Keith S. Hadley

DECOUPLING TREE-RING SIGNATURES OF CLIMATE VARIATION, FIRE, AND INSECT OUTBREAKS IN CENTRAL OREGON

Dendroecological methods play a critical role in developing our understanding of forest processes by contributing historical evidence of climate variability and the temporal characteristics of disturbance. We seek to contribute to these methods by developing a research protocol for decoupling radial-growth signatures related to climate, fire, and insect outbreaks in central Oregon. Our methods are based on three independent, crossdated tree-ring data sets: 1) a 545-year tree-ring climate reconstruction, 2) a 550-year fire history, and 3) a 250-year pandora moth outbreak history derived from host (Pinus ponderosa) and non-host (Abies grandis-Abies concolor) tree-ring chronologies. Based on these data, we use visual criteria (marker and signature rings), statistical comparisons, and Superposed Epoch Analysis (SEA) to identify the timing of growth anomalies and establish the temporal relationships between drought, climate variation (ENSO and PDO), fire events, and pandora moth (Coloradia pandora) outbreaks. Our results show pandora moth outbreaks generally coincide with periods of below-average moisture, whereas fire in central Oregon often follows a period of wetter than average conditions. Fire events in central Oregon appear to be related to shifts in hemispheric climate variability but the relationship between fire and pandora moth outbreaks remains unclear.

A 545-YEAR DROUGHT RECONSTRUCTION FOR CENTRAL OREGON

Using a 545-year ponderosa pine (Pinus ponderosa) tree-ring chronology, we examine the drought history of central Oregon to: (1) determine the relationship among drought, ENSO (El Niño/Southern Oscillation), and the PDO (Pacific Decadal Oscillation), and (2) compare the climatic sensitivity of ponderosa pine and western juniper (Juniperus occidentalis) to determine their suitability as interchangeable climate proxies. Our climatic reconstruction explained 35% of the variance in historical Palmers Drought Severity Index (PDSI) values and revealed severe drought periods during the 1480s, 1630s, 1700s, and 1930s. The most sustained drought period in our reconstruction occurred during the 1930s, with the most severe single drought year occurring in 1489. We found a significant (p ≤ .01) but weak relationship between our ponderosa pine chronology and ENSO and the PDO, explaining 9% and 12% of the variation respectively. Both ponderosa pine and western juniper record periods of severe regional drought, but western juniper is more sensitive to regional and seasonal climatic variations, whereas ponderosa pine is more responsive to temperature change. These differences suggest that their substitutability as climate proxies in dendroecological studies is limited.

Geomorphic Change and Vegetation Development on the Muddy River Mudflow Deposit

Geomorphic disturbances are widely recognized as important processes that influence plant-community development and landscape-scale vegetation patterns [e.g., Veblen and Ashton (1978), Garwood et al. (1979), Swanson et al. (1988), and Malanson (1993)]. In volcanically active areas such as the PacificNorthwest,mudflows are locally important geomorphic disturbance events governing shortand long-term ecological conditions. Volcanic mudflows can scour and inundate river valleys with large volumes of debris (Janda et al. 1981; Pierson 1985; Vallance and Scott 1997; Scott 1988; Vallance 2000; Kovanen et al. 2001) and influence plant succession tens of kilometers downstream from their points of origin (Halpern andHarmon 1983; Adams andDale 1987;Wood and delMoral 1987; Frenzen et al. 1988). In addition to altering plant succession, large volcanic mudflows can initiate a cascading chain of secondary disturbances that further modify the landscape and affect subsequent ecological responses (see Swanson and Major, Chapter 3, this volume). The comparatively high disturbance intensity but spatially variable nature of volcanic mudflows provide unique opportunities to study complex interactions between geomorphic processes and ecological succession (Beardsley and Cannon 1930; del Moral 1998; Kroh et al. 2000). Nonetheless, few studies examined plant succession on mudflow deposits before the 1980 eruption of Mount St. Helens (Frehner 1957). Research subsequent to that eruption has shown that plant succession on mudflow deposits is highly variable in response to local substrates, plant reproductive strategies, distances to seed sources, and chance dispersal events (Halpern and Harmon 1983; del Moral 1998). “Biological legacies,” such as floated logs, remnant snags, and shallowly buried residual plants, also play important roles in vegetation development on mudflow deposits (Frehner 1957; Franklin et al. 1985; Frenzen et al. 1988; Halpern and Harmon 1983; del Moral 1998; Kroh et al. 2000; Weber 2001). Vegetation succession on mudflow deposits can follow an initialor relay-floristics model (sensu Egler 1954) or some combination of the two (del Moral 1998) and can lead to the compositional convergence or divergence of neighboring communities (Franklin et al. 1985;Wood and delMoral 1987;Kroh et al. 2000). Although earlier studies of vegetation recovery on mudflowdeposits provide important insights into the dynamics of herbaceous plant communities, few of these studies examined succession over decades after a disturbance (Frenzen et al. 1988; Kroh et al. 2000). In this chapter, we present a case study of geomorphic and vegetation responses at four sites along the Muddy River to large (up to 107 m3) mudflows triggered by the May 18, 1980 eruption of Mount St. Helens. Our objective is to describe and qualitatively compare geomorphic changes and vegetation development along distinct reaches that represent a range of mudflow-induced disturbance intensities and environmental settings. We address three questions:

