Dispersal of ponderosa pine (Pinus ponderosa) seeds by shadow

DISPERSAL OF PONDEROSA PINE (PINUS PONDEROSA) SEEDS BY SHADOW CHIPMUNKS (TAMIAS SENEX) IN A MANAGED FOREST

by

Craig Matthew Fiehler

A Thesis Presented to The Faculty of Humboldt State University

In Partial Fulfillment Of the Requirements of the Degree Master of Science In Natural Resources: Wildlife

May, 2007

ABSTRACT Dispersal of ponderosa pine (Pinus ponderosa) seeds by shadow chipmunks (Tamias senex) in a managed forest Craig Matthew Fiehler

I examined dispersal of ponderosa pine (Pinus ponderosa) seeds by the shadow chipmunk (Tamias senex) on thinned and unthinned forest units in the Goosenest Adaptive Management Area (Goosenest Adaptive Management Area) from 2001-2002. I placed 1000 radiolabelled ponderosa pine seeds on three thinned and three unthinned units and tracked the movement of the seeds using a Geiger counter. Tamias senex was the only small mammal observed gathering ponderosa pine seeds at videotaped feeding stations. Seeds were removed from their original locations in less than 24 hours on all but one unit. Between 0.1 and 5.1 % of seeds were found in dispersed caches (1-51 seeds), approximately 1-3 cm under the soil surface 1-7 days after the seeds were deployed. At each cache, I measured the number of seeds (cache size), cache substrate (needle litter or soil), distance moved, and the distance to the nearest trees using the point-centered quarter method. Chipmunks transported seeds farther on thinned than unthinned units (P = 0.027) but cache size (seeds per cache) did not differ significantly between thinned (13.79 ± 1.25) and unthinned (12.84 ± 1.21) units. On unthinned forest units, chipmunks placed caches in areas farther from trees than expected by chance (P = 0.048). Regardless of unit treatment, chipmunks placed caches in soil substrate more often than expected based on its availability (χ2 = 173.76, P < 0.0001). Chipmunk abundance on each unit was positively correlated with the number of caches found and

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negatively correlated with the number of seeds per cache (r2 = 0.48, r2 = 0.86, respectively). Average (± SE) number of seeds removed was greater on thinned units (11.4 ± 2.9%/day) than on unthinned units (8.6 ± 2.1%/day). The cone crop in 2002 was very light for ponderosa pines and nonexistent for white fir (Abies concolor). Tamias senex tended to place caches in locations that favored recruitment and establishment of ponderosa pine seedlings (i.e. in mineral soil and in forest openings) and therefore may contribute to the natural regeneration of ponderosa pine forest.

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ACKNOWLEDGEMENTS

I thank Dr. Luke George for his invaluable assistance at every level of my project. I also would like to thank my hard-working field assistants Kelly Stewart and Kate Leonard. Thanks to my committee members Dr. Rick Golightly and Dr. Mike Mesler for their counsel and support throughout. I thank Dr. Steve Vander Wall for sharing his knowledge of radiolabelling techniques. Thanks to Dr. Steve Zack for funding assistance. Thanks to Kevin Creed for his patience and help in the permitting process. I thank Robyn Conwell for providing housing and moral support when both were sorely needed. I thank John DeLong for his review of previous drafts. I thank Aaron DiOrio and Jesse Conklin for their assistance in the field. I thank all of my labmates and other grad students who helped on this project. I would also like to thank Bill Reynolds of Goosenest Ranger District, Klamath National Forest for procuring vehicles and housing, and for logistical support during my project. Lastly, thanks to the U.S. Forest Service Pacific Southwest Research Station without whose funding and support, this project would not have been possible.

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TABLE OF CONTENTS

Page ABSTRACT....................................................................................................................... iii ACKNOWLEDGEMENTS................................................................................................ v TABLE OF CONTENTS................................................................................................... vi LIST OF TABLES........................................................................................................... viii LIST OF FIGURES ........................................................................................................... ix INTRODUCTION .............................................................................................................. 1 MATERIALS AND METHODS........................................................................................ 4 Study Site ........................................................................................................................ 4 Seed Preparation ............................................................................................................. 7 Seed Dispersal and Removal .......................................................................................... 7 Small Mammal Trapping .............................................................................................. 12 Videography.................................................................................................................. 13 Cone Crop Estimation................................................................................................... 13

