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Extent and Spatial Patterns of Grass Bald Land Cover Change (1948-2000), Oregon Coast Range, USA Harold Zald, Forest Science, Oregon State University Marys.

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Presentation on theme: "Extent and Spatial Patterns of Grass Bald Land Cover Change (1948-2000), Oregon Coast Range, USA Harold Zald, Forest Science, Oregon State University Marys."— Presentation transcript:

1 Extent and Spatial Patterns of Grass Bald Land Cover Change ( ), Oregon Coast Range, USA Harold Zald, Forest Science, Oregon State University Marys Peak, OR

2 Grasslands and Meadows are in Decline Globally Major component of “Biome Crisis” Hoekstra et al Ecology Letters Ecological Implications Habitat loss, degradation, & fragmentation Energy balance Carbon and nutrient cycling

3 Regional Declines Cascades and Olympics Alpine and Subalpine (Franklin et al. 1971, Woodward et al. 1995, Rochefort and Peterson 1996, Millar and Halpern 1998) Cascades Mid-Montaine (Millar and Halpern 1998, Haugo and Halpern 2007) Willamette Valley and Puget Trough Lowlands (Johannessen et al. 1971, Foster and Shaff 2003)

4 Coast Range Grass Balds Graminoid dominated vegetation communities on the high peaks of the Oregon Coast Range. Pre-date European Settlement Saddle Mountain Mount Hebo Bald Mountain Marys Peak Grass Mountain Prairie Peak Roman Nose Mountain Tyee Mountain Oregon

5 Importance of Grass Balds Endemics Disjunct populations Federal & State protected species Unique habitat Recreation © E. Guerrant No detailed studies of: Historical or current bald extent Extent of land cover change Types of land cover change Spatial patterns of land cover change

6 Study Objectives Determine if grass balds declined over the past five decades ( ) If they have declined, determine what they have changed into Quantify the spatial pattern of tree encroachment in the grass balds Quantify habitat loss and fragmentation

7 Study Area 8 major balds, 5 studied Maritime Climate Underlain by Mafic Intrusions, Sandstones, and Siltstones Encroaching tree species include: Pseudotsuga menziesii, Abies procera, and Tsuga heterophylla. Saddle Mountain Tyee Mountain Oregon Mount Hebo (41 yrs) Bald Mountain (52 yrs) Marys Peak (46 yrs) Grass Mountain (46 yrs) Prairie Peak (46yrs) Roman Nose Mountain

8 Methods: Imagery Historical (1948/1953) Aerial Photos: Scanned hardcopies (UO Map Library) Monochromatic spectral resolution (grayscale) 8bit radiometric resolution m post-rectification spatial resolution (re- sampled to 1m) Recent (1994/2000) Aerial Photos: Digital Orthophoto Quadrangles (DOQs) UTM, NAD 1983, Zone 10N, Spheroid GRS 1980 Monochromatic spectral resolution (grayscale) 8bit radiometric resolution 1m spatial resolution

9 Methods: Image Processing Historical Image Rectification Image Filtering Land Cover Classification Change Detection

10 Matrix Change Detection Mount Hebo (1953) Mount Hebo (1994) Mount Hebo Change ( ) Forest Grass Bald Bare Ground Roads & Buildings Forest No Change Grass Bald No Change To Grass Bald Grass Bald Loss

11 Matrix Change Detection Forest No Change Grass Bald No Change To Grass Bald Grass Bald Loss Grass Mountain Change ( )

12 Matrix Change Detection Forest No Change Grass Bald No Change To Grass Bald Grass Bald Loss Prairie Peak Change ( )

13 Extent of Grass Bald Land Cover Change Study AreaDateBald Area (ha) Δ ha (%) Mount Hebo ha (-83.6%) Bald Mountain ha (-70.2%) Marys Peak ha (-34.8%) Grass Mountain ha (-47.1%) Prairie Peak ha (-66%) Totals ha (-65.8%) All grass balds studied have declined in extent

14 Types of Grass Bald Land Cover Change Study AreaDatesType Δ Δ ha (%) Mount Hebo Forest Encroachment201 (96%) Roads & Buildings 8 (4%) Bald Mountain Forest Encroachment 15 (85%) Roads & Buildings 2 (14%) Marys Peak Forest Encroachment 47 (94%) Roads & Buildings 3 (6%) Grass Mountain Forest Encroachment 22 (98%) Roads & Buildings 0.4 (2%) Prairie Peak Forest Encroachment 63 (95%) Roads & Buildings 2 (14%) TotalsForest Encroachment 349 (95%) Roads & Buildings 15 (4.2%) Tree encroachment the dominant type of bald land cover change

15 Spatial Patterns of Tree Encroachment Tree encroachment is inversely related to distance from nearest potential parent trees

16 Decline and Fragmentation Study AreaDate# of BaldPatchWeightedEdge PatchesSize Patch Size Density (m 2 )(m 2 )(m/ha) Bald Mountain Grass Mountain Marys Peak Mount Hebo Prairie Peak All Study Areas48/ / Bald patches have become fewer in number, smaller in area, and edgier

17 Proximate Causes of Grass Bald Decline Two factors spatially correlated with distance from forest edge Competition with Bald Vegetation Pseudotsuga menziesii, Abies procera, and Tsuga heterophylla seedlings have lower establishment and growth rates when completing with dense grass and forb vegetation Seed Dispersal Limitation Seeds (like encroachment patterns) display inverse relationships with distance from parent tree. However all most all Grass Band land cover lies within 100 meters of trees.

18 Ecological Implications Reduced and fragmented habitat generally has negative impacts on species populations. Remnant patches are closer to forest and have higher edge density, Reduced grass and forb competition Increased seed density Suggests tree encroachment will increase

19 Limitations of Remotely Sensed Research Cannot determine habitat quality Snap shots in time Landscape metrics of habitat loss and fragmentation are imperfect substitutes Cannot determine fundamental causes of tree encroachment

20 Fundamental Causes of Grass Bald Decline Climate Variation Native ignitions, big fires, and fire suppression Grazing and grazing cessation

21 Acknowledgements: Jonathan Thompson (OSU Forest Science) for GIS advice Colin Kelly (UO Map Library) for assistance with historical aerial photos


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