Xiaohua Wei

Global pattern for the effect of climate and land cover on water yield

Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial. Here we use published data worldwide to examine the validity of Fuhs equation, which relates annual water yield (R) to a wetness index (precipitation/potential evapotranspiration; P/PET) and watershed characteristics (m). We identify two critical values at P/PET=1 and m=2. m plays a more important role than P/PET when m<2, and a lesser role when m>2. When P/PET<1, the relative water yield (R/P) is more responsive to changes in m than it is when P/PET>1, suggesting that any land cover changes in non-humid regions (P/PET<1) or in watersheds of low water retention capacity (m<2) can lead to greater hydrological responses. m significantly correlates with forest coverage, watershed slope and watershed area. This global pattern has far-reaching significance in studying and managing hydrological responses to land cover and climate changes.

Quantifying streamflow change caused by forest disturbance at a large spatial scale: A single watershed study

Climatic variability and forest disturbance are commonly recognized as two majordrivers influencing streamflow change in large‐scale forested watersheds. The greatestchallenge in evaluating quantitative hydrological effects of forest disturbance is theremoval of climatic effect on hydrology. In this paper, a method was designed to quantifyrespective contributions of large‐scale forest disturbance and climatic variability onstreamflow using the Willow River watershed (2860 km

Impacts of eucalyptus (Eucalyptus exserta) plantation on sediment yield in Guangdong Province, Southern China—a kinetic energy approach

The relationship between the kinetic energy of waterdrops (rainfall and throughfall) and sediment yield (suspended solid (SS) and bed load (BL)) was studied in paired watersheds (one without vegetation and the other covered by an eucalyptus (Eucalyptus exserta) plantation) in Guangdong Province, Southern China. The results showed that there was a significant correlation between the kinetic energy of waterdrops and sediment yield in both watersheds. Sediment yield in the unvegetated watershed is significantly affected by the kinetic energy of atmospheric raindrops. Sediment yield in the plantation watershed, however, is significantly related to the kinetic energy of throughfall waterdrops, but not to the atmospheric rainfall intensity or the rainfall kinetic energy. When rainfall amount is greater than 5 mm, and their intensities are less than 20 mm h � 1 , the singlelayer eucalyptus plantations significantly increased the kinetic energy of waterdrops to the land surface, and consequently, accelerated soil erosion. However, these plantations do have positive impacts on the reduction of soil erosion for the rainfall events of larger intensities (particularly >40 mm h � 1 ). Management implications of these results are discussed in the context of soil protection

Disturbances and the sustainability of long-term site productivity in lodgepole pine forests in the central interior of British Columbia—an ecosystem modeling approach

Abstract The ecosystem-management model FORECAST was used to compare some ecological impacts of natural disturbance (wildfire) and timber harvesting. The scientific objective of the study was to assess whether or not two types of timber harvesting at various rotation lengths would have biogeochemical and biomass implications that are within the natural range of variation caused by wildfire. The practical objective was to identify management strategies that would sustain or improve long-term site productivity in lodgepole pine forests in the central interior of British Columbia. We defined three fire severity categories (low, medium and high), three fire return intervals (40, 80 and 120 years), two utilization levels (including stem-only harvesting [SOH] and whole-tree harvesting [WTH]), and three timber production rotation lengths (40, 80 and 120 years). Differences in simulated productivity, decomposing litter mass, total available soil nitrogen and nitrogen removals were compared for all 15 combinations of the five levels of disturbance at the three frequencies. The simulated nutritional impacts of timber harvesting were within the simulated range of impacts caused by the wildfire defined in this study. They were similar to the simulated long-interval, low-severity wildfire regimes. Simulations suggest that ecological rotation lengths for long-term site productivity for lodgepole pine forests in the study area would be 80–120 years. These rotation lengths are close to the average wildfire return intervals (100–125 years) in the study area, supporting the idea that the present harvesting strategies should sustain tree growth at this frequency of harvest and severity of harvesting impacts. Both WTH and SOH are acceptable harvesting methods for the maintenance of long-term site productivity in these lodgepole pine forests if harvest intervals are 80 years or longer. However, SOH is a more nutrient conservative harvest method, and should be used instead of WTH for rotations less than 80 years. The importance of initial site quality in assessing sustainable long-term site productivity by modeling is demonstrated.