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Analysis......................................................................................................................... 14 RESULTS ......................................................................................................................... 15 Seed Dispersal and Removal ........................................................................................ 15 Small Mammal Trapping .............................................................................................. 19 Videography.................................................................................................................. 19 Cone Crop Estimation................................................................................................... 19 DISCUSSION ................................................................................................................... 26 LITERATURE CITED ..................................................................................................... 32

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LIST OF TABLES

Table

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Table 1. Number of radioactive ponderosa pine seeds placed in 100 petri dish stations at increasing distances from the focal tree. The dishes containing the seeds were arranged in 10 1-m wide concentric rings around a focal tree. The arrangement simulated initial wind dispersal of the seeds...................................................... 10 Table 2. Fates of the 6000 radioactive ponderosa pine seeds placed on six study units (three unthinned units and three thinned units) on the Little Horse Peak Research Area in fall 2001 and 2002................................................................. 16 Table 3. Number of caches, mean and range of cache sizes, and mean minimum and maximum cache depth for caches found around six “focal” trees at the Little Horse Peak Research Area in 2001 and 2002.................................................... 17 Table 4. Half-life and daily removal rates of seeds deployed individually at the Little Horse Peak Research Area, California in 2001 and 2002.................................. 24 Table 5. The 2002 cone crop for the dominant conifer species at the Little Horse Peak Research Area, California.................................................................................. 25

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LIST OF FIGURES

Figure

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Figure 1. Location of the six units at the Little Horse Peak Research Area used in this study. The thinned units (7, 12, and 19) are referred to as “pine emphasis” in this figure. The unthinned units (4, 10, and 18) are referred to as the “control” treatment in this figure. ...................................................................................... 5 Figure 2. Schematic of the 60 × 60 m search grid with 5 m spacing (filled circles) established on each of the study units. Small mammal trapping was conducted on a 40 x 40m grid with 10 m spacing (triangles) and centered on the larger grid...................................................................................................................... 8 Figure 3. Average distances (dotted lines) that irradiated seeds were moved on unthinned and thinned units on the Little Horse Peak Research Area in fall 2001 and 2002. The boundary of the box indicates the 25th and 75th percentiles. The solid line indicates the median, dotted line the mean, whiskers above and below the boxes represent the 90th and 10th percentiles, dots are outliers...... 18 Figure 4. Plot of number of seeds per cache abundance of Tamias senex on thinned and unthinned units at the Little Horse Peak Research Area in 2001 and 2002. .... 20 Figure 5. Plot of number of caches versus abundance of Tamias senex on thinned and unthinned units at the Little Horse Peak Research Area in 2001 and 2002. .... 21 Figure 6. Cache substrate selection of Tamias senex on unthinned and thinned units. Expected values were computed based on substrate type at random locations.22 Figure 7. Survivorship curves of 100 seeds placed on unthinned, thinned, and thinned and burned units at the Little Horse Peak Research Area. ............................... 23

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INTRODUCTION

Seed dispersal is a critical part of the life history of plants. Pines are among the many plant species that show morphological adaptations for both wind- and animalmediated seed dispersal (Benkman et al. 1984). Seeds of many pine species have samaras (also called wings) that allow the seeds to be dispersed from the parent plant by wind (Greene and Johnson 1989). Animal-dispersed pine seeds lack wings and are usually harvested directly from the cone (Vander Wall 1994). Ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi) have winged seeds that facilitate wind dispersal from the parent plant and but are also commonly gathered and dispersed by scatter-hoarding rodents and corvids (Saigo 1969, Vander Wall 1992b). Early studies of seed dispersal in Ponderosa and Jeffrey pines assumed that wind was the primary means of dispersal and establishment and that small mammals were seed predators (Curtis 1948, Tevis 1953, Radvanyi 1966, Shearer and Schmidt 1971, Sullivan 1978). However, more recent studies have demonstrated that small mammals have a much greater role in seed dispersal than previously thought. Small mammals may be the primary vectors for seed establishment in these species by placing seeds in dispersed caches (Vander Wall 1992a, 1992b, 1993, 1994). Chipmunks (Tamias spp.) have been identified as the primary seed dispersers for both ponderosa and Jeffrey pines (West 1968, Saigo 1969, Vander Wall 1992a). Chipmunks remove pine seeds from the forest floor quickly and either sequester them in dens, place them in small temporary caches just under the soil surface (scatter-hoard), or consume them (Radvanyi 1966, Abbot and Quink 1970, Price and Jenkins 1986, Vander

