UNIVERSITY OF WASHINGTON
The Trees of the Yosemite Forest Dynamic Plot
College of the Environment - School of Forest Resources Environmental Science Resource Management - Capstone
By: Hunter W. Decker
Advisor: Dr. James A. Lutz
2011
TABLE OF CONTENTS
LIST OF FIGURES ...... i LIST OF TABLES...... ii Introduction to Yosemite 25.6-ha Forest Dynamic Plot ...... 1 Introduction to Yosemite National Park ...... 1 Location and Description of Yosemite Forest National Park ...... 1 Main Vegetation Types ...... 2 Foothill Woodland Zone ...... 2 Lower Montane Zone ...... 2 Upper Montane Zone ...... 3 Subalpine Zone ...... 3 Alpine Meadow Zone ...... 4 Yosemite 25.6-ha Forest Plot ...... 5 Plot Establishment ...... 5 Topographic Survey ...... 5 Tree Mapping ...... 5 Topography and Soil ...... 6 Species Composition and Community Structure ...... 7 Species Descriptions ...... 10 Abies concolor ...... 10 Pinus lambertiana ...... 14 Cornus nuttallii ...... 17 Calocedrus decurrens ...... 19 Quercus kelloggii ...... 22 Prunus virginiana ...... 25 Prunus emarginata ...... 27 Abies magnifica ...... 31 Pseudotsuga menziesii...... 33 Pinus ponderosa ...... 35 Rhamnus californica ...... 37 Conclusion ...... 38 References ...... 40
LIST OF FIGURES
Figure 1: The location of Yosemite National Park in California...... 1 Figure 2: The location of the 25.6-ha forest plot in Yosemite National Park...... 1 Figure 3: YFDP elevation grid from the plot survey points (Lutz 2011)...... 6 Figure 4: YFDP species DBH ≥ 1 cm spatial distribution...... 8 Figure 5: YFDP species DBH ≥ 50 cm spatial distribution...... 8 Figure 6: YFDP DBH distribution of individuals < 50 cm...... 9 Figure 7: YFDP DBH distribution of individuals ≥ 50 cm...... 9 Figure 8: YFDP diameter distribution of Abies concolor < 50 cm in the plot...... 12 Figure 9: YFDP diameter distribution of Abies concolor ≥ 50 cm in the plot...... 12 Figure 10: YFDP spatial distribution of Abies concolor DBH ≥ 1 cm...... 13 Figure 11: YFDP spatial distribution of Abies concolor DBH ≥ 50 cm...... 13 Figure 12: YFDP diameter distribution of Pinus lambertiana < 50 cm...... 15 Figure 13: YFDP diameter distribution of Pinus lambertiana ≥ 50 cm...... 15 Figure 14: YFDP spatial distribution of Pinus lambertiana DBH ≥ 1 cm...... 16 Figure 15: YFDP spatial distribution of Pinus lambertiana DBH ≥ 50 cm...... 16 Figure 16: YFDP diameter distribution of Cornus nuttallii < 50 cm...... 18 Figure 17: YFDP spatial distribution of Cornus nuttallii DBH ≥ 1 cm...... 18 Figure 18: YFDP diameter distribution of Calocedrus decurrens < 50 cm...... 20 Figure 19: YFDP diameter distribution of Calocedrus decurrens ≥ 50 cm...... 20 Figure 20: YFDP spatial distribution of Calocedrus decurrens DBH ≥ 1 cm...... 21 Figure 21: YFDP spatial distribution of Calocedrus decurrens DBH ≥ 50 cm...... 21 Figure 22: YFDP diameter distribution of Quercus kelloggii < 50 cm...... 23 Figure 23: YFDP diameter distribution of Quercus kelloggii ≥ 50 cm...... 23 Figure 24: YFDP spatial distribution of Quercus kelloggii DBH ≥ 1 cm...... 24 Figure 25: YFDP spatial distribution of Quercus kelloggii DBH ≥ 50 cm...... 24 Figure 26: YFDP diameter distribution of Prunus virginiana < 50 cm...... 26 Figure 27: YFDP spatial distribution of Prunus virginiana DBH ≥ 1 cm...... 26 Figure 28: YFDP diameter distribution of Prunus emarginata < 50 cm...... 27 Figure 29: YFDP spatial distribution of Prunus emarginata DBH ≥ 1 cm...... 28 Figure 30: YFDP diameter distribution of Salix scouleriana < 50 cm...... 30 Figure 31: YFDP spatial distribution of Salix scouleriana DBH ≥ 1 cm...... 30 Figure 32: YFDP spatial distribution of Abies magnifica DBH ≥ 1 cm...... 32 Figure 33: YFDP spatial distribution of Abies magnifica DBH ≥ 50 cm...... 32 Figure 34: YFDP spatial distribution of Pseudotsuga menziesii DBH ≥ 1 cm...... 34 Figure 35: YFDP spatial distribution of Pseudotsuga menziesii DBH ≥ 50 cm...... 34 Figure 36: YFDP spatial distribution of Pinus ponderosa DBH ≥ 1 cm...... 36 Figure 37: YFDP spatial distribution of Rhamnus californica DBH ≥ 1 cm...... 37
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LIST OF TABLES8
Table 1: YFDP species-abundance distribution...... 7 Table 2: YFDP diameter distribution of Abies magnifica...... 31 Table 3: YFDP diameter distribution of Pseudotsuga menziesii...... 33 Table 4: YFDP diameter distribution of Pinus ponderosa...... 35
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Introduction to Yosemite 25.6-ha Forest Dynamic Plot
Introduction to Yosemite National Park
Location and Description of Yosemite Forest National Park
Yosemite National Park is located in the central area of California within the Sierra Nevada Mountains. It is one of the larges and least fragmented habitat blocks in the Sierra Nevada, and the park supports a diversity of plants and animals. The park covers 308,074 hectares of land ranging in elevation from 648 m to 3,997 m. The park contains five major vegetation types; foothill woodland, lower montane, upper montane, subalpine, and alpine (Fites- Kaufman et al. 2007).
