Dry forest articles (Biotropica 46(1); January 2014)

January 2014 Volume 46(1)

Three out of fourteen articles covered dry forest topics. Not bad coverage. Not surprisingly, given the pervasive human influence on tropical dry forests all of these studies focus on successional or disturbed sites.

Neves et al. examined how insect herbivory varies with successional stage and canopy height at Mata Seca State Park in Minas Gerais state, Brazil. This looks like an interesting site where a good body of research is being established. Their findings, overall:

We found that the richness of sap-sucking insect increased along the successional gradient at both spatial scales studied (tree and plot scales), but trends were mixed for the other tested variables. We also detected a vertical stratification in insect diversity which is affected by the interaction between guild and period of the rainy season. Such successional and vertical differences were also observed for leaf damage. Finally, we verified a decrease in morphospecies richness and abundance of both sap-sucking and chewing at the end of the rainy season.

Peguero and Espelta looked at tree regeneration triggers in the Miraflor-Moropotente plateau in northwestern Nicaragua. They described the area as "a partially protected landscape, i.e., silvo-pastoralism is allowed but some practices such as logging and fire are precluded" which has resulted in "a mosaic of wooded rangelands surrounded by secondary and remnant NDF [Neotropical Dry Forest] patches". They fed the fruits of three dry forest tree species (Acacia pennatula, Enterolobium cyclocarpum, and Guazuma ulmifolia) to calves (to determine feeding preference), and then subjected seeds of the same species to a rather fascinating system designed to simulate gut passage. 

To simulate the effects of gut passage on the seeds, we developed a three-step—(1) rumen; (2) abomasum-duodenum; (3) intestine—in vivo–in vitro standardized procedure... Fruits from five individuals of each species were hand-harvested and manually dehisced to obtain their seeds. Once in the laboratory, the seeds of each species from different individuals were pooled and put into sealed nylon bags in separate groups ... and then in the rumen of a cannulated cow. After 48 h of rumen suspension, the bags were placed in glass incubation bottles containing 2 l of 0.1 N HCl adjusted to pH 1.9 with 1 g/l of pepsin... ).

Finally, to reproduce the anaerobic intestinal environment, rectal feces samples from three different cows were collected in plastic bags saturated with CO₂ and immediately placed in a water-bath with a buffer solution of salt minerals (NaCl, KCl, NaPO₄, KPO₄) at 39 °C. The feces were manually crumbled in order to re-suspend fiber-associated bacteria and the solution was filtered through a 250 μm mesh screen and completed with a buffer solution of salt minerals until reaching a dilution of 0.2 g fecal sample per ml of buffer (adapted from Bindelle et al. 2007). The bags with the intestinal bacterial inoculum were incubated 24 h more with constant rotation at 39 °C in anaerobic conditions. 

They then simulated fire by exposing the seeds to thermal shocks (60, 90, and 120 °C) and observed germination success. They found an additive effect of gut passage and 'fire' on seed germination. They ended with a lot of vague generalities about megafauna dispersal syndrome and the role of pasture trees as roosts for seed dispersers. Seeing someone else do it makes me acutely aware of how much of my dissertation must read.

The final one of these three articles deals with fruit and flower availability along a restoration gradient (which is, in fact, the very matter-of-fact, descriptive title of the article). This is another Brazilian study, this time semideciduous Atlantic forest in São Paulo state. All of these sites were former sugarcane plantations, and all were intentionally restored. The sites were 12, 23 and 55 years old, and were paired with a reference site in intact forest. Their findings:

Our data suggest that a wide range of plant growth forms provides resource complementarities to those of planted tree species. Different flower phenologies between trees and non-trees seem to be more evident in a forest with high non-tree species diversity. We recommend examples of ideal species for planting, both at the time of initial planting and post-planting during enrichment. These management actions can minimize shortage and periods of resource scarcity for frugivorous and nectarivorous fauna, increasing probability of restoring ecological processes and sustainability in restoration sites.

• Neves, Federico S., Silva, Jhonathan O., Espírito-Santo, Mário M., Fernandes, and Geraldo W. 2014. Insect Herbivores and Leaf Damage along Successional and Vertical Gradients in a Tropical Dry Forest. Biotropica 46(1):14-24 DOI: 10.1111/btp.12068
• Peguero, Guille, and Espelta, Josep M. 2014. Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: an Experimental Test. Biotropica 46(1):83-89 DOI: 10.1111/btp.12076
• Garcia, Letícia C., Hobbs, Richard J., Mäes dos Santos, Flavio A., Rodrigues, and Ricardo R. 2014. Flower and Fruit Availability along a Forest Restoration Gradient. Biotropica 46(1):114-123 DOI: 10.1111/btp.12080

Two other articles earn 'honorable mention' in the dry forest category: Zeilhofer et al.'s jaguar habitat modelling paper (since it looks at cerrado which is, arguably, dry forest) and Domic et al.'s article about Polylepsis tomentella regeneration in semiarid Andean valleys. These are technically too dry and possibly too cold to meet most definitions of dry forest, but the underlying processes (and problems) related to regeneration would probably be familiar to dry forest species.

• Zeilhofer, Peter, Cezar, Adelaine, Tôrres, Natália M., Jácomo, Anah T. de Almeida, and Silveira, Leandro. 2014. Jaguar Panthera onca Habitat Modeling in Landscapes Facing High Land-use Transformation Pressure—Findings from Mato Grosso, Brazil. Biotropica 46(1):98-105 DOI: 10.1111/btp.12074

• Domic, Alejandra I., Camilo, Gerardo R., and Capriles, José M. 2014. Small-scale Farming and Grazing Reduce Regeneration of Polylepis tomentella (Rosaceae) in the Semiarid Andes of Bolivia. Biotropica 46(1):106-113 DOI: 10.1111/btp.12075

So what is this thing, really?

Figured I'd try writing something for a more general audience.

Visit the tropical dry forest in the wet seasons and no one would fault you if you went home and told your friend about your trip to the rainforest. But come back a few months later and you'll wonder where all the green went. Many of the trees are now leafless; most of the rest still have some of their leaves, but they've lost a lot of them. The leaves that are left have a yellowed, bleached-out quality to them. And with their leaves gone, you notice how thorny a lot of the trees are. Not what you remember from your first visit, not at all.[read more]