The land use of the ancient Maya strongly affected the environment of the previously forested Maya Lowlands. A forest grew back after the Maya “collapse”, some 1100 years ago. Two activities of the ancient Maya could have had widespread effects on the tree species composition of the regrown, modern forest. First, in areas with topographic relief Maya agriculture caused substantial soil erosion and accumulation, changing soil depth and character. Soil character is associated with differential distributions and abundances of many tree species in the Maya Lowlands. To the extent that soil character on the modern landscape differs from that on the pre-Maya landscape, regrown forests on the modern landscape would differ from pre-Maya forests. Second, the ancient Maya cleared much forest but likely also cultivated or favored certain tree species in home gardens, regenerating farm plots, and patches of older growth. A rigorous study suggests that descendants of favored tree species persist in elevated abundance in some areas of the modern forest but not in other areas. After c. 1100 years of regrowth in some places, the legacy of the ancient Maya in the modern forest likely ranges from strong to absent across the varied landscape of the Lowlands. An ancient mosaic of forest patches would have provided a species-rich, multiple-point source for forest regrowth. Such a mosaic is lacking in modern deforested tropical landscapes, likely inhibiting recovery of a species-rich forest.

We studied species composition and spatial distributions of tree species, and the underlying topography and soil, in subtropical forests of northwest Belize, a region in the Maya Lowlands. Our goal was to learn how much the spatial distributions of species vary and are predictable over the landscape. The study was done in old-growth, subtropical moist forest on limestone-derived topography and soil. We identified to species all trees ≥10 cm DBH in 209 400-m2 plots. For each plot, we characterized topographic setting and analyzed soil nutrients and texture. We recorded 3,984 individual trees of ∼140 tree species and used the 3,775 individuals of the 69 species occurring in ≥5 plots in multivariate analyses, including Nonmetric Multidimensional Scaling (NMS). NMS showed that 73% of the variation in species composition per plot was associated with the first three ordination axes. Sixteen out of the 34 quantitative variables we measured were correlated at R 2 > 10% with the axes. Of the categorical variables, Topographic Class was strongly associated with species composition, and USDA Texture Class less so. Of the 69 focal tree species, the abundances of 21 were correlated at R 2 > 10% with one or more axes of the NMS ordination. Importantly, these 21 species accounted for 68% of all individual trees sampled in the 209 plots. Twenty-three species were indicators of particular topographic and soil classes. We conclude that patterns of tree species distribution are strongly and predictably associated with different topographic and soil conditions in this landscape. In the past, the ancient Maya could have used this type of predictable plant–soil relationship to optimize their agriculture. In the future, our results are a basis for predicting local shifts in tree species distributions due to climate change.

We review research on ancient and modern environments in the Programme for Belize Archaeology Project (PfBAP), focusing on studies of the vegetation. A goal is to show how these studies complement each other. To describe the ancient environment, paleobotany uses fossil pollen, phytoliths, starch grains, and geochemical signatures. In recent research, phytoliths and starch grains are collected from surface samples and paired with geochemical signatures, floral inventories, and contemporary pollen signatures to construct environmental analogues of ancient environments. To study the modern environment, forest ecology uses repeated inventories of tree species in forest stands. These studies have shown how variable the old-growth forests of the area are in in space and in time. Forests range greatly in composition of tree species, tree stem density, number of tree species, and in rates of tree mortality, recruitment, and growth. This variation can be related to underlying variation in soil and slope, and patterns resulting from natural disturbance by flooding and wind. We give examples of synergy between the study of ancient and modern environments in the Maya region that demonstrate fruitful interactions between these disciplines for paleobotanists, ecologists, and archaeologists.

Abstract Climate change and disturbance make it difficult to project long‐term patterns of carbon sequestration in tropical forests, but large ecosystem experiments in these forests can inform predictions. The Canopy Trimming Experiment (CTE) manipulates two key components of hurricane disturbance, canopy openness and detritus deposition, in a tropical forest in Puerto Rico. We documented how the CTE and a real hurricane affected tree recruitment, biomass, and aboveground carbon storage over 15 years. In the CTE treatments, we trimmed branches, but we did not fell trees. We expected that during the 14‐year period after initial canopy trimming, regrowth of branches and stems and stem recruitment stimulated by increased light and trimmed debris would help restore biomass and carbon loss due to trimming. Compared to control plots, in the trimmed plots recruitment of palms and dicot trees increased markedly after trimming, and stem diameters of standing trees increased. Data showed that recruitment of small trees adds little to aboveground carbon, compared to the amount in large trees. Nevertheless, this response restored pretreatment biomass and carbon in the experimental period. In particular, the experimental additions of trimmed debris on the forest floor seemed to stimulate increase in aboveground carbon. Toward the end of the experimental period, Hurricane Maria (Category 4 hurricane) trimmed and felled some trees but reduced aboveground carbon less in the plots (including untrimmed plots) than experimental trimming had. Thus, it appears that the amount of regrowth recorded after experimental trimming could also restore aboveground carbon in the forest after a severe hurricane in the same time span. However, Hurricane Maria, unlike the trimming treatments, felled large trees, and it may be that with predicted, more frequent severe hurricanes, that the continued loss of large trees would over the long term decrease aboveground carbon stored in this Puerto Rican forest and likewise in other tropical forests affected by cyclonic storms.

