Invasive plants can gain a foothold in new environments by manipulating soil conditions through allelopathy or through the disruption of associations between native plants and their mycorrhizal associates. The resulting changes in soil conditions can affect the recovery of habitats long after the invasive plant has been removed. We conducted a series of greenhouse experiments to examine the effects of soil conditioned by pale swallow-wort [Vincetoxicum rossicum (Kleopow) Barbarich; Apocynaceae], on the growth of native plants. Additionally, we tested the effects of aqueous extracts of common milkweed (Asclepias syriaca L.; Apocynaceae), a related plant with known allelopathic effects, on the regrowth of V. rossicum from transplanted root crowns. Soil from a 15-yr-old V. rossicum infestation reduced seedling emergence in A. syriaca as well as in V. rossicum itself. Conversely, the same soil had no effect on the growth of mature A. syriaca plants. Soil conditioned by V. rossicum growth in the greenhouse had no effect on the biomass and percentage cover generated by two restoration seed mixes. Soil conditioned by A. syriaca, however, yielded lower biomass and percentage cover from both seed mixes. In contrast to the allelopathic effects of A. syriaca on seedlings, aqueous extracts of A. syriaca increased aboveground plant growth in V. rossicum. Our results suggest that the effects of V. rossicum–conditioned soil on native plants are concentrated at the seedling establishment phase. Additionally, the use of diverse native seed mixes shows great potential for restoring productivity to ecosystems affected by V. rossicum.

Biological invasions pose a major threat to biodiversity conservation in protected areas, with roads, tracks, and trails being the main pathways for the spread of non-native species. This study aimed to assess the distribution patterns of non-native and native plant species in relation to elevational gradient, public use intensity, and disturbance by roads and trails in a protected tropical mountain forest in southeastern Brazil. Specifically, we recorded plant species along this gradient and tested whether the richness of native and non-native species differed with elevation. Additionally, we investigated whether the high-altitude non-native species community was a subset of lower-elevation communities and whether non-native species richness was linked to anthropogenic disturbances and public use intensity. Our findings revealed that native and non-native species richness varied along the elevational gradient. Native species exhibited a hump-shaped pattern, with richness peaking at mid-elevations. In contrast, non-native species did not show a clear trend along the altitudinal gradient. Notably, higher non-native species richness was observed in roadside and trailside plots. The non-native species communities at higher altitudes were not simply subsets of those found at lower elevations. Thus, while the richness and composition of native species appeared to be driven by environmental factors along the elevational gradient, the presence of non-native species was more closely associated with anthropogenic disturbances. In summary, our results indicate that non-native plants, although widespread along trails and roads, establish primarily in the most disturbed areas. Therefore, roads, trails, and human and vehicular traffic are key determinants of biological invasions in this mountainous protected area.

Flowering rush (Butomus umbellatus L.) is an emergent perennial monocot that has invaded aquatic systems along the U.S.–Canadian border. Currently, there are two known cytotypes of flowering rush, diploid and triploid, within the invaded range. Although most studies have focused on the triploid cytotype, little information is known about diploid plants. Therefore, phenology and resource allocation were studied on the diploid cytotype of flowering rush in three study sites (Mentor Marsh, OH; Tonawanda Wildlife Management Area, NY; and Unity Island, NY) to understand seasonal resource allocation and environmental influences on growth, and to optimize management strategies. Samples were harvested once a month from May to November at each site from 2021 to 2023. Plant metrics were regressed to air temperature, water temperature, and water depth. Aboveground biomass peaked from July to September and comprised 50% to 70% of total biomass. Rhizome biomass peaked from September to November and comprised 40% to 50% of total biomass. Rhizome bulbil densities peaked from September to November at 3,000 to 16,000 rhizome bulbils m−2. Regression analysis resulted in strong negative relationships between rhizome starch content and air temperature (r2 = 0.52) and water temperature (r2 = 46). Other significant, though weak, relationships were found, including a positive relationship between aboveground biomass and air temperature (r2 = 0.17), a negative relationship between rhizome bulbil biomass and air temperature (r2 = 0.18) and a positive relationship between leaf density and air temperature (r2 = 0.17). Rhizomes and rhizome bulbils combined stored up to 60% of total starch, and therefore, present a unique challenge to management, as these structures cannot be reached directly with herbicides. Therefore, management should target the aboveground tissue before peak production (July) to reduce internal starch storage and aim to limit regrowth over several years.

