P-J is not just one vegetation type: key variation in structure and disturbance dynamics

Transcription

1 P-J is not just one vegetation type: key variation in structure and disturbance dynamics Bill Romme, Colorado State University PJ symposium, Albuquerque, Oct. 12, 2016 (Photo by Dan Binkley)

2 Workshop in Boulder, CO August 2006 Academic and agency researchers from throughout the West Experience from throughout the 100 million acres of PJ vegetation in the West Objectives: Summarize the science -- what we know with high / moderate / low confidence Assemble & weigh the evidence Interpret both pattern & process

3 Participants & regions of experience: New Mexico Craig Allen, Brandon Bestelmeyer, Esteban Muldavin Arizona John Bailey, Dave Huffman, Tom Swetnam Colorado Bill Baker, Karen Eisenhart, Lisa Floyd-Hanna, Bill Romme Utah Peter Brown Nevada Robin Tausch, Peter Weisberg Oregon Rick Miller

4 Major Findings Geographic variation critical! Dominant species Climate (temperature & timing of precipitation) Historical stand & landscape structures Historical fire regimes Patterns & mechanisms of 20 th century change But some patterns & processes apply to all

5 Some sources of information Forest Restoration Institutes New Mexico (Highlands U.) Colorado (CSU) Arizona (NAU) clearinghouses of information workshops, meetings & field trips focused research to address the most pressing questions Historical and Modern Disturbance Regimes of Piñon-Juniper Vegetation in the Western U.S A short version (published by TNC) is available online as pdf (CFRI or TNC websites) And a longer version, with full literature review & citations, is available online as pdf, with paper copies available soon (published by CFRI) e.edu/coloradoforestrestoration institute/wpcontent/uploads/sit es/32/2016/05/2007_pjdisturb anceregimes_synthesis.pdf state.edu/coloradoforestres torationinstitute/publicatio ns/

6 Proportion of Total Annual Precipitation that Falls During the Growing Season (Related to the Summer Monsoon) and Distribution of Piñon-Juniper Woodlands (shown in black) figure prepared by Brian Jacobs, Bandelier NM & CSU DRY SUMMERS WET SUMMERS

7 Three pinyons in three different climate zones Figure by Brian Jacobs

8 Three pinyons in three different climate zones Pinus monophylla in the west Nevada, SE California, W Utah, S idaho * DRY SUMMERS Figure by Brian Jacobs

9 Three pinyons in three different climate zones Pinus monophylla in the west Nevada, SE California, W Utah, S idaho * DRY SUMMERS Pinus edulis in the east: New Mexico, Colorado, SE Utah, NE Arizona * WET SUMMERS OR BIMODAL PRECIPITATION Figure by Brian Jacobs

10 Three pinyons in three different climate zones Pinus monophylla in the west Nevada, SE California, W Utah, S idaho * DRY SUMMERS Pinus edulis in the east: New Mexico, Colorado, SE Utah, NE Arizona * WET SUMMERS OR BIMODAL Pinus cembroides in the south: S Arizona, Texas * WET SUMMERS Figure by Brian Jacobs

11 Five junipers in different climate zones figure by Brian Jacobs

12 Five junipers in different climate zones Juniperus occidentalis in the west Nevada, SE California, SW Idaho * DRY SUMMERS figure by Brian Jacobs

13 Five junipers in different climate zones Juniperus occidentalis in the west Juniperus monosperma & deppeana in the southeast: SE New Mexico, SE Colorado, S Arizona * WET SUMMERS Nevada, SE California, SW Idaho * DRY SUMMERS figure by Brian Jacobs

14 Five junipers in different climate zones Juniperus occidentalis in the west Nevada, SE California, SW Idaho * DRY SUMMERS figure by Brian Jacobs Juniperus monosperma & deppeana southeast: SE New Mexico, SE Colorado, S Arizona * WET SUMMERS Juniperus osteosperma in the north N New Mexico W Colorado E Utah N Arizona * BIMODAL PRECIPITATION