Greening China Naturally

China leads the world in afforestation, and is one of the few countries whose forested area is increasing. However, this massive “greening” effort has been less effective than expected; afforestation has sometimes produced unintended environmental, ecological, and socioeconomic consequences, and has failed to achieve the desired ecological benefits. Where afforestation has succeeded, the approach was tailored to local environmental conditions. Using the right plant species or species composition for the site and considering alternatives such as grassland restoration have been important success factors. To expand this success, government policy should shift from a forest-based approach to a results-based approach. In addition, long-term monitoring must be implemented to provide the data needed to develop a cost-effective, scientifically informed restoration policy.

Effects of nitrogen deposition on carbon sequestration in Chinese fir forest ecosystems.

Nitrogen deposition and its ecological effects on forest ecosystems have received global attention. We used the ecosystem model FORECAST to assess the effects of nitrogen deposition on carbon sequestration in Chinese fir planted forests in SE China. This topic is important as China is intensifying its reforestation efforts to increase forest carbon sequestration for combating climate change impacts, using Chinese fir as the most important plantation species. A series of scenarios including seven N deposition levels (1, 5, 10, 20, 30, 40 and 50kg ha(-1)y(-1)), three management regime (rotation lengths of 15, 30 and 50 years) and two site qualities (nutrient poor and fertile sites) were defined for the simulations. Our results showed that N deposition increased carbon sequestration in Chinese fir forests, but the efficiency of the increasing effect is reduced as N deposition levels increase. When N deposition levels exceeded 20-30kg ha(-1)y(-1), the incremental effects of N deposition on forest C pools were marginal. This suggests that N deposition levels above 20-30kg ha(-1)y(-1) could lead to N saturation in Chinese fir forest soils. Any additional amounts of N input from deposition would likely be leached out. Total above-ground C was more sensitive to N deposition than to rotation length and site quality. It was also estimated that the contributions of N deposition to C sequestration in all Chinese fir forests in South-East China are 7.4×10(6)MgCy(-1) under the current N deposition levels (5 to 10kg ha(-1)y(-1)) and could reach up to 16×10(6)MgCy(-1) if N deposition continues increasing and reaches levels of 7.5 to 15kg N ha(-1)y(-1).

Simulations on impacts of different management strategies on long-term site productivity in lodgepole pine forests of the central interior of British Columbia

Abstract Impacts of different management strategies on long-term site productivity over a period of 240 years were simulated using the ecosystem Model FORECAST for lodgepole pine forests of the central interior of British Columbia (BC). Results suggested that the sustainable management strategies for maintaining long-term site productivity in lodgepole pine forests would be 80–120-year rotation lengths, with either stem-only or whole-tree harvesting. However, because of more nutrient conservation stem-only harvesting can achieve higher productivity (3.5–8.5%) than whole-tree harvesting does. The thinning strategy (from 4000 to 1000 stems/ha) would not increase total productivity over a period of 240-year simulation. Thinning, however, can increase the habitat value for Caribou. The best thinning strategies await further simulations on effects of various stocking levels in a broader context. The simulations also showed that organic matter and below-ground woody debris are critical for maintaining long-term site productivity in lodgepole pine forests in the study area, and a significant removal of such material may cause yield decline.

