Water stress represents a common mechanism for many of the primary disturbances affecting forests, and forest management needs to explicitly address the very large physiological demands that vegetation has for water. This study demonstrates how state-of-science ecohydrologic models can be used to explore how different management strategies might improve forest health.
Widespread threats to forests due to drought stress prompt re-thinking of priorities for water management on forest lands. In contrast to the widely held view that forest management should emphasize providing water for downstream uses, we argue that maintaining forest health in the face of environmental change may require focusing on the forests themselves and strategies to reduce their vulnerability to increasing water stress in the context of a changing climate. Management strategies would need to be tailored to specific landscapes but could include: a) thinning; 2) encouraging drought-tolerant species; 3) irrigation; and 4) strategies that make more water available to plants for transpiration. Hydrologic modeling reveals that specific management actions could reduce tree mortality due to drought stress. Adopting water conservation for vegetation as a priority for managing water on forest lands would represent a fundamental change in perspective and potentially involve tradeoffs with other downstream uses of water.
This project was a pilot effort to construct climate-connected state and transition models for a large landscape in eastern central Arizona. The objective was to use state and transition models developed as a part of the Integrated Landscape Assessment Project and Dynamic Global Vegetation Model outputs from the model MC1 to construct and test the modeling approach.
This project will connect state and transition models developed as a part of the Integrated Landscape Assessment Project with Dynamic Global Vegetation Model outputs for Southeastern Oregon. The objective is to develop a set of vegetation modeling tools that can be used by local land managers and collaborative groups to examine potential rangeland management scenarios and interactions with possible climate change impacts.
This project will connect state and transition models developed as a part of the Integrated Landscape Assessment Project with Dynamic Global Vegetation Model outputs for Southwestern Oregon. The objective is to develop a set of vegetation modeling tools that can be used by local land managers and collaborative groups to examine potential forest management scenarios and interactions with possible climate change impacts.
Washington State Department of Natural Resources, Oregon State University, Institute for Natural Resources, US Forest Service
Computer simulation models are often used to project vegetation responses to changing CO2 (carbon dioxide) and climate. We developed a process that links the mechanistic power of dynamic global vegetation models with the detailed vegetation dynamics of state-and-transition models to project local vegetation shifts driven by projected climate change. We applied our approach to central Oregon (USA) ecosystems using three climate change scenarios to assess potential future changes in species composition and community structure.
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Our results suggest that: (1) legacy effects incorporated in state-and-transition models realistically dampen climate change effects on vegetation; (2) species-specific response to fire built into state-and transition models can result in increased resistance to climate change, as was the case for ponderosa pine (Pinus ponderosa) forests, or increased sensitivity to climate change, as was the case for some shrublands and grasslands in the study area; and (3) vegetation could remain relatively stable in the short term, then shift rapidly as a consequence of increased disturbance such as wildfire and altered environmental conditions. Managers and other land stewards can use results from our linked models to better anticipate potential climate-induced shifts in local vegetation and resulting effects on wildlife habitat.
Restoring riparian forests on streams where historic land uses have created open meadows could reduce maximum stream temperatures by as much as 7o C relative to current conditions, even under a future climate when air temperatures are 4o C warmer than today.
Summer maximum stream temperatures are near thresholds of thermal tolerance for salmon and trout in many streams throughout the interior Columbia River Basin. Salmon and trout populations in many of these streams are severely depressed, resulting in efforts to restore stream and riparian habitat. Climate change raises serious questions about the long-term outcomes of restoration because projected warming could make many of these streams and rivers uninhabitable for salmon and trout within a few decades.
We used the mechanistic stream temperature model, HeatSource, to examine future changes in stream temperature on the upper Middle Fork John Day River. Our model scenarios examined: 1) a +4 oC increase in air temperature; 2) ±30% changes in stream discharge from both changes in irrigation withdrawals and climate-change related loss of winter snowpacks; and 3) four riparian vegetation scenarios: 3a) current conditions where effective stream shade averages 19%; 3b) a post-wild fire scenario with maximum vegetation height of 1 m and 10% canopy density resulting in 7% effective stream shade; 3c) an intermediate condition representing a young-open forest or tall-shrub dominated vegetation with trees or shrubs 10-m tall and with 30% canopy density resulting in 34% effective shade; and 3d) a restored riparian forest with trees 30-m high and canopy density of 50% resulting in 79% effective stream shade.
Our model results showed the composition and structure of riparian vegetation were the single biggest factor determining future stream temperatures. In contrast, changing air temperature or stream discharge had relatively small influence on future stream temperatures. The post-wildfire and the current-vegetation scenarios were warmer than today, but in both cases, effective shade was low, so the stream was sensitive to air temperature increases due to climate change. The intermediate restoration, simulating a young-open forest or a tall-shrub dominated riparian zone, was slightly cooler than today. The biggest change resulted from restoring the riparian forest which decreased summer maximum temperatures by ~ 7 oC.