Alan Tepley

Alan Tepley
Cal Poly Humboldt University · Department of Forestry and Wildland Resources

PhD

About

61
Publications
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Introduction
Alan does research in Forest Ecology, Geography, and Biogeography. His research focuses on fire and other disturbances, with particular emphasis on the responses and ecological feedbacks to altered disturbance regimes in the context of global change.

Publications

Publications (61)
Article
Mixed-severity fire regimes may be the most extensive yet poorly understood fire regimes of western North America. Understanding their long-term spatiotemporal dynamics is central to debates regarding altered fire regimes and the need for restoration in the context of changing climate and nearly a century of active fire suppression. However, the co...
Article
Full-text available
Altered fire regimes in the face of climatic and land-use change could potentially transform large areas from forest to shorter-statured or open-canopy vegetation. There is growing concern that once initiated, these nonforested landscapes could be perpetuated almost indefinitely through a suite of positive feedbacks with fire. The rapid deforestati...
Article
In the context of ongoing climatic warming, certain landscapes could be near a tipping point where relatively small changes to their fire regimes or their postfire forest recovery dynamics could bring about extensive forest loss, with associated effects on biodiversity and carbon-cycle feedbacks to climate change. Such concerns are particularly val...
Article
Full-text available
Abstract 1. In the context of ongoing climatic warming, forest landscapes face increasing risk of conversion to non-forest vegetation through alteration of their fire regimes and their post-fire recovery dynamics. However, this pressure could be amplified or dampened, depending on how fire-driven changes to vegetation feed back to alter the extent...
Article
Full-text available
As the climate warms, drought will increasingly occur under elevated temperatures, placing forest ecosystems at growing risk of extensive dieback and mortality. In some cases, increases in tree density following early 20th‐century fire suppression may exacerbate this risk. Treatments designed to restore historical stand structure and enhance resist...
Article
Full-text available
As the climate changes, warmer spring temperatures are causing earlier leaf-out1–3 and commencement of CO2 uptake1,3 in temperate deciduous forests, resulting in a tendency towards increased growing season length3 and annual CO2 uptake1,3–7. However, less is known about how spring temperatures affect tree stem growth8,9, which sequesters carbon in...
Article
Full-text available
Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the...
Article
Ecosystems are dynamic systems with complex responses to environmental variation. In response to pervasive stressors of changing climate and disturbance regimes, many ecosystems are realigning rapidly across spatial scales, in many cases moving outside of their observed historical range of variation into alternative ecological states. In some cases...
Preprint
Full-text available
As the climate changes, warmer spring temperatures are causing earlier leaf-out1–6 and commencement of net carbon dioxide (CO2) sequestration2,4 in temperate deciduous forests, resulting in a tendency towards increased growing season length1,4,5,7–9 and annual CO2 uptake2,4,10–14. However, less is known about how spring temperatures affect tree ste...
Article
Full-text available
Climate change is leading to increased drought intensity and fire frequency, creating early-successional landscapes with novel disturbance–recovery dynamics. In the Klamath Mountains of northwestern California and southwestern Oregon, early-successional interactions between nitrogen (N)-fixing shrubs (Ceanothus spp.) and long-lived conifers (Dougla...
Article
Full-text available
Tree rings provide an invaluable long‐term record for understanding how climate and other drivers shape tree growth and forest productivity. However, conventional tree‐ring analysis methods were not designed to simultaneously test effects of climate, tree size, and other drivers on individual growth. This has limited the potential to test ecologica...
Article
Full-text available
Ecosystems are changing in complex and unpredictable ways, and analysis of these changes is facilitated by coordinated, long‐term research. Meeting diverse societal needs requires an understanding of what populations and communities will be dominant in 20, 50, and 100 yr. This paper is a product of a synthesis effort of the U.S. National Science Fo...
Article
Full-text available
Exotic forest insects and pathogens (EFIP) have become regular features of temperate forest ecosystems, yet we lack a long-term perspective on their net impacts on tree mortality, carbon sequestration, and tree species diversity. Here, we analyze 3 decades (1987–2019) of forest monitoring data from the Blue Ridge Mountains ecoregion in eastern Nort...
Article
As climate change drives increased drought in many forested regions, mechanistic understanding of the factors conferring drought tolerance in trees is increasingly important. The dendrochronological record provides a window through which we can understand how tree size and traits shape growth responses to droughts. We analyzed tree‐ring records for...
Article
Full-text available
Stand-density reduction treatments are widely applied to restore historic stand structure and increase resistance to high-severity fire in dry ponderosa pine forests. Little is known about whether the removal of competition also alters tree responses to drought, and if so, how long those effects persist, or the underlying mechanisms. This study eva...
Article
Full-text available
Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest...
Article
Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of various disturbance characteristics required in management applications are rare in longer‐term historical studies. Thus, our objectives were to: (1) q...
Article
Full-text available
1.Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling, and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosys...
Article
Full-text available
1.The climate sensitivity of forest ecosystem woody productivity (ANPPstem ) influences carbon cycle responses to climate change. For the first time, we combine long-term annual growth and forest census data of a diverse temperate broadleaf deciduous forest, seeking to resolve whether ANPPstem is primarily moisture- or energy-limited and whether cl...
Article
Disentangling the importance of developmental vs. environmental drivers of variation in forest biomass is key to predicting the future of forest carbon sequestration. At coarse scales, forest biomass is likely to vary along major climatic and physiographic gradients. Natural disturbance occurs along these broad biophysical gradients, and depending...
Article
Full-text available
The collection of tree-ring data from living trees is widespread and highly valuable in ecological and dendro-climatological research, yet there is concern that coring injures trees, potentially contributing to mortality. Unlike resinous conifers that can quickly compartmentalize wounds, less decay-resistant angiosperms may face more pronounced ris...
Article
Full-text available
Wildfire is a dominant disturbance in many ecosystems, and fire frequency and intensity are being altered as climates change. Through effects on mortality and regeneration, fire affects plant community composition, species richness, and carbon cycling. In some regions, changes to fire regimes could result in critical, non‐reversible transitions fro...
Article
Full-text available
The impacts of climatic changes on forests may appear gradually on time scales of years to centuries due to the long generation times of trees. Consequently, current forest extent may not reflect current climatic patterns. In contrast with these lagged responses, abrupt transitions in forests under climate change may occur in environments where alt...
Article
Full-text available
Forests play an influential role in the global carbon (C) cycle, storing roughly half of terrestrial C and annually exchanging with the atmosphere more than ten times the carbon dioxide (CO2) emitted by anthropogenic activities. Yet, scaling up from field‐based measurements of forest C stocks and fluxes to understand global scale C cycling and its...
Preprint
As trees are long-lived organisms, the impacts of climate change on forest communities may not be apparent on the time scale of years to decades. While lagged responses to environmental change are common in forested systems, potential for abrupt transitions under climate change may occur in environments where alternative vegetation states are influ...
Article
Drought disproportionately affects larger trees in tropical forests, but implications for forest composition and carbon (C) cycling in relation to dry season intensity remain poorly understood. In order to characterize how C cycling is shaped by tree size and drought adaptations and how these patterns relate to spatial and temporal variation in wat...
Article
Full-text available
Tree mortality is one of the most influential drivers of forest dynamics, and characterizing patterns of tree mortality is critical to understanding forest dynamics and ecosystem function in the present era of global change. Here, we use a unique data set of mortality in a temperate deciduous forest to characterize rates and drivers of mortality. A...
Article
Full-text available
In the context of global warming and increasing impacts of invasive plants and animals, we examine how positive fire–vegetation feedbacks are increasing the vulnerability of pyrophobic temperate forests to conversion to pyrophytic non-forest vegetation in southern South America and New Zealand. We extensively review the relevant literature to revea...
Conference Paper
In the face of on-going climatic warming and land-use change, there is growing concern that temperate forest landscapes could be near a tipping point where relatively small changes to the fire regime or altered post-fire vegetation dynamics could lead to extensive conversion to shrublands or savannas. To evaluate vulnerability and resilience to suc...
Article
The risk of bark beetle outbreaks is widely predicted to increase because of a warming climate that accelerates temperature-driven beetle population growth and drought stress that impairs host tree defenses. However, few if any studies have explicitly evaluated climatically enhanced beetle population dynamics in relation to climate-driven changes i...
Article
Mixed-severity fire regimes may be the most extensive yet poorly understood fire regimes of western North America. Understanding their long-term spatiotemporal dynamics is central to debates regarding altered fire regimes and the need for restoration in the context of changing climate and nearly a century of active fire suppression. However, the co...
Article
Full-text available
Forest disturbance and long-term succession towards old-growth are thought to increase nitrogen (N) availability and N loss, which should increase soil δ15N values. We examined soil and foliar patterns in N and δ15N, and soil N mineralization, across 800 years of forest succession in a topographically complex montane landscape influenced by human l...
Article
Full-text available
