Research

As a physical geographer my research interests focus on understanding spatial and temporal variations in climate

and the patterns of vegetation on the landscape. My research interests are interdisciplinary in nature, drawing on concepts and theory derived from climatology, biogeography, and paleoecology. My research can be broken into several subject areas, but in practice, I typically employ methodologies and explore questions from each of these fields simultaneously. This allows a more detailed analysis of the complex, interactive problems related to changes in the surrounding environment.

That said, my research is increasingly taking on a much more paleoclimate oriented focus. I continue to be intrigued and challenged by the intircate relationships between tree growth and climate, particularly exhibited by whitebark pine and subalpine larch. I am continuing to explore the results of my dissertation work in this field and hope to embark on new research to address some of the questions that arose during that work. Of particular interest is the development of moisture sensitive chronologies in the vicinity of the Selway-Bitterroot Wilderness Area and an investigation of anomalous growth trends in five-needled pines in the west.

My dissertation research focused on assessing links between fire occurrence in subalpine forests and climate at interannual timescales. I

developed crossdated fire histories in four subalpine watersheds and compared these with reconstructed summer temperature from the region (completed as part of this research), as well as the Cook et al. (1999) gridded reconstruction of summer PDSI, and Stahle et al. (1998) SOI reconstruction. The research relied on a suite of dendrochronological techniques including the reconstruction of climate and fire history using tree rings. I also examined the patterns of forest recovery by analyzing the estimated germination dates of trees colonizing a stand following a fire. My dissertation research rested upon the dendrochronological dating of more than 2000 trees. This represented an enormous investment in time from a field work and lab processing perspective but was a very rewarding experience. Crossdating tree rings provides a certain type of escape I guess. One of the most interesting things to come of this research (at least the fire portion) was an indication that fires in subalpine forests occur following two consecutive dry years.

The reconstruction of summer temperature was developed from tree rings collected from whitebark pine and subalpine larch. I developed six ring width chronologies from three sites in the Selway. One whitebark pine chronology extends to 721 AD and includes one tree that spans the entire time period, 1,278 years. This tree is shown near the top of this page and is the oldest known whitebark pine. The longest subalpine larch chronlogy extens to 12 AD and was developed with the help of Peter M. Brown and Connie A. Woodhouse. Larch are notorious for being rotten near their centers. A 65 cm DBH tree yielded a core about 10 cm in length with more than 800 rings, so these are very old trees. The longest chronology is largely composed of remnant materials prior to about 1100, but almost all trees spanning 1100-1997 were living. The remnants were collected mostly by Peter and Connie (during less than ideal conditions if I remember correctly). Multiple regression techniques were used to develop the transfer function to reconstruct climate and relied heavily on subalpine larch chronologies. The photo on the left shows the 1801 "light ring" present in nearly every sample (regardless of species) I collected. I suspect it has something to do with the early onset of winter possibly related to volcanic forcing, although the only volcano erupting at that time was Mt. St. Helens, and it wasn't a large eruption. It may have been close enough to have an impact but I'm still looking into it at this time. Interestingly, 1601 has a similar appearance (Huaynaputina, Peru--1600), as do several others.

The third aspect of my research examined the patterns of forest recovery following fires in the four watersheds. Relatively young forests, about 100-200 years old, are mostly dominated by lodgepole pine with limited understory development. There are, however, instances of young forests without any lodgepole pine regeneration which might reflect fire intervals that are too short to permit the development of lodgepole pines old enough to bear seeds. On the other hand, forests developing following a fire that occurred in old forests with no lodgepole pines might also result in early regeneration dominated by either spruce or fir.

To learn more about my dissertation research feel free to contact me at kurt@umn.edu or follow the link at the bottom of the page for reprint files.

