Plastic response of Pacific madrones to environmental stressors
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Plastic response of Pacific madrones
to environmental stressors
1
Monica Eskander, 1Katie L Smith, 2Monique Messih, and 3Makayla Monds
1
University of California, Davis; 2University of California, Riverside; 3University of California, Los Angeles
ABSTRACT
Montane meadows provide a wide range of ecosystem services and host rich
biodiversity. These regions of increased biodiversity are under the threat of conifer
encroachment due to changes in climatic conditions. Pioneer species established along
meadow edges, such as Pacific madrone (Arbutus menziesii), have been shown to
facilitate Douglas fir (Pseudotsuga menziesii) encroachment into meadows. By
biologically altering the soil through mycorrhizal associations, madrones create suitable
conditions for coniferous growth. Our results suggest that Pacific madrones
physiologically adjust leaf thickness for optimal resource allocation depending on
climatic conditions. In meadow edges, Pacific madrones show an increase in leaf
thickness when compared to trees in their ideal forest habitat. This plasticity allows
madrones to inhabit meadow edges, leading to further facilitation of conifer
encroachment into montane meadows.
Keywords: madrones, meadows, encroachment, plasticity
INTRODUCTION Lubetkin et al. 2017). Over the last 60 years,
the proportion of tree occupation in
In temperate forest ranges, meadows meadows has increased from 8% to 35% in
support rich biodiversity. Meadows provide the Pacific Northwest (Zald et al. 2012)
fundamental ecological services by Montane meadows are usually unable to
regulating groundwater distribution into support woody vegetation due to their
streams and offering specialized habitat for shallow, clay soils and bedrock basins.
nesting, courtship, foraging, and pollination During the winter rainfall season and
(Lubetkin et al. 2017). A rapid decline in groundwater travels from mountain tops,
meadows over recent years has posed a meadow soils are saturated with water.
considerable threat to forest ecosystems. Excess water prevents young saplings from
This is predominantly attributable to conifer establishing in these meadows due to root
encroachment, which has been triggered by rot (Lubetkin et al. 2017). However,
changes in climate and precipitation (Arno depressed precipitation could decrease the
and Gruell 1986, Haugo and Halpern 2007,
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CEC Research https://doi.org/10.21973/N3SH44 Spring 2021 Vol. 3, Issue 3 1/6
levels of saturation that usually prevent and Penuelas 2006, Mitchess et al. 2008),
woody plant encroachment. we used leaf thickness as a metric of water
In addition to the abiotic drivers of conifer retention and desiccation defense. We
expansion, neighboring Pacific madrones quantified differences in the physiological
(Arbutus menziesii) facilitate conifer growth response of madrones between habitats.
as well. Madrone roots form mycorrhizal We hypothesized that at the edges of
associations that alter soil composition, meadows, madrone leaves would increase
benefiting adjacent coniferous growth and in thickness as overall water availability
encouraging recruitment near meadows increases and sunlight intensifies. Plastic
(Amaranthus and Perry 1989). Although physiological responses to differential
madrones are capable of establishing along habitat resources are indicative of resilience
meadows, those located in habitat edges to environmental stressors. This work may
endure more severe conditions than those contribute towards the understanding of
deeper in the forest, such as increased conifer encroachment and the application
water saturation and sunlight exposure of efficient conservation efforts.
(McDonald and Tappeiner 1990).
As a pioneer species, madrones quickly METHODS
emerge following a disturbance and exploit
newly available resources (McDonald and 2.1 Study site
Tappeiner 1990; Amaranthus and Perry
Our research was conducted at the
1988). Madrones thrive in disturbed
Angelo Coast Range Reserve in Mendocino
conditions, yet increased sun exposure and
County, California, which is part of the
soil water levels threaten their survival
University of California’s Natural Reserve
when they sprout near meadows
System. We conducted research from May
(McDonald and Tappeiner 1990). Despite
3 to 9, 2021. The reserve lies in the upper
being a strong competitor along meadow
watershed of the South Fork of the Eel
edges, forested areas are the optimal
River. The reserve covers 7,660 acres of land
madrone habitat, as canopy cover and
and consists of nine terrace meadows and their
quickly draining soil on slopes offer
upland slopes which are populated chiefly
improved living conditions (McDonald and
by Douglas fir (Pseudotsuga menziesii),
Tappeiner 1990). Changing climate is a well-
tanoak (Notholithocarpus densiflorus), live
documented mechanism of conifer
oak (Quercus spp.), California bay laurel
encroachment into meadows (Lubetkin et
(Umbellularia californica) and Pacific
al. 2017; Hughes 1990, Arno 1986). Less
madrone (Arbutus menziesii). The reserve
studied, however, is how madrones are
has a Mediterranean climate with a high of
surviving along meadow edges to
31oC during summer and a low of 3oC in
supplement conifer growth.
winter. The average annual precipitation is
This study investigates differences in
215.6 cm.
resource allocation between meadow and
forest madrones, and potential indicators of
stress on plants, such as foliar fungal
infections. Following (Búrquez 1987, Ogaya
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CEC Research https://doi.org/10.21973/N3SH44 Spring 2021 Vol. 3, Issue 3 2/62.2 Research Design
We surveyed Pacific madrones at the
edges of meadows and in forested areas.
