Ecology Section - Forest, Carbon and Climate Change

In this section, you would primarily rely on leaf morphology to identify tree species (Leaf shape: Simple vs Compound, Leaf arrangement: Alternate vs Opposite, etc). While you are studying this section, please bear the following questions in mind (*None of these will be in exam/quiz, I will include my thoughts at the end of this page in a few days):

(A) If all trees with diverse leaf shapes (Simple vs Compound) could trace back to a single common ancestor, what might the leaf morphology of this single common ancestor "tree" look like based on the variety we see today, Simple or Compound leaf?

(B) If you think the common ancestor tree may have a simple leaf, and compound leaves emerged later through evolution, do you think the evolutionary trend in leaf morphology is towards increasing complexity (e.g., from simple to compound) or is it more random? Justify your answer.

(C) If the simple leaves came first in evolution, then why the compound leaves could emerge later? How might different leaf shapes confer advantages in different environments or conditions? Why might one shape be favored over another in a specific context?

(D) Do you think that climate plays a role in the evolution of leaf morphology? If the current theory of global warming is correct, with the rising CO2 level and increasing average temperature, can you imagine what the leaf morphology would change correspondingly?

(E) If a particular leaf morphology offers significant advantages in certain environments, what might be happening on a genetic level to propagate that trait?

(F) How quickly do you think a tree species can evolve a new leaf morphology (trait) in response to environmental changes? Decades, Centuries, or Millennia?

(G) If you had the resources to conduct an experiment studying the evolution of leaf morphology, what question(s) would you ask? How would you design it? What factors would you manipulate, and what parameter(s) would you measure? (*We mentioned in class, change only one parameter at one time for clear result interpretation)

(H) How does an understanding of the evolution of leaf morphology contribute to our broader understanding of ecosystems, biodiversity, and the history of life on Earth?

(I) If you had the opportunity to travel back in time and share a dinner with Charles Darwin, what would you discuss with him regarding the evolution of leaf morphology over the ages? (*Charles Darwin is also a plant biologist at that time. He had several publications just on plants to show his appreciation for the evolutionary processes at work in the plant kingdom. This also demonstrated that he has recognized the same principles of natural selection and adaptation that apply to the animals also govern the evolution of plants)

Before diving into any of the above questions, I urge you to pause and reflect. Rather than rushing to an answer, spend a few moments breaking down the complex query into smaller, more specific, and testable questions. Formulate a hypothesis based on your careful thoughts, and then consider its alternative hypothesis. Contemplate how you might go about testing these hypotheses and the kinds of results you anticipate. By adopting this methodical approach, you are embarking on the journey of 'scientific thinking'.

In this Ecology - Forest, Carbon and Climate Change section, we will explore the roles of forests play in carbon fixation and how the climate change would impact the forests to fulfill their roles.

Background:

Forests play key roles in the global carbon cycle, including the storage and sequestration of carbon, with carbon flowing in from the atmosphere through photosynthesis and being stored in living trees, seedlings, saplings, and cycling through non-live pools such as dead wood. litter layer and soils.

Hypothesis:

Tree density and species diversity affect the overall carbon storage capacity of forests.

Alternative/Null Hypothesis:

Tree density or species diversity does not dramatically affect the overall capabilities of forests to store carbon. (We will come down to this, how to construct null hypothesis later, one-tailed or two-tailed)

Study Area:

Two college forests (Trail Forest and Ravine Forest);

Approaches:

Take the Trail Forest for example. This forest has been divided into four distinct rectangular sections. In each of these sections, four trees have been selected as marker trees and all are clearly labeled. Around each marker tree, within a 5m radius, measure and collect the following information:

(A) The total number of trees within the 5m range;

(B) The number of different species present within the 5m range;

(D) Breast Height Diameter (BHD) of every tree in the unit of cm within the 5m range.

We will use the data collected to calculate total carbon fixation amount in both forests, and their distribution according to species richness.

Do you know that a report released by USDA Forestry Service in July 2023 suggests that, in North America, the forests will turn to a major carbon emitter rather than a sink by year 2070? Basically, the forests will emit more carbon into the global carbon cycle than the amount they could sequestrate, based on their predictions.

To understand what's the change and whether their predictions are correct, we need to know about the ecological regions within the North America continent.