During the course of collecting data for my dissertation I became interested in the role of mountain pine beetles in subalpine forests. After spending some time in the Selway-Bitterroot it becomes painfully evident that whitebark pine has experienced dramatic declines. While this is true within the Selway, it has also been documented across the enitre range of whitebark pine. There are possibly three factors responsible for whitebark pine declines including the effects of fire suppression altering competitve interactions between the whitebark and other high elevation conifers. Whitepine blister rust (Cronartarium ribicola) has also been identified as a factor in recent declines of the species. The third culprit, though less understood, are episodic MLB Pial Ghosts

outbreaks of mountain pine beetle. Large areas of whitebark pine were killed during the late 1920s and early '30s in the northern Rockies and another (comparable) outbreak maybe underway.

The watersheds I investigated for fire history contained large numbers of whitebark pine that appeared to have been killed by mountain pine beetle. I investigated the temporal patterns of beetle induced mortality by collecting increment cores from dead trees. Most of the mortality was associated with the well known 20s-30s outbreak but outbreaks in the 1960s and 1980s were also identified. Using the dates of whitebark pine mortality and aerial survey data I examined the climatic features associated with these events. I also developed a preliminary model of climate-beetle mortality using regression analysis. One of the interesting results of this research pointed toward muliple climatic relationships that influence beetle-induced mortality in the region. The outbreak around the 1930s was coincident with drought conditions in the region. But the aerial survey data indicated beetle-induced mortality was related to wet conditions. Beetles may flourish to some extent during wet conditions because trees are growing relatively well and provide an abundant, nutritious food source. During dry conditions, however, trees may have a diminished capacity to defend themselves, resulting in high mortality levels.

In any case much more research needs to be done on these problems, particularly in light of the potential of warming temperatures related to anthropogenic activities. The beetles usually require two years to mature in whitebark pine dominated forests because temperatures are generally pretty cool during the summer months. If temperatures continue to warm as expected, the life cycle of the beetles could shorten to only a single year for a generation and may result in more frequent outbreaks. This could have important impacts on the continued persistence of whitebark pine in the region.

Southwestern Drought
As a post doc I was involved to various degrees in an effort to assess relatively recent drought in the southwest. With Malcolm Hughes, Fenbio Ni, and Matthew Salzer we have examined the most recent drought (ca. 1998-present) with respect to droughts over the last 1000+ years. The general message is that the recent drought is certainly severe, but not outside the bounds of past droughts. When considered over multiple years, the recent drought does not appear to be as severe as many droughts in the past. The challenge for water managers and the general public, however, is the increasing reliance on water for development in the Southwest. In other words, the impacts today are likely more severe than droughts of similar magnitude in the past (although I'm not so sure the cliff dwellers would agree). Much of this work has evolved through collaborative research with personnel at the Institute for the Study of Planet Earth and the CLIMAS project. I have provided some links to this past work below.
CLIMAS Paleodrought Pages
Assessment of the Salzer Reconstruction

Modeling Low Frequency Climate Variability
Also as a post doc I worked with Malcolm Hughes and Dave Meko at the LTRR modeling and assessing our ability to capture low frequency climate variability using tree rings. We developed a hypothetical climate signal (based on the properties of long instrumental records) and are "growing" trees based on the synthetic signal to build chronologies. The synthetic trees are based on different parameters of tree growth including the degree of correlation with climate of any single tree, autocorrelation of tree growth, age-related trend, and random error. The parameters used to model the trees are based on examininations of several different tree-ring chronologies. These synthetic chronologies can then be standardized using a variety of techniques including regional curve standardization, age-banding, and other more traditional approaches to compare the efficiency of recovering low frequency variations.

Climate Variability in Minnesota
We recently began a project aimed at reconstructing past climate in Minnesota using tree rings. During summer 2005 Grant Elliott (Ph.D. student @UMN) and myself had the fortune to spend time collecting increment cores from several sites located in the Boundary Waters Canoe Area Wilderness and also Lake Itasca State Park. It was a really great way to do research, aside from trying to cross an immense amount of blown down forest. As relative newbies to canoeing we managed to fare pretty well. We collected samples from around 200 trees. This work is ongoing and we expect to have some reconstructions completed in the coming months.