# Tropical Dry Forest Diversity, Climatic Response, and Resilience in a Changing Climate
## 2 Components of Tropical Dry Forests
### Above-Ground Biomass (AGB)  
On a continental scale, there is a latitudinal gradient both in the current aboveground biomass and the potential AGB. AGB is a measure of all living plant mass that is located above the ground [64]. Mass from stems, leaves, seeds, branches, and bark [64]. These values are directly correlated to precipitation values and the number of dry season months [28]. Mexico and Brazil are found to have the lowest biomass present, while the highest values are found in Costa Rica [28]. The potential for the recovery of AGB is vital in secondary TDFs, and the highest potential ABG resides in the central latitudes, with lower values away from the equator [65]. Tree growth and mortality drive biomass change between years (i.e., the potential for biomass). Tree mortality in early stage TDF is quite small; however, this rate increases to a level comparable to wet forests in late successional stages [66]. This low mortality among early TDF stages reduces species turnover and the rate of AGB accumulation in these forests [66].  
There is no consistent difference between the AGB in TDFs and nearby moist forests. Some studies find TDF sites with far less AGB than floodplain forests, but 3-4 times more when compared to pastures [48; 67]. In Mexico, ABG varied across latitudinal gradients and between successional stagesbut had only 25% of the biomass when compared against the values found in the same stages of wet forests [66]. There is a similar situation in Venezuela where TDFs exhibit the lowest biomass of all biomes [49]; however, this is not consistently replicated by other studies which finds that TDFs have a much higher biomass compared to rainforests of a similar age [68; 69; 70; 71; 72; 73]. The types of plants that contribute the most to biomass also differ between wet and TDFs. In the TDF, the contribution of multi-stemmed individuals was higher than moist forests (45.8%-56% of the AGB) [66].  
In Mexico, the AGB is typically dependent on a few select species, although the exact composition is site dependent. Some sites have 80% of the AGB explained by two species from the _Mimosa_ genus (_Mimosa acantholoba_ var. and _Mimosa tenuiflora_), while others have eight species accounting for the same biomass [66]. The Chamela Biological Station (Jalisco, Mexico) has the most number of species accounting for AGB at 16-17 species [66]. On a micro level, these differences could be due to the factors impacting the forest growth and development, with the variability in AGB in Southern Mexico predicted by the distance to streams, solar irradiance, and altitude [74] in some sites and elevation and slopes found as the most important in other plots [48].  
Despite micro-scale variations in above-ground biomass, which are driven by species composition and micro topographical features, there is an overall continental latitudinal trend in above-ground biomass. The above-ground biomass is, in general, highest in the equatorial regions, and reduces moving farther away from the equator [49; 66; 68; 69; 70; 71; 72; 73]. Much of the current AGB and growth research uses traditional forest inventories; however, dendrochronological methodologies have recently been used to more accurately describe growth patterns at a fine temporal resolution in the boreal forests [75; 76]. These approaches could be transferred to TDF regions to explore their growth response and incorporate them into non-linear models [75; 76].