3 years ago

Intra- and inter-specific variation of the maximum size-density relationship along an aridity gradient in Iberian pinewoods

Intra- and inter-specific variation of the maximum size-density relationship along an aridity gradient in Iberian pinewoods
The diverse applications of the maximum size-density relationship (MSDR) in monospecific and mixed forests, such as in ecological and economic aspects, lead to continuous advances in our knowledge on this issue. One of the most recent advances was the inclusion of climatic variables in these studies, revealing the variation in MSDR depending on environmental conditions. However, the importance of climatic conditions on the intra- and inter-specific variation of MSDR is still poorly understood. The aim of this paper is to explore the dependence of MSDR on climatic conditions for the five principal pine species in the Iberian Peninsula (P. halepensis Mill., P. nigra Arn., P. pinea L., P. pinaster Ait., and P. sylvestris L.) and to analyse the importance of this dependence on the relative carrying capacities in mixed stands. Data from the Third Spanish National Forest Inventory (NFI) were used together with four simple climatic indices calculated from raster maps. Using a quantile regression, a MSDR basic model, relating the maximum number of trees and the quadratic mean diameter, was fitted to the data from the plots in monospecific stands. In a second step, the coefficients of basic model were parameterized as a function of climatic variables. The resulting climate-dependent model was also fitted to the plots. Competition equivalence coefficients (CEC) in mixed stands (i.e. ratio between maximum stand density indices of the two species) were calculated from the resulting models. The differences among species’ MSDRs confirm the inter-specific variability of maximum densities and the need for species-specific models. According to the Akaike information criteria, the climate-dependent models, and particularly those dependent on Martonne aridity index, were always better than basic models. Although the higher the aridity the lower the maximum stand density, the influence of climate on the MSDR also varies according to the species considered, this influence being more evident for P. pinaster and P. halepensis, which also display high ecological plasticity. The CEC derived from the basic model for pine-pine mixtures range from 1.10 to 1.70. However, when aridity is considered, these coefficients almost always decrease. Our results highlight the importance of considering environmental variables to better describe and compare the potential density in monospecific and mixed stands and therefore, the utility of species-specific climate dependent models for management decision support.

Publisher URL: www.sciencedirect.com/science

DOI: S037811271731681X

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