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1.
Although the removal or addition of understory vegetation has been an important forest management practice in forest plantations, the effects of this management practice on soil respiration are unclear. The overall objective of this study was to measure and model soil respiration and its components in a mixed forest plantation with native species in south China and to assess the effects of understory species management on soil respiration and on the contribution of root respiration (Rr) to total soil respiration (Rs). An experiment was conducted in a plantation containing a mixture of 30 native tree species and in which understory plants had been removed or replaced by Cassia alata Linn. The four treatments were the control (Control), C. alata addition (CA), understory removal (UR) and understory removal with C. alata addition (UR + CA). Trenched subplots were used to quantify Rr by comparing Rs outside the 1-m2 trenched subplots (plants and roots present) and inside the trenched subplots (plants and roots absent) in each treatment. Annual soil respiration were modeled using the values measured for Rs, soil temperature and soil moisture. Our results indicate that understory removal reduced Rs rate and soil moisture but increased soil temperature. Regression models revealed that soil temperature was the main factor and soil moisture was secondary. Understory manipulations and trenching increased the temperature sensitivity of Rs. Annual Rs for the Control, CA, UR and UR + CA treatments averaged 594, 718, 557 and 608 g C m−2 yr−1, respectively. UR decreased annual Rs by 6%, but CA increased Rs by about 21%. Our results also indicate that management of understory species increased the contribution of Rr to Rs.  相似文献   

2.
After a wildfire, the management of burnt wood may determine microclimatic conditions and microbiological activity with the potential to affect soil respiration. To experimentally analyze the effect on soil respiration, we manipulated a recently burned pine forest in a Mediterranean mountain (Sierra Nevada National and Natural Park, SE Spain). Three representative treatments of post-fire burnt wood management were established at two elevations: (1) “salvage logging” (SL), where all trees were cut, trunks removed, and branches chipped; (2) “non-intervention” (NI), leaving all burnt trees standing; and (3) “cut plus lopping” (CL), a treatment where burnt trees were felled, with the main branches lopped off, but left in situ partially covering the ground surface. Seasonal measurements were carried out over the course of two years. In addition, we performed continuous diurnal campaigns and an irrigation experiment to ascertain the roles of soil temperature and moisture in determining CO2 fluxes across treatments. Soil CO2 fluxes were highest in CL (average of 3.34 ± 0.19 μmol m−2 s−1) and the lowest in SL (2.21 ± 0.11 μmol m−2 s−1). Across seasons, basal values were registered during summer (average of 1.46 ± 0.04 μmol m−2 s−1), but increased during the humid seasons (up to 10.07 ± 1.08 μmol m−2 s−1 in spring in CL). Seasonal and treatment patterns were consistent at the two elevations (1477 and 2317 m a.s.l.), although respiration was half as high at the higher altitude.Respiration was mainly controlled by soil moisture. Watering during the summer drought boosted CO2 effluxes (up to 37 ± 6 μmol m−2 s−1 just after water addition), which then decreased to basal values as the soil dried. About 64% of CO2 emissions during the first 24 h could be attributed to the degasification of soil pores, with the rest likely related to biological processes. The patterns of CO2 effluxes under experimental watering were similar to the seasonal tendencies, with the highest pulse in CL. Temperature, however, had a weak effect on soil respiration, with Q10 values of ca. 1 across seasons and soil moisture conditions. These results represent a first step towards illustrating the effects of post-fire burnt wood management on soil respiration, and eventually carbon sequestration.  相似文献   

3.
Because soil CO2 efflux or soil respiration (RS) is the major component of forest carbon fluxes, the effects of forest management on RS and microbial biomass carbon (C), microbial respiration (RH), microbial activity and fine root biomass were studied over two years in a loblolly pine (Pinus taeda L.) plantation located near Aiken, SC. Stands were six-years-old at the beginning of the study and were subjected to irrigation (no irrigation versus irrigation) and fertilization (no fertilization versus fertilization) treatments since planting. Soil respiration ranged from 2 to 6 μmol m−2 s−1 and was strongly and linearly related to soil temperature. Soil moisture and C inputs to the soil (coarse woody debris and litter mass) which may influence RH were significantly but only weakly related to RS. No interaction effects between irrigation and fertilization were observed for RS and microbial variables. Irrigation increased RS, fine root mass and microbial biomass C. In contrast, fertilization increased RH, microbial biomass C and microbial activity but reduced fine root biomass and had no influence on RS. Predicted annual soil C efflux ranged from 8.8 to 10.7 Mg C ha−1 year−1 and was lower than net primary productivity (NPP) in all stands except the non-fertilized treatment. The influence of forest management on RS was small or insignificant relative to biomass accumulation suggesting that NPP controls the transition between a carbon source and sink in rapidly growing pine systems.  相似文献   