Figure: North America is divided into 15 Level-I ecological regions, which are further subdivided into 52 Level II regions, and even more intricately divided into 182 Level III regions. (Source: USDA Forestry Service)

In order to understand the roles that forests play in the fields, let's first look at the North America ecological system as a whole. Think about Canada, United States and Mexico, from the icy tundra of the Arctic to the arid deserts of the Southwest, and from the dense rainforests of the Pacific Northwest to the expansive grasslands of the Great Plains, no wonder that the continent boasts a rich tapestry of ecosystems, vast and diverse, spanning a range of climates and habitats.

To gain a deeper insight into North America's ecological diversity, the nuances of human activities, its varied physical landscapes, and the distribution of natural resources, the continent is segmented into 15 Level I ecological regions. Ever wondered where your hometown fits in? Check the figure above and explore the regions:

1. Arctic Cordillera; 2. Tundra; 3. Taiga; 4. Hudson Plains; 5. Northern Forests; 6. Northwestern Forested Mountains; 7. Marine West Coast Forests; 8. Eastern Temperate Forests; 9. Great Plains; 10. North American Deserts; 11. Mediterranean California; 12. Southern Semi-Arid Highlands; 13. Temperate Sierras; 14. Tropical Dry Forests; 15. Tropical Humid Forests.

Count the names that have "Forests" in them, and you'll see the pivotal role forests play in setting those unique habitat.

Pennsylvania is within the "8. Eastern Temperate Forests" Level-I, "64. Northern Piedmont" Level-II, and "64.C Piedmont Uplands" Level-III ecological region.

Source: USDA Forestry Service

The Eastern Temperate Forests (Level I Ecoregion 8) covers a large portion of the eastern U.S. and is characterized by a temperate climate with distinct seasons. In Pennsylvania, you may have experienced cold winters and hot summers.

If you take a view from Google Map, you may find that the entire Eastern Temperate Forest form a vast forest canopy with mostly of tall broadleaf, deciduous trees and needle-leaf conifers. It has a diversity of tree, shrub, vine and herb layers.

Common trees:

Oaks (White Oak, Red Oak) , Hickories, Maples (Sugar Maple, Red Maple), Pines, Ashes, Elms, Black cherry, Yellow poplar, Sweet gum, Basswood, Hackberry, Common persimmon, Eastern red cedar, Flowering dogwood.

Pennsylvania has one of the nation's largest state park system, 121 state parks in total in nearly 300,000 acres. Forests, including those in regions like Philadelphia, Pennsylvania, are dynamic entities that orchestrate a multitude of Earth's biogeochemical cycles. Their indispensable roles in the planet's ecological balance can be keenly observed across numerous elemental cycles.

What are the Forests' Roles in these Cycles?

Starting with the carbon cycle, forests are paramount carbon sinks. They absorb vast amounts of carbon dioxide during photosynthesis, storing this carbon in their trunks, branches, leaves, and extensive root systems. This sequestration is especially crucial in urban forests like those in Philadelphia, where the trees act as vital counterpoints to urban emissions, helping to offset the carbon footprint of city activities.

The oxygen cycle is closely linked with the carbon cycle. As forests capture carbon, they simultaneously release oxygen. Philadelphia's urban forests, such as Fairmount Park — one of the largest urban park systems in the country — not only provide recreational spaces but also act as the city's lungs, offering a fresh supply of oxygen and enhancing the overall air quality for its residents.

In the nitrogen cycle, forests play a multifaceted role. Trees, along with their symbiotic fungi, fix atmospheric nitrogen, making it available to other plants and organisms in the ecosystem. This is of particular importance in places like Philadelphia, where industrial activities and vehicular emissions release various nitrogen compounds. Forests help in assimilating some of this nitrogen, preventing it from becoming a pollutant.

Forests' involvement in the phosphorus cycle revolves around the decomposition of organic matter. As leaves, branches, and other organic materials decay, they release phosphorus back into the soil, replenishing it for the nourishment of future generations of plants. In Philadelphia, where urban development often challenges natural processes, the forests' role in cycling phosphorus ensures the sustainability of green spaces.

The sulfur cycle is another where forests demonstrate their regulatory prowess. Trees and forest soils absorb sulfur, especially in areas impacted by industrial activities. Philadelphia, with its rich industrial history, has seen its share of sulfur emissions. The city's forests play an understated but vital role in absorbing atmospheric sulfur, thus moderating potential environmental hazards like acid rain.

