1

Department of Integrative Biology, Lab & Field Ecology, University of Guelph

Influences of Relative Forest Position & Variation in

Environmental Conditions on Seasonal Phenological

Responses in Several Deciduous Tree Species

S. Hudson

Abstract

The purpose of this study was to demonstrate what phenological differences in leaf

senescence and leaf fall exist across several deciduous tree species in the University of Guelph

Arboretum. Phenological changes were analysed in respect to differential environmental

conditions predicted to occur both between tree locations across the forest, and relative canopy

heights. We observed the seasonal transitions of leaf senescence and leaf fall for 46 individuals

of five separate species for approximately one month, comparing and contrasting dates of major

phenological events between species, edge and interior forest sites, as well as for sub-canopy and

canopy level trees. Forest edge trees were found to reach final senescent colour change and leaf

fall significantly earlier than those trees in the forest interior. Differences in canopy level on

phenological response however, showed no general effect, unless analyzed as an interaction with

species type on a species-specific scale. Overall, tree phenological responses between and within

species were found to be primarily determined by local habitat factors and various species-

specific adaptations to environmental conditions.

2

Introduction

Autumnal colour change and leaf fall of trees across the Northern Hemisphere is a

brilliant sight to behold, and is induced by seasonal changes in biotic and abiotic factors that

trees are tuned to detect and respond to (Lim, et al. 2007). The coordination and magnitude of

this event has encouraged abundant scientific research into its component processes; due to its

scale, biological importance to winter tree survival, and key ecological function (Feild, Lee &

Holbrook, 2001). This process is commonly summarized as leaf senescence - defined as the

degenerative breakdown of leaf structure, with the aim of recycling nutrients within the tree in a

form of genetically regulated cellular aging, due to organism-level responses to seasonal climatic

variations and local habitat factors (Gan & Amasino, 1997; Lim, et al. 2007).

Most previous research has focused on the physiological, biochemical or molecular

aspects of senescence on the organism level. These studies have shown that leaf senescence

involves major changes in cell structure, metabolic rates and gene expression, over relatively

short time scales (Gan & Amasino, 1997). Leaf proteins, RNA, membrane lipids and even

chloroplasts, which compose up to 70% of leaf protein, are all broken down to facilitate this

seasonal transition (Gan & Amasino, 1997). These broken down components are then

catabolized into useable nutrients, to be recycled and used in seed production the following year

(Gan & Amasino, 1997). In terms of gene expression, mRNA transcription of photosynthetic

proteins decreases sharply, while transcription of degradative enzymes that facilitate senescence

increases (Gan & Amasino, 1997).

Research into abiotic effects that induce senescence has also been studied. In vivo

experiments conducted by Vitasse et al. (2008) on four deciduous tree species, demonstrated

3

quantitatively that leaf senescence occurs earlier and correlates with lower temperatures and

shorter photoperiod. In contrast, higher temperatures and longer photoperiods confer a senescent

change delayed by up to 61 days. Nutrient concentrations and limitations also play a role in

senescence, with the timing of leaf colour change varying dependent upon the amount of

nitrogen within the leaves (Schaberg et al. 2003). Trees with low nitrogen levels have been

shown to senesce earlier and more completely that those with higher levels; most likely due to

the trees need to save enough nitrogen for the following years seed production (Schaberg et al.

2003). This process is initiated by early production of anthocyanin, a pigment that protects leaves

from damage during nutrient re-translocation (Archetti et al. 2009).

Biotic habitat factors have also been shown to play a large part in the timing of leaf

senescence (Auspurger & Bartlett, 2003). Comparative studies within the species Acer

saccharum confirmed that younger and smaller individuals of the species, which are usually

shaded out by larger and older canopy trees, showed an increase in average leaf retention time of

seven days compared to their older counterparts (Auspurger & Bartlett, 2003). This is most likely

due to an adaptive phenological trait that promotes late leaf senescence in order to maximize the

amount of time that younger trees are not shaded out by the canopy (Auspurger & Bartlett,

2003).

