The importance of shrub cover for four cactus species differing in growth form in an Andean semi‐desert

Abstract

Question: Factors influencing seedling establishment are known to vary between open sites and those protected by plant cover. In many desert regions, protected microhabitats below shrubs are essential for establishment of many cactus species. Very little is known about these factors for Andean cacti and how the importance of vegetation cover varies with cactus species. Are Andean cacti associated more frequently to vegetation cover than to open ground? Are they associated to certain shrub species? Is the distributional pattern in relation to cover similar for different cactus species? In what microhabitat (below or away from shrubs) are cactus seeds more abundant? These questions are addressed for the case of an Andean semi‐desert. Location: Semi‐arid tropical Andes, La Paz department, Bolivia. Methods: We examined 132 isolated shrubs = 50 cm along a line across two microhabitats: areas below and away from shrubs/trees. Shrub crown size was measured. The among‐shrub samples were taken from open spaces contiguous to each of the sampled shrubs. In both microhabitats, all cactus species were recorded. The cardinal direction of the cacti was also registered. Correlation between canopy diameter and number of beneficiaries was evaluated for Prosopis flexuosa. The cactus seed bank in each microhabitat was also studied. Results and Conclusions: The four cactus species found behaved differently in relation to shrub canopies. These distributional differences could be due to differences in growth form. Columnar cacti apparently need the shade of shrubs. Only the columnar species is able to grow near the base of the tallest nurse species. The opuntioid cacti studied seem more facultative: although apparently preferring shrub un‐der‐canopies, they are able to establish in open ground. The globose cactus is the most indifferent to the presence of plant cover. These patterns parallel others found in North America. The capacity of different cacti to appear in open spaces could be related to vegetative propagation, and not necessarily to seedling tolerance of heat.

Dinâmica espaço-temporal de Melocactus ernestii subsp. ernestii (Cactaceae) no Nordeste do Brasil

“…Em ambientes áridos e semi-áridos a associação preferencial entre determinadas espécies de plantas já estabelecidas parece ser fundamental na germinação e no recrutamento de novos indivíduos nas populações de algumas espécies de cactáceas (Mandujano et al 1998, Valiente-Banuet & Ezcurra 1991. No entanto, a ocorrência de plântulas e juvenis de M. ernestii de forma isolada em fendas de rocha e sob blocos de pedra coaduna com as hipóteses de exclusividade de habitat e de facilitação por estruturas do microrrelevo (nurse objects), uma vez que a necessidade de uma planta berçário (nurse plant) nestas circunstâncias é altamente facultativa (Mandujano et al 2002, López & Valdivia 2007, Larrea-Alcázar & Soriano 2008, Munguía-Rosas & Sosa 2008.…”

“…nurse plants ou plantas berçário (Flores & Jurado 2003, López & Valdivia 2007, Larrea-Alcázar & Soriano 2008. Embora associações entre cactos e plantas perenes tenham sido documentadas (Franco & Nobel 1989, Valiente-Banuet & Ezcurra 1991, Arriaga et al 1993, Reyes-Olivas et al 2002, Godínez-Álvarez & Valiente-Banuet 2004, Godínez-Álvarez et al 2005, Larrea-Alcázar & Soriano 2008, a importância destas associações na distribuição espacial de cactos globosos é pouco estudada (Mandujano et al 2002, Reyes-Olivas et al 2002, Larrea-Alcázar & Soriano 2008.…”

“…Cactos globulares ocorrem em microhabitats sob arbustos e também são capazes de se estabelecer em áreas abertas, sugerindo que a associação positiva entre cactos e plantas perenes é facultativa (Mandujano et al 2002, López & Valdivia 2007, Larrea-Alcázar & Soriano 2008.…”

Potencial reproductivo de Stenocerus queretaroensis (Cactaceae) de San José de Cosalima, Zacatecas

“…ex Mottram. Otras investigaciones subrayan de manera general que la emergencia y establecimiento de plántulas de diversas especies de cactáceas es beneficiada por la sombra de las especies con las cuales se asocian (López y Valdivia, 2007;Méndez et al, 2006;Valiente-Banuet y Ezcurra, 1991), disminuyendo así la evapotranspiración y amortiguando la temperatura (Godínez-Álvarez et al, 2003).…”

Nurse tree canopy shape, the subcanopy distribution of cacti, and facilitation in the Sonoran Desert

“…While it is possible such small plants could nurse a Carnegiea gigantea, the author has never observed it directly. Lopez and Valdivia (2007) studied cacti and their leguminous nurses and observed that nurse individuals without protégé cacti, ''were mostly small trees'' (p. 267-268). As this study seeks to quantify Cercidium canopy shape, Cercidium individuals were sampled randomly.…”