4.
This study was conducted to determine carbon (C) dynamics following forest tending works (FTW) which are one of the most important forest management activities conducted by Korean forest police and managers. We measured organic C storage (above- and below-ground biomass C, forest floor C, and soil C at 50 cm depth), soil environmental factors (soil CO2 efflux, soil temperature, soil water content, soil pH, and soil organic C concentration), and organic C input and output (litterfall and litter decomposition rates) for one year in FTW and non-FTW (control) stands of approximately 40-year-old red pine (Pinus densiflora S. et Z.) forests in the Hwangmaesan Soopkakkugi model forest in Sancheonggun, Gyeongsangnam-do, Korea. This forest was thinned in 2005 as a representative FTW practice. The total C stored in tree biomass was significantly lower (P < 0.05) in the FTW stand (40.17 Mg C ha−1) than in the control stand (64.52 Mg C ha−1). However, C storage of forest floor and soil layers measured at four different depths was not changed by FTW, except for that at the surface soil depth (0–10 cm). The organic C input due to litterfall and output due to needle litter decomposition were both significantly lower in the FTW stand than in the control stand (2.02 Mg C ha−1 year−1 vs. 2.80 Mg C ha−1 year−1 and 308 g C kg−1 year−1 vs. 364 g C kg−1 year−1, respectively, both P < 0.05). Soil environmental factors were significantly affected (P < 0.05) by FTW, except for soil CO2 efflux rates and organic C concentration at soil depth of 0–20 cm. The mean annual soil CO2 efflux rates were the same in the FTW (0.24 g CO2 m−2 h−1) and control (0.24 g CO2 m−2 h−1) stands despite monthly variations of soil CO2 efflux over the one-year study period. The mean soil organic C concentration at a soil depth of 0–20 cm was lower in the FTW stand (81.3 g kg−1) than in the control stand (86.4 g kg−1) but the difference was not significant (P > 0.05). In contrast, the mean soil temperature was significantly higher, the mean soil water content was significantly lower, and the soil pH was significantly higher in the FTW stand than in the control stand (10.34 °C vs. 8.98 °C, 48.2% vs. 56.4%, and pH 4.83 vs. pH 4.60, respectively, all P < 0.05). These results indicated that FTW can influence tree biomass C dynamics, organic C input and output, and soil environmental factors such as soil temperature, soil water content and soil pH, while soil C dynamics such as soil CO2 efflux rates and soil organic C concentration were little affected by FTW in a red pine stand.  相似文献   

5.
Quantitative information on the relationships between site quality and plantation productivity (dominated by the exotic species Pinus radiata) is required to achieve goals for sustainable forest production. Soil quality is a key component of site quality. A nationwide study of soil quality measurements is reported for 35 representative forest sites, covering a wide range of climatic and edaphic conditions found throughout New Zealand's plantation forest estate, representing most of the soils used for plantation forestry in New Zealand. The objectives of the study were to find the most important soil properties that discriminated among eight New Zealand Soil Orders and determine relationships between Soil Orders and early tree growth rates for P. radiata and Cupressus lusitanica. Soil physical and chemical properties were measured to identify key soil indicators of soil quality related to tree productivity. Tree growth was measured after four years on small plots planted at very high stand density (40 000 stems ha−1). A factorial design was used to examine the influence of three factors on tree productivity: two species, P. radiata D. Don (ectomycorrhizal) and C. lusitanica Miller (endomycorrhizal); with and without fertilizer; and low or high disturbance (soil compaction and/or topsoil scalping by machinery). Carbon content, Phosphorus (P) retention, and soil physical properties that index the degree of soil compactness were strongly correlated to Soil Order. These properties are similar to soil quality factors that correlated with tree growth. Discriminant analyses of soil quality parameters by Soil Order clustered soils based on P retention (phosphate absorption capacity), subsoil Carbon (C), and subsoil air capacity (volume % of voids at 10 kPa matric potential). Allophanic Soils and Podzols clustered (from plots of first versus second canonical variates) separately from the other Soil Orders, which were somewhat clustered on the second variate within a broad clustering on the first variate. Soil Orders were ranked for tree growth rates for both species: pumice Andisols > Inceptisols > tephric Andisols > Entisols > Ultisols > Spodosols (NZ classification: for P. radiata is Pumice > Brown > Pallic > Allophanic > Recent > Raw > Ultic > Podzol and for C. lusitanica Pumice > Pallic > Allophanic > Brown > Raw > Ultic > Recent > Podzol).  相似文献   

