Light Transmissivity of Tree Shelters Interacts with Site Environment and Species Ecophysiology to Determine Outplanting Performance in Mediterranean Climates

Juan A Oliet,Alberto Vázquez De Castro,Patricio Valenzuela,Jaime Puértolas

doi:10.3390/land10070753

Abstract

Plastic tree shelters are commonly used in plantations under Mediterranean climates to protect against herbivory and enhance outplanting performance. However, effects on outplanting performance cannot be generalized due to the complexity of plant responses to microenvironmental conditions within the tube wall. The interactions between the light transmissivity of the tubes and species-specific responses to light and site environment on two-year outplanting performance were studied in two species with contrasting shade tolerance planted inside tree shelters with four different light transmissivities and a non-tree shelter control at two Mediterranean sites with contrasting rainfall and temperature. In general, increasing light transmissivity enhanced biomass accumulation, suggesting that the use of clear tubes might be advisable. However, the shade-tolerant Q. ilex did not benefit from the greater light transmissivity in the most arid site, indicating that the positive effect of clear tubes depends on water stress experienced by seedlings, which ultimately is determined by drought resistance strategies and site conditions. The growth of both species and survival of P. halepensis were higher within clear tubes in the continental site than in unsheltered plants, which suggests that factors other than light, such as warmer daytime temperatures or the prevention of dust deposition, can explain this beneficial site-dependent effect of tree shelters. In conclusion, our results confirm the hypothesis that the effect of tree shelter and its light transmission on outplanting performance is site and species-specific, but further research is needed to identify the effect of other effects not related to light transmission.

Highlights

Tree planting is recognized as an effective way to conduct forest landscape restoration in all biomes [1,2]
Q. ilex survival was significantly lower at the coastal subdesertic site (Alicante), while for P. halepensis it was generally lower at the continental semi-arid site (Alcázar) (Tables 1 and 2)
For P. halepensis, a significant site × shelter interaction was observed during the second year of planting (Table 2), as the control plants had significantly lower survival than the tree shelters only in Alcázar, with very high survival in Alicante in all treatments for this species

Summary

Introduction

Tree planting is recognized as an effective way to conduct forest landscape restoration in all biomes [1,2]. Shallow and unfertile soils are frequent in these biomes [3]; biotic stress such as predation by small mammals, birds or ungulates is a common disturbance in these landscapes that hampers survival and growth [4,5]. Along with these factors, intense summer drought occurring in Mediterranean areas simultaneously with high radiation levels is the main source of abiotic stress, causing significant failures and subsequent economic loss [6,7]. The current scenario of climate change, with higher probabilities of extreme, harsh summers [8], suggests that the success of restoration programs in dry Mediterranean environments will require improvements in planting techniques aimed at ameliorating the degree of stress affecting the seedlings [9,10]

Objectives

Methods

Results

Discussion

Conclusion