Shrub Grassland Research Articles

Traditional knowledge of fire use by the Confederated Tribes of Warm Springs in the eastside Cascades of Oregon

We examined traditional knowledge of fire use by the Ichishikin (Sahaptin), Kitsht Wasco (Wasco), and Numu (Northern Paiute) peoples (now Confederated Tribes of Warm Springs, CTWS) in the eastside Cascades of Oregon to generate insights for restoring conifer forest landscapes and enhancing culturally-valued resources. We examined qualitative and geospatial data derived from oral history interviews, participatory GIS focus groups, archival records, and historical forest surveys to characterize cultural fire regimes (CFRs) –an element of historical fire regimes– of moist mixed conifer (MMC), dry mixed conifer (DMC), and shrub-grassland (SG) zones. Our ethnohistorical evidence indicated a pronounced cultural fire regime in the MMC zone, but not in the two drier zones. The CFR of the MMC zone was characterized by frequent (few-year recurrence), low-severity burns distributed in a shifting pattern. This regime helped to maintain forest openings created by previous ignitions, resulting from lightning or possibly human-set, that had burned large areas. The CFR was influenced by the CTWS traditional knowledge system, which consisted of four elements: fire use and associated resource tending practices, tribal ecological principles, the seasonal round (the migratory pattern to fulfill resource needs), and culture. Thinleaf huckleberry (Vaccinium membranaceum), a cultural keystone species, occurs primarily in the MMC zone and was a principle focus of traditional fire use of the CTWS peoples. Fire was deployed to maintain shrub productivity and site access for harvesting. Cessation of fire use by ∼1940 has caused a decline in huckleberry productivity throughout much of the historical harvest zone. Our findings about CFR scale show how a nested, multi-level framework (patch- and landscape-levels) may be employed to reintroduce fire and thereby promote forest restoration and enhance culturally-valued resources. Our findings also highlight the utility of engaging the communities that hold traditional knowledge in the forest management and planning process.

Shrub patches capture tumble plants: potential evidence for a self-reinforcing pattern in a semiarid shrub encroached grassland

The development of fertile patches within an infertile matrix is a common phenomenon in drylands. Shrub-centered expansion of fertile islands is generally attributed to processes of sediment erosion and deposition, but there have been fewer studies of how litter might contribute to the development of fertile islands in semiarid shrub grassland. We quantified the capture of two tumble plant species (Cleistogenes squarrosa, Salsola collina; also known as tumble weeds) by shrubs across ten sites across 38,000 km2 of a semiarid grassland encroached by Caragana microphylla. Tumble plants are plants that blow across the grassland propelled by strong winds. Both tumble plant species were found over extensive areas of semiarid grassland, and their distribution coincides with the distribution of Caragana microphylla. Biomass production of both tumble plants averaged 12.2 g m−2 (range: 1.0 to 25.0 g m−2) and litter accumulation (amount accruing from wind-blown plants) of both tumble plants was significantly greater beneath shrubs (94.5 ± 28.9 g m−2 mean ± SE) than in the interspaces (3.3 ± 1.4 g m−2). Most of the material collecting under Caragana microphylla comprised tumble plants. Increases in the area of Caragana microphylla patches did not correspond to greater tumble plant capture. However, the supply of tumble plants was the strongest predictor of capture within shrub hummocks, suggesting that tumble plant capture is source limited rather than sink limited. Our structural equation model indicates that increases in grass cover and height were indirectly and negatively associated with tumble plant capture by reducing the tumble plant supply. Contrary to prediction, shrub height and shrub patch area had no overall effect on the tumble plant capture. Overall, we maintain that the capture of tumble plants by shrubs is an important self-maintaining mechanism of shrub-encroached grasslands. Tumble plant abundance is predicted to increase with increasing surface human disturbance and aridity. Therefore, the “shrub-litter island” effect is likely to be an important mechanism for maintaining and promoting the encroachment of shrubs into semiarid grasslands.

Rapid Sequestration of Ecosystem Carbon in 30-year Reforestation with Mixed Species in Dry Hot Valley of the Jinsha River.

