Fernando Cornejo

Markedly divergent estimates of Amazon forest carbon density from ground plots and satellites

Aim The accurate mapping of forest carbon stocks is essential for understanding the global carbon cycle, for assessing emissions from deforestation, and for rational land-use planning. Remote sensing (RS) is currently the key tool for this purpose, but RS does not estimate vegetation biomass directly, and thus may miss significant spatial variations in forest structure. We test the stated accuracy of pantropical carbon maps using a large independent field dataset. Location Tropical forests of the Amazon basin. The permanent archive of the field plot data can be accessed at: http://dx.doi.org/10.5521/FORESTPLOTS.NET/2014_1 Methods Two recent pantropical RS maps of vegetation carbon are compared to a unique ground-plot dataset, involving tree measurements in 413 large inventory plots located in nine countries. The RS maps were compared directly to field plots, and kriging of the field data was used to allow area-based comparisons. Results The two RS carbon maps fail to capture the main gradient in Amazon forest carbon detected using 413 ground plots, from the densely wooded tall forests of the north-east, to the light-wooded, shorter forests of the south-west. The differences between plots and RS maps far exceed the uncertainties given in these studies, with whole regions over- or under-estimated by > 25%, whereas regional uncertainties for the maps were reported to be < 5%. Main conclusions Pantropical biomass maps are widely used by governments and by projects aiming to reduce deforestation using carbon offsets, but may have significant regional biases. Carbon-mapping techniques must be revised to account for the known ecological variation in tree wood density and allometry to create maps suitable for carbon accounting. The use of single relationships between tree canopy height and above-ground biomass inevitably yields large, spatially correlated errors. This presents a significant challenge to both the forest conservation and remote sensing communities, because neither wood density nor species assemblages can be reliably mapped from space.

SEASONAL FOOD SHORTAGE, WEIGHT-LOSS, AND THE TIMING OF BIRTHS IN SADDLE-BACK TAMARINS (SAGUINUS-FUSCICOLLIS)

SUMMARY (1) Annual birth peaks in the breeding of several primate species are thought to correlate with seasonal changes in food availability, yet no study published to date has both correlated birth seasonality with food availability, and shown that the physical conditions of individuals decline during annual periods of food scarcity. (2) We document the following observations in a population of saddle-back tamarins (Saguinusfuscicollis Spix; Callitrichidae) at the Cocha Cashu Biological Station in Perus Manu National Park. (3) The availability of both fruits and insects was substantially lower during the annual 4-month dry season (May-September) than at other times of the year. (4) Individual tamarins lost an average of 5% of their weight over this period. (5) Three-quarters of twenty-two S. fuscicollis births at this site occurred between November and February, and none occurred between mid-March and mid-August. (6) We suggest that tamarin births at Cocha Cashu are timed such that lactation and weaning occur when food is abundant, because during the period of low food availability, there would be insufficient food to meet the demands of lactation and to serve as easily obtainable weaning foods. In this sort of seasonal environment, tamarins appear to be constrained, by the seasonality of their food supply, from breeding as frequently as they do in captivity.

Are all seeds equal? Spatially explicit comparisons of seed fall and sapling recruitment in a tropical forest

Understanding demographic transitions may provide the key to explain the high diversity of tropical tree communities. In a faunally intact Amazonian forest, we compared the spatial distribution of saplings of 15 common tree species with patterns of conspecific seed fall, and examined the seed-to-sapling transition in relation to locations of conspecific trees. In all species, the spatial pattern of sapling recruitment bore no resemblance to predicted distributions based on the density of seed fall. Seed efficiency (the probability of a seed producing a sapling) is strongly correlated with distance from large conspecific trees, with a >30-fold multiplicative increase between recruitment zones that are most distant vs. proximal to conspecific adults. The striking decoupling of sapling recruitment and conspecific seed density patterns indicates near-complete recruitment failure in areas of high seed density located around reproductive adults. Our results provide strong support for the spatially explicit predictions of the Janzen-Connell hypothesis.

Seasonal drought limits tree species across the Neotropics

Within the tropics, the species richness of tree communities is strongly and positively associated with precipitation. Previous research has suggested that this macroecological pattern is driven by the negative effect of water-stress on the physiological processes of most tree species. This process implies that the range limits of taxa are defined by their ability to occur under dry conditions, and thus in terms of species distributions it predicts a nested pattern of taxa distribution from wet to dry areas. However, this ‘dry-tolerance’ hypothesis has yet to be adequately tested at large spatial and taxonomic scales. Here, using a dataset of 531 inventory plots of closed canopy forest distributed across the Western Neotropics we investigated how precipitation, evaluated both as mean annual precipitation and as the maximum climatological water deficit, influences the distribution of tropical tree species, genera and families. We find that the distributions of tree taxa are indeed nested along precipitation gradients in the western Neotropics. Taxa tolerant to seasonal drought are disproportionally widespread across the precipitation gradient, with most reaching even the wettest climates sampled; however, most taxa analysed are restricted to wet areas. Our results suggest that the ‘dry tolerance’ hypothesis has broad applicability in the worlds most species-rich forests. In addition, the large number of species restricted to wetter conditions strongly indicates that an increased frequency of drought could severely threaten biodiversity in this region. Overall, this study establishes a baseline for exploring how tropical forest tree composition may change in response to current and future environmental changes in this region.

Identifying keystone plant resources in an Amazonian forest using a long-term fruit-fall record

The keystone plant resources (KPR) concept describes certain plant species in tropical forests as vital to community stability and diversity because they provide food resources to vertebrate consumers during the season of scarcity.Here,weusean8-y,continuousrecordoffruitfallfroma1.44-hamatureforeststandtoidentifypotentialKPRs in a lowland western Amazonian rain forest. KPRs were identified based on four criteria: temporal non-redundancy; year-to-year reliability; abundance of reproductive-size individuals and inferred fruit crop size; and the variety of vertebrateconsumersutilizingtheirfruit.Overall,sevenspecieswereconsideredexcellentKPRs:twoofthesebelongto thegenusFicus,confirmingthatthis taxonis aKPRas previouslysuggested.Celtisiguanaea(Cannabaceae) - acanopy liana - has also been previously classified as a KPR; in addition, Pseudomalmea diclina (Annonaceae), Cissus ulmifolia (Vitaceae), Allophylus glabratus (Sapindaceae) and Trichilia elegans (Meliaceae) are newly identified KPRs. Our results confirmthataverysmallfraction(<5%)oftheplantcommunityconsistentlyprovidesfruitforabroadsetofconsumers during the period of resource scarcity, which has significant implications for the conservation and management of Amazonian forests.

Plot Data from: "Long-term decline of the Amazon carbon sink."

Atmospheric CO2 records indicate that the land surface has acted as a strong global carbon sink over recent decades, with a substantial fraction of this sink likely located in the tropics, particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historic evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that the Amazon has acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above ground biomass declined by a third during the last decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while reduction in biomass due to tree mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include a greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale, and is contrary to expectations based on models.