In most research, factors that influence leaf senescence are analyzed at physiological,

organismic and species-specific scales, citing factors such as temperature, photoperiod and light

competition as variables that induce change (Gan & Amasino, 1997). Some studies do compare

phenology between species; however, the literature lacks comprehensive comparisons within

taxa, as well as in regards to how senescence changes with age and in human-managed forests

like the Guelph Arboretum. In any case, area-specific case studies of leaf senescence from year

4

to year are a useful and informative tool to gauge the ever changing dynamics of forest

ecosystems (Clark et al. 2001).

To fill these gaps in our knowledge, and to create a better understanding of differential

leaf senescence, we conducted a comparative study between and within tree taxa across the

University of Guelph Arboretum. This study aims to demonstrate what phenological differences

in leaf senescence and leaf fall exist between several deciduous tree species, in respect to their

relative positions and various functional traits within the forest.

Our first hypothesis postulates that tree position with respect to the edge of the forest will

have an effect on the timing of leaf senescence and leaf fall, due to the differential exposure to

abiotic factors between individuals at the edge of the forest and those within. Edge areas are

assumed to be colder and more exposed to changes in photoperiod, due to the lack of insulating

and light blocking canopy found within dense forest (Harper et al. 2005). Our second hypothesis

postulates that sub-canopy trees will enter senescence and drop their leaves later than canopy-

level trees, in order to maximize the time in which their leaves are free of canopy shade. This

adaptation would maximize light acquisition and carbon fixation for trees usually shaded out by

the canopy above them (Jolly et al. 2004).

Following these hypotheses, we predict that a) all trees both between and within species that are

exposed to edge effects will experience leaf senescence and leaf fall earlier than those trees

located in the interior of the forest, and b) that sub-canopy trees both between and within species

will exhibit leaf senescence and leaf fall later than canopy-level trees.

5

Methods

Study Site

The study site used to test our hypotheses was the University of Guelph Arboretum. The

Arboretum is approximately 165 hectares in area; composed of gardens, forests, trails,

restoration areas and a nature reserve (Stantec, 2013). Overall tree diversity within the

Arboretum was last recorded at 151 different species of woody trees and shrubs (University of

Guelph, 2012). Data collection was conducted within the two largest and least disturbed areas of

forest within this area; the Wild Goose Woods and Victoria Woods.

Set-Up and Pairing of Trees

Set-up began by first defining what would constitute the “edge” and “interior” sites for

categorization of specific tree locations. Edge areas were generally characterized according to

attributes described by Matlack (1994), where forest edges have high densities of saplings,

adventitious limbs and open-area species, as well as higher abundances of shrubs and vines. To

define edge species, a buffer zone of 10 meters was used, with the primary determinant being

that the selected tree must have an area significantly devoid of trees and tree cover within 10

meters of its trunk. This included open areas such as a fields, ponds or canopy gaps. Interior

species were then defined as having no space devoid of trees within this 10 meter radius, and

were characterized antithetically to the edge attributes described above.

Trees were also split into sub-canopy or canopy groups. Sub-canopy trees were

characterized as growing significantly below the main canopy crown, while at the same time

being shaded out by larger trees above them. In addition to forest position characteristics, DBH

trunk diameter at 1.3 meters was also measured. Diameter was considered to be a parameter of

6

relative age, used as an additional indicator of sub-canopy and canopy trees. It also acted as a

filter to exclude smaller trees with few leaves. Trees below five centimeters in diameter were

therefore not included.

As the study was primarily comparison based, a pair-wise transect method was used to

pair and contrast members of the same species. Focus was on species that were common in both

edge and interior areas, including: Acer saccharum, Acer negundo, Juglans cinerea, Fraxinus

americana and Populus tremuloides. Pairing was accomplished by first establishing and

identifying a suitable tree at some point along the forests edge, then classifying it as a canopy or

sub-canopy tree.