6.
Tropical plantation forests are meeting an increasing proportion of global wood demand and comprehensive studies assessing the impact of silvicultural practices on tree and soil functioning are required to achieve sustainable yields. The objectives of our study were: (1) to quantify the effects of contrasting organic residue (OR) retention methods on tree growth and soil nutrient pools over a full Eucalyptus rotation and (2) to assess the potential of soil analyses to predict yields of fast-growing plantations established on tropical sandy soils. An experiment was set up in the Congo at the harvesting of the first rotation after afforestation of a native herbaceous savanna. Six treatments were set up in 0.26 ha plots and replicated in 4 blocks, with OR mass at planting ranging from 0 to 46.5 Mg ha−1. Tree growth over the whole rotation was highly dependent on OR management at planting. Over-bark trunk volume 7 years after planting ranged from 96 m3 ha−1 in the treatment with forest floor and harvest residue removal at planting to 164 m3 ha−1 in the treatment with the largest amount of OR. A comparison of nutrient stocks within the ecosystem at planting and at the end of the rotation suggested that nutrient contents in OR were largely involved in the different response observed between treatments. OR management treatments did not significantly modify most of the nutrient concentrations in the upper layers of the mineral soil. Conventional soil analyses performed before planting and at ages 1 and 3 years were unable to detect differences between treatments despite large differences in tree growth. In contrast, linear regressions between stand aboveground biomass at harvesting and OR mass at planting (independent variable) showed that OR mass was an excellent predictor of stand yield (R2 = 0.99). A large share of soil fertility comes from organic material above the mineral soil in highly weathered sandy soils and OR mass at planting might be used in conjunction with soil analyses to assess the potential of these soils to support forest plantations.  相似文献   

7.
The effects of 4 years of simulated nitrogen (N) and sulfur (S) depositions on gross N transformations in a boreal forest soil in the Athabasca oil sands region (AOSR) in Alberta, Canada, were investigated using the 15N pool dilution method. Gross NH4+ transformation rates in the organic layer tended to decline (P < 0.10, marginal statistical significance, same below) in the order of control (CK, i.e., no N or S addition), +N (30 kg N ha−1 yr−1), +S (30 kg S ha−1 yr−1), and +NS treatments, with an opposite trend in the mineral soil. Gross NH4+ immobilization rates were generally higher than gross N mineralization rates across the treatments, suggesting that the studied soil still had potential for microbial immobilization of NH4+, even after 4 years of elevated levels of simulated N and S depositions. For both soil layers, N addition tended to increase (P < 0.10) the gross nitrification and NO3− immobilization rates. In contrast, S addition reduced (P < 0.001) and increased (P < 0.001) gross nitrification as well as tended (P < 0.10) to reduce and increase gross NO3− immobilization rates in the organic and mineral soils, respectively. Gross nitrification and gross NO3− immobilization rates were tightly coupled in both soil layers. The combination of rapid NH4+ cycling, negligible net nitrification rates and the small NO3− pool size after 4 years of elevated N and S depositions observed here suggest that the risk of NO3− leaching would be low in the studied boreal forest soil, consistent with N leaching measurements in other concurrent studies at the site that are reported elsewhere.  相似文献   

