@article {JRN55373, title = {Mechanisms and drivers of alternative shrubland states}, journal = {Ecosphere}, volume = {13}, year = {2022}, month = {03 April 2022}, pages = {e3987}, abstract = {Grassland-to-shrubland state change has been widespread in arid lands globally. Long-term records at the Jornada Basin USDA-LTER site in the North American Chihuahuan Desert document the time series of transition from grassland dominance in the 1850s to shrubland dominance in the 1990s. This broadscale change ostensibly resulted from livestock overgrazing in conjunction with periodic drought and represents the classic {\textquotedblleft}grassland-to-shrubland{\textquotedblright} regime shift. However, finer-scale observations reveal a more nuanced view of this state change that includes transitions from dominance by one shrub functional type to another (e.g., based on leaf habit [evergreen vs. deciduous], N2 fixation potential, and drought tolerance). We analyzed the Jornada Basin historic vegetation data using a fine-scale grid and classified the dominant vegetation in the resulting 890 cells on each of four dates (1858, 1915, 1928, and 1998). This analysis allowed us to quantify on contrasting soil geomorphic units the rate and spatial distribution of: (1) state change from grasslands to shrublands across the Jornada Basin, (2) transitions between shrub functional groups, and (3) transitions from shrub-to-grass dominance. Results from our spatially explicit, decadal timescale perspective show that: (1) shrubland ecosystems developing on former grasslands were spatially and temporally more dynamic than has been generally presumed, (2) in some locations, shrublands initially developing on grasslands subsequently transitioned to ecosystems dominated by a different shrub functional type, with these changes in shrub composition likely involving changes in soil properties, and (3) some shrub-dominated locations have reverted to grass dominance. Accordingly, traditional, broad characterizations of {\textquotedblleft}grassland-to-shrubland{\textquotedblright} state change may be too simplistic. An accounting of these complexities and transitions from one shrub functional group to another is important for projecting state change consequences for ecosystem processes. Understanding the mechanisms, drivers, and influence of interactions between patterns and processes on transitions between shrub states defined by woody plant functional types will be germane to predicting future landscape change.}, keywords = {desertification, drylands, plant functional types, regime shifts, shrub growth form, shrubland transitions, Special Feature: Dynamic Deserts}, doi = {10.1002/ecs2.3987}, url = {files/bibliography/22-005.pdf}, author = {Steven R. Archer and Debra C. Peters and N. Dylan Burruss and Jin Yao} } @article {JRN54290, title = {An ecosystem services perspective on brush management: research priorities for competing land-use objectives}, journal = {Journal of Ecology}, volume = {102}, year = {2014}, pages = {1394-1407}, abstract = {

1. The vegetation of semi-arid and arid landscapes is often comprised of mixtures of herbaceous and woody vegetation. Since the early 1900s, shifts from herbaceous to woody plant dominance, termed woody plant encroachment and widely regarded as a state change, have occurred world-wide. This shift presents challenges to the conservation of grassland and savanna ecosystems and to animal production in commercial ranching systems and pastoral societies.
2. Dryland management focused on cattle and sheep grazing has historically attempted to reduce the abundance of\  encroaching woody vegetation (hereafter, {\textquoteleft}brush management{\textquoteright}) with the intent of reversing declines in forage production, stream flow or groundwater recharge. Here, we assess the known and potential consequences of brush management actions, both positive and negative, on a broader suite of ecosystem services, the scientific challenges to quantifying these services and the trade-offs among them.
3. Our synthesis suggests that despite considerable investments accompanying the application of brush management practices, the recovery of key ecosystem services may be short-lived or absent. However, in the absence of such\  interventions, those and other ecosystem services may be compromised, and the persistence of grassland and savanna\  ecosystem types and their endemic plants and animals threatened.
4. Addressing the challenges posed by woody plant encroachment will require integrated management systems using diverse theoretical principles to design the type, timing and spatial arrangement of initial management actions and follow-up treatments. These management activities will need to balance cultural traditions and preferences, socio-economic constraints and potentially competing land-use objectives.
5. Synthesis. Our ability to predict ecosystem responses to management aimed at recovering ecosystem services where grasslands and savannas have been invaded by native or exotic woody plants is limited for many attributes (e.g. primary\  production, land surface{\textendash}atmosphere interactions, biodiversity conservation) and inconsistent for others (e.g. forage\  production, herbaceous diversity, water quality/quantity, soil erosion, carbon sequestration). The ecological community is challenged with generating robust information about the response of ecosystem services and their interactions if we are to position land managers and policymakers to make objective, science-based decisions regarding the many trade-offs and competing objectives for the conservation and dynamic management of grasslands and savannas.