Once classified, a transect was set up perpendicular to the edge of the forest, and was

extended for at least 10 meters in until a partner was found. The transect range was set to five

meters wide on each side, increasing the chances of finding a partner tree. Both trees were

marked with numbered flagging tape; edge trees marked with a letter designation and a 1,

interior trees with a letter and a 2. If no suitable partner could be found, a new transect was

drawn with a new edge tree, or a partner from a similar or nearby location was substituted. 23

pairs were made across the two sites, with the five separate species represented at relatively

equal proportions within the 46 individuals.

Data Collection

The study collection period began on October 1st, 2014 and concluded on November 2

nd,

2014. To measure the abiotic and biotic influences predicted to effect senescent phenological

differences between tree species, location and canopy height; both light intensity and

temperature were recorded.

7

These two factors were measured on the first day of data collection as descriptors of

variation between sites. Light intensity was measured as photo-synthetically active radiation

(𝑢𝑚𝑜𝑙

𝑚 ∙ 𝑠𝑒𝑐) at each individual tree, recorded using the Apogee Light Meter. The light meter was

used only on overcast days as recommended by Apogee Instruments, Inc. The measure of light

intensity was used to gauge how much light reached trees on the interior of the forest versus

those on the edge, as well as for how shaded sub-canopy trees differed in light exposure

compared to those in the open. Ambient air temperature was also measured between edge and

interior sites to determine if temperature within the forest differed from that of the exterior.

At the same time, each tree was also assessed for its state of senescent colour change and

leaf fall: its phenological response indicators. The degrees of colour change and amount of leaf

fall were assessed by eye, and observations were taken every two to three days until the end of

the data collection period. Dates were recorded for the first Julian calendar date of first leaf

colour change, first leaf fall, 50% colour change, 50% leaf fall and 90-100% leaf colour change

and leaf fall.

Data Analysis

To determine the variation in environmental conditions between edge and interior sites,

differences in average light intensity and temperature were analyzed using two paired t-tests.

Both t-tests were performed with p = 0.05, and were used to fully quantify the differences in

environmental conditions predicted to occur within each microhabitat.

To determine whether tree phenological responses differed significantly between

treatment groups, two 3-Way ANOVA tests were used (p = 0.05). The first ANOVA test

analyzed differences in dates of leaf colour change, the second for differences in dates of leaf

8

fall. The independent treatments included: species type, forest location (edge or interior) and

canopy level (canopy or sub-canopy). These variables were predicted to effect change in both

dates of senescent colour change and leaf fall. Response dates of first, 50%, and 90-100% colour

change or leaf fall were measured in days post the first day of observation.

Results

Abiotic Variation in Forest Structure

Between edge and interior sites, tree position with respect to the edge of the forest was

predicted to have an effect on the timing of leaf senescence and leaf fall, due to the differential

exposure to seasonal decreases in temperature and light intensity. Between edge and interior

sites, light intensity was significantly different (t = 7.29, df = 22, p-value = 2.68 x 10-7

), with an

average increase of 45.48 +/- 29.27 (𝑢𝑚𝑜𝑙

𝑚 𝑥 𝑠𝑒𝑐) for edge tree sites. Temperature however, did not

differ significantly between the two areas (t = 0.59, df = 22, p-value = 0.56).

Influences of Forest Location

Tree location in respect to the edge of the forest had a significant main effect upon the

timing of phenological events across species, for both senescent colour change (F1, 27 = 6.09, p-

value = 0.02, Fig. 1) and leaf fall (F1, 28 = 5.91, p-value = 0.02, Fig. 2). On average, trees at the

edge of the forest began senescence 1.49 days earlier, and started losing leaves 1.43 days earlier,

compared to interior trees (Fig. 1 & 2). They also completed senescence 3.43 days earlier and

leaf loss 3.61 days earlier, again compared to interior trees (Fig. 1 & 2). These results indicate

that trees closer to the interior of the forest senesce and lose their leaves later than those on the

edge.

