William Farfan-Rios

Productivity and carbon allocation in a tropical montane cloud forest in the Peruvian Andes

Background: The slopes of the eastern Andes harbour some of the highest biodiversity on Earth and a high proportion of endemic species. However, there have been only a few and limited descriptions of carbon budgets in tropical montane forest regions. Aims: We present the first comprehensive data on the production, allocation and cycling of carbon for two high elevation (ca. 3000 m) tropical montane cloud forest plots in the Kosñipata Valley, Peruvian Andes. Methods: We measured the main components and seasonal variation of net primary productivity (NPP), autotrophic (R a) and heterotrophic (R h) respiration to estimate gross primary productivity (GPP) and carbon use efficiency (CUE) in two 1-ha plots. Results: NPP for the two plots was estimated to be 7.05 ± 0.39 and 8.04 ± 0.47 Mg C ha−1 year−1, GPP to be 22.33 ± 2.23 and 26.82 ± 2.97 Mg C ha−1 year−1 and CUE was 0.32 ± 0.04 and 0.30 ± 0.04. Conclusions: We found strong seasonality in NPP and moderate seasonality of R a, suggesting that forest NPP is driven by changes in photosynthesis and highlighting the importance of variation in solar radiation. Our findings imply that trees invest more in biomass production in the cooler season with lower solar radiation and more in maintenance during the warmer and high solar radiation period.

Seasonal production, allocation and cycling of carbon in two mid-elevation tropical montane forest plots in the Peruvian Andes

Background: Tropical montane cloud forests (TMCF) are unique ecosystems with high biodiversity and large carbon reservoirs. To date there have been limited descriptions of the carbon cycle of TMCF. Aims: We present results on the production, allocation and cycling of carbon for two mid-elevation (1500–1750 m) tropical montane cloud forest plots in San Pedro, Kosñipata Valley, Peru. Methods: We repeatedly recorded the components of net primary productivity (NPP) using biometric measurements, and autotrophic (R a) and heterotrophic (R h) respiration, using gas exchange measurements. From these we estimated gross primary productivity (GPP) and carbon use efficiency (CUE) at the plot level. Results: The plot at 1500 m was found very productive, with our results comparable with the most productive lowland Amazonian forests. The plot at 1750 m had significantly lower productivity, possibly because of greater cloud immersion. Both plots had similar patterns of NPP allocation, a substantial seasonality in NPP components and little seasonality in Ra . Conclusions: These two plots lie within the ecotone between lower and upper montane forests, near the level of the cloud base. Climate change is likely to increase elevation of the cloud base, resulting in shifts in forest functioning. Longer-term surveillance of the carbon cycle at these sites would yield valuable insights into the response of TMCFs to a shifting cloud base.

Spatial patterns of above-ground structure, biomass and composition in a network of six Andean elevation transects

Background: The Amazon to Andes transition zone provides large expanses of relatively pristine forest wilderness across environmental gradients. Such elevational gradients are an excellent natural laboratory for establishing long-term interactions between forest ecosystems and environmental parameters, which is valuable for understanding ecosystem responses to environmental change. Aims: This study presents data on elevational trends of forest structure (biomass, basal area, height, stem density), species richness, and composition from six elevational transects in the Andes. Methods: We analysed the spatial patterns of forest structure, above-ground biomass and composition from 76 permanent plots, ranging from lowland Amazonian rain forest to high-elevation cloud forests in Ecuador, Peru, and Bolivia. Results: Forest above-ground woody biomass stocks ranged from 247 Mg ha−1 (Peru, 210 m) to 86 Mg ha−1 (Peru, 3450 m), with significantly decreasing trends of tree height and biomass and an increasing trend of stem density with increasing elevation. We observed an increase in forest richness at three taxonomic levels at mid-elevation, followed by a decrease in richness within the cloud immersion zone. Conclusions: The transects show an increase in stem density, a decline in tree height and above-ground coarse wood biomass and a hump-shaped trend in species richness with increasing elevation. These results suggest that environmental change could lead to significant shifts in the properties of these ecosystems over time.

Ancient human disturbances may be skewing our understanding of Amazonian forests

Significance The Amazon harbors thousands of species and plays a vital role in the Earth’s climate and carbon cycles. Much of what we know about the Amazon is based on censuses of only a small number of forest inventory plots, an even smaller number of which are censused repeatedly and used to study forest dynamics and carbon fluxes. The effects of ancient human impacts have never been properly assessed or accounted for in studies of Amazonian plots. New spatial analyses show that plots significantly oversample areas with high abundances of archaeological evidence of past human activities. This suggests that our interpretations of the Amazon’s structure, composition, and function are based disproportionately on forests still reflecting the legacies of past human disturbances. Although the Amazon rainforest houses much of Earth’s biodiversity and plays a major role in the global carbon budget, estimates of tree biodiversity originate from fewer than 1,000 forest inventory plots, and estimates of carbon dynamics are derived from fewer than 200 recensus plots. It is well documented that the pre-European inhabitants of Amazonia actively transformed and modified the forest in many regions before their population collapse around 1491 AD; however, the impacts of these ancient disturbances remain entirely unaccounted for in the many highly influential studies using Amazonian forest plots. Here we examine whether Amazonian forest inventory plot locations are spatially biased toward areas with high probability of ancient human impacts. Our analyses reveal that forest inventory plots, and especially forest recensus plots, in all regions of Amazonia are located disproportionately near archaeological evidence and in areas likely to have ancient human impacts. Furthermore, regions of the Amazon that are relatively oversampled with inventory plots also contain the highest values of predicted ancient human impacts. Given the long lifespan of Amazonian trees, many forest inventory and recensus sites may still be recovering from past disturbances, potentially skewing our interpretations of forest dynamics and our understanding of how these forests are responding to global change. Empirical data on the human history of forest inventory sites are crucial for determining how past disturbances affect modern patterns of forest composition and carbon flux in Amazonian forests.

Assessing above-ground woody debris dynamics along a gradient of elevation in Amazonian cloud forests in Peru: balancing above-ground inputs and respiration outputs

Background: Dead biomass, including woody debris (WD), is an important component of the carbon cycle in tropical forests. Aims: This study analyses WD (>2 cm) and other above-ground fluxes in mature tropical forest plots along an elevational gradient (210–3025 m above sea level) in southern Peru. Methods: This work was based on inventories of fine and coarse WD (FWD and CWD, respectively), above-ground biomass, and field-based and experimental respiration measurements. Results: Total WD stocks ranged from 6.26 Mg C ha−1 at 3025 m to 11.48 Mg C ha−1 at 2720 m. WD respiration was significantly correlated with moisture content (P < 0.001; R 2 = 0.25), temperature (P < 0.001; R 2 = 0.12) and wood density (P < 0.001; R 2 = 0.16). Controlled experiments showed that both water content and temperature increased respiration rates of individual WD samples. The full breadth of the temperature sensitivity coefficient, or Q 10, estimates, ranging from 1.14–2.13, was low compared to other studies. In addition, temperature sensitivity of WD respiration was greater for higher elevations. Conclusions: Carbon stocks, mortality and turnover of above-ground biomass varied widely and were not significantly related with elevation or slope. This study demonstrates that some forests may be a carbon source due to legacies of disturbance and increasing temperatures, which may cause additional, short-term carbon efflux from WD. Predictions of tropical forest carbon cycles under future climate should incorporate WD dynamics and related feedback.

Large-scale patterns of turnover and Basal area change in Andean forests.

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.