Drylands are Earth's largest terrestrial biome and support one‐third of the global population. However, they are also highly vulnerable to land degradation. Despite widespread demand for dryland ...restoration and rehabilitation, little information is available to help land managers effectively re‐establish native perennial vegetation across drylands.
RestoreNet is an emerging dryland restoration network that systematically tests revegetation techniques across environmental gradients. Using the RestoreNet experimental framework, we tested the effectiveness of restoration treatments (i.e. ConMod nurse plant structures, mulch, pits) that increase soil moisture and seed mixes with different climatic niches to achieve revegetation goals.
Across sites, seedling recruitment was consistently influenced by treatment and seed mix type. Pit and mulch treatments increased total seedling density, with pits promoting the highest seeded species recruitment while limiting non‐native species establishment. Seeding increased total seedling density regardless of seed mix type, but cooler‐adapted seed mixes promoted greater seeded species density and resulted in lower density of unseeded (non‐native) species relative to warmer‐adapted mixes.
Seedling recruitment was also controlled by the temporal and environmental context of restoration with the positive effect of high precipitation greatest in the weeks immediately following seeding. Above‐average precipitation during the study period across most of the sites may partially explain why the highest seeded species recruitment occurred in pit treatments and seed mixes with cooler, wetter niche requirements.
Synthesis and applications. Results from the dryland restoration network, RestoreNet help to better understand variation in seeding and restoration treatment success across space and time in drylands. Relationships between restoration practices and environmental conditions in our study suggest the importance of anticipatory restoration strategies that forecast seasonal and sub‐seasonal weather conditions and select plant species with climate niche requirements appropriate for current and future climate conditions. This information is critical to land managers tasked with improving ecosystem conditions across degraded dryland regions.
Results from the dryland restoration network, RestoreNet help to better understand variation in seeding and restoration treatment success across space and time in drylands. Relationships between restoration practices and environmental conditions in our study suggest the importance of anticipatory restoration strategies that forecast seasonal and sub‐seasonal weather conditions and select plant species with climate niche requirements appropriate for current and future climate conditions. This information is critical to land managers tasked with improving ecosystem conditions across degraded dryland regions.
Drylands are highly vulnerable to land degradation, and despite increasing efforts, restoration success remains low. Although often ignored in the design and deployment of management strategies, soil ...microbial communities might be critical for dryland restoration due to their central role in promoting soil stability, nutrient cycling and plant establishment.
We collected soil samples from eight dryland restoration sites within RestoreNet, a restoration field trial network, and determined their soil microbiome using 16S rRNA (bacteria and archaea) and ITS (fungi) amplicon sequencing. Each previously degraded site was treated with monoculture (single species) and polyculture (multiple species) seedling plantings.
Contrary to our initial expectations, we found that these different revegetation interventions did not trigger changes in microbial diversity, composition or relative abundance of functional groups across sites after 1 year of revegetation.
Synthesis and applications. Considering the crucial role of soil micro‐organisms in dryland ecosystem functions, our results suggest that site‐specific targeted microbiome restoration should be considered to accelerate the establishment of desired microbial communities. Plant community‐based restoration practices such as revegetation have a limited impact on soil micro‐organisms in the short term.