Adaptive management studies of invasive plants on non-agricultural lands typically employ an empirical approach based on designed field experiments that permit rigorous statistical analysis of results to quantify outcomes and assess the efficacy of management practices. When habitat restoration is the primary goal of a project, traditional plot-based study designs (e.g., the randomized complete-block design) are sometimes infeasible (this is often true in aquatic habitats) or inappropriate (e.g., when the goal is to assess effects of management practices on survival or resprouting of individual plants, such as trees or shrubs). Moreover, the assumptions of distribution-specific parametric statistical methods such as ANOVA often cannot be convincingly verified or are clearly untenable when properly assessed. For these reasons, it is worthwhile to be aware of alternative study designs that do not employ plots as experimental units and nonparametric statistical methods that require only weak distributional assumptions. The purpose of this paper is to review several of these alternative study designs and nonparametric statistical methods that we have found useful in our own studies of invasive aquatic and terrestrial plants. We motivate each statistical method by a research question it is well suited to answer, provide corresponding references to the statistical literature, and identify at least one R function that implements the method. In the Supplementary Material, we present additional technical information about the statistical methods, numerical examples with data, and a set of complete R programs to illustrate application of the statistical methods.

Youngia japonica (L.) DC. was recently discovered on the Azorean island of São Miguel. This species is a cosmopolitan herb that has been reported to be invasive in several regions of the world. It is unclear when and how this plant arrived in São Miguel, Azores. Nevertheless, we hypothesize that this is an unintentional and recent introduction. The populations are expanding in São Miguel, and action is needed to mitigate potential damage to native ecosystems.

Phenological studies for Cuban bulrush [Oxycaryum cubense (Poepp. & Kunth) Lye] have been limited to the monocephalous form in Lake Columbus (Mississippi). Accordingly, there is little available information on potential phenological differences among O. cubense forms (monocephalous vs. polycephalous) and populations in other geographic locations in the United States. Therefore, seasonal patterns of biomass and starch allocation in O. cubense were quantified from two populations in Lake Columbus on the Tennessee-Tombigbee Waterway in Mississippi (monocephalous), two populations from Lake Martin in Louisiana (polycephalous), and two populations from Orange Lake in Florida (polycephalous). Monthly samples of O. cubense inflorescence, emergent, and submersed tissue were harvested from two plots per state from October 2021 to September 2022. During monthly data collection, air temperature and photoperiod were recorded. Starch allocation patterns were similar among all sites, with starch storage being less than 1.5% dry weight for all plant tissues. Biomass was greatest in Lake Columbus (monocephalous; 600.7 g dry weight [DW] m−2) followed by Lake Martin (polycephalous; 392.3 g DW m−2) and Orange Lake (polycephalous; 233.85 g DW m−2). Peak inflorescence biomass occurred in the winter for the Lake Martin and Orange Lake populations and in the summer for the Lake Columbus population. Inflorescence biomass in Lake Columbus had a positive relationship (r2 = 0.53) with warmer air temperatures. Emergent and submersed biomass generally had negative relationships with both photoperiod and temperature (r2 = 0.02 to 0.77) in all sites. Peak biomass was also negatively related to temperature and photoperiod. Results from this study indicate that there are differences in biomass allocation between the two growth forms of O. cubense and that growth can occur at temperatures below freezing. Low temperature tolerance may allow this species to expand its range farther north than previously suspected.

Removal and disposal of nonnative trees is expensive and time-consuming. Using these nonnative trees as a substrate to produce edible mushrooms could diversify farming operations and provide additional income to small-scale farmers. This research compared the production of shiitake mushrooms (Lentinula edodes) on nonnative tree logs to shiitake mushroom production on native oak (Quercus L.) logs, which are the traditional substrate. In a 2-yr study, we evaluated nonnative tree species as alternate substrates for growing shiitake mushrooms at farms in northern Florida and southern Georgia. A mix of native Quercus spp. and nonnative trees was targeted for removal on participating farms. Five nonnative tree species were initially tested for their ability to produce edible mushrooms, either shiitake or oyster (Pleurotus ostreatus var. florida). Of the nonnative trees we tested: Chinaberry (Melia azedarach L.), Chinese tallowtree [Triadica sebifera (L.) Small], silktree (Albizia julibrissin Durazz.), earleaf acacia (Acacia auriculiformis A. Cunn. ex Benth.), and paperbark tree [Melaleuca quinquenervia (Cav.) S.F. Blake], only T. sebifera produced shiitake mushrooms, and none produced native Florida oyster mushrooms. In on-farm trials, Quercus spp. logs produced more total mushrooms and more mushrooms per log and had a higher total mushroom yield per log. However, mushrooms produced on T. sebifera logs had higher mean weight per mushroom. Edible fungi can be used to recycle invasive, nonnative T. sebifera and transform their biomass from waste into an income-producing resource.