}, keywords = {bush clearing, drylands, ecosystem services, shrub encroachment, state change, vegetation change, woody plant encroachment, woody weeds}, doi = {10.1111/1365-2745.12314}, url = {files/bibliography/JRN00621.pdf}, author = {Steven R. Archer and K. Predick} } @inbook {49922, title = {Brush management as a rangeland conservation strategy: a critical evaluation}, booktitle = {Conservation benefits of rangeland practices: assessment, recommendations, and knowledge gaps}, year = {2011}, publisher = {Allen Press}, organization = {Allen Press}, address = {Lawrence, KS}, abstract = {

Rangelands support the majority of the world{\textquoteright}s livestock production (Safriel and Adeel 2005) and play an important role in\  human health and global carbon, water, and nitrogen cycles (Campbell and Stafford Smith 2000). Their extensive airsheds and watersheds provide habitat for game and nongame wildlife and myriad ecosystem goods and services important to rapidly\  growing settlements and cities that may be geographically distant. Rangelands thus have considerable, multidimensional\  conservation value. Stewardship of vegetation composition, cover, and production is the foundation of sustainable rangeland management, a key component of which is maintaining vegetation within a desirable mix of herbaceous and woody plants\  (WPs).

}, keywords = {book, brush management, chapter, conservation, rangeland management, report}, url = {files/bibliography/JRN00556.pdf}, author = {Steven R. Archer and K. W. Davies and Fulbright, T. E. and K. C. McDaniel and Wilcox, B.P. and K. Predick} } @conference {50069, title = {Does woody plant encroachment increase ecosystem carbon stocks?}, booktitle = {Ecological Society of America 94th Annual Meeting}, year = {2009}, month = {August 2009}, pages = {PS 46-59}, address = {Albuquerque, NM, August 2-7, 2009}, abstract = {Drylands account for ~30-35\% of terrestrial primary production and are an important component of the global carbon cycle. Changes in dryland vegetation thus have implications for carbon uptake and storage. One widely observed change is the conversion of grasslands to shrublands and woodlands. Although regarded as significantly impacting the North American terrestrial carbon sink, estimates are highly uncertain. Shrub proliferation typically increases aboveground carbon pools. However, the majority of organic carbon in drylands resides as soil organic carbon (SOC). Reports of impacts of shrub proliferation on SOC are equivocal and range from substantial decreases to no net change to substantial increases.~We quantified changes in ecosystem carbon pools accompanying shrub (Prosopis velutina) proliferation in Arizona grasslands. Size and location of P. velutina plants in a 0.4 ha area were determined in 1932, 1948 and 2006. Aboveground C mass of P. velutina was calculated using allometric equations. SOC (0-20 cm) was quantified along bole-to-dripline transects for a range of shrub sizes. A predictive model of SOC mass as a function of shrub size (basal diameter) was developed, applied to each individual on each date and summed across all shrubs to estimate aboveground shrub and SOC stocks over time (g C m-2).~Results/Conclusions: Aboveground shrub C mass increased from 1932 (217 g m-2) to 1948 (362 g m-2) and then declined to 224 g m-2 in 2006 as a result of an herbicide application in 1965/66. The herbicide application ostensibly shifted the population structure to smaller plants (mean plant canopy area declined from 6.3 [1948] to 3.8 m2 [2006]), but was coupled with an increase in plant density (323 ha-1 in 1948; 443 ha-1 in 2006).~SOC comprised 72-81\% of the soil plus aboveground shrub carbon pool. In the absence of shrubs, SOC mass was 896 g C m-2; accounting for the influence of shrubs increased SOC mass to 912 g C m-2 in 1932 and to 940 kg C m-2 by 2006, a 3\% increase despite the herbicide application. Our results confirm Prosopis encroachment into semi-arid grasslands will increase carbon storage in both the aboveground and near-surface SOC pools. Because SOC accumulation increases with tree size, historically invaded landscapes with larger individuals will be greater carbon sinks than more recently invaded landscapes.~ Land management practices (brush control) can dramatically reduce the aboveground C pool, but it recovers fairly quickly, with a potentially lagged, but poorly understood impact on the SOC pool.}, keywords = {cargon, terrestrail;}, author = {Steven R. Archer and Heather L. Throop and Dawn M. Browning and K. Predick} }