Kenneth P. Lertzman

WEAK CLIMATIC CONTROL OF STAND‐SCALE FIRE HISTORY DURING THE LATE HOLOCENE

Forest fire occurrence is affected by multiple controls that operate at local to regional scales. At the spatial scale of forest stands, regional climatic controls may be obscured by local controls (e.g., stochastic ignitions, topography, and fuel loads), but the long-term role of such local controls is poorly understood. We report here stand-scale (<100 ha) fire histories of the past 5000 years based on the analysis of sediment charcoal at two lakes 11 km apart in southeastern British Columbia. The two lakes are today located in similar subalpine forests, and they likely have experienced the same late-Holocene climatic changes because of their close proximity. We evaluated two independent properties of fire history: (1) fire-interval distribution, a measure of the overall incidence of fire, and (2) fire synchroneity, a measure of the co-occurrence of fire (here, assessed at centennial to millennial time scales due to the resolution of sediment records). Fire-interval distributions differed between the sites prior to, but not after, 2500 yr before present. When the entire 5000-yr period is considered, no statistical synchrony between fire-episode dates existed between the two sites at any temporal scale, but for the last 2500 yr marginal levels of synchrony occurred at centennial scales. Each individual fire record exhibited little coherency with regional climate changes. In contrast, variations in the composite record (average of both sites) matched variations in climate evidenced by late-Holocene glacial advances. This was probably due to the increased sample size and spatial extent represented by the composite record (up to 200 ha) plus increased regional climatic variability over the last several millennia, which may have partially overridden local, non-climatic controls. We conclude that (1) over past millennia, neighboring stands with similar modern conditions may have experienced different fire intervals and asynchronous patterns in fire episodes, likely because local controls outweighed the synchronizing effect of climate; (2) the influence of climate on fire occurrence is more strongly expressed when climatic variability is relatively great; and (3) multiple records from a region are essential if climate-fire relations are to be reliably described.

Canopy Gaps and the Landscape Mosaic in a Coastal Temperate Rain Forest

We studied canopy gaps over a range of stand ages and site moisture classes in the temperate rain forest of Clayoquot Sound, southwestern British Columbia, Canada. We tested predictions about the landscape mosaic at three levels of resolution: the forest as a whole, gaps, and gapmakers. In addition to canopy gaps arising from the patchy mortality of dominant trees (developmental gaps), we described the prevalence and characteristics of gaps arising from edaphic and topographic features. Roughly 56% of the forest area is influenced to some degree by canopy openings (canopy gap + expanded gap), with 30% of forest area in canopy gaps averaged over all sites (14% developmental canopy gaps and 16% in edaphic canopy gaps). Within the most intensively sampled biogeoclimatic subzone, 73% of gaps were developmental in origin. The majority of edaphic gaps result from streamcourses. Though percent area in developmental canopy gaps was similar across stand age classes, gaps and gapmakers were more common in old growth than in mature stands. Most developmental gaps resulted from the mortality of more than one tree: 96% of the developmental gaps had more than one gapmaker, and 50% had three or more. Mature stands had a significantly higher number of gapmakers per gap than old-growth stands. Old-growth forests were thus dominated by many small gaps and mature forests by fewer larger gaps. Drier and wetter sites had more gapmakers per gap than did stands on mesic sites. The number of decay classes of gapmakers in developmental gaps increases with number of gapmakers per gap, indicating that larger gaps represent the combined effects of distinct mortality events separated in time, rather than single large events. Gapmakers in developmental gaps were distributed broadly and evenly over the range of decay classes, suggesting a continuous pattern of recruitment of gapmakers rather than larger episodic mortality events. The snapping of boles and standing death were the most common modes of gapmaker mortality, together accounting for 76% of the mortality of all gapmakers. Uprooting was the least common mode of gapmaker mortality in both mature and old-growth forests (23.6% and 15.6%, respectively; 20.6% of all gapmakers) and uprooting was more common in drier and wetter sites than in mesic sites. These general trends in gap-phase structure and gap formation processes are consistent with data on gaps and forest age structure collected elsewhere on the British Columbia coast, suggesting that a regime of small-scale, low-intensity disturbance is common in the old-growth forests of coastal British Columbia. We estimate that, in the absence of large-scale disturbances, turnover time for this forest is between 350 and 950 yr, resulting in ubiquitous late successional character throughout the landscape mosaic. Silvicultural practices intended to emulate the natural disturbance regime of these forests should create small gaps of 3-10 trees in an otherwise continuous forest matrix and should retain substantial late-successional characteristics within managed forests.