8.
Greenhouse gas emissions from managed peatlands are annually reported to the UNFCCC. For the estimation of greenhouse gas (GHG) balances on a country-wide basis, it is necessary to know how soil–atmosphere fluxes are associated with variables that are available for spatial upscaling. We measured momentary soil–atmosphere CO2 (heterotrophic and total soil respiration), CH4 and N2O fluxes at 68 forestry-drained peatland sites in Finland over two growing seasons. We estimated annual CO2 effluxes for the sites using site-specific temperature regressions and simulations in half-hourly time steps. Annual CH4 and N2O fluxes were interpolated from the measurements. We then tested how well climate and site variables derived from forest inventory results and weather statistics could be used to explain between-site variation in the annual fluxes. The estimated annual CO2 effluxes ranged from 1165 to 4437 g m−2 year−1 (total soil respiration) and from 534 to 2455 g m−2 year−1 (heterotrophic soil respiration). Means of 95% confidence intervals were ±12% of total and ±22% of heterotrophic soil respiration. Estimated annual CO2 efflux was strongly correlated with soil respiration at the reference temperature (10 °C) and with summer mean air temperature. Temperature sensitivity had little effect on the estimated annual fluxes. Models with tree stand stem volume, site type and summer mean air temperature as independent variables explained 56% of total and 57% of heterotrophic annual CO2 effluxes. Adding summer mean water table depth to the models raised the explanatory power to 66% and 64% respectively. Most of the sites were small CH4 sinks and N2O sources. The interpolated annual CH4 flux (range: −0.97 to 12.50 g m−2 year−1) was best explained by summer mean water table depth (r2 = 64%) and rather weakly by tree stand stem volume (r2 = 22%) and mire vegetation cover (r2 = 15%). N2O flux (range: −0.03 to 0.92 g m−2 year−1) was best explained by peat CN ratio (r2 = 35%). Site type explained 13% of annual N2O flux. We suggest that water table depth should be measured in national land-use inventories for improving the estimation of country-level GHG fluxes for peatlands.  相似文献   

9.
In the western United States, mechanical thinning and prescribed fire are common forest management practices aimed at reducing potential wildfire severity and restoring historic forest structure, yet their effects on forest microclimate conditions are not well understood. We collected microclimate data between 1998 and 2003 in a mixed-conifer forest in California's Sierra Nevada. Air and soil temperatures, relative humidity, photosynthetically active radiation (PAR), wind speed, soil heat flux, and soil volumetric moisture were measured at the center of 18 four-ha plots. Each plot was assigned one of six combinations of thinning and burning treatments, and each treatment was thus given three replications. We found that spatial variability in microclimate, quantified as standard deviations among monthly values of each microclimatic variable across different locations (n ≤ 18), was significantly high and was influenced primarily by elevation and canopy cover. The combination of thinning and burning treatments increased air temperature from 58.1% to 123.6%. Soil temperatures increased in all thinned plots. Air moisture variables indicated that treatments made air drier, but soil moisture increased in the range 7.9–39.8%, regardless of treatment type. PAR increased in the range 50.4–254.8%, depending on treatment type. Treatments combining thinning and burning increased wind speed by 15.3–194.3%. Although soil heat flux increased dramatically in magnitude in some plots, overall treatment effects on G were not statistically significant. We discussed the significance and implications of the spatial variability of microclimate and the treatment effects to various ecological processes and to forest management.  相似文献   

10.
The effects of experimental site preparation treatments on soil respiration were studied in a boreal mixedwood forest. The treatments were: (1) intact forest (uncut); (2) clearcut without site preparation (cut); (3) clearcut followed by mixing of organic matter with mineral horizons (mixed); and (4) plots from which all organic matter was removed (screefed). Soil respiration was measured as carbon dioxide (CO2) evolution from surface soil once a month from June to October, 1994 in the field using infra-red gas analyzer (IRGA). In addition, soil temperature and moisture content were determined once a month during the 1994 growing season and soil organic matter content was determined once in July 1994. Mixed plots had the highest soil respiration rates (0.86 to 0.98 g m−2 h−1), followed by the clearcut (0.68 to 0.84 g m−2 h−1) and uncut plots (0.56 to 0.82 g m−2 h−1), with screefed plots having the lowest respiration rates (0.24 to 0.52 g m−2 h−1) from June to September. Soil respiration of the cut plots was not significantly different from that of the uncut control. The site preparation treatments reduced soil moisture and soil organic matter contents significantly. Changes in soil temperature within treatment at 0, 5 and 10 cm depths and between the treatments were not significant. Observed soil respiration patterns were attributed to changes in soil moisture and organic matter content associated with the various treatments. A laboratory incubation experiment elucidated the effects of organic matter, soil moisture, and temperature on soil respiration rates. Site preparation treatments in boreal mixedwood forests affect soil respiration by modifying the moisture and organic matter content of the soil.  相似文献   