Among the most widely distributed species globally, common reed [Phragmites australis (Cav.) Trin. ex Steud.] has generated extensive interest in invasive plant science and management because its introduced strains are highly invasive and often form monocultures that alter ecosystem properties. In desert wetlands in Las Vegas, NV, USA, where management goals included reducing hazardous P. australis fuels and increasing native plant diversity, we assessed variation in P. australis cover, the degree of native plant colonization, and soil seedbanks after P. australis management treatments (cutting, glyphosate–imazapyr herbicide) and wildfires across gradients in soil properties. Based on change in P. australis cover during six measurement events over 24 mo, 24 study sites formed three groups: (1) decreasing cover, where initially high P. australis cover (60% to 85%) decreased to <5% following multiple cutting or herbicide treatments; (2) sustaining low cover, where wildfire or clearing was associated with initially low P. australis cover which remained low (<30%) after multiple herbicide applications; and (3) sustaining high cover (45% to 100% initially and remaining at 30% to 100%), including sites unmanaged or treated/burned only once. High soil salinity correlated with low postmanagement P. australis cover. No native plants were detected in the sustaining high P. australis cover group, despite natives occurring in the seedbank. Where management reduced P. australis cover, minimal native plant colonization did occur. Secondary invasion by other non-native plants was nearly absent. Our results suggest that if P. australis can be initially cleared, multiple herbicide applications can persistently keep cover low, especially on drier, saline soils. Slow native plant colonization suggests that a phased approach may be useful to initially reduce P. australis cover, keep it low via repeated treatments, and actively revegetate sites with native species tailored to the moisture–salinity gradient across P. australis–invaded habitats.

Fireweed (Senecio madagascariensis Poir.) has invaded and colonized numerous habitats in the coastal areas of southeastern Australia and is a major weed in cultivated lands as well as in poorly grassed, neglected, and highly grazed pastures. To examine the seed germination ecology of two populations (Felton and Gatton) of S. madagascariensis, experiments were conducted in the laboratory and screen house. The germination of both populations increased as the alternating temperatures increased from the coolest temperatures (15/5 C) to warmer temperatures (25/15 C). However, the highest temperature regime (35/25 C) resulted in the lowest germination rates. The Gatton population exhibited greater tolerance to higher temperatures, resulting in significantly higher germination (2.4 times) than the Felton population at the highest alternating temperature of 35/25 C. Compared with the Felton population, the Gatton population demonstrated higher tolerance to salt and water stress. In comparison to alternating light and dark periods (12 h each) (97% to 98%), the germination of both populations of S. madagascariensis was significantly reduced under complete darkness (24 h) (33% to 39%). A screen house seed burial depth experiment revealed similar emergence of S. madagascariensis seedlings between the populations. The maximum emergence (60%) was observed for seeds placed at the soil surface, followed by a dramatic decline in seedling emergence with an increase in depth. No seedlings emerged from a burial depth of 4 cm. With the addition of wheat (Triticum aestivum L.) crop residue to the soil surface at rates comparable to 4,000 to 8,000 kg ha−1, seedling emergence of S. madagascariensis decreased significantly. Information acquired from this study could be utilized to manage and develop effective weed management strategies for controlling S. madagascariensis in different agroecological conditions.