The ability to predict growth and potential yield is essential for planning forest management. Here we developed a narrow size-class diameter model to simulate growth in a mature plantation (age 42 years) of big-leaf mahogany (Swietenia macrophylla King) in a subtropical moist forest in Puerto Rico. We calculated optimal rotation age by means of the biological and economic criteria. The analyses involved diameter measurements over 31 years and a variety of contrasting economic scenarios, which were evaluated by means of the Faustman formula and sensitivity analyses. The optimal biological rotation was 90 years while the optimal economic rotation was 42 years in most of the scenarios, regardless of wood prices and costs of reforestation. Conspicuous changes in the optimal economic rotation were only observed under low interest rates, in which it was prolonged to around 80 years, close to the optimal biological rotation. Abundant natural regeneration and a prolonged biological rotation suggest that other silvicultural systems, rather than traditional clear-cutting and replanting could be adopted. However, to evaluate alternative silvicultural strategies we would need to improve our ability to predict growth. This would require expansion of our database to include information on growth conditions of individual trees and young tree dynamics, as well as size and growth of other species, to model natural regeneration and competition.

Swietenia species are the most valuable American tropical timbers and have been heavily overexploited for decades. The three species are listed as either vulnerable or endangered by IUCN and are included on Appendix II of CITES, yet illegal exploitation continues. Here, we used restriction associated DNA sequencing to develop a new set of 120 SNP markers for Swietenia sp., suitable for MassARRAY®iPLEX™ genotyping. These markers can be used for population genetic studies and timber tracking purposes.

Substantial lake core and other evidence shows accelerated soil erosion occurred in the Maya Lowlands of Central America over ancient Maya history from 3000 to 1000years ago. But we have little evidence of the wider network of the sources and sinks of that eroded sediment cascade. This study begins to solve the mystery of missing soil with new research and a synthesis of existing studies of tropical forest soils along slopes in NW Belize. The research aim is to understand soil formation, long-term human impacts on slopes, and slope stability over time, and explore ecological implications. We studied soils on seven slopes in tropical forest areas that have experienced intensive ancient human impacts and those with little ancient impacts. All of our soil catenas, except for one deforested from old growth two years before, contain evidence for about 1000years of stable, tropical forest cover since Maya abandonment. We characterized the physical, chemical, and taxonomic characteristics of soils at crest-shoulder, backslopes, footslopes, and depression locations, analyzing typical soil parameters, chemical elements, and carbon isotopes (δ13C) in dated and undated sequences. Four footslopes or depressions in areas of high ancient occupation preserved evidence of buried, clay-textured soils covered by coarser sediment dating from the Maya Classic period. Three footslopes from areas with scant evidence of ancient occupation had little discernable deposition. These findings add to a growing corpus of soil toposequences with similar facies changes in footslopes and depressions that date to the Maya period. Using major elemental concentrations across a range of catenas, we derived a measure (Ca+Mg)/(Al+Fe+Mn) of the relative contributions of autochthonous and allochthonous materials and the relative age of soil catenas. We found very low ratios in clearly older, buried soils in footslopes and depressions and on slopes that had not undergone ancient Maya erosion. We found high (Ca+Mg)/(Al+Fe+Mn) values on slopes with several lines of evidence that suggest relative youth, soils possibly formed since Maya abandonment. Carbon isotopes (δ13C) also provide some evidence of past vegetation change on slopes. We found strong evidence for maize or other alien C4 species in an ancient terrace soil and additional evidence in buried footslopes but only evidence for C3 species (like tropical trees) on the backslopes and other crest-shoulders. The fact that steep slopes preserved no evidence of C4 species inputs may mean that the ancient Maya maintained forests here. Alternatively, ancient Maya land uses eroded slopes, with the δ13C signatures detected today being the result of more recent soil development under forest over the last millennium. Additional evidence that these soils are recent in age includes elevated (Ca+Mg)/(Al+Fe+Mn) values, skeletal soil profiles, and low soil magnetic susceptibility. Besides the evidence for truncating backslopes and aggrading footslopes, the ancient Maya built agricultural terraces that accumulated soils and altered drainage. All these ancient Maya slope alterations would have influenced modern tree distributions, because many tree species in the modern forest show strong preferences for different soil types and topographic situations that the ancient Maya changed.

In natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented.EDITED BY Nicholas Brokaw

Illegal logging is one of the main causes of ongoing worldwide deforestation and needs to be eradicated. The trade in illegal timber and wood products creates market disadvantages for products from sustainable forestry. Although various measures have been established to counter illegal logging and the subsequent trade, there is a lack of practical mechanisms for identifying the origin of timber and wood products. In this study, six nuclear microsatellites were used to generate DNA fingerprints for a genetic reference database characterising the populations of origin of a large set of mahogany (Swietenia macrophylla King, Meliaceae) samples. For the database, leaves and/or cambium from 1971 mahogany trees sampled in 31 stands from Mexico to Bolivia were genotyped. A total of 145 different alleles were found, showing strong genetic differentiation (δGregorious=0.52, FST=0.18, GST(Hedrick)=0.65) and clear correlation between genetic and spatial distances among stands (r=0.82, P<0.05). We used the genetic reference database and Bayesian assignment testing to determine the geographic origins of two sets of mahogany wood samples, based on their multilocus genotypes. In both cases the wood samples were assigned to the correct country of origin. We discuss the overall applicability of this methodology to tropical timber trading.

Cedrela odorata (Spanish cedar) is a neotropical broadleaf tree species that is in high demand for furniture and interior fittings. In 1998, seed collections were made from Spanish cedar in the Yucatan Peninsula, Mexico, for genetic conservation and tree improvement projects. Progeny from these collections were established in genetic trials at Bacalar, Noh Bec, and Zoh Laguna in the Yucatan. Survival at 2 years was 73.5% at Bacalar, 72% at Noh Bec, but only 20% after 6 months for several replicates at Zoh Laguna. Mean 2-year height, number of years of Hypsipyla attack on apical shoots (over 2 or 3 years) and total branching over 2 years, were 1.3m, 0.04 years, and 2.5 branches at Bacalar, and 1.9m, 0.35 years, and 1.6 branches at Noh Bec. Selection of the three best provenances (Escárcega, Bacalar, and Calakmul) would result in an estimated cross-site gain of 8.6% in 2-year height. Within-provenance, cross-site heritabilities for 2-year height, shoot borer attack, and branching were 0.1±0.02, 0.0±0.02, and 0.0±0.02, respectively. Single-site heritabilities for height at 2 years, shoot borer attack, and branching were 0.09±0.05, 0.02±0.04, and 0.09±0.05 at Bacalar and 0.16±0.07, 0.0±0.06, and 0.0±0.07 at Noh Bec. Given the known advantage of rapid growth to avoid Hypsipyla damage over the long term and the stable performance of provenances across sites for growth traits, we recommend provenance selection over multiple trials to reduce the risk of serious damage by the insect. Good provenances and other suitable seed sources, as well as proper site selection and silvicultural practices, are important tools for increasing yields from plantations of C. odorata.

Stocks of the valuable big-leaf mahogany (Swietenia macrophylla King) are declining, and trials for growth and pest resistance are needed to select material for plantations. Seeds were collected from 67 open-pollinated trees from five provenances in the Yucatan Peninsula of Mexico and planted in three provenance/progeny trials in the state of Quintana Roo, Mexico, in order to characterize genetic variation in growth traits and for Hypsipyla resistance or recovery, and to assess the potential for genetic gain. Differentiation among provenances was found only for relative height growth rate (RHGR). The total years of apical attack by Hypsipyla grandella varied by a magnitude of 100% among families but showed little heritability. After 4 years, mean height per family ranged from 328 to 564cm, 160 to 381cm, and 253 to 390cm at each site. Although heritabilities for height were too low for cross-site selection, sufficient heritability (hI2=0.26), additive genetic coefficients of variation (AGCV=22%), and type B genetic correlations (rb(f)=0.74) for RHGR across the two sites with poorer growth indicated that this trait might be used as a surrogate. This would yield an estimated gain of about 17% for the best 15% of trees. At the site with better growth, there was sufficient heritability (hI2=0.31) and AGCV (20%) for height at year 5 to obtain an estimated gain of 15% for the best 15% of trees. We suggest a selection strategy using the best germplasm from the best performing trial to exploit the resources on high quality sites, and the best material from the poorer sites for lower quality areas.

While the demand for big-leaf mahogany and Spanish cedar timber does not decline, the supply of these regionally important fine hardwood species has dwindled significantly. Plantations can help meet this demand, if the shoot borer is controlled through silvicultural techniques as well as selected seed sources. A participatory domestication program was implemented to improve germplasm quality and access in the Yucatan peninsula. Medium and short term strategies included the establishment of provenance/progeny trials, the conservation of a natural seed stand, and selection of urban seed trees. Five and two year data show significant differences between seed sources for growth and pest attack characteristics, indicating potential for genetic and economic gain. The process used for selection of seed trees in a 400 ha forest was simple and inexpensive, but also demonstrated that many trees may not be suitable for seed sources. The use and comparison of seed from urban trees is a useful educational tool in the domestication process. All of these efforts show the importance of a wide genetic base in reforestation programs. As with other timber species, specific steps can be taken to improve germplasm quality, and thus economic livelihood of people who plant trees.