9

Influences of Canopy Level and Species Type

Canopy height, predicted to be a primary biotic influence on phenological events, had

neither a significant main effect upon senescent colour change (F1,27 = 0.05, p-value = 0.82, Fig.

3), nor leaf fall (F1,28 = 0.95, p-value = 0.34, Fig. 4). Across species, dates for both senescent

colour change and leaf fall did not differ significantly between canopy and sub-canopy trees.

However, the timing of phenological events did differ significantly between species; for

both senescent colour change (F4, 27 = 9.86, p-value = 4.72 x 10-5

, Fig. 5) and leaf fall (F4, 28 =

10.41, p-value = 2.7 x 10-5

, Fig. 6). Two species: Fraxinus americana and Juglans cinerea, both

reached 90-100% colour change and leaf fall far earlier than the other focal species. Compared to

the next earliest tree species, F. americana and J. cinerea completed senescence 7.43 and 5.97

days earlier, and reached final leaf loss 7.89 and 7.31 days earlier respectively (Fig. 5 & 6). The

three later-changing species, A. saccharum, A. negundo, and P. tremuloides, reached 90-100%

colour change and leaf fall within 3 and 5 days of each other respectively (Fig. 5 & 6). This

relationship indicates that there are species-specific differences and groupings in timing of

phenological events.

These species-specific differences also extended into the effects of canopy height on

phenological events. Despite the majority of factor interactions within the two 3-Way ANOVAS

being insignificant, summarized in Tables 1.1 and 1.2, the interaction between species and

canopy height on tree leaf fall was significant (F4, 28 = 5.48, p-value = 0.0022, Fig. 7). Although

canopy level had no general effect across species, the timing of 90-100% leaf fall between

individuals of canopy and sub-canopy levels within species did differ.

10

However, the canopy level that reached 90-100% leaf fall first was not consistent, and

differed across all five focal species. On average, canopy trees of J. cinerea and A. negundo

reached 90-100% leaf fall 14 and 3.83 days earlier than their sub-canopy counterparts (Fig. 7). In

contrast, sub-canopy trees of P. tremuloides, A. saccharum and F. americana, reached 90-100%

leaf fall 18, 2.35 and 0.25 days earlier than their canopy-level counterparts respectively (Fig. 7).

Discussion

The results of this study show that tree location with respect to the edge of the forest, and

species-specific responses to changes in environmental conditions, were the primary

determinants of initiation and conclusion dates of phenological events. Differences in canopy

level on phenological response however, showed no general effect, unless analyzed as an

interaction with species type on a species-specific scale. Across all species, trees at the forest

edge reached final senescent colour change and leaf fall significantly earlier than those within the

interior of the forest. Dates of final colour change and leaf fall also differed between species, as

well as between individuals of those species differing in canopy level. However, species-specific

results varied widely, suggesting that each species has its own specific responses and adaptations

to seasonal changes in environmental conditions.

The earlier initiations and conclusions of edge tree senescence and leaf fall, compared to

interior trees, can be explained by differences in both environmental conditions and local habitat

factors. Differences in photoperiod and temperature were predicted to be the primary effectors of

differential phenological response, however, only photoperiod was found to change significantly

between sites. Increased exposure to changes in photoperiod within exposed edge sites compared

to sheltered interior sites, is likely a significant contributor to the earlier phenological response of

edge trees.

11

Contrary to our prediction of temperature differences between edge and interior sites,

temperatures differed little between those of the edge and those within. This excludes

temperature as a significant contributor to differential phenological response within our study.

However, temperature was only measured once at the beginning of the study period, which

excludes the fact that temperature may have differed between sites under certain conditions and

at certain times over the rest of the study period. Literature pertaining to temperature gradients

across forest structure often shows that temperatures can differ between these areas, but are

highly variable, under the influence of several factors, including: forest structure, forest

fragmentation, local and regional climate factors, as well as latitude and elevation (Harper et al.