Figure 2: The location of Yosemite National Park in Figure 1: The location of the 25.6-ha forest plot in California (USGS 2008) Yosemite National Park (Yosemite 2002)
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Main Vegetation Types
Foothill Woodland Zone
This is the lowest elevation zone in the park and is found in the areas of the Hetch Hetchy Reservoir and El Portal. This zone is the foothill woodland zone ranging in elevation from 300- m to 900 m. This area is hot and dry in the summer with very little or no snow in the winter. The plants within this zone include Adenostoma fasciculatum Hook. & Arn (chamise), Ceanothus integerrimus Hook. & Arn (deer brush), Arctostaphylos patula Greene (manzanita), Quercus douglasii Hook. & Arn. (blue oak), Quercus wislizeni A.DC. (interior live oak), and Pinus sabiniana D. Don (gray or foothill pine) (Fites-Kaufman et al. 2007).
Lower Montane Zone
In the lower montane vegetation comprises of two main forest types the Ponderosa Pine and Douglas-Fir-Mixed Conifer type which dominate much of the lower montane zone occurring in the range of 300 m to 1,800 m and the Abies concolor-Mixed Conifer type establishing dominance on deeper soils and higher elevations ranging from 1,250 m to 2,200 m which is where the Yosemite Forest Dynamics Plot lies. The Lower Montane zone is also known as the Yellow Pine Forest but most commonly known as the Sierra Mixed-Conifer forest zone where the dominate tree species can include Pinus ponderosa C. Lawson (ponderosa pine), Pseudotsuga menziesii (Mirb.) Franco (douglas- fir), and Abies concolor (Gord. & Glend) Lindl. Ex Hildeber (white fir) have overlapping distributions that contribute to the classification of such a system (Fites-Kaufman et al. 2007). Pinus ponderosa which extends well below the Pseudotsuga meniezzii range and up through the range of the Abies concolor (silvs). Other common trees include Pinus lambertiana Douglas (sugar pine), Calocedrus decurrens (Torr.) Florin (incense cedar), and Quercus kelloggii Newberry (california black oak) also have a high degree of local spatial diversity and lead to marrying mixtures of dominant species in any one site (Fites-Kaufman et al. 2007). The determination of the structure and composition are determined primarily by the climate and fire history. This vegetation type is characterized by its climate with an annual precipitation of 1,066 mm, soil water capacity of 80 mm, and annual maximum and minimum temperatures in January (10.01° C to -1.82° C) and July (27.14° C to 13.9° C) all which
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constitute for its hot, dry summers and cool, moist winters where several feet of snow accumulate during the winter and it is not uncommon for it to remain on the ground for several months (Lutz et al. 2010, Fites-Kaufman et al. 2007). Important factors that govern the composition and successional pattern of the species are the shade and drought tolerance, and response to fire. Fire exclusion has resulted in dense stands in this forest type.
Upper Montane Zone
The upper montane zone is the transition from lower montane forests where elevations are above the Abies concolor and mixed-conifer. Elevations are from 2,591 m in the central and northern Sierra Nevada and from 2,200 m to 2,500 m in the southern Sierra Nevada. This zone has pure stands of Abies magnifica A. Murray bis (california red fir), Pinus contorta Loudon subsp. Murrayana (Grev. & Balf.) Critchf. (lodgepole pine), and Pinus jeffreyi Grev. & Balf. (jeffery pine). Also in addition to these forests there are non-forested rock outcrops, montane meadows and chaparral, and aspen. This vegetation type is characterized by its annual precipitation of 1422 mm, soil water capacity of 80 mm, and annual maximum and minimum temperatures in January (6.08° C to -8.78° C) and July (22.4° C to 5.86° C) all which constitute for its short, moist, cool summers and cold, wet winter climate (Lutz et al. 2010). It also receives most of its annual precipitation from annual snow packs which begin in November and may accumulate to depths up to 1.8 m and remain until June. The summers are mostly dry but connective storms are prevalent in the months of August and September (Fites-Kaufman et al. 2007). Fire also plays an important role in these forests, but is not as frequent as the lower montane forests (van Wagtendonk 2007).