Reforestation plays an important role in the carbon cycle and climate change. However, knowledge of ecosystem carbon sequestration through reforestation with mixed species is limited. Especially in dry hot valley of the Jinsha River, no studies cover total ecosystem carbon sequestration level in mature mixed plantations for a limited area of mixed plantations and difficulty in the sampling of plant roots and deep soil. In this study, carbon sequestration of seven mixed plantations of different ages in dry hot valley of the Jinsha River was investigated with analogous sites method. The results are as follows: 1) Deep soil organic carbon (SOC) storage significantly increased with stand age (p = 0.025), possibly due to fine root exudates and dissolved organic carbon transportation into deep soil and retention. 2) Total biomass carbon storage in the 30-year-old mixed plantation was 77.78 t C ha−1, 54 times reference wasteland and 9 times reference natural recovery shrub-grassland. However, total biomass carbon storage of 30-year-old mixed plantation was insignificantly lower than that of reference natural forest (p = 0.429). After 30 years of reforestation, plantation biomass carbon storage recovered to reference level, and its sequestration rate was 2.54 t C ha−1 yr−1. 3) The total ecosystem carbon storage of 30-year-old mixed plantation was 185.50 t C ha−1, 2.38 times reference wasteland, 2.29 times reference natural recovery shrub grassland, and 29% lower than reference natural forest. It indicated that niche complementary, good stand structure, and characteristics of dominant species Leucaena leucocephala in mixed plantations facilitate more rapid carbon sequestration, especially biomass carbon in the dry hot valley.

Variations and Indications of δ13CSOC and δ15NSON in Soil Profiles in Karst Critical Zone Observatory (CZO), Southwest China

Soil carbon and nitrogen storage and stabilization are the key to solving the problems of mitigation of global warming and maintaining of crop productivity. In this study, the contents of soil organic carbon (SOC) and soil organic nitrogen (SON) and their stable isotope compositions (δ13CSOC and δ15NSON) in soil profiles were determined in two agricultural lands (including a farmland and an abandoned farmland) and four non-agricultural lands (including two shrub-grass lands and two shrub lands) in the karst critical zone observatory (CZO), Southwest China. The contents of SOC and SON were used for research on the effects of land use on SOC and SON storage, and the change of δ13CSOC and δ15NSON values in soil profiles were used to indicate SOC and SON stabilization. The results showed that agricultural activities reduced SOC and SON storage in the whole soil layers of farmland compared to non-agricultural lands, and farmland abandonment slightly increased SOC and SON storage. Crop rotation between peanut (C3) and corn (C4) affected the δ13CSOC in surface soils of agricultural lands (−21.6‰), which were intermediate between shrub lands (−22.7‰) and shrub-grass lands (−19.6‰). 15N-depleted SON in surface soils in farmland compared to those soil in other lands possibly associated with synthetic N fertilizer application. In soil layers below 30 cm depth the δ13CSOC deceased with depth, while the δ15NSON displayed irregular fluctuation. The change in δ13CSOC and δ15NSON through soil profiles in karst soils were more intensive than those in semiarid grassland soils indicating the less stabilization of SOC and SON in karst soils.

Influence of Land Management Strategies on Browse and Nutritional Quality of Grassland Shrub

Influence of Land Management Strategies on Browse and Nutritional Quality of Grassland Shrub

Insects of Dominant Shrub Communities at Pawnee and Comanche National Grasslands, Colorado

Terrestrial insects associated with shrubs at Pawnee National Grassland in northeastern Colorado and Comanche National Grassland in southeastern Colorado were identified to family or genus with some taxa to species. Six species of grassland shrubs were sampled using a funnel-bucket method each month from June-September 2014 and 2015. Insect diversity and abundance differed between the grasslands. Chrysomelidae, Cicadellidae, Cleridae, Formicidae, Meloidae, and Miridae were abundant at Pawnee National Grassland, primarily from four-winged saltbush (Atriplex canescens) (Pursh.) Nutt). Acrididae, Aphididae, Chrysomelidae, Cleridae, Coccinellidae, Formicidae, Lygaeidae, Miridae, and Reduviidae collected from sandsage (Artemisia filifolia Torr.), four-winged saltbush, rabbitbrush (Ericameria nauseosa (Pallas ex. Pursh), greasewood (Sarcobatus vermiculatus (Hook) Torr.), skunkbush (Rhus trilobata Nutt.), and one-seed juniper (Juniperus monosperma (Engelm.) were abundant at Comanche National Grassland.

