Interactions Across Spatial Scales Among Forest Dieback, Fire, and Erosion in Northern New Mexico Landscapes
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Papers in Natural Resources Natural Resources, School of 10-3-2007 Interactions Across Spatial Scales among Forest Dieback, Fire, and Erosion in Northern New Mexico Landscapes Craig D. Allen US Geological Survey, Jemez Mountains Field Station, Los Alamos, New Mexico, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/natrespapers Part of the Natural Resources and Conservation Commons Allen, Craig D., "Interactions Across Spatial Scales among Forest Dieback, Fire, and Erosion in Northern New Mexico Landscapes" (2007). Papers in Natural Resources. 104. https://digitalcommons.unl.edu/natrespapers/104 This Article is brought to you for free and open access by the Natural Resources, School of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in Natural Resources by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Ecosystems (2007) 10: 797–808 DOI: 10.1007/s10021-007-9057-4 Interactions Across Spatial Scales among Forest Dieback, Fire, and Erosion in Northern New Mexico Landscapes Craig D. Allen* US Geological Survey, Jemez Mountains Field Station, Los Alamos, New Mexico 87544, USA ABSTRACT Ecosystem patterns and disturbance processes at trated by changes in historic fire regimes where one spatial scale often interact with processes at patch-scale grazing disturbance led to regional- another scale, and the result of such cross-scale scale collapse of surface fire activity and subsequent interactions can be nonlinear dynamics with recent increases in the scale of extreme fire events thresholds. Examples of cross-scale pattern-process in New Mexico. Vegetation dieback interacts with relationships and interactions among forest die- fire activity by modifying fuel amounts and con- back, fire, and erosion are illustrated from northern figurations at multiple spatial scales. Runoff and New Mexico (USA) landscapes, where long-term erosion processes are also subject to scale-depen- studies have recently documented all of these dis- dent threshold behaviors, exemplified by ecohy- turbance processes. For example, environmental drological work in semiarid New Mexico stress, operating on individual trees, can cause tree watersheds showing how declines in ground sur- death that is amplified by insect mortality agents to face cover lead to non-linear increases in bare propagate to patch and then landscape or even patch connectivity and thereby accelerated runoff regional-scale forest dieback. Severe drought and and erosion at hillslope and watershed scales. unusual warmth in the southwestern USA since Vegetation dieback, grazing, and fire can change the late 1990s apparently exceeded species-specific land surface properties and cross-scale hydrologic physiological thresholds for multiple tree species, connectivities, directly altering ecohydrological resulting in substantial vegetation mortality across patterns of runoff and erosion. The interactions millions of hectares of woodlands and forests in among disturbance processes across spatial scales recent years. Predictions of forest dieback across can be key drivers in ecosystem dynamics, as spatial scales are constrained by uncertainties illustrated by these studies of recent landscape associated with: limited knowledge of species-spe- changes in northern New Mexico. To better antic- cific physiological thresholds; individual and site- ipate and mitigate accelerating human impacts to specific variation in these mortality thresholds; and the planetary ecosystem at all spatial scales, positive feedback loops between rapidly-respond- improvements are needed in our conceptual and ing insect herbivore populations and their stressed quantitative understanding of cross-scale interac- plant hosts, sometimes resulting in nonlinear tions among disturbance processes. ‘‘pest‘‘ outbreak dynamics. Fire behavior also exhibits nonlinearities across spatial scales, illus- Key words: disturbance interactions; forest die- back; fire; erosion; fire history; cross-scale rela- Received 11 September 2006; accepted 10 April 2007; published online tionships; thresholds; New Mexico; southwestern 20 June 2007. *Corresponding author; e-mail: [email protected] USA. 797 798 C. D. Allen CLIMATE (drought, temperature); Figure 1. Diagram representing interactions OVERGRAZING by livestock across spatial scales for three different disturbance processes (forest dieback, fire, erosion) in northern New Mexico landscapes, building upon Figure 1(a) in Peters and others (2007). Dashed black arrows represent High tree density, death of Patchy stand- Landscape-scale pattern-process feedbacks within three individual trees scale mortality forest mortality