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Coastal dune restoration often focuses on weed removal to reestablish native vegetation communities. Point Reyes National Seashore (PRNS) initiated large‐scale dune restoration after becoming concerned about loss of dune and rare species habitat from spread of non‐nativeAmmophila arenaria(European beachgrass). Two projects removed beachgrass from 146 ha of heavily invaded dunes using either mechanical removal or herbicide treatment. PRNS conducted pre‐ and post‐restoration vegetation monitoring for 10 years post‐implementation, evaluating success in (1) eradicating beachgrass and (2) reestablishing vegetation communities similar to native dunes in cover, diversity, and species composition. Both methods eradicated beachgrass with annual retreatment. However, they were less successful in rebuilding vegetation communities with comparable native species cover and/or richness. Mechanical removal areas remained largely barren expanses of sand that struggled to support native plants except for a rare perennial, Tidestrom's lupine (Lupinus tidestromii). Tidestrom's lupine and other rare plants now number in the hundreds of thousands. Conversely, herbicide‐treated backdunes were dominated by standing dead beachgrass that resisted decomposition even after 7 years, which hampered native and rare plant establishment. Delayed decomposition was less of an issue in herbicide‐treated foredunes, because sand overwash buried necromass. Restored areas also contended with subsequent invasion by secondary plant invaders. By 2021, only older herbicide‐treated backdunes, and to a lesser extent, mechanical backdunes, showed signs of convergence with native dunes. Successful convergence may be hindered by lingering physical and microbial legacy effects of beachgrass invasion and treatment method. Adaptive restoration may be needed to counter effects and improve project success.
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Functional trait‐based restoration alters nutrient cycling and invasion rates in H awaiian lowland wet forest
Abstract Many degraded ecosystems have altered nutrient dynamics due to invaders’ possessing a suite of traits that allow them to both outcompete native species and alter the environment. In ecosystems where invasive species have increased nutrient turnover rates, it can be difficult to reduce nutrient availability. This study examined whether a functional trait‐based restoration approach involving the planting of species with conservative nutrient‐use traits could slow rates of nutrient cycling and consequently reduce rates of invasion. We examined a functional trait restoration initiative in a heavily invaded lowland wet forest site in Hilo, Hawaiʻi. Native and introduced species were chosen to create four experimental hybrid forest communities, in comparison to the invaded forest, with a factorial design in which communities varied in rates of carbon turnover (slow or moderate [SLOW, MOD]), and in the relationship of species in trait space (redundant or complementary [RED, COMP]). After the first 5 years, we evaluated community‐level outcomes related to nutrient cycling: carbon (C), nitrogen (N), and phosphorus (P) via litterfall, litter decomposition, and outplant productivity and rates of invasion. We found that (1) regardless of treatment, the experimental communities had low rates of nutrient cycling through litterfall relative to the invaded reference forest, (2) the MOD communities had greater nutrient release via litterfall than the SLOW communities, (3) introduced species had greater nutrient release than native species in the two MOD experimental communities, and (4) within treatments, there was a positive relationship between nutrient levels and outplant basal area, but outplant basal area was negatively associated with rates of invasion. The negative relationships among basal area and weed invasion, particularly for the two COMP treatments, suggest species existing in different parts of trait space may help confer some degree of invasion resistance. The diversification of trait space was facilitated by the use of introduced species, a new concept in Hawaiian forest management. Although challenges remain in endeavors to restore this heavily degraded ecosystem, this study provides evidence that functional trait‐based restoration approaches using carefully crafted hybrid communities can reduce rates of nutrient cycling and invasion in order to reach management goals.
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- Award ID(s):
- 1754844
- PAR ID:
- 10442045
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecological Applications
- Volume:
- 33
- Issue:
- 6
- ISSN:
- 1051-0761
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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