Predicting the responses of forest distribution and aboveground biomass to climate change under RCP scenarios in southern China.

In the past three decades, our global climate has been experiencing unprecedented warming. This warming has and will continue to significantly influence the structure and function of forest ecosystems. While studies have been conducted to explore the possible responses of forest landscapes to future climate change, the representative concentration pathways (RCPs) scenarios under the framework of the Coupled Model Intercomparison Project Phase 5 (CMIP5) have not been widely used in quantitative modeling research of forest landscapes. We used LANDIS-II, a forest dynamic landscape model, coupled with a forest ecosystem process model (PnET-II), to simulate spatial interactions and ecological succession processes under RCP scenarios, RCP2.6, RCP4.5 and RCP8.5, respectively. We also modeled a control scenario of extrapolating current climate conditions to examine changes in distribution and aboveground biomass (AGB) among five different forest types for the period of 2010-2100 in Taihe County in southern China, where subtropical coniferous plantations dominate. The results of the simulation show that climate change will significantly influence forest distribution and AGB. (i) Evergreen broad-leaved forests will expand into Chinese fir and Chinese weeping cypress forests. The area percentages of evergreen broad-leaved forests under RCP2.6, RCP4.5, RCP8.5 and the control scenarios account for 18.25%, 18.71%, 18.85% and 17.46% of total forest area, respectively. (ii) The total AGB under RCP4.5 will reach its highest level by the year 2100. Compared with the control scenarios, the total AGB under RCP2.6, RCP4.5 and RCP8.5 increases by 24.1%, 64.2% and 29.8%, respectively. (iii) The forest total AGB increases rapidly at first and then decreases slowly on the temporal dimension. (iv) Even though the fluctuation patterns of total AGB will remain consistent under various future climatic scenarios, there will be certain responsive differences among various forest types.

[Impacts of drought and stand factors on tree mortality: A case study of national forests in east Texas, USA.] / å¹²æ—±å’Œæž—åˆ†å› å­å¯¹æ ‘æœ¨æ­»äº¡çš„å½±å“­­ä»¥ç¾Žå›½å¾·å ‹è¨æ–¯å·žä¸œéƒ¨å›½å®¶æ£®æž—为例.

To explore the effects of multiple time-scales, climatic and stand factors on tree mortality in forests, we examined the changes in annual and inventory-cycle tree mortality patterns across 264 forest inventory plots in four national forests of eastern Texas. These data were obtained from the Forest Inventory and Analysis (FIA) Program and the plots had been individually surveyed in four inventory cycles over the past 20 years. The generalized linear mixed effects model (GLMM) was used to explore the effects of climatic factors (drought severity, duration of drought, mean annual temperature, and mean annual precipitation), tree size (diameter at breast height) and stand factors (basal area, stand density, and stand age) on tree mortality. The results showed that tree mortality rates increased by 151% in the particular year with severe drought and by 123% during exceptional inventory cycle during the inventory cycle with severe drought. The major cause of death was weather (exceptional drought and large hurricanes). Both drought severity as measured by standardized precipitation evapotranspiration index (SPEI) and the duration of drought had significant negative effects, whereas annual precipitation had a significant positive effect on tree survival. Tree basal area had a significant negative effect, while tree size, stand age and stand density had significant positive effects on tree survival. Trees with larger size (DBH) were more vulnerable to drought than smaller ones. During the exceptional drought, tree mortality rate of pine species (2.1%) was lower than that of hardwood species (3.9%), while tree mortality in the natural forests (3.0%) was higher than that in the pine plantations (1.9%). Our results suggested that it was essential to consider the relative importance of both intrinsic (tree size) and extrinsic (stand factors and climatic factors) factors in analyzing tree mortality.

Stage-structured matrix models for organisms with non-geometric development times.

Matrix models have been used to model population growth of organisms for many decades. They are popular because of both their conceptual simplicity and their computational efficiency. For some types of organisms they are relatively accurate in predicting population growth; however, for others the matrix approach does not adequately model growth rate. One of the reasons for the lack of accuracy is that most matrix-based models implicitly assume a specific degree of variability in development times for the organism. Because the variability is implicit, the implied variances are often not verified with experimental data. In this paper, we shall present extensions to the stage-classified matrix models so that organisms with arbitrary means and standard deviations of development times can be modeled.

Quantifying ecosystem service trade-offs for plantation forest management to benefit provisioning and regulating services.

There is increasing interest worldwide regarding managing plantation forests in a manner that maintains or improves timber production, enhances ecosystem services, and promotes long-term sustainability of forest resources. We selected the Gan River Basin, the largest catchment of Poyang Lake and a region with a typical plantation distribution in South China, as the study region. We evaluated and mapped four important forest ecosystem services, including wood volume, carbon storage, water yield, and soil retention at a 30 × 30 m resolution, then quantified their trade-offs and synergies at the county and subwatershed scales. We found that the wood volume and carbon storage services, as well as the soil retention and water yield, exhibited synergistic relationships. However, the carbon storage displayed a trade-off relationship with the water yield. Additionally, we compared the beneficial spatial characteristics among dominant species in the study region. The results showed that the Chinese fir forest and the pine forest exhibited lower overall benefits than natural forests including the broad-leaved forest and the bamboo forest. To propose a suitable management strategy for the study region, method of spatial cluster analysis was used based on the four eco-services at the subwatershed scale. The basin was divided into four management groups instead of treating the region as a homogenous management region. Finally, we proposed more specific and diverse management strategies to optimize forest benefits throughout the entire region.

