hamid soofi mariv

We assessed how climate change may impact net primary production (NPP) and reference evapotranspiration (ET0) from the Zagros region of western Iran covered extensively by oak, -Quercus branti Lindl. forests. The daily meteorological parameters of temperature (T), precipitation (P), relative humidity (RH), wind speed (WS), and sunshine hours were obtained from 20 meteorological stations throughout the region over a 30-year period (1988-2017). Net primary production and ET0 were estimated by the synthetic and the FAO Penman-Monteith models, respectively. A non-dimensional relative sensitivity coefficient was used to examine the sensitivity of NPP and ET0 to changes in the meteorological parameters. The sensitivity analyses were carried out for T, P, and WS within a possible range of ± 10%, ± 30%, and ± 10%, respectively, from the long-term mean. Except for the P with no notable trend, other meteorological parameters exhibited upward or downward trends. The mean NPP and ET0 values were estimated to be 6.5 t ha-1 y-1 and 3.9 mm d-1 across the Zagros region, respectively. Net primary production was found to be more sensitive to precipitation with a sensitivity coefficient of 0.66 and less sensitive to temperature with a sensitivity coefficient of 0.40. The ET0 sensitivity coefficients in response to T changes doubled relative to WS (0.33 against 0.63). Identifying the contributing factors in NPP and ET0 trends is important for understanding the relative impacts of climate change and human activities in arid and semi-arid regions.

In the present study, we detected the characteristics of precipitation (the amount and the number of events) in the Saharo-Sindian vegetation region located in the south and southeast of Iran over the last three decades. Daily precipitation data during 1987-2019, recorded by eighteen meteorological stations were analyzed. The Mann-Kendall (MK) test was used for trend analysis. Over the past thirty-three years, the mean annual precipitation was 214 mm (SD: 61 mm). Mean maximum and minimum yearly precipitations were recorded in Dogonbadan (439 mm) and Iranshahr (109 mm), respectively. Out of the eighteen stations, only two stations, Ramhormoz and Kish Island, showed significant annual precipitation trends (11% of the total trends). During 33 years, a total of 17275 events (mean event: 7.5 mm; SD: 6.9 mm) were recorded in the stations. The correlation coefficient (r) between the amount of precipitation and the number of events varied from 0.41 to 0.86 (mean: 0.67; SD: 0.13). We found that 83% of the mean annual precipitation occurred during the autumn and winter seasons. The highest and lowest yearly precipitations fell within the 20-40 mm (21%, 45 mm) and over 40 mm (30%, 64 mm) classes, respectively. Over the past three decades, the mean number of dry days per year was 336. Any changes in precipitation characteristics severely impact the vulnerable forest ecosystems in the Saharo-Sindian vegetation region.

The objective was to investigate if changes in annual, monthly, and seasonal precipitation are associated with emergence of declining oak trees in Iran. Daily precipitation data were obtained from 20 synoptic stations distributed over the Zagros area from 1988-2019. Non-parametric Mann-Kendall (MK) test and Sen's Slope estimator (Qmed value) were applied to identify significant trends in the precipitation data. ‘‘De Martonne’’ climate classification (i.e., De Martonne aridity index (IDM) was used for climate classification. Although most stations showed decreasing trends in annual precipitation during the studied period (1988-2019), these trends were statistically significant at only two stations. The mean number of events per year pre- and post- oak decline was not significantly different (68 events before against 71 events after decline). Most of the annual precipitation in the Zagros region falls in winter and spring (80% in total). However, this ratio decreased after the year 2000 by 6% (not significant) compared with before. The difference between the average annual precipitation, before (1988-2000) and after (2000-2019) the emergence of the oak decline phenomenon, were not statistically significant in any of the climate types (semi-arid: 406 mm vs. 378 mm), Mediterranean (530 mm vs. 489 mm), and humid (924 mm vs. 912 mm) as well as in whole Zagros region (537 mm vs. 508 mm). Although our data suggested insignificant trends in precipitation for most stations, future research should investigate if rising temperature in the Zagros area has resulted in higher evaporation and drier soil thereby accelerating the oak tree decline.

Forest canopy height is an important input variable to derive a set of essential parameters of forest stands, which is yet costly and time consuming when measured based on ground surveys. The satellite-based laser scanner data from ICESat-GLAS provide a 3D representation of gorund objects by measuring the distance from spacecraft to the objects on the earth surface. By means of these data, this study aims to estimate forest canopy height in a portion of mountainous Kheyroud experimental forests in north of Iran. An ICESat-GLAS dataset was analyzed. Several metrics including waveform extent, lead-edge extent and trail-edge extent were extracted from waveform data, and a terrain index was additionally calculated based on a digital elevation model at the location of all laser footprints. Forest canopy height was retrieved by calculating difference between signal begin and ground peak (direct estimation) and regression models (indirect estimation). For fitting the regression, a number of 330 highest trees were measured in 33 circular plots (70 meter diameter) which were collocated with LiDAR footprints. The directly estimated height produced and RMSE values of 0.56 and 10.32 m, respectively. Compared to this, regression models based on combined waveform metrics and digital elevation model provided better results. Best model fit with lowest AIC= 204.55 was achieved using waveform extent and terrain index variables (=0.82; RMSE= 6.16m). The ICESat-GLAS therefore concluded to be able to retrieve a relatively accurate estimate of maximum forest canopy height in such steep mountainous area, especially on small scales. Better results are assumed to be achieved using other statistical methods, as well as by an improved waveform processing techniques.

The aim of this work was to assess the characteristics of Poplar root system. Root Area Ratio (RAR) values were obtained using profile trenching method. First a starting point along the row of trees was randomly selected. Then a ten meters contiguous profile was dug along the row of trees and roots on both trenches (At a distance of 0. 5 and 1. 0 meter from the trunks) were measured. RAR values of roots were obtained at depth increments of 0. 1 m. Also 30 root specimens were analyzed for tensile strength. The results indicated that RAR declined mostly in depth and distance from the stems. This decrease approximated a power function. In most cases the maximum RAR values are located within the first layers، with maximum rooting depth at about 1. 0 m. The minimum and maximum RAR values along the profiles were 0. 004% and 0. 534% for nearer and 0. 001% and 0. 314% for farther trenches to stem respectively. The results of traction tests revealed that a positive power function existed between tensile force and root diameter. The mean root tensile strength and diameter were 19. 92 ± 4. 12 MPa and 1. 51 ± 0. 95 mm respectively. The root tensile strength values showed that root strength decreases with diameter following a power law equation. The data presented in this study expand the knowledge on most important biotechnical properties of Poplar growing in Iran.