Increasing aridity may reduce productivity and soil organic carbon storage with woody plant encroachment

Aims We have found a positive effect of woody plants on total plant carbon (C) storage in less arid grassland was shifted to a negative effect in arid grasslands in Xinjiang, a typical arid region in China. In this study, we further assessed the effects of woody plants on aboveground primary productivity (ANPP) and soil organic C (SOC) storage and explored the mediation of climate conditions on these effects. We also aimed to elucidate the reasons for the effects on SOC storage in terms of ANPP and belowground biomass C (BGC). Methods We compared the difference in ANPP and SOC content between pure and wooded grasslands and evaluated the relation between SOC content and ANPP and BGC in six grassland types along the altitude (climatic) gradients. Results In three arid types, woody plants had a negative effect on ANPP due to their more negative impacts on herbaceous plants and lower ANPP. The negative effect on ANPP and BGC led to that on SOC storage in these types. In less arid types, there had a positive effect on ANPP because woody plants had weaker negative impacts on herbaceous plants and higher ANPP. A positive effect on ANPP combined with a neutral impact on BGC contributed to a positive effect on SOC storage in these types. Conclusions Woody plants had a negative effect on ANPP and SOC storage in most arid grasslands in Xinjiang. We predicted that increasing aridity may reduce ANPP and SOC storage with woody plant encroachment in the future.

Factors Influencing County Commissioners’ Decisions about Burn Bans in the Southern Plains, USA

Woody plant encroachment in North American rangelands has led to calls for greater use of prescribed fire to reduce fuel loads and restore grazing productivity and grassland biodiversity. However, the use of prescribed fire during periods when woody plant mortality is maximized has often been limited by temporary restrictions on outdoor burning enacted by regional or local governmental entities. This study reports the results of a survey assessing the familiarity with and attitudes toward prescribed fire in Texas and Oklahoma, USA, of officials tasked with implementing restrictions on outdoor burning and how these attitudes influence their decisions. Most responding officials considered prescribed fire to be a safe and beneficial land management tool that should be used more frequently. Self-reported familiarity with prescribed fire was the most significant explanatory variable for this attitude. Further, familiarity with prescribed fire was influenced by respondent participation in or being invited to participate in a prescribed fire. Such invitations came mostly from private landowners. Landowners wishing to use prescribed fire may benefit from building trust with local officials by demonstrating they are qualified to conduct such fires safely. This could help reduce the frequency of burn restrictions and may increase the likelihood that officials will grant burn ban exemptions to qualified burn managers. Additionally, because officials’ primary sources of prescribed fire information were reported to be local fire departments and emergency services, educating those entities about the benefits of prescribed fire for reducing wildfire risks could help reduce pressure on officials to enact or maintain burning restrictions. These findings highlight opportunities for reducing the frequency of burning restrictions, increasing opportunities for land managers to effectively halt or reverse woody plant encroachment.

Seasonal Spectral Separation of Western Snowberry and Wolfwillow in Grasslands with Field Spectroradiometer and Simulated Multispectral Bands

Woody plant encroachment (WPE), the expansion of native and non-native trees and shrubs into grasslands, has led to degradation worldwide. In the Canadian prairies, western snowberry and wolfwillow shrubs are common encroachers, whose cover is currently unknown. As the use of remote sensing in grassland monitoring increases, opportunities to detect and map these woody species are enhanced. Therefore, the purpose of this study is to identify the optimal season for detection of the two shrubs, to determine the sensitive wavelengths and bands that allow for their separation, and to investigate differences in separability potential between a hyperspectral and broadband multispectral approach. We do this by using spring, summer, and fall field-based spectra of both shrubs for the calculation of spectral separability metrics and for the simulation of broadband spectra. Our results show that the summer offers higher discrimination between the two species, especially when using the red and blue spectral regions and to a lesser extent the green region. The fall season fails to provide significant spectral separation along the wavelength spectrum. Moreover, there is no significant difference in the results from the hyperspectral or broadband approach. Nevertheless, cross-validation with satellite imagery is needed to confirm the current results.

Microclimate feedbacks sustain power law clustering of encroaching coastal woody vegetation

The spatial pattern of vegetation patchiness may follow universal characteristic rules when the system is close to critical transitions between alternative states, which improves the anticipation of ecosystem-level state changes which are currently difficult to detect in real systems. However, the spatial patterning of vegetation patches in temperature-driven ecosystems have not been investigated yet. Here, using high-resolution imagery from 1972 to 2013 and a stochastic cellular automata model, we show that in a North American coastal ecosystem where woody plant encroachment has been happening, the size distribution of woody patches follows a power law when the system approaches a critical transition, which is sustained by the local positive feedbacks between vegetation and the surrounding microclimate. Therefore, the observed power law distribution of woody vegetation patchiness may be suggestive of critical transitions associated with temperature-driven woody plant encroachment in coastal and potentially other ecosystems.