different spatial scale domains, with one Treefall example of pattern and process shown for FOREST each domain for each disturbance. Solid black DIEBACK arrows indicate the overarching direct effects Physiological tree stress, Beetle population Beetle outbreak of widespread environmental drivers or beetles attack weak grows rapidly, overwhelms even disturbances (climate, overgrazing) on and dying trees colonizing more trees healthy trees patterns and processes at all scales. Blue Between-patch Long-distance fire Within-patch surface and canopy spread beyond L fuel arrows indicate the point at which altered fuel connectivity fuel connectivity connections feedbacks at finer spatial scales induce changes in feedbacks at broader scales (for FIRE example, fine-scale changes cascade to broader scales), and also where changes at Fire ignition and Torching and between- Explosive crown fire. broader scales overwhelm pattern-process surface fire spread patch fire spread Self-generated weather relationships at finer scales. Red dashed arrows Grass cover, within- Percolating network L-scale illustrate some text examples of amplifying patch bare connectivity of bare IC patches connectivity of (positive feedback) interactions between sediment flux disturbance processes, within and between EROSION spatial scales; green dashed arrows illustrate dampening (negative feedback) interactions Runoff and erosion, Hillslope between disturbance processes. L landscape; drier microsite, Net loss of water and runoff/erosion IC intercanopy (interspaces between tree within IC patch soil from watershed canopies). Fine Intermediate Broad SPATIAL SCALE their emphasis on the importance of the interaction INTRODUCTION of disturbance transfer processes with spatial het- Ecosystem patterns and disturbance processes at erogeneity (Peters and others 2007). This paper one spatial scale often interact with processes at illustrates examples of nonlinear interactions across another scale, and the result of such cross-scale spatial scales among forest dieback, fire, and ero- interactions can be nonlinear dynamics with sion from landscapes in the southwestern USA thresholds (Gunderson and Holling 2002). Such (Figure 1), particularly northern New Mexico, interactions change the pattern-process relation- where long-term studies centered on Bandelier ships across scales such that fine-scale processes can National Monument in the Jemez Mountains have influence a broad spatial extent, or broad-scale recently documented all of these disturbance pro- drivers can interact with fine-scale processes to cesses (Allen 1989). determine system dynamics (Peters and others Methods used to develop the presented examples 2007). Non-linear disturbance propagation and include: dendrochronological dating of fire scars amplification across spatial scales commonly in- (Touchan and others 1996) and tree population volve positive feedback loops or spatial pattern- demographies (Swetnam and Betancourt 1998), process thresholds, differing from linear relation- weekly dendrometer measurements of ponderosa ships observed with simple repetition of patterns pine (Pinus ponderosa) and pin˜ on (Pinus edulis) tree- from fine to broad scales. Cross-scale interactions growth since 1991 and 1993 (CD Allen, unpub- involving disturbance processes are increasingly lished data), monitoring of basal cover of herba- recognized as important drivers of ecosystem ceous vegetation at centimeter resolution along dynamics (Nepstad and others 2001; Turner 2005; 3 km of permanently marked line-intercept tran- Burkett and others 2005; Bodin and others 2006; sects since 1991 (CD Allen, unpublished data), Peters and others 2007). Spatially explicit ap- photographic and remote-sensing delineation of proaches differ from non-spatial approaches in forest dieback (Allen and Breshears 1998; Bres- Cross-Scale Disturbance Interactions in New Mexico 799 Figure 2. Extent of Pinus 0 100 200 Km edulis dieback from 1997 to 2004 in the Four Corners N states of Arizona, New Mexico, Colorado, and Utah. Based upon annual aerial insect pest inventories by the US Forest Service. 3000 2500 2000 1500 1000 Acres (1,000) Acres 500 17. 32. 0.3 12. 36. 0 1997 1998 1999 2000 2001 2002 2003 2004 Year hears and others 2005), aerial surveys of forest be attributable to a single cause. For example, veg- insect pest activity (US Forest Service 2003), and etation dieback (and associated insect outbreaks) detailed multi-scale measurements of runoff and have affected millions of hectares of forests and erosion since 1993 (Wilcox and others 2003). These woodlands in the Southwest since the late 1990s diverse methods provide multiple perspectives on (Figure 2), a period of severe drought and unusual ecosystem patterns and processes across