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Wall 1992a, Vander Wall 1993). Seeds placed in larders or dens are generally either consumed by the hoarder, attacked by insects or microbial/fungal pathogens, pilfered by other rodents, or are too deep to germinate (Stapanian and Smith 1978, Vander Wall 1994, Jenkins et al. 1995). However, seeds that are scatter-hoarded often are placed in locations that are conducive to germination (Vander Wall 1992b, 1993). Scatter-hoarded pine seeds have a better chance of germination and establishment than those that are larder-hoarded or left on the forest floor. Chipmunks have been found to cache preferentially in soil consisting predominately of inorganic matter (mineral soil), and to avoid caching in the thick needle litter found under the tree canopy (Vander Wall 1993, 1995). Conifer seeds germinate and establish more effectively in mineral soil than in needle litter (Zhong and van der Kamp 1999, Bai et al. 2000). Ponderosa pine seedlings have been found to grow more successfully under the light conditions that characterize open canopy (Aztet and Waring 1970). Therefore, by caching pine seeds in mineral soil and high light conditions, chipmunks may place seeds in microsites that are favorable to germination and growth. The availability of appropriate microsites for seed germination is linked to the condition of the forest in which the seeds are introduced. Ponderosa pine forests have undergone dramatic changes over the last 150 years. Pre-settlement ponderosa pine forests were characterized by open, park-like conditions with an understory composed primarily of perennial grasses and few shrubs (Laudenslayer and Darr 1990). Starting in the late 1800’s, logging, grazing, and fire exclusion resulted in the alteration of ponderosa pine forest structure throughout most of its range (Bailey and Covington 2002). In the ponderosa pine forest of California’s Cascade Range, these human-induced effects

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resulted in the encroachment of white fir (Abies concolor), an increase in the proportion of smaller and younger trees, and an increase in the amount of shrubs and small trees under the canopy (Laudenslayer and Darr 1990). In response to this alteration, various projects have been initiated to restore late successional ponderosa pine forests in the western United States. (Covington et al. 1997, Ritchie and Harcksen 1999). The prescription for ponderosa pine restoration has often called for a combination of selective logging, fuel reduction or removal, and prescribed burning (Covington et al. 1997). I investigated the effects of forest management (i.e. selective logging) on seed caching behavior of the shadow chipmunk (T. senex) and on the subsequent germination of pine seedlings. The yellow pine chipmunk (T. amoenus) disperses seeds of the Jeffrey pine (Vander Wall 1992a), but it is not known whether or not T. senex has a similar relationship with ponderosa pines. With the recent efforts to restore ponderosa pine forest to historic conditions (Covington et al. 1997), it is becoming increasingly important to understand the role of common small mammal species such as T. senex in that process. My objectives were to determine whether T. senex was a seed disperser, a seed predator, or both. I then evaluated the role of T. senex in the recruitment of ponderosa pines on thinned and unthinned forest units.

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MATERIALS AND METHODS

Study Site

The study site was within the Little Horse Peak Research Area of the Goosenest Adaptive Management Area, Klamath National Forest, Siskiyou County, California (Figure 1). This site was located 1 km east of the town of Tennant (latitude 41°58’, longitude 121°28’) in northeastern California. Adaptive management areas were established in 1994 by the Northwest Forest Plan with the intention of developing and testing scientific and social approaches to attaining ecological, economic, and social goals on federal lands (Ritchie and Harcksen 1999). The primary objective for the Goosenest Adaptive Management Area was to accelerate the development of late successional ponderosa pine habitat (Ritchie and Harcksen 1999). Four treatments with five replicates each were created at the Little Horse Peak Research Area in a completely randomized design for a total of 20 units (Ritchie and Harcksen 1999). A unit in this case was a 40-ha component of the total research area. At the start of all silvicultural treatments, all units were of homogeneous age and species composition. Of the four silvicultural treatments applied at the Little Horse Peak Research Area, three were included in this study. The “pine emphasis” treatment (hereafter referred to as thinned) at the Little Horse Peak Research Area consisted of the removal of small diameter trees and leaving large diameter (>30cm diameter at breast height) ponderosa pines (Ritchie and Harcksen 1999). The “pine with fire” treatment (hereafter referred to as thinned and burned) called for the same tree removal scheme as the pine emphasis treatment with the

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5

Tennant

Figure 1. Location of the six units at the Little Horse Peak Research Area used in this study. The thinned units (7, 12, and 19) are referred to as “pine emphasis” in this figure. The unthinned units (4, 10, and 18) are referred to as the “control” treatment in this figure.

addition of periodic prescribed fire (Ritchie and Harcksen 1999). Both thinned and thinned and burned units contained several small (