A Hobbyist’s Guide to Trees

Dendrology in California

Introduction

“The creation of a thousand forests is in one acorn” ― Ralph Waldo Emerson

The importance of trees cannot be overstated. This is a hobbyist's introductory guide to the process of tree identification. This guide is specifically based on native California trees. The best way for the layman to acquaint themselves with this exercise is to begin by practicing observation of their local trees. Hopefully, this activity will encourage your environmental awareness and stewardship.
Forests not only help regulate the climate, but also recycle the carbon dioxide we produce into oxygen, as well as provide clean water and habitat to two-thirds of terrestrial wildlife and plants. Additionally providing many resources to human civilization. Forests are invaluable in combating climate change and biodiversity loss. Forests are regularly impacted by illegal logging and other harmful practices. Furthermore, trees are threatened by introduced diseases and insects, atmospheric pollution or drought often prompted by climate change.
You can be an advocate of trees by learning about them in addition to supporting conservation advocacy groups, and land preservation while planting native species and acquiring a more sustainable lifestyle. Use the resources page to find various entities that support the conservation of trees.

Taxonomy

Merriam-Webster dictionary defines "Taxonomy" as the, "orderly classification of plants and animals according to their presumed natural relationships." Taxonomy is a method used by various scientists and hobbyists for the purpose of accurately identifying and categorizing plants and animals.
Taxonomy is often used in conjunction with other classification methods in order to correctly identify and distinguish species.
Taxonomic hierarchies are structured as follows:

• Kingdom
• Division
• Class
• Order
• Family
• Genus
• Species

For example: A common pine, the "Jeffrey Pine" or by its' binomial name "Pinus jeffreyi":

1. Kingdom - Example: Plantae
2. Division - Example: Pinophyta
3. Class - Example: Pinopsida
4. Order - Example: Pinales
5. Family - Example: Pinaceae
6. Genus - Example: Pinus
7. Species - Example: Jeffreyi

This is how a taxonomic hierarchy would look if you were to break it down and compare the classification of a Jeffrey pine (evergreen) to a Quaking Aspen (deciduous):

Taxonomic Classification Comparison

	Kingdom	Phylum	Class	Order	Family	Genus	Species
Jeffrey Pine	Plantae	Coniferophyta	Pinopsida	Pinales	Pinaceae	Pinus	jeffreyi
Quaking Aspen	Plantae	Magnoliophyta	Dilleniidae	Salicales	Calicaceae	Populus	tremuloides

Identification is particularly important when deciphering between closely related and similar-looking species. The Jeffrey pine is closely related to the Ponderosa pine and is extremely similar in appearance. In these instances, further classification structures are needed in order to identify the individual species. Important factors to consider when attempting to identify a species include: zones (or range) and habitat, bark, leaves, twigs, flowers, fruits and seeds.

Hybridization

Defined as, "an offspring of two animals or plants of different subspecies, breeds, varieties, species, or genera." Related species of trees have the ability and potential to interbreed. These hybrids generally share and represent intermediate characteristics. While you may find hybrids in the field, they cannot be confirmed without chemical or DNA testing.
Hybrid trees, like plants and animals, may have various genetic benefits of hybridization such as disease resistance, increased yields, more predictable growing seasons and uniform appearances. While there may be various benefits from hybridization, it also poses ecological threats when it benefits the growth and reproduction of invasive species.
An example would be the hybrid willow which is a cross between the "white willow" or Salix alba and the "corkscrew willow" or Salix matsudana. Willows commonly grow around creeks and riverbeds, fortifying soils and preventing erosion.
The 'Weeping Willow' is also a hybrid of the aforementioned "white willow" and the "Peking willow" (Salix babylonica) from China.

Species Subdivisions

Further methods of classification are often used beyond taxonomic hierarchies to further narrow down variation. Individual variation in the wild is considered form while produced variation is deemed cultivation.
Many pine trees will vary in shape, size and overall appearance, often related to the associated geography. Piñon and Juniper pines are often present as desert-like chaparral and shrubbery at lower elevations and drier regions while they grow to look like full-sized pine trees at high elevations. Water and oxygen availability as well as exposure can also impact growth.

Common Names

Common names are a great method for the layman to quickly acquaint themselves with their local flora and fauna. Pinus jeffreyi can be referred to as the "Jeffrey pine" or "Western yellow pine", however using common names can present problematic as different species may share the same common name. The Jeffrey pine can also be referred to as the Ponderosa pine in spite of Pinus ponderosa being a different species.