11.
In the future it may become common practice to return wood-ash to forest ecosystems in order to replenish nutrients removed when brash has been extracted as a source of bioenergy. Wood-ash contains most of the nutrients that are present in the brash before its removal and burning, with the important exception of nitrogen (N). In the present paper we report measurements of CO2 emissions and net N mineralisation in the humus layer and the upper 5 cm of mineral soil 12 years after the application of wood-ash to two study sites, representing different tree species, climatic conditions and N deposition histories. We hypothesized that application of wood-ash would increase both carbon (C) and net N mineralisation rates at Torup, an N-rich site with Norway spruce (Picea abies (L.) Karst.) in the south, whereas the net N mineralisation rates would not be affected at Vindeln, an N-poor site with Scots pine (Pinus sylvestris L.) in the north, where a possible N-limitation would restrict any N mineralisation. The treatments, comprising additions of 0, 1, 3 or 6 Mg of granulated wood-ash ha−1, were applied in a randomised block design, replicated three times. Wood-ash from the same batch was used for all treatments at both sites. All factors were measured under laboratory conditions with controlled temperature and moisture levels. The potential CO2 emissions (kg ha−1 year−1 of CO2–C) at Torup were significantly higher in the 3 and 6 Mg ha−1 treatments than in the control treatment, and the highest application resulted in an extra loss of 0.5 Mg ha−1 of soil C annually as compared to the control. No such differences were detected at Vindeln. The results suggest that wood-ash application can deplete soil organic C at locations with similar characteristics (N-rich soil, spruce dominated, warm climate) as at Torup in this study.  相似文献   

12.
Incorporation of forest slash during stand establishment is proposed as a means of increasing soil carbon and nutrient stocks. If effective, the increased soil carbon and nutrient status may result in increased aboveground tree growth. Eight years after study installation, the impact of forest slash incorporation into the soil on soil carbon and nutrient stocks, foliar nutrients and loblolly pine growth are examined on mineral and organic sites on the North Carolina Lower Coastal Plain. Treatments include leaving forest slash on the surface and flat planting (control); V-shear and bedding (conventional), mulch forest slash followed by bedding (strip mulch) and mulch forest slash and till into the soil followed by bedding (strip mulch till). After eight years, mulching and/or tillage did not have a significant impact (p > 0.05) on soil bulk density or soil chemical properties (pH, cation exchange capacity, soil nutrients). Additionally, neither tree foliar nutrients nor stand volume were significantly impacted. However, significant effects were observed for soil phosphorus contents and stand volume between the control plots and the other treatment plots. For example, the mean stand volumes on the mineral site were 24.49 ± 1.28, 38.16 ± 2.90, 44.59 ± 3.07 and 46.96 ± 2.74 m3 ha−1 for the control, conventional, strip mulch and strip mulch till plots. These observations are more likely due to the effect of bedding rather than mulching or tillage of the forest slash. These results are consistent for the mineral and the organic sites. Considering the greater expense to install the mulch and tillage treatments, the lack of a treatment effect on soil carbon and nutrient stocks and tree growth does not justify these treatments on these sites.  相似文献   