旱地生态系统中植物多样性的恢复是否能引起土壤微生物组的伴随性恢复？
旱地生态系统极易发生水土流失, 且生态恢复代价高，难度大。土壤微生物在过去的生态恢复的规划与实施中常常被忽略, 但其在土壤稳定性、营养循环、植物建成方面的核心作用显示土壤微生物对于旱地生态系统恢复可能是至关重要的。
我们从由美国地质调查局 (USDA) 主导的旱地恢复实地试验网络 (RestoreNet) 中选取了八个正在进行生态恢复的场地采集土样, 提取并扩增细菌与古菌的16S核糖体核糖核酸(rRNA)与真菌的内部转录间隔区 (ITS) 序列并测序, 用于分析单一种植试验田与混合种植试验田中土壤微生物系群的区别。
得到的试验结果与最初的预测相反, 在为期一年对生态恢复后, 单一种植试验田与混合栽培试验田中的微生物多样性、群落组成、或是微生物功能组的相对丰度没有显著区别。
分析与应用：土壤微生物在生态系统功能发挥着极其重要的功能, 我们的结果指出对于土壤微生物群落对生态恢复应当有针对性且因地制宜。传统植物群落主导的恢复措施如植被恢复在短时间内对土壤微生物的影响非常有限。
Considering the crucial role of soil micro‐organisms in dryland ecosystem functions, our results suggest that site‐specific targeted microbiome restoration should be considered to accelerate the establishment of desired microbial communities. Plant community‐based restoration practices such as revegetation have a limited impact on soil micro‐organisms in the short term.
Because Upper Midwest temperate forests lack native earthworms, the invasions of European and Asian earthworms can significantly alter soils and understory vegetation. Earthworms’ ability to increase ...leaf litter decay, alter nutrient cycling by mixing the organic layer with mineral soil, and decrease plant species richness leads to concern about the Asian ‘jumping earthworm’ (
Amynthas agrestis
and
A. tokioensis
) species that were recorded in the University of Wisconsin—Madison Arboretum in 2013. In 2015, we found
A. agrestis
and
A. tokioensis
in a distinct 8-ha region of a 23-ha hardwood forest surveyed in the Arboretum; by 2016
A. agrestis
and
A. tokioensis
had spread over an additional 7 ha. Plots also contained the European earthworm species
Lumbricus terrestris
,
L. rubellus
, and
Apporectodea
spp., whose distributions decreased from 2015 to 2016. While leaf litter, plant species richness, and tree and shrub seedling abundance were generally reduced in areas with European earthworms, they were typically slightly increased in areas with
A. agrestis
and
A. tokioensis
versus those without. Although our results do not show substantial impacts of
A. agrestis
and
A. tokioensis
on vegetation in the initial years of invasion, the rapid replacement of European earthworms by
A. agrestis
and
A. tokioensis
suggests continued monitoring of these new invasive species is important to better understand their potential to change the Upper Midwest’s forests.
The ecosystems along the border between the United States and Mexico are at increasing risk to wildfire due to interactions among climate, land-use, and fuel loads. A wide range of fuel treatments ...have been implemented to mitigate wildfire and its threats to valued resources, yet we have little information about treatment effectiveness. To fill critical knowledge gaps, we reviewed wildfire risk and fuel treatment studies that were conducted near the US-Mexico border and published in the peer-reviewed literature between 1986 and 2019. The number of studies has grown during this time in warm desert to forest ecosystems on primarily federal lands. The most common study topics included fire effects on native species, the role of invasive species and woody encroachment on wildfire risk, historical fire regimes, and remote sensing and modeling to study wildfire risk across the landscape. A majority of fuel treatment studies focused on prescribed burns, and fuel treatments collectively had mixed effects on mitigating future wildfire risk and threats to ecosystems depending on vegetation and fire characteristics. The diversity of ecosystems and land ownership along the US-Mexico border present unique challenges for understanding and managing wildfire risk, and also create opportunities for collaboration and cross-site studies to promote knowledge across broad environmental gradients.