2005).

In addition to the effects of photoperiod and temperature on the date of phenological

events, other, biotic factors may also be at play. Forest edges have been shown to have lower soil

nutrient content, higher species diversity and more competitive interactions compared forest

interiors (Riutta et al. 2012; Gehlhausen et al. 2000). These additional stresses of nutrient

limitation and competition may be factors that promote early senescence in edge trees, as

individuals attempt to conserve their limiting nutrients for the following year (Schaberg et al.

2003; Gordon et al. 1989).

Dates of leaf senescence and leaf fall were also significantly different between species.

Both F. americana and J. cinerea reached 90-100% colour change and leaf fall more than one

week before the other three focal species: A. saccharum, A. negundo, and P. tremuloides. Within

these groups, species were clumped by date of completion, finishing senescence and leaf fall

within three to five days of one another. This distinct separation of certain species and taxa to

certain times of leaf senescence is consistent with the prevailing theories regarding leaf

12

phenology of deciduous trees; where intraspecific variation in phenological response is primarily

under genetic control (Lei & Lechowicz, 1990; Lim, et al. 2007). Differences in dates of leaf

phenology observed within our study can be attributed to variation between species in

characteristics such as: xylem size and number, vulnerability to freezing-induced cavitation,

shade tolerance, nutrient requirements and life history traits (Lei & Lechowicz, 1990). Trees

such as F. americana, with fast growth rates, low shade tolerance and high nutrient level

requirements, tend to senesce earlier than those with slower growth rates, high shade tolerance

and lower nutrient requirements, such as A. saccharum (Schlesinger, 1965).

Canopy level, unless stratified by species, showed neither differences in dates of leaf

senescence nor leaf fall between canopy and sub-canopy trees. Tree canopy level, predicted to be

a primary determinant of differential phenological response, had no effect across species. When

stratified by species however, canopy levels showed significant differences in date of final leaf

fall. However, the canopy level that reached 90-100% leaf fall first was not consistent between

species. This variation between species is most likely why the effect of canopy level type across

species was insignificant. These results suggest that phenological responses to seasonal changes

in environmental conditions are species-specific, with different species having either canopy

level trees or sub-canopy level trees reaching total leaf loss first. Phenological responses may

also be age specific, with shade tolerance and leaf retention being high during the juvenile stage,

then decreasing throughout the life of the tree as the adult passes the threshold of light limitation

(Schlesinger, 1965). Trees that have longer, juvenile sub-canopy leaf retention, have most likely

adapted to late leaf senescence in order to maximize the amount of time that younger trees are

not shaded out by the canopy (Auspurger & Bartlett, 2003) This strategy would allow them to

carry out additional photosynthesis later on in the year, without being shaded out by the trees

13

above them (Auspurger & Bartlett, 2003). However, extended leaf senescence and leaf retention

times may also be phenotypically plastic, as trees that are newly shaded or exposed by canopy

gaps, are able to change the dates at which they transition through phenological events

(Auspurger & Bartlett, 2003). This ability is of particular interest, as the species A. saccharum

has been confirmed as having plastic phenological responses to environmental conditions

(Auspurger & Bartlett, 2003). To test whether phenological events are plastic between other

species, differences in dates of leaf senescence and leaf fall would have to be analyzed

throughout a range of inter-annual variations in seasonal climes over several years (Auspurger &

Bartlett, 2003).

This community-wide study demonstrates that differences in tree phenological responses

between and within species are primarily determined by local habitat factors and species-specific

adaptations to environmental conditions. Compared to the forest interior, we found that forest

edge environments promote both earlier senescent colour change and leaf fall, most likely due to

the increased exposure to changes in photoperiod, nutrient limitations and competition stresses

(Schaberg et al. 2003; Gordon et al. 1989). Differential phenological responses between canopy

levels were only found to be significant at the species-scale, with responses varying and most

likely dependent upon the species-specific physiology, age, adaptations to shading, or plastic

responses to changes in light availability (Schlesinger, 1965; Auspurger & Bartlett, 2003).