Distributions of exotic plants in eastern Asia and North America.

Although some plant traits have been linked to invasion success, the possible effects of regional factors, such as diversity, habitat suitability, and human activity are not well understood. Each of these mechanisms predicts a different pattern of distribution at the regional scale. Thus, where climate and soils are similar, predictions based on regional hypotheses for invasion success can be tested by comparisons of distributions in the source and receiving regions. Here, we analyse the native and alien geographic ranges of all 1567 plant species that have been introduced between eastern Asia and North America or have been introduced to both regions from elsewhere. The results reveal correlations between the spread of exotics and both the native species richness and transportation networks of recipient regions. This suggests that both species interactions and human-aided dispersal influence exotic distributions, although further work on the relative importance of these processes is needed.

Soil Infiltration Characteristics in Agroforestry Systems and Their Relationships with the Temporal Distribution of Rainfall on the Loess Plateau in China.

Many previous studies have shown that land use patterns are the main factors influencing soil infiltration. Thus, increasing soil infiltration and reducing runoff are crucial for soil and water conservation, especially in semi-arid environments. To explore the effects of agroforestry systems on soil infiltration and associated properties in a semi-arid area of the Loess Plateau in China, we compared three plant systems: a walnut (Juglans regia) monoculture system (JRMS), a wheat (Triticum aestivum) monoculture system (TAMS), and a walnut-wheat alley cropping system (JTACS) over a period of 11 years. Our results showed that the JTACS facilitated infiltration, and its infiltration rate temporal distribution showed a stronger relationship coupled with the rainfall temporal distribution compared with the two monoculture systems during the growing season. However, the effect of JTACS on the infiltration capacity was only significant in shallow soil layer, i.e., the 0-40 cm soil depth. Within JTACS, the speed of the wetting front's downward movement was significantly faster than that in the two monoculture systems when the amount of rainfall and its intensity were higher. The soil infiltration rate was improved, and the two peaks of soil infiltration rate temporal distribution and the rainfall temporal distribution coupled in rainy season in the alley cropping system, which has an important significance in soil and water conservation. The results of this empirical study provide new insights into the sustainability of agroforestry, which may help farmers select rational planting patterns in this region, as well as other regions with similar climatic and environmental characteristics throughout the world.

The effects of Herba Andrographitis hedgerows on soil erodibility and fractal features on sloping cropland in the Three Gorges Reservoir Area.

To evaluate if hedgerows could improve the soil physicochemical properties and enhance the soil anti-scouring and anti-shearing capabilities, the effects of Herba Andrographitis hedgerows on soil erodibility and fractal features on sloping cropland in the Three Gorges Reservoir Area were investigated. Results showed that: (1) the clay particle accumulation around the hedgerows was significantly affected by the hedgerows; (2) the fractal dimension of soil particles was positively correlated with both silt and clay contents and had a negative linear correlation with sand content; (3) fine-grained content significantly influenced fractal dimension of the soil particles; (4) soil erodibility K was significantly and positively correlated with the sand content (correlation coefficient r=0.870), but significantly and negatively correlated with the silt content (r=-0.538), clay content (r=-0.739), organic carbon content (r=-0.603), the aggregation degree (r=-0.486), and soil fractal dimension (r=-0.538); and (5) the contents of organic matter and clay particles in the soil were found to be the effective indicators for soil erodibility at the Three Gorges Reservoir Area. The hedgerows may improve soil fractal features and decrease soil erodibility. The effective distance between hedgerows on a slope of 10° was less than 6 m.

Intercropping competition between apple trees and crops in agroforestry systems on the Loess Plateau of China.

Agroforestry has been widely practiced in the Loess Plateau region of China because of its prominent effects in reducing soil and water losses, improving land-use efficiency and increasing economic returns. However, the agroforestry practices may lead to competition between crops and trees for underground soil moisture and nutrients, and the trees on the canopy layer may also lead to shortage of light for crops. In order to minimize interspecific competition and maximize the benefits of tree-based intercropping systems, we studied photosynthesis, growth and yield of soybean (Glycine max L. Merr.) and peanut (Arachis hypogaea L.) by measuring photosynthetically active radiation, net photosynthetic rate, soil moisture and soil nutrients in a plantation of apple (Malus pumila M.) at a spacing of 4 m × 5 m on the Loess Plateau of China. The results showed that for both intercropping systems in the study region, soil moisture was the primary factor affecting the crop yields followed by light. Deficiency of the soil nutrients also had a significant impact on crop yields. Compared with soybean, peanut was more suitable for intercropping with apple trees to obtain economic benefits in the region. We concluded that apple-soybean and apple-peanut intercropping systems can be practical and beneficial in the region. However, the distance between crops and tree rows should be adjusted to minimize interspecies competition. Agronomic measures such as regular canopy pruning, root barriers, additional irrigation and fertilization also should be applied in the intercropping systems.