The relative importance of people and climate in shaping prehistoric fire regimes is debated around the world, and this discussion has helped inform our understanding of past and present ecosystem dynamics. Evidence for extensive anthropogenic burning of temperate closed-canopy forests prior to European settlement is geographically variable, and th...
Article
Analyses of how organisms are likely to respond to a changing climate have focused largely on the direct effects of warming temperatures, though changes in other variables may also be important, particularly the amount and timing of precipitation. Here, we develop a network of eight growth-increment width chronologies for freshwater mussel species...
Article
Full-text available
Early-seral ecosystems make important contributions to regional biodiversity by supporting high abundance and diversity of many plant and animal species that are otherwise rare or absent from closed-canopy forests. Therefore, the period of post-fire tree establishment is a key stage in forest stand and ecosystem development that can be viewed in th...
Conference Paper
Background/Question/Methods Understanding historical fire regimes is fundamental to understanding the factors guiding heterogeneity in forest structure within stands and across landscapes. Although mixed-conifer forests are extensive in western North America and commonly noted for their fine-grained mosaics of varying stand structure and species...
Article
Full-text available
The increased incidence of large fires around much of the world in recent decades raises questions about human and non-human drivers of fire and the likelihood of increased fire activity in the future. The purpose of this paper is to outline a conceptual framework for examining where human-set fires and feedbacks are likely to be most pronounced in...
Article
Full-text available
Forests dominated by Douglas-fir and western hemlock in the Pacific Northwest of the United States have strongly influenced concepts and policy concerning old-growth forest conservation. Despite the attention to their old-growth characteristics, a tendency remains to view their disturbance ecology in relatively simple terms, emphasizing infrequent,...
Article
Recent increases in computation power have prompted enormous growth in the use of simulation models in ecological research. These models are valued for their ability to account for much of the ecological complexity found in field studies, but this ability usually comes at the cost of losing transparency into how the models work. In order to foster...
Article
Full-text available
This project consisted of organizing and executing a one-day symposium on “Wildfire Regime Shifts in Temperate Forest Ecosystems” in conjunction with the triennial meeting of the Southern Connection Congress. The VIIth Southern Connection Congress drew together more than 350 environmental scientists and resource managers for its triennial meeting i...
Chapter
Full-text available
Disturbances are relatively discrete events in time that substantially influence ecosystem composition, structure, and function. Natural disturbances (such as hurricanes, avalanches, fires, and floods) play important roles in shaping landscapes and the biota that evolved with them. With increasing human population growth and resource demand, the di...
Thesis
Graduation date: 2011 Descriptions of the fire regime in the Douglas-fir/western hemlock region of the Pacific Northwest traditionally have emphasized infrequent, predominantly stand-replacement fires and an associated linear pathway of stand development, where all stands proceed along a common pathway until reset by the next fire. Although such a...
Conference Paper
Background/Question/Methods Although mixed-severity fire regimes are widespread in the western United States, including a substantial portion of the productive Douglas-fir region west of the crest of the Cascade Mountains, a conceptual framework for this complex regime is lacking. We consider mixed-severity systems as those where burn severity in...
Conference Paper
Although mixed-severity fire regimes are widespread in the western United States, including a substantial portion of the productive Douglas-fir region west of the crest of the Cascade Mountains, a conceptual framework for this complex regime is lacking. We consider mixed-severity systems as those where burn severity in individual events and over su...
Conference Paper
Background/Question/Methods Although the western spruce budworm (Choristoneura occidentalis Freeman) is known as an important disturbance agent in dry, mixed-conifer forests of eastern Oregon, little is known about budworm activity in mesic forests west of the crest of the Cascades. Despite abundant host trees and documented endemic budworm popula...
Technical Report
Full-text available
Great Lakes coastal wetland research and efforts to restore coastal wetlands have focused primarily on herbaceous meadows and marshes. Although swamp forests typically occur immediately inland of these wetlands, a detailed understanding of their physiography, hydrologic regime, soil properties, vegetation, and factors that account for the regional...
Technical Report
Floodplain forests occupy the low-lying areas adjacent to streams and rivers which are third order or greater and subject to periodic over-the-bank flooding and cycles of erosion and deposition. The floodplain forest is a broadly defined community type, where species composition and community structure vary regionally along with varying flooding fr...
Technical Report
Full-text available
Although much of the Lake Huron shoreline was historically lined with swamp forests, many of the coastal swamp forests have been lost over the last 150 years through drainage or conversion to other wetland types as a result of intensive logging followed by agricultural and urban development. The loss of the historical swamp forests is most apparent...

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