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1. Shaping Baltimore’s urban forests: past insights for present-day ecology

   https://doi.org/10.1007/s10980-024-01931-y  

   Sonti, Nancy F ; Baker, Matthew E ; Lagrosa, John J ; Allman, Michael ; Grove, J Morgan ; Katoski, Michelle P ( August 2024 , Landscape Ecology)

   Land use history of urban forests impacts present-day soil structure, vegetation, and ecosystem function, yet is rarely documented in a way accessible to planners and land managers.

   To (1) summarize historical land cover of present-day forest patches in Baltimore, MD, USA across land ownership categories and (2) determine whether social-ecological characteristics vary by historical land cover trajectory.

   Using land cover classification derived from 1927 and 1953 aerial imagery, we summarized present-day forest cover by three land cover sequence classes: (1) Persistent forest that has remained forested since 1927, (2) Successional forest previously cleared for non-forest vegetation (including agriculture) that has since reforested, or (3) Converted forest that has regrown on previously developed areas. We then assessed present-day ownership and average canopy height of forest patches by land cover sequence class.

   More than half of Baltimore City’s forest has persisted since at least 1927, 72% since 1953. About 30% has succeeded from non-forest vegetation during the past century, while 15% has reverted from previous development. A large proportion of forest converted from previous development is currently privately owned, whereas persistent and successional forest are more likely municipally-owned. Successional forest occurred on larger average parcels with the fewest number of distinct property owners per patch. Average tree canopy height was significantly greater in patches of persistent forest (mean = 18.1 m) compared to canopy height in successional and converted forest patches (16.6 m and 16.9 m, respectively).

   Historical context is often absent from urban landscape ecology but provides information that can inform management approaches and conservation priorities with limited resources for sustaining urban natural resources. Using historical landscape analysis, urban forest patches could be further prioritized for protection by their age class and associated ecosystem characteristics.

    

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2. Increase in nonnative understorey vegetation cover after nonnative conifer removal and passive restoration

   https://doi.org/10.1111/aec.12812  

   Sample, Martha ; Aslan, Clare E. ; Policelli, Nahuel ; Sanford, Robert L. ; Nielsen, Erik ; Nuñez, Martín A. ( August 2019 , Austral Ecology)

   Nonnative conifers are widespread in the southern hemisphere, where their use as plantation species has led to adverse ecosystem impacts sometimes intensified by invasion. Mechanical removal is a common strategy used to reduce or eliminate the negative impacts of nonnative conifers, and encourage native regeneration. However, a variety of factors may preclude active ecological restoration following removal. As a result, passive restoration – unassisted natural vegetation regeneration – is common following conifer removal. We asked, ‘what is the response of understorey cover to removal of nonnative conifer stands followed by passive restoration?' We sampled understorey cover in three site types: two‐ to ten‐year‐old clearcuts, native forest and current plantations. We then grouped understorey species by origin (native/nonnative) and growth form, and compared proportion and per cent cover of these groups as well as of bare ground and litter between the three site types. For clearcuts, we also analysed the effect of time since clearcut on the studied variables. We found that clearcuts had a significantly higher average proportion of nonnative understorey vegetation cover than native forest sites, where nonnative vegetation was nearly absent. The understorey of clearcut sites also averaged more overall vegetation cover and more nonnative vegetation cover (in particular nonnative shrubs and herbaceous species) than either plantation or native forest sites. Notably, 99% of nonnative shrub cover in clearcuts was the invasive nonnative species Scotch broom (Cytisus scoparius). After ten years of passive recovery since clearcutting, the proportion of understorey vegetation cover that is native has not increased and remains far below the proportion observed in native forest sites. Reduced natural regeneration capacity of the native ecosystem, presence of invasive species in the surrounding landscape and land‐use legacies from plantation forestry may inhibit native vegetation recovery and benefit opportunistic invasives, limiting the effectiveness of passive restoration in this context.

   Abstract in Spanish is available with online material.

    

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3. The mechanisms affecting seedling establishment in restored savanna understories are seasonally dependent

   https://doi.org/10.1111/1365-2664.13354  

   Sorenson, Quinn_M ; Damschen, Ellen_I ; Lee, ed., Tien_Ming ( March 2019 , Journal of Applied Ecology)

   Agricultural land is being increasingly abandoned on a global scale, with over 200 million hectares recovering from agricultural use. Plant community regeneration differs greatly in structure and composition after agricultural impacts, yet the mechanisms underpinning these dramatic changes are poorly understood. It is critical to determine the relative importance of abiotic and biotic factors that limit plant establishment and success during the recovery process. In particular, below‐ground competition for resources in soils affected by former agricultural uses may play an important role in limiting plant establishment. Yet, below‐ground competition is generally studied less than above‐ground, especially in the context of land‐use history.