HOLOCENE FIRE HISTORY OF A COASTAL TEMPERATE RAIN FOREST BASED ON SOIL CHARCOAL RADIOCARBON DATES

The long-term role of fire in coastal temperate rain forest is poorly under- stood. To determine the historical role of fire on western Vancouver Island (British Co- lumbia, Canada), we constructed a long-term spatially explicit fire history and examined the spatial and temporal distribution of fire during the Holocene. Two fire-history parameters (time-since-fire (TSF) and fire extent) were related to three landscape parameters (landform (hill slope or terrace), aspect, and forest composition) at 83 sites in a 730-ha low-elevation (less than ;200 m) area of a mountainous watershed. We dated fires using tree rings (18 sites) and 120 soil-charcoal radiocarbon dates (65 sites). Comparisons among multiple radiocarbon dates indicated a high probability that the charcoal dated at each site represented the most recent fire, though we expect greater error in TSF estimates at sites where charcoal was very old (.6000 yr) and was restricted to mineral soil horizons. TSF estimates ranged from 64 to ;12 220 yr; 45% of the sites have burned in the last 1000 yr, whereas 20% of the sites have not burned for over 6000 yr. Differences in median TSF were more significant between landform types or across aspects than among forest types. Median TSF was sig- nificantly greater on terraces (4410 yr) than on hill slopes (740 yr). On hill slopes, all south-facing and southwest-facing sites have burned within the last 1000 yr compared to only 27% of north- and east-facing sites burning over the same period. Comparison of fire dates among neighboring sites indicated that fires rarely extended .250 m. During the late Holocene, landform controls have been strong, resulting in the bias of fires to south-facing hillslopes and thus allowing late-successional forest structure to persist for thousands of years in a large portion of the watershed. In contrast, the early Holocene regional climate and forest composition likely resulted in larger landscape fires that were not strongly controlled by landform factors. The millennial-scale TSF detected in this study supports the distinction of coastal temperate rain forest as being under a fundamentally different disturbance regime than other Pacific Northwest forests to the east and south.

Patterns of Gap-Phase Replacement in a Subalpine, Old-Growth Forest

Small-scale natural disturbances involving the death of one to a few trees and creating gaps in the forest canopy are key processes in the population and community ecology of many forests. I examined the patterns of replacement in gaps in a subalpine old-growth forest in southern coastal British Columbia to assess their role in the forest community. I found no evidence that self replacement or reciprocal replacement act to maintain the current community composition. Gapmaker-gapfiller comparisons indicated preferential replacement of all species by Pacific silver fir (Abies amabilis), suggesting that the community is undergoing successional change. Nor did gap size, location within a gap, or local canopy composition appear to exert a strong influence on the species composition of regeneration within the gap. The only circumstance where Pacific silver fir was not overwhelmingly dominant among gapfillers was on stumps, where almost all successful western hemlock (Tsuga heterophylla) gapfillers were located. These patterns suggest that neither species-specific interactions between gapmakers and gapfillers nor variability in gap environments is adequate to maintain the current composition of the forest canopy. How- ever, caution is indicated in projecting a long-term trend from this short-term assessment of community trajectory.

Forest fire and climate change in western North America: insights from sediment charcoal records

Millennial-scale records of forest fire provide important baseline information for ecosystem management, especially in regions with too few recent fires to describe the historical range of variability. Charcoal records from lake sediments and soil profiles are well suited for reconstructing the incidence of past fire and its relationship to changing climate and vegetation. We highlight several records from western North America and their relevance in reconstructing historical forest dynamics, fire-climate relationships, and feedbacks between vegetation and fire under climate change. Climatic effects on fire regimes are evident in many regions, but comparisons of paleo-fire records sometimes show a lack of synchrony, indicating that local factors substantially affect fire occurrence, even over long periods. Furthermore, the specific impacts of vegetation change on fire regimes differ among regions with different vegetation histories. By documenting the effects on fire patterns of major changes in climate and vegetation, paleo-fire records can be used to test the mechanistic models required for the prediction of future variations in fire.

Landscape pattern in topographically complex landscapes: issues and techniques for analysis

Ecological research provides ample evidence that topography can exert a significant influence on the processes shaping broad-scale landscape vegetation patterns. Studies that ignore this influence run the risk of misinterpreting observations and making inappropriate recommendations to the management community. Unfortunately, the standard methods for landscape pattern analysis are not designed to include topography as a pattern-shaping factor. In this paper, we present a set of techniques designed to incorporate the topographic mosaic into analyses of landscape pattern and dynamics. This toolbox includes adjustments to ‘classic’ landscape indices that account for non-uniform landscape topography, indices that capture associations and directionality in vegetation pattern due to topographic structure, and the application of statistical models to describe relationships between topographic characteristics and vegetation pattern. To illustrate these methods, we draw on examples from our own analysis of landscape pattern dynamics in logged and unlogged forest landscapes in southwestern British Columbia. These examples also serve to illustrate the importance of considering topography in both research and management applications.