贵州省后寨河小流域地形因子、人为干扰与石漠化定量研究

PDF HTML阅读 XML下载 导出引用 引用提醒 贵州省后寨河小流域地形因子、人为干扰与石漠化定量研究 DOI: 10.5846/stxb201809111955 作者: 作者单位: 贵州大学贵州省森林资源与环境研究中心/林学院,贵州大学贵州省森林资源与环境研究中心/林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重大科学研究计划项目（2013CB956702）；贵州省一流学科建设项目（GNYL[2017]007）；贵州省“百层次”培养计划（QKHRC-2015-4022） Quantitative relationships among topography anthropogenic disturbance, and rocky desertification in the Houzhai River Basin, Guizhou Province, China Author: Affiliation: Guizhou University, Institute for Forest Resources ＆ Environment of Guizhou/ College of Forestry,Guizhou University, Institute for Forest Resources ＆ Environment of Guizhou/ College of Forestry Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为定量研究喀斯特区域地形因子、人为干扰和石漠化之间的关系。基于网格法和实地观测，建立后寨河流域石漠化信息数据库并分析。结果表明：后寨河流域石漠化面积为14.43 km2，不同利用类型石漠化面积呈以下规律：荒地 > 坡耕地 > 乔木林地 > 耕地 > 灌木林地 > 灌草地 > 草地 > 弃耕地 > 园地 > 乔灌木林地 > 水田 > 经果林地；流域内岩石裸露率和土壤厚度主要受到坡度、坡位和人为干扰的制约，而人为干扰具有主观性，主要在岩石裸露率低、土壤较厚和坡度较缓的区域进行农业生产活动。荒地和弃耕地占据了石漠化面积的32.64％，且存在较大潜在石漠化的风险。回归模型发现人为干扰程度对岩石裸露率（负效应-0.286）和土壤厚度（正效应0.264）的直接效应最大，坡向对岩石裸露率（正效应0.067）和土壤厚度（负效应-0.054）的直接效应最小。认清地形因子、人为干扰和石漠化之间的耦合关系有利于喀斯特小流域石漠化治理。 Abstract:The relationship among topographic factors, human disturbance, and rocky desertification in karst areas was quantitatively assessed. A rocky desertification information database was established for the Houzhai River Basin and analyzed using grid-sampling and field observation. Rocky desertification affected a total of 14.43 km2, and affected multiple land use types, including uncultivated lands, sloping croplands, arbor forestlands, arable land, shrub lands, shrub grass-lands, grasslands, abandoned lands, garden lands, arbor-shrub mixed forestlands, paddy lands, and artificial fruit forestlands. The rock exposure rate and soil thickness were mainly restricted by slope gradient, slope position, and human disturbance. Otherwise, human disturbance is subjective, mainly in areas with low rock exposure, thick soil, and gentle slope gradient. Uncultivated lands and abandoned lands accounted for 32.64% of the rocky desertification area, and there was a greater risk rocky desertification under these types of land use. A regression model revealed that the degree of human disturbance directly affects both rock exposure rate (negative effect:-0.286) and soil thickness (positive effect:0.264). However, only insignificant effects were observed for slope direction on either rock bareness (positive effect:0.067) or soil thickness (negative effect:-0.054). According to these findings, rocky desertification in karst mountainous basin can be easily remedied by, understanding its relationships with topography and human disturbance. 参考文献 相似文献 引证文献

Carbon Sequestration Anticipation Response to land use change in a mountainous karst basin in China

The present article reports an assessment of afforestation potential and anticipation of carbon sequestration in the Houzhai River Basin in Guizhou Province in southwestern China. Total of 2755 soil profiles consisting of 22,057 soil samples were collected according to a grid-sampling method at a 150 m scale in the Houzhai River basin, and the SOC contents in soil samples were analyzed using a titration method. General information regarding the geographic characteristics of each sampling grid was recorded in the field. The results indicate that land use in the Houzhai River Basin is very complex. Land use status and land use change in the study area were closely associated with local geographic characteristics and variations in economic structures. There were approximately 15.26 km2 of land that could or should be rearranged as afforestation land in the Houzhai River Basin. The increased SOC storage (0.00–1.00 m soil horizon) would be up to 5.48 × 104 Mg, 6.42 × 104 Mg, 4.77 × 104 Mg and 3.18 × 104 Mg when all of the calculated lands became shrub-grass lands, shrub lands, arbor-shrub forest lands and arbor forest lands, respectively. The increased SOC percentages would be 52.16%, 61.13%, 45.39% and 30.32%, respectively, in comparison with the present SOC storage in these lands.