15 And the fifth juniper: Juniperus scopulorum at higher elevations Rocky Mountains & Great Basin New Mexico to British Columbia * COOLER TEMPS BUT VARIABLE PRECIP Figure by Brian Jacobs

16 To summarize for New Mexico If you re working in southern New Mexico, you ll have: - Pinus edulis (Colorado pinyon) and/or Pinus cembroides (Mexican pinyon) - Juniperus monosperma (one-seed juniper) and/or Juniperus deppeana (alligator juniper) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations) If you re working in central New Mexico, you ll have: - Pinus edulis (Colorado pinyon) - Juniperus monosperma (one-seed juniper) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations) If you re working in northern New Mexico, you ll have: - Pinus edulis (Colorado pinyon) - Juniperus osteosperma (Utah juniper especially in northwest) - Juniperus monosperma (one-seed juniper especially in northeast) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations)

17 To summarize for New Mexico If you re working in southern New Mexico, you ll have: - Pinus edulis (Colorado pinyon) and/or Pinus cembroides (Mexican pinyon) - Juniperus monosperma (one-seed juniper) and/or Juniperus deppeana (alligator juniper) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations) If you re working in central New Mexico, you ll have: - Pinus edulis (Colorado pinyon) - Juniperus monosperma (one-seed juniper) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations) If you re working in northern New Mexico, you ll have: - Pinus edulis (Colorado pinyon) - Juniperus osteosperma (Utah juniper especially in northwest) - Juniperus monosperma (one-seed juniper especially in northeast) - Juniperus scopulorum (Rocky Mountain juniper at higher elevations) SO, NOT JUST ONE TYPE OF PINYON JUNIPER VEG IN NEW MEXICO

18 Stand dynamics: lots of variability four basic kinds

19 Expansion establishment of pinyon and/or juniper trees in former grasslands or shrublands. A widespread phenomenon during the modern period (post- 1880) invasion encroachment Associated with land use change & climate (more later on mechanisms) Especially prominent with one-seed juniper

20 Expansion establishment of pinyon and/or juniper trees in former grasslands or shrublands. A widespread phenomenon during the modern period (post- 1880) invasion encroachment Associated with land use change & climate (more later on mechanisms) Especially prominent with one-seed juniper But expansion is not occurring everywhere

21 Brian Jacobs work

22 Brian Jacobs work Young stands (post-1880 origin, expansion) most likely on concave or depositional sites, and in southeast

23 Brian Jacobs work Old stands (pre-1880 origin) most likely on convex or erosive sites, and in northwest Young stands (post-1880 origin, expansion) most likely on concave or depositional sites, and in southeast

24 Infill the process of increasing tree density Widespread in the 20 th century not the same as expansion occurring in places that were already woodland prior to the modern period Associated largely with climate (land use change may play a role also) Has occurred in most kinds of pinyon-juniper but not in all places within existing woodlands.

25 Contraction reduction in tree density and cover due to drought, insects, or fire Widespread occurrence in past 20 years Drought, insect outbreaks, fire Probably occurred historically as well old stands commonly have lots of ancient dead wood small decrease in PJ extent in two Colorado landscapes 1910s-1980s ( photo by Diana Selby)

26 Recovery tree re-establishment following severe disturbance, e.g., stand-replacing fire or chaining. easy to mistake areas of recovery for expansion key difference is that recovery occurs after disturbance of a previously existing woodland, whereas expansion involves establishment of a new woodland in a place that was formerly shrubland or grassland.

27 1. 1. Three broad types of piñon-juniper vegetation 1. Persistent woodland 2. Wooded shrubland 3. Savanna 2. 3.

28 1. 1. Three broad types of piñon-juniper vegetation 1. Persistent woodland 2. Wooded shrubland 3. Savanna Must emphasize: much additional variation this is just a start at characterizing this diverse vegetation type!

