Does Climate Change or Human Activity Lead to the Degradation in the Grassland Ecosystem in a Mountain-Basin System in an Arid Region of China?

Round 1

Reviewer 1 Report

Dear Authors

In my opinion the theme of the article is very actual and interesting for the readers of the journal.

The present research studied the main factors responsible for ecological degradation in arid regions in mountain-basin systems.

The Kulusitai grassland was the selected area to analyze the grassland degradation process as well as its possible causes and the potential for ecological restoration.

The trends of the deterioration of the grassland ecosystem and its spatial characteristic in Kulusitai, located at an arid region of Northwest China, were determined by combining spatial analysis with statistical methods.

The authors aimed to distinguishing and explaining the laws of grassland ecosystem deterioration in a mountain-basin system and identifying the key factors responsible. The authors also intended to evaluating whether damaged grasslands ecosystem have the potential for natural revegetation.

The results indicated vegetation degradation in high coverage grassland. Furthermore, the areas with reduced grassland productivity accounted for 82.77% of the total area.

Trend tests showed that both the vegetation coverage and productivity exhibited decreasing trends. Whereas, the temperature vegetation drought index) exhibited a significant increasing trend.

The study shows that drainage of groundwater and climate warming were the critical triggers that leaded to the soil drought. Soil drought and overgrazing, resulted from the impact of human activities, were the main factors responsible for the deterioration of the grassland ecosystems.

The possibility of limiting the number of the livestock to a reasonable scale and reducing the irrigated area may help to increase the soil moisture, thus promoting the germination of soil seed banks and facilitating the normal growth of grassland vegetation. Therefore, it is vital to determine how to stimulate soil seed germination to facilitate ecological restoration in this mountain basin grassland system.

The results of the manuscript under revision could provide a scientific basis and practical guide for the recovery of mountain-basin grassland systems in arid regions.

The paper is well structured, well written, the language is correct and clear, and the title and abstract clearly describe the content of the manuscript.

Best regards

Author Response

The comments are all from reviewer 2, so no response to reviewer 1.

Reviewer 2 Report

Good manuscript. I suggest to improve the language usage. Moreover, introduction and conclusions are not of the same quality of the rest of the ms. Introduction should be improved with a thorough revision of the state of the art, especially with focus on Europe and North America literature. Conclusions should better evidence the novelty and originality of the paper.

Author Response

Comment 1: Good manuscript. I suggest to improve the language usage. Moreover, introduction and conclusions are not of the same quality of the rest of the ms. Introduction should be improved with a thorough revision of the state of the art, especially with focus on Europe and North America literature. Conclusions should better evidence the novelty and originality of the paper.

Reply 1: Thank you for your valuable suggestion.

1) In order to improve the language usage, we send the manuscript to a colleague majoring in English to refine the language usage. And wrongly written character and unfluent sentences were checked and revised to our best though out the whole manuscript.

2) The introduction was recomposed. Conclusions and opinions from Europe and North America researches were focused to support the argument of our paper. The revised introduction is as follow:

 As one of the most widely distributed vegetation types on the Earth [1], grasslands play a significant role in wind-breaking and sand-fixing, water conservation, maintaining biodiversity, and forage production[2-3]. However, considerable research revealed that nearly half of the world's grasslands have degraded to varying degrees [4-5], making it one of main threats to ecological security. And the grassland degradation in arid and semi-arid region is even becoming worse [6]. In arid regions of Central Asia, grassland vegetation is usually distributed in the mountain-basin system, a kind of landform composed of alternating distribution of mountains and basins [7-8]. Restoring the degraded grassland ecosystem in the mountain-basin system is usually the general focus of ecological conservations in the arid region [9].

Grassland ecosystems are highly sensitive to climate change and disturbance of human activities [10-12]. Understanding various issues related to grassland deterioration is crucial for restoration in grassland ecosystems [12-14]. Climate change, such as global warm and altered precipitation patterns, and human activities, such as reclamation of grassland and overgrazing, are generally accepted to be the underlying drivers associated with grassland degradation [5,15-19]. In mountain-basin system of the arid regions, water is the primary restrict factor for vegetation dynamics [20-21], less precipitation and climate warming can readily cause soil droughts, thereby resulting in deterioration of the grassland vegetation system due to water deficit [11]. More importantly, increasing human-induced disturbances may convey a large proportion of water resources from mountainous area to oases for economic and social development; the ecological water supply may decrease rapidly to exacerbate the ecological imbalance in grassland ecosystems [22-23]. Therefore, it is necessary to find solutions that might address the problems caused by climate change and human activities in order to provide scientific guidance to facilitate the recovery of fragile ecosystems.  

Various methods such as enclosure, moderate grazing, and sowing grass seeds have been used to recover grassland ecosystems in arid regions [24-26]. However, the natural resilience of ecosystems should be estimated before applying recovery measures. For instance, the soil seed bank should be considered in restoration of grassland. The soil seed bank is important for the recovery and maintaining the integrity of the plant community [27-29]. In regions with grassland degradation, effective activation of the soil seed bank can help to recover the natural vegetation gradually and reduce the cost of ecological restoration without manually sowing seeds.

Many studies [30-32] have applied either remote sensing or mathematical statistics to obtain information about the area, coverage, and productivity of the grassland in hopes to reveal the laws of grassland degradation in arid regions. Under the background global warming, phenology of vegetation in many parts of the word has altered [33-34]. As the grazing should be adapted to grassland phenology, mismatch between the grazing and changes of grassland vegetation could be one of the key factors for the grassland degradation [35-36]. Yet, seldom were the changes of phenology considered in the restoring of the degraded grassland ecosystem.

The Kulusitai grassland is located at the northwest border of China, where it not only constitutes a natural barrier in maintaining the ecological security, but also provides important production base for animal husbandry [37]. However, due to the influence of climate change, expansion of cultivated land, overgrazing and other possible factors, the area of grassland is shrinking, the productivity and livestock capacity of the natural grassland have declined rapidly [38]. Some parts of the grassland have become sand or desert already.

Therefore, in this study, we selected the Kulusitai grassland as a representative of the mountain-basin system in the arid region of Central Asia. The degradation process of the grassland was investigated by combining methods of spatial analysis and statistical analysis, and data obtained from remote sensing, meteorology, field investigation and socioeconomic analyses. We aim to determine the potential for natural revegetation during the recovery of the grassland and to propose specific measures that might facilitate ecological restoration for the damaged grassland ecosystem.

3) Conclusions were also revised to better evidence the novelty and originality of the paper. The revised Conclusions are as follow:

In order to understand the main factors responsible for ecological degradation in arid regions in mountain-basin systems, we selected the Kulusitai grassland as a study area to analyze the grassland degradation process as well as its possible causes and the potential for ecological restoration.

Both the vegetation coverage and productivity exhibited decreasing trends in the Kulusitai grassland, indicating a continuous degrading process. And the process was characterized by degradation in high coverage grassland.

Based on analyzing of the changes in phenology, the optimum period for grass clipping and storage is from July 29 to August 5 in Kulusitai grassland. Utilization model of the grassland in similar mountain-basin system should be adjusted to match the phenology of the grassland vegetation to achieve maximum grass yield as well as guarantee the sustainability of the grassland ecosystem.