13.
This study examined the effect of tree species identity and diversity on soil respiration in a 3-year-old tropical tree biodiversity plantation in Central Panamá. We hypothesized that tree pairs in mixed-species plots would have higher soil respiration rates than those in monoculture plots as a result of increased primary productivity and complementarity leading to greater root and microbial biomass and soil respiration. In addition to soil respiration, we measured potential controls including root, tree, and microbial biomass, soil moisture, surface temperature, bulk density. Over the course of the wet season, soil respiration decreased from the June highs (7.2 ± 3.5 μmol CO2/(m2 s−1) to a low of 2.3 ± 1.9 μmol CO2/(m2 s−1) in the last 2 weeks of October. The lowest rates of soil respiration were at the peak of the dry season (1.0 ± 0.7 μmol CO2/(m2 s−1)). Contrary to our hypothesis, soil respiration was 19–31% higher in monoculture than in pairs and plots with higher diversity in the dry and rainy seasons. Although tree biomass was significantly higher in pairs and plots with higher diversity, there were no significant differences in either root or microbial biomass between monoculture and two-species pairs. Path analyses allow the comparison of different pathways relating soil respiration to either biotic or abiotic controls factors. The path linking crown volume to soil temperature then respiration has the highest correlation, with a value of 0.560, suggesting that canopy controls on soil climate may drive soil respiration.  相似文献   

14.
There is limited understanding of the carbon (C) storage capacity and overall ecological structure of old-growth forests of western Montana, leaving little ability to evaluate the role of old-growth forests in regional C cycles and ecosystem level C storage capacity. To investigate the difference in C storage between equivalent stands of contrasting age classes and management histories, we surveyed paired old-growth and second growth western larch (Larix occidentalis Nutt)–Douglas-fir (Pseudostuga menziesii var. glauca) stands in northwestern Montana. The specific objectives of this study were to: (1) estimate ecosystem C of old-growth and second growth western larch stands; (2) compare C storage of paired old-growth–second growth stands; and (3) assess differences in ecosystem function and structure between the two age classes, specifically measuring C associated with mineral soil, forest floor, coarse woody debris (CWD), understory, and overstory, as well as overall structure of vegetation. Stands were surveyed using a modified USFS FIA protocol, focusing on ecological components related to soil, forest floor, and overstory C. All downed wood, forest floor, and soil samples were then analyzed for total C and total nitrogen (N). Total ecosystem C in the old-growth forests was significantly greater than that in second growth forests, storing over 3 times the C. Average total mineral soil C was not significantly different in second growth stands compared to old-growth stands; however, total C of the forest floor was significantly greater in old-growth (23.8 Mg ha−1) compared to second growth stands (4.9 Mg ha−1). Overstory and coarse root biomass held the greatest differences in ecosystem C between the two stand types (old-growth, second growth), with nearly 7 times more C in old-growth trees than trees found on second growth stands (144.2 Mg ha−1 vs. 23.8 Mg ha−1). Total CWD on old-growth stands accounted for almost 19 times more C than CWD found in second growth stands. Soil bulk density was also significantly higher on second growth stands some 30+ years after harvest, demonstrating long-term impacts of harvest on soil. Results suggest ecological components specific to old-growth western larch forests, such as coarse root biomass, large amounts of CWD, and a thick forest floor layer are important contributors to long-term C storage within these ecosystems. This, combined with functional implications of contrasts in C distribution and dynamics, suggest that old-growth western larch/Douglas-fir forests are both functionally and structurally distinctive from their second growth counterparts.  相似文献   

15.
Ammonium nitrate (NH4NO3) was applied monthly (from June to October) for 3 years in a balsam fir (Abies balsamea (Linné) Miller) and a black spruce (Picea mariana (Mill.) BSP) boreal forest in Québec (Canada). The design was composed of nine experimental units of 10 m × 10 m for each site. Application rates were 3 and 10 times the atmospheric N deposition measured at each site which was 6 and 3 kg ha−1 year−1 for the fir and the spruce sites, respectively. Soil solution composition (30 and 60 cm), tree growth, and foliar concentrations were analysed. The inorganic N in the soil solution of the control plots of both sites was low, particularly at the spruce site indicating that these forests are actively accumulating the atmospheric deposited N. Nitrogen additions regularly caused sudden and large inorganic N increases in the soil solution at both sites, both treatments and both sampling depths. However, these increases were transitory in nature and no persistent changes in inorganic N were observed. It was estimated that more than 95% of the added N was retained above the rooting zone at both sites. Nitrogen addition increased N, Ca, Mg and Mn foliar concentrations at the black spruce site but had no effects at the balsam fir site. After 3 years of N application, tree growth was similar in the control and the treated plots at both sites. Our results show that slow growing black spruce boreal forests with low ambient N deposition are responsive (in term of foliar N, Ca, Mg and Mn concentrations) to even small increases in N inputs, compared to higher growth balsam fir boreal forests with higher N deposition.  相似文献   