Maps

One of the foremost and most viable means of identification is the use of maps and zones. While some species may be tolerant of various climates and soil types, others have a stricter regional distribution and may only be scattered within very specific areas. The USFS provides regional maps of local flora and fauna, this can be supplemented by a guide or internet research of species; most compiled information will provide an additional map of locations that have been surveyed and identified as zones and habitats for specific species. Since there are "escaped" or invasive species across California, it is worthwhile to use your supplemental guide or internet resource to confirm the native distribution of a suspected species. While even in California, there are various locations where one can observe the beautiful Magnolia trees, this species is in fact not native, as are various conifer species such as the Canary Island pine and Norfolk Island pine that have been transplanted for their cosmetic and aesthetic appearance. There is an area in the Siskiyou Wilderness Area in California that is referred to as the "Miracle Mile" and it consists of 18 different species of conifers (evergreens) within this one-mile stretch.
USFS Interactive Tree Map

Zones

USDA provides a plant hardiness zone map. This map uses average minimum winter temperature values to define regions. These defined regions can generally deduce the average growing season length of a specific region and can be helpful in determining the regions a specific tree species may find habitable or uninhabitable.

Habitat

A distinguishing feature of any tree species is the habitat they prefer and thrive in. Some species have a preference for dry soils over wet soils. Some soils are medial and are therefore considered mesic. Several aspects of a species's habitat should be considered when evaluating: soil type, soil moisture, microclimate and access to water. Each species has its own climate preferences, though since soil can be difficult to discern for the hobbyist or layman, local or tree guides are a useful resource to refer to when evaluating species and their local climate.

Tree Identification

Due to the variable nature amongst species (or individual tree populations), it is helpful to use multiple diagnostic methods in order to accurately identify trees. A tree's overall growth form or its "habit" is a useful tool in the identification process due to its predominant genetic nature, though environment can also influence overall growth. Overall growth can be associated with factor such as size, shape, arrangement and branching patterns often common to a specific genus.

Leaves

Leaves can obscure the overall shape of a tree if attempting to identify a tree by its overall shape in the summer. Alternatively, during the winter months when deciduous trees have shed their leaves, distinguishing trees by overall shape can become easier. It is nonetheless recommended to apply different methods of identification for the best "guess" as to a specific species (Note: Per the earlier mention that a species can only be accurately identified through genetic testing).

Evergreen vs. Deciduous

While deciduous trees can be differentiated more easily in the winter months, what is to be said of evergreens? First we need to define and identify the differences between evergreen and deciduous trees:

Evergreen

Defined as having foliage that remains green and functional through more than one growing season. (Interestingly, California is home to 52 native conifer species) Example: Jeffrey pine; Pinus jeffreyi

Deciduous

Described as falling off or shed seasonally or at a certain stage of development in the life cycle. Example: California Black Oak; Quercus kelloggii

The cycle of shed and yearly lifespan of deciduous leaves are affected by local climate. There are further distinctions made within deciduous trees based on these growth and shedding periods. Drought-deciduous (e.g. Quaking Aspen; Populus tremuloides) trees are trees that lose their leaves during the dry season. Trees that keep their leaves for a full twelve months are referred to as semi-evergreen or tardily evergreen (e.g. California Blue Oak; Quercus douglasii).

California Native Trees

	Evergreen	Deciduous
NorCal	Douglas Fir	Quaking Aspen
	Jeffrey Pine	Black Oak
Central Cal	Western Juniper	Blue Oak
	Two-needle Pinyon	Coast Live Oak
SoCal	Big Cone Douglas Fir	California Sycamore
	California Juniper	Coast Live Oak

Size

Due to the variable nature of leaves themselves, it is generally difficult to identify a species based purely on the size of a singular leaf. However, when comparing the overall appearance of a tree and its' respective leaf sizes, distinctions can be made. (e.g. California Black Oak versus California Blue Oak)
The size of gymnosperm needles seem to be more valuable in making immediate distinctions between evergreen species. For instance, the Jeffrey pine has notoriously long pine needles; when comparing these needles to that of a Lodgepole pine, you can distinguish the two species based on needle size alone. There are other identifying factors such as bark that can be used to further distinguish the two species.

Shape

While other features are more easily distinguishable, another useful identifying factor is leaf shape. When studying leaf shape, it is important to consider the following: veining patterns, leafstalk length (stalk length is generally consistent among most species), the shape of the base and tip of the leaf itself, whether the leaf is lobed or unloabed and if margins are smooth or serrated (also referred to as "toothed").