Oasis microclimate effects under different weather events in arid or hyper arid regions: a case analysis in southern Taklimakan desert and implication for maintaining oasis sustainability

The vegetation of desert oasis regulates the regional microclimate in arid or hyper-arid regions. A wide range of studies on the oasis microclimate effects have been conducted under sunny conditions. However, less concern has been focused on microclimatic variations of oasis effects caused by the influences of different types and coverage of vegetation in oasis during other different weather events, especially during catastrophic weather conditions. Based on the measurements from 1 August, 2010 to 30 December, 2014 in the Qira oasis, a hyper arid zone of southern Taklimakan desert, Northwest China, this paper investigates the existences and variabilities of the oasis microclimate effects during dust storm, blown sand, floating dust, and rain events and analyzes the impacts of different types of vegetation (bare desert, sparse desert grassland, desert oasis dense shrub grassland and forests, and oasis crops and fruit trees) on desert oasis microclimates. Moreover, the importance of maintaining the oasis sustainability mirrored by the oasis microclimate effects is highlighted and discussed. Results show that the oasis with abundant vegetation exerts cooling and humidifying effects under four weather events relative to bare desert land. As a result of high wind velocities, the oasis microclimatic effects are weakened during catastrophic weather conditions such as dust storm or blown sand events. The type and coverage of vegetation and the topography as well as weather events jointly impact on the oasis microclimate effects. The findings of this work provide an implication for the conservation and restoration of oasis vegetation to maintain both the oasis microclimate environment and the sustainability of desert oasis.

Differing ecosystem responses of vegetation cover to extreme drought on the Big Sur coast of California

Impacts of the extreme 2013 to 2014 drought on vegetation canopy cover in the Big Sur region of central coastal California were assessed using a combination of satellite image analysis and in situ measurements of soil moisture. Landsat and moderate resolution imaging spectroradiometer satellite images were analyzed and compared across six ecosystems representative of the predominant vegetation types of the region at the U. S. Forest Service’s Brazil Ranch study site. Results showed that differing spatial densities of woody plants among these ecosystems corresponded to the observed changes in the normalized difference vegetation index (NDVI) over the period of 2010 to 2016, with the herbaceous-dominated coastal terrace, open shrub, and ridge-top grassland ecosystems declining 30% in greenness during the extreme drought period of 2012 to 2014. Landsat images from the month of peak annual NDVI confirmed this as a statistically significant difference in the loss of green cover in open shrub and grassland ecosystems during the 2012 to 2014 drought, compared to the closed shrubland and redwood-dominated ecosystems that were relatively unaffected at the study site.

Dynamic Changes of the Bush Encroachment in Low Altitude Area of Ethiopia

Bush encroachment is widely distributed in arid and semi-arid regions, and it has a serious impact on livestock production, especially in Africa where livestock is a primary source for the livelihoods of many people. In this study, methods of supervised classification and decision tree classification, and indexes of a land use change significance index (Ci) and a single land use dynamic degree, were applied to remote sensing imagery of Ethiopia for 1986–2016. The results show the dynamic characteristics of grassland bush encroachment in low altitude areas (pastures <1500 m above sea level) of Ethiopia in the 30 year period studied. The results revealed several interesting features of this phenomenon. (1) The area of bush encroachment showed an increasing trend, with a maximum of 3.74×103 km2 in 2003, which represented 68.97% of the total area, and declined slightly from 2003∼2016. (2) Among classification types, the area of severe shrub grassland was the largest, accounting for 28.36–49.10% of the total area, while the area of moderate bush encroachment accounted for 9.77–16.68%, and slight bush encroachment accounted for 5.52–7.57%. (3) The expansion rate of shrubby grassland was 0.74% for the 30 year period, while the average annual expansion rate was 2.16% for the 8 years from 1995–2003. (4) Forest land and grassland were the two main land use types of shrub grassland transformation in low altitude areas and bush encroachment changed large amounts of forest land into grassland due to shrub grassland management. The results of this study provide basic data for revealing the impacts of development processes on subsequent bush encroachment and can inform better management for the sustainable development of grasslands in low altitude systems.

Spatiotemporal distribution and the characteristics of the air temperature of a river source region of the Qinghai-Tibet Plateau.

