Soils and Vegetation—Lecture 2
Species Density BA Freq
Author Date Title Publisher, Journal, page
Moisture and Distribution
Plant species need an adequate amount of moisture. They don’t want too much moisture, and
they also don’t want too little moisture.
xerophytes=species in dry environments. There are three strategies: escapees, avoiders, and
Escapees are seeds that escape from low-moisture conditions in their environment. They occur
in areas like deserts. They don’t experience drought.
Tolerators can become completely dry, and if you throw water on them, can come back to life.
These things occur in the Sonoma desert, and they can withstand extreme drying. A lot of
energy is needed to suck moisture out of the soil.
Cacti are the ultimate moisture stress avoiders. They are a new world family whose leaves are
quite small and are restricted to subtropics. They have a root system, needles and stem tissues,
and CAM photosynthesis.
CAM photosynthesis allows us to store CO2 as a malic acid. Stomata opens at night, gas
exchange, take in CO2, and CAM pathway can convert it to something that can be stored.
Roots need oxygen because they have to do cell functions. Cells in roots get oxygen.
Adaptations? Mangroves tolerate really saline water as well as the fact that their roots are submerged and tend to have pneumatopores which allow the roots to exchange oxygen.
Silt roots are branches that exchange down to allow gas and water exchange.
Pneumatophores peak up above water from the root system.
Soil nutrients is a critical physical factor, and has a bigger global role in determining plant
functioning than was previously assumed. All micronutrients come out of the mineral matter
that is part of the soil body. Depending on the type of rock available, you will have a different
proportion and availability of nutrients.
Soils that are farmed repeatedly are not replacing their share of micronutrients from
Humidity and Wind
Humidity is moisture in the atmosphere. The Rh is higher than the absolute humidity. If it is less
humid, there is less moisture.
Adaptations lead to different growth rates. Cusion plants are low-growing on the ground. Small
leaves that don’t get dessicated vs waxy leaves.
Ice tends to act like glass. In cushion plants, you have damaged tissues from whipping ice
crystals. In environments like where we are living, you get major damages from winds like
hurricanes. Wind affects transpiration rates. It can result in death and widespread destruction
during severe storm or hurricane events(wind). When hurricane activity hits land, the effect on
plant communities is huge.
High Park Field Trip
-Black Oak/Woodland Savanna
-it is ecologically significant because <1% of oak savannah remains worldwide. High Park is the
4 largest remnant globally
savanna: comprised of scattered isolated trees within a matrix of shrubby and herbaceous
vegetation dominated by graminoids and forbs
-frequent fires are set in the park
-As we move out west, the climate gets drier. In Ontario near the great lakes, the savanna
occurs because of the soil conditions. Sand is a large particle that tends to have a lower area
than clay or silt.
Ecological restoration: the practice of rebuilding the biological and physical environment of
ecosystems which have been damaged or completely destroyed by human impacts
It involves reintroducing native species, restoring natural processes, removing