In essence, these cycles are intricately connected and do not function in isolation. For instance, the availability of nitrogen can influence the rate of carbon sequestration through photosynthesis. Philadelphia's urban forests, in their quiet majesty, showcase the intricate dance of these elemental cycles, emphasizing the importance of conserving and expanding these green havens in urban landscapes.

Water Cycle

Sulfur Cycle

Oxygen Cycle

Nitrogen Cycle

Phosphorus Cycle

Carbon Cycle

How the Biodiversity of Forests' impact the Forest?

Biodiversity, or the variety of life within an ecosystem, plays a crucial role in how forests regulate biogeochemical cycles. The diversity of species in forests, including those in urban landscapes like Philadelphia, Pennsylvania, directly and indirectly influences the efficiency and resilience of these cycles.

Carbon Cycle: Different tree species have varying rates of carbon sequestration. Some trees grow faster and absorb more carbon dioxide than others. The diversity ensures that, overall, the forest has a robust response to changing conditions, optimizing carbon uptake throughout varied environmental situations. Furthermore, a diverse understorey, comprising shrubs, grasses, and herbaceous plants, can also contribute significantly to carbon storage.

Oak Trees (e.g., Quercus spp.): These trees have a long lifespan and can store large amounts of carbon over time. Their dense wood contributes significantly to carbon sequestration.
Pines (e.g., Pinus spp.): Fast-growing species like loblolly pine can rapidly sequester carbon, especially in their early growth stages.

Oxygen Cycle: Biodiversity impacts photosynthetic efficiency. A diverse forest will have species that can photosynthesize under a range of light conditions, temperatures, and moisture levels. This variation ensures a steady release of oxygen even under fluctuating environmental conditions.

Eucalyptus Trees (e.g., Eucalyptus spp.): Known for their rapid growth rates, eucalyptus trees have a high rate of photosynthesis and consequently release large amounts of oxygen.
Maples (e.g., Acer spp.): With their broad leaves, maples have a substantial surface area for photosynthesis, contributing to oxygen production.

Nitrogen Cycle: Different species of plants have unique relationships with various nitrogen-fixing bacteria and fungi. A higher diversity of plants means a greater diversity of these microorganisms, leading to more efficient nitrogen fixation. Moreover, certain plants, like legumes, are especially effective at drawing nitrogen from the atmosphere, enriching the soil for other plants.

Alder Trees (e.g., Alnus spp.): Alders have a symbiotic relationship with nitrogen-fixing bacteria in their root nodules, which allows them to enrich the soil with nitrogen.
Leguminous Trees (e.g., Robinia pseudoacacia, Black Locust): Similar to alders, leguminous trees can fix atmospheric nitrogen through symbiotic relationships with root bacteria.

Phosphorus Cycle: Different plants have distinct mechanisms for acquiring phosphorus. Some plants release specific organic acids to solubilize phosphorus from soil minerals, while others may rely on mycorrhizal fungi. A diverse forest will utilize multiple strategies to access and recycle phosphorus.

Beech Trees (e.g., Fagus spp.): These trees often form symbiotic relationships with mycorrhizal fungi, which aid in extracting phosphorus from soil particles.
Conifers (e.g., Spruce, Picea spp.): Their association with ectomycorrhizal fungi can enhance phosphorus uptake in low-phosphorus soils.

Sulfur Cycle: Biodiversity affects the sulfur cycle primarily through varied rates of uptake and deposition. Different species have unique tolerances and needs for sulfur. A diverse forest can help stabilize sulfur concentrations in both the atmosphere and the soil.

Willows (e.g., Salix spp.): Located often in wet areas, willows can uptake sulfur effectively, especially in riparian zones where sulfur deposition can be higher.
Cedars (e.g., Cedrus spp.): Their needle-like leaves can intercept and absorb atmospheric sulfur, especially in areas with high sulfur emissions.