Japanese hop (Humulus japonicus Siebold & Zucc.) is an emerging invasive plant that has been observed to invade and spread throughout wetlands. As an annual vine, H. japonicus can smother native vegetation, forming dense stands and reducing biodiversity. At a restored floodplain forest in Joslin, IL, formerly used as an experimental site to test the effectiveness of different reforestation methods, H. japonicus has invaded stands of the previously dominant invasive, reed canarygrass (Phalaris arundinacea L.). We conducted an observational field study to examine the spatiotemporal dynamics of H. japonicus invasion relative to gradients in canopy cover and species composition. Ten transects, with half the transect extending into and half extending beyond H. japonicus patches, were established in October 2022. Seven quadrats per transect were surveyed for vegetation cover and canopy cover in October 2022, June 2023, and October 2023. Transects were evenly split between forested and open areas based on the reforestation treatments. Humulus japonicus cover significantly increased from October 2022 to October 2023, resulting in a slight decrease and replacement of P. arundinacea across the site. Shade reduced H. japonicus cover, indicating its preference for sunlit conditions. Species richness was higher in forested transects compared with open ones, most likely due to the absence of both P. arundinacea and H. japonicus in shaded transects. Along transects, quadrats that had been invaded by H. japonicus differed in species composition from quadrats that had not been invaded in both October 2022 and October 2023. Humulus japonicus cover was much lower in June than October, suggesting that temporal niche partitioning may allow P. arundinacea to persist, and indicating that monitoring for H. japonicus should occur late in the growing season. Both invasive species are shade intolerant, suggesting that planting fast-growing trees should be an effective long-term solution for controlling invasion.

Effective regulation is essential for preventing the establishment of new invasive plants and managing the environmental, social, and economic impacts of those already established. Invasive plants are regulated by jurisdictions at a mix of local, regional, national, and international levels. Enhanced coordination of policy and regulations has been identified as a key strategy for addressing the impacts of invasive species; however, coordination between jurisdictions, and even within jurisdictions, is not always considered. To review regulatory coordination in Australia, we compiled a comprehensive dataset of noxious weeds (defined as invasive plants and potentially invasive plants with controls specified in regulation) in each Australian jurisdiction (i.e., state or territory). We found that jurisdictions on average shared ca. 67% (SD = 15%) of noxious weed listings. Neighboring jurisdictions were not more similar than separated jurisdictions in their noxious weed listings. There were significant differences in the biogeographic native ranges of noxious weeds between jurisdictions, with species native to temperate Asia being most frequently listed overall. The predominant likely entry pathway for noxious weeds in Australia was the ornamental trade. Listings were primarily dedicated to proactive control, prohibiting the cultivation of noxious weeds to avoid their naturalization. There were 415 noxious weeds regulated in a harmonious manner across jurisdictions. However, there were 327 noxious weeds regulated by jurisdictions in a discordant manner, potentially leaving neighboring jurisdictions vulnerable to invasion. We suggest jurisdictions reassess the regulation of these 327 discordant noxious weeds in Australia and utilize a national taxonomic standard to avoid problematic synonyms. Improved cohesion of policies could be achieved through wider adoption of existing regulatory systems and codevelopment of regulations between government and industry.

Invasive thistles reduce the productivity of pastures and rangelands because their structural defenses make them unpalatable to grazing livestock. However, plants potentially alter their growth patterns, including their allocation of resources to defense, in response to the presence of competing vegetation. Understanding the effects of competition on the structural defense of problematic pasture weeds can inform management plans that reduce the economic harm caused by these pests. We grew musk thistle (Carduus nutans L., also commonly called nodding thistle) in a fully crossed factorial field experiment in a single abandoned pasture in 2017 with two experimental factors: the level of thistle infestation (1 thistle or 5, resulting in densities of 4 or 20 plants m−2) and the presence or absence of grazing (simulated by weekly trimming of competing vegetation). We assessed the effects of treatments on defense by counting prickles >3-mm long on leaves. Our analysis included leaf age and leaf size as covariates. Competition reduced the number of prickles present on leaves. Regression analysis showed that an increase from, for example, 50 g to 200 g of competing vegetation within 50 by 50 cm study plots reduced the expected average number of prickles on intermediate-aged leaves with average length 25.5 cm by 76.9 prickles per leaf, or 41%. This pattern was similar for leaves of all ages, although the oldest leaves generally had fewer prickles than younger leaves. We did not observe differences in defense structures between plants neighbored by conspecifics and those neighbored by other competitors. Carduus nutans has been previously managed using high densities of grazers, and this practice may be more likely to damage less-defended individuals such as those we observed in our treatments with competition. This finding suggests that maintaining competition in pastures may increase C. nutans vulnerability to grazing.

