorms, ice storms, and landslides (Figure 1). Each disturbance affects forests differently. Some cause large-scale tree mortality, whereas others affect community structure and organization without causing massive mortality (e.g., ground fires). Forest disturbances influence how much carbon is stored in trees or dead wood. All these natural disturbances interact with human-induced effects on the environment, such as air pollution and land-use change resulting from resource extraction, agriculture, urban and suburban expansion, and recreation. Some disturbances can be functions of both natural and human conditions (e.g., forest fire ignition and spread) (Figure 2).
Each disturbance has both social and economic effects (Table 1). Estimating the costs of each of these disturbances is very difficult; these estimates for the United States are illustrative only. Of the eight forest disturbances considered, ice storms are the least costly, averaging about $10 million and more than 180,000 ha annually (Michaels and Cherpack 1998). Insects and pathogens are the most expensive, with costs exceeding $2 billion and 20.4 million ha per year (USDA 1997). The socioeconomic aspects of these damages are only part of the cost. Costs of impacts to ecological services (e.g., water purification) can be large and long term.
This article examines how eight disturbances influence forest structure, composition, and function and how climate change may influence the severity, frequency, and magnitude of disturbances to forests. We focus on examples from the United States, although these influences occur worldwide. We also consider options for coping with disturbance under changing climate. This analysis points to specific research needs that should improve the understanding of how climate change affects forest disturbances.
This paper is one in a series developed by the forest sector of the US National Assessment of the Potential Consequences of Climate Variability and Change. In examining how forests may be affected by climate change, the Forest Sector Committee divided the topic into four areas (processes, diversity, disturbances, and socioeconomics), each of which is the focus of an article in this issue of BioScience. Impacts of climate changes on aquatic disturbances are critical, but this paper focuses on direct terrestrial impacts. The effects of a rise in sea level, coastal processes, and salinity on terrestrial systems are examined in the coastal sector of the national assessment (NAST 2000).
ABSTRACT: Climate change affects forests both directly and indirectly through disturbances. Disturbances are a natural and integral part of forest ecosystems, and climate change can alter these natural interactions. When disturbances exceed their natural range of variation, the change in forest structure and function may be extreme. Each disturbance affects forests differently. Some disturbances have tight interactions with the species and forest communities which can be disrupted by climate change. Impacts of disturbances and thus of climate change are seen over a board spectrum of spatial and temporal scales. Future observations, research, and tool development are needed to further understand the interactions between climate change and forest disturbances.
SUMMARY: On Independence Day, 1999, a storm system that originated over the Gulf of Mexico and passed through North Dakota dealt a severe blow to nearly half a million acres of the Superior National Forest in northern Minnesota. The blowdown, or derecho, packed winds exceeding 90 miles per hour and left in its wake downed and damaged trees and a dangerously high fuel load. Nearly half a million acres of forest were affected, primarily in the Boundary Waters Canoe Area Wilderness (BWCAW) and the Gunflint Trail Corridor, a strip of land in public and private ownership that supports a thriving tourist trade in the world’s premier canoe wilderness. Immediately after the blowdown, the Forest Service began to implement a strategy to reduce risks to life and property in the corridor. Within the BWCAW, some exceptions to the Wilderness Act regulating human activity in primitive areas were allowed in accordance with the Forest Service mandate to ensure wildfire does not exit the wilderness. Prescribed fire applied on strategic sites at the boundary of the wilderness area later proved successful at containing a wildfire in 2006, but a second, human-caused fire in 2007 caused significant damage to buildings in the corridor. A number of research projects comparing treatments allowed in the corridor, including salvage logging and prescribed fire, helped guide the long-term management plan for the area. Results are not always clear, however, and managers have to consider a number of tradeoffs, balancing the risks to life and property versus the overall health of an ecosystem and the flora and fauna that have evolved along with moderate to severe fire with a return interval of approximately 70 years. Moreover, as the climate warms, managers may confront more-frequent severe weather events that will challenge their ability to respond.
Mohan, J. E., Cox, R. M., Iverson, L. R. (2009). Composition and carbon dynamics of forests in northeastern North America in a future, warmer world.. Canadian Journal of Forest Research 39 (2): 213-230
ABSTRACT: Increasing temperatures, precipitation extremes, and other anthropogenic influences (pollutant deposition, increasing carbon dioxide) will influence future forest composition and productivity in the northeastern United States and eastern Canada. This synthesis of empirical and modeling studies includes tree DNA evidence suggesting tree migrations since the last glaciation were much slower, at least under postglacial conditions, than is needed to keep up with current and future climate warming. Exceedances of US and Canadian ozone air quality standards are apparent and offset CO2 -induced gains in biomass and predispose trees to other stresses. The deposition of nitrogen and sulfate in the northeastern United States changes forest nutrient availability and retention, reduces reproductive success and frost hardiness, causes physical damage to leaf surfaces, and alters performance of forest pests and diseases. These interacting stresses may increase future tree declines and ecosystem disturbances during transition to a warmer climate. Recent modeling work predicts warmer climates will increase suitable habitat (not necessarily actual distribution) for most tree species in the northeastern United States. Species whose habitat is declining in the northeastern United States currently occur in Canadian forests and may expand northward with warming. Paleoecological studies suggest local factors may interact with, even overwhelm, climatic effects, causing lags and thresholds leading to sudden large shifts in vegetation.
ABSTRACT: Models of climate change effects should incorporate land-use changes and episodic disturbances such as fires and insect epidemics.
ABSTRACT: The objective of this study was to dynamically simulate the response of vegetation distribution, carbon, and fire to the historical climate and to two contrasting scenarios of climate change in California. The results of the simulations for the historical climate compared favorably to independent estimates and observations, but validation of the results was complicated by the lack of land use effects in the model. The response to increasing temperatures under both scenarios was characterized by a shift in dominance from needle-leaved to broad-leaved life-forms and by increases in vegetation productivity, especially in the relatively cool and mesic regions of the state. The simulated response to changes in precipitation were complex, involving not only the effect of changes in soil moisture on vegetation productivity, but also changes in tree–grass competition mediated by fire. Summer months were warmer and persistently dry under both scenarios, so the trends in simulated fire area under both scenarios were primarily a response to changes in vegetation biomass. Total ecosystem carbon increased under both climate scenarios, but the proportions allocated to the wood and grass carbon pools differed. The results of the simulations underscore the potentially large impact of climate change on California ecosystems, and the need for further use and development of dynamic vegetation models using various ensembles of climate change scenarios.