This study provides a comprehensive comparison of changes in leaf phenological events

between and within species across gradients in forest structure; and allows us to further

understand how dynamic forest processes change with environmental conditions and in unique

human-managed ecosystems like the Guelph Arboretum. Additional studies are needed in this

field to further explore the influences of intense community interactions on tree performance and

14

dates of phenological events, to understand in what ways competitive or facilitative species

delay, hasten or otherwise influence tree responses to seasonal changes in environmental

conditions. Also, plastic phenological responses of species such as A. saccharum should be

explored, to gauge to what degree dates of phenological events may differ from year to year,

with inter-annual variations in seasonal conditions. Area-specific case studies of leaf senescence

are a useful and informative tool to gauge the ever changing dynamics of forest ecosystems, and

should be continued in future.

Acknowledgements

I would like to thank my peers S. Cady, D. Cronin, A. Sauk, C. Trombley and J. Wade

for their contributions to experimental design and field data collection, without which this study

could not have taken place. Also, I would like to thank my advisors H. Maherali and R. Norris

for their knowledgeable instruction, thorough critiquing of draft manuscripts, and overall support

throughout the course of this study. This project was completed through the University of

Guelph, Department of Integrative Biology.

15

Tables and Figures

Figure 1: Average dates of leaf senescence stages between edge (n = 22) and interior (n = 23) trees within the University of

Guelph Arboretum. Trees on the edge of the forest underwent leaf senescence earlier than those on the interior (F1, 27 = 6.09, p-

value = 0.02). Error bars represent standard error of the mean.

Figure 2: Average dates of leaf fall stages between edge (n = 22) and interior (n = 23) trees within the University of Guelph

Arboretum. Trees on the edge of the forest underwent leaf fall earlier than those on the interior (F1, 28 = 5.91, p-value = 0.02).

Error bars represent standard error of the mean.

0

2

4

6

8

10

12

14

16

18

1st Color Change 50% Color Change 90-100% Color Change

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Senescence

Edge

Interior

0

5

10

15

20

25

1st Leaf Fall 50% Leaf Fall 90-100% Leaf Fall

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Fall

Edge

Interior

16

Figure 3: Average dates of leaf senescence stages between canopy (n = 29) and sub-canopy (n = 16) trees within the University of

Guelph Arboretum. There were no significant differences in dates of leaf senescence stages between canopy levels (F1, 27 = 0.05,

p-value = 0.82). Error bars represent standard error of the mean.

Figure 4: Average dates of leaf fall stages between canopy (n = 29) and sub-canopy (n = 16) trees within the University of

Guelph Arboretum. There were no significant differences in dates of leaf fall stages between canopy levels (F1, 28 = 0.95, p-value

= 0.34). Error bars represent standard error of the mean.

0

2

4

6

8

10

12

14

16

1st Color Change 50% Color Change 90-100% Color Change

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Senescence

Canopy Trees

Subcanopy Trees

0

5

10

15

20

25

1st Leaf Fall 50% Leaf Fall 90-100% Leaf Fall

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Fall

Canopy Trees

Subcanopy Trees

17

Figure 5: Average dates of leaf senescence stages between the species Acer negundo (n = 9), Acer saccharum (n = 14), Fraxinus

americana (n = 8), Juglans cinerea (n = 6) and Populus tremuloides (n = 8) within the University of Guelph Arboretum. Timing

of leaf senescence stages differed significantly between species (F4, 27 = 9.86, p-value = 4.72 x 10-5). Error bars represent standard

error of the mean.

Figure 6: Average dates of leaf fall stages between the species Acer negundo (n = 9), Acer saccharum (n = 14), Fraxinus

americana (n = 8), Juglans cinerea (n = 6) and Populus tremuloides (n = 8) within the University of Guelph Arboretum. Timing

of leaf fall stages differed significantly between species (F4, 28 = 10.41, p-value = 2.7 x 10-5). Error bars represent standard error of

the mean.