Restoration in dryland ecosystems often has poor success due to low and variable water availability, degraded soil conditions, and slow plant community recovery rates. Restoration treatments can ...mitigate these constraints but, because treatments and subsequent monitoring are typically limited in space and time, our understanding of their applicability across broader environmental gradients remains limited. To address this limitation, we implemented and monitored a standardized set of seeding and soil surface treatments (pits, mulch, and ConMod artificial nurse plants) designed to enhance soil moisture and seedling establishment across RestoreNet, a growing network of 21 diverse dryland restoration sites in the southwestern USA over 3 years. Generally, we found that the timing of precipitation relative to seeding and the use of soil surface treatments were more important in determining seeded species emergence, survival, and growth than site‐specific characteristics. Using soil surface treatments in tandem with seeding promoted up to 3× greater seedling emergence densities compared with seeding alone. The positive effect of soil surface treatments became more prominent with increased cumulative precipitation since seeding. The seed mix type with species currently found within or near a site and adapted to the historical climate promoted greater seedling emergence densities compared with the seed mix type with species from warmer, drier conditions expected to perform well under climate change. Seed mix and soil surface treatments had a diminishing effect as plants developed beyond the first season of establishment. However, we found strong effects of the initial period seeded and of the precipitation leading up to each monitoring date on seedling survival over time, especially for annual and perennial forbs. The presence of exotic species exerted a negative influence on seedling survival and growth, but not initial emergence. Our findings suggest that seeded species recruitment across drylands can generally be promoted, regardless of location, by (1) incorporation of soil surface treatments, (2) employment of near‐term seasonal climate forecasts, (3) suppression of exotic species, and (4) seeding at multiple times. Taken together, these results point to a multifaceted approach to ameliorate harsh environmental conditions for improved seeding success in drylands, both now and under expected aridification.
Background
Wildland fire in arid and semi-arid (dryland) regions can intensify when climatic, biophysical, and land-use factors increase fuel load and continuity. To inform wildland fire management ...under these conditions, we developed high-resolution (10-m) estimates of fine fuel across the Altar Valley in southern Arizona, USA, which spans dryland, grass-dominated ecosystems that are administered by multiple land managers and owners. We coupled field measurements at the end of the 2021 growing season with Sentinel-2 satellite imagery and vegetation indices acquired during and after the growing season to develop predictions of fine fuel across the entire valley. We then assessed how climate, soil, vegetation, and land-use factors influenced the amount and distribution of fine fuels. We connected fine fuels to fire management points, past ignition history, and socio-economic vulnerability to evaluate wildfire exposure and assessed how fuel related to habitat of the endangered masked bobwhite quail (
Colinus virginianus ridgwayi
).
Results
The high amount of fine fuel (400–3600 kg/ha; mean = 1392 kg/ha) predicted by our remote sensing model (
R
2
= 0.63) for 2021 compared to previous years in the valley was stimulated by near-record high growing season precipitation that was 177% of the 1990–2020 mean. Fine fuel increased across the valley if it was contained within the wildlife refuge boundary and had lower temperature and vapor pressure deficit, higher soil organic content, and abundant annual plants and an invasive perennial grass (
R
2
= 0.24). The index of potential exposure to wildfire showed a clustering of high exposure centered around roads and low-density housing development distant from fire management points and extending into the upper elevations flanking the valley. Within the Buenos Aires National Wildlife Refuge, fine fuel increased with habitat suitability for the masked bobwhite quail within and adjacent to core habitat areas, representing a natural resource value at risk, accompanied with higher overall mean fine fuel (1672 kg/ha) in relation to 2015 (1347 kg/ha) and 2020 (1363 kg/ha) means.
Conclusions
By connecting high-resolution estimates of fine fuel to climatic, biophysical and land-use factors, wildfire exposure, and a natural resource value at risk, we provide a pro-active and adaptive framework for fire risk management within highly variable and rapidly changing dryland landscapes.
The ecological literature offers many conflicting recommendations for how managers should respond to ecosystem change and novelty. We propose a framework in which forest managers may achieve desired ...forest characteristics by combining strategies for (1) restoring historical conditions, (2) maintaining current conditions, and (3) transitioning toward novel conditions. Drawing on policy studies and the ecological and social sciences, we synthesize research on factors that shape forest management responses to ecosystem novelty and change. Although the ecological literature often suggests the likelihood of transitions to novelty, we found that a management focus on restoration and persistence strategies was supported by landowners, private and public lands policy, and forest manager capacity and culture. In this era of unprecedented change, managers and policy makers must address ecosystem novelty to achieve desired forest futures without eroding support for forest conservation and management.
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