Influence of Western Dwarf Mistletoe (Arceuthobium campylopodum Engelm.) on Surface Fuels and Snag Abundance in Mature Ponderosa Pine and Mixed Conifer Stands in Central Oregon

ABSTRACT: We examined the influence of western dwarf mistletoe (Arceuthobium campylopodum) infestation on fuel loads in mature mixed-conifer forest in Crater Lake National Park and unmanaged ponderosa pine (Pinus ponderosa) stands in Lave Cast Forest, Oregon. We measured biomass of woody surface fuels (1-, 10-, 100-, and 1000-hr), litter and duff, and snag basal area in 29 stands infested with mistletoe and 21 non-infested stands. Univariate tests revealed no significant differences in total surface fuel loads or snag basal area between infested and non-infested plots in either stand type, but there were more fine fuels and litter in infested stands at Lava Cast Forest. Ordination analyses showed that stand level variables other than mistletoe abundance explained more variance in fuel loads. Ponderosa pine basal area and stand age were stronger predictors of fuel loads in pure ponderosa pine stands at Lava Cast Forest, while basal area of non-host fir was a key explanatory variable in the mixed-conifer stands at Crater Lake. Our results indicate that mistletoe has weak direct and indirect effects on fuel loads in mature forests, resulting primarily in greater accumulations of fine woody fuels.

Lewis and Clarks’ Tempest: The ‘perfect storm’ of November 1805, Oregon, USA

Three weeks after arriving near the Pacific Northwest (PNW) coast in November 1805, Lewis and Clarks’ Corps of Discovery experienced a two-day windstorm that may have rivaled the strongest historically documented storms of the nineteenth and twentieth centuries. Based on the Corps’ detailed historical accounts describing the event as the perfect storm, we characterized the severity of the 1805 windstorm using tree-ring growth anomalies from windsnapped Sitka spruce collected at three sites along the northern Oregon Coast. We compared the 1805 gale to eight other documented events with comparable storm tracks and exceptional magnitude including the 1880 and 1951 events that each caused more than a billion board feet (c. 2.4 million m3) of windthrow. Statistical comparison of tree-growth responses revealed that the 1805 windstorm was the only event to differ significantly (χ2; test, p < 0.05, d.f. = 1) from all other storms. Our findings demonstrate the potential application of tree-ring data and historical documents to understand previously obscure climatic events similar to the extreme droughts that led to the demise of the Roanoke Colony during the sixteenth century and adversity experienced by the Jamestown Colony during the seventeenth century. Specifically, we identify the Lewis and Clark tempest of 1805 as being among the most severe PNW windstorms during the past two centuries, and may have contributed to the Corps’ dismal view of coastal Pacific Northwest weather.

A Multi-Scale Assessment of Avian Diversity Following Stream Rewatering, Owens River Gorge, California

ABSTRACT: We employed a multi-scale approach to examine the evolving spatial patterns of avian diversity following rewatering (1991–1999) of the Owens River Gorge in eastern California. We based our analysis on three independent data sets representing 18 canyon locations (4 reference and 14 rewatered) consisting of bird counts, measures of landscape variation (canyon dimensions), and vegetation structure and composition (foliage height diversity, total vegetation volume, and plant species diversity). We analyzed our data by grouping sites according to bird diversity and environmental factors using Sørensons similarity index and cluster analysis and by employing correlation (Spearman rank) and regression (multiple and backward stepwise) procedures to determine the relative importance of environmental factors on avian diversity at different spatial scales. Our results revealed: (1) that valley bottom width determines the extent of riparian vegetation (rs = .73, P < 0.01) and, indirectly, bird species diversity (rs = .52, P < 0.05) at the landscape scale; and (2) that avian diversity at the habitat scale is most strongly correlated with plant species diversity (rs = .57, P < 0.05). These results indicate avian diversity is responding to habitat restoration resulting from the rewatering of the Owens River Gorge but is spatially constrained by canyon dimensions that limit the area of riparian habitat and, indirectly, plant species diversity. We suggest future evaluations of stream restoration and its role on animal communities consider the merits of a multi-scale analysis.