Summer Solstice Walk in the Elfin Forest

©Bob Field 2005

The diversity, abundance, and distribution of life depend on seasonal changes in the interactions of sunlight and water. We will discuss the influence of the oceans on everything you can see in the Elfin Forest and we will describe a variety of plant adaptations to seasonal change.

1. What is a solstice? What does the Sun do on a solstice?

a. The first day of summer is the longest day of the year and is the day when the Sun’s rays are most vertical; i.e., the Sun appears highest in the sky at mid-day (not noon).

a. Solstice literally means the Sun stands still. This refers to the fact that the length of day and the locations of sunrise and sunset on the horizon are not changing daily on a solstice whereas they change rapidly on an equinox.

b. In fact the Sun is not doing anything special on a solstice; the Earth’s axis of rotation is fixed in space (except for the ~26000 year precession) and its tilt relative to the Sun varies during the year as the Earth orbits the Sun.

c. The north pole of the Earth’s axis of rotation is tilted directly toward the Sun today exposing the northern hemisphere to maximum peak and average sunlight.

d. Seasonal changes influence everything you see here in the Elfin Forest.

e. Seasonal changes depend on the amount of sunlight reaching our latitude.

f. The planet responds to the cumulative effects of more sunlight resulting in moisture and other weather changes that may be delayed from the actual solar peak.

2. The ocean is the source of all water on the Earth.

a. Water influences the weather, life, and the shape of the land.

b. Wind and water are driven by the absorption and scattering of sunlight in the air and the water.

c. All of the sand in the dunes under the Elfin Forest was formed and transported by wind and water.

d. Tides depend on the pull of the Sun and the Moon and vary during the day and during the year, affecting the lifestyles of many creatures.

3. The plants you see in the Elfin Forest are adapted to this environment.

a. The variations in sunlight and moisture and the limited supply of essential nutrients like nitrates and phosphates determine which plants will do well here.

b. Pygmy oak is a variety of the same species of oak seen throughout the California coast. But its reduced height and slow growth pattern are adaptations that do well here. Its acorns would not produce a standard looking oak if planted elsewhere. A standard oak acorn would not produce a pygmy oak if planted here. It may survive, it may struggle, or it may die, but it would not be a pygmy oak.

c. Fuchsia flower gooseberry goes completely dormant in the summer.

d. Chamise has a dual root system – shallow and deep.

e. Manzanita and ceanothus are well adapted to seasonal change – they become dormant in summer, thereby minimizing their need for water and nutrients.

f. Deerweed and bush lupine are legumes like peas and have nitrogen-fixing backteria in their root nodules. No plant can fix atmospheric nitrogen.

g. Dudleya is a succulent – its stomata open at night to let carbon dioxide in because less water is lost when the air is cool and damp. It retains the gas until it needs it the next day for photosynthesis.

h. The annual wildflowers flowers like poppies have a simple adaptation – they die – they don’t have to survive the summer in order to produce viable offspring the following spring.

4. The Elfin Forest is full of examples of plants and animals that interact to survive. Siena’s Point provides an opportunity for a close look at the estuary and the birds that depend on it. Everything you see depends on things you don’t see. Evolution is driven by cooperation and competition in ecosystems.

5. The Elfin Forest has five interacting kingdoms: plants, animals, bacteria, algae, and fungus.

a. Lichen is not a plant; it is a symbiotic community of algae and fungus.

b. Plants cannot use the nitrogen in the air and cannot extract phosphate from most materials. They rely on bacteria and fungi to do these jobs. Plants came from green algae that were able to adapt to the land with the help of bacteria and fungi.

c. Plants have chloroplasts that convert sunlight, water, and carbon dioxide into glucose which is used for plant bodies and for storing energy for metabolic processes. The chloroplasts of their algae ancestors were acquired by endosymbiosis with cyanobacteria, which had previously ruled the world for billions of years causing the oxygen holocaust and saving the oceans from evaporating as the Sun grew brighter and hotter over time.

d. Plants are able to produce highly diverse offspring as a result of genetic mixing that occurs in the process of sexual reproduction.

e. While some plants spread their pollen and their seeds with the help of the wind, many plants have formed symbiotic relationships with animals.

i. Flowering plants co-evolved with insects and sometimes with birds and mammals. Bees and birds are important pollinators, being rewarded with nectar.

ii. Mammals are important seed dispersers, being rewarded with fruits and nuts.

6. How did plants and animals acquire seasonal adaptations?

a. An individual’s inheritance influences its ability to survive and produce offspring in any particular physical and biological environment.

b. The environment selects individual organisms based on their inherited adaptations.

c. The environment shapes individuals, but rarely alters the inheritance of their offspring.

d. In general, seasonal changes favor plants and animals that happened to have traits that provide survival advantages when the environment changes.

e. The diversity of offspring insures that some individuals are genetically endowed to survive change.

f. The ability to survive a changing environment also provides survival traits for plants and animals that are dispersed into new environments, wetter, drier, hotter, colder, nutrient poor, or whatever.