Subalpine Zone
Near 2,750 m in elevation fire is rare because of small accumulation of litter and the open stand structures. The climate is cooler with an even shorter growing season that lasts 6 to 9 weeks is the subalpine zone. The climate is cooler with the shorter growing season due to long, cold, and snowy winters where the snow typically accumulates from 1 m to 2.5 m and by this freezing weather and wind conditions can lower the soil temperature and increase the plant water stress (Fites-Kaufman et al. 2007). The forests are open stands of conifers that generally
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establish on sandy soils or rocky slopes comprised of rock outcrops, meadows, scrub vegetation types, and subalpine forests/woodlands.The most common tree species is the Pinus albicaulis Engelm. (whitebark pine) which dominates the tree line in the northern Sierra Nevada. The Pinus monticola Douglas ex D. Don (western white pine), Tsuga mertensiana (Bong.) Carrière (mountain hemlock), Pinus contorta Loudon subsp. Murrayana (Grev. & Balf.) Critchf. (Lodgepole pine), Juniperous occidentalis Hook. Var. Australis (Vasek) A. H. Holmgren & N. H. Holmgren (sierra juniper), and Pinus flexilis E. James (limber pine) are also found in this forest (Parker 1989).
Alpine Meadow Zone
Beginning near 2,900 m elevation, the Alpine Meadow zone is easily distinguished as above the tree line. No trees grow in this zone due to the harsh climatic conditions of short, cool summers, with long, cold, snowy winters, and the existence of a shallow water table (Fites- Kaufman et al. 2007). The exposed granitic outcroppings, talus slopes, and boulder fields has limited the amount of vegetation that grows here. The herbaceous plants in this zone need to flower and produce their seeds quickly during the short, frost-free period of the summer in order for survival.
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Yosemite 25.6-ha Forest Plot Plot Establishment The Yosemite Forest Dynamics Plot is located near Crane Flat in Yosemite National Park (37.76° N, 119.82° W). The YFDP is a square 25.6-ha plot, oriented to the four cardinal directions rotated 3° clockwise from true north. It is in the lower montane area lying in an old- growth, Pinus lambertiana/Abies concolor forest. Yosemite plot ranges 320 m from south to north, and extends 800 m from east to west.
Topographic Survey
The first phase of the project, was the survey of the grid for the 25.6-ha Forest Dynamics Plot (FPD). Using a total station, a survey team laid out the 25.6-ha FDP in 640 20 m x 20 m quadrats (horizontal distance). At the corners of the 20 m subplots, stainless steel rods were hammered into the ground with approximately 5 cm showing, control points were established with black pipe and each point was sighted and back-sighted, and elevation recorded. The protruding portion of the stainless steel rods were tagged with a stainless steel tag wired to the grid marker and flagged with a blue flag on a ~40 cm PVC post. Grid markers that are offset (presence of a rock or tree at the true location) were flagged with a blue flag and pink/orange flagging. There are 697 grid markers with identifiers from the alphanumerically lowest value of the surrounding tags. The “A1” grid cell is in the southwest corner, and the “A- 1” grid marker is in the southwest corner of that grid square. The northeast corner is grid cell “P40”, and the northeast-most grid marker is “Q-41”.
Tree Mapping
The second phase of the project was the mapping of the entire free-standing trees ≥ 1 cm DBH. During this phase of the census, teams carried out the mapping and data recording for every tree. Each tree was measured at 1.37 m in height, using a DBH tape. When the diameter could not be measured at 1.37 m, it was taken at a different height and that point of measure was noted on the data sheet. Each tree was given a tag that had been made out of steel material and was stamped with the plot and tree number.
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Topography and Soil The plot is characterized by rugged terrain: altitude varies from 1774.1 m to 1911.3 m above sea level, and the mean elevation is 1842.73 m (Figure 3). With the plot being located in the Lower Montane zone in the Abies concolor-Mixed Conifer forest we can infer that the site is located on relatively deeper soils than the surrounding vegetation zones.
Figure 3: YFDP elevation grid from the plot survey points (Lutz 2011).
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Species Composition and Community Structure There were 34,467 stems (DBH ≥ 1 cm) recorded in the plot for live trees, belonging to 12 species. The maximal DBH is 229.1 cm and the mean value of DBH is 15.6 cm in the plot. The DBH size of individuals in the plot follows the distribution of an inverse “J” shape (Figure 2.3). Abies concolor is the dominate species but Pinus lambertiana, Cornus nuttallii, Calocedrus decurrens, Quercus kelloggii, Prunus virginiana, Prunus emarginata, Salix scouleriana, Abies magnifica, Pseudotsuga menziesii, Pinus ponderosa, and Rhamnus californica are also included throughout the plot (Figure 4). Fire plays an important role in the spatial pattern and landscape in the plot. Fire history in this area has played an important role in the spatial pattern and composition of the landscape in the plot and surrounding forest (Agee 1993). Fire suppression has altered the historic fire regime allowing the build up debris and creating closely compacted understories with dominating shade-tolerant species such as the Abies concolor (Table 1) (Fites-Kaufman et al. 2007).
