Mesoamerican Semi-Evergreen Forest - Code: Ne4B

Rainfall of the semi-evergreen rainforests is comparable to that of some lowland rainforests, approximately 48–75 in. (1,200–1,900mm) annually, although the rainforests also grow at much higher rainfalls than this. This climate (Koppen Awb  )has an uneven monsoonal distribution of the rainfall with a dry season of reduced rainfall of up to six months and a few exceedingly dry months with almost no rainfall, along with excessive evapotranspiration rates. So even though for much of the year, it appears an ideal growing environment, it is the harsh months that is  primary driver of this ecosystem.
Much of what is called rainforest in southern Mexico and Central America is actually semi-evergreen forest. The confusion arises because for much of the year, Mesoamerican semi-evergreen forest appears very similar to Mesoamerican lowland rainforest in the wet season with tall trees that grow to around 130 ft. (40m), have large, laurel-shaped leaves, and are draped by numerous lianas. The typical trees that are evergreen, that is they retain their leaves throughout the year, include Jobillo (Astronium graveolens), which  has a very straight trunk, large buttresses that can be 2m (6ft) tall, and can sometimes be so dominant that they forest could be regarded as a Jobillo Forest. Other common canopy evergreen trees that are also found in surrounding rainforests include the  Sapodilla Sapote Tree (Manilkara zapota, Santa Maria (Calophyllum brasilensis),  and possibly the strangest named of any of the rainforest trees, the Horse Balls Tree (Taberneaemontana donnel-smithii), whose fruit is composed of 2 very large separate carpels; botany would be so much easier if all plants were described like this.
In the drier months however, semi-evergreen forest looks very different, with numerous bare branches on those trees. This semi-evergreen nature becomes evident in the dry season, and . although only 30% of the canopy trees are deciduous, losing their leaves in the dry season. Here the deciduous trees become very obvious with the main emergent tree of the forest, the Kapok Ceiba (Ceiba pentandra), losing its leaves and making the large pods hanging from the mare branches very obvious. Other deciduous canopy trees include Hormigo (Platymiscium dimorphandrum), and  Ramon (Brosimium alicastrum) which can lose its leaves twice a year.  Another significant proportion of the canopy trees are semi-evergreen, losing their leaves only in the years when rainfall is reduced to a degree that stresses them, and include species such as Honduran Mahogany (Swietenia macrophylla) and Spanish Cedar (Cedrela odorata).
 It is a little more open than lowland rainforest, with upper canopy coverage at around 80%, which allows for an overall two-canopy structure to the forest, including a distinct and complete middle canopy. Some of the middle canopy trees are also deciduous such as such as the Pink Poui (Tabebuia rosea), but many are evergreen such as Allspice (Pimenta dioica) and Holywood,(Guaiacum sanctum), the latter sometimes becoming  a very dominant mid canopy tree.
Many of the less conspicuous middle-canopy trees species are microphyllous (having small, narrow leaves) rather than deciduous and are more similar to the species of the Mesoamerican Deciduous forest than to lowland rainforest trees. 

These lower-level trees tend to flower in the dry season, and the combination of a colorful lower canopy and a more barren upper canopy makes this forest easier to identify at this time of the year. Epiphytes and mosses are not as numerous as in Neotropical lowland rainforest or Neotropical cloud forest, a fact that becomes obvious only when you are inside the forest looking up. Palms such as the Escobo (Cryosophila stauracantha) are common in the understory, though because they usually only grow to around 7m (22ft) they are not obvious in the mid canopy. Guarumo (Cecropia peltata), is a very common and conspicuous tree with its hand shaped leaves. It is one of the first colonizers where an area is exposed such as road cuttings or light gaps, and are usually replaced by other trees over time. Undergrowth in the semi-evergreen forest is also diminished, due to the heavy lower canopy, so walking around in this forest feels similar to walking in lowland rainforest. 
One of the fascinating aspects of these forests in Mexico is that they may have been extremely denuded by the Mayans in the very recent past. Many of the prime examples of these forests are in areas surrounding deserted Mayan cities such as Tikal and Calakmul, where seemingly timeless forests have formed on fallow land in recent soils derived from denuded hillsides. No doubt, some of the forests cut by the Mayans were lowland rainforests, but the extent that the existing forests can be seen as advanced secondary rainforests or climax semi-evergreen forests is in need of further research.