As the backland of the Qinghai-Tibet Plateau, the river source region is highly sensitive to changes in global climate. Air temperature estimation using remote sensing satellite provides a new way of conducting studies in the field of climate change study. A geographically weighted regression model was applied to estimate synchronic air temperature from 2001 to 2015 using Moderate-Resolution Imaging Spectroradiometry (MODIS) data. The results were R2 = 0.913 and RMSE = 2.47°C, which confirmed the feasibility of the estimation. The spatial distribution and variation characteristics of the average annual and seasonal air temperature were analyzed. The findings are as follows: (1) the distribution of average annual air temperature has significant terrain characteristics. The reduction in average annual air temperature along the elevation of the region is 0.19°C/km, whereas the reduction in the average annual air temperature along the latitude is 0.04°C/degree. (2) The average annual air temperature increase in the region is 0.37°C/decade. The average air temperature increase could be arranged in the following decreasing order: Yangtze River Basin > Mekong River Basin > Nujiang River Basin > Yarlung Zangbo River Basin > Yellow River Basin. The fastest, namely, Yangtze River Basin, is 0.47°C/decade. (3) The average air temperature rise in spring, summer, and winter generally increases with higher altitude. The average annual air temperature in different types of lands following a decreasing order is as follows: wetland > construction land > bare land glacier > shrub grassland > arable land > forest land > water body and that of the fastest one, wetland, is 0.13°C/year.

Modern pollen assemblages and their relationships to vegetation and climate in the Lhasa Valley, Tibetan Plateau, China

Forty-seven surface pollen samples and 141 vegetation quadrats were investigated in the Lhasa Valley in order to assess the relationships between local modern pollen assemblages and vegetation and climate. The regional climatic data for each sample are mean annual precipitation (Pann), mean annual temperature (Tann), summer temperature (Tsummer), actual evapotranspiration (AET), potential evapotranspiration (PET), and moisture index (MI), estimated by co-kriging using meteorological data from 16 climate stations in or near the Lhasa Valley. Cluster analysis, principal components analysis (PCA), Procrustes analysis, and co-correspondence analysis (Co-CA) were used to evaluate the relationship between modern pollen assemblages and contemporary vegetation. Linear regression was used to examine the relationships between pollen ratios (Artemisia/Chenopodiaceae (A/C), Artemisia/Cyperaceae (A/Cy), Artemisia + Chenopodiaceae/Cyperaceae (AC/Cy)), aridity pollen index, total arboreal pollen (AP), and the climatic variables. Cluster analysis and PCA results are generally consistent, and differentiate between pollen assemblages from arid conditions and those from more humid conditions. However, the PCA results distinguish pollen assemblages from shrubland slightly more clearly than the cluster analysis does. The PCA results show a general agreement between the modern pollen assemblages and contemporary vegetation types, but pollen assemblages from coniferous (Juniperus) woodland cannot be distinguished from shrub grassland, meadow, or shrub meadow pollen assemblages in the PCA results. Both Procrustes analysis and associated permutation tests and Co-CA show a strong statistically significant relationship between modern pollen and vegetation composition. Analysis of the relationship between the climatic variables and vegetation types suggests that humidity (Pann and MI) is the main variable related to the vegetation types within the restricted areas of the Lhasa Valley. Neither the A/C ratio nor the aridity pollen index is a reliable aridity indicator in the Lhasa Valley. The AP sum may be a weak precipitation indicator, whereas the A/Cy and AC/Cy ratios appear to be robust indicators of precipitation, aridity, and temperature at the scale of the Lhasa Valley.

Responses of normalized difference vegetation index (NDVI) to precipitation changes on the grassland of Tibetan Plateau from 2000 to 2015.

Precipitation change is an important factor in the inter-annual variation of grassland growth on the Tibetan Plateau. The total amount, distribution pattern and concentration time are three basic characteristics of precipitation change. The temporal and spatial characteristics of precipitation change were analyzed based on climate data of 145 meteorological stations on the Tibetan Plateau and nearby areas from 2000 to 2015. The total precipitation amount was characterized by annual precipitation, distribution pattern of precipitation during the year was characterized by improved precipitation concentration index (PCI), and precipitation centroid (PC) was defined to indicate the change in precipitation concentrated time. To better illustrate the response of grassland to precipitation change, vegetation growth status was characterized by the maximum value of normalized difference vegetation index (NDVImax). Results indicated that the annual precipitation and PCI had an apparent gradient across the whole plateau and the latest PC occurred in the southern plateau. NDVImax of alpine shrub grassland was significantly correlated with the change of PCI,increased with even distribution of precipitation during growth period, and limited by the total annual precipitation. Alpine meadow did not show significantly correlations with these three indices. The inter-annual variability of NDVImax of steppe was controlled by both PCI and PC. NDVImaxof alpine desert grassland was mainly controlled by annual precipitation. In addition to annual total amount of precipitation, the distribution characteristics of precipitation should be further considered when the influence of precipitation change on different types of vegetation on the Qinghai Tibet Plateau was studied.