Arrangement

The method by which leaves grow along twigs can be strongly indicative of specific species. It is therefore an incredibly useful method in tree identification. Identification by arrangement is still useful in the winter when you can evaluate leaf scars on bare twigs.
Singular leaves that grow on twigs without leaves growing directly across are referred to as alternates. Leaves growing directly across from one another in pairs are called opposite. Leaves of three or more growing from the same position on the twig are considered whorled. Example: Dogwoods are known to have an opposite leaf arrangement pattern. Pacific Dogwood trees will be indicative of such.

Broadleaf

Broad, flatleaf blades with net-like veins. Common in most angiosperms. Monocots (e.g. palms) are an exception. Example: Quaking Aspen

Needle-leaf

Scale-like or needle-like leaves with parallel veins. Common in most gymnosperms. Example: Jeffrey Pine, Two-needle Pinyon

Branching

Branching patterns can be observed through leaves and new growth twigs. Twigs can be differentiated from the previous seasons' growth branchlets which are discernibly grey-brown in appearance. Alternatively, twigs usually emerge as bright green in the spring after new growth, taking about one to two years to turn a grey-brown.
Twigs of opposite branching are generally straight. Alternate branching twigs have a zigzag appearance. Branching patterns can appear as a trait among some species. Some twigs have a hairy or velvety texture upon close examination. Other twigs have "banded" lenticels (pores) that can also appear as small pale spots or raised, rough spots on other species.
As previously mentioned, bud scale scars on twigs can also be useful in distinguishing between seasonal growth. Buds on alternate branching patterns influence the general zigzag shape of the twig itself.

Bark

In my own experience identifying trees as a hobbyist, I have found bark to be one of the most useful methodologies in determining a species. Though this distinguishing factor becomes less clear as the tree continues to age.
While there are acute differences in the bark patterns of a Jeffrey pine in comparison to the Lodgepole pine, the California Juniper and the Quaking Aspen, this cannot be generalized. To the untrained eye, a Red Alder and Quaking Aspen may look extremely similar when studying their respective bark, to the point of being indiscernible. Other identifying factors will need to be used to further explore their differences.

Flowers and Fruit

It is important to understand the difference between gymnosperms and angiosperms as only angiosperms will produce flowers and fruits as a result of different reproductive structures.

Gymnosperm ("Naked Seeds")

Defined as, "any of a class (Gymnospermae) of vascular plants that produce seeds not enclosed in an ovary, possess separate male and female reproductive strobili, and include the conifers, cycadophytes, gnetophytes, and gingko." Example: Jeffrey Pine, Two-needle Pinyon

Angiosperm ("Enclosed Seeds")

Defined as, "any of a class (Angiospermae) of vascular plants that have male and female reproductive structures enclosed in a flower, that have seeds which arise from ovules contained in the ovaries, and that produce dry or fleshy fruits after double fertilization." Example: Quaking Aspen, Western Juniper, California Juniper

Flower Structure

A flower is defined as, "the specialized part of an angiospermous plant that occurs singly or in clusters, possesses whorls of often colorful petals or sepals, and bears the reproductive structures (such as stamens or pistils) involved in the development of seeds and fruit." More simply put, it is the reproductive organ of a plant.
A flower is generally structured with petals surrounding and protecting the reproductive parts of the flower itself. These petals are surrounded by green, leaf-like structures called sepals. Within the flower itself, an ovary is encased by the pistil. A pistil may be surrounded by male stamens which end in pollen-bearing anthers. Not all flowers will contain both male and female reproductive parts.

Male vs. Female

Perfect flowers have functional male and female parts.
Staminate flowers are male flowers with functioning stamens. Males produce pollen.
Pistillate (or Carpellate) flowers are female. Only female flowers are capable of producing fruit.
Many species have separate male and female flowers on different trees which means they are dioecious. Trees that have male and female flowers on the same tree are considered monoecious.

Phenology

Defined as, "a branch of science dealing with the relations between climate and periodic biological phenomena (such as bird migration or plant flowering)."
Although timing can vary from year to year, genetic and environmental factors are generally consistent amongst individual species. As a result, seasonal cycles can offer clues for identification.