   We compare plant establishment with and without below‐ground competition in the context of a large‐scale experiment manipulating land‐use histories (i.e. with and without a history of agriculture) and restoration of historical vegetation structure (i.e. thinned and unthinned canopy trees) and determine how life stage and the local environment (e.g. soil water holding capacity, vegetation cover) influence this relationship.

   For three of our four target species, below‐ground competition strongly limited establishment success, but did not interact with land‐use history and canopy thinning directly. Instead, land‐use history and canopy thinning interacted to affect establishment during germination and survival in spring, while below‐ground competition limited growth during the summer. The strength of below‐ground competition was affected by local resources, but the directionality of this relationship depended on agricultural history and canopy thinning.

   Synthesis and applications. Because adding seeds increased establishment in all cases, we recommend confronting land‐use legacies by overcoming dispersal limitation with seed additions (even in degraded sites) and ensuring that below‐ground structures are managed during restoration, especially in summer. In addition, managers should consider how the relationship between local resources and below‐ground competition at individual sites might depend on land‐use history or canopy thinning.

    

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4. Bee diversity decreases rapidly with time since harvest in intensively managed conifer forests

   https://doi.org/10.1002/eap.2855  

   Zitomer, Rachel_A ; Galbraith, Sara_M ; Betts, Matthew_G ; Moldenke, Andrew_R ; Progar, Robert_A ; Rivers, James_W ( May 2023 , Ecological Applications)

   Despite widespread concerns about the anthropogenic drivers of global pollinator declines, little information is available about the impacts of land management practices on wild bees outside of agricultural systems, including in forests managed intensively for wood production. We assessed changes in wild bee communities with time since harvest in 60 intensively managed Douglas‐fir (Pseudotsuga menziesii) stands across a gradient in stand ages spanning a typical harvest rotation. We measured bee abundance, species richness, and alpha and beta diversity, as well as habitat characteristics (i.e., floral resources, nesting substrates, understory vegetation, and early seral forest in the surrounding landscape) during the spring and summer of 2018 and 2019. We found that bee abundance and species richness declined rapidly with stand age, decreasing by 61% and 48%, respectively, for every 5 years since timber harvest. Asymptotic estimates of Shannon and Simpson diversity were highest in stands 6–10 years post‐harvest and lowest after the forest canopy had closed, ~11 years post‐harvest. Bee communities in older stands were nested subsets of bee communities found in younger stands, indicating that changes were due to species loss rather than turnover as the stands aged. Bee abundance—but not species richness—was positively associated with floral resource density, and neither metric was associated with floral richness. The amount of early seral forest in the surrounding landscape seemed to enhance bee species richness in older, closed‐canopy stands, but otherwise had little effect. Changes in the relative abundance of bee species did not relate to bee functional characteristics such as sociality, diet breadth, or nesting substrate. Our study demonstrates that Douglas‐fir plantations develop diverse communities of wild bees shortly after harvest, but those communities erode rapidly over time as forest canopies close. Therefore, stand‐scale management activities that prolong the precanopy closure period and enhance floral resources during the initial stage of stand regeneration will provide the greatest opportunity to enhance bee diversity in landscapes dominated by intensively managed conifer forests.

    

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5. A dryland re‐vegetation in northern China: Success or failure? Quick transitions or long lags?

   https://doi.org/10.1002/ecs2.2678  

   Chen, Ning ; Ratajczak, Zak ; Yu, Kailiang ( April 2019 , Ecosphere)

   Intensified anthropogenic activities have drastically altered many ecosystems, motivating the use of restoration to regain key ecosystem functions and services and to stem biodiversity losses. Restoration is particularly difficult when human activities have pushed an area into a new state with self‐reinforcing feedbacks. This study investigated a long‐term restoration project in a dryland ecosystem of the Tengger Desert in northwestern China, initiated in 1956. We analyzed shrub and grass cover for 49 yr after the installation of restoration infrastructure that altered external conditions (i.e., using packed straw to reduce wind erosion) and system state (by planting shrubs). After 37–40 yr, the re‐vegetation project was successful in restoring the system to a state similar to native vegetation, with high grass cover (30–50%), low shrub cover (8–10%), and a thick biological soil crust (biocrust). However, the shift to high grass cover did not begin until year 37, before which shrub cover was high (15–20%) and grasses were subdominant (usually <10%). The shift from shrub to grass dominance was abrupt, registering significant nonlinear changes over time and relative to a key driver of vegetation dynamics, estimated biocrust thickness. Biocrust thickness increased gradually over time, which reduced rainfall infiltration into deep soil and thus increased soil moisture available for the shallow‐rooted grasses. The shift from the bare soil state to the steppe state exhibited a long time lag, suggesting that it can take decades to determine whether dryland restoration efforts succeed. The results indicate that persistence might be critical to forcing desired state transitions and that dryland restoration can proceed as a series of time lags, punctuated by abrupt changes in ecosystem state.

    

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