Invasive plants may cause significant environmental risks by affecting biological diversity, ecosystem services, agriculture, and forestry. Safe utilization of invasive plant biomass by obtaining new outcome products useful for bioeconomics is a challenging but promising solution. Hydrothermal carbonization (HTC) presents a sustainable and cost-effective approach to transforming invasive plant biomass into new products while simultaneously supporting carbon capture aims. This study utilized invasive plants such as lupine [Lupinus polyphyllus Lindl.], Sosnowsky’s hogweed [Heracleum sosnowskyi Manden.], and Japanese knotweed [Polygonum cuspidatum Siebold & Zucc.] as biomass sources for HTC to produce artificial humic substances (AHS). The greatest impact on the yield of AHS (maximum gained yield of 62%) was the duration of the HTC process (up to 6 h) and temperature of the treatment (from 160 up to 250 C), as well as the catalyst used (an alkaline medium is preferable). During the HTC treatment, significant changes in the invasive plant biomass composition occur, as indicated by the removal of labile components of organic matter. The AHS obtained are essentially similar to natural humic matter and have biostimulatory properties; thus, they can be applied in agriculture and other areas of bioeconomics.

Non-native plants negatively impact ecosystems via a variety of mechanisms, including in forested riparian areas. Japanese knotweed [Polygonum cuspidatum Siebold & Zucc.] and its hybrids (referred to as Polygonum spp. hereafter) are widely spread throughout North America and can impact flora and fauna of riparian habitats. Thus, information improving our ability to understand and predict the potential spread and colonization of Polygonum spp. is valuable. One dispersal mechanism is hydrochory (i.e., dispersal by water), including the downstream dispersal of viable stems that can facilitate rapid invasion within a watershed. We used passive integrated transponder (PIT) telemetry in experimental releases of Polygonum spp. stems to track the downstream transport of Polygonum spp. in a small (second-order) stream in northern New Hampshire, USA, in the summers of 2021 and 2022. A total of 180 (90 each year) Polygonum spp. stems were released at three sites within the stream reach, with 185 (∼98%) being recaptured at least once, with a total of 686 recaptures. Individual relocated stems moved a maximum distance of 30 to 875 m downstream in 2021 and 13 to 1,233 m in 2022 during regular flows; however, a high-streamflow event in July 2021 flushed out all remaining stems downstream of the study area. Generalized additive mixed models (GAMMs) identified site-specific differences in stem movement rates and a general reduction in movement rates with increased duration of time elapsed since post-release. In general, Polygonum spp. stems moved farther downstream in sites with lower channel sinuosity, although other fine-scale habitat factors (e.g., water depth, habitat type, and presence of wood and debris jams) likely contribute to the ability for Polygonum spp. to further disperse or otherwise be retained within the channel. Thus, stream morphology and stream flow are likely to affect where Polygonum spp. stems will be retained and potentially reestablish. Predictive tools identifying areas of higher probability of hydrochory-based dispersal could help to focus removal efforts when employed or to identify riparian habitats at highest risk for spread.

The southern African shrub boneseed [Chrysanthemoides monilifera subsp. monilifera (L.) Norl.] is a perennial shrub that is a significant threat to natural ecosystems and is listed as a Weed of National Significance in Australia. In Western Australia (WA) it has spread across peri-urban and natural environments. We assembled a single standardized database containing more than 2,050 presence records for individual plants and 135 absence records at a local population level. We further refined the populations into 89 sites that require different management trajectories due to topography and capacity of land managers to implement control. Forty-nine of these sites were in urban regions and 40 sites were in regional WA. We split these 89 sites into three near-term management goals: watch (12), extirpate (68), and contain (9). The 12 watch sites are those where all available evidence suggests that there have been no new inputs into the seedbank for 15 yr. The 68 sites marked for extirpation are those where delimitation is already achieved or easily achievable, where there have been minimal seed inputs into the soil seedbank in recent years due to consistent surveillance and control, and where surveys for new plants are likely to be efficient to conduct. Finally, for nine sites in urban regions around Perth, we recommend containment in the near term with a longer-term goal to achieve delimitation and extirpation. To achieve the objective of state-level eradication, a coordinated and sustained campaign involving three components—delimitation of all sites, prevention of further inputs into the soil seedbank, and systematic field surveys to remove plants—must commence without delay. While resourcing requirements for delimitation and overall program management are not possible to estimate, our prior experience suggests that it will take at least 1,900 h of on-ground surveying by experienced personnel to achieve extirpation of C. monilifera subsp. monilifera in WA.

