On the importance of topography, site quality, stock quality and planting date in a semiarid plantation: Feasibility of using low-density LiDAR

Abstract

Pine seedling survival and growth in eastern Spain have often been related to site preparation, planting date and seedling stock. However, in spite of the acknowledged importance of spatial heterogeneity in seedling performance, little is understood about how topography-related spatial patterns may modify seedling response to plantation, particularly on dry sites. We tested the hypotheses that growth and survival of Pinus halepensis seedlings are related to stock quality, plantation date and topographic conditions, as well as the spatial pattern of environmental variables using a spatially explicit design. The plantation treatment consisted of three seedling stocks, two plantation dates and two contrasted quality sites. Topographic features, such as slope, aspect, Compound Topographic Index and flow accumulation, were measured using GPS and low density LiDAR, with growth and survival monitored over a period of one and two years, respectively. The spatial pattern of the study variables was examined via spatial analysis by distance indices (SADIE). The relative importance of each topographic variable explaining the spatial pattern (local aggregation indices, ν) of seedling response was examined using ordinary least squares (OLS) regressions. P. halepensis seedlings showed higher survival and growth in better sites and early plantations, but they were very similar between seedling stocks. A significantly greater proportion of seedlings survived in early date of plantation (54%) compared to medium date (36%), and in the favorable site (51%) versus the restrictive site (38%). Seedlings also grew significantly faster for those treatments during the first year. However, stock quality had few effects on survivorship and growth. All the topographic and seedling response variables exhibited an aggregated spatial pattern. Seedling survival was clearly associated with topographic patterns, particularly to those related to water availability (CTI and flow accumulation), indicating that on topographic-spatial scales, seedling response is driven by soil-water dynamics in Mediterranean ecosystems. The topographic morphology described by LiDAR was also closely linked to seedling response, thus suggesting the potential of these data to evaluate reforestation success. Accurate maps of topographic factors may indicate whether a plantation has a higher survival and growth potential and with routine reforestation planning activities such as soil preparation.