0

2

4

6

8

10

12

14

16

18

20

1st Color Change 50% Color Change 90-100% Color Change

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Senescence

Acer Negundo

Acer Saccharum

Fraxinus americana

Juglans cinerea

Populous tremuloides

0

5

10

15

20

25

30

1st Leaf Fall 50% Leaf Fall 90-100% Leaf Fall

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Fall

Acer negundo

Acer saccharum

Fraxinus americana

Juglans cinerea

Populous tremuloides

18

Table 1.1: 3-Way ANOVA table showing main effects (Species, Location (edge or interior), and Canopy Level (canopy or sub-

canopy)) and interactions of factors on final leaf senescence date of trees across the University of Guelph Arboretum. Significant

effects are bolded.

Factors Df Sum

Squares

Mean

Squares

F-

Value

P-Value

Species 4.00 763.90 190.97 9.86 4.72 x 10-5

Location 1.00 118.00 117.99 6.09 0.02

Canopy Level 1.00 1.10 1.05 0.05 0.82

Species: Location 4.00 52.50 13.12 0.68 0.61

Species : Canopy Level 4.00 110.60 27.65 1.43 0.25

Location : Canopy Level 1.00 1.60 1.56 0.08 0.78

Species: Location:

Canopy Level

2.00 30.70 15.34 0.79 0.46

Residuals 27.00 522.80 19.36

Table 1.2: 3-Way ANOVA table showing main effects (Species, Location (edge or interior), and Canopy Level (canopy or sub-

canopy)) and interactions of factors on final leaf fall date of trees across the University of Guelph Arboretum. Significant effects

are bolded.

Factors Df Sum

Squares

Mean

Squares

F-

Value

P-Value

Species 4.00 1055.1 267.78 10.412 2.70 x 10-5

Location 1.00 149.80 149.76 5.91 0.02

Canopy Level 1.00 24.00 23.99 0.95 0.34

Species: Location 4.00 40.40 10.09 0.40 0.81

Species : Canopy Level 4.00 555.30 138.83 5.48 2.18 x 10-3

Location : Canopy Level 1.00 5.10 5.06 0.20 0.66

Species: Location:

Canopy Level

2.00 33.40 16.71 0.66 0.52

Residuals 28.00

19

Figure 7: Average dates of leaf fall stages between canopy levels stratified by species within the University of Guelph

Arboretum. Species included: Acer negundo (n Canopy = 4, n Sub-Canopy = 6), Acer saccharum (n Canopy = 10, n Sub-Canopy = 4),

Fraxinus americana (n Canopy = 4, n Sub-Canopy = 4), Juglans cinerea (n Canopy = 5, n Sub-Canopy = 1) and Populus tremuloides (n Canopy

= 6, n Sub-Canopy = 2) Timing of leaf fall stages differed significantly between individuals of canopy and sub-canopy levels within

species (F4, 28 = 5.48, p-value = 0.0022). “C” denotes canopy trees, while “SC” denotes sub-canopy trees. Error bars represent

standard error of the mean.

0

5

10

15

20

25

30

35

1st Leaf Fall 50% Leaf Fall 90-100% Leaf Fall

Day

sco

re (

Day

s fr

om

Oct

ob

er

1st

)

Stage of Leaf Fall

Acer negundo (C)

Acer negundo (SC)

Acer saccharum (C)

Acer sacchraum (SC)

Fraxinus americana (C)

Fraxinus americana (SC)

Juglans cinerea (C)

Juglans cinerea (SC)

Populous tremuloides (C)

Populous tremuloides (SC)

20

Literature Cited

Archetti, M., T.F. Döring, S. B. Hagen, N. M. Hughes, S. R. Leather, D.W. Lee, S. Lev-Yadun,

Y. Manetas, H. J. Ougham, P. G. Schaberg and H. Thomas (2009) Unravelling the evolution of

autumn colours: an interdisciplinary approach. Trends in Ecological Evolution, 24, 3: 155-173.

