Recruitment and facilitation in Pinus hartwegii, a Mexican alpine treeline ecotone, with potential responses to climate warming

• Published in: Trees (Berlin, West) Vol. 33; no. 4; pp. 1087 - 1100
• Main Authors: Astudillo-Sánchez, Claudia C., Fowler, Mike S., Villanueva-Díaz, José, Endara-Agramont, Angel R., Soria-Díaz, Leroy
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2019; Springer Nature B.V
• Subjects: Agriculture; Biomedical and Life Sciences; Climate; Climate change; Dendrochronology; Elevation; Forestry; Generalized linear models; Global warming; Growing season; Life Sciences; Low density lipoprotein; Original Article; Plant Anatomy/Development; Plant Pathology; Plant Physiology; Plant Sciences; Recruitment; Regression models; Shelters; Shrubs; Soil moisture; Statistical models; Tree Rings; Treeline; Facilitation; Climate warming; Treeline; Recruitment
• ISSN: 0931-1890; 1432-2285
• DOI: 10.1007/s00468-019-01844-3

Key message
Under climate warming the presence of key microsite facilitators modify soil moisture levels associated with successful tree recruitment at the treeline ecotone of
Pinus hartwegii
.
Alpine treelines in Mexico are represented by high-elevation forests dominated by
P. hartwegii
Ldl. To address the degree to which the presence of suitable microsite facilitators are factors for successful recruitment within the treeline ecotone of
P. hartwegii
and modulate their responses to climate warming, year of natural tree establishment, number of trees recruited, and the presence of shelter elements at different exposures of Monte Tlaloc (in the Trans-Mexican Volcanic System) were recorded. For tree recruitment and microsite facilitation we recorded each tree and the type of potentially protective elements that may improve microsite conditions within a total of 32 circular plots (
r
 = 18 m) in the alpine treeline ecotone (above 4000 m). Temperatures for Monte Tlaloc at 4000 m were estimated using the thermal gradient for the study area, and standard dendrochronological methods and a regression model were used to date tree recruitment. Vector generalized linear models show that maximum growing season temperatures have significantly influenced the temporal pattern of tree recruitment in this system over the past 50 years, but this influence was mediated by the presence (or absence) of specific shelter elements (shrubs, soil depressions, rocks or bare soil) within a specific treeline ecotone exposure, also shaping the spatial pattern of tree recruitment. The response of the treeline ecotone to climate warming at local scales is qualitatively modified by the presence of microscale features, requiring sufficient soil moisture to be available on the site of recruitment.