16.
Reduced soil respiration in gaps in logged lowland dipterocarp forests   总被引：1，自引：0，他引：1  
We studied the effects of forest composition and structure, and related biotic and abiotic factors on soil respiration rates in a tropical logged forest in Malaysian Borneo. Forest stands were classified into gap, pioneer, non-pioneer and mixed (pioneer, non-pioneer and unclassified trees) based on the species composition of trees >10 cm diameter breast height. Soil respiration rates did not differ significantly between non-gap sites (1290 ± 210 mg CO2 m−2 h−1) but were double those in gap sites (640 ± 130 mg CO2 m−2 h−1). Post hoc analyses found that an increase in soil temperature and a decrease in litterfall and fine root biomass explained 72% of the difference between gap and non-gap sites. The significant decrease of soil respiration rates in gaps, irrespective of day or night time, suggests that autotrophic respiration may be an important contributor to total soil respiration in logged forests. We conclude that biosphere-atmosphere carbon exchange models in tropical systems should incorporate gap frequency and that future research in tropical forest should emphasize the contribution of autotrophic respiration to total soil respiration.  相似文献   

17.
Silvicultural canopy gaps are emerging as an alternative management tool to accelerate development of complex forest structure in young, even-aged forests of the Pacific Northwest. The effect of gap creation on available nitrogen (N) is of concern to managers because N is often a limiting nutrient in Pacific Northwest forests. We investigated patterns of N availability in the forest floor and upper mineral soil (0–10 cm) across 6–8-year-old silvicultural canopy gaps in three 50–70-year-old Douglas-fir forests spanning a wide range of soil N capital in the Coast Range and Cascade Mountains of western Oregon. We used extractable ammonium (NH4+) and nitrate (NO3−) pools, net N mineralization and nitrification rates, and NH4+ and NO3− ion exchange resin (IER) concentrations to quantify N availability along north-south transects run through the centers of 0.4 and 0.1 ha gaps. In addition, we measured several factors known to influence N availability, including litterfall, moisture, temperature, and decomposition rates. In general, gap-forest differences in N availability were more pronounced in the mineral soil than in the forest floor. Mineral soil extractable NH4+ and NO3− pools, net N mineralization and nitrification rates, and NH4+ and NO3− IER concentrations were all significantly elevated in gaps relative to adjacent forest, and in several cases exhibited significantly greater spatial variability in gaps than forest. Nitrogen availability along the edges of gaps more often resembled levels in the adjacent forest than in gap centers. For the majority of response variables, there were no significant differences between northern and southern transect positions, nor between 0.4 and 0.1 ha gaps. Forest floor and mineral soil gravimetric percent moisture and temperature showed few differences along transects, while litterfall carbon (C) inputs and litterfall C:N ratios in gaps were significantly lower than in the adjacent forest. Reciprocal transfer incubations of mineral soil samples between gap and forest positions revealed that soil originating from gaps had greater net nitrification rates than forest samples, regardless of incubation environment. Overall, our results suggest that increased N availability in 6–8-year-old silvicultural gaps in young western Oregon forests may be due more to the quality and quantity of litterfall inputs resulting from early-seral species colonizing gaps than by changes in temperature and moisture conditions caused by gap creation.  相似文献   

