Major Defining Features
Life zone system Classification by the Holdridge life zone system categorizes dry forests as areas that receive an average of 250-2000 mm of rain per year, exhibit an average biotemperature greater than 17°C, and where potential evapotranspiration (PET) is greater than precipitation (P). [3]. |
Structure of canopy/understory
While canopy levels in tropical dry forests (TDF) are fewer and are less dense, ground vegetation is usually greater than in wet forests. Dry forests exhibit lower above-ground biomass than wet forests, and while underground biomass levels are not well known, dry forests typically have a larger percentage of biomass as root growth.
[3].
This greater percentage of root growth is most likely due to lower rainfall amounts, which means a greater need for morphological advantages that allow for increased water absorption.
Tropical dry forests have a large mixture of deciduous and evergreen trees due to their variable environmental conditions. Both of these two types of trees are apparent in the canopy and understory composition of the tropical dry forest. Both types of trees have developed mechanisms to increase survival in a droughty ecosystem and defenses against herbivory. Deciduous trees will drop their leaves during periods of dryness and only show leaf growth during wet seasons; they tend to have physical adaptations that allow for more efficient photosynthesis and use of water. Evergreen trees do not drop their leaves at all and instead focus on physical adaptations that allow for effective water retention. Evergreen trees also tend to spend more energy on producing physical compounds and higher amounts of lignins and fibers to defend against herbivory. Although evergreens tend to have much higher amounts of these phenolic compounds to deter herbivores, they are also found in some deciduous tree species, but in much smaller amounts.
[8].