Mesoamerican Lowland Rainforest - Code: Ne4D

A must-see for anyone with the vaguest interest in nature, this is the luxious habitat that many people think of when they first imagine the Neotropics. 
We tend to think of lowland rainforest as a single entity, yet this habitat is deceivingly heterogeneous with a melange of different forest microhabitats depending on localized hydrology, slope, soil fertility, and underlying rock type, as well as temporal factors such as disturbance due to flooding, hurricanes, fire and landslides. There are variations within the forest microhabitat type at any one locality, but taken as a whole, the habitat and the bird assemblages in it remain fairly constant over large areas, so the bird lists for locations in southern Mexico will be fairly similar to that of lowland rainforest in Costa Rica. However, the experience of being in the lowland rainforest at the local scale varies greatly depending on where you are in the canopy profile. 
The high amounts of precipitation between 48in (1200mm) and  80in (2,000 millimeters), regular rainfall without long dry seasons or intense drought periods,  and relatively constant temperatures (Koppen Ama) results in a surprisingly uniform leaf structure in canopy trees: medium-size leaves that appear similar to those of temperate trees from the laurel family. 
Conifers are notably rare in tropical lowland rainforests. The northern conifers such as spruce, fir, larch and juniper are all missing in these tropical forests; Tabla (Podocarpus matudae), which if mainly a cloud forest tree but grows down to 800m, and other popocarpus are from the southern hemisphere “Gondwanan conifers”are remnants from when these forests were dominated
Deciduous trees are rare in this forest, but notable exception are the “ Kapok” trees, which are Ceiba spp such as  Pochote (Ceiba aesculifolia),  and  occur as an emergents, so while not being dominant, are certainly obvious.With no drought or temperature extremes, deciduous species had no reason to evolve, and nearly all the trees are broadleaf evergreens, most of which lose their old leaves and grow new ones throughout the year. The few trees that do drop their leaves at the same time do so at random times and are not triggered by drought or season, unlike many trees of Mesoamericanl semi-evergreen forest. The canopy is very dense and tall 100ft (30m) with occasional emergents up to 150ft (45m), with multiple  layers of plant growth (strata). The uniform nature of leaf size and texture in the canopy masks remarkable diversity, though the forest may superficially look no richer than a deciduous forest of the e. United States in summer. Typical canopy trees include, Araracanga (Aspidosperma megalocarpon), Guapaque (Dialium guianense), sapodilla sapote (Manilkara zapota),  gavilán (Pentaclethra macroloba), Cacaotillo (Virola guatemalensis), Cassipourea elliptica and, and  the very fast growing (Vochysia guatemalensis). Palms make up only a minor fraction of the rainforest canopy and are noted more for being easily recognizable than for their abundance. 
Although from a distance the forest may look uniform, underneath it is far from it. The understory of the rainforest, which includes the subcanopy and lower stratas is lush, with a variety of smaller trees, which mostly have oversize leaves with large drip tips. Below the sub-canopy, which is almost always over 15 ft. (5m) high, this habitat is very open with a lot of exposed ground.
When canopy trees fall and create an opening in the forest, plants like Guarumo (cecropia obtusifolia)  Mexican Pepperleaf (Piper auritum)  and Alligatorwood (Guarea glabra) rapidly fill the light gap. Over time, saplings from the canopy trees, lying in wait on the forest floor, grow through these pioneer cecropias and reestablish the closed forest canopy.

The higher parts of the rainforest where is is not prone to inundation is often referred to as Terrafirme, and away from the thick forest edge and any light gaps, you will be surprised by just how dark, cool and open the ground level is under the thick, closed canopy and the multiple sub-canopies. This is in stark contrast with the cloudforests where the understory and ground cover can be extremely thick.
Palms are not particularly common in the terrafirma, but In the lower laying swampy areas,  there are patches palms such as Trooli Palm (Manicaria saccifera) and Raffia Palm (Raphia taedigera)  that form thick, almost impenetrable  groves. These groves have different bird assemblages and are always worth exploring, though you’ll need to stand on the terra firma and look in.
 You can spend many days in it and always concentrate on a new environment with a different suite of species; you will have different experiences and find different species in the understories and canopies of the forest edge and light gaps, the palm forest, and lowland rainforest’s dry terra firma (dry parts that are never covered with water). 
A highlight of any visit to these humid forests is to come across an Army Ant swarm. It can be well argued that the habitat changes during a swarm to a completely different environment, and an ant swarm area could be regarded as an extremely temporal micro habitat. (see sideboxXXX)

Much is written about lowland rainforests forming in certain soil types, but most of this is not the case. Other than the extremely nutrient deficient quartzites (which can be pretty close to pure glass), rainforests will form on soils formed over most rock types though the amount of rainfall required for growth may differ; we can generalize and say that the more productive the soil parent material (the rock or sediment the soil is forming in), the lower the rainfall required for rainforest formation. In environments with very nutrient rich bedrocks such as the igneous basalts or gabbros or alluvial sediments, red-brown soils form easily and rainforest growth is possible with 1200 mm of rainfall. At the other extreme, with metamorphic rocks such as gneiss, or the igneous rocks such as granites and rhyolites, rainforest only forms in very stable environments where soil development is faster than erosion, and rainfall is very high. Given the right conditions, weathering of a granite will provide the nutrients required for luxious growth, but because the minerals in a granite weather much slower than in a basalt, they need much longer to weather and release their nutrients.