Tree Species Species code Stems ≥ 1 cm Stems ≥ 50 cm Abies concolor ABCO 24,496 809 Pinus lambertiana PILA 4,745 784 Cornus nuttallii CONU 2,370 0 Calocedrus decurrens CADE 1,591 143 Quercus kelloggii QUKE 1,109 6 Prunus virginiana PRVI 105 0 Prunus emarginata PREM 20 0 Salix scouleriana SASC 11 0 Abies magnifica ABMA 11 2 Pseudotsuga menziesii PSME 7 2 Pinus ponderosa PIPO 2 1 Rhamnus californica RHCA 1 0
Table 1: YFDP species-abundance distribution.
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Figure 4: YFDP species DBH ≥ 1 cm spatial distribution.
Figure 5: YFDP species DBH ≥ 50 cm spatial distribution.
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Figure 6: YFDP DBH distribution of individuals < 50 cm.
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Figure 7: YFDP DBH distribution of individuals ≥ 50 cm.
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Species Descriptions
Abies concolor (Gord. & Glend.) Lindl. ex Hildebr (white fir):
Abies concolor is the most abundant species in the plot (Table 1) reaching its best development and maximum size in central Sierra Nevada and is associated in the mixed conifer forest of California (Laacke 1990). Abies concolor has a mean elevation of 2,083 m growing in areas where the soil water capacity is 113 mm, annual precipitation ranging from 889 mm to 1905 mm or more, and snow packs provide more than 80 percent of the moisture (Lutz et al. 2010). Studies indicate that high-elevation stands grow best in years with precipitations as low as 38 percent of normal usually meaning early snowmelt and a longer growing season (Guarin & Taylor 2005). Climate change could become a major factor in the future has it can have the ability to speed up the entire process making the Abies concolor thrive.
Abies concolor is a major climax component throughout the mixed conifer forests within its range. Abies concolor in the upper elevation limits of the mixed conifer forest occasionally forms pure stands and in the southern Sierra Nevada it generally tolerates canopy closure better and dominates on nutrient-rich sites (Laacke 1990). From the spatial distribution (Figure 10) perhaps a pattern of canopy dominance does in fact indicate that Abies concolor tolerate canopy closure and dominate on nutrient-rich sites. Abies concolor can survive and grow beneath heavy brush cover and eventually overtop the brush and dominate the site, many pure stand exist in otherwise mixed conifer areas where Abies concolor dominates closed forests where there are low light levels, combined with their shade tolerance gives them the ability to maintain a continued dominance. So that even with a gap phase disturbance (ex. falling Pinus lambertiana), will release any regeneration, but more importantly the reestablishment of Abies concolor to continue canopy dominance (Parker 1986).
Many of the Abies concolor trees have been severely infested by a species of Arceuthobium (mistletoe) and the parasite is present in other forest types that contain Abies concolor. Heavily infected trees suffer significant growth losses and are prone to attack by Scolytus ventralis (Fir engraver beetle), which can further reduces the trees growth (Fites- Kaufman et al. 2007).
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At elevations from 1,200 m to 2,100 m, Abies concolor is an aggressive, tolerant species that appears to have been held in check by frequent natural fires. Extensive fire control efforts enforced by the US Forest Service, has reduced fire frequency (Laacke 1990). As a result, Abies concolor is becoming a major stand component in California at elevations and on sites where originally it was minor (Laacke 1990).
With closely compacted fir regenerations beneath older stands of less tolerant trees are common and threaten a major change in species composition (Parker 1989). In the YFPD, especially with Pinus lambertiana, such changes are undesirable for the natural history of the stands composition, and control measures including reintroduction of fire will be necessary if the objectives are to restore it to its historical composition (Lutz et al. 2009).
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Figure 8: YFDP diameter distribution of Abies concolor < 50 cm in the plot.
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Figure 9: YFDP diameter distribution of Abies concolor ≥ 50 cm in the plot.
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Figure 10: YFDP spatial distribution of Abies concolor DBH ≥ 1 cm.
Figure 11: YFDP spatial distribution of Abies concolor DBH ≥ 50 cm.
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Pinus lambertiana Douglas (sugar pine):
Pinus lambertiana is a main component in the forest cover type, though it rarely forms pure stands, it grows singly or in small groups of trees (Figure 14) (Harry et al. 1983). Pinus lambertiana tolerates shade better than Pinus ponderosa but is slightly less tolerant than Calocedrus decurrens and Pseudotsuga menziesii and much less so than Abies concolor (Harry et al. 1983). As a species that repeatedly follows the same behavior pattern, it becomes less tolerant with age, and overtopped trees decline unless released (Kinloch & Scheuner 1990). These dominant Pinus lambertiana in old-growth stands were probably dominant from the start, or released by natural causes early in life.
Pinus lambertiana typically grows on many different soils and thrives over a broad range of elevations. The best stands are at the middle and higher elevations in the western Sierra Nevada, were massive, old Pinus lambertiana are surpassed in sheer bulk only by Sequoiadendron giganteum (Lindl.) Buchholz (giant sequoia). Pinus lambertiana grows at elevations from 575-m to 2,375 m in the central Sierra Nevada, and may be as genetically diverse in growth and adaptation as the similarly ranging Pinus lambertiana and Abies concolor. Growth is strongly correlated with seed source elevation in some conifers, but not in others. Whether Pinus lambertiana has adapted to environmental gradients associated with elevation is unknown (Harry et al. 1983).
