**3. Results**

forest litter from 2005 to 2015,

forest litter, followed by 2005 and

#### *3.1. Annual Changes in Litter and Composition in Different Years*

3.1.1. Annual Variation in Litter Components and Total Amounts in Different Years It can be seen from Table 1 that the total amount of litter from 2005 to 2015 was between 7704.15 and 8817.50 kg·hm−2·a<sup>−</sup><sup>1</sup> and the order of magnitude was 2005 > 2015 > 2010. The litter amount fluctuated from year to year, and the coefficient of variation was 7.03%. The composition of litter mainly includes litter branches, litter leaves, litter fruits (flowers), and other litter components (bark, moss lichens, debris, etc.), among which litter branches and other components are significantly different from litter leaves and litter fruits (flowers)(*p* < 0.05), but the difference between litter branches and other components is not significant (*p* > 0.05). Each component of litter and its proportion to the total forest litter in different years are as follows: litter leaves > litter branches> other components> litter fruits (flowers),and the total average percentage is: 50.89% > 25.28% > 15.86% > 7.97%. Litter leaves are the absolute dominant component of the litter in the evergreen broad-leaved forest community in Ailao Mountain, accounting for 41.70%–61.52% of the total litter in different years, the highest in 2010 and the lowest in 2015. Litter branches, litter fruits (flowers), and other components accounted for 17.26%–32.05%, 6.29%–9.37%, and 14.57%–16.88% of the total

> It accounted

 for the highest percentage

 of total

#### **Table 1.** Annual variation of litter components in different years (kg/hm2).

respectively.

2010.


Note: the percentage of litter amount of each component in the total litter amount of the whole year is shown in brackets. Different capital letters in the same column indicate significant differences between different years, and different lowercase letters in the same row indicate significant differences between different litter components in the same year (*p* < 0.05).

#### 3.1.2. Monthly Dynamics of Litter Components in Different Years

It can be seen from Figure 2 that in 2005, the total amount of litter and each component exhibited an irregular pattern, with multiple peaks, in which the total amount of litter showed a four-peak pattern with peaks in February, April, August, and November (727.71, 943.44, 1647.86, and 764.36 kg/hm2, respectively). The total amount of litter in August was significantly higher than in the other months. Leaves showed a bimodal pattern, with the first peak in April at 693.59 kg/hm<sup>2</sup> and the second peak in November at 499.74 kg/hm2. The number of litter branches also significantly increased in February (310.23 kg/hm2) and August (982.01 kg/hm2), whereas the monthly variations in fruits (flowers) and other components were relatively flat. In 2010, the total amount of litter and the amount of litter leaf showed a double peak curve, one in April and the other in November. The difference between the two peaks was obvious, but they both appeared in the dry season, among which the peak of the litter was in April. The span of the twigs was larger, and

the amount of litter was higher, which was significantly higher than that in November, and the litter branches and other components also showed obvious unimodal monthly variation characteristics, which were all significantly increased in April. In 2015, the highest value of the total amount of litter and the amount of each component was concentrated in January, and then the number dropped sharply and then slightly rebounded in March and September. Overall, the litter in 2015 showed a single peak pattern throughout the year. The amount of litter in January was higher than the annual average, and the peaks were mainly concentrated in the dry season rather than the rainy season. In 2005, 2010, and 2015, the annual changes in the total amount of litter in the study area were 161.50%, 209.12%, and 359.37%, respectively, of which 2015 had the largest change, indicating that the intermonthly variation of the litter amount was more severe, while in 2005 The smallest variation range indicated that the monthly variation of litter in this year was relatively gentle.

#### 3.1.3. Seasonal Dynamics of Litter Fractions in Different Years

Seasons in this experiment were divided as follows: March–May for spring, June–August for summer, September–November for autumn, and December–February for winter. The monthly litter of different components in different years exhibited significantly different seasonal variation (Figure 3). The total amount of litter in different years was significantly higher than that of other components. In 2005, the components with the highest amount of litter in the other three seasons were leaves, except in summer, which was dominated by branches. The distribution of branch components across seasons peaked in summer. Leaves represented the highest proportion in spring, which then fluctuated and decreased with the passage of summer, autumn, and winter; fruit drop (flower) slowly rose from spring to winter. Other components rose from spring to summer, and then decreased gradually after reaching a high point in summer, with small fluctuations. In 2010, litter was composed mostly of leaves and least by fruit (flower). The seasonal variation in fruit (flower) was lowest in spring. After reaching a peak in summer, fruit (flower) remained stable until autumn, decreased from autumn to winter, and reached the lowest value in winter. The seasonal variation in other components was similar, showing a peak in spring, followed by a sharp decline. In 2015, the maximum value of litter component in winter was branches, and the component with the highest amount of litter in the other three seasons was leaves. The seasonal variation in each component was highest in spring, then decreased reaching the lowest values in summer, and rose thereafter.

