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Community Ecology

, Volume 3, Issue 1, pp 9–18 | Cite as

A multivariate approach to the study of the spatial structure of treeline ecotones

  • J. J. CamareroEmail author
  • E. Gutiérrez
Open Access
Article

Abstract

We study the structure of two contrasting alpine forest-pasture ecotones located in the Central Pyrenees (sites Ordesa and Tessó). We define ecotone structure as the spatial distribution of trees of different size classes and growth-forms, and the relationship between these aspects and the spatial distribution of understory vegetation and substrate. The studied ecotones are dominated by Pinus uncinata and have been little affected by recent anthropogenic disturbances (logging, grazing). One rectangular plot (30 × 140 m2) was located within each site encompassing treeline and timberline with its longest side parallel to the slope. The distribution of size and growth-form classes at Ordesa followed a clear sequence of increasing size downslope, from shrubby krummholz individuals to bigger arborescent trees. At Ordesa, regeneration was concentrated near the krummholz area and over rocky substrates. At Tessó, regeneration was abundant above the treeline, where the cover of the dominant understory shrub (Rhododendron ferrugineum) decreased. Detrended canonical correspondence analysis of tree and plant cover data, with respect to spatial location in the ecotone and substrate cover, demonstrated that elevation was an important factor controlling the distribution of trees and understory plants in both ecotones. Finally, k-means clustering with spatial constraint revealed abrupt spatial clusters along the slope at Ordesa. However, the ecotone at site Tessó was composed of elongated downslope spatial clusters suggesting greater spatial heterogeneity and subtle gradual changes due to other factors in addition to the altitudinal gradient (snow avalanches). These contrasting structures correspond well with the ecotone (sharp boundary, Ordesa) and ecocline (gradual transition, Tessó) concepts. This suggests the dominant role of different local environmental factors: wind at site Ordesa and avalanches at Tessó. Positive feedbacks, like facilitation among P. uncinata individuals (nurse effect), may maintain and intensify the sharpness of the ecotone at Ordesa.

Keywords

Detrended Canonical Correspondence Analysis Ecocline k-means clustering Pinus uncinata Spatial pattern Timberline 

Abbreviations

A

adults

CCA

Canonical Correspondence Analysis

D

dead individuals

db

diameter at stem base

dbh

diameter at breast height

DCCA

Detrended Canonical Correspondence Analysis

FPE

Forest Pasture Ecotone

h

tree height

K

krummholz

KM

flagged krummholz

NDST

number of dead stems per individual

NLST

number of living stems per individual

NST

total number of stems per individual

O

Ordesa site

P

poles

S

saplings

SE

seedlings

T

Tessó site

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© Akadémiai Kiadó, Budapest 2001

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Authors and Affiliations

  1. 1.Departament d’EcologiaUniversitat de BarcelonaBarcelona, CatalunyaSpain

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