Climate change and culture change on the southern coast of british columbia 2400-1200 cal. B.P : An hypothesis

The Marpole phase of the Gulf of Georgia, SW British Columbia (2400–1200 cal B.P.) is recognized by many archaeologists as a significant period of culture change. Concurrent with this cultural phase is a climatic regime characterized by a substantial increase in forest fires associated with persistent summer drought: the Fraser Valley Fire Period (FVFP). Culturally, the Marpole phase is characterized by the widespread appearance of large houses, standardized art forms, and elaborate burials. Interactions among people of this region intensified and were, as today, economically, socially, and ideologically linked to the lower Fraser River system. Ecologically, the FVFP likely resulted in a regional decline in salmon abundance and/or predictability, especially in small streams and offshore areas, but also more berries and wildlife, and easier overland access via trail networks. The ecological diversity of the lower Fraser region, both terrestrial and riverine, resulted in both more abundant and more predictable resources than surrounding areas during this period of changing climate. We hypothesize that social and economic networks throughout the Gulf of Georgia were solidified during the Marpole phase to ensure access to Fraser resources and allow social buffering of resource uncertainty. We suggest that the differential availability of resources also allowed and encouraged individuals who had access to Fraser Valley resources to gain relatively greater prestige.

Archaeological data provide alternative hypotheses on Pacific herring (Clupea pallasii) distribution, abundance, and variability

Significance Over the last century, Pacific herring, a forage fish of tremendous cultural, economic, and ecological importance, has declined in abundance over much of its range. We synthesize archaeological fisheries data spanning the past 10,000 y from Puget Sound in Washington to southeast Alaska to extend the ecological baseline for herring and contextualize the dynamics of modern industrial fisheries. While modern herring populations can be erratic and exhibit catastrophic declines, the archaeological record indicates a pattern of consistent abundance, providing an example of long-term sustainability and resilience in a fishery known for its modern variability. The most parsimonious explanation for the discrepancy between herring abundance in the ancient and more recent past is industrial harvesting over the last century. Pacific herring (Clupea pallasii), a foundation of coastal social-ecological systems, is in decline throughout much of its range. We assembled data on fish bones from 171 archaeological sites from Alaska, British Columbia, and Washington to provide proxy measures of past herring distribution and abundance. The dataset represents 435,777 fish bones, dating throughout the Holocene, but primarily to the last 2,500 y. Herring is the single-most ubiquitous fish taxon (99% ubiquity) and among the two most abundant taxa in 80% of individual assemblages. Herring bones are archaeologically abundant in all regions, but are superabundant in the northern Salish Sea and southwestern Vancouver Island areas. Analyses of temporal variability in 50 well-sampled sites reveals that herring exhibits consistently high abundance (>20% of fish bones) and consistently low variance (<10%) within the majority of sites (88% and 96%, respectively). We pose three alternative hypotheses to account for the disjunction between modern and archaeological herring populations. We reject the first hypothesis that the archaeological data overestimate past abundance and underestimate past variability. We are unable to distinguish between the second two hypotheses, which both assert that the archaeological data reflect a higher mean abundance of herring in the past, but differ in whether variability was similar to or less than that observed recently. In either case, sufficient herring was consistently available to meet the needs of harvesters, even if variability is damped in the archaeological record. These results provide baseline information prior to herring depletion and can inform modern management.

Long-Term Fire Regime Estimated from Soil Charcoal in Coastal Temperate Rainforests

Coastal temperate rainforests from southeast Alaska through to southern Oregon are ecologically distinct from forests of neighboring regions, which have a drier, or more continental, climate and disturbance regimes dominated by fires. The long-term role of fire remains one of the key outstanding sources of uncertainty in the historical dynamics of the wetter and less seasonal forests that dominate the northerly two thirds of the rainforest region in British Columbia and Alaska. Here, we describe the long-term fire regime in two forests on the south coast of British Columbia by means of 244 AMS radiocarbon dates of charcoal buried in forest soils. In both forests, some sites have experienced no fire over the last 6000 years and many other sites have experienced only one or two fires during that time. Intervals between fires vary from a few centuries to several thousand years. In contrast to other conifer forests, this supports a model of forest dynamics where fires are of minor ecological importance. Instead, forest history is dominated by fine-scale processes of disturbance and recovery that maintain an ubiquitous late-successional character over the forest landscape. This has significant implications for ecosystem-based forest management and our understanding of carbon storage in forest soils.

The Paradigm of Management, Management Systems, and Resource Stewardship

Abstract The idea of “management” is central to our understanding of how people interact with their resources, but many challenges have arisen to traditional concepts of western, science-based resource management. Management is a set of actions taken to guide a system towards achieving desired goals and objectives. A Management System is the sum of these actions, goals and objectives, the process through which they are legitimized by social norms, and the institutions and actors involved in carrying them out. Reframing the concept from management to management system provides a tool for better understanding how social and ecological dynamics act as coupled drivers of managed ecosystems. Seen from this perspective, there are strong parallels between the traditional resource management systems of indigenous peoples and western science-based management systems. Stewardship is a western concept which resonates with the foundations of traditional resource management systems. Both systems of management can be understood on gradients of human influence on ecosystems and of management intensity. Sustainability can emerge across various locations along these gradients. Achieving an integrated understanding of the coupled dynamics of social and ecological systems is a central challenge for both managers and for researchers.