The role of nurse plants in the establishment of shrub seedlings in the semi-arid subtropical Andes

Abstract

In the nurse plant syndrome, or nurse association, seedlings (beneficiaries) are associated with adult shrubs/trees (benefactors). This phenomenon has been documented in several regions of the planet. Abiotic stress amelioration (one mechanism of facilitation) is one of the causes of this association. Most of the studies addressing the nurse syndrome have been conducted on spatial scales of a few hectares and have focused on only one or a few species. Moreover, there is an almost complete lack of studies addressing the incidence and characteristics of the nurse phenomenon in the arid Andes of South America. We undertook a first approximation to the study of facilitation in these ecosystems. The study was conducted at local and regional scales and involved the assessment of the spatial distribution of juveniles (seedlings and saplings) of 51 populations of 16 shrub and 12 cactus species in relation to shrub cover at 20 localities of the Prepuna (subtropical Andes of Bolivia and Argentina, 20-26 degrees S). In terms of spatial distribution, the juveniles of most of the populations of shrubs studied were distributed both under the shrubs and in open spaces, thereby showing an apparent indifference to microhabitat. Globose and opuntioid cacti were preferentially distributed below the canopies of shrubs and were usually more associated with the dominant shrub species, which stood out as better potential nurses. The pattern was consistent throughout the region, including the more mesic and arid localities. The fact that Prepuna woody species are capable of establishing in open spaces would confer this region a greater resilience. Our findings further suggest that community dynamics in arid and semi-arid environments are more variable than previously thought.

Effects of a nurse shrub on seed deposition and seedling recruitment of the annual <i>Agriophyllum squarrosum</i>

“…The lack of the nurse effect in this study may be due to the following factors. Firstly, the recruitment of the pioneer annual A. squarrosum in this mobile sandy habitat of the semi-arid Horqin desert does not necessarily depend on nurse effect; instead, this species is capable of colonizing and establishing in bare sandy patches without requiring the moderate conditions existing under shrub canopies, as suggested by a recent study in the semi-arid subtropical Andes (López et al 2007). Secondly, when seedlings were established in July-August, it was the period when most of rainfall was received in the region.…”

“…5). In natural ecosystems, facilitation and competition are co-occurring processes in the nurse association (López et al 2007), and the net effect between the facilitation and competition of shrubs (benefactors) on herb seedlings (beneficiaries) may vary with environmental conditions and identity of interacting species (reviewed by López et al 2007). The observed negative response of seedling establishment in A. squarrosum to the presence of A. halodendron shrubs may be due to stronger competitive effects than facilitative effects of nurse shrubs on recruitment.…”

ESTRUCTURA ESPACIAL DE Pachycereus weberi (Coult.) Backeb. EN LA CAÑADA DEL ZOPILOTE, GUERRERO

“…Cactus species have a well-documented relationship with bush and tree species that act as facilitators through the so-called nurse plant syndrome (Reyes-Olivas et al, 2002;López et al, 2007;Larrea-Alcázar et al, 2008;Larrea-Alcázar and Soriano, 2008;Zenteno-Ruiz et al, 2009). The fact that there is a positive spatial correlation at short distances (0-3 m) between P. weberi juveniles and Figura 4 se presenta la correlación espacial entre juveniles y adultos de P. weberi y Acacia tenuifolia.…”

“…En especies de cactáceas está ampliamente documentada la relación con especies arbustivas y arbóreas que funcionan como facilitadoras a través del síndrome de nodricismo (Reyes-Olivas et al, 2002;López et al, 2007;Larrea-Alcázar et al, 2008;Larrea-Alcázar y Soriano, 2008;Zenteno-Ruiz et al, 2009). El hecho de que se presente una correlación espacial positiva a distancias cortas (0-3 m) entre juveniles de P. weberi e individuos de Acacia tenuifolia, puede ser un indicio de la existencia de dicho síndrome.…”

Population structure and spatial pattern of Caragana tibetica communities in Nei Mongol shrub-encroached grassland

“…The mature individuals negatively interacted with juveniles at the scale of larger than 2.2 m, but unassociated at the other scales. Key words shrub-encroached grassland; Caragana tibetica; point pattern; spatial distribution pattern (Archer, 1989;Grover & Musick, 1990), 并引起全球广泛关注(van Auken, 2000;Jackson et al, 2002;Maestre et al, 2009)。 目前国外主要关注于北美 (Buffington & Herbel, 1965;Archer et al, 1988;Knapp et al, 2008)和非洲 南部 (Eldridge et al, 2011)的灌丛化草原, 集中研究 草原灌丛化的成因 (Knoop & Walker, 1985;Bond & Midgley, 2001;Coetzee et al, 2007)和灌丛化对生态 系统生产力 (Phinn et al, 1996;Oba et al, 2000;Knapp et al, 2008)、生物多样性 (Eldridge et al, 2011)和土壤碳储量 (Jackson et al, 2002)的影响。在 国内, 主要集中于内蒙古灌丛化草原的研究 (周道 玮, 1990;刘书润, 1991;Chen et al, 2015), 涉及灌 丛化的驱动因子 (Chen et al, 2015 (Wiegand et al, 2000b;López et al, 2007)。已有研究 表明, 在干旱的环境中, 灌木的冠幅与高度之间的 关系和灌木的发育阶段有显著的相关关系 (Ludwig et al, 1975;Reynolds et al, 1999)。本文通过分析毛 (Ripley, 1977;Legendre & Fortin, 1989)和修正函数L(r)函数 (Besag, 1977)对毛 刺锦鸡儿种群个体在不同范围内的空间分布格局进 行分析。单变量K(r)函数公式如下: Archer S (1989). Have southern texas savannas been converted to woodlands in recent history?…”