In places like Philadelphia, where urban forests like Fairmount Park are interspersed with developed areas, the biodiversity within these green spaces becomes even more critical. A diverse forest can respond to a range of stressors, from pollution to changing climate conditions, ensuring the continuous regulation of essential elemental cycles. For an urban environment like Philadelphia, Pennsylvania, tree species like oaks and maples are quite common and play a role in carbon sequestration and oxygen release, respectively. The presence of specific species in such environments can influence not only the aesthetic and recreational value of urban green spaces but also their efficiency in contributing to biogeochemical cycles. Recognizing the role of individual species can inform urban forestry practices, ensuring that city forests optimally support these critical ecosystem functions.

Furthermore, diversity in fauna, from decomposers to herbivores, plays a role in nutrient cycling. Decomposers, like fungi and bacteria, break down organic matter, while herbivores influence plant growth and litter deposition. The interplay between various trophic levels in a biodiverse forest ensures efficient nutrient cycling and ecosystem resilience.

In conclusion, species diversity amplifies the forest's ability to regulate biogeochemical cycles, bolstering its resilience against disturbances and providing a more stable environment. As cities like Philadelphia recognize the importance of urban green spaces, efforts to maintain and enhance biodiversity become paramount in ensuring the health and sustainability of these ecosystems.

CARBON SEQUESTRATION AND EMISSION

Credit: USDA Forest Services, Forest Atlas of the United States (2022)

From USDA Forest Atlas of the United States (2022):

"Forests sequester carbon from the atmosphere through photosynthesis and stores it as plant mass or eventual wood products. When trees collapse, carbon continue to remain in the forest ecosystem and cycle through collapsed trees (or wood products), downed wood, forest floor, soil organic carbon, and eventually, to the atmosphere through decay or combustion."

Credit: USDA Forest Services, Forest Atlas of the United States (2022)

Now, let's see how to calculate the amount of carbon stored in a tree...

Since we are going to use the equations to estimate total stored carbon within the trees in a given unit area.

Estimating the amount of carbon stored in a tree involves considering the tree's biomass and understanding that roughly half of that biomass is carbon. Here's a general method to estimate carbon storage:

1. Determine the Biomass of the Tre

The most common method to estimate a tree's biomass is by using its diameter at breast height (DBH). There are various allometric equations developed for different tree species and regions to estimate tree biomass from DBH. An allometric equation relates one measurable attribute of an organism (in this case, DBH) to another attribute (biomass).

This DBH is routinely used in forestry. We will also use this parameter to gauge the carbon stored in the tree. We will go to the College Ravine Forest to measure the DBH of each individual tree within the pre-determined plot using the D tape and calculate the total DBH of each plot.

2. Convert Biomass to Carbon Content

Once you have an estimate for the total biomass of the tree, you can estimate its carbon content. It is widely accepted that about 50% of a tree's dry biomass is carbon. We will also the 50% conversion ratio in our analysis.

3. Consider Other Components (optional)

While the above steps give a broad estimate for the trunk or bole of the tree, trees also have roots, branches, and leaves that contain carbon. Some allometric equations already factor in these components, while others only consider the trunk. Ensure you know what your chosen equation covers. If you have an equation only for the trunk, and you wish to get a more holistic estimate, you may need to use different equations for different parts of the tree and sum them up.

4. Adjustments for Region and Species

The type of tree and where it grows can influence carbon content. Tropical hardwoods, for instance, may have different carbon content than pine trees in temperate regions. Be sure to use allometric equations that are specific to the tree species and region under study for accurate results.

5. Use Tools and Databases

There are various tools, databases, and software available that can simplify this process for you. For instance, the U.S. Forest Service has a tool called the CO2FIX model which can help estimate carbon sequestration in forests.

6. Remember the Limitations

These calculations provide an estimate. Actual carbon content can vary based on numerous factors, including the health of the tree, its age, the soil it's grown in, and more.

If you're doing this for a research project, forest management, or carbon offset program, it's crucial to ensure that your methods align with established protocols and guidelines.

Tree Species Identification in College Forests

In this first ecology session, we will delve into the roles that forests play in the global carbon cycle and examine how Climate Change affects forests' ability to fulfill this role. As we showed above, diversity in tree species distribution could dramatically affect the forests' roles in carbon fixation. Therefore, in order to bettter address this question, we first need to learn how to identify individual tree species.

There are multiple ways that we can identify Trees, such as using leaves, twigs, bark, buds, flowers and fruits. While we will use leaf shape to identify trees. Since when people started to use various morphologic traits to systematically classify plants?