Within the reserve, we surveyed a total of
13 Pacific madrones in the White House
Meadow, Wilderness Lodge Meadow, South
Meadow, Sprague Meadow, Lower Walker
Meadow, Upper Walker Meadow, Angelo
Meadow and USGS Meadow (Fig. 1). In
forested sites, we surveyed a total of 27
Pacific madrones along the Alquist Trail,
Guimelli Trail and Main Road Trail. We
surveyed madrones in meadows that had Figure 1: Map of the meadows (blue) and forested
canopies that reached the open meadow, areas (red) that we surveyed at Angelo Coast Range
whereas forest madrones were located at Reserve.
least 50 m from a meadow. Each tree Table 1: The scale that we used to rate the infection
measured greater than 0.15 m of each madrone leaf across both sites.
circumference at breast height. At each
meadow site, every madrone was sampled
along the meadow’s edge. Within the forest
sites, we targeted madrones with leaves
that could be reached by hand or removed
with a 12-foot pole. Madrone leaves grow
in distinct clumps. We gathered the lowest
three clumps and randomly selected 5 focal
leaves. At each tree, we recorded
circumference at breast height, any
surrounding woody vegetation with a
diameter larger than 0.15 m within a 7 m
2.3 Statistical Analysis
radius, as well as the length, width,
thickness, and cover of fungal infection of All statistical analyses were conducted
the 5 focal leaves. To quantify fungal using JMP statistical software v15.0. We ran
infection, leaves were rated on a scale from ANOVA to test for differences in madrone
0–5 according to percent cover (Table 1). leaf thickness and infection between
meadows as well as the forested areas.
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CEC Research https://doi.org/10.21973/N3SH44 Spring 2021 Vol. 3, Issue 3 3/6RESULTS
In total, we sampled 40 madrones across
8 meadows and 3 forests. Average leaf
thickness was larger in meadow madrones
compared to forest madrones (n = 40, F =
16.08, p = 0.0003, Fig. 2). Foliar fungal
infection cover was also higher in meadow
madrones than those that reside in forests
(n = 40, F = 33.4464, p = 0.0001, Fig. 3).
There was no difference in leaf length (n =
200, F = 1.7474, p = 0.1941) or width (n =
200, F = 0.6892, p = 0.4116) between the
two habitats. Figure 3: The average leaf infection of madrone
trees in meadows versus in forested areas. The left
bar represents the madrone leaves found in the
meadows which were much more infected than the
right bar which are the madrone leaves found in the
forested areas.
DISCUSSION
The results of our study support our
hypothesis that Pacific madrones
individuals adjacent to meadows produce
thicker leaves than individuals in the forest.
This could indicate differential responses
depending on different environmental
pressures. There is no reason to believe
Figure 2: The average leaf thickness of the madrone
trees in meadows versus in forested areas. The left madrone individuals in the meadows are
bar represents the leaves in the meadows which genetically distinct from individuals in the
were thicker than the right bar which represents the forests, which suggests this species may be
leaves in the forested areas. able to alter its resource allocation. In the
meadow, resources may be allocated to
producing thicker leaves as a defense
against desiccation due to the increased
sunlight exposure (Ogaya and Penuelas
2006). This physiological response may
provide a competitive benefit for madrone
survival under stressful environmental
conditions, such as intensified sunlight at
the edges of meadows.
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CEC Research https://doi.org/10.21973/N3SH44 Spring 2021 Vol. 3, Issue 3 4/6Pacific madrones also had a higher degree in meadows provides a better environment
of foliar fungal infection when adjacent to for establishing seedlings to compete
the meadows, compared to forest against meadow vegetation (Lubetkin et al.
individuals. This higher prevalence and 2017). In addition, decreased winter rainfall
severity of foliar fungal infection can be provides a longer growing season for
attributed to higher humidity and seasonal conifer and madrone seedlings to take
meadow streams spreading foliar fungal advantage of the lower water content in
spores, as these fungal spores spread via meadows (Lubetkin et al. 2017). These
water and wind (Elliott 1995). However, factors could contribute to meadow
drier climatic conditions may decrease the encroachment if current climatic models
transmission of fungal infections between are accurate in their predictions of
individuals, resulting in reduced mortality in increased annual temperatures (Lubetkin et
Pacific madrone at the edges of meadows al. 2017). These findings emphasize the
(Elliot 1995). possible ecological threats arising from
Pacific madrone’s ability to physiologically species interactions that can enable conifer
respond to environmental pressures could encroachment, resulting in ecosystem shifts
be a driver of conifer encroachment. and the loss of meadow biodiversity as
Studies have shown that hardwood tree global climate change progresses.
species, like Pacific madrones, show a
positive correlation between thicker leaves ACKNOWLEDGMENTS
and water deficits, as thicker leaves provide
a defense against desiccation (Mitchell et al. We thank Dr. Krikor Andonian, Dr. Renske
2008; Burquez 1987; Ogaya and Penuelas Kirchholtes, and Robert Blenk for their
2006). This response increases madrone’s mentorship, patience, and encouragement.
survival at the edges of meadows, and This work was performed at the University
mycorrhizal associations provided by the of California’s Angelo Coast Range Reserve,
madrone can enable conifer establishment doi:10.21973/N3R94R.
into meadows (Amaranthus and Perry
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