Gymnosperm Cones

Gymnosperm cones are often useful when attempting to identify or differentiate individual species. While certain evergreens such as the Jeffrey Pine and the Lodgepole pine can be distinguished by their cones alone, cones are an additional characteristic that can help to determine closely related and similarly appearing species such as the Jeffrey pine and the Ponderosa pine.
Visible cones on gymnosperms are referred to as "seed cones" and are female while the less conspicuous male cones produce pollen in the spring and dislodge shortly thereafter.

Angiosperm Fruit

Produced fruit of angiosperms can lend to easy identification of tree groups although botanists maintain different parameters for defining and differentiating produce (e.g. fruit, nuts, follicles, pods, etc.).

Overall Shape

When attempting to identify a particular species, it is important to use a combined approach. This guide provides information on varying methods of identification that can be used in the process. The overall shape of a tree, its' size, leaves and their arrangement as well as its branching pattern and appearance of bark are all markers that can help distinguish species. Being able to differentiate gymnosperms from angiosperms also plays a vital roll in one's ability to determine a tree species.

Resources

In order to provide the most accurate information at my disposal, I used various scholarly resources in order to compile the information provided on this website. See below for a list of cited resources that you can reference outside of this guide to assist you with your identification practice. Citations of photos, maps and other graphic content will be provided as well.

• Alcyon, L. (2019, August 24). Conifers on The Miracle Mile [Review of Conifers on The Miracle Mile]. American Conifer Society. https://www2.conifersociety.org/blogpost/2082607/490139/Conifers-on-The-Miracle-Mile
• Conway, S. (n.d.). Beyond Pine Cones: An Introduction to Gymnosperms (pp. 1–13) [Review of Beyond Pine Cones: An Introduction to Gymnosperms]. The Arnold Arboretum of Harvard University. Retrieved September 14, 2024, from https://arboretum.harvard.edu/wp-content/uploads/2020/08/2013-70-4-beyond-pine-cones-an-introduction-to-gymnosperms.pdf
• Environment, U. (2023). Forests. UNEP - UN Environment Programme. https://www.unep.org/topics/forests?gad_source=1&gclid=CjwKCAjwl6-3BhBWEiwApN6_kuF-30FXaOlaN0iQw-1g02JCJZFknC0D0uht3qjpJAUS36ctanosfBoCZq8QAvD_BwE
• Graham. (2024, May 7). Deforestation and Degradation - Coalition for Rainforest Nations. Coalition for Rainforest Nations. https://www.rainforestcoalition.org/deforestation-and-degradation/?gad_source=1&gclid=CjwKCAjwl6-3BhBWEiwApN6_krexGr0evOUPUrFoDUUy8HaXz5WJUNEtBLFfUPctVjr1d5f_kDVSnxoCWh4QAvD_BwE
• 8.1: Gymnosperms. (2021, June 3). Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Botany/Botany_in_Hawaii_(Daniela_Dutra_Elliott_and_Paula_Mejia_Velasquez)/08%3A_Gymnosperms/8.01%3A_Gymnosperms
• 26.2: Gymnosperms. (2015, November 2). Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_1e_(OpenStax)/5%3A_Biological_Diversity/26%3A_Seed_Plants/26.2%3A_Gymnosperms
• Individual Tree Species Parameter Maps. (n.d.). Www.fs.usda.gov. https://www.fs.usda.gov/foresthealth/applied-sciences/mapping-reporting/indiv-tree-parameter-maps.shtml
• Riley, Karin L.; Grenfell, Isaac C.; Finney, Mark A.; Shaw, John D. 2021. TreeMap 2016: A tree-level model of the forests of the conterminous United States circa 2016. Fort Collins, CO: Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2021-0074
• Sibley, D. (2009). The Sibley guide to trees. Alfred A. Knopf ; New York.
• (n.d.). TreeMap DATA [Review of TreeMap DATA]. U.S. Department of Agriculture. Retrieved September 18, 2024, from https://apps.fs.usda.gov/lcms-viewer/treemap.html
• USDA. (2020). USDA plant hardiness zone map. United States Department of Agriculture. https://planthardiness.ars.usda.gov/
• Merriam-Webster. (2022). Merriam-Webster Dictionary. Merriam-Webster.com. https://www.merriam-webster.com/dictionary/
• >
• Why Forests Matter | Forest Stewardship Council. (2024, June 24). Why Forests Matter | Forest Stewardship Council. https://fsc.org/en/why-forests-matter?gad_source=1&gclid=CjwKCAjwl6-3BhBWEiwApN6_ktlVWafQGXiM5BZMFteIWiJkWRQYc5MYzpzNs_Xy4oPx3Z32YAZq1hoCwNIQAvD_BwE

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