Courtesy by The Metropolitan Museum of Arts

One early work that played a significant role in the formal identification and classification of plants is Herbarum vivae eicones (Living Images of Plants) by Otto Brunfels (see left). It was published in year 1530 and contained detailed illustrations and descriptions of plants, aiding in their identifications.

Now let's head to the Ursinus Forest to identify the tree species...

Ecologists rely on multiple traits to identify tree species, such as leaf morphology, seed/fruit type, flower shape, bark appearance, etc.

Leaf Type - Scale-like | Broad flat | Needles

Leaf Arrangement - Alternate | Opposite | Whorled

Leaf Structure - Simple Leaf | Pinnately Compound Leaf | Palmately Compound Leaf

Leaf Margin - Serrate | Double Serrate | Dentate | Lobed | Entire

Hint: Look for the position of the Axillary Bud.

Identifying_Pennsylvania_Trees_1-3_PSU TreeID Program.pdf

Summer_Key_for_Pennsylvania_Trees_SummerTreeKey.pdf

Common_Trees_of_Pennsylvania_comm-trees.pdf

Let's see if you could use the leaf traits to identify which tree species they are. These are all commonly found in both College Forests:

Red Maple Acer rubrum

Sugar Maple Acer saccharum

Red Oak Quercus rubra

White Oak Quercus alba

Bitternut Hickory

Flowering Dogwood

Cornus florida

These are the most common tree species that you could find at Ursinus Forests:

Hickory: Bitternut, Shagbark

Oak: Red Oak, White Oak, Chestnut Oak

Maple: Red Maple, Sugar Maple, Silver Maple, Boxelder/Ash-leaf Maple

Coniferous: Eastern White Pine, Eastern Red Cedar

Compound: Walnut, White Ash

Simple: Hackberry, Slippery Elm, Black Cherry, Black Birch, American Holly, Beech

You may use the following diagrams to better identify them.

Common Tree Species in Pennsylvania

American Beech Fagus grandifolia

Yellow Birch Betula alleghaniensis

Sweet (Black) Birch Betula lenta

Paper Birch Betula papyrifera

Eastern Hemlock Tsuga canadensis

Eastern Redcedar Juniperus virginiana

Balsam Fir Abies balsamea

Norway Spruce Picea abies

Eastern White Pine Pinus strobus

Horse Chestnut Aesculus hippocastanum

Red Pine Pinus resinosa

American Elm Ulmus americana

Bitternut Hickory Carya cordiformis

Pitch Pine Pinus rigida

Black Cherry Prunus serotina

Black Walnut Juglans nigra

American Larch Larix laricina

White Ash Fraxinus americana

Sycamore Platanus occidentalis

Sassafras Sassafras albidum

Cucumber-tree Magnolia Magnolia acuminata

Sweetgum Liquidambar styraciflua

Norway Maple Acer platanoides

Black Locust Robinia pseudoacacia

Striped Maple Acer pensylvanicum

Smooth Sumac Rhus glabra

Yellow poplar Liriodendron tulipifera

Common Tree Species in Pennsylvania

Red Maple Acer rubrum

Sugar Maple Acer saccharum

Flowering Dogwood Cornus florida

Northern Red Oak Quercus rubra

White Oak Quercus alba

American Beech Fagus grandifolia

Yellow Birch Betula alleghaniensis

Sweet (Black) Birch Betula lenta

Paper Birch Betula papyrifera

Eastern Hemlock Tsuga canadensis

Eastern Redcedar Juniperus virginiana

Balsam Fir Abies balsamea

Norway Spruce Picea abies

Eastern White Pine Pinus strobus

Horse Chestnut Aesculus hippocastanum

Red Pine Pinus resinosa

American Elm Ulmus americana

Bitternut Hickory Carya cordiformis

Pitch Pine Pinus rigida

Black Cherry Prunus serotina

Black Walnut Juglans nigra

American Larch Larix laricina

White Ash Fraxinus americana

Sycamore Platanus occidentalis

Sassafras Sassafras albidum

Cucumber-tree Magnolia Magnolia acuminata

Sweetgum Liquidambar styraciflua

Norway Maple Acer platanoides

Black Locust Robinia pseudoacacia

Striped Maple Acer pensylvanicum

Smooth Sumac Rhus glabra

Yellow poplar Liriodendron tulipifera

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