Abies concolor would be the climax species in mixed conifer forests in the absence of any natural disturbance such as fire because disturbances frequently cause gaps, in which will allow the release of the relative tolerant Pinus lambertiana that are adapted to grow in this area (Harry et al. 1983). For these reasons, Pinus lambertiana is often adapted to regenerate in a shelterwood silvicultural system (Kinloch & Scheuner 1990).
Fire exclusion has resulted in dense stands in this forest type and many others, which may create additional stress for these generally shade-intolerant pines (Agee 1993). Fire exclusion also allows fuels to accumulate, and it is unclear how affected populations will respond to the reintroduction of fire (Van Mantgem et al. 2004).
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Figure 12: YFDP diameter distribution of Pinus lambertiana < 50 cm.
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Figure 13: YFDP diameter distribution of Pinus lambertiana ≥ 50 cm.
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Figure 14: YFDP spatial distribution of Pinus lambertiana DBH ≥ 1 cm.
Figure 15: YFDP spatial distribution of Pinus lambertiana DBH ≥ 50 cm.
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Cornus nuttallii Audubon (Pacific dogwood):
Occupying the moist conifer forest floor in the low valleys of the plot, Cornus nuttallii is common in the lower montane zones establishing in Pinus ponderosa/mixed conifer forests. It is a native tree of the Sierra Nevada that typically grows in the shade at the bases of giant conifers, a habitat in which few other hardwoods can only survive (Arno 1973). Studies of the closely related eastern dogwood have revealed that this specie is successful in growing beneath dense forest canopies because Cornus carries out maximum photosynthesis under conditions of only 1/3 of full sunlight (Arno 1973).
The fire regime for Cornus nuttallii is dependent on the overstory community, site conditions, and historical disturbances (USDA 2011). Following a fire the root crown will sprout new growth.
While it occupies the moist conifer forest floor growing to a 6 m to 20 m tree, Cornus nuttallii ranges in areas that are from -1° C to 10° C in winter temperatures, 15.6° C to 22.6° C in summer temperatures. It has the ability to tolerate 310 mm of water and is moderately shade tolerate making it common along stream banks where water holding capacity is 150 cm to 250 cm and in the elevations below 1,981 m (Figure 17) in the plot (USDA 2011)
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Figure 16: YFDP diameter distribution of Cornus nuttallii < 50 cm.
Figure 17: YFDP spatial distribution of Cornus nuttallii DBH ≥ 1 cm.
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Calocedrus decurrens (Torr.) Florin (Incense cedar):
Calocedrus decurrens grows on a wide variety of sites ranging from shaded streams to exposed slopes, which describes the spatial arrangement of Calocedrus decurrens in the plot (Figure 20). It grows well on hot, dry sites and commonly occupies an upper canopy position (USDA 2011). Calocedrus decurrens is very drought tolerant growing in areas where the mean soil water capacity is 130 mm and at a mean elevation of 1,763 m within Yosemite National Park, but it is intolerant of flooding which may explain why they are spatially higher up in elevation in the plot (Lutz et al. 2010).
Calocedrus decurrens increases in the absence of fire. Historically, frequent, low-severity fire thinned sapling and pole-sized incense-cedars in the understory of mixed-conifer forests. Fire exclusion since the early 1900s has allowed continuous recruitment of Calocedrus decurrens and Abies concolor, resulting in dense understory thickets of these shade-tolerant, fire- sensitive species in many mixed-conifer forests (van Wagtendonk et al. 2002).
There are not as many large diameter Calocedrus decurrens throughout the plot (Figure 21). This could be interpreted as a change in the forest structure from where fire has been excluded compared to areas that had experienced fire (Lutz et al. 2009).
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Figure 18: YFDP diameter distribution of Calocedrus decurrens < 50 cm.
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Figure 19: YFDP diameter distribution of Calocedrus decurrens ≥ 50 cm.
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Figure 20: YFDP spatial distribution of Calocedrus decurrens DBH ≥ 1 cm.
Figure 21: YFDP spatial distribution of Calocedrus decurrens DBH ≥ 50 cm.
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Quercus kelloggii Newb. (California black oak):
Quercus kelloggii is most common in mixed-conifer forests, where it is more often an associate than a dominant species (McDonald 1990). Quercus kelloggii co-occurs with Pinus ponderosa throughout nearly all of Quercus kelloggii’s distribution. Abies concolor, Calocedrus decurrens, and Pinus lambertiana are additional important associates in mixed-conifer forests and are all located in the plot. Quercus kelloggii can grow from level valley floors to alluvial slopes, rocky ridges, and steep slopes. It is most common at elevations of 910 m to 2,000 m, in areas where mean soil water capacity is 123 mm, and in temperatures from -20° C to 39° C (Lutz et al. 2010). It is most abundant and reaches its greatest size exceeding 36 m in height and 2 m in DBH on west- facing slopes of the Sierra Nevada (Figure 24) (McDonald 1990).