#### *3.2. Dynamic Characteristics of Litter Nutrient Contents in Different Years*

#### 3.2.1. Annual Average Nutrient Contents of Litter Components in Different Years

The nutrient content of all years was higher in litter than in branches, while the concentration of different nutrients was C > Ca > N > K > Mg > S > P (Table 2). The C content was not significantly different (*p* > 0.05) between branches and leaves in all years except for 2010. The overall distribution of C in the two organs was relatively average, and the distribution of C content in the leaves was only slightly higher than that in the branches. Branches and leaves showed significant differences (*p* < 0.05) between 2005, 2010, and 2015 in N and K contents, whereas P, S, Ca, and Mg contents were not significantly different (*p* > 0.05) between the years. C, Ca, and Mg contents in branches were the same in different years, with the highest in 2005 and the lowest in 2015. The trends in N and S content were also 2010 > 2005 > 2010, and the P and K contents showed the highest levels in 2015 (0.48 and 0.87 g/kg). The P content and K content were the lowest in 2005 and 2010, respectively. In leaves, the annual average contents of N, P, and S increased with the year, while the content of C, K, Ca, and Mg is 2005 > 2010 > 2015.

**Figure 2.** Monthly dynamics of litter components and totals in 2005, 2010, and 2015. (**a**) Monthly dynamics of litter components and totals in 2005; (**b**) monthly dynamics of litter components and totals in 2010; (**c**) monthly dynamics of litter components and totals in 2015.

(**c**) 

**Figure 3.** Seasonal dynamics of litter in 2005, 2010, and 2015. (**a**) Seasonal dynamics of litter in 2005; (**b**) seasonal dynamics of litter in 2005; (**c**) seasonal dynamics of litter in 2005.

The values of C/N, C/P and N/P of litter in 2005, 2010, and 2015 were 57.66, 658.05, 19.02; 47.88, 998.59, 20.86; 55.65, 869.55, 15.63, respectively. The ratios of C/P and N/P were 42.27, 772.86, 18.29; 36.73, 685.47, 18.66; 33.78, 573.80, 16.99, respectively. The mean ratios of C/N, C/P and N/P of litter were 48.65, 904.69, 18.59; 41.45, 803.68, 18.66; 41.89, 684.83, 16.35, respectively.



Note: the percentage of litter amount of each component in the total litter amount of the whole year is shown in brackets. Different capital letters in the same column indicate significant differences between different years, and different lowercase letters in the same row indicate significant differences between different litter components in the same year (*p* < 0.05).

#### 3.2.2. Seasonal Dynamics of the Nutrient Contents of Each Component of Litter in Different Years

It can be seen from Table 3 that the order of nutrient content of each component in each season is C > Ca > N > K > Mg > S > P. Therefore, C, Ca, N, K and Mg are the major elements of the evergreen broad-leaved forest, and S and P are the trace elements. The seasonal dynamic change characteristics of nutrient content of each component of litter in different years are quite different, and the seasonal change regularity of the content of each element is uncertain. In 2005, the seasonal variation of C nutrient content was spring > winter > summer > autumn, while the seasonal sequence of N content was completely opposite; P. The contents of K, Mg, S, and Ca are higher in winter and lower in summer. In 2010, the seasonal variation of C and Mg nutrient content was the same, which was summer > spring > autumn > winter; N. The nutrient contents of P, K, and S were the highest in summer and the lowest in spring. In 2015, C and Mg nutrient contents were the highest in spring and the lowest in summer; N. On the contrary, the contents of P, Ca, and other macroelements were the highest in summer and the lowest in spring; K content sequence is consistent with that in 2005; S content is similar to 2010.

**Table 3.** Seasonal dynamics of nutrient content of branches and leaves in different years (g/kg).


#### *3.3. Characteristics of Nutrient Return of Litter in Different Years* 3.3.1. Annual Nutrient Return from Litter

The nutrient return in other years generally showed C > Ca > N > K > Mg > S > P (Table 4), and litter was higher than branches, which is consistent with the order of annual average nutrient concentrations of each component. Among branches, the returns of C and Ca were highest in 2005 (1191 kg/hm2), and then decreased year by year. The return of N, P, K, S, and Mg was highest in 2010, followed by 2005, and lowest in 2015. Among leaves, C, N, P, K, S, and Mg restitution was highest in 2015, and only Ca restitution was different in order of size, with the highest in 2005 and the lowest in 2010.

#### 3.3.2. Seasonal Dynamics of Nutrient Return from Litter in Different Years

As shown in Table 5, In 2005, the maximum value of the nutrient return of each element in the litter branches was concentrated in summer and winter, the minimum value was concentrated in spring and autumn, and the seasonal change order of nutrient return of each element in the litter was opposite, the maximum value was in spring and autumn, and the minimum value was concentrated in summer and winter. In 2010, the maximum value of the nutrient return of each element in the litter branches was spring, followed by summer, and the minimum value fluctuated in winter and autumn. The order of nutrient return of most elements in the litter leaves was consistent with that in 2005. The nutrient return amount of most elements in the litter branches and leaves in 2015 was basically consistent with the seasonal fluctuation law of the litter leaves in 2010.


column indicate significant differences between different years, and different lowercase letters in the same row indicate significant differences between different

litter components in the same year (*p* < 0.05).



**Table 5.** Seasonal dynamics of litter nutrient return in different years (kg/hm2).
