Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth （diameter at breast height, total height）, natural pruning （height to fir...Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth （diameter at breast height, total height）, natural pruning （height to first dead and first live branch and branchiness） and stem and crown form of 24-year-old pedunculate oak （Quercus robur [L.]） and European ash （Fraxinus excelsior [L.]） were affected by initial spacing. Data were recorded from two replicate single-species Nelder wheels located in southern Germany with eight initial stocking regimes varying from 1,020 to 30,780 seedlings·ha？1. Mortality substantially decreased with increasing initial growing space but significantly differed among the two species, averaging 59% and 15% for oak and ash plots, respectively. In contrast to oak, the low self-thinning rate found in the ash plots over the investigated study period resulted in a high number of smaller intermediate or suppressed trees, eventually retarding individual tree as well as overall stand development. As a result, oak gained greater stem dimensions throughout all initial spacing regimes and the average height of ash significantly increased with initial growing space. The survival of lower crown class ashes also appeared to accelerate self-pruning dynamics. In comparison to oak, we observed less dead and live primary branches as well as a smaller number of epicormic shoots along the first 6 m of the lower stem of dominant and co-dominant ashes in all spacing regimes. Whereas stem form of both species was hardly affected by initial growing space, the percentage of brushy crowns significantly increased with initial spacing in oak and ash. Our findings suggest that initial stockings of ca. 12,000 seedlings per hectare in oak and 2,500 seedlings per hectare in ash will guarantee a sufficient number of at least 300 potential crop trees per hectare in pure oak and ash plantations at the end of the self-thinning phase, respectively. If the problem of epicormic shoots and inadequate self-pruning can be controlled with trainer species, the initial stocking may be reduced significantly in oak.展开更多
Improvements in the acquisition of three-dimensional(3D)information from the Airborne Laser Scanner(ALS)increase its applications for studying Earth’s surface.The use of ALS data in natural resource inventories is st...Improvements in the acquisition of three-dimensional(3D)information from the Airborne Laser Scanner(ALS)increase its applications for studying Earth’s surface.The use of ALS data in natural resource inventories is still in an experimental stage in central Europe.Here,a survey was completed in Germany,where plot-level features from LANDSAT Thematic Mapper and ALS data were applied.An automated process was developed for forest stratification using orthoimages.A genetic algorithm was applied for variable screening.Variable subsets of different sizes were employed for simultaneous predictions of structural forest attributes using the‘Random Forest’(RF)method.Performance was assessed by leave-one-out cross-validations on bootstrap resample data.Results indicate that the stratification of forest notably improved the results of predictions.The improvements were more obvious for the strata-related attributes.Accuracy was enhanced as the number of selected variables increased.However,parsimonious models are still essentially required for practical applications.The RF errors were slightly greater than those from least squares regression,as the non-parametric methods do not share the same mix of error components as regression.Through the combination of remote sensing and modelling,we conclude that our results are helpful for bridging the gap between regional earth observation and on-the-ground forest structure.展开更多
文摘Initial growing space is of critical importance to growth and quality development of individual trees. We investigated how mortality, growth （diameter at breast height, total height）, natural pruning （height to first dead and first live branch and branchiness） and stem and crown form of 24-year-old pedunculate oak （Quercus robur [L.]） and European ash （Fraxinus excelsior [L.]） were affected by initial spacing. Data were recorded from two replicate single-species Nelder wheels located in southern Germany with eight initial stocking regimes varying from 1,020 to 30,780 seedlings·ha？1. Mortality substantially decreased with increasing initial growing space but significantly differed among the two species, averaging 59% and 15% for oak and ash plots, respectively. In contrast to oak, the low self-thinning rate found in the ash plots over the investigated study period resulted in a high number of smaller intermediate or suppressed trees, eventually retarding individual tree as well as overall stand development. As a result, oak gained greater stem dimensions throughout all initial spacing regimes and the average height of ash significantly increased with initial growing space. The survival of lower crown class ashes also appeared to accelerate self-pruning dynamics. In comparison to oak, we observed less dead and live primary branches as well as a smaller number of epicormic shoots along the first 6 m of the lower stem of dominant and co-dominant ashes in all spacing regimes. Whereas stem form of both species was hardly affected by initial growing space, the percentage of brushy crowns significantly increased with initial spacing in oak and ash. Our findings suggest that initial stockings of ca. 12,000 seedlings per hectare in oak and 2,500 seedlings per hectare in ash will guarantee a sufficient number of at least 300 potential crop trees per hectare in pure oak and ash plantations at the end of the self-thinning phase, respectively. If the problem of epicormic shoots and inadequate self-pruning can be controlled with trainer species, the initial stocking may be reduced significantly in oak.
文摘Improvements in the acquisition of three-dimensional(3D)information from the Airborne Laser Scanner(ALS)increase its applications for studying Earth’s surface.The use of ALS data in natural resource inventories is still in an experimental stage in central Europe.Here,a survey was completed in Germany,where plot-level features from LANDSAT Thematic Mapper and ALS data were applied.An automated process was developed for forest stratification using orthoimages.A genetic algorithm was applied for variable screening.Variable subsets of different sizes were employed for simultaneous predictions of structural forest attributes using the‘Random Forest’(RF)method.Performance was assessed by leave-one-out cross-validations on bootstrap resample data.Results indicate that the stratification of forest notably improved the results of predictions.The improvements were more obvious for the strata-related attributes.Accuracy was enhanced as the number of selected variables increased.However,parsimonious models are still essentially required for practical applications.The RF errors were slightly greater than those from least squares regression,as the non-parametric methods do not share the same mix of error components as regression.Through the combination of remote sensing and modelling,we conclude that our results are helpful for bridging the gap between regional earth observation and on-the-ground forest structure.