Crown fires kill tress of all ages and ground fires are often fatal. Radiant heat can kill the cambium and small amounts of flame along the trunk can leave long vertical wounds. Bark thickness on mature trees varies from 2 cm to 5 cm, but even the thickest bark provides little insulation to fire (USDA 2011). Quercus kelloggii sprouts profusely after trees are cut or burned. Most sprouts develop from latent buds, which lie under the bark at, or slightly above, the root collar (McDonald 1990).
Quercus kelloggii often replaces Ceanothus and Manzanita species in low montane zones by growing through shrub stands in low-elevation sites. Quercus kelloggii is a late-successional species on some chaparral-conifer forest ecotones, forming a stable, transitional hardwood forest between chaparral and coniferous forest (McDonald 1990).
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Figure 22: YFDP diameter distribution of Quercus kelloggii < 50 cm.
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Figure 23: YFDP diameter distribution of Quercus kelloggii ≥ 50 cm.
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Figure 24: YFDP spatial distribution of Quercus kelloggii DBH ≥ 1 cm.
Figure 25: YFDP spatial distribution of Quercus kelloggii DBH ≥ 50 cm.
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Prunus virginiana L. var. demissa (Nutt.) Torr. (Western chokecherry):
Prunus virginiana is a native, deciduous, small tree. Stems are numerous and slender, either branching from the base or with main branches upright and spreading. Heights vary considerably according to variety and site quality, ranging from 1 m to 6 m (USDA 2011). It grows at low to mid-elevations in positions in the landscape where combinations of soil and topography permit greater than average accumulation of moisture. These sites include riparian areas, wooded draws, and steep ravines (USDA 2011).
Prunus virginiana can tolerate weakly saline soils but is intolerant of poor drainage and prolonged flooding. It can grow in sparse stands, dense thickets, and under open forest canopies, but persists under closed canopies in mature conifer forests and in riparian areas where it is shade tolerant, but reaches its greatest density near forest edges or open gaps (Figure 27) (Jepson 1993).
Prunus virginiana is well adapted to disturbance by fire. Although susceptible to top-kill by fire, it re-sprouts rapidly either the same year following a spring burn or by the next growing from surviving root crowns and rhizomes (USDA 2011).
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Figure 26: YFDP diameter distribution of Prunus virginiana < 50 cm.
Figure 27: YFDP spatial distribution of Prunus virginiana DBH ≥ 1 cm.
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Prunus emarginata (Hook.) Walp. (Bitter cherry):
Prunus emarginata is a native growing in elevations of 600 m to 2,700 m in cool, moist, and well drained soils. Often forming compact thickets, it generally persists as a medium to tall shrub, 1 m to 6 m in height with associated species such as Calocedrus decurrens, Pinus lambertiana, and Cornus nuttallii. With abundant moisture and deep fertile soil, Prunus emarginata may reach a tree height of 15 m in some areas (Peterson & Peterson 1975).
Prunus emarginata is a generally shade intolerant species of sparse woods, riparian sites, and open areas where there is often evidence of past disturbance. Prunus emarginata sprouts vigorously following fire with approximately 15 to 50 sprouts per plant can be produced. Post fire regeneration also includes germination from on-site seed, and probably also from off-site seed dispersed by birds and mammals (Jepson 1993).
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Figure 28: YFDP diameter distribution of Prunus emarginata < 50 cm.
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Figure 29: YFDP spatial distribution of Prunus emarginata DBH ≥ 1 cm.
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Salix scouleriana Hook. (Scouler’s willow): In the northern part of its distribution, Salix scouleriana is a common understory component of several forest types, including California firs. Generally a shrub, but occasionally growing as a tree, reaching 2 m to 20 m in height, it occurs in thickets and forests’ forming a tall shrub layer in young stands, but is intolerant of shade and can persist only under thin canopies (Jepson 1993). Beneath a tree canopy, Salix scouleriana exhibits a tall, upright growth form, but if top-killed by disturbance it sprouts from the root crown creating a round growth form up to 14.8 m in diameter (Jepson 1993).
Salix scouleriana has a wide range of adaptation. It is found in drier habitats than most willows, occurring as scattered individuals on dry uplands as well as swamps, and mountain streams, and is capable of establishing in dry rocky conditions (Jepson 1993). Salix scouleriana commonly grows on gentle to moderate slopes. While it does occur in riparian areas, Salix scouleriana is more common on upland sites above riparian areas, and is found primarily in forests, meadows, on slopes and in transitional zones between riparian and upland areas (Jepson 1993).
Willows are greatly favored by fire in most habitats. As a survivor and off-site colonizer, Salix scouleriana is abundant following fire and has a moderate regeneration period (Jepson 1993). It is adapted to fire by rapidly re-sprouting from the root crown and establishes from seed on severely burned sites.
Salix scouleriana plants that experience severe canopy mortality apparently concentrate their nutrients into vigorous new growth more than plants which experience only light canopy mortality (Jepson 1993).
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7
6
5
4
3 Stem Stem Count 2
1
0 2 3 4 DBH (cm)
Figure 30: YFDP diameter distribution of Salix scouleriana < 50 cm.
