Rubber plantations are an economically viable land-use type that occupies large swathes of land in Southeast Asia that have undergone conversion from native forest to intensive plantation forestry. ...Such land-use change has a strong impact on carbon, energy, and water fluxes in ecosystems, and uncertainties exist in the modeling of future land-use change impacts on these fluxes due to the scarcity of measured data and poor representation of key biogeochemical processes. In this current modeling effort, we utilized the Community Land Model Version 5 (CLM5) to simulate a rubber plant functional type (PFT) by comparing the baseline parameter values of tropical evergreen PFT and tropical deciduous PFT with a newly developed rubber PFT (focused on the parameterization and modification of phenology and allocation processes) based on site-level observations of a rubber clone in Indonesia. We found that the baseline tropical evergreen and baseline tropical deciduous functions and parameterizations in CLM5 poorly simulate the leaf area index, carbon dynamics, and water fluxes of rubber plantations. The newly developed rubber PFT and parametrizations (CLM-rubber) showed that daylength could be used as a universal trigger for defoliation and refoliation of rubber plantations. CLM-rubber was able to predict seasonal patterns of latex yield reasonably well, despite highly variable tapping periods across Southeast Asia. Further, model comparisons indicated that CLM-rubber can simulate carbon and energy fluxes similar to the existing rubber model simulations available in the literature. Our modeling results indicate that CLM-rubber can be applied in Southeast Asia to examine variations in carbon and water fluxes for rubber plantations and assess how rubber-related land-use changes in the tropics feedback to climate through carbon and water cycling.
Land use changes and land use intensification are considered important processes contributing to the increasing concentrations of the greenhouse gases nitrous oxide (N2O) and methane (CH4) and of ...nitric oxide (NO), a precursor of ozone. Studies on the effects of land use changes and land use intensification on soil trace gas emissions were mostly conducted in Latin America and only very few in Asia. Here we present results from Central Sulawesi where profound changes in land use and cultivation practices take place: traditional agricultural practices like shifting cultivation and slash‐and‐burn agriculture are replaced by permanent cultivation systems and introduction of income‐generating cash crops like cacao. Our results showed that N2O emissions were higher from cacao agroforestry (35 ± 10 μg N m−2 h−1) than maize (9 ± 2 μg N m−2 h−1), whereas intermediate rates were observed from secondary forests (25 ± 11 μg N m−2 h−1). NO emissions did not differ among land use systems, ranging from 12 ± 2 μg N m−2 h−1 for cacao agroforestry and secondary forest to 18 ± 2 μg N m−2 h−1 for maize. CH4 uptake was higher for maize (−30 ± 4 μg C m−2 h−1) than cacao agroforestry (−18 ± 2 μg C m−2 h−1) and intermediate rates were measured from secondary forests (−25 ± 4 μg C m−2 h−1). Combining these data with results from other studies in this area, we present chronosequence effects of land use change on trace gas emissions from natural forest, through maize cultivation, to cacao agroforestry (with or without fertilizer). Compared to the original forests, this typical land use change in the study area clearly led to higher N2O emissions and lower CH4 uptake with age of cacao agroforestry systems. We conclude that this common land use sequence in the area combined with the increasing use of fertilizer will strongly increase soil trace gas emissions. We suggest that the future hot spot regions of high N2O (and to a lesser extend NO) emissions in the tropics are those areas where climatic and edaphic conditions allow for intensive agriculture. This scenario is probably preferable over the alternative of agriculture extensification, which would imply a dramatic increase in deforestation rates with accompanying CO2 emissions.
•Nutrient limitation was species-dependent with no tree species limited by N.•Beech growth was facilitated by enhanced levels of P and K in mix-species stands.•Nutrient response efficiencies can be ...optimized by selecting species mixtures.
There are contrasting reports whether and how tree diversity influences stand productivity in temperate deciduous forests. Tree species diversity may increase stand productivity in temperate forests through complementary resource use and/or facilitation if the resource considered limits productivity. In unpolluted temperate forests, net primary production is typically limited by nitrogen (N). However, in many parts of Europe high N deposition has alleviated N limitation and there is some evidence that phosphorus (P) and/or potassium (K) limitation has become more widespread. Here, we report on a study where we investigated whether complementarity and/or facilitation increase productivity in a typical German deciduous forest with tree species of beech (Fagus sylvatica), oak (Quercus petraea and Quercus robur), hornbeam (Carpinus betulus) and lime (Tilia cordata and Tilia platyphyllus). We measured biomass production and availability of soil N, P, K, calcium (Ca) and magnesium (Mg) in stands of single species (mono-species stands) and in stands with different combinations of three of the tree species above (mix-species stands). We used nutrient response efficiency (NRE) to evaluate whether a specific nutrient limits tree growth. At a stand level, above-ground net primary productivity did not differ between mono- and mix-species stands. At a tree level, using a neighborhood approach, relative growth rates of beech trees in mono-species stands were smaller than when they were in mix with lime and hornbeam whereas growth of lime trees in mono-species stands was larger than in mix with beech and oak. The NRE curve for beech showed that beech trees in mix-species stands had optimal P and K response efficiencies whereas beech trees in mono-species stands showed P and K limitations. The NRE curve for oak with exchangeable soil K showed that K levels were beyond the optimum NRE and thus K was not limiting oak growth. NRE curves for hornbeam and lime showed no significant relationships with any of the soil nutrients. Hence, nutrient limitation was species-dependent. Our results showed that using both NRE and a neighborhood approach are useful tools in quantifying the effects of individual tree species on a species’ productivity between mono- and mix-species stands. Such tools provide important basis for improving management of typical mix-species, temperate forests.
