Effects of different land-use systems (grazing and understory cultivation) on growth and yield of semi-arid oak coppices

Abstract

The present study examines the extent of negative effects of traditional multiple land-use systems on oak coppices, from a forest management point of view. The study area was located in approximately 10,000 ha of hilly Brant’s oak (Quercus brantii Lindl.) woodlands in the central Zagros Mountains. In the same site-quality class, three land-use systems were compared: simple coppice (Co), coppice in conjunction with small ruminant grazing (CoG), and coppice with understory rain-fed wheat cultivation plus grazing (CoCG). Data on total wood volume of trunk and major branches, and annual ring growth, were collected and analyzed from 74 stands in 15 coppiced woodland patches. The results showed the advantage of Co over CoG and CoCG land-uses by 43 and 60 m3 of mean accumulated wood volume per hectare, respectively. The diameter growth analysis also revealed an annual increase in wood production of trees in Co land-uses over 43 years, with an exception of the recent decade, when growth coincided with a severe drought. Using a back-extrapolation method, the minimum rotation age of woodlands in Co land-use was found to be 23.6 years, 5 and 7 years shorter than those of CoG and CoCG land-uses, respectively. Unlike CoCG, woodlands located in Co and CoG land-use systems demonstrated a high level of agreement with self-thinning rule of − 3/2. Values for the stand density index for coppiced oak woodlands were between more than 1000 for the least disturbed (Co) and less than 400 for the most disturbed woodlands (CoCG). The structure and growth rate of the coppiced oak woodlands were irreversibly disrupted by understory tillage plus grazing and in less extent by grazing alone. It was concluded that ending undergrowth cultivation in semi-arid oak coppices should be addressed as a priority by adopting minimum regulations.