Figure 31: YFDP spatial distribution of Salix scouleriana DBH ≥ 1 cm.
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Abies magnifica A. Murray bis (California red fir):
Abies magnifica is a climax species nearly everywhere it is found. It shares climax status with Abies concolor at the upper limit of the Abies concolor zone, although at any given place Abies concolor or Abies magnifica regeneration may predominate. Abies magnifica dominates at higher elevations in the subalpine zone 2,050 m to 2,700 m (USDA 2011) where mean soil water capacity is 83 mm and winters feature a heavy snowpack (Lutz et al. 2010). Abies magnifica regenerates in greater numbers on a wider range of sites, but suffers greater mortality than Abies concolor (Laacke 1990). Abies magnifica reproduces in greater numbers and on a wider variety of sites. Patterns of Abies magnifica regeneration and canopy dominance can be viewed as adaptive responses to characteristic environmental and site historical conditions in the Sierra Nevada montane and subalpine forests. Abies magnifica dominates nutrient-poor, disturbed settings (Laacke 1990).
Abies magnifica uses widespread and prolific seedling establishment to insure colonization of a variety of disturbed, open sites (Jepson 1993). Although seedling mortality is high and shade tolerance is low, Abies magnifica maintains a broad habitat range by successful colonization of periodically disturbed sites in the Sierra Nevada subalpine forests (van Wagtendonk et al. 2002). Correlations of Abies magnifica canopy dominance with fire scares and fallen logs support this interpretation of its disturbance related distributional pattern (Laacke 1990).
DBH (cm) Stems Count 5 6 35 3 40 1 45 1 60 1 110 1
Table 2: YFDP diameter distribution of Abies magnifica.
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Figure 32: YFDP spatial distribution of Abies magnifica DBH ≥ 1 cm.
Figure 33: YFDP spatial distribution of Abies magnifica DBH ≥ 50 cm.
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Pseudotsuga menziesii (Mirbel) Franco var. menziesii (Douglas-fir):
With only seven known individuals in the plot, Pseudotsuga menziesii grows from west- central British Columbia southward to central California. In California, it is found in the Klamath and Coast ranges as far south as the Santa Cruz Mountains, and in the Sierra Nevada as far south as the Yosemite Region (Hermann & Lavender 1990) therefore this grouping is far south of its range.
Adapted to a moist, mild climate, Pseudotsuga menziesii grows bigger and more rapidly than the inland variety. Trees in diameter of 150 cm to180 cm and 76 m or more in height are common in old-growth stands and in the Abies concolor zone of northern California, Douglas-fir is seral, but as sites become drier it may assume climax dominance (Fites-Kaufamn et al. 2007).
Coast Douglas-fir is more fire resistant than many of its associates and can survive moderately intense fires. Thick, corky bark on the lower bole and roots protects the cambium from heat damage (Hermann & Lavender 1990).
DBH (cm) Stem Count 5 1 10 2 15 1 35 1 105 1 125 1
Table 3: YFDP diameter distribution of Pseudotsuga menziesii.
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Figure 34: YFDP spatial distribution of Pseudotsuga menziesii DBH ≥ 1 cm.
Figure 35: YFDP spatial distribution of Pseudotsuga menziesii DBH ≥ 50 cm.
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Pinus ponderosa Douglas ex Lawson & C. Lawsone (Ponderosa pine):
Throughout its range, Pinus ponderosa, is dependent upon several site variables such as soils, elevation, climate, and is shade intolerant growing most rapidly in near full sunlight which would explain that there is only two known stems in the plot (Figure 36). Soil moisture is the variable most often limiting growth, especially in the summer months when rainfall is deficient (Oliver & Ryker 1990). Pinus ponderosa has the potential for achieving large dimensions. Stems of 263 cm in DBH and 70.7 m in height have been recorded. Diameters at breast height of 76 cm to127 cm and heights of 27.4 m to 39.6 m are common throughout its range (USDA 2011).
The western slope of California's northern Sierra Nevada may be the wettest area supporting Pinus ponderosa, with a mean soil water capacity reaching 139 cm (Lutz et al. 2010). In contrast, this species occupies areas in California where extreme rainfall deficiencies occur during July and August where precipitation about 2.5 cm or less (Oliver & Ryker 1990). Pinus ponderosa response to fire will vary according to fire severity, tree age, and season (Agee 1993). High-severity fires that occur during periods of high stress will generally result in death. Low- to medium-severity fires will generally restrict the growth and regeneration of the tree, but recovery is usually evident the following year (Fites-Kaufman et al. 2007).
DBH (cm) Stem Count 5 1 65 1
Table 4: YFDP diameter distribution of Pinus ponderosa.
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Figure 36: YFDP spatial distribution of Pinus ponderosa DBH ≥ 1 cm.
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Rhamnus californica Eschsch. (California coffeeberry):
With only one known species in the plot, Rhamnus californica generally grows as a small tree in windy or exposed areas and usually do not exceed 1 m to 2 m in height or width, but with stems growing in inland areas or sheltered canyons it can spread to 8 m wide. In elevations ranging from 317 m to 1,055 m, Rhamnus californica can establish on sites that have moist slopes, ravines, and rocky ridges. Soils are typically dry and well drained can establish trees that tolerate full sun to moderate shade (USDA 2011).