The lower montane forest zone of Indonesia is undergoing rapid conversion of indigenous forests to agriculture. In this tropical region, however, the effects of forest conversion on soil N processes ...have not been investigated. Corn (Zea mays L.) and cacao (Theobroma cacao L.)-coffee (Coffea canephora Pierre ex Froehner) agroforestry are the main land use types in cleared lower montane forests in Central Sulawesi, Indonesia. Our main objective was to compare the soil N dynamics under agroforest systems and corn cultivation with indigenous forest. We measured the gross rates of N transformation processes using 15N pool dilution. The agroforest systems and indigenous forests had higher gross N mineralization rates and faster turnover rates of NH4(+) and microbial N pools than the long-term cultivated corn sites. Faster soil N turnover rates in agroforest systems suggest a more dynamic soil N cycling. Leguminous shade trees, which are important components of these agroforest systems, may have influenced the fast microbial N cycling through release of N-rich root exudates and plant residues. Our results show that compared with corn, agroforestry is a better option in terms of sustainability in the N-supplying capacity of the soil. In addition, we measured higher 15NH4(+) recoveries than 15NO3(-) recoveries after 15 min of 15N addition in all our sites. Our measured rates of gross nitrification were very low to negligible, due to rapid disappearance of added 15NO3(-). Such fast reaction of NO3(-) warrants further investigation, especially in tropical areas where 15N studies are very few.
The study aimed to assess soil biochemical properties and nutrient leaching in palm oil plantation. The research was conducted in smallholder oil palm plantations which were located in Jambi Province ...- Indonesia. Nutrient leaching was determined by measuring nutrient concentration in soil solution bi-weekly and monthly in the frond stacked and fertilized areas; soil water samples were collected by using suction cup lysimeter. The result showed that the application of mineral fertilizer (e.g. NPK) and dolomite resulted higher base saturation, exchangeable Ca, and available P in the fertilized than frond stacked and inter row areas (p ≤ 0.05). Stacking palm oil frond increased the soil macro-porosity, hence decreased leaching of K, Mg, Na, P, and total Al in the frond stacked than in the fertilized areas. The lower leaching losses and the higher soil macroporosity in the frond stacked than in the fertilized areas indicated that either the water did not dilute nutrient in the soil due to bypass flow, or the nutrient release from mineralization did not surpass nutrient demand which is quickly uptaken by palm root. Proper soil management through synchronizing rate of fertilizer application with nutrient output or frequency of fertilizer application may potentially minimize leaching losses.
Land-use transitions can enhance the livelihoods of smallholder farmers but potential economic-ecological trade-offs remain poorly understood. Here, we present an interdisciplinary study of the ...environmental, social and economic consequences of land-use transitions in a tropical smallholder landscape on Sumatra, Indonesia. We find widespread biodiversity-profit trade-offs resulting from land-use transitions from forest and agroforestry systems to rubber and oil palm monocultures, for 26,894 aboveground and belowground species and whole-ecosystem multidiversity. Despite variation between ecosystem functions, profit gains come at the expense of ecosystem multifunctionality, indicating far-reaching ecosystem deterioration. We identify landscape compositions that can mitigate trade-offs under optimal land-use allocation but also show that intensive monocultures always lead to higher profits. These findings suggest that, to reduce losses in biodiversity and ecosystem functioning, changes in economic incentive structures through well-designed policies are urgently needed.