Effects of rapid urban sprawl on urban forest carbon stocks: Integrating remotely sensed, GIS and forest inventory data

Research on the effects of urban sprawl on carbon stocks within urban forests can help support policy for sustainable urban design. This is particularly important given climate change and environmental deterioration as a result of rapid urbanization. The purpose of this study was to quantify the effects of urban sprawl on dynamics of forest carbon stock and density in Xiamen, a typical city experiencing rapid urbanization in China. Forest resource inventory data collected from 32,898 patches in 4 years (1972, 1988, 1996 and 2006), together with remotely sensed data (from 1988, 1996 and 2006), were used to investigate vegetation carbon densities and stocks in Xiamen, China. We classified the forests into four groups: (1) forest patches connected to construction land; (2) forest patches connected to farmland; (3) forest patches connected to both construction land and farmland and (4) close forest patches. Carbon stocks and densities of four different types of forest patches during different urbanization periods in three zones (urban core, suburb and exurb) were compared to assess the impact of human disturbance on forest carbon. In the urban core, the carbon stock and carbon density in all four forest patch types declined over the study period. In the suburbs, different urbanization processes influenced forest carbon density and carbon stock in all four forest patch types. Urban sprawl negatively affected the surrounding forests. In the exurbs, the carbon stock and carbon density in all four forest patch types tended to increase over the study period. The results revealed that human disturbance played the dominant role in influencing the carbon stock and density of forest patches close to the locations of human activities. In forest patches far away from the locations of human activities, natural forest regrowth was the dominant factor affecting carbon stock and density.

Effects of forest type, stand age, and altitude on soil respiration in subtropical forests of China

Abstract An automated chamber system was used to study how soil respiration (R S) differed with stand age (SA), altitude (AL), and forest type (FT), in subtropical China. From 2006 to 2008, measurements of soil-surface CO2 efflux and associated environmental factors were made in an evergreen broad-leaved forest (EB), and five aged Chinese fir [Cunninghamia lanceolata Hook.] plantations (CF), and three altitudinal Moso bamboo [Phyllostachys pubescens Mazel ex J. Houz.] plantations (MB), in Dagangshan mountain range, Jiangxi Province. Multivariate analysis of covariance with soil temperature (T) and soil water content (SWC) as the covariates showed that FT and AL as the independent factors had a significant effect on R S (P<0.01, P<0.05, respectively). The R S in the CF differed significantly from EB and MB (P<0.001), but not between EB and MB. The R S was positively correlated with T, and responded to changes in SWC at higher Ts. The correlation between R S and SWC was improved when the R S was normalized to 10°C. Annual mean R S differed significantly with SA and were ranked in the order (from high to low) of 21–25, 26–35, 11–20, >36, and 1–10 years. The conclusion of this study is that T, SWC, AL, FT, and SA all have significant effects on R s in subtropical China.

Significant increase in ecosystem C can be achieved with sustainable forest management in subtropical plantation forests

Subtropical planted forests are rapidly expanding. They are traditionally managed for intensive, short-term goals that often lead to long-term yield decline and reduced carbon sequestration capacity. Here we show how it is possible to increase and sustain carbon stored in subtropical forest plantations if management is switched towards more sustainable forestry. We first conducted a literature review to explore possible management factors that contribute to the potentials in ecosystem C in tropical and subtropical plantations. We found that broadleaves plantations have significantly higher ecosystem C than conifer plantations. In addition, ecosystem C increases with plantation age, and reaches a peak with intermediate stand densities of 1500–2500 trees ha−1. We then used the FORECAST model to simulate the regional implications of switching from traditional to sustainable management regimes, using Chinese fir (Cunninghamia lanceolata) plantations in subtropical China as a study case. We randomly simulated 200 traditional short-rotation pure stands and 200 sustainably-managed mixed Chinese fir – Phoebe bournei plantations, for 120 years. Our results showed that mixed, sustainably-managed plantations have on average 67.5% more ecosystem C than traditional pure conifer plantations. If all pure plantations were gradually transformed into mixed plantations during the next 10 years, carbon stocks could rise in 2050 by 260.22 TgC in east-central China. Assuming similar differences for temperate and boreal plantations, if sustainable forestry practices were applied to all new forest plantation types in China, stored carbon could increase by 1,482.80 TgC in 2050. Such an increase would be equivalent to a yearly sequestration rate of 40.08 TgC yr−1, offsetting 1.9% of China’s annual emissions in 2010. More importantly, this C increase can be sustained in the long term through the maintenance of higher amounts of soil organic carbon and the production of timber products with longer life spans.