## 1 Introduction  
Biochar (BC) is a carbonaceous material that results from the pyrolysis of biomass in an inert atmosphere or in the limited presence of air [1]. The dominant factors that influence the physicochemical properties of biochar and its end applications are the feedstock type and the thermochemical parameters, namely, pyrolysis temperature, residence time, and heating rate [2, 3]. BC can be produced from a variety of organic feedstocks, including sewage sludge [4], animal manure [5, 6, 7], deinking paper sludge [8], and pruning waste [9], among others. Different feedstocks result in differences in the physical and chemical properties of biochar. Lignocellulosic biomass, which includes agricultural residues, forest debris, and industrial waste, is receiving interest due to its profuse availability and low cost. Commonly, lignocellulosic waste is categorized into two main classes: woody and herbaceous or nonwoody waste [10; 11; 12]. Woody plants have a relatively higher lignin content, but herbaceous plants have higher cellulose and hemicellulose contents. Therefore, the biomass from herbaceous plants has lower thermal stability, and their macromolecules undergo carbonization more easily during pyrolysis. These wastes, when used for the preparation of biochar, can fix carbon and contribute to environmental conservation, helping to achieve sustainable development objectives. Regarding pyrolysis conditions, in general, BC production is conducted via slow pyrolysis, which typically takes place using a heating rate of <2 \({}^{\circ}\)C s\({}^{-1}\); slow pyrolysis can produce comparatively high-quality BC with a stable carbon content and a low H/C ratio. Temperature has a significant effect on the physiochemical properties of BC, including its functional groups, surface area, and porosity. Previous investigations showed that the temperature of slow pyrolysis mostly varies between 300 and 600 \({}^{\circ}\)C depending on the intended BC use [3; 5; 13]. Residence times may vary from minutes to days; a moderate-length residence time is required to optimize the biochar production both in terms of yield and physicochemical properties [11; 14]. Common gorse (_Ullex europaeus_, L.) and scotch broom (_Cytisus scoparius_, L. (Link)) are evergreen nitrogen-fixing shrubs belonging to the legume family; gorse is a spiny or thorny plant. Both shrubs are distributed worldwide, either as native or introduced species. As a native species, gorse is most abundant along the western coast of Europe and in the British Isles [15], and it is widespread near the western Mediterranean Sea. Scotch broom, as a native species, is most common in central Europe and the British Isles, from Ireland to Ukraine, and from southern Spain to southern Norway [16; 17]. Both legume shrubs have been widely introduced around the world for different reasons. According to the International Union for Conservation of Nature, introduced stands of gorse and broom are most abundant in maritime regions at temperate latitudes, in the United States, Canada, South Africa, New Zealand, and Australia [18; 19; 20; 21; 22; 23]. They are also established at subtropical latitudes, for example, in several mountains areas from India and Brazil [24; 25], and on islands such as Hawaii [26] and Reunion [27]. As an invasive species, gorse and Scotch broom have been recorded in 52 and 54 countries and islands, respectively [22; 23]. Although several beneficial attributes of gorse and broom have been identified, they are now viewed as prolific seeders that escaped from cultivation and had become invasive species and noxious weeds in most of the countries to which they have been introduced. Moreover, even though these species have been present in European countries for centuries, they are often considered a weed due to their several detrimental effects [28]. On the other hand, the positive effects of these shrubs are associated with their ability to fix nitrogen.