Crested floating heart [Nymphoides cristata (Roxb.) Kuntze] is an invasive aquatic plant in the southeastern United States. For clonal plants like N. cristata, clonal diversity may influence response to control tactics and/or evolutionary potential. However, little is known about the diversity of introduced N. cristata. In this study, we used genotyping by sequencing to quantify N. cristata diversity in the southeastern United States and determine how that diversity is distributed across the invaded range. Our results show that at least three distinct genetic lineages of N. cristata are present in the southeastern United States. Geographic distribution of the lineages varied, with one widespread lineage identified across several states and others only found in a single water body. There is also evidence of extensive asexual reproduction, with invaded water bodies often host to a single genetic lineage. The genetic diversity reported in this study likely results from multiple introductions of N. cristata to the southeastern United States and should be considered by managers when assessing control tactics, such as screening for biocontrol agents or herbicide testing. The extent and distribution of genetic diversity should also be considered by researchers studying the potential for invasive spread of N. cristata within the United States or hybridization with native Nymphoides species.

Regularly mown road verges are an important habitat for conservation of grassland vegetation. Disturbance and movement of seed-contaminated soil during road construction and maintenance makes road verges susceptible to the establishment of invasive alien plants such as garden lupine (Lupinus polyphyllus Lindl.). To combat the spread of L. polyphyllus via seeds, we tested methods for seed destruction using heat. This study aimed at developing heat eradication methods for dry and imbibed L. polyphyllus seeds applying dry heat (88, 93, 98, 103 C for 1, 3, 5, 10 min) in a laboratory, steam (85, 90, 95 C for 3, 5, 10 min) in a test box steaming device, and (97 C at 10 to 17 min; dry seeds only) in a stationary soil-steaming machine (S30). To speed up water absorption and posttreatment germination, the imbibed seeds were manually scarified before the heat treatment and the dry seeds afterward. Additionally, germination of two seed batches of different ages was tested applying dry heat (88, 98 C at 3, 5 min). Steam treatments inhibited seed germination more than dry heat in both dry and imbibed seeds. Germination dropped to <5% when steamed at ≥90 C or dry heated at >100 C. Seed germination decreased with higher temperatures and longer exposure times. Imbibed seeds exhibited lower germination compared with dry seeds for dry and steam heat. Approximately 0.5% of dry seeds germinated when steamed using the S30. The seeds collected in 2022 were less sensitive to dry heat than seeds from 2020. In conclusion, hot steam is more effective in reducing L. polyphyllus seed germination than dry heat. Thus, to successfully eradicate L. polyphyllus seeds in soil masses, we recommend steaming them at 97 C for at least 10 min.

White-tailed deer (Odocoileus virginianus) (hereafter, ‘deer’) and invasive plants affect forest understories, but few studies have investigated their interaction. We investigated long-term (11-yr) effects of excluding deer and removing the invasive shrub, Amur honeysuckle [Lonicera maackii (Rupr.) Herder], on plants in southwest Ohio. Deer exclusion enhanced tree seedling richness and density, but reduced annual and bare ground cover. Vine density was reduced by Lonicera, especially where deer were excluded. Seedlings of several tree species, the invasive shrub, burning bush  [Euonymus alatus (Thunb.) Siebold], and the invasive vine, winter creeper [Euonymous fortunei (Turcz.) Hand.-Maz.], were indicator species of the deer exclosure by Lonicera removal treatment combination. The effect of deer on cover of native species depended on Lonicera treatment: where shrubs were removed, cover was higher where deer were excluded, but where shrubs were present, cover was higher where deer had access. We attribute these interactions to the reduced growth of, and shading by, Lonicera where deer had access and browsed this invasive shrub. Some of these effects were evident in the first 6 yr, but are now larger. Other effects were not evident in the earlier evaluation. These findings inform management of areas with high densities of deer and invasive shrubs palatable to deer. Control of only invasive shrubs will reduce native cover and not improve tree regeneration. Managing only deer will increase woody plants but reduce native cover. Management of both stressors is needed to promote tree regeneration and restoration of plant communities.