Spatio-temporal variations of conservation hotspots based on ecosystem services in Xishuangbanna, Southwest China.

Integrating biodiversity and ecosystem services (BES) has been viewed as an appropriate approach to identifying conservation priorities. Taking Xishuangbanna tropical region in Southwest China, different BESs (habitat quality [used as a proxy for biodiversity], carbon storage, and water yield) were quantified using the InVEST model and conservation hotspots from 1976, 1990, and 2010 were identified by overlapping and ranking the service layers. Results showed that BESs areas were unevenly distributed. High habitat quality and carbon storage areas located in the eastern part of the region were mainly occupied by broad-leaved forest, while high water yield areas were covered by grassland and tropical forests. Recognized hotspots were primarily composed of the broad-leaved forest and shrub grassland. However, these habitat types declined by nearly 50% from 1.25×105 ha to 0.63×105 ha and became more fragmented during the study period. We also found that the sub-watersheds which decreased in BES had fewer hotspots distributed and suffered greater landscape fragmentation. Our study further explored the impacts of land-use conversion on BES, and illustrated the necessity and feasibility of BESs in identifying potential conservation areas.

Land use change characteristics affected by water saving practices in Manas River Basin, China using Landsat satellite images

The characteristics and influencing factors of land use change under arid conditions were studied in the Manas River Basin in Xinjiang Region, Northwest China. Landsat satellite images acquired in 1976, 1990, 2000, 2010 and 2015 over the study area were used as basic data. Land use change, the rate of change of land use, land use transfer and other aspects revealed the characteristics of land use change and related factors as influenced by water conditions in the basin. The results showed that: (1) Over nearly 50 years, land reclamation in the Manas River Basin resulted in the rapid expansion of an artificial oasis area, and promoted the process of ‘oasis urbanization’, and accelerated the development of the river basin economy. (2) In 2000, the popularization of drip irrigation under mulch technology led to the rapid growth of cultivated land and development land in the watershed. Meanwhile, the water table declined in the desert area of the lower reaches of the river basin, and the area occupied by sparse shrub forest and grassland decreased. (3) Before popularization of water-saving technology, woodland, grassland and development land transformed to cultivated land in the amounts of 93.46 km2, 2542.93 km2 and 137.53 km2, respectively, and woodland transformed in the amount of 189.64 km2. After water-saving technology was popularized, woodland, grassland and development land were transformed into cultivated land in the amounts of 567.41 km2, 1756.2 km2 and 37.36 km2, respectively. (4) The popularization of water-saving technology made the dynamic degree of cultivated land and development land more active, and further increased landscape fragmentation and landscape heterogeneity. The level of urbanization development, the level of economic development and the dry humidity of the basin became the main factors affecting the change of land use in the basin. Keywords: land-use change, spatial characteristics, influencing factor, Manas River Basin, Landsat satellite images DOI: 10.25165/j.ijabe.20171006.3435 Citation: Yang G, Chen D, He X L, Long A H, Yang M J, Li X L. Land use change characteristics affected by water saving practices in Manas River Basin, China using Landsat satellite images. Int J Agric & Biol Eng, 2017; 10(6): 123–133.

Rangifer management controls a climate-sensitive tundra state transition.