Auspurger, C, K. and E. A. Bartlett (2003) Differences in leaf phenology between juvenile and

adult trees in a temperate deciduous forest. Tree Physiology, 23: 517-525.

Clark, J.S., S.R. Carpenter, M. Barber, S. Collins, A. Dobson, J.A. Foley, D.M. Lodge, M.

Pascual, R. Pielke, W. Pizer, C. Pringle, W.V Reid, K.A. Rose, O. Sala, W.H. Schlesinger, D.H.

Wall, and D.Wear (2001) Ecological forecasts: an emerging imperative. Science, 293: 657-660.

Feild, T.S., D.W. Lee, and N.M. Holbrook (2001) Why leaves turn red in autumn. The role of

anthocyanins in senescing leaves of Red-Osier Dogwood. Plant Physiology, 127: 566–574.

Gan, S. and R. M. Amasino (1997) Making sense of senescence. Plant Physiology, 113: 313-

319.

Gehlhausen, S.M., M.W. Schwartz, and C.K. Augspurger (2000) Vegetation and microclimatic

edge effects in two mixed-mesophytic forest fragments. Plant Ecology, 147: 21–35.

Gordon, D.R., J.M. Menke, and K.J. Rice (1989) Competition for soil water between annual

plants and blue oak (Quercus douglasii) seedlings. Oecologia, 79, 4: 533–541.

Harper, K.A., S.E. Macdonald, P.J. Burton, J. Chen, K.D. Brosofske, S.C. Saunders, E.S.

Euskirchen, D. Roberts, M.S. Jaiteh, and P.A. Esseen (2005). Edge influence on forest structure

and composition in fragmented landscapes. Conservation Biology, 19, 3: 768–782.

Jolly, W.M., R. Nemani, and S.W. Running (2004) Enhancement of understory productivity by

asynchronous phenology with overstory competitors in a temperate deciduous forest. Tree

Physiology, 24, 9: 1069–1071.

Lei, T.T., and M.J. Lechowicz (1990) Shade adaptation and shade tolerance in saplings of three

Acer species from eastern North America. Oecologia, 84, 2: 224–228.

Lim, P.O., H.J. Kim, and H.G. Nam (2007) Leaf senescence. Annual Review of Plant Biology,

58: 115–36.

Matlack, G.R. (1994) Vegetation dynamics of the forest edge: trends in space and successional

time. Journal of Ecology, 82: 113-123.

Riutta, T., E.M. Slade, D.P. Bebber, M.E. Taylor, Y. Malhi, P. Riordan, D.W. Macdonald, and

M.D. Morecroft (2012) Experimental evidence for the interacting effects of forest edge, moisture

and soil macrofauna on leaf litter decomposition. Soil Biology and Biochemistry, 49: 124–131.

21

Schaberg, P.G., A.K. Van den Berg, P.F. Murakami, J.B. Shane, and J.R. Donnelly (2003)

Factors influencing red expression in autumn foliage of sugar maple trees. Tree Physiology, 23,

5: 325-333.

Schlesinger, R.C. (1965) Fraxinus americana. Pages 333-338 in Burns, R.M., and B.B. Barbara,

editors. Silvics of North America: Volume 2 Hardwoods. USDA, Washington, D.C, USA.

Stantec Consulting (2013) University of Guelph Victoria Lands Environmental Impact Study.

Stantec. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/24622238.

University of Guelph (2012) Arboretum. Guelph, ON: University of Guelph. Accessed from

http://www.uoguelph.ca/arboretum/.

Vitasse, Y., A.J. Porte, A. Kremer, R. Michalet, and D. Sylvain (2009) Responses of canopy

duration to temperature changes in four temperate tree species: relative contributions of spring

and autumn leaf phenology. Oecologia, 161, 1: 187-98.