18.
An accurate characterization of tree carbon (TC), forest floor carbon (FFC) and soil organic carbon (SOC) in tropical forest plantations is important to estimate their contribution to global carbon stocks. This information, however, is poor and fragmented. Carbon contents were assessed in patula pine (Pinus patula) and teak (Tectona grandis) stands in tropical forest plantations of different development stages in combination with inventory assessments and soil survey information. Growth models were used to associate TOC to tree normal diameter (D) with average basal area and total tree height (HT), with D and HT parameters that can be used in 6–26 years old patula pine and teak in commercial tropical forests as indicators of carbon stocks. The information was obtained from individual trees in different development stages in 54 patula pine plots and 42 teak plots. The obtained TC was 99.6 Mg ha−1 in patula pine and 85.7 Mg ha−1 in teak forests. FFC was 2.3 and 1.2 Mg ha−1, SOC in the surface layer (0–25 cm) was 92.6 and 35.8 Mg ha−1, 76.1 and 19 Mg ha−1 in deep layers (25–50 cm) in patula pine and teak, respectively. Carbon storage in trees was similar between patula pine and teak plantations, but patula pine had higher levels of forest floor carbon and soil organic carbon. Carbon storage in trees represents 37 and 60% of the total carbon content in patula pine and teak plantations, respectively. Even so, the remaining percentage corresponds to SOC, whereas FFC content is less than 1%. In summary, differences in carbon stocks between patula pine and teak trees were not significant, but the distribution of carbon differed between the plantation types. The low FFC does not explain the SOC stocks; however, current variability of SOC stocks could be related to variation in land use history.  相似文献   

19.
Tree thinning reduces tree-to-tree competition and likely contributes to the improvement of tree water status and productivity in water-limited systems. In this study, we examined the importance of competition for water among Quercus ilex trees in open woodlands by comparing the water consumption and physiological status of trees located along stand density gradients which ranged from 10% (low density; LD) to 100% (high density; HD) of canopy cover. The study was carried out at two sites which differed in mean annual rainfall (506 and 816 L m−2; Dsite and Wsite, respectively). Predawn and midday leaf water potential (ψd and ψm, respectively) and CO2 assimilation rate (A) were measured every two weeks from mid May to mid September, in eight trees located along a stand density gradient at each site. Sap flow and soil moisture were measured only at Dsite. Sap flow was continuously recorded by sap flowmeters (constant heating method) installed in 12 trees along two stand density gradients. Soil moisture (?) was measured every 20 cm for the first meter and then every 50 cm up to 250 cm. Measurements were conducted in 18 soil profiles, 6 located in HD and 12 in LD (six beneath and six out the canopy). At Wsite, differences among stand densities for ψ and A were very small and emerged only at the end of the dry season. At Dsite, ψ (both predawn and midday), A, ?, and sap flow density were significantly higher in LD trees than in HD ones. At Dsite, some water remained unused in the soil at the end of the dry season beyond the canopy in the LD areas, and trees did not experienced such an acute water deficit (ψd > −1 MPa) as the HD trees did (ψd < −3 MPa). Summer tree transpiration at the stand level (Estand) tended to saturate with the increase of canopy cover. Estand increases by 32% when canopy cover goes from 50% to 100%. Results confirmed that the increase of tree-to-tree competition with stand density was much more significant at dry sites. In these sites, tree thinning is recommended as a way to maintain tree functioning.  相似文献   

20.
We measured the change in above- and below-ground carbon and nutrient pools 11 years after the harvesting and site preparation of a histic-mineral soil wetland forest in the Upper Peninsula of Michigan. The original stand of black spruce (Picea mariana), jack pine (Pinus banksiana) and tamarack (Larix laricina) was whole-tree harvested, and three post-harvest treatments (disk trenching, bedding, and none) were randomly assigned to three Latin square blocks (n = 9). Nine control plots were also established in an adjoining uncut stand. Carbon and nutrients were measured in three strata of above-ground vegetation, woody debris, roots, forest floor, and mineral soil to a depth of 1.5 m. Eleven years following harvesting, soil C, N, Ca, Mg, and K pools were similar among the three site preparation treatments and the uncut stand. However, there were differences in ecosystem-level nutrient pools because of differences in live biomass. Coarse roots comprised approximately 30% of the tree biomass C in the regenerated stands and 18% in the uncut stand. Nutrient sequestration, in the vegetation since harvesting yielded an average net ecosystem gain of 332 kg N ha−1, 110 kg Ca ha−1, 18 kg Mg ha−1, and 65 kg K ha−1. The likely source for the cations and N is uptake from shallow groundwater, but N additions could also come from non-symbiotic N-fixation and N deposition. These are the only reported findings on long-term effects of harvesting and site preparation on a histic-mineral soil wetland and the results illustrate the importance of understanding the ecohydrology and nutrient dynamics of the wetland forest. This wetland type appears less sensitive to disturbance than upland sites, and is capable of sustained productivity under these silvicultural treatments.  相似文献   

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