Rangifer (caribou/reindeer) management has been suggested to mitigate the temperature-driven transition of Arctic tundra into a shrubland state, yet how this happens is uncertain. Here we study this much focused ecosystem state transition in riparian areas, where palatable willows (Salix) are dominant tall shrubs and highly responsive to climate change. For the state transition to take place, small life stages must become tall and abundant. Therefore we predicted that the performance of small life stages (potential recruits) of the tall shrubs were instrumental to the focal transition, where Rangifer managed at high population density would keep the small-stage shrubs in a "browse trap" independent of summer temperature. We used a large-scale quasi-experimental study design that included real management units that spanned a wide range of Rangifer population densities and summer temperatures in order to assess the relative importance of these two driving variables. Ground surveys provided data on density and height of the small shrub life stages, while the distributional limit (shrubline) of established shrublands (the tall shrub life stage) was derived from aerial photographs. Where Rangifer densities were above a threshold of approximately 5 animals/km2 , we found, in accordance with the expectation of a "browse trap," that the small life stages of shrubs in grasslands were at low height and low abundance. At Rangifer densities below this threshold, the small life stages of shrubs were taller and more abundant indicating Rangifer were no longer in control of the grassland state. For the established shrubland state, we found that the shrubline was at a 100-m lower elevation in the management units where Rangifer had been browsing in summer as opposed to the migratory ranges with no browsing in summer. In both seasonal ranges, the shrubline increased 100m per 1°C increment in temperature. Our study supports the proposal that Rangifer management within a sustainable range of animal densities can mitigate the much-focused transition from grassland to shrubland in a warming Arctic.

Root channels to indicate the increase in soil matrix water infiltration capacity of arid reclaimed mine soils

Soil matrix flow plays a critical role in redistributing the precipitation input and enhancing water storage in arid areas. Root channels can result in macropore flow which strongly influences soil infiltration. Prior research has addressed the influence of vegetation on erosion and runoff, but the effects of root channels on infiltration capacity are less studied. In this study, we studied the root channels and soil water infiltration rates in ten artificial grasslands in an arid area. The results showed that the average root channel diameter (ARCD) of leguminous grasslands and of shrub grasslands were greater than that of gramineous grasslands (p<0.05). Importantly, the ARCD and root channel area (RCA) were significantly and positively related to the average infiltration rate in stage I (AIRS I) and the initial infiltration rate (IIR). The IIR and the AIRS I increased at rates of 31.13 and 14.60mmh−1, respectively, and at the same time there was an increase in ARCD. Overall, our results suggest that root channels played a significant role in the matrix infiltration capacity, resulting in a higher infiltration rate in leguminous grasslands and in mixed sown grasslands than in gramineous grasslands. We suggest that leguminous grasslands or the combination of leguminous and gramineous species in grassland should be given greater attention as suitable materials for mine-soil reclamation in arid regions. Our research improve the understanding of the influence of vegetation on soil hydrological processes and of the hydrology of reclaimed mine soils in arid regions.

An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape

Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstructed pre-encroachment vegetation cover percentages and the National Land Cover Database (NLCD 2006) vegetation map were used to estimate parameters for encroachment factors to represent juniper encroachment in CATGraSS. Model sensitivity experiments examined the influence of each encroachment factor and their combinations on trajectories of modeled percent cover of each plant functional type and emergent spatial vegetation patterns in the modeled domain. Simulation results identified grazing as the key factor leading to juniper encroachment, by reducing shrub and grass cover and promoting the formation of juniper tree clusters. Reduced fire frequency and increased seed dispersal by grazers further amplified juniper encroachment into grassland patches between clusters of juniper trees. Each encroachment factor showed different consequences on modeled vegetation patterns. Time series of modeled plant cover and spatial patterns of plant functional types were found to be consistent with an existing conceptual model described in the literature. The proposed model provides a tool that can be used to improve our understanding of the drivers and processes of woody plant encroachment and vegetation response to global change.

Impacts of reforestation on woody species composition, species diversity and community structure in dry-hot valley of the Jinsha River, southwestern China

To understand the impacts of reforestation on woody species composition, species diversity and community structure, seven plantation forests in dry-hot valley of the Jinsha River in Southwest China were investigated, with adjacent wastelands, natural shrub grassland and a natural forest as references. Species importance value, species richness, species heterogeneity and Sorenson similarity index between plantations and the natural forest were analyzed. Results indicated that compared to wastelands and natural shrub grassland, reforestation improved species diversity and community structure, and more forest woody species found suitable habitats in plantations. Species diversity in understory of plantations and Sorenson similarity index were significantly negatively correlated with stem density in mature plantations (26-31 years old). Higher species diversity and Sorenson similarity index existed in mature sparse plantations due to lower stem density and more tree species planted initially. In contrast, reference natural forest, with species heterogeneity of 2.28 for shrub layer, showed the highest species diversity. It would take a long time for species composition and diversity to recover through reforestation in a dry-hot valley. Therefore, it was essential to protect remnant natural forests strictly and reforest with suitable management such as lower stem density and increasing genetic diversity of trees planted.