29 1. Persistent piñon-juniper woodland Found where site conditions have long been inherently favorable for piñon and juniper Typically shallow rocky soils (though not always) and moderate climate Infrequent fire (always) Stands may be dense or sparse, depending on site conditions & history Tree density fluctuates with climate & disturbance but piñon and juniper always well represented historically and currently

30 2. Wooded shrubland Found where climate & soils are suitable for piñon and/or juniper and for shrubs, and where fire occurs periodically Shrubs are the dominant & consistent life form on the site Tree densities wax & wane over decades & centuries increase during wet periods decrease during dry periods drought, insects, fire Photo by Brian Jacobs

31 3. Piñon-juniper savanna Found where climate & soils are suitable for piñon and/or juniper and for grasses Many savannas have only juniper, no piñon Grasses are the dominant & consistent life form on the site Tree densities wax & wane over decades & centuries increase during wet periods decrease during dry periods drought, insects, fire

32 Extensive infill & expansion in southwestern savannas during the past century Nogal Mesa Circa 1900 Nogal Mesa - Today (Photo comparison by Hollis Fuchs, slide shared with me by Sid Goodloe)

33 Extensive infill & expansion in southwestern savannas during the past century Nogal Mesa Circa 1900 Nogal Mesa - Today (Photo comparison by Hollis Fuchs, slide shared with me by Sid Goodloe) This kind of change has been most prominent where one-seed juniper or alligator juniper is the major tree

34 What was/is the mechanism driving juniper expansion? Fire exclusion? Logical but little empirical data on pre-1880 fire history in these ecosystems few fire scars Livestock grazing? Inconsistent evidence for direct grazing effect often little/no difference in tree densities with vs. without grazing but indirect effect of grazing, by reducing/eliminating fine fuels, could be a reason for reduced fire frequency Climate? Documented pulses of recruitment during wet periods, and 20 th century climate was generally favorable for trees but was that enough to explain the magnitude of change? Increasing CO2 concentration also may enhance juniper growth & survival

35 What was/is the mechanism driving juniper expansion? Fire exclusion? Logical but little empirical data on pre-1880 fire history in these ecosystems few fire scars Livestock grazing? Inconsistent evidence for direct grazing effect often little/no difference in tree densities with vs. without grazing but indirect effect of grazing, by reducing/eliminating fine fuels, could be a reason for reduced fire frequency Climate? Documented pulses of recruitment during wet periods, and 20 th century climate was generally favorable for trees but was that enough to explain the magnitude of change? Increasing CO2 concentration also may enhance juniper growth & survival * A key research priority identified by the 2006 PJ group *

36 Recent studies have provided empirical evidence that fire was important in maintaining lowdensity savannas Rowe Mesa savanna, New Mexico (Ellis Margolis) Pinyon & juniper with multiple fire scars pre-1880 Onset of grazing in ca followed by abrupt cessation of frequent & extensive fires, and by pulse of pinyon & juniper establishment Savanna areas in Davis Mtns & Big Bend NP in Texas (Poulos et al.) Pinyon & juniper with multiple fire scars pre-1880 Multi-age pinyon cohorts Wupatki National Monument Fires began to occur soon after cessation of grazing Fire-scarred pinyon (shared with me by Sid Goodloe)

37 Wupatki: Heavy grazing ca s less intense grazing through 1989 no fires of any size during that time Grazing terminated in 1989 Six fires since 1989 in 1995, 2000, 2002 (two fires), 2013, & 2016 Total area burned = 3,600 acres = 22% of grassland area in monument 2013 fire, photo 2 years later 2000 fire, photo 15 years later 2013 fire, photo 3 weeks later (photo by Paul Whitefield) 2013 fire, photo 2 years later

38 Has the 20 th century expansion event ended?

39 Has the 20 th century expansion event ended? Will contraction be our management challenge in the 21 st century?