Fertilization experiments in tropical forests have shown that litterfall increases in response to the addition of one or more soil nutrients. However, the relationship between soil nutrient ...availability and litterfall is poorly defined along natural soil fertility gradients, especially in tropical montane forests. Here, we measured litterfall for two years in five lower montane 1‐ha plots spanning a soil fertility and precipitation gradient in lower montane forest at Fortuna, Panama. Litterfall was also measured in a concurrent nitrogen fertilization experiment at one site. Repeated‐measures ANOVA was used to test for site (or treatment), year, and season effects on vegetative, reproductive and total litterfall. We predicted that total litterfall, and the ratio of reproductive to leaf litterfall, would increase with nutrient availability along the fertility gradient, and in response to nitrogen addition. We found that total annual litterfall varied substantially among 1‐ha plots (4.78 Mg/ha/yr to 7.96 Mg/ha/yr), and all but the most aseasonal plot showed significant seasonality in litterfall. However, litterfall accumulation did not track soil nutrient availability; instead forest growing on relatively infertile soil, but dominated by an ectomycorrhizal tree species, had the highest total litterfall accumulation. In the fertilization plots, significantly more total litter fell in nitrogen addition relative to control plots, but this increase in response to nitrogen (13%) was small compared to variation observed among 1‐ha plots. These results suggest that while litterfall at Fortuna is nutrient‐limited, compositional and functional turnover along the fertility gradient obscure any direct relationship between soil resource availability and canopy productivity.
An ongoing roof experiment, where N and acid inputs were reduced to the recommended critical load levels, has been conducted since 1991 in an N-saturated spruce stand in Soiling, Germany. Our study ...was aimed at (1) quantifying the changes in gross rates of microbial N cycling under ambient and reduced N conditions, and (2) relating the soil N dynamics to the changes in N leaching and N status of trees. Two roofs were used, one to achieve "ambient" and the other reduced ("clean rain") inputs, with a roofless plot as a control for possible roof effects. In 2001, the ambient roof and ambient no-roof plots showed an apparent decrease in gross N mineralization rates and significantly lower microbial NH4
+immobilization rates and turnover rates of NH4
+and microbial N pools. The microbial NO3
-immobilization rates and NO3
-pool turnover rates were lower than the microbial NH4
+immobilization rates and NH4
+pool turnover rates, showing that less NO3
-cycled through microorganisms than NH4
+. There was also low abiotic NO3
-immobilization. High NO3
-input from throughfall and low microbial turnover rates of the NO3
-pool, combined with low abiotic NO3
-retention, may have contributed to the high NO3
-leaching losses in these ambient plots. The clean rain plot showed a slight increase in gross N mineralization rates and significantly higher microbial NH4
+immobilization rates and turnover rates of NH4
+and microbial N pools. Neither nitrification nor soil NO3
-was detectable. There was an increase in abiotic NO3
-immobilization. Foliar N concentration had decreased but was still adequate. An efficient cycling of NH4
+through microorganisms, combined with the high abiotic NO3
-immobilization, indicated efficient mineral N retention in the clean rain plot. These results indicated that long-term reduction of throughfall N and acid inputs had induced high but tightly coupled microbial NH4
+cycling and an increase in abiotic NO3
-retention, which contributed to the reversal of N saturation.
Rainforest conversion to woody croplands impacts the carbon cycle via ecophysiological processes such as photosynthesis and autotrophic respiration. Changes in the carbon cycle associated with ...land-use change can be estimated through Land Surface Models (LSMs). The accuracy of carbon flux estimation in carbon fluxes associated with land-use change has been attributed to uncertainties in the model parameters affecting photosynthetic activity, which is a function of both carboxylation capacity (Vcmax) and electron transport capacity (Jmax). In order to reduce such uncertainties for common tropical woody crops and trees, in this study we measured Vcmax25 (Vcmax standardized to 25 °C), Jmax25 (Jmax standardized to 25 °C) and light-saturated photosynthetic capacity (Amax) of Elaeis guineensis Jacq. (oil palm), Hevea brasiliensis (rubber tree), and two native tree species, Eusideroxylon zwageri and Alstonia scholaris, in a converted landscape in Jambi province (Sumatra, Indonesia) at smallholder plantations. We considered three plantations; a monoculture rubber, a monoculture oil palm, and an agroforestry system (jungle rubber plantation), where rubber trees coexist with some native trees. We performed measurements on leaves at the lower part of the canopy, and used a scaling method based on exponential function to scale up photosynthetic capacity related traits to the top of the canopy. At the lower part of the canopy, we found (i) high Vcmax25 values for H. brasiliensis from monoculture rubber plantation and jungle rubber plantation that was linked to a high area-based leaf nitrogen content, and (ii) low value of Amax for E. guineensis from oil palm plantation that was due to a low value of Vcmax25 and a high value of dark respiration. At the top of the canopy, Amax varied much more than Vcmax25 among different land-use types. We found that photosynthetic capacity declined fastest from the top to the lower part of the canopy in oil palm plantations. We demonstrate that photosynthetic capacity related traits measured at the lower part of the canopy can be successfully scaled up to the top of the canopy. We thus provide helpful new data that can be used to constrain LSMs that simulate land-use change related to rubber and oil palm expansion.
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