DIAMETRIC SITE INDEX: AN ALTERNATIVE METHOD TO ESTIMATE SITE QUALITY IN Nothofagus obliqua AND N. alpina FORESTS

Abstract

ABSTRAT:The first step for constructing models of tree growth and yield is site quality assessment. To estimate this attribute, several methodologies are available in which site index (SI) is a standard one. However, this approach, that uses height at a reference age of trees, can be simplified if age is replaced by another reference variable easier to measure. In this case, the diametric site index (DSI) represents the mean height of dominant trees at a reference mean diameter at breast height. The aim of this work was to develop DSI in pure and mixed Nothofagus alpina and N. obliqua forests, and compare these models with the classical proposals based on height-age variables, within the temperate forest of northwestern Patagonia from Argentina, South America. Data originated from temporary plots and stem analyses were used. Tree age and diameter at breast height were obtained from each plot and used for establishing DSI family functions, following the guide-curve methodology. Site classes were proportionally represented among DSI curves of 17.0, 21.5, 26.0, 30.5 and 35.0 m of dominant tree height. Reference diameter instead of reference age can be cautiously used in order to fit site index models. ÍNDICE DE SÍTIO DIAMÉTRICO: UM MÉTODO ALTERNATIVO PARA ESTIMAR A QUALIDADE DO SÍTIO EM FLORESTAS DE Nothofagus obliqua E N. alpinaRESUMO: primeiro passo para a construção de modelos de crescimento e produção de árvores e a avaliação da qualidade do sítio. Para estimar este atributo, várias metodologias estão disponíveis, na qual o índice de sítio (IS) é padrão. No entanto, esta abordagem, que utiliza uma altura na idade de referência, pode ser simplificada se a idade é substituída por outra variável de referência mais fácil de medir. Neste caso, o índice de índice de sítio diamétrico (ISD) representa a altura média das árvores dominantes de um diâmetro à altura do peito referência. O objetivo deste trabalho foi desenvolver ISD para florestas puras e mistas de Nothofagus alpina e N. obliqua, e comparar esses modelos com as propostas clássicas baseadas nas variáveis altura-idade, para a floresta temperada do noroeste da Patagônia da Argentina, América do Sul. Dados provenientes de parcelas temporárias e análises de tronco foram utilizados. Foram obtidos idade e diâmetro à altura do peito de cada parcela e utilizados para o estabelecimento das funções da família DSI, seguindo a metodologia da curva-guia. Classes de sítio foram proporcionalmente representados entre curvas DSI de 17,0; 21,5; 26,0; 30,5 e 35,0 m de altura da árvore dominante. O diâmetro de referência em vez da idade de referência pode ser usado com cautela para ajustar modelos de índice de sítio.

Assessing site form as an indicator of site quality in even-aged Pinus radiata D. Don stands in north-western Spain

“…Nevertheless, this is significant because there was just one report of its use from 1995 to 2016 (Herrera-Fernández et al 2004) several papers. The present findings can contribute to demonstrate the usefulness of SF as a reliable estimator of site quality in pure even-aged stands, which has also been suggested by Beltran et al (2016). In consequence, the performance of SF observed in this study as indicator of site quality can be the cornerstone for a renewable interest in the use of SF for management of even-aged stands at large scales, where the lack of age information usually leads to more complex methodological solutions (i.e.…”

“…The evolution of dominant height over dominant diameter (SF curves) was modelled with similar accuracy than the evolution of dominant height over time (SI curves) for our case study. The goodness-of-fit statistics obtained for the SF models were superior to those obtained by Beltran et al (2016) for Nothofagus alpine and Nothofagus obliqua temperate forest, even-aged mature stands in north-western Patagonia (Argentina).…”

“…Some studies have analysed the relationship between SI and SF for a given species and between these indices and variables traditionally used as measures of site quality (Huang and Titus 1993;Wang 1998;Buda and Wang 2006;Beltran et al 2016;Fu et al 2018). However, only Wang (1998) and Beltran et al (2016) considered species growing in even-aged stands. It must also be noted that the comparative performance of SI and SF can only be properly carried out in even-aged stands because SI, as was previously defined, has no significance in uneven-aged stands.…”

Karst tiankengs as refugia for indigenous tree flora amidst a degraded landscape in southwestern China

“…Tree size distribution is the fundamental forest stand structure from which we can judge or model forest age and growth status 34 – 36 . The contrasting tree size structure between the inside-tiankeng and the outside-tiankeng forest communities again showed the old-growth and isolated nature of the inside-tiankeng habitats.…”

“…The histograms show the full spectra of the tree DBH distribution and give an impressive representation of the approximate stand age of each habitat, since DBH at community level is a good proxy variable for stand age, given similar forest types (e.g., all are natural hardwood forest.) 34 , 35 , 49 .…”