Rhamnus californica is a long-lived and moderately shade-tolerant tree that is highly persistent within chaparral, hardwood woodland, and open conifer forests (USDA 2011). With extended fire –free-intervals it is able to outlive, overtop, and shade out many shorter-lived species (USDA 2011).
As a component of relatively open canopied stands, individuals persist until the next fire occurs (USDA 2011), at which time sprouted individuals will become part of the initial post burn vegetation.
Figure 37: YFDP spatial distribution of Rhamnus californica DBH ≥ 1 cm.
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Conclusion
My assumptions on the plot using the data collected is that the differences in fir canopy dominance and response to disturbance events may be related to a complex elevation gradient of the plot (Figure 3). In this lower montane forest, there could be a larger nutrient pool based on 300 year old soil particulate matter and reduced cold stresses that are allowing the greater tree species diversity than in subalpine forests. This increased diversity could promote a complex successional sequence of dominant tree species. Within this successional sequence, Abies concolor has developed a tolerant regeneration mode, where if it keeps on this same trend, it will indefinitely maintain canopy dominance in this compositionally stable forest.
Before Euro-American settlement, the diversity of these mixed conifer forests were increased by periodic fires, which fostered the coexistence of both tolerant and intolerant species (Scholl & Taylor 2006, Fites-Kaufman et al 2007). Reduction of fire frequencies in this montane forest of the Sierra Nevada has triggered canopy closures and shifts in species composition toward more tolerant species, such as Abies concolor.
The structure of this stand is similar to those described for old-growth mixed conifer stands under the influence of nearly a century of fire exclusion by the US Forest Service. Historically moderate severity surface fires killed mainly the seedlings, saplings, and small- diameter trees, but inferring that there has not been a fire in nearly 90 years, the seedling, saplings, and small-diameter trees (Figure 6) are in greater abundance than the large-diameter trees (Figures 7). Thick barked, large-diameter trees such as the large Pinus lambertiana and Pseudotsuga Menziesii are more fire-resistant than species of fir (Guarin & Taylor 2005). The presence of large diameter Abies concolor, which is relatively fire-sensitive, in all stands suggests that the burns where light and patchy enough to allow Abies concolor to grow to a fire- resistant size (Lutz et al. 2009, Agee 1993). Thus, frequent fires promote the development of open forests consisting of mainly large diameter fire-resistant trees that vary in age.
Due to the lack of surface fires, large population of young (<100 years old) fire-intolerant Abies concolor and Calocedrus decurrens are now established beneath the overstory of the older pines and Calocedrus decurrens as evidence from the plot data in relative diameter distributions (Figures 8, 9, 18, 19). Inferring that the stand is now experiencing a shift in proportional
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abundance, mixed forests dominated by pine and cedar are changing to forests that are dominated by Calocedrus decurrens and Abies concolor.
Concluding and inferring from the data that fire exclusion in this plot has caused the stand density to increase from large diameter trees (Figure 7) to small diameter trees (Figure 6), in the long run this could predispose the forest to higher mortality rates from drought.
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References
Agee, James K., 1993. Fire ecology of pacific northwest forests. International Journal of Wildland Fire 4.3: Pages 1-26. Arno, Stephen F., 1973. Discovering sierra trees. Yosemite National Park, Calif.: Yosemite Natural History Association. Fites-Kaufman, J. A., Phil Rundel, Nathan Stephenson, and Dave A. Weixelman., 2007. Terrestrial Vegetation of California, Montane and Subalpine Vegetation of the Sierra Nevada and Cascade Ranges. Chapter 17. Pages 454-501. Guarin, A., and A. Taylor., 2005. Drought triggered tree mortality in mixed conifer forests in Yosemite National Park, California, USA. Forest Ecology and Management 218.1: Pages 229-244. Harry, David E., James L. Jenkinson, and Bohun B. Kinloch., 1983. Early growth of sugar pine from an elevational transect. Forest Science, Society of American Foresters 29.3: Pages 660-669. Hermann, R. K. and Lavender, D. P., 1990. Pseudotsuga menziesii (Mirb.). Douglas-Fir. Pages 1080-1108 in R. M. Burns, and B. H. Honkala, editors. Silvics of North America. USDA Agriculture Handbook 654. Volume 1: Conifers. USDA, Washington, D.C., USA. Jepson, Willis Linn, James C. Hickman, and Willis Linn Jepson 1993. The Jepson Manual: Higher plants of California. Berkeley: University of California.
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Peterson, P. Victor, and Peter Victor Peterson., 1975. Native trees of the Sierra Nevada. Berkeley: University of California, 1975. Scholl, Andrew E., and Alan H. Taylor., 2006. Regeneration Patterns in Old-growth Red Fir– western White Pine Forests in the Northern Sierra Nevada, Lake Tahoe, USA. Forest Ecology and Management 235.1-3: Pages 143-154. USDA 2011. Natural Resources Conservation Service. Plants Database.
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