Evaluating nurse plants for restoring native woody species to degraded subtropical woodlands

Abstract

Harsh habitats dominated by invasive species are difficult to restore. Invasive grasses in arid environments slow succession toward more desired composition, yet grass removal exacerbates high light and temperature, making the use of “nurse plants” an appealing strategy. In this study of degraded subtropical woodlands dominated by alien grasses in Hawai'i, we evaluated whether individuals of two native (Dodonaea viscosa, Leptocophylla tameiameia) and one non-native (Morella faya) woody species (1) act as natural nodes of recruitment for native woody species and (2) can be used to enhance survivorship of outplanted native woody species. To address these questions, we quantified the presence and persistence of seedlings naturally recruiting beneath adult nurse shrubs and compared survival and growth of experimentally outplanted seedlings of seven native woody species under the nurse species compared to intact and cleared alien-grass plots. We found that the two native nurse shrubs recruit their own offspring, but do not act as establishment nodes for other species. Morella faya recruited even fewer seedlings than native shrubs. Thus, outplanting will be necessary to increase abundance and diversity of native woody species. Outplant survival was the highest under shrubs compared to away from them with few differences between nurse species. The worst habitat for native seedling survival and growth was within the unmanaged invasive grass matrix. Although the two native nurse species did not differentially affect outplant survival, D. viscosa is the most widespread and easily propagated and is thus more likely to be useful as an initial nurse species. The outplanted species showed variable responses to nurse habitats that we attribute to resource requirements resulting from their typical successional stage and nitrogen fixation capability.

Using priority effects to manipulate competitive relationships in restoration

“…Although it did not occur in our restoration experiments or the research covered by our literature review, one possible outcome of a priority experiment could be that later arrivals actually perform better when preceded by a given guild of early arrivals. The various expressions of such facilitative (as opposed to competitive) plant–plant relationships in the context of restoration have already been explored elsewhere (Padilla & Pugnaire ; Brooker et al ; Ren et al ; Yelenik et al ), and may involve the suppression of weedy species by the earlier plantings that can assist in the establishment of later planted species (Kuusipalo et al ; Parrotta et al ; D'Antonio & Meyerson ; Jones et al ; Wilsey et al ).…”

Effects of invasive knapweed (Centaurea stoebesubsp.micranthos) on a threatened native thistle (Cirsium pitcheri) vary with environment and life stage

“…Additionally, the pattern among treatments in both experiments suggests that plant neighbors actually facilitated initial seedling establishment on the perched dunes, where surface soil moisture was less limiting. Facilitative interactions such as this, in which established plants enhance seedling performance, usually referred to as "nurse plant" effects, are common (e.g., Raffaele and Veblen 1998;Armas and Pugnaire 2005;Yelenik et al 2015). The mechanisms underlying nurse plant effects vary among systems, but facilitation is often driven by modification of resources, such as increases in soil moisture or quality, or by protection from disturbance and herbivory (Callaway 1995).…”

“…Similarly, the direction and magnitude of plant-plant interactions can vary among demographic stages (Leger and Espeland 2010). For example, nurse plants are often important facilitators of seedling emergence and early survivorship, despite negative competitive effects at later life-history stages (Franco and Noble 1989;Callaway 1994Callaway , 1995Yelenik et al 2015). Yet, the occurrence of such conditional outcomes rarely has been examined for invasive plant -rare native plant interactions.…”

Facilitation and herbivory during restoration of California coastal sage scrub

“…Established biotic benefactors, such as trees and shrubs, are also called nurse plants and are ideal for facilitation because they reduce photoinhibition, high soil temperatures, freezing, or sunburn damage to apical meristems. Nurse plants also increase water reserves or mycorrhizal associations for neighboring seedlings (Franco & Nobel ; Castro et al ; Padilla & Pugnaire ; Luzuriaga et al ; Kleinhesselink et al ; Yelenik et al ). Extensive global research in arid and semiarid environments supports facilitation as an approach to restoration of degraded and resource‐limited habitats (Castro et al ; Padilla & Pugnaire ; Brooker et al ; Siles et al ; Badano et al ; Chacón‐Labella et al ).…”

“…In degraded semiarid and arid environments, restoration practitioners have often used nurse plants to enhance native seedling growth, survival, and establishment when resources are limited or abiotic conditions are extremely harsh (Castro et al ; Padilla & Pugnaire ; Yelenik et al ). For example, mature saguaro cacti facilitate the growth and survival of other saguaro seedlings in Arizona (Nobel ).…”