Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091179

    Examining interactions between long-term climatic fluctuations and Douglas-fir productivity in the BC interior
Project lead: Green, Scott (University of Northern British Columbia)
Contributing Authors: Green, D. Scott; Griesbauer, Hardy P.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Tree growth is controlled by climate processes that occur over a range of temporal scales. Interannual (high-frequency) climate variation is an important process that influences tree growth on a short time scale. Longer term (low-frequency) climate trends have also been shown to influence tree growth over long periods, and may have implications regarding long-term forest productivity and adaptation to climate change. As well, research has shown that low-frequency quasi-periodic climate/ocean processes such as El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) may influence tree productivity in certain habitats in western North America. It is important to elucidate the complex interactions between climate processes at various temporal scales and their impacts on tree growth and productivity in order to better understand the potential responses and adaptation of B.C.’s forests to climate change.

There is a current lack of knowledge regarding how the productivity of many commercial tree species in B.C. may be affected by climate change. This project addresses a specific knowledge gap regarding species-specific growth responses to low-frequency climate change in the B.C. Interior. The purpose of this research project is to complement and expand the research under FSP #Y071270 by examining how Douglas-fir productivity and climate-growth responses over the species’ geographic and climatic range in the B.C. Interior may be affected by low-frequency climate trends and climate fluctuations such as PDO and ENSO. Specifically, this project seeks to identify possible regions or ecological conditions that may represent significant and dramatic changes in Douglas-fir productivity responses as a result of low-frequency climate change.

This study is unique from the project funded under FSP #Y071270, which described an ecological pattern of climate-related interannual growth variation in Douglas-fir, with a focus on examining potentially strong climate-growth relationships at the abiotic limits of the species. In FSP #Y071270 climate-growth relationships were examined over the full climate record (~1900 to present). The study proposed here will examine temporal patterns in climate-growth relationships embedded in the full climate record that may be related to low-frequency climate trends or oscillations such as PDO and ENSO. The proposed objectives represent an additional important aspect of tree productivity responses to climate change that will enhance the foundational information generated by FSP #Y071270.

Low-frequency climate trends and oscillations form the temporal focus of this proposed examination. Low-frequency climate trends are defined here as gradual and directional changes in temperature and precipitation that are occurring in the province over multiple decades; low-frequency climate oscillations are defined here as somewhat periodic climate fluctuations that can range from several years to several decades.

A directional climatic trend (increasing) in average and minimum monthly temperatures has been described in British Columbia over the past century, with a stronger increase in the northern half of the province. This trend is expected to continue; various climate-change models predict that mean annual temperatures in B.C. by 2100 could be 2-7 °C above the mean for the previous 1000 years. Long-term precipitation changes are also evident across the province, however, they show greater regional differentiation and are more difficult to predict. Directional changes in temperature and precipitation may cause tree growth to respond to climate in new and complex ways over periods of decades. A preliminary analysis of data collected under FSP #Y071270 has identified abrupt shifts in climate-growth relationship in Douglas-fir populations in at least some regions in British Columbia. For example, growth in northern populations of Douglas-fir was positively correlated to summer temperatures during a cool period from approximately 1940 to 1977; after 1977, this relationship reversed, with growth having a negative correlation (see Figure 1). A similar phenomenon (6 - please see Section 5 for literature cited) has been observed in Yukon and Alaskan boreal forests in the past decade. This proposed study will examine the temporal “stability” in climate-growth relationships in Douglas-fir stands across British Columbia in response to gradual but directional temperature and precipitation changes. The scope of this project covers the geographic and climatic range of the species in the interior, which should allow for spatial and ecological patterns of temporal changes in climate-growth relationships to be described. This will be valuable in identifying regions and ecological conditions where climate-growth relationships are particularly unstable over time, which will be a critical foundation in effective management of this species.

In addition to directional climate change, this project will examine the influence of low-frequency climatic oscillations (e.g., PDO and ENSO) on Douglas-fir growth. These large-scale processes affect climate in British Columbia at regional levels over a period from several years to several decades. The ENSO alternates between warm (El Niño) and cool (La Nina) phases every 3 to 7 years. The PDO alternates between warm and cool phases approximately every 20 to 30 years. Warm and dry (cool and wet) phases tend to result in warmer (cooler) temperatures and lower (higher) precipitation over much of the province.

The ENSO and PDO have been shown to affect tree growth in high-elevation coastal stands of Douglas-fir in the Pacific Northwest region of the United States (5). The influence of PDO in growth responses has also been observed in other species in western North America. PDO and ENSO may affect growth in high-elevation and northern sites due to an influence on winter snowpacks and temperatures, both of which may limit growth in these habitats. Warm and dry phases of PDO and ENSO may result in lower snowpacks and warmer winter temperatures; as a result, stands may be snow-free sooner in the spring, thereby lengthening the growing season and allowing for more radial growth (though the actual response is likely quite species specific). A knowledge gap exists regarding the influence of these quasi-periodic climate oscillations on Douglas-fir growth in the British Columbia Interior.

This project will examine the influence of PDO and ENSO on Douglas-fir growth across the B.C. interior (including six high-elevation and five northern Douglas-fir stands that were sampled under FSP #Y701270). By examining PDO- and ENSO-growth relationships over the climatic range of the species, important temporal, ecological, and spatial climate-growth patterns in relation to PDO and ENSO will be determined. This will help clarify the importance of these quasi-periodic climate processes on forest productivity.

Potential applications of study findings include projections of future Douglas-fir productivities over the species range, including identification of regions or ecological conditions where productivity is temporally unstable and most at risk from climate change. These results can be implemented into various aspects of timber supply management, such as estimating forest productivity changes, choosing alternative silviculture systems, choosing alternate reforestation species, and modeling species range-shifts. As well, the results from this project relate directly to the objectives established in the B.C. Ministry of Forests and Range’s Future Forest Ecosystems Initiative. This research project, in conjunction with FSP #Y071270, will develop a methodology that will be applicable in the research of climate-growth responses of other commercial tree species in British Columbia. As a result, this project will help provide a foundation for future